Positive Electrode Active Material for Lithium Secondary Battery, Method for Producing the Same, and Lithium Secondary Battery Containing the Same

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same, wherein the positive electrode active material is a lithium nickel-based compound particle having an Ni content of 75 mol % or more, and the difference in Al concentration between the center and surface of the lithium nickel-based compound particle is 1 mol % or less.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same.

Background Art

[0002] Recently, pushed by the explosive increase in demand for electric vehicles and the requirement for an increase in driving distance, the development of secondary batteries having a high capacity and a high energy density that can be applied thereto has been actively promoted worldwide.

[0003] In particular, in order to manufacture such a high-capacity battery, a high-capacity positive electrode active material is required. As such a high-capacity positive electrode active material, a strategy of applying a lithium nickel cobalt manganese-based positive electrode active material having a high nickel content has been proposed.

[0004] However, a lithium nickel cobalt manganese-based positive electrode active material having a high nickel content has a problem that the temperature at which it decomposes when the temperature increases in the charged state becomes low due to an increase in structural instability due to an increase in nickel content.

Summary of the Invention

Problems to be Solved by the Invention

[0005] One embodiment provides a positive electrode active material for a lithium secondary battery that has excellent thermal stability while reducing the initial resistance and the resistance increase rate while maintaining the capacity.

[0006] Another embodiment provides a method for producing a positive electrode active material for a lithium secondary battery.

[0007] Still another embodiment provides a lithium secondary battery including the positive electrode active material.

Means for Solving the Problems

[0008] The cathode active material for a lithium secondary battery according to one embodiment is lithium nickel-based compound particles with a Ni content of 75 mol% or more, and the concentration difference of Al between the central part and the surface part of the lithium nickel-based compound particles may be 1 mol% or less.

[0009] The average particle size (D50) of the lithium nickel-based compound particles may be 10 μm to 20 μm.

[0010] The lithium nickel-based compound particles may be represented by the following Chemical Formula 1. Li a Ni x Co y Mn z Al 1-(x+y+z) O2 In Chemical Formula 1, a is 0.95 ≦ a ≦ 1.15, x is 0.75 ≦ x ≦ 0.98, y is 0 < y < 0.2, z is 0 < z < 0.2, and y + z ≦ 0.25.

[0011] In one embodiment, in Chemical Formula 1, x + y + z may be in the range of 0.98 to 0.999.

[0012] The surface part may be a region corresponding to a depth of 30% or less of the average radius of the lithium nickel-based compound particles in the depth direction from the outermost surface of the lithium nickel-based compound particles.

[0013] The method for manufacturing a cathode active material for a lithium secondary battery according to another embodiment may include the steps of: coprecipitating a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and an aluminum raw material substance in a solvent to produce a precursor compound; mixing the precursor compound and a lithium raw material substance to form a mixture; and firing the mixture.

[0014] The coprecipitation step can be carried out at a pH of 11.0 to 12.0.

[0015] Further, it may be 0.1 mol% to 2 mol% based on the total amount of metal elements excluding lithium in the lithium nickel-based compound particles.

[0016] Furthermore, a lithium secondary battery according to another embodiment can include a positive electrode containing the positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

Advantages of the Invention

[0017] The positive electrode active material for a lithium secondary battery according to one embodiment has Al uniformly contained as the entire positive electrode active material, improves the normal temperature and high temperature life characteristics while ensuring high capacity, is excellent in thermal stability, and is excellent in initial resistance characteristics, and can provide a lithium secondary battery with a significantly reduced resistance increase rate.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example and the present invention is not limited thereby, and the present invention is defined only by the scope of the claims described later.

[0020] In this specification, unless otherwise specified, % means weight%, and 1 ppm means 0.0001 weight%.

[0021] The positive electrode active material for a lithium secondary battery according to one embodiment is lithium nickel-based compound particles with a Ni content of 75 mol% or more, and the concentration difference of Al between the central part and the surface part of the lithium nickel-based compound particles may be 1 mol% or less.

[0022] According to one embodiment, the concentration difference of Al between the central part and the surface part of the lithium nickel-based compound particles may be 0 mol% to 1 mol%. In one embodiment, the concentration difference of Al being 0 mol% between the central part and the surface part means that they are substantially the same. The concentration of Al in the central part and the surface part means the average concentration of Al present in each region, and the concentration difference only means the difference in the concentration of Al present in the central part and the surface part, not just that the concentration of Al in the central part is at most 1 mol% greater than that in the surface part. For example, the concentration of Al in the central part may be 0.52 mol%, the concentration of Al in the surface part may be 0.45 mol%, and the concentration of Al in the central part may be greater than that in the surface part; or the concentration of Al in the central part may be 0.92 mol%, the concentration of Al in the surface part may be 0.97 mol%, and the concentration of Al in the central part may be less than that in the surface part.

[0023] Also, the fact that the concentration difference of the doping element Al between the central part and the surface part is included within the above range means that Al is substantially uniformly present throughout the interior of the positive electrode active material particles, that is, it means that there is substantially little concentration difference of the doping element Al between the central part and the surface.

[0024] In this way, when the doping element Al is located at a uniform concentration throughout the interior of the positive electrode active material particles, the positive electrode active material can significantly improve the normal temperature and high temperature cycle life characteristics while maintaining a high capacity. Also, lithium ions can form a smooth path, the initial resistance and the resistance increase rate can be reduced, the structural stability can be ensured, and the thermal stability can be improved.

[0025] Here, the surface part means a region corresponding to a depth of 30% or less of the average radius of the lithium nickel-based compound particles in the depth direction from the outermost surface of the lithium nickel-based compound particles. Explaining this with reference to FIG. 1, it means a region corresponding to a depth (b) of 30% or less of the radius (a) in the depth direction from the outermost surface of the lithium nickel-based compound particles. For example, if the particle size of the lithium nickel-based compound particles is 10 μm, the radius is 5 μm, and thus, a region corresponding to 1.5 μm in the depth direction (i.e., the center side) from the outermost surface means the surface part.

[0026] In one embodiment, the lithium nickel-based compound particles may be represented by the following Chemical Formula 1. Li a Ni x Co y Mn z Al 1-(x+y+z) O2 In Chemical Formula 1, a is 0.95 ≦ a ≦ 1.15, x is 0.75 ≦ x ≦ 0.98, y is 0 < y < 0.2, z is 0 < z < 0.2, and y + z ≦ 0.25.

[0027] In one embodiment, in Chemical Formula 1, x + y + z may be in the range of 0.98 to 0.999, or more specifically, in the range of 0.99 to 0.999. That is, the content of the doping element Al may be in the range of 0.1 mol% to 2 mol% based on the total metal elements excluding lithium in the lithium nickel-based compound particles, or in the range of 0.1 mol% to 1 mol%. When the content of the doping element satisfies the above range, it is possible to realize a cathode active material with excellent normal temperature and high temperature life characteristics while ensuring high capacity.

[0028] In one embodiment, x may be from 0.80 to 0.96. That is, the lithium nickel-based compound is a high-nickel (high-Ni) compound having a nickel content of 75 mol% or more, and a cathode active material having high output characteristics can be realized. The cathode active material according to one embodiment having such a composition has a high energy density per unit volume, so that the capacity of a battery to which it is applied can be improved, and it is also suitable for use in electric vehicles.

[0029] The tap density of the cathode active material may be in the range of 2.3 g / cc to 2.7 g / cc, more specifically in the range of 2.45 g / cc to 2.7 g / cc. When the tap density satisfies the above range, a large amount of the cathode active material can be introduced into an electrode of the same volume, so that the energy density per unit volume can be increased. Thereby, the internal primary particles can be protected from HF generated by the decomposition of a lithium salt in the electrolyte, for example, LiPF6. Thereby, the life characteristics of the lithium secondary battery can be improved.

[0030] The average particle diameter (D50) of the cathode active material may be in the range of 10 μm to 20 μm, more specifically in the range of 12 μm to 18 μm. Since it reacts in a similar pH range to other metal raw materials in the coprecipitation step, the doping element can be easily and uniformly positioned inside the particles without adjusting the pH range, and it can be grown into an active material having such an average particle diameter. The cathode active material according to one embodiment may be a single particle, or may be a secondary particle having a large particle diameter formed by granulating at least one primary particle having a small particle diameter. Therefore, the average particle diameter (D50) may be the particle diameter of the secondary particle. In this case, it is only necessary that the average particle diameter (D50) of the secondary particle is included in the above range, and the average particle diameter (D50) of the primary particle does not need to be limited.

[0031] Unless otherwise defined herein, the average particle diameter (D50) means the diameter of particles having a cumulative volume of 50% by volume in the particle size distribution, and can be measured by a PSA (particle size analyzer).

[0032] Thus, in the cathode active material of this embodiment, during the production of the precursor, an Al raw material is introduced as a doping element in the coprecipitation process to produce a precursor doped with Al, and then, to produce the cathode active material, the concentration of Al is uniform throughout the particles. Therefore, the lithium secondary battery applying the cathode active material of this embodiment exhibits excellent discharge capacity, and at the same time, shows improved initial efficiency, excellent normal temperature and high temperature life characteristics. In addition, the initial resistance, resistance increase rate, average leakage current, heat generation peak temperature, and heat generation amount can be significantly reduced.

[0033] A method for manufacturing a cathode active material for a lithium secondary battery according to another embodiment includes a step of coprecipitating a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and an aluminum raw material substance in a solvent to produce a coprecipitation product; a step of mixing the coprecipitation product and a lithium raw material substance to produce a mixture; and a step of firing the mixture.

[0034] Hereinafter, the manufacturing method will be described in more detail. Specific characteristics regarding the cathode active material manufactured by such a method are the same as those described in one embodiment, and thus will be omitted here.

[0035] First, a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and an aluminum raw material substance are coprecipitated in a solvent to produce a precursor compound.

[0036] The nickel raw material substance may be a hydroxide, oxide, carbonate, sulfate, nitrate, hydrates thereof, or a combination thereof containing nickel. The cobalt raw material substance may be a hydroxide, oxide, carbonate, sulfate, nitrate, hydrates thereof, or a combination thereof containing cobalt. Further, the manganese raw material substance may be a hydroxide, oxide, carbonate, sulfate, nitrate, hydrates thereof, or a combination thereof containing manganese.

[0037] The aluminum raw material substance may be Al2(SO4)3, Al(NO3)3, Al2(CO3)3, or a combination thereof. Since Al(OH)2, which is not the aluminum raw material substance, is insoluble in water, it cannot be applied to the coprecipitation process according to one embodiment.

[0038] Thus, in the method for producing a positive electrode active material according to one embodiment, since an aluminum raw material substance containing aluminum as a doping element is added in the coprecipitation process for producing a precursor together with nickel, cobalt, and manganese raw material substances, a separate coprecipitation process may not be necessary. Further, since the aluminum raw material substance is added in the coprecipitation process for producing a precursor, Al can be uniformly contained as a whole inside the positive electrode active material of the final product, that is, it can be located. For example, the concentration difference of Al between the central part and the surface part may be 1 mol% or less, or may be 0 mol% to 1 mol%.

[0039] The mixing ratios of the nickel raw material substance, the cobalt raw material substance, the manganese raw material substance, and the aluminum raw material substance can be appropriately adjusted so that the composition of Chemical Formula 1, which is the final active material, can be obtained.

[0040] Water can be used as the solvent.

[0041] The coprecipitation process can be carried out by purging an inert gas to prevent oxidation of metal ions, and can be carried out at a temperature of 20°C to 60°C.

[0042] The inert gas may be N2, argon gas, or a combination thereof.

[0043] Further, the coprecipitation reaction can be carried out by adding a chelating agent and a pH adjuster to the aqueous metal salt solution. The chelating agent may be NH4(OH), C3H6O3, or a combination thereof, and the pH adjuster may be NaOH, NaCO3, NH4HCO3, or a combination thereof.

[0044] The usage amount of the chelating agent can be appropriately adjusted and used so that the coprecipitation process occurs. The pH adjuster can be appropriately adjusted and used so that the coprecipitation process occurs under the conditions of pH 6.5 to 8 and 11.0 to 12.0. When the pH of the coprecipitation process is within the above range, there are advantages such as less generation of fine powder, increased sphericity of the surface, and improved electrochemical properties.

[0045] The drying process can be carried out at 100°C to 160°C for 1 hour to 24 hours.

[0046] Before the drying process, a filtration process can be further carried out. Such a filtration process can be carried out by a normal method.

[0047] The precursor compound and the lithium raw material substance are mixed to form a mixture. The mixing ratio of the precursor compound and the lithium raw material substance can be appropriately adjusted so that the product composition of the target chemical formula 1 can be obtained.

[0048] The lithium raw material substance may be a hydroxide, oxide, carbonate, sulfate, nitrate, hydrate thereof, or a combination thereof containing lithium.

[0049] Next, the mixture is fired to produce a positive electrode active material for a lithium secondary battery.

[0050] The firing process can be carried out while oxygen flows in at 500 L / min to 1000 L / min. Further, the firing process can be carried out, for example, by maintaining in the range of 300°C to 500°C for 1 hour to 5 hours, then raising the temperature to the range of 700°C to 900°C at a heating rate of 1°C / min to 3°C / min, and then maintaining at this temperature for 8 hours to 15 hours.

[0051] After the firing process, a water washing process can be further carried out to remove residual lithium on the surface.

[0052] Still another embodiment provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte.

[0053] The positive electrode includes a current collector and a positive electrode active material layer including a positive electrode active material formed on the current collector. The positive electrode active material includes a positive electrode active material according to one embodiment.

[0054] In the positive electrode, the content of the positive electrode active material may be 90% by weight to 98% by weight with respect to the total weight of the positive electrode active material layer.

[0055] In one embodiment, the positive electrode active material layer may further include a binder and a conductive agent. At this time, the content of the binder and the conductive agent may each be 1% by weight to 5% by weight with respect to the total weight of the positive electrode active material layer.

[0056] The binder serves to well adhere the positive electrode active material particles to each other and to well adhere the positive electrode active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0057] The conductive agent is used to impart conductivity to the electrode, and in the battery formed, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive agent include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0058] As the current collector, aluminum foil, nickel foil, or a combination thereof can be used, but it is not limited thereto.

[0059] The positive electrode active material layer is formed by mixing a positive electrode active material, a binder, and optionally a conductive agent in a solvent to produce an active material composition, and applying this active material composition to a current collector. Since such a method for forming the active material layer is well-known in the art, a detailed description thereof is omitted herein. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto.

[0060] The negative electrode can include a current collector and a negative electrode active material layer formed on the current collector and containing a negative electrode active material.

[0061] In the negative electrode active material layer, the content of the negative electrode active material in the negative electrode active material layer may be 80% by weight to 98% by weight based on the total weight of the negative electrode active material layer.

[0062] The negative electrode active material layer contains a binder and may further optionally contain a conductive agent. The content of the binder in the negative electrode active material layer may be 1% by weight to 5% by weight based on the total weight of the negative electrode active material layer. Further, when a conductive agent is further included, 90% by weight to 98% by weight of the negative electrode active material, 1% by weight to 5% by weight of the binder, and 1% by weight to 5% by weight of the conductive agent can be used.

[0063] The negative electrode active material includes a substance capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a substance capable of doping and dedoping lithium, or a transition metal oxide.

[0064] As the substance capable of reversibly inserting / desorbing lithium ions, as carbon materials, any of the carbon-based negative electrode active materials generally used in lithium ion secondary batteries can be used. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof.

[0065] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0066] As the substance capable of doping and undoping lithium, Si, SiO x (0 < x < 2), Si-Y alloy (wherein Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Si), Sn, SnO2, Sn-Y (wherein Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and a combination thereof, and is not Sn), and the like can be mentioned.

[0067] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like. The negative electrode active material layer further contains a binder and may selectively further contain a conductive agent.

[0068] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof can be used.

[0069] Examples of the non-aqueous binder include ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0070] Examples of the aqueous binder may include styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polymers containing ethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0071] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0072] The conductive agent is used to impart conductivity to the electrode, and in the battery being constructed, any electron conductive material can be used as long as it does not cause a chemical change. Examples of the conductive agent include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0073] As the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0074] The negative electrode is formed by mixing a negative electrode active material, a binder, and optionally a conductive agent in a solvent to produce an active material composition, and applying this active material composition to a current collector. As the solvent, N-methylpyrrolidone can be used, and when an aqueous binder is used as the binder, water can be used.

[0075] Since such a method for forming a negative electrode is well-known in the art, detailed description thereof is omitted in this specification.

[0076] The electrolyte contains a non-aqueous organic solvent and a lithium salt.

[0077] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0078] As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as the ketone solvent, cyclohexanone, etc. can be used. Furthermore, as the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. can be used.

[0079] The non-aqueous organic solvent can be used alone or in combination of one or more. When used in combination of one or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0080] In addition, in the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed and used at a volume ratio of 1:1 to 1:9, the performance of the electrolyte can be excellent.

[0081] When using a mixture of the non-aqueous organic solvents, the mixed solvent of cyclic carbonate and chain carbonate can be a mixed solvent of cyclic carbonate and propionate solvent, or a mixed solvent of cyclic carbonate, chain carbonate and propionate solvent. As the propionate solvent, methyl propionate, ethyl propionate, propyl propionate, or a combination thereof can be used.

[0082] At this time, when using a mixture of cyclic carbonate and chain carbonate, or a mixture of cyclic carbonate and propionate solvent, mixing and using at a volume ratio of 1:1 to 1:9 can result in excellent performance of the electrolyte. Also, when using a mixture of cyclic carbonate, chain carbonate and propionate solvent, it can be mixed and used at a volume ratio of 1:1:1 to 3:3:4. Of course, the mixing ratio of the solvents may be appropriately adjusted according to the desired physical properties.

[0083] The non-aqueous organic solvent may further contain an aromatic hydrocarbon organic solvent in the carbonate solvent. At this time, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed at a volume ratio of 1:1 to 30:1.

[0084] As the aromatic hydrocarbon organic solvent, the aromatic hydrocarbon compound of the following Chemical Formula 2 can be used.

[0085]

Chemical Formula

[0086] (In the Chemical Formula 2, R1 to R6 are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and a combination thereof.)

[0087] Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.

[0088] In order to improve the battery life, the electrolyte may further contain vinylene carbonate or an ethylene carbonate compound of the following Chemical Formula 3 as a life improvement additive.

[0089]

Chem.

[0090] (In the Chemical Formula 3, R7 and R8 are the same as or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, and at least one of R7 and R8 is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R7 and R8 are not all hydrogen.)

[0091] Typical examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like. When such a life-improving additive is further used, its usage amount can be appropriately adjusted.

[0092] The electrolyte can further contain vinyl ethylene carbonate, propane sultone, succinonitrile, or a combination thereof. At this time, the usage amount can be appropriately adjusted.

[0093] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB), and includes one or more selected from the group as a supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0094] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Of course, mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0095] Lithium secondary batteries are classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, classified into cylindrical, square, coin type, pouch type, etc. depending on the form, and divided into bulk type and thin film type depending on the size. Since the structures and manufacturing methods of such batteries are widely known in this field, detailed descriptions will be omitted.

Examples

[0096] Hereinafter, examples of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby. The present invention is defined only by the scope of the claims described later.

[0097] (Example 1 - 0.005 mol of doping element was added during coprecipitation) (1) Production of positive electrode active material precursor As the nickel raw material substance, NiSO4·6H2O, as the cobalt raw material substance, CoSO4·7H2O, as the manganese raw material substance, MnSO4·H2O, and as the aluminum raw material substance, Al2(SO4)3·14~18H2O were dissolved in distilled water to produce an aqueous metal salt solution.

[0098] Using the aqueous metal salt solution in a coprecipitation reactor, purging with N2 was carried out, and while maintaining the temperature of the reactor at 50°C, NH4(OH) was introduced into the coprecipitation reactor as a chelating agent, and NaOH was added for pH adjustment to carry out the coprecipitation process.

[0099] The precipitate obtained by the coprecipitation process was filtered, washed with distilled water, and then dried in an oven at 100 °C for 24 hours to produce a (Ni 0.795 Co 0.10 Mn 0.10 Al 0.005 )(OH)2 cathode active material precursor.

[0100] (2) Production of cathode active material The (Ni 0.795 Co 0.10 Mn 0.10 Al 0.005 )(OH)2 cathode active material precursor and LiOH·H2O (Samchun Chemicals, battery grade) were uniformly mixed at a molar ratio of 1:1.03 to produce a mixture. The mixture was charged into a tube furnace and fired while flowing oxygen at 200 mL / min. This firing process was carried out by first heat-treating at 480 °C for 5 hours, then raising the temperature to 760 °C at a heating rate of 2.5 °C / min, and then maintaining this temperature for 12 hours.

[0101] The obtained fired product was subjected to a water washing process, and the produced cathode active material had an average particle size (D50) of 15 μm, and the overall composition was Li 1.03 Ni 0.795 Co 0.10 Mn 0.10 Al 0.005 O2.

[0102] (Comparative Example 1 - Production of non-doped cathode active material) (1) Production of cathode active material precursor As the nickel raw material, NiSO4·6H2O, as the cobalt raw material, CoSO4·7H2O, and as the manganese raw material, MnSO4·H2O were dissolved in distilled water to produce an aqueous metal salt solution.

[0103] Using a coprecipitation reactor, the metal salt aqueous solution was purged with N2. While maintaining the temperature of the reactor at 50 °C, NH4(OH) was introduced into the coprecipitation reactor as a chelating agent, and NaOH was added for pH adjustment to carry out the coprecipitation process. This coprecipitation process was carried out under the conditions of pH 11 - 12.

[0104] The precipitate obtained from the coprecipitation process was filtered, washed with distilled water, and then dried in an oven at 100 °C for 24 hours to produce a (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 cathode active material precursor.

[0105] (2) Production of cathode active material The (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 cathode active material precursor and LiOH·H2O (Samchun Chemicals, battery grade) were uniformly mixed at a molar ratio of 1:1.03 to produce a mixture. The mixture was charged into a tube furnace and fired while flowing oxygen at 200 mL / min. This firing process was carried out with a primary heat treatment at 480 °C for 5 hours, and then the temperature was raised to 760 °C at a heating rate of 2.5 °C / min and maintained at this temperature for 12 hours.

[0106] The obtained fired product was subjected to a water washing process to produce a cathode active material. The produced cathode active material had an average particle size (D50) of 15 μm, and the overall composition was Li 1.03 Ni 0.8 Co 0.1 Mn 0.1 O2.

[0107] (Comparative Example 2 - 0.005 mol of doping element was added during lithium raw material mixing) (1) Production of cathode active material precursor As the nickel raw material substance, NiSO4·6H2O, as the cobalt raw material substance, CoSO4·7H2O, and as the manganese raw material substance, MnSO4·H2O were dissolved in distilled water to produce a metal salt aqueous solution.

[0108] Next, after preparing a coprecipitation reactor, during the coprecipitation reaction, N2 was purged to prevent oxidation of metal ions, and the temperature of the reactor was maintained at 50 °C.

[0109] NH4(OH) was introduced into the coprecipitation reactor as a chelating agent, and NaOH was used for pH adjustment.

[0110] The precipitate obtained from the coprecipitation process was filtered, washed with distilled water, and then dried in an oven at 100 °C for 24 hours to produce a cathode active material precursor with a composition of (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2.

[0111] (2) Production of cathode active material (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 cathode active material precursor, LiOH·H2O (Samchun Chemicals, battery grade), and Al(OH)2 (Samchun Chemicals) were uniformly mixed in a molar ratio of 1:1.03:0.005 to produce a mixture. The mixture was charged into a tube furnace and fired while flowing oxygen at 200 mL / min. This firing process was carried out by first heat-treating at 480 °C for 5 hours, then raising the temperature to 760 °C at a rate of 5 °C / min and maintaining this temperature for 12 hours.

[0112] The obtained fired product was subjected to a water washing process to produce a cathode active material. The produced cathode active material had an average particle size (D50) of 15 μm, and the overall composition was Li 1.03 Ni 0.795 Co 0.1 Mn 0.1 Al 0.005 O2.

[0113] (Comparative Example 3 - 0.01 mol of doping element was added during lithium raw material mixing) (Ni 0.8 Co 0.1 Mn 0.1)(OH)2 cathode active material precursor, LiOH·H2O (Samchun Chemicals, battery grade), and Al(OH)2 (Samchun Chemicals) were uniformly mixed in a molar ratio of 1:1.03:0.010, and then the procedure was carried out in the same manner as in Comparative Example 2 to produce a cathode active material with a Li 1.03 Ni 0.79 Co 0.1 Mn 0.1 Al 0.01 O2 composition.

[0114] (Comparative Example 4 - 0.02 mol of doping element was added during lithium raw material mixing) (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2 cathode active material precursor, LiOH·H2O (Samchun Chemicals, battery grade), and Al(OH)2 (Samchun Chemicals) were uniformly mixed in a molar ratio of 1:1.03:0.020, and then the procedure was carried out in the same manner as in Comparative Example 2 to produce a cathode active material with a Li 1.03 Ni 0.78 Co 0.1 Mn 0.1 Al 0.02 O2 composition.

[0115] (Example 2 - 0.01 mol of doping element was added during coprecipitation) (1) Production of cathode active material precursor Except that the mixing amounts of the nickel raw material substance and the doping raw material substance were adjusted so that the overall composition of the particles of the produced cathode active material precursor was (Ni 0.79 Co 0.1 Mn 0.1 Al 0.01 )(OH)2, a cathode active material precursor was produced in the same manner as in (1) of Example 1.

[0116] (2) Production of cathode active material The above (Ni 0.79 Co 0.1 Mn 0.1 Al 0.01)(OH)2 cathode active material precursor was used to prepare a cathode active material with a Li 1.03 Ni 0.79 Co 0.1 Mn 0.1 Al 0.01 O2 composition in the same manner as in (2) of Example 1.

[0117] (Example 3 - 0.02 mol of doping element was added during coprecipitation) (1) Preparation of cathode active material precursor The cathode active material precursor was prepared in the same manner as in (1) of Example 1, except that the mixing amounts of the nickel raw material and the doping raw material were adjusted so that the overall composition of the particles of the prepared cathode active material precursor was (Ni 0.78 Co 0.1 Mn 0.1 Al 0.02 )(OH)2.

[0118] (2) Preparation of cathode active material Using the (Ni 0.78 Co 0.1 Mn 0.1 Al 0.02 )(OH)2 cathode active material precursor, a cathode active material with a Li 1.03 (Ni 0.78 Co 0.1 Mn 0.1 Al 0.02 )O2 composition was prepared in the same manner as in (2) of Example 1.

[0119] (Comparative Example 5 - Preparation of non-doped cathode active material) (1) Preparation of cathode active material precursor The cathode active material precursor was prepared in the same manner as in Comparative Example 1, except that the mixing ratio of the nickel raw material, cobalt raw material, and manganese raw material was adjusted to prepare a cathode active material precursor with a (Ni 0.92 Co 0.04 Mn 0.04 )(OH)2 composition.

[0120] (2) Preparation of cathode active material Using the positive electrode active material precursor of (1) above, in the same manner as (2) of Comparative Example 1, the overall composition is Li 1.03 Ni 0.92 Co 0.04 Mn 0.04 O2 positive electrode active material was produced.

[0121] (Comparative Example 6 - 0.005 mol of doping element was added during lithium raw material mixing) (1) Production of positive electrode active material precursor In the same manner as (1) of Comparative Example 5, a positive electrode active material precursor with a composition of (Ni 0.92 Co 0.04 Mn 0.04 )(OH)2 was produced.

[0122] (2) Production of positive electrode active material Using the positive electrode active material precursor of (1) above, except that 0.005 mol of Al(OH)3 (Samchun Chemicals) was mixed, in the same manner as (2) of Comparative Example 2, Li 1.03 Ni 0.915 Co 0.04 Mn 0.04 Al 0.005 O2 positive electrode active material was produced.

[0123] (Example 4 - 0.005 mol of doping element was added during coprecipitation) (1) Production of positive electrode active material precursor Except for adjusting the mixing amounts of nickel, cobalt, manganese raw material substances, and doping raw material substances so that the overall composition of the particles of the produced positive electrode active material precursor becomes (Ni 0.915 Co 0.04 Mn 0.04 Al 0.005 )(OH)2, a positive electrode active material precursor was produced in the same manner as (1) of Example 1.

[0124] (2) Production of positive electrode active material Using the (Ni 0.915 Co 0.04 Mn 0.04 Al 0.005 )(OH)2 positive electrode active material precursor, in the same manner as (2) of Example 1, Li1.03 Ni 0.915 Co 0.04 Mn 0.04 Al 0.005 A cathode active material with an O2 composition was produced.

[0125] (Example 5 - Addition of 0.01 mol of doping element during coprecipitation) (1) Production of cathode active material precursor Except for adjusting the mixing amounts of nickel, cobalt, and manganese raw material substances and doping raw material substances so that the composition of the whole particles of the produced cathode active material precursor becomes (Ni 0.91 Co 0.04 Mn 0.04 Al 0.01 )(OH)2, a cathode active material precursor was produced in the same manner as in (1) of Example 1.

[0126] (2) Production of cathode active material Using the (Ni 0.91 Co 0.04 Mn 0.04 Al 0.01 )(OH)2 cathode active material precursor, a cathode active material with an Li 1.03 Ni 0.91 Co 0.04 Mn 0.04 Al 0.01 O2 composition was produced in the same manner as in (2) of Example 1.

[0127] (Comparative Example 7 - Production of undoped cathode active material) (1) Production of cathode active material precursor Except for adjusting the mixing ratio of nickel raw material substance and cobalt raw material substance to produce a cathode active material precursor with a (Ni 0.96 Co 0.04 )(OH)2 composition, excluding the manganese raw material substance, a cathode active material precursor was produced in the same manner as in Comparative Example 1.

[0128] (2) Production of cathode active material Using the (Ni 0.96 Co 0.04 )(OH)2 cathode active material precursor, the overall composition was LiNi0.96 Co 0.04 The positive electrode active material of CoO₂ was produced.

[0129] (Comparative Example 8 - 0.005 mol of doping element was added during the mixing of lithium raw materials) (1) Production of the positive electrode active material precursor In the same manner as in (1) of Comparative Example 7, a positive electrode active material precursor with a composition of (Ni 0.96 Co 0.04 )(OH)₂ was produced.

[0130] (2) Production of the positive electrode active material Using the (Ni 0.96 Co 0.04 )(OH)₂ positive electrode active material precursor, except that 0.005 mol of Al(OH)₂ (Samchun Chemicals) was mixed, a positive electrode active material with a composition of Li 1.03 Ni 0.955 Co 0.04 Al 0.005 O₂ was produced in the same manner as in (2) of Comparative Example 2.

[0131] (Example 6 - 0.005 mol of doping element was added during coprecipitation) (1) Production of the positive electrode active material precursor Except for excluding the manganese raw material substance and adjusting the mixing amounts of the nickel raw material substance and the cobalt raw material substance so that the overall composition of the particles of the produced positive electrode active material precursor becomes (Ni 0.955 Co 0.04 Al 0.005 )(OH)₂, a positive electrode active material precursor was produced in the same manner as in (1) of Example 1.

[0132] (2) Production of the positive electrode active material Using the (Ni 0.955 Co 0.04 Al 0.005 )(OH)₂ positive electrode active material precursor, a positive electrode active material with a composition of Li 1.03 Ni 0.955 Co 0.04 Al 0.005 O₂ was produced in the same manner as in (2) of Example 1.

[0133] (Example 7 - Adding 0.01 mol of doping element during coprecipitation) Except for adjusting the mixing amounts of the nickel raw material substance and the cobalt raw material substance by excluding the manganese raw material substance so that the composition of the whole particles of the produced cathode active material precursor becomes (Ni 0.95 Co 0.04 Al 0.01 )(OH)2, the cathode active material precursor was produced in the same manner as in (1) of Example 1.

[0134] (2) Production of cathode active material Using the (Ni 0.95 Co 0.04 Al 0.01 )(OH)2 cathode active material precursor, a cathode active material with a composition of Li 1.03 Ni 0.95 Co 0.04 Al 0.01 O2 was produced in the same manner as in (2) of Example 1.

[0135] (Comparative Example 9 - Al doping in LCO during coprecipitation) Except for adjusting the mixing amounts of the nickel raw material substance and the cobalt raw material substance by excluding the manganese raw material substance so that the composition of the whole particles of the produced cathode active material precursor becomes Co(OH)2, the cathode active material precursor was produced in the same manner as in (1) of Example 1.

[0136] (2) Production of cathode active material Using the Co(OH)2 cathode active material precursor, a cathode active material with a composition of Li 1.03 Co 0.99 Al 0.01 O2 was produced in the same manner as in (2) of Example 1. The produced cathode active material had an average particle size (D50) of 8 μm.

[0137] (Comparative Example 10 - Case of pH adjustment and Al doping after NC reaction) NiSO4·6H2O was used as the nickel raw material substance, and CoSO4·7H2O was used as the cobalt raw material substance. These raw materials were dissolved in distilled water to produce a first metal salt aqueous solution.

[0138] Also, as the aluminum raw material substance, Al2(SO4)3·14~18H2O was dissolved in distilled water to produce a second metal salt aqueous solution.

[0139] Next, after preparing a coprecipitation reactor, during the coprecipitation reaction, N2 was purged to prevent oxidation of metal ions, and the temperature of the reactor was maintained at 50°C.

[0140] Using the first metal salt aqueous solution in a coprecipitation reactor, purging with N2, while maintaining the temperature of the reactor at 50°C, NH4(OH) as a chelating agent was introduced into the coprecipitation reactor, and NaOH was added for pH adjustment, and the coprecipitation process was carried out under pH conditions of 11~12 to produce (Ni 0.96 Co 0.04 )(OH)2. After that, using the second metal salt aqueous solution, the coprecipitation process was carried out under the conditions of pH 9.0~10.0 to produce (Ni 0.92 Co 0.04 Al 0.04 )(OH)2.

[0141] The obtained precipitate was filtered, washed with distilled water, and then dried in an oven at 100°C for 24 hours to produce a cathode active material precursor with a composition of (Ni 0.92 Co 0.04 Al 0.04 )(OH)2.

[0142] (2) Production of cathode active material Using the cathode active material precursor of (Ni 0.92 Co 0.04 Al 0.04 )(OH)2, in the same manner as in (2) of Example 1, a cathode active material with a composition of Li 1.03 Ni 0.92 Co 0.04 Al 0.04 O2 was produced. The produced cathode active material had an average particle size (D50) of 14 μm.

[0143] (Experimental Example 1) X-ray diffraction evaluation The lattice constants of the cathode active materials produced according to Examples 1 to 7 and Comparative Examples 1 to 8 were obtained by X-ray diffraction measurement using CuKα radiation. The measured lengths of the a-axis and c-axis are shown in Table 1 below. Also, the distance ratio between crystal axes (c / a axis ratio) is shown in Table 1 below.

[0144] Also, the crystalline size of the active material was measured and shown in Table 1 below.

[0145] Next, using CuKα radiation as the target radiation, an X-ray diffraction measurement test was carried out on the cathode active material using an X’Pert powder (PANalytical) XRD apparatus under the measurement conditions of 2θ = 10° to 130°, scan speed (° / S) = 0.328, and step size of 0.026° / step to obtain the intensities (peak areas) of the (003) plane and (104) plane. From this result, I(003) / I(104) was calculated and the result is shown in Table 1 below.

[0146] For crystallographic consideration of doping, Rietveld analysis was carried out using high score plus Rietveld software, and the result is shown in Table 1 below as the R-factor.

[0147] XRD measurement for Rietveld analysis was carried out using CuKα radiation as the target radiation, using an X’Pert powder (PANalytical) XRD apparatus under the measurement conditions of 2θ = 10° to 130°, scan speed (° / S) = 0.328, and step size of 0.026° / step to obtain the intensities of the (006) plane, (102) plane, and (101) plane. From this result, the R-factor was calculated according to the following formula 1, and the result is shown in Table 1 below. From this result, it can be said that the result of the Rietveld structure analysis is a reliable value because the GOF (Goodness of Fit) value is calculated to be within 1.2. R-factor = {I(006) + I(102)} / I(101)

[0148] The tap density was measured using a tap density measuring instrument (JEL STAV II, J.Engelsmann AG). Specifically, 100 g of the positive electrode active material was tapped 3000 times using a 100 ml graduated cylinder to measure the density.

[0149] In Table 1 below, M means Ni x Co y Mn z means.

[0150]

Table 1

[0151] Referring to Table 1, it can be confirmed that the factor values indicating the crystal structure analyzed by XRD change depending on the doping element input timing and doping amount. In particular, it can be seen that the crystal grain size changes significantly even under the same firing conditions depending on the Al doping amount. On the other hand, when doping with Al, it was found that the a value and c value decreased slightly. Therefore, in the case of Al doping, it is predicted that Al is doped into the Ni sites in the nickel cobalt manganese based positive electrode active material and appropriately plays a role in improving the structural stability. As a result, the initial efficiency and electrochemical physical properties can be generally improved.

[0152] Also, even when doping with the same doping amount, when comparing the case of producing a positive electrode active material after producing a precursor doped with Al by introducing an Al raw material substance together with nickel, cobalt and manganese raw material substances during coprecipitation, and the case of producing a positive electrode active material by mixing an Al raw material substance together with a lithium raw material substance after producing the precursor, the crystal grain size and R - factor all decreased. That is, it can be confirmed once again that producing a positive electrode active material after producing a precursor doped by introducing an Al raw material substance as the doping raw material during coprecipitation has a positive effect on the performance of the positive electrode active material.

[0153] On the one hand, the I(003) / I(104) value, which is the cation mixing index, did not decrease significantly. In particular, when comparing the case of manufacturing the cathode active material by mixing the doping raw material in powder form with the lithium raw material after the production of the precursor, it can be confirmed that when manufacturing the precursor by introducing the Al raw material substance during coprecipitation and then manufacturing the cathode active material, the change range of the c value is large and the change in the crystal grain size is small. From this result, it is expected that when manufacturing the cathode active material according to the examples, the electrochemical properties will be improved, and it can be predicted that the thermal stability will be improved and the DSC peak temperature will be greatly increased.

[0154] (Experimental Example 2) Evaluation of Electrochemical Performance (1) Manufacture of Coin-Type Half-Cell Coin-type half-cells were manufactured using the cathode active materials produced according to Examples 1 to 7 and Comparative Examples 1 to 10.

[0155] Specifically, the cathode active material, Denka black conductive agent, and polyvinylidene fluoride binder (trade name: KF1100) were mixed at a weight ratio of 96.5:1.5:2, and this mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 30% by weight to produce a cathode active material slurry.

[0156] The slurry was coated on an aluminum foil (Al foil, thickness: 15 μm) of the cathode current collector using a doctor blade, dried, and then rolled to produce a cathode. The loading amount of the cathode was about 14.8 mg / cm 2 and the rolling density was about 3.2 g / cm 3 at that time.

[0157] Using the above-mentioned positive electrode, lithium metal negative electrode (200 μm, Honzo metal), electrolyte, and polypropylene separator, a 2032 coin-type half-cell was fabricated by a conventional method. The electrolyte used was a mixed solution prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DEC) with a volume ratio of EC:DMC = 1:1.

[0158] (2) Capacity evaluation After aging the coin-type half-cell at room temperature (25 °C) for 10 hours, a charge-discharge test was carried out.

[0159] For capacity evaluation, a reference capacity of 200 mAh / g was used. The charge-discharge conditions were CC / CV 2.5 V to 4.25 V, 1 / 20C cut-off condition. After charging at 0.1C and discharging at 0.1C, and then charging and discharging at 0.2C, the initial capacity was measured.

[0160] For room temperature cycle life characteristics, measurements were taken at room temperature (25 °C), and for high temperature cycle life characteristics, measurements were taken at high temperature (45 °C) under the condition of 0.3C charge / 0.3C discharge for 30 cycles. Then, the ratio of the 30th discharge capacity to the 1st discharge capacity was measured.

[0161] The results are shown in Tables 2, 3, and 4 below.

[0162] (3) Measurement of resistance characteristics The high-temperature initial resistance (direct current internal resistance: DC-IR) was measured by performing 0.2C charge and 0.2C discharge once on the battery at 45 °C under the constant current-constant voltage conditions of 2.5 V to 4.25 V and 1 / 20C cut-off condition. After charging to 100% at 4.25 V and applying a discharge current, the voltage value after 60 seconds was measured and calculated. The results are shown in Tables 2, 3, and 4 below.

[0163] The resistance increase rate was measured by conducting the measurement in the same manner as the method for measuring the initial resistance after 30 cycles of life with respect to the resistance initially measured at a high temperature (45 °C) (high-temperature initial resistance), and converting the increase rate into a percentage (%). The results are shown in Tables 2, 3, and 4 below.

[0164] The average leakage current was measured by measuring the current generation during a 120-hour period while maintaining the half-cell at 4.7 V at a high temperature of 55 °C, and obtaining the average value of the measured values. The results are shown in Tables 2, 3, and 4 below.

[0165] (4) Thermal stability evaluation Differential scanning calorimetry (DSC) analysis was performed as follows: After charging the half-cell to 4.25 V under an initial 0.1C charging condition, the half-cell was disassembled to separately obtain only the positive electrode. This positive electrode was washed 5 times with dimethyl carbonate and prepared. After impregnating the washed positive electrode into the crucible for DSC with the electrolyte, while increasing the temperature to 265 °C, the heat quantity change was measured using the DSC1 star system of Mettler Toledo by a DSC instrument. The results of the obtained DSC peak temperature and heat generation amount are shown in Tables 2, 3, and 4 below. The DSC peak temperature indicates the temperature at which the exothermic peak appears.

[0166]

Table 2

[0167] Table 2 shows the results of measuring the electrochemical properties of the cathode active materials of Comparative Examples 1 to 4 and Examples 1 to 3 in which the Al doping amount was changed based on 0.80 mol of Ni, 0.10 mol of Co, and 0.10 mol of Mn. At the same time, for comparison, after producing an LCO precursor doped with Al by introducing Al during coprecipitation, the electrochemical properties of Comparative Example 9 in which the cathode active material was produced and Comparative Example 10 in which the pH range was adjusted after the nickel and cobalt reactions, and an aluminum-doped precursor was produced by introducing an aluminum doping raw material and then the cathode active material was produced are also shown in Table 2. Referring to Table 2, in the case of Comparative Example 1 where no metal element was doped, the discharge capacity was 210.1 mAh / g, and the normal temperature and high temperature life were 96% and 93% respectively, but it can be confirmed that the resistance increase rate was 113% and the average leakage current was 0.51 mA, which were very high. In particular, it can be confirmed that the DSC peak temperature indicating the thermal stability index was 225.2 °C, and the thermal stability was very low.

[0168] In the case of Comparative Examples 2 to 4 in which an Al-doped cathode active material was produced by mixing Al with a lithium raw material after the production of the precursor, the structure was slightly stabilized, and when compared with Comparative Example 1, the average leakage current and DSC were slightly improved, and the normal temperature and high temperature cycle life characteristics were improved, but the capacity decreased significantly.

[0169] Also, in the case of Comparative Example 9 which is an Al-doped LCO cathode material, it can be confirmed that the resistance characteristics were slightly improved, and the thermal stability and life characteristics were also slightly improved, but the capacity was significantly low.

[0170] At the same time, in the case of Comparative Example 10, it can be confirmed that the initial resistance and the resistance increase rate were very high, the initial efficiency and thermal stability decreased, and all the normal temperature and high temperature life characteristics and capacity characteristics decreased.

[0171] In contrast, after manufacturing a doped precursor by adding an Al raw material together in the coprecipitation process for manufacturing the precursor and then manufacturing a positive electrode active material, in the cases of Examples 1 to 3 of manufacturing the positive electrode active material, although not excellent in capacity, it can be confirmed that the normal temperature and high temperature life characteristics, high temperature initial resistance, resistance increase rate, and average leakage current characteristics are significantly improved. In particular, since the DSC peak temperature is also very high, it can be confirmed that the structural stability is ensured.

[0172] When considering such results, it can be confirmed that manufacturing a positive electrode active material after manufacturing a precursor doped by adding Al during coprecipitation brings very advantageous results to the physical properties of the positive electrode active material.

[0173]

Table 3

[0174]

Table 4

[0175] Table 3 shows the results of measuring the electrochemical characteristics of the positive electrode active materials of Comparative Examples 5 to 6 and Examples 4 to 5 in which the doping amount of Al was changed based on 0.92 mol of Ni, 0.04 mol of Co, and 0.04 mol of Mn. Table 4 shows the results of measuring the electrochemical characteristics of the positive electrode active materials of Comparative Examples 7 to 8 and Examples 6 to 7 in which the doping amount of Al was changed based on 0.96 mol of Ni and 0.04 mol of Co.

[0176] Referring to Table 3 and Table 4, it can be seen that they show a form similar to the results of Table 2.

[0177] It can be seen that in the positive electrode active materials of Examples 4 to 7 in which Al was doped in the coprecipitation process, since Al was uniformly doped to the inside of the positive electrode active material, the capacity decrease was small and the normal temperature and high temperature life characteristics increased. At the same time, it can be seen that the initial resistance, resistance increase rate, and average leakage current decreased.

[0178] In addition, it was confirmed that the structural stability of the positive electrode active material particles increased and the DSC temperature increased.

[0179] When considering such results, as in the present invention, when manufacturing a positive electrode active material after manufacturing a doped precursor by introducing an Al doping raw material in the coprecipitation step during the manufacture of the precursor, it can be seen that the performance of the positive electrode active material with a very high nickel content can be remarkably improved.

[0180] (Experimental Example 3) Cross-sectional analysis of positive electrode active material (FIB-EDS(Al) analysis) For the positive electrode active materials manufactured according to Example 3 and Comparative Example 4, the cross-section was cut with FIB (Focused Ion Beam, SEIKO 3050SE), and element mapping was performed using an SEM (Scanning Electron Microscope, JEOL JSM-6610) apparatus.

[0181] Specifically, at a point with a uniform distance from the inside to the surface of the secondary particles in the cross-section of the positive electrode active material, line scanning was performed for the Al element. The results are shown in FIGS. 2 and 3. That is, FIGS. 2 and 3 are the results of analyzing the Al element present inside the positive electrode active materials manufactured according to Example 3 and Comparative Example 4, respectively. The spectrum is the position shown in the SEM photograph, and the numerical value indicates the Al mol% present at that position.

[0182] Referring to FIG. 2, it can be confirmed that the concentration of Al is uniformly maintained at the particle surface and the center of the positive electrode active material of Example 3, and the average concentration of Al in the central portion and the surface portion (spectra 1-3: corresponding to about 30% of the radius) is all about 1.4 mol%, and it can be seen that there is no concentration difference.

[0183] In contrast, as shown in FIG. 3, in the positive electrode active material of Comparative Example 4, the Al concentration is higher toward the particle surface and lower toward the particle center, and the average Al concentrations in the central part and the surface part (Spectra 1-3, which corresponds to a length of about 30% of the radius) are about 1.5 mol % and about 2.87 mol %, respectively, and it can be seen that the concentration difference of Al between the central part and the surface part is as large as about 1.37 mol %.

[0184] Together with this, in the same manner as in Example 3 and Comparative Example 4, the Al concentrations in the surface part and the central part of the positive electrode active materials manufactured by Examples 1, 2, and 4 to 7 and Comparative Examples 1 to 3 and 5 to 8 were measured, and the results are shown in Table 5 below. For comparison, the results of Example 3 and Comparative Example 4 are also shown in Table 5 below.

[0185]

Table 5

[0186] As shown in Table 5 above, in the case of Examples 1 to 7, the concentration difference of Al between the central part and the surface part is 0 mol % to 1 mol %, whereas in the case of Comparative Examples 2-4, 6, and 8 doped with Al, the concentration difference is 1.32 mol % to 1.41 mol %, and it can be seen that it is very large.

[0187] The present invention is not limited to the above examples and can be manufactured in various different forms. Those having ordinary knowledge in the technical field to which the present invention pertains will understand that it can be implemented in other specific forms without changing the technical idea and essential features of the present invention. Therefore, it must be understood that the above-described examples are illustrative in all respects and not restrictive.

Claims

1. Lithium nickel-based compound particles with a Ni content of 75 mol% or more, wherein the concentration difference of Al between the central part and the surface part of the lithium nickel-based compound particles is 1 mol% or less, the surface part is a region corresponding to a length of 30% or less of the average radius of the lithium nickel-based compound particles in the depth direction from the outermost surface of the lithium nickel-based compound particles, the average concentration of Al in the central part of the lithium nickel-based compound particles is 0.52 to 1.4 mol%, a positive electrode active material for a lithium secondary battery.

2. The average particle diameter (D50) of the lithium nickel-based compound particles is 10 μm to 20 μm, and the positive electrode active material for a lithium secondary battery according to Claim 1.

3. The lithium nickel-based compound particles are represented by the following Chemical Formula 1, and the positive electrode active material for a lithium secondary battery according to Claim 1. Li ａ Ni ｘ Co ｙ Mn ｚ Al １－（ｘ＋ｙ＋ｚ） O ２ (In the Chemical Formula 1, a is 0.95 ≤ a ≤ 1.15, x is 0.75 ≤ x ≤ 0.98, y is 0 < y < 0.2, z is 0 < z < 0.2, and y + z ≤ 0.25)

4. In the Chemical Formula 1, x + y + z is in the range of 0.98 to 0.999, and the positive electrode active material for a lithium secondary battery according to Claim 3.

5. A step of co-precipitating a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and an aluminum raw material substance in a solvent to produce a precursor compound; a step of mixing the precursor compound and a lithium raw material substance to form a mixture; and a method for producing a positive electrode active material for a lithium secondary battery including a step of firing the mixture, wherein the positive electrode active material for a lithium secondary battery is lithium nickel-based compound particles with a Ni content of 80 mol% or more, and the concentration difference of Al between the central part and the surface part of the lithium nickel-based compound particles is 1 mol% or less, the surface part is a region corresponding to a depth of 30% or less of the average radius of the lithium nickel-based compound particles in the depth direction from the outermost surface of the lithium nickel-based compound particles, a method for producing a positive electrode active material for a lithium secondary battery.

6. The step of co-precipitation is carried out at a pH of 11.0 to 12.0, and the method for producing a positive electrode active material for a lithium secondary battery according to Claim 5.

7. The Al content in the lithium nickel-based compound particles is, The method for producing a positive electrode active material for a lithium secondary battery according to claim 5, wherein the amount is 0.1 mol% to 2 mol% based on the total metal elements excluding lithium in the lithium nickel-based compound particles.

8. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 4; a negative electrode; and a non-aqueous electrolyte A lithium secondary battery comprising the same.

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