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

Abstract

The positive electrode active material according to an embodiment of the present invention may comprise a lithium composite transition metal oxide represented by chemical formula 1. [Chemical formula 1] LiaNibMncTidZreMfO2. In chemical formula 1, M is Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Zn, F, P, S, Y, W, Mo, B, or a combination thereof, 0.8≤a≤1.2, 0.6≤b<1.0, 0.2≤c≤0.5, 0<d≤0.1, 0<e≤0.1, 0≤f≤0.01, and b+c+d+e+f=1.

Description

Cathode active material, cathode, and lithium secondary battery

[0001] [Cross-reference with related applications]

[0002] This application claims the benefit of priority to Korean Patent Application No. 2023-0150224, filed November 2, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] [Technical Field]

[0005] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0006] Lithium secondary batteries, which allow for repeated charging and discharging, are attracting attention as an alternative to fossil fuels. Lithium secondary batteries have been primarily used in traditional handheld devices such as cell phones, video cameras, and power tools. However, their applications are gradually expanding to include electric vehicles (EVs, HEVs, PHEVs), large-capacity energy storage systems (ESSs), and uninterruptible power supply systems (UPSs). A lithium secondary battery consists of an electrode assembly, which is a collection of unit cells each having a structure in which a positive and negative electrode plates, each coated with an active material on a current collector, are arranged with a separator between them, and an outer case, i.e., a battery case, that seals and encloses the electrode assembly together with an electrolyte.

[0007] Lithium composite transition metal oxides are used as positive electrode active materials for lithium secondary batteries, and among these, lithium cobalt oxide of LiCoO2, lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate compound (LiFePO4), or LiNiO2 are mainly used. In addition, as a method to improve the low thermal stability of LiNiO2 while maintaining the excellent reversible capacity, nickel manganese lithium composite metal oxides in which some of the nickel is replaced with manganese, which has excellent thermal stability, and NCM in which manganese and cobalt are replaced are being used.

[0008] However, in the case of cobalt, the cost is high and there are environmental issues in the process of supplying raw materials, so research is being conducted recently on methods for manufacturing cobalt-free positive electrode active materials with no or very small amounts of cobalt.

[0009] However, in the case of cobalt-free cathode active materials, Li is relatively low due to the lack of cobalt. + / Ni 2+ There was a problem that cation mixing increased, resulting in inferior capacity and initial resistance performance, and operation at a relatively high voltage (4.4 V or higher) was essential to overcome the insufficient energy density and capacity performance compared to cathode materials with a high cobalt content.

[0010] Accordingly, in the case of cobalt-free cathode active materials, they are manufactured in the form of single particles to prevent cracks due to greater shrinkage and expansion of lattice parameters during the charge and discharge process when driven at high voltage. However, single particles also deteriorate when driven at high voltage, such as irreversible phase transitions caused by cation mixing of Li+ / Ni2+, and the inferiority in capacity, life characteristics, and initial resistance performance becomes more prominent. Therefore, a doping technology that can lower resistance while obtaining structural stability is needed to prevent this.

[0011] [Prior Art Literature]

[0012] [Patent Document]

[0013] (Patent Document 0001) KR 10-2020-0047116 A

[0014] The problem to be solved by the present invention is to provide a cobalt-free positive electrode active material having excellent structural stability and excellent life characteristics.

[0015] (1) The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Li a Ni b Mn c Ti d Zr e M f O2

[0018] In the above chemical formula 1, M is Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Zn, F, P, S, Y, W, Mo, B or a combination thereof,

[0019] 0.8≤a≤1.2, 0.5≤b<0.8, 0.2≤c≤0.5, 0 <d≤0.1, 0<e≤0.1, 0≤f≤0.01, b+c+d+e+f=1이다.

[0020] (2) The present invention provides a positive electrode active material having a capacity retention rate of 92.5% or more after 50 or more charge / discharge cycles, for a half coin cell including a positive electrode including the positive electrode active material and a lithium metal negative electrode, when the positive electrode potential at full charge is 4.45 V based on Li potential, in the above (1).

[0021] (3) The present invention provides a positive electrode active material having an initial resistance value of 45.0Ω or less when the positive electrode potential at full charge is 4.45 V based on Li potential, for a half coin cell including a positive electrode including the positive electrode active material and a lithium metal negative electrode in the above (1) or (2).

[0022] (4) The present invention provides a positive electrode active material that satisfies 0.001≤d≤0.05 in the chemical formula 1 in any one of the above (1) to (3).

[0023] (5) The present invention provides a positive electrode active material that satisfies 0.001≤e≤0.05 in the chemical formula 1 in any one of the above (1) to (4).

[0024] (6) The present invention provides a positive electrode active material according to any one of the above (1) to (5), wherein the positive electrode active material further includes Co, but includes Co in an amount of 0.04 mol% or less based on the total content of Ni, Mn, Ti, Zr, M, and Co.

[0025] (7) The present invention provides a positive electrode active material in any one of the above (1) to (6), wherein the lithium composite transition metal oxide does not contain Co.

[0026] (8) The present invention provides a positive electrode active material in any one of the above (1) to (7), wherein Ti and Zr of the above chemical formula 1 are incorporated into the crystal lattice structure of the above lithium composite transition metal oxide.

[0027] (9) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (8).

[0028] (10) The present invention provides a lithium secondary battery including a positive electrode according to (9).

[0029] The cathode active material according to the present invention is a cobalt-free cathode active material, has excellent structural stability, and has excellent life characteristics.

[0030] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0031] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0032]

[0033] In the present invention, the term 'average particle diameter (D 50 )' means the particle size at the 50% point of the volume cumulative distribution according to particle size. The above average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., S3500 from Microtrac), and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where it becomes 50% of the volume cumulative distribution according to particle size in the measuring device, thereby obtaining D 50 can measure

[0034]

[0035] In the following specification, a cobalt-free positive electrode active material means that the lithium composite transition metal oxide included in the cobalt-free positive electrode active material does not include cobalt, or even if it does, it includes cobalt in an amount of 0.04 mol% or less, 0.035 mol% or less, 0.03 mol% or less, 0.025 mol% or less, or 0.02 mol% or less, relative to the total content of all transition metals (including cobalt) included in the lithium composite transition metal oxide.

[0036]

[0037] <Cathode active material>

[0038] The present invention provides a positive electrode active material.

[0039] In the case of conventional cobalt-free cathode active materials, the Li + / Ni 2+As the cation mixing increases, the capacity and initial resistance performance are inferior, the resistance increase rate increases at high temperatures, and the lifespan decreases. In particular, in the case of a cobalt-free cathode active material with a layered structure and a high-nickel polycrystalline structure containing more than 60 mol% of nickel (Ni) among metals other than lithium, expansion and contraction of the lattice structure occurs when charge and discharge are performed, and the electrolyte penetrates into the resulting microcracks, resulting in rapid deterioration such as a decrease in lifespan and an increase in resistance. In addition, in the case of a polycrystalline cathode active material, there is a problem of gas generation due to particle cracking and electrolyte side reactions in a high-voltage driving environment of 4.4 V or higher.

[0040]

[0041] The inventors of the present invention have discovered that when a cobalt-free cathode active material is doped with specific metal elements, namely Ti and Zr, in a predetermined amount or more, the initial resistance is reduced when driven at a high voltage of 4.4 V or higher, and the capacity retention rate in long-term high-voltage / high-temperature cycles (4.4 V or higher, 45°C or higher, 50 cycles or higher) is improved, thereby completing the invention.

[0042]

[0043] In the following specification, when a metal element is said to be "doped" into the positive electrode active material, it may mean that the metal element does not form a chemical bond with the lithium composite transition metal oxide and its constituent elements, but at least a portion of the metal element is incorporated into the crystal lattice structure of the lithium composite transition metal oxide and is physically / crystallographically connected. In this case, at least a portion of the metal element incorporated into the crystal lattice structure of the lithium composite transition metal oxide may be, for example, inserted into an empty crystal lattice structure of the lithium composite transition metal oxide and is physically / crystallographically connected without forming a chemical bond with the lithium composite transition metal oxide.

[0044] If, instead of doping the lithium composite transition metal with these metal elements, a coating layer containing these metal elements is formed on the outside of the lithium composite electric metal, Ti 4+ , Zr 4+ It is difficult to obtain the stability improvement effect at the time of phase transition (H2-H3 phase transition) that occurs in high-valenced ion doping such as , and the metal element coating layer on the surface is Li during charge / discharge. + It can act as a resistor by hindering the movement of ions, and when the layered cathode active material is driven at high voltage, the irreversible capacity of the active material increases due to the rapid volume change accompanying the phase transition, and stability problems arise due to side reactions with the electrolyte.

[0045]

[0046] A cathode active material according to one embodiment of the present invention includes a lithium composite transition metal oxide represented by the following chemical formula 1.

[0047] [Chemical Formula 1]

[0048] Li a Ni b Mn c Ti d Zr e M fO2

[0049] In the above chemical formula 1, M is Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Zn, F, P, S, Y, W, Mo, B or a combination thereof,

[0050] 0.8≤a≤1.2, 0.5≤b<0.8, 0.2≤c≤0.5, 0 <d≤0.1, 0<e≤0.1, 0≤f≤0.01, b+c+d+e+f=1이다.

[0051]

[0052] According to one embodiment of the present invention, the a represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be 0.8 or more and 1.2 or less, and as a specific example, may be 0.84 or more, 0.88 or more, 0.92 or more, 0.96 or more, or 1.00 or more, and may also be 1.18 or less, 1.16 or less, 1.14 or less, 1.12 or less, 1.10 or less, 1.08 or less, 1.06 or less, or 1.04 or less.

[0053]

[0054] According to one embodiment of the present invention, the b represents the molar ratio of nickel in the lithium composite transition metal oxide, and may be 0.5 or more and less than 0.8, and for specific examples, may be 0.52 or more, 0.54 or more, 0.56 or more, 0.58 or more, or 0.6 or more, and may also be 0.78 or less, 0.76 or less, 0.74 or less, 0.72 or less, 0.70 or less, or 0.68 or less. When the above range is satisfied, excellent charge / discharge efficiency and excellent lifespan stability can be secured at the same time. If the molar ratio of nickel in the lithium composite transition metal oxide exceeds the above range, stability at high voltage decreases, and thus stable output and lifespan stability may not be achieved. In addition, when the molar ratio of nickel in the lithium composite transition metal oxide is less than the above range, excellent charge / discharge efficiency may not be achieved.

[0055]

[0056] According to one embodiment of the present invention, c represents a molar ratio of manganese in a lithium composite transition metal oxide, and may be 0.2 or more and 0.5 or less, and as a specific example, may be 0.22 or more, 0.24 or more, 0.26 or more, 0.28 or more, or 0.3 or more, and further, may be 0.48 or less, 0.46 or less, 0.44 or less, 0.42 or less, or 0.4 or less.

[0057]

[0058] According to one embodiment of the present invention, the titanium doped in the positive electrode active material is a cation, i.e., Ti 4+ It exists as Ti 4+ is nickel in lithium complex transition metal oxide, i.e. Ni 2+ Similar size (Ti 4+ : 0.61Å, Ni 2+ : 0.69Å), so T is the midpoint of the path that the Ni ion moves. d By stably positioning it at the (tetrahedral site) and suppressing Ni migration, cation mixing can be reduced, and by providing a stable structure, electrochemical properties can be improved.

[0059] According to one embodiment of the present invention, the d represents the molar ratio of titanium in the lithium composite transition metal oxide, and may be greater than 0 and less than or equal to 0.1, and for specific examples, may be 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, or 0.005 or more, and may also be 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, or 0.05 or less. When titanium is doped in an amount less than the above range, the effect of improving the electrochemical characteristics of the titanium ion is not exhibited, and when titanium is doped in an amount exceeding the above range, the doped titanium may act as surface resistance, which may reduce the charge / discharge capacity.

[0060]

[0061] According to one embodiment of the present invention, Zr for the layered positive electrode active material 4+ Doping of Zr is known to promote lithium ion insertion and deintercalation reactions through expansion of the transition metal-lithium layer. 4+ It has strong binding energy with the oxygen lattice and can improve the life stability by suppressing the irreversible deformation of the layered structure.

[0062] According to one embodiment of the present invention, the e represents the molar ratio of zirconium in the lithium composite transition metal oxide, and may be greater than 0 and less than or equal to 0.1, and for specific examples, may be 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, or 0.005 or more, and may also be 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, or 0.05 or less. When zirconium is doped in an amount less than the above range, the effect of improving the electrochemical characteristics of the zirconium ion is not exhibited, and when zirconium is doped in an amount exceeding the above range, the doped zirconium may act as surface resistance, thereby reducing the charge / discharge capacity.

[0063]

[0064] According to one embodiment of the present invention, the lithium composite transition metal oxide can maximize the stability effect of each layered structure through Ti4+ doping in the transition metal layer and Zr4+ doping in the lithium ion layer. In recent research trends, composite doping through analysis of binding energy of metal elements is in the spotlight, and when composite doping of various elements is performed, it can have lower binding energy and higher stability compared to when doping with a single element.

[0065]

[0066] According to one embodiment of the present invention, the f represents the molar ratio of M in the lithium composite transition metal oxide, and may be greater than 0 and less than or equal to 0.1, and as a specific example, may be 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, or 0.005 or more, and further may be 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, or 0.05 or less.

[0067] According to one embodiment of the present invention, the M may be Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, F, P, S, Zr, Zn, Y, Ti, W, Mo, B or a combination thereof.

[0068]

[0069] By having the composition as described above, the positive electrode active material according to one embodiment of the present invention can have a reduced initial resistance when driven at a high voltage of 4.4 V or higher, and an improved capacity retention rate in a long-term high voltage / high temperature cycle (4.4 V or higher, 45°C or higher, 50 cycles or higher).

[0070] According to one embodiment of the present invention, when the positive electrode active material has a positive electrode potential of 4.45 V based on Li potential at full charge, the capacity retention rate after 50 or more charge / discharge cycles may be 92.5% or more, and specifically, 92.8% or more, 93% or more, 93.3% or more, 93.4% or more, 93.5% or more, 93.6% or more, 93.7% or more, or 93.8% or more.

[0071] According to one embodiment of the present invention, when the positive electrode active material has a positive electrode potential of 4.45 V based on Li potential at full charge, the initial resistance value may be 45.0 Ω or less, and specifically, 44.4 Ω or less, 44.3 Ω or less, 44.2 Ω or less, 44.1 Ω or less, 44 Ω or less, 43.9 Ω or less, or 43.8 Ω or less.

[0072]

[0073] <Method for manufacturing positive electrode active material>

[0074] The present invention provides a manufacturing method for manufacturing the positive electrode active material.

[0075] A method for manufacturing a positive electrode active material according to one embodiment of the present invention comprises the steps of: supplying a transition metal-containing solution including a transition metal-containing raw material including nickel and manganese, an ammonium cation complex forming agent, and a basic compound to a reactor while performing a co-precipitation reaction to form precursor particles for a positive electrode active material; washing the precursor particles for a positive electrode active material with water to manufacture a precursor for a positive electrode active material; and mixing the precursor for a positive electrode active material, a lithium raw material, and a doping element raw material including Ti and Zr, and firing the mixture at 800°C to 950°C.

[0076] According to one embodiment of the present invention, the step of forming the precursor particles for the positive electrode active material may be prepared by, for example, dissolving each transition metal-containing raw material in a solvent to prepare a transition metal-containing solution, then mixing the transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound, and then performing a coprecipitation reaction. In addition, an oxidizing agent or oxygen gas may be additionally added during the coprecipitation reaction, if necessary.

[0077] According to one embodiment of the present invention, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel sulfide, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, manganese sulfide, etc.

[0078] According to one embodiment of the present invention, the ammonium cation complex forming agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0079] According to one embodiment of the present invention, the basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a precursor in the form of a hydroxide may be obtained, and when Na2CO3 is used as the basic compound, a precursor in the form of a carbonate may be obtained. In addition, when a basic compound and an oxidizing agent are used together, a precursor in the form of an oxide may be obtained.

[0080] According to one embodiment of the present invention, the precursor for the positive electrode active material may be in the form of a hydroxide, oxide or carbonate.

[0081] According to one embodiment of the present invention, the step of washing the precursor particles for the positive electrode active material with water can be performed using deionized water, and it is preferable that no other substance is added during the washing.

[0082] According to one embodiment of the present invention, the lithium raw material may include, for example, lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3)), chlorides (e.g., lithium chloride (LiCl)), etc., and one of these may be used alone or a mixture of two or more thereof may be used.

[0083] According to one embodiment of the present invention, the precursor for the positive electrode active material and the lithium raw material can be mixed in an amount such that the molar ratio of the total transition metal (Ni+Mn):Li is 1:1.02 to 1:1.2, preferably 1:1.03 to 1:1.15, and more preferably 1:1.06 to 1:1.1.

[0084] According to one embodiment of the present invention, the firing may be performed at a temperature of 800°C to 950°C, preferably 850°C to 950°C, and more preferably 870°C to 920°C. When the firing temperature is 800°C or higher, the structural completeness can be improved, but it is preferable not to exceed 950°C in order to prevent excessive growth of primary particles. The firing time may be 5 hours to 20 hours, and preferably 9 hours to 15 hours. In addition, the firing atmosphere may be an air atmosphere or an oxygen atmosphere, and for example, may be an atmosphere containing 20 to 100 volume% of oxygen.

[0085]

[0086] Bipolar

[0087] According to one embodiment of the present invention, a positive electrode including the positive electrode active material described above is provided.

[0088] 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 including the positive electrode active material described above.

[0089] According to one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0090] According to one embodiment of the present invention, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above.

[0091] According to one embodiment of the present invention, at this time, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0092] According to one embodiment of the present invention, the binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0093] According to one embodiment of the present invention, the positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode active material layer forming composition, which is manufactured by mixing or dispersing the positive electrode active material and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0094] According to one embodiment of the present invention, the solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0095] Additionally, in another method, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0096]

[0097] Lithium secondary battery

[0098] According to one embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0099] According to one embodiment of the present invention, the lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0100] According to one embodiment of the present invention, in the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0101] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0102] According to one embodiment of the present invention, the negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0103] According to one embodiment of the present invention, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples 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 alloy, Sn alloy, or Al alloy; SiO x(0 < x < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0104] Additionally, the binder and the conductive material may be the same as those described above for the positive electrode.

[0105] According to one embodiment of the present invention, the negative electrode active material layer may be manufactured by, for example, applying a negative electrode forming composition prepared by 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 coating, or by casting the negative electrode forming composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative electrode current collector.

[0106] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0107] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0108] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0109] According to one embodiment of the present invention, the organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0110] According to one embodiment of the present invention, the lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0111] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0112] According to one embodiment of the present invention, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0113]

[0114] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0115]

[0116] Example 1

[0117] Ni, a cathode active material precursor having an average particle size of 9 ㎛ 0.77 Mn 0.23 (OH)2 TiO2 raw material and ZrO2 raw material were weighed in amounts of 1 mol% and 0.24 mol% of the precursor, respectively, and lithium raw material LiOH H2O was simultaneously added to a paste mixer (300 cc) so that the final Li / Me(Ni,Mn) molar ratio was 1.07 to prepare a mixture. The mixture was mixed using an acoustic mixer at 40 G (Gravitational Force) for 1 minute, then at 50 G for 1 minute, then at 60 G for 1 minute, and then at 70 G for 1 minute, for a total of 4 minutes of mixing. The mixed powder was placed in a 200 cc alumina crucible and fired in an oxygen (O2) atmosphere at 810 ℃ for 9 hours to prepare a cathode active material.

[0118]

[0119] Example 2

[0120] A cathode active material was manufactured as in Example 1, except that the TiO2 raw material was measured in an amount of 2 mol% of the precursor.

[0121]

[0122] Comparative Example 1

[0123] A cathode active material was manufactured as in Example 1, except that 1 mol% of TiO2 raw material and 0.24 mol% of ZrO2 raw material were not added.

[0124]

[0125] Comparative Example 2

[0126] A positive electrode active material was manufactured as in Example 1, except that 0.24 mol% of ZrO2 raw material was not added.

[0127]

[0128] Comparative Example 3

[0129] A positive electrode active material was manufactured as in Example 1, except that 1 mol% of TiO2 raw material was not added.

[0130]

[0131] Comparative Example 4

[0132] Ni, a cathode active material precursor having an average particle size of 9 ㎛ 0.77 Mn 0.23 (OH)2 and lithium raw materials LiOH·H2O were simultaneously added to a paste mixer (300 cc) so that the final Li / Me(Ni,Mn) molar ratio was 1.07. The mixture was mixed using an acoustic mixer at 40 G (Gravitational Force) for 1 minute, then at 50 G for 1 minute, then at 60 G for 1 minute, and then at 70 G for 1 minute, for a total of 4 minutes of mixing. The mixed powder was placed in a 200 cc alumina crucible and fired in an oxygen (O2) atmosphere at 810°C for 9 hours to manufacture a cathode active material.

[0133] Afterwards, TiO2 raw material and ZrO2 raw material were weighed in amounts of 1 mol% and 0.24 mol% of the moles of transition metals in the manufactured positive electrode active material, respectively, and simultaneously added to a paste mixer (300 cc) to prepare a mixture. The mixture was mixed for 2 minutes at 60 G using an acoustic mixer, for a total of 2 minutes. The mixed powder was placed in a 200 cc alumina crucible and fired for 6 hours and 30 minutes in an oxygen (O2) atmosphere at 700°C to prepare a positive electrode active material coated with TiO2 and ZrO2.

[0134]

[0135] Comparative Example 5

[0136] Ni, a cathode active material precursor having an average particle size of 9 ㎛ 0.78 Co 0.02 Mn 0.2 (OH)2, TiO2 raw material, ZrO2 raw material, and Co(OH)2 raw material were weighed in amounts of 1 mol%, 0.24 mol%, and 3 mol% of the precursor, respectively, and lithium raw material LiOH·H2O was simultaneously added to a paste mixer (300 cc) so that the final Li / Me(Ni, Co, Mn) molar ratio was 1.07 to prepare a mixture. The mixture with a Co content of 5 mol% was mixed using an acoustic mixer at 40 G (Gravitational Force) for 1 minute, then at 50 G for 1 minute, then at 60 G for 1 minute, and then at 70 G for 1 minute, for a total mixing time of 4 minutes. The mixed powder was placed in a 200 cc alumina crucible and calcined in an oxygen (O2) atmosphere at 810 ℃ for 9 hours to prepare a cathode active material.

[0137]

[0138] Comparative Example 6

[0139] Ni, a cathode active material precursor having an average particle size of 9 ㎛ 0.85 Mn0.15 (OH)2 TiO2 raw material and ZrO2 raw material were weighed in amounts of 1 mol% and 0.24 mol% of the precursor, respectively, and lithium raw material LiOH H2O was simultaneously added to a paste mixer (300 cc) so that the final Li / Me(Ni,Mn) molar ratio was 1.07 to prepare a mixture. The mixture was mixed using an acoustic mixer at 40 G (Gravitational Force) for 1 minute, then at 50 G for 1 minute, then at 60 G for 1 minute, and then at 70 G for 1 minute, for a total of 4 minutes of mixing. The mixed powder was placed in a 200 cc alumina crucible and fired in an oxygen (O2) atmosphere at 800°C for 9 hours to prepare a cathode active material.

[0140]

[0141] Experimental Example 1 - Measurement of Elemental Content

[0142] The element content of each positive electrode active material manufactured in the above examples and comparative examples was measured by SEM-EDS analysis using FESEM (JSM7610F, Jeol Co.), and is listed in Table 1 below. The EDS system injects X-rays of a specific wavelength range into a sample, and then analyzes the unique energy emission of each element to indicate the abundance ratio of the element.

[0143]

[0144] Transition metal (mol %)Example 12123456Ni76.4074.4677.0976.1276.5477.0174.1184.44Co------5.02-Mn22.4323.4322.9122.9423.1821.7019.7714.28Ti0.951.92-0.94-1.020.921.04Zr0.220.19--0.280.270.180.24

[0145] Experimental Example 2 - Life Characteristics Evaluation

[0146] Each of the positive electrode active materials, carbon black, conductive agent, and PVDF binder manufactured in the above examples and comparative examples was mixed in an N-methylpyrrolidone solvent at a weight ratio of 97.5:1:1.5 to manufacture a positive electrode slurry, which was then applied to an aluminum current collector, dried at 130°C, and rolled to a porosity of 24% to manufacture a positive electrode. Lithium metal was used as the negative electrode.

[0147] Lithium metal was used as a counter electrode, and a half coin cell was manufactured using a porous polyethylene separator and an electrolyte consisting of 1.0 M lithium hexafluorophosphate (LiPF6) in a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) (volume ratio = 3 / 4 / 3).

[0148] For each lithium secondary battery half coin cell manufactured as described above, the capacity retention rate was measured when a charge / discharge experiment was performed 50 times by charging at 0.5 C to 4.45 V in CC / CV mode at 45°C and discharging at a constant current of 1 C to 2.5 V, and the results are shown in Table 2 below.

[0149]

[0150] Experimental Example 3 - Evaluation of Charge-Discharge Efficiency and Resistance Characteristics

[0151] Each of the positive electrode active materials, carbon black, conductive agent, and PVDF binder manufactured in the above examples and comparative examples was mixed in an N-methylpyrrolidone solvent at a weight ratio of 97.5:1:1.5 to manufacture a positive electrode slurry, which was then applied to an aluminum current collector, dried at 130°C, and rolled to a porosity of 24% to manufacture a positive electrode. Lithium metal was used as the negative electrode.

[0152] Lithium metal was used as a counter electrode, and a half coin cell was manufactured using a porous polyethylene separator and an electrolyte consisting of 1.0 M lithium hexafluorophosphate (LiPF6) in a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) (volume ratio = 3 / 4 / 3).

[0153] For each lithium secondary battery half coin cell manufactured as described above, the charge / discharge efficiency and initial resistance, which are defined as the ratio of the discharge capacity to the charge capacity, were measured using the voltage change over 60 seconds when charging to 4.45 V at 0.1 C in CC / CV mode at 25°C and discharging to 2.5 V at a constant current of 0.1 C, and are listed in Table 2 below.

[0154]

[0155] 4.45V, 0.1C charge / discharge 4.45V, 45℃ 50 cycle charge / discharge efficiency (%) Initial resistance (Ω) Capacity retention rate (%) Example 188.64 3.89 3.8 Example 288.14 2.79 2.7 Comparative example 189.24 98 6.6 Comparative example 288.64 5.89 1.3 Comparative example 388.54 6.89 2.1 Comparative example 489.55 5.49 4.3 Comparative example 590.145.889.1 Comparative example 691.04 7.19 0.8

[0156] Referring to Tables 1 and 2 above, it was confirmed that in the case of Examples 1 and 2 in which Ti and Zr were compositely doped, low initial resistance and excellent capacity retention were secured.

[0157]

[0158] In the case of Comparative Example 4 coated with Ti and Zr, it was confirmed that the initial resistance was significantly lower compared to Examples 1 and 2. This is interpreted as the Ti and Zr coating layer formed on the particle surface acting as a resistor in the insertion and deintercalation reaction of lithium ions.

[0159]

[0160] In the case of Comparative Example 5, in which Co was doped at 5 mol%, it was confirmed that the capacity retention rate was inferior compared to Examples 1 and 2.

[0161]

[0162] In the case of Comparative Example 6 with a Ni content of 80% or more, it was confirmed that the initial resistance and capacity retention rate were inferior compared to Examples 1 and 2.

Claims

1. A cathode active material comprising a lithium composite transition metal oxide represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Mn c You d Zr e M f O2 In the above chemical formula 1, M is Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Zn, F, P, S, Y, W, Mo, B or a combination thereof, 0.8≤a≤1.2, 0.5≤b<0.8, 0.2≤c≤0.5, 0 <d≤0.1, 0<e≤0.1, 0≤f≤0.01, b+c+d+e+f=1이다.

2. In paragraph 1, A positive electrode active material having a capacity retention rate of 92.5 or more after 50 or more charge / discharge cycles, for a half coin cell including a positive electrode including the above positive electrode active material and a lithium metal negative electrode, when the positive electrode potential at full charge is 4.45 V based on Li potential.

3. In paragraph 1, A positive electrode active material having an initial resistance value of 45.0 Ω or less when the positive electrode potential at full charge is 4.45 V based on Li potential, for a half coin cell including a positive electrode including the above positive electrode active material and a lithium metal negative electrode.

4. In paragraph 1, A positive electrode active material that satisfies 0.001≤d≤0.05 in the above chemical formula 1.

5. In paragraph 1, A positive electrode active material that satisfies 0.001≤e≤0.05 in the above chemical formula 1.

6. In paragraph 1, The above positive electrode active material further includes Co, A cathode active material comprising Co in an amount of 0.04 mol% or less relative to the total content of Ni, Mn, Ti, Zr, M, and Co.

7. In paragraph 1, The above lithium composite transition metal oxide is a cathode active material that does not contain Co.

8. In paragraph 1, A cathode active material in which Ti and Zr of the above chemical formula 1 are incorporated into the crystal lattice structure of the above lithium composite transition metal oxide.

9. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 8.

10. A lithium secondary battery comprising a positive electrode according to claim 9.