Cathode active material for lithium secondary battery, preparation method therefor, and lithium secondary battery comprising same

Abstract

The present embodiments relate to a cathode active material for a lithium secondary battery, a preparation method therefor, and a lithium secondary battery comprising same. The cathode active material for a lithium secondary battery, according to one embodiment, comprises: a lithium metal oxide including nickel, manganese, a cation doping element (M), an anion doping element (A) and oxygen; and a surface part on at least a portion of the surface of the lithium metal oxide, wherein the lithium metal oxide can satisfy relation 1. [Relation 1] 8 < [Mn] / ([M]+[A]) ≤ 25 Relation 1 is the same as that defined in the detailed description.

Description

A positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same

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

[0002] This application claims priority to Korean Patent Application No. 10-2024-0190998, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003] As the application range of lithium-ion batteries expands from small electronic devices to electric vehicles and power storage devices, there is a growing demand for cathode materials with excellent high energy density and high power characteristics.

[0004] In this regard, lithium manganese oxides with excess lithium and manganese are attracting attention as next-generation cathode active materials due to their very high capacity of over 240 mAh / g, and research on them is currently being actively conducted.

[0005] However, since lithium and manganese-excess lithium transition metal oxides utilize oxygen oxidation-reduction reactions in addition to the transition metal, oxygen on the surface or within the bulk is prone to emitting as oxygen gas. Consequently, dense, non-reactive, or low-reactivity spinel / rock salt structures can easily form within the particles, leading to increased structural instability and, as a result, a problem of degraded electrochemical properties such as capacity and output characteristics.

[0006] In this embodiment, we aim to provide a positive electrode active material for a lithium secondary battery having excellent electrochemical performance, such as excellent capacity and output characteristics, a method for manufacturing the same, and a lithium secondary battery including the same.

[0007] A positive electrode active material for a lithium secondary battery according to one embodiment comprises a lithium metal oxide comprising nickel, manganese, a cation-doping element (M), an anion-doping element (A), and oxygen; and a surface portion located on at least a part of the surface of the lithium metal oxide, wherein the lithium metal oxide may satisfy Formula 1 below.

[0008] [Equation 1]

[0009] 8 < [Mn] / ([M]+[A]) ≤ 25

[0010] In the above Equation 1, [Mn] is the molar ratio of manganese based on 1 mole of total transition metal excluding lithium, [M] is the molar ratio of the cation doping element based on 1 mole of total transition metal excluding lithium, and [A] is the molar ratio of the anion doping element substituted at the oxygen site.

[0011] The above cation doping elements may include W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

[0012] The content of the above-mentioned cation doping element may be 0.01 mole or less based on 1 mole of total metal excluding lithium in the above-mentioned lithium metal oxide.

[0013] The above anion doping elements may include F, S, Cl, Br, or a combination thereof.

[0014] The molar ratio of the anion doping element substituted at the oxygen site may be in the range of 0.01 to 0.05.

[0015] In one embodiment, the surface portion may include a coating element that is Al, B, Co, or a combination thereof.

[0016] The content of the above coating element may be 1000 ppm or less based on the entire anode active material.

[0017] The above surface portion may include Al2O3 or LiAlO2 particles with an average particle size of 200 nm or less.

[0018] The nickel content in the above lithium metal oxide may be in the range of 0.30 to 0.50 moles based on 1 mole of total metal excluding lithium.

[0019] In one embodiment, the manganese content in the lithium metal oxide may be in the range of 0.40 to 0.65 moles based on 1 mole of total metal excluding lithium.

[0020] The average oxidation number of nickel in the above positive active material may be 2.10 or less.

[0021] The above lithium metal oxide further contains cobalt, and the content of the cobalt may be 0.1 mole or less based on 1 mole of total metal excluding lithium.

[0022] The above lithium metal oxide may be represented by the following chemical formula 1.

[0023] [Chemical Formula 1]

[0024] Li 1+a (Ni x Co y Mn z M b ) 1-a O 2-c A c

[0025] In the above chemical formula 1, 0.1≤a≤0.3, 0.35 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.05, 0.45 ≤ z ≤ 0.65, 0 < b ≤ 0.01, 0 < c ≤ 0.1, x+y+z+b=1, M is W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe or a combination thereof, and A is F, Cl, Br, I or a combination thereof.

[0026] A method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment may include: a step of preparing a metal precursor comprising nickel and manganese; a step of mixing the metal precursor, a lithium raw material, a cation-doping raw material, and an anion-doping raw material, and then calcining to produce a lithium metal oxide; and a step of mixing the lithium metal oxide and a coating raw material, and then heat-treating to obtain a lithium metal oxide having a surface portion formed on at least a part of the surface.

[0027] The above cation doping raw material may include at least one of WO3, WO2, WSe2, WC, and WOCl4.

[0028] The above anion doping raw material may include lithium fluoride (LiF), polytetrafluoroethylene (PTFE), or a combination thereof.

[0029] In the step of manufacturing the lithium metal oxide, the lithium raw material may be introduced such that the molar ratio (Li / Me) of lithium (Li) to the total metal (Me) excluding lithium in the lithium metal oxide is in the range of 1.07 to 1.20.

[0030] The above firing may be performed at 650°C to 850°C for 5 to 15 hours.

[0031] The above coating raw material may include an Al coating raw material.

[0032] The above Al coating raw material is Al(OH)3, It may include at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0033] The above heat treatment can be performed at 650°C to 750°C for 3 to 9 hours.

[0034] A positive electrode for a lithium secondary battery according to another embodiment may include a positive electrode active material according to one embodiment.

[0035] A lithium secondary battery according to another embodiment may include a positive electrode comprising a positive electrode active material according to one embodiment.

[0036] According to the present embodiment, by doping a lithium metal oxide with a high manganese content with appropriate amounts of cation and anion doping elements to satisfy a specific range based on the manganese content, it is possible to realize a positive electrode active material with excellent capacity, lifespan, and output characteristics while having minimal voltage reduction.

[0037] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0038] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0039] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0040] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0041] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0042] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0043] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0044]

[0045] Cathode active material for lithium secondary batteries

[0046] A positive electrode active material for a lithium secondary battery according to one embodiment comprises a lithium metal oxide comprising nickel, manganese, a cation-doping element (M), an anion-doping element (A), and oxygen; and a surface portion located on at least a part of the surface of the lithium metal oxide, wherein the lithium metal oxide may satisfy Formula 1 below.

[0047] [Equation 1]

[0048] 8 < [Mn] / ([M]+[A]) ≤ 25

[0049] In the above Equation 1, [Mn] is the molar ratio of manganese based on 1 mole of total transition metal excluding lithium, [M] is the molar ratio of the cation doping element based on 1 mole of total transition metal excluding lithium, and [A] is the molar ratio of the anion doping element substituted at the oxygen site.

[0050] The above Equation 1 is based on the content of manganese, cation doping elements, and anion doping elements of a lithium metal oxide, and the value of Equation 1 may be greater than 8 and less than or equal to 25, and more specifically, may be in the range of 9 to 24 or 10 to 22. When the value of Equation 1 satisfies the above range, it is possible to realize a lithium secondary battery with excellent capacity and life characteristics, as well as excellent output characteristics and a low power reduction rate, that is, excellent resistance characteristics.

[0051] As mentioned above, lithium manganese-based oxides with excess lithium and manganese have the advantage of possessing a high theoretical capacity, but they are difficult to activate, so it is necessary to maximize the capacity. In this embodiment, by considering the manganese content of the lithium metal oxide and doping with appropriate amounts of cationic and anionic elements, the reduction of the transition metal is induced to activate the oxygen reaction, and consequently, a lithium secondary battery with high energy density can be realized. In addition, since more manganese, which is cheaper than nickel and cobalt, is used, the production cost in the manufacture of the cathode active material can be lowered, thereby improving economic efficiency.

[0052] In one embodiment, the cation doping element may include W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof, and more specifically, the doping element may be W.

[0053] The content of the above-mentioned cation doping element may be 0.01 mole or less based on 1 mole of total metal excluding lithium in the above-mentioned lithium metal oxide, and more specifically, may be in the range of 0.001 mole to 0.01 mole or 0.002 mole to 0.009 mole.

[0054] In this embodiment, by doping with cation doping elements within an appropriate content range, the reduction of nickel, cobalt, and manganese can be induced to activate the oxygen reaction, and in this case, excellent capacity of the lithium secondary battery can be secured.

[0055] In one embodiment, the anion doping element may include F, S, Cl, Br, or a combination thereof, and more specifically, the anion doping element may be F.

[0056] The above anion doping element is substituted at the oxygen site of a lithium secondary battery. The molar ratio of the above anion doping element substituted at the oxygen site may be in the range of 0.01 to 0.05, and more specifically, may be 0.01 to 0.04 or 0.02 to 0.04.

[0057] In this embodiment, by doping an anion doping element within an appropriate content range, oxygen can be partially substituted in the manganese-excess lithium oxide to suppress oxygen release and improve the thermal stability of the cathode active material. Additionally, the interfacial stability between the cathode active material and the electrolyte can be improved by reducing the reactivity with the electrolyte at the surface of the cathode active material.

[0058] In this embodiment, by simultaneously doping a cation doping element and an anion doping element, the structural stability of the lithium metal oxide can be improved, thereby enhancing lifespan characteristics. In addition, by promoting ion diffusion and simultaneously reducing interfacial resistance, a lithium secondary battery with excellent output characteristics can be realized.

[0059] In one embodiment, the surface portion where the lithium metal oxide is located on the surface may include a coating element which is Al, B, Co, or a combination thereof, and more specifically, the surface portion may include Al. The coating element may include Al2O3 or LiAlO2 particles having an average particle size of 200 nm or less.

[0060] At this time, the content of the coating element may be 1000 ppm or less based on the entire positive electrode active material, and more specifically, may be in the range of 100 ppm to 1000 ppm, 250 ppm to 750 ppm, or 400 to 600 ppm. When the content of the coating element satisfies the above range, the leaching of manganese from the surface of the lithium metal oxide can be suppressed, and the decomposition of the electrolyte and side reactions on the surface of the positive electrode active material can be suppressed to improve interfacial stability, and as a result, lifespan characteristics can be improved while reducing voltage drop during the charging and discharging process.

[0061] In one embodiment, the nickel content in the lithium metal oxide may be 0.30 to 0.50 moles, more specifically 0.35 to 0.45 moles, based on 1 mole of the total metal excluding lithium. When the nickel content satisfies the above range, the capacity, output, and lifespan characteristics of the battery can be more preferably realized. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction increases too much, and the lifespan characteristics may deteriorate. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, and the capacity and output characteristics may deteriorate.

[0062] The average oxidation number of nickel in the positive active material of the present embodiment may be 2.10 or less, more specifically 1.8 to 2.10 or 2.0 to 2.10.

[0063] In addition, the manganese content in the lithium metal oxide may be 0.40 to 0.65 moles, more specifically 0.45 to 0.60 moles, based on 1 mole of the total metal excluding lithium. If the manganese content is too low, manufacturing costs increase, the safety of the active material decreases, and the capacity improvement effect due to the excessive manganese content may be negligible. If the manganese content is too high, the lifespan characteristics may deteriorate due to the excessive use of oxygen in oxidation / reduction reactions, and there may be a problem of manganese leaching.

[0064] Lithium transition metal oxides with an excess composition of lithium and manganese have a low nickel content, but during battery operation, they can involve oxidation / reduction reactions of anions (oxygen) as well as potential metals. Additionally, since excess lithium can exist in the transition metal layer in addition to the lithium layer, the insertion and extraction efficiency of lithium ions can be increased. As a result, the initial discharge capacity is 240 mAh / g or higher, which can significantly improve capacity characteristics compared to conventional NCM cathode materials. Furthermore, it is economically advantageous because the content of relatively expensive nickel and cobalt can be reduced, while the content of inexpensive manganese can be increased. In other words, when the molar ratio of manganese to nickel satisfies the above range, it is possible to manufacture a cathode active material that is economically advantageous while also having excellent capacity and lifespan characteristics.

[0065] The above metal oxide may further contain cobalt. In this case, the content of cobalt in the metal oxide may be 0.1 mole or less, more specifically in the range of 0.01 mole to 0.05 mole, based on 1 mole of the total metal excluding lithium. Cobalt is usually added in a predetermined amount to improve the lifespan and output characteristics of a battery, but there is a problem with its high cost. In this embodiment, even if the cobalt content is reduced to the above range, good lifespan and output characteristics can be achieved by activating the oxygen reaction through doping with tungsten. Accordingly, the cathode active material of this embodiment can simultaneously achieve economic efficiency and product quality.

[0066] Specifically, the lithium metal oxide can be represented by the following chemical formula 1.

[0067]

[0068] [Chemical Formula 1]

[0069] Li 1+a (Ni x Co y Mn z M b ) 1-a O 2-c A c

[0070] In the above chemical formula 1, 0.1≤a≤0.3, 0.35 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.05, 0.45 ≤ z ≤ 0.65, 0 < b ≤ 0.01, 0 < c ≤ 0.1, x+y+z+b=1, M is W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe or a combination thereof, and A is F, Cl, Br, I or a combination thereof.

[0071] In the lithium transition metal oxide of Chemical Formula 1 above, lithium may be included in an amount corresponding to 1+a, where a may be 0.1≤a≤0.3. If a is too small, the effect of improving capacity characteristics due to the excess lithium content may be negligible. However, if a is too large, lifespan characteristics may deteriorate due to reduced phase stability.

[0072] In the lithium transition metal oxide of Chemical Formula 1 above, nickel may be included in an amount corresponding to x, i.e., 0.35 ≤ x ≤ 0.45. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction increases too much, and the lifespan characteristics may deteriorate. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, and the capacity and output characteristics may deteriorate.

[0073] In the lithium transition metal oxide of Chemical Formula 1 above, cobalt may be included in an amount corresponding to y, i.e., 0 ≤ y ≤ 0.05. If the cobalt content is too high, the cost of the raw material increases overall and the reversible capacity may decrease.

[0074] In the lithium transition metal oxide of Chemical Formula 1 above, manganese may be included in an amount corresponding to z, i.e., 0.45 ≤ z ≤ 0.65. If the manganese content is too low, the production cost may increase, the stability of the active material may decrease, and the capacity may deteriorate. If the manganese content is too high, there may be a decrease in lifespan characteristics due to excessive use of oxygen oxidation / reduction reactions and a problem with manganese leaching.

[0075] In the lithium transition metal oxide of Chemical Formula 1 above, the cation doping element M may be included in an amount corresponding to b, i.e., 0 < b ≤ 0.1. The content of the doping element may be appropriately selected and controlled to achieve a doping effect within a range that does not degrade electrochemical properties. In this case, M may be W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, or a combination thereof.

[0076] A is an anionic doping element that can substitute for the oxygen site in the lithium transition metal oxide of Chemical Formula 1. It may be included in an amount corresponding to A, i.e., 0 < c ≤ 0.1. Here, A may be F, Cl, Br, I, or a combination thereof.

[0077] Meanwhile, the metal oxide of the present embodiment may have a layered crystal structure and may be a secondary particle formed by the aggregation of a plurality of primary particles.

[0078] In this specification, “secondary particle” means an aggregate, i.e., a secondary structure, formed by the aggregation of tens to hundreds of primary particles by physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles.

[0079] In addition, “primary particle” refers to the smallest particle unit that is distinguished as a single mass when the cross-section of the positive active material is observed through a scanning electron microscope (SEM), and it may consist of a single crystal grain or multiple crystal grains.

[0080]

[0081] Method for manufacturing a positive electrode active material for a lithium secondary battery

[0082] A method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment may include: a step of preparing a metal precursor comprising nickel and manganese; a step of simultaneously mixing the metal precursor, a lithium raw material, a cation-doping raw material, and an anion-doping raw material, and then calcining to produce a lithium metal oxide; and a step of mixing the lithium metal oxide and a coating raw material, and then heat-treating to obtain a lithium metal oxide having a surface portion formed on at least a part of the surface.

[0083] First, prepare a metal precursor containing nickel and manganese.

[0084] The above metal precursor may be prepared by, for example, by co-precipitating a transition metal-containing solution containing nickel raw material and manganese raw material by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to the transition metal-containing solution.

[0085] The above nickel raw material is not particularly limited as long as it is used in the industry for manufacturing a cathode active material precursor. For example, the above nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0086] The above manganese raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0087] The above transition metal-containing solution may be prepared by adding nickel raw material and manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent that can be uniformly mixed with water (e.g., alcohol).

[0088] The above-mentioned complexing agent-containing solution performs the role of forming a complex, and may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent, but is not limited thereto. Meanwhile, the above-mentioned complexing agent-containing solution may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol, etc.) may be used as the solvent.

[0089] Next, the step of manufacturing a lithium metal oxide is performed by simultaneously mixing the metal precursor, lithium raw material, cation-doping raw material, and anion-doping raw material, and then calcining them.

[0090] Here, the lithium raw material may be introduced such that the molar ratio (Li / Me) of lithium (Li) to the total metal (Me) excluding lithium in the lithium metal oxide is in the range of 1.07 to 1.20, more specifically in the range of 1.09 to 1.12. As the lithium content increases, the amount of lithium involved in the insertion and extraction of lithium ions increases, thereby improving capacity characteristics. However, if the lithium content becomes too high, problems with phase stability may arise due to excessive occurrence of oxygen oxidation / reduction reactions, which may lead to a decrease in lifespan characteristics; therefore, it is desirable for the molar ratio of lithium to the total metal to satisfy the above range.

[0091] Next, the lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof, but is not limited thereto.

[0092] The above cation-doping raw material may include at least one of WO3, WO2, WSe2, WC, and WOCl4. In this embodiment, in order to reduce elements such as nickel, cobalt, and manganese, 6 + It is desirable to use a W-doped raw material having the oxidation number of .

[0093] If necessary, additional doping raw materials may be added at this stage, for example, raw materials including B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, or combinations thereof may be used.

[0094] The above anion doping raw material may be lithium fluoride (LiF), polytetrafluoroethylene (PTFE), or a combination thereof, but is not necessarily limited thereto. In this embodiment, it is preferable to use an F-doping raw material because it can improve the structural stability of the cathode active material by partially replacing oxygen to suppress oxygen release, and improve the interfacial stability between the cathode active material and the electrolyte by suppressing electrolyte decomposition and HF generation.

[0095] In this embodiment, productivity can be improved by reducing the number of process steps by simultaneously mixing the cation-doped raw material and the anion-doped raw material and then performing calcination.

[0096] In one embodiment, the calcination may be performed at 650°C to 850°C for 5 to 15 hours. If the calcination temperature or time is too low or too short, the layered lithium metal oxide structure may not form well, and the electrochemical properties of the active material may deteriorate. If the calcination temperature or time is too high or too long, crystal defects may occur due to over-calcination, and the electrochemical properties may deteriorate.

[0097] In the step of manufacturing the lithium metal oxide described above, calcination may be performed in an air or oxygen atmosphere. In particular, as calcination proceeds in an oxygen atmosphere, sufficient oxidation of the metal precursor occurs during the calcination process, allowing for better electrochemical properties to be realized, but is not limited thereto.

[0098] Subsequently, a step is performed to obtain a lithium metal oxide in which a surface portion is formed on at least a part of the surface by mixing the lithium metal oxide and the coating raw material and then heat-treating.

[0099] The above coating raw material may include an Al coating raw material.

[0100] More specifically, the above Al coating raw material is Al(OH)3, It may include at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3. By forming a surface portion on the surface of a lithium metal oxide using such an Al coating raw material, interfacial side reactions between the positive electrode active material and the electrolyte can be suppressed, and a lithium secondary battery with improved capacity and resistance characteristics can be manufactured.

[0101] In one embodiment, the heat treatment may be performed at 650°C to 750°C for 3 to 9 hours. If the heat treatment process satisfies the above conditions, the amount of lithium remaining on the surface can be reduced while simultaneously stabilizing the surface structure.

[0102]

[0103] anode

[0104] In another embodiment, a positive electrode for a lithium secondary battery comprising a positive electrode active material according to one embodiment is provided.

[0105] The above positive electrode may include a current collector and a positive active material layer located on one side of the current collector, and the positive active material layer includes a positive active material of one embodiment.

[0106] The characteristics of the positive active material constituting the above positive active material layer are the same as those previously described. Therefore, a detailed description of the positive active material will be omitted.

[0107] The above current collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.

[0108] Meanwhile, the above positive active material layer may include a binder and a conductive material.

[0109] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0110] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the positive electrode active material layer.

[0111] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0112] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0113] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0114] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0115]

[0116] lithium secondary battery

[0117] In another embodiment, a lithium secondary battery including the anode is provided.

[0118] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to 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. Additionally, the lithium secondary battery may optionally further include a battery container housing an electrode assembly comprising the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0119] In the above lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0120] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0121] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0122] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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 alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, 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.

[0123] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0124] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0125] In addition, regarding the above lithium secondary battery, the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing a lithium secondary battery, but is not limited to these.

[0126] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0127] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0128] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0129]

[0130] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0131]

[0132] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0133]

[0134] Example 1

[0135] (Preparation of precursor) (Ni 0.40 Co 0.02 Mn0.58 Prepare a precursor of the (OH)2 composition.

[0136] (Mixing) The above precursor was mixed with WO3 as a cation-doping raw material, LiF as an anion-doping raw material, and LiOH·H2O as a lithium raw material in a molar ratio of 0.995 : 0.005 : 0.028 : 1.25.

[0137] After (calcination), the above mixture was calcined at a temperature of 750°C for 10 hours under an oxygen atmosphere to prepare a lithium metal oxide. The composition of the obtained lithium metal oxide is Li 1.111 Ni 0.353 Co 0.018 Mn 0.513 W 0.004 O 1.980 F 0.020 It was.

[0138] (Discharge) Next, the above lithium metal oxide was discharged by natural cooling.

[0139] (Coating) A positive electrode active material with a surface portion formed was prepared by dry mixing the above lithium metal oxide and Al2O3 nanopowder with an average particle size of 200 nm or less as a coating raw material, followed by heat treatment at 700°C for 5 hours in an air atmosphere. At this time, the Al2O3 nanopowder was mixed at a content of 500 ppm of Al based on the total amount of the prepared positive electrode active material.

[0140]

[0141] Example 2 and Comparative Examples 1 to 5

[0142] A positive electrode active material was prepared in the same manner as in Example 1, except that the raw materials were mixed such that the molar ratio of each element in the chemical formula below was as shown in Table 1 below.

[0143] Li 1+a (Ni x Co y Mn z W b ) 1-a O 2-c F c

[0144] [Table 1]

[0145]

[0146]

[0147] Experimental Example 1: Coin Cell Fabrication and Electrochemical Characteristics Evaluation

[0148] CR2032 coin cells were manufactured using the positive electrode active materials prepared in the examples and comparative examples in the following manner, and their electrochemical characteristics were evaluated and are shown in Table 2 below.

[0149] (1) Coin cell manufacturing

[0150] The slurry for electrode manufacturing was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF1100) in a ratio of 92.5 : 3.5 : 4 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content was approximately 30%. The prepared slurry was coated onto a 15㎛ thick Al foil using a doctor blade, and the cathode was manufactured by dry rolling. The electrode loading amount was 14.6 mg / cm². 2 It was, and the rolled density (25℃, 20kN) was 3.1 g / cm³ 3 It was.

[0151] A 2032 coin-type half-cell was manufactured using the above-mentioned positive electrode, lithium negative electrode (200 μm, Honzo metal), electrolyte, and polypropylene separator in a conventional manner. At this time, the electrolyte was prepared by adding 3.0 vol% of vinylene carbonate (VC) to the total amount of electrolyte to 1M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate (mixing ratio EC:DMC:EMC = 3:4:3 volume%) to prepare a mixed solution.

[0152] (2) Evaluation of initial discharge capacity

[0153] The coin cell prepared in (1) was aged at 25°C for 12 hours, and then formation was performed at 25°C. At this time, charging was performed up to 4.7V with a constant current of 0.1C and a reference capacity of 200 mAh / g. After charging, a rest time of 20 minutes was taken, and then discharging was performed until 2.5V was reached with a constant current of 0.1C and a reference capacity of 200 mAh / g. After formation, one more cycle was repeated under the same conditions to evaluate the initial discharge capacity. The results are shown in Table 1 below.

[0154] (3) Output characteristic evaluation (2C / 0.2C)

[0155] After evaluating the initial discharge capacity, the ratio of the discharge capacity to

[0156] (4) Life characteristic evaluation (25℃, 50 cycles)

[0157] From the second cycle onwards, following the initial discharge capacity evaluation, the device was charged to 4.5V with a constant current of 0.5C and then had a rest time of 20 minutes. Afterward, the device was discharged with a constant current of 0.5C until it reached 2.5V. Fifty charge-discharge cycles were performed under the same conditions as the second cycle, and the discharge capacity retention rate of the 50th cycle was calculated relative to the second cycle. The results are shown in Table 1 below.

[0158] (5) Voltage reduction measurement (25℃, 50 cycles)

[0159] From the second cycle onwards, following the initial discharge capacity evaluation, the device was charged to 4.5V with a constant current of 0.5C and then rested for 20 minutes. Afterward, the device was discharged with a constant current of 0.5C until it reached 2.5V. Fifty charge-discharge cycles were performed under the same conditions as the second cycle, and the voltage of the 50th cycle was measured relative to the second cycle to calculate the voltage decrease. The results are shown in Table 1 below.

[0160] Classification 0.1C Discharge Capacity (mAh / g) Output, 2C / 0.2C Discharge Capacity Ratio (%) Lifespan, 50 th / 1 st Discharge capacity ratio (%) voltage decrease, 1 st -50 th (mV) Example 1 241.588.49562.8 Example 2 240.888.194.862.1 Comparative Example 1 232.282.389.778.3 Comparative Example 2 240.788.593.174.1 Comparative Example 3 238.082.19463.2 Comparative Example 4 239.988.494.268.9 Comparative Example 5 234.888.393.362.9

[0161] Referring to Table 1, it can be seen that the cathode active materials prepared according to Examples 1 and 2, which are doped with W and F within the range satisfying Equation 1, exhibit high discharge capacity, possess structural stability capable of inserting and extracting many lithium ions, and have excellent energy density. Furthermore, since the output and lifespan characteristics are excellent, it can be predicted that the structural stability of the cathode active material is maintained during the charging and discharging process and that side reactions in the electrolyte are effectively suppressed. In addition, since the voltage drop is small, it can be seen that the increase in internal resistance during charging and discharging is suppressed. In contrast, it can be confirmed that the cathode active materials prepared according to Comparative Example 1, which is not doped with either W or F, and Comparative Example 2, which is not doped with F, have significantly lower output and lifespan characteristics and larger voltage drop values ​​compared to Examples 1 and 2.

[0162] Even in the case of the positive electrode active materials prepared according to Comparative Example 3, which is not doped with W, and Comparative Examples 4 and 5, which are doped with F but whose content does not satisfy the range of Formula 1, the overall discharge capacity is low, the lifespan characteristics are inferior to those of Examples 1 and 2, and the voltage drop value is also large.

[0163] That is, it can be confirmed that the positive active material according to the present embodiment can realize a positive active material with excellent capacity, lifespan, and output characteristics, while having minimal voltage reduction, by controlling the content of cation doping elements and anion doping elements based on the manganese content to satisfy Equation 1.

[0164]

[0165] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0166] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A lithium metal oxide comprising nickel, manganese, a cation-doping element (M), an anion-doping element (A), and oxygen; and It includes a surface portion located on at least a part of the lithium metal oxide surface, and The above lithium metal oxide is a positive electrode active material for a lithium secondary battery satisfying Formula 1 below: [Equation 1] 8 < [Mn] / ([M]+[A]) ≤ 25 In the above Equation 1, [Mn] is the molar ratio of the above manganese based on 1 mole of total transition metals excluding lithium, and [M] is the molar ratio of the above-mentioned cation-doping element based on 1 mole of total transition metal excluding lithium, and [A] above is the molar ratio of an anion doping element substituted at the oxygen site.

2. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the above-mentioned cation doping element comprises W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

3. In Paragraph 1, The content of the above-mentioned cation-doping element is, A positive electrode active material for a lithium secondary battery, having 0.01 mole or less based on 1 mole of total metal excluding lithium in the above lithium metal oxide.

4. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the above-mentioned anion doping element comprises F, S, Cl, Br, or a combination thereof.

5. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the molar ratio of the anion doping element substituted at the oxygen site is in the range of 0.01 to 0.

05.

6. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the above surface portion comprises a coating element that is Al, B, Co, or a combination thereof.

7. In Paragraph 6, A positive electrode active material for a lithium secondary battery, wherein the content of the above-mentioned coating element is 1000 ppm or less based on the entire positive electrode active material.

8. In Paragraph 1, The above surface portion comprises Al2O3 or LiAlO2 particles having an average particle size of 200 nm or less, a positive electrode active material for a lithium secondary battery.

9. In Paragraph 1, The above lithium metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1. [Chemical Formula 1] Li 1+a (Ni x Co y Mr z M b ) 1-a O 2-c A c (In the above chemical formula 1, 0.1≤a≤0.3, 0.35 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.05, 0.45 ≤ z ≤ 0.65, 0 < b ≤ 0.01, 0 < c ≤ 0.1, x+y+z+b=1, M is W, B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe or a combination thereof, and A is F, Cl, Br, I or a combination thereof) 10. A step of preparing a metal precursor containing nickel and manganese; A step of simultaneously mixing the above metal precursor, lithium raw material, cation-doping raw material and anion-doping raw material, and then calcining to produce a lithium metal oxide; and A step of obtaining a lithium metal oxide in which a surface portion is formed on at least a part of the surface by mixing the above lithium metal oxide and coating raw material and then heat-treating; A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising 11. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above-mentioned cation-doping raw material comprises at least one of WO3, WO2, WSe2, WC, and WOCl4.

12. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above-mentioned anion doping raw material comprises lithium fluoride (LiF), polytetrafluoroethylene (PTFE), or a combination thereof.

13. In Paragraph 10, In the step of manufacturing the above lithium metal oxide, the lithium raw material is, The above lithium metal oxide is introduced such that the molar ratio (Li / Me) of lithium (Li) to the total metal (Me) excluding lithium is in the range of 1.07 to 1.

20. Method for manufacturing a positive electrode active material for a lithium secondary battery.

14. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above calcination is performed at 650°C to 850°C for 5 to 15 hours.

15. In Paragraph 14, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the heat treatment is performed at 650°C to 750°C for 3 to 9 hours.

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