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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, the cathode active material comprising lithium metal oxide particles having a composition with excess lithium and manganese and doped with sodium, wherein the lithium metal oxide has a structure in which lithium layers and transition metal layers are alternately stacked, the sodium is more heavily doped into the lithium layers than into the transition metal layers, and the sodium is predominantly doped at the surface of the lithium metal oxide particles.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

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

[0002]

[0003] As the scope of application of lithium secondary batteries expands from small electronic devices to electric vehicles and power storage devices, the demand for cathode materials with excellent high energy density and high output characteristics is increasing.

[0004] In this regard, lithium and manganese-rich layered lithium transition metal oxides have a very high capacity of over 240 mAh / g and are attracting attention as candidates for next-generation cathode active materials, and research on them is actively being conducted recently.

[0005] However, lithium and manganese-rich layered lithium transition metal oxides utilize oxygen oxidation / reduction reactions in addition to transition metal oxidation / reduction due to the high lithium content and relatively low transition metal ratio in the structure compared to conventional cathode active materials. Since this oxygen oxidation / reduction reaction is driven at a high voltage during the first charge, it causes electrolyte decomposition due to the high reactivity with the electrolyte on the surface, and since irreversible migration of transition metals occurs, the number of lithium reinsertion sites decreases during discharge, which causes a problem of lowering the initial efficiency. In addition, there is a problem of deterioration of the life characteristics due to the acceleration of phase decomposition due to the generation of oxygen gas during subsequent cycles.

[0006]

[0007] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery, which is a lithium metal oxide having an excess composition of lithium and manganese, and which not only improves capacity characteristics due to improved initial efficiency but also has improved lifespan characteristics, a method for producing the same, and a lithium secondary battery including the same.

[0008]

[0009] One embodiment of the present invention provides a cathode active material for a lithium secondary battery, comprising lithium metal oxide particles having a lithium and manganese excess composition and doped with sodium, wherein the lithium metal oxide has a structure in which lithium layers and transition metal layers are alternately laminated, wherein the sodium is doped more into the lithium layer among the lithium layers and transition metal layers, and the sodium is concentratedly doped on the surface portion of the lithium metal oxide particles.

[0010] When XPS (X-ray Photoelectron Spectroscopy) is analyzed on the outermost surface of the lithium metal oxide particles, the molar ratio of sodium to manganese (Na / Mn) may be 342 times or more the average molar ratio of sodium to manganese (Na / Mn) in the lithium metal oxide.

[0011] When XPS (X-ray Photoelectron Spectroscopy) analysis is performed on the outermost surface of the lithium metal oxide particles, the molar ratio of sodium to manganese (Na / Mn) may be 0.58 or more.

[0012] The above lithium metal oxide may have a molar ratio of sodium to lithium metal oxide of 0.01 to 0.2.

[0013] The above lithium metal oxide may have a molar ratio of cobalt to lithium metal oxide of 0.05 or less.

[0014] The above lithium metal oxide may have a molar ratio of lithium to lithium metal oxide of 1.1 to 1.3.

[0015] The above lithium metal oxide may have a molar ratio of nickel to lithium metal oxide of 0.1 to 0.3.

[0016] The above lithium metal oxide may have a molar ratio of manganese to lithium metal oxide of 0.5 to 0.7.

[0017] The average particle diameter (D50) of the above lithium metal oxide particles may be 10 μm or less.

[0018] The above lithium metal oxide can be represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li 1+a (Ni x Co y Mn z Na w1 M w2 )O2

[0021] In the above chemical formula 1, 0.1≤a≤0.3, 0.1≤x≤0.3, 0≤y≤0.05, 0.5≤z≤0.7, 0.01≤w1≤0.2, 0≤w2≤0.2, a+x+y+z+w1+w2=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

[0022]

[0023] Another embodiment of the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: forming a mixture by grinding and mixing a lithium raw material, a nickel raw material, a manganese raw material, and a sodium raw material; first firing the mixture to form lithium metal oxide particles having an excess composition of lithium and manganese; and second firing the lithium metal oxide particles to form lithium metal oxide particles having sodium concentrated on a surface portion, wherein the first firing temperature is 420 to 800°C, and the second firing temperature is 820 to 930°C.

[0024] The above first firing temperature may be 420 to 600°C.

[0025] The above grinding and mixing can be performed by solid-phase grinding and mixing.

[0026] The above grinding and mixing can be performed at a stirring speed of 200 to 600 rpm.

[0027] The above grinding and mixing can be performed for 5 to 15 hours.

[0028]

[0029] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0030] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0031]

[0032] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises lithium metal oxide particles having a lithium and manganese excess composition, wherein sodium is preferentially doped into the lithium layer and concentratedly doped on the surface of the lithium metal oxide particles, thereby improving initial efficiency and enhancing capacity characteristics, as well as improving life characteristics. In addition, the cathode active material for a lithium secondary battery according to one embodiment of the present invention can have improved rate characteristics.

[0033]

[0034] Figure 1 is a conceptual diagram showing a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0035] Figure 2 is a graph showing the results of thermogravimetric analysis (TGA) of a mixture according to Experimental Example 1.

[0036] Figure 3 is a graph showing the results of X-ray diffraction (XRD) analysis of a sintered product according to Experimental Example 2.

[0037] Figure 4 is a graph showing the results of X-ray diffraction (XRD) analysis of positive electrode active materials manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0038] Figure 5 is a TEM-EDS elemental mapping image of the positive electrode active material manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0039] Figure 6 is a graph showing the results of SEM-EDX line scan Na concentration analysis of positive electrode active materials manufactured according to Example 1 and Comparative Example 2.

[0040] Figure 7 is a graph showing the results of XPS (X-ray Photoelectron Spectroscopy) analysis of positive electrode active materials manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0041] Figure 8 is a graph showing the evaluation of the initial discharge capacity at high temperature 60°C of lithium secondary batteries manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0042] Figure 9 is a graph showing the evaluation of the initial discharge capacity at high temperature of 45°C of lithium secondary batteries manufactured according to Examples 1 to 2, 4 to 5, Comparative Example 1, and Comparative Example 2.

[0043] Figure 10 is a graph showing the evaluation of the life characteristics at room temperature of 25°C of lithium secondary batteries manufactured according to Examples 1 to 2, 4 to 5, Comparative Example 1, and Comparative Example 2.

[0044] Figure 11 is a graph showing the rate characteristic evaluation of lithium secondary batteries manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0045]

[0046] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0048] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0049] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0050] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0051] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0052] 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.

[0053]

[0054] 1. Positive active material

[0055] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium transition metal oxide having a lithium and manganese excess composition. Although the lithium and manganese excess composition of the lithium transition metal oxide has a low nickel content, it can involve oxidation / reduction reactions of not only the transition metal but also anions (oxygen) during battery operation. In addition, since the excess lithium can exist in the transition metal layer as well as the lithium layer, the insertion and de-insertion efficiency of lithium ions can be increased. As a result, the initial discharge capacity can be 240 mAh / g or more, which is significantly improved in capacity characteristics compared to cathode materials with a conventional NCM composition. In addition, the cost-effectiveness is excellent because the content of relatively expensive nickel and cobalt can be reduced and the content of inexpensive manganese can be increased.

[0056] More specifically, the lithium metal oxide may have a molar ratio of lithium to lithium metal oxide of 1.1 to 1.3. As the lithium content increases, the amount of lithium that can participate in the insertion and deintercalation of lithium ions increases, thereby improving capacity characteristics. However, if the lithium content increases too much, phase stability problems may occur due to excessive occurrence of oxygen oxidation / reduction reactions, which may result in deterioration of life characteristics.

[0057] In addition, the lithium metal oxide may have a molar ratio of manganese to lithium metal oxide of 0.5 to 0.7. If the manganese content is too low, manufacturing costs increase, the safety of the active material decreases, and the capacity improvement effect due to excessive manganese content may be minimal. If the manganese content is too high, the life characteristics may be deteriorated due to excessive use of oxygen oxidation / reduction reactions, and there may be a problem of manganese dissolution.

[0058] In addition, the lithium metal oxide may have a molar ratio of nickel to lithium metal oxide of 0.1 to 0.3. When the nickel content satisfies the above range, the capacity, output, and life characteristics of the battery can be more preferably implemented. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction increases too much, which may deteriorate the life characteristics. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, which may deteriorate the capacity and output characteristics.

[0059] In addition, the lithium metal oxide according to the present invention may be a compound of a solid solution phase in which Li2MnO3 having a monoclinic structure and LiMO2 (M=Ni, Co, Mn, Na, Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir or a combination thereof) having a rhombohedral structure are mixed.

[0060] Meanwhile, the lithium metal oxide according to the present invention is in the form of a secondary particle formed by agglomeration of a plurality of primary particles. As used herein, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be formed of a single crystal grain or a plurality of crystal grains. As used herein, the term "crystal grain" refers to a distinct region in which atoms within a primary particle form a lattice structure with a certain direction.

[0061] However, transition metal oxides with a lithium and manganese excess composition utilize oxygen oxidation / reduction reactions in addition to transition metal oxidation / reduction due to the high lithium content and relatively low transition metal ratio in the structure compared to conventional cathode materials. Since this oxygen oxidation / reduction reaction is driven at a high voltage during the first charge, it causes electrolyte decomposition due to the high reactivity with the electrolyte on the surface, and causes irreversible transition metal migration and oxygen gas release, which reduces the number of lithium reinsertion sites during discharge, resulting in a problem of lowering the initial efficiency. In addition, there is a problem of deterioration of the life characteristics due to the accelerated phase decomposition caused by the release of oxygen gas during subsequent cycles.

[0062]

[0063] Accordingly, the lithium metal oxide according to the present invention has a structure in which lithium layers and transition metal layers are alternately laminated, and is doped with sodium, but the sodium is doped more into the lithium layer among the lithium layer and the transition metal layer. More specifically, sodium has a property of doping only into lithium ion layers having similar ion sizes, and thus has a greater doping preference into the lithium layer than into the transition metal layer. Accordingly, the irreversible oxygen gas evolution of the lithium transition metal oxide can be alleviated, thereby improving the initial discharge capacity and rate characteristics according to the initial efficiency improvement, and the cycle life characteristics can be improved by delaying phase decomposition. Meanwhile, the doping preference of sodium into the lithium layer can be confirmed through XRD and DFT calculation analysis.

[0064] In addition, the sodium is concentratedly doped on the surface of the lithium metal oxide particles. Accordingly, the problem of oxygen gas emission, which occurs particularly concentratedly on the surface of the lithium metal oxide particles, can be more effectively alleviated, thereby improving the initial discharge capacity and rate characteristics due to improved initial efficiency, and improving the cycle life characteristics by delaying phase decomposition.

[0065] Meanwhile, in the present specification, the “surface portion” of a lithium metal oxide particle may mean an area within a distance of (4 / 5)r to r from the center of the particle, when the distance from the center of the lithium metal oxide particle to the surface is r.

[0066] As sodium is concentratedly doped on the surface of the lithium metal oxide particles in this way, the molar ratio of sodium to manganese (Na / Mn) when analyzed by XPS (X-ray Photoelectron Spectroscopy) on the outermost surface of the lithium metal oxide particles may be 342 times or more the average molar ratio of sodium to manganese (Na / Mn) in the lithium metal oxide, and more specifically, may be 350 times, 355 times, or 360 times or more and 380 times or less.

[0067] Alternatively, the molar ratio of sodium to manganese (Na / Mn) may be 0.58 or more when XPS (X-ray Photoelectron Spectroscopy) is analyzed on the outermost surface of the lithium metal oxide particles, and more specifically, may be 0.60 or 0.61 or more and 0.70 or less.

[0068] If the molar ratio of sodium to manganese (Na / Mn) at the top surface is too low, the surface-concentrated doping effect of sodium may be reduced, which may reduce the improvement in initial discharge capacity, rate characteristics, and life characteristics. If the molar ratio of sodium to manganese (Na / Mn) at the top surface is too high, the excess sodium may act as an impurity phase, which may actually deteriorate the initial discharge capacity, rate characteristics, and life characteristics.

[0069] Meanwhile, the structure of concentrated doping of sodium on the surface of lithium metal oxide particles can be easily obtained by controlling the mixing and grinding process and sintering process conditions of the raw materials as described later, and this will be described in more detail in the method for manufacturing a positive electrode active material described later.

[0070] In addition, the lithium metal oxide may have a molar ratio of sodium to lithium metal oxide of 0.01 to 0.2. If the sodium content in the lithium metal oxide is too low, the surface concentration doping effect of sodium may also be reduced, and thus the effect of improving the initial discharge capacity, rate characteristics, and life characteristics may be reduced. If the sodium content in the lithium metal oxide is too high, the excess sodium may act as an impurity, which may actually deteriorate the initial discharge capacity, rate characteristics, and life characteristics.

[0071] In addition, the lithium metal oxide may have a molar ratio of cobalt to lithium metal oxide of 0.05 or less, 0.03 or less, and may not contain cobalt. Cobalt is usually added in a certain amount to improve the lifespan and rate characteristics of a battery, but there was a problem of high price. As described above, the lithium metal oxide according to the present invention can instead implement the effect of improving the lifespan and rate characteristics by concentrated doping of sodium on the surface, so that even if the content of cobalt is reduced to the above range, the lifespan and rate characteristics can be implemented well. Accordingly, the cathode active material according to the present invention can implement both economic feasibility and good electrochemical characteristics.

[0072] The average particle diameter (D50) of the lithium metal oxide particles may be 10 μm or less, and more specifically, 5 μm or less. The inventors of the present invention were able to confirm that the average particle diameter (D50) of the lithium metal oxide particles manufactured according to the manufacturing method of the present invention is obtained as small as the above range. Accordingly, the effect of improving capacity and rate characteristics by reducing the diffusion distance of lithium ions can be more preferably implemented.

[0073] In this specification, the average particle diameter (D50) can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter (D50) can be measured using, for example, the laser diffraction method.

[0074]

[0075] The lithium metal oxide according to the present invention can be more specifically represented by the following chemical formula 1.

[0076] [Chemical Formula 1]

[0077] Li 1+a (Ni x Co y Mn z Na w1 M w2 )O2

[0078] In the above chemical formula 1, 0.1≤a≤0.3, 0.1≤x≤0.3, 0≤y≤0.05, 0.5≤z≤0.7, 0.01≤w1≤0.2, 0≤w2≤0.2, a+x+y+z+w1+w2=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof.

[0079] In the lithium metal oxide of the above chemical formula 1, 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 capacity characteristic improvement effect due to excessive lithium content may be minimal. However, if a is too large, the life characteristics may deteriorate due to decreased phase stability.

[0080] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 0.1≤x≤0.3. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction may increase too much, which may deteriorate the life characteristics. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction may decrease, which may deteriorate the capacity and output characteristics.

[0081] In the lithium metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.05 or 0≤y≤0.03. If the cobalt content is too low, it may be difficult to achieve sufficient rate characteristics. If the cobalt content is too high, the overall cost of the raw material may increase and the reversible capacity may decrease.

[0082] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0.5≤z≤0.7. If the manganese content is too low, production costs may increase and capacity may deteriorate. If the manganese content is too high, there may be a decrease in life characteristics due to excessive use of oxygen oxidation / reduction reactions and manganese dissolution problems.

[0083] In the lithium metal oxide of the above chemical formula 1, sodium may be included in an amount corresponding to w1, that is, 0.01≤w1≤0.2. If the sodium amount is too low, the surface concentration doping effect of sodium may also be reduced, and thus the effect of improving the initial discharge capacity, rate characteristics, and life characteristics may be reduced. If the sodium amount is too high, the excess sodium may act as an impurity, which may actually deteriorate the initial discharge capacity, rate characteristics, and life characteristics.

[0084] In the lithium metal oxide of the above chemical formula 1, M, which is another doping element, may be included in a content corresponding to w2, that is, 0≤w2≤0.2. At this time, M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir, or a combination thereof. M, which is another doping element, may be included in an appropriate content to implement other doping effects within a range in which the electrochemical characteristics of the battery are not deteriorated.

[0085]

[0086] 2. Method for manufacturing positive electrode active material

[0087] Figure 1 is a conceptual diagram showing a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention.

[0088] Referring to FIG. 1, another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: forming a mixture by grinding and mixing a lithium raw material, a nickel raw material, a manganese raw material, and a sodium raw material; first firing the mixture to form lithium metal oxide particles having an excess composition of lithium and manganese; and second firing the lithium metal oxide particles to form lithium metal oxide particles having sodium concentratedly doped on a surface thereof, wherein the first firing temperature is 420 to 800°C, and the second firing temperature is 820 to 930°C.

[0089] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described step by step.

[0090]

[0091] First, lithium raw material, nickel raw material, manganese raw material, and sodium raw material are ground and mixed to form a mixture.

[0092] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0093] The above lithium raw material may be more suitably LiOHㆍH2O. Accordingly, since the melting point of LiOHㆍH2O is low, the reactivity of lithium ions is maximized first, so that the concentrated doping effect of sodium on the surface of lithium metal oxide particles can be more preferably implemented.

[0094] The above sodium raw material is a sodium-containing compound, and may be Na2CO3, NaSO4, NaF, NaCl, or a combination thereof, but is not necessarily limited thereto.

[0095] The above sodium raw material may be more suitably Na2CO3. Accordingly, Na2CO3 Because the melting point is high, the concentrated doping effect of sodium on the surface of lithium metal oxide particles can be more preferably implemented.

[0096] The above grinding and mixing may be mechanical grinding and mixing, and may be performed, for example, by a ball mill process.

[0097] At this time, the grinding and mixing can be performed at a stirring speed of 200 to 600 rpm. If the stirring speed is too low during the grinding and mixing, sodium may aggregate, which may reduce the concentrated doping effect of sodium on the surface of lithium metal oxide particles. If the stirring speed is too high during the grinding and mixing, the size of the sodium precursor may become too small, which may cause sodium diffusion in the solid state, which may reduce the concentrated doping effect of sodium on the surface of lithium metal oxide particles.

[0098] In addition, the above grinding and mixing can be performed for 5 to 15 hours. If the grinding and mixing time is too short, the sodium may not be well mixed, which may reduce the concentrated doping effect of sodium on the surface of the lithium metal oxide particles. If the grinding and mixing time is too long, the sodium may be excessively ground, which may cause sodium diffusion even in a solid state, which may reduce the concentrated doping effect of sodium on the surface of the lithium metal oxide particles.

[0099] In addition, the above-mentioned grinding and mixing may be performed as a solid-phase grinding and mixing rather than a wet-phase grinding and mixing. When the grinding and mixing is performed in a solid-phase, agglomeration of the material is alleviated, so that the concentrated doping effect of sodium on the surface of the lithium metal oxide particles can be more preferably implemented.

[0100] Meanwhile, the input amounts of lithium raw material, nickel raw material, manganese raw material, and sodium raw material can be appropriately adjusted and input in a stoichiometric ratio suitable for the composition of the target lithium metal oxide.

[0101]

[0102] Next, the mixture is first calcined to form lithium metal oxide particles having a lithium and manganese excess composition.

[0103] Thereafter, the lithium metal oxide particles are subjected to secondary calcination to form lithium metal oxide particles in which sodium is concentratedly doped on the surface.

[0104] Through the above first and second sintering, lithium metal oxide particles having a structure in which sodium is concentratedly doped on the surface of the lithium metal oxide particles can be formed. Specifically, through the first sintering, lithium metal oxide having a lithium and manganese-excess composition with a certain degree of crystallinity can be initially formed. Thereafter, through the second sintering, lithium metal oxide particles having a structure in which sodium is concentratedly doped on the surface of the lithium metal oxide particles can be formed.

[0105] The above first firing temperature may be 420 to 800°C, and more specifically, 420 to 600°C. The above first firing temperature range is a temperature range higher than the melting point of the lithium raw material, but lower than the melting point of the sodium raw material. Accordingly, during the first firing, lithium ions are diffused into the crystal structure to form a lithium metal oxide having a certain degree of crystallinity, while the amount of sodium doping can be reduced as much as possible. Accordingly, through a subsequent second firing process, lithium metal oxide particles having a structure in which sodium is concentratedly doped on the surface of the lithium metal oxide particles can be formed. If the first firing temperature is too low, the crystallinity of the lithium metal oxide may be excessively deteriorated, which may deteriorate the electrochemical characteristics. If the first firing temperature is too high, the effects of improving the initial discharge capacity, rate characteristics, and life characteristics due to concentrated doping of sodium on the surface may be reduced.

[0106] The above first firing time may be 6 to 14 hours, and more specifically, 8 to 12 hours. If the first firing time is too short, the crystallinity of the lithium metal oxide may be excessively deteriorated, which may deteriorate the electrochemical characteristics. If the first firing time is too long, the initial discharge capacity, rate characteristics, and life characteristics improvement effects due to concentrated sodium doping on the surface may be reduced.

[0107] In addition, the secondary firing temperature may be 820 to 930°C, and more specifically, 850 to 920°C. The secondary firing temperature range is a temperature range higher than the melting point of the sodium raw material. Accordingly, during the secondary firing, sodium can be intensively doped into the lithium metal oxide, and lithium metal oxide particles having a structure in which sodium is intensively doped on the surface of the lithium metal oxide particles can be formed. If the secondary firing temperature is too low, sodium doping itself into the lithium metal oxide may not be properly performed, and thus the initial discharge capacity, rate characteristics, and life characteristic improvement effects due to the concentrated doping of sodium on the surface may be reduced. If the secondary firing temperature is too high, sodium may be excessively doped into the interior of the lithium metal oxide particles, and thus the initial discharge capacity, rate characteristics, and life characteristic improvement effects due to the concentrated doping of sodium on the surface may be reduced.

[0108] The secondary firing time may be 6 to 14 hours, and more specifically, 8 to 12 hours. If the secondary firing time is too short, sodium doping into the lithium metal oxide itself may not occur well, and thus the initial discharge capacity, rate characteristics, and lifespan characteristic improvement effect due to surface-concentrated doping of sodium may be reduced. If the secondary firing time is too long, sodium may be excessively doped into the interior of the lithium metal oxide particles, and thus the initial discharge capacity, rate characteristics, and lifespan characteristic improvement effect due to surface-concentrated doping of sodium may be reduced.

[0109] The above first and second calcinations can be performed in an oxygen atmosphere. Accordingly, the crystallinity of the lithium metal oxide is improved, so that more desirable electrochemical properties can be realized.

[0110]

[0111] 3. Cathode ray and lithium secondary battery

[0112] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0113] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and including the positive electrode active material described above.

[0114] 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 positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0115] The above-described positive electrode active material layer may include a binder and / or a conductive material together with the above-described positive electrode active material.

[0116] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one kind alone or a mixture of two or more kinds thereof may be used, but is not limited thereto. 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.

[0117] And, 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 special restrictions. 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. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. 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.

[0118] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

[0119] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on 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.

[0120] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account 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.

[0121] Alternatively, 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.

[0122]

[0123] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0124] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0125] The above lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0126] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0127] 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.

[0128] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0129] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the 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.

[0130] The above binder and conductive material may be the same as those described above for the positive electrode.

[0131]

[0132] The above 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 any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption 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, may 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. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0133]

[0134] The above electrolyte may include, but is 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.

[0135] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0136] The organic solvent may be used without any 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), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and 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.

[0137] 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.

[0138] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric 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.

[0139] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, 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).

[0140] Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0141] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0142]

[0143] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0144]

[0145] Example 1

[0146] (1) Manufacturing of positive electrode active material

[0147] (Grinding Mixing) LiOH·H2O (Aldrich), Ni(OH)2 (Aldrich), and MnCO3 (Aldrich), Na2CO3 (Aldrich) were placed in a ball mill device in a solid state and ground and mixed at a stirring speed of 500 rpm for 10 hours to form a mixture. At this time, the average particle diameter (D50) of Na2CO3 was 100 nm.

[0148] (1st firing) After that, the mixture was fired for the first time at 550℃ in an air atmosphere for 10 hours to form a 1st fired product.

[0149] (Secondary firing) Afterwards, the primary fired material was subjected to secondary firing at 900°C for 10 hours in an air atmosphere to form the final lithium metal oxide.

[0150] The composition of the final lithium metal oxide is Li 1.15 Na 0.05 Ni 0.2 Mn 0.6 It was O2.

[0151] (2) Lithium secondary battery manufacturing

[0152] The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (carbon black, denka black): binder (PVDF, KF1100) = 92.5:3.5:4 wt%, and the viscosity was adjusted so that the solid concentration was approximately 30% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 15 μm thick Al foil using a doctor blade, dried, and then rolled. At this time, the electrode loading amount was approximately 14 mg / cm 2 It was.

[0153] The electrolyte was 1M LiPF6in EC:EMC=3:7 (vol%), with 3.0 vol% FEC added to the total amount of the electrolyte, and a CR2032 coin cell was manufactured using a PP separator and a lithium negative electrode (200 μm, Honzo metal).

[0154]

[0155] Example 2

[0156] In the first firing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the firing temperature was set to 500°C.

[0157]

[0158] Example 3

[0159] In the first firing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the firing temperature was set to 600°C.

[0160]

[0161] Example 4

[0162] In the first firing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the firing temperature was set to 700°C.

[0163]

[0164] Example 5

[0165] In the first firing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the firing temperature was set to 800°C.

[0166]

[0167] Reference Example 1

[0168] In the grinding and mixing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the average particle diameter (D50) of Na2CO3 was set to 300 nm.

[0169]

[0170] Reference Example 2

[0171] In the grinding and mixing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the stirring was performed at a stirring speed of 650 rpm.

[0172]

[0173] Reference Example 3

[0174] In the grinding and mixing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that wet grinding was performed with a wet ball mill instead of a solid ball mill.

[0175]

[0176] Comparative Example 1

[0177] In the grinding and mixing step, the cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that Na2CO3 (Aldrich) was not added and the single-stage firing was performed at 900°C for 10 hours without dividing the first and second firings. The composition of the manufactured lithium metal oxide was Li 1.2 Ni 0.2 Mn 0.6 It was O2.

[0178]

[0179] Comparative Example 2

[0180] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the first and second firings were not performed separately and a single firing was performed at 900°C for 10 hours. The composition of the manufactured lithium metal oxide was Li 1.15 Na 0.05 Ni 0.2 Mn 0.6 It was O2.

[0181]

[0182] Comparative Example 3

[0183] In the grinding and mixing step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the stirring was performed at a stirring speed of 100 rpm.

[0184]

[0185] Tables 1 and 2 below are tables summarizing the process conditions of examples, comparative examples, and reference examples, and Tables 3 to 5 below are tables summarizing the results of evaluating the physical properties of positive electrode active materials and the electrochemical characteristics of lithium secondary batteries according to Experimental Examples 6 and 7 described below.

[0186] Composition Sodium Raw Material Crushing Mixing Type Average Particle Size (D50) (nm) Process Type Stirring Speed ​​(rpm) Crushing Time (h) Example 1 Li 1.15 Na 0.05 Ni 0.2 Mn 0.6O2Na2CO3100Solid ball mill50010Example 2100500Example 3100500Example 4100500Example 5100500Comparative example 1Li 1.2 Ni 0.2 Mn 0.6 O2--500 Comparison Example 2Li 1.15 Na 0.05 Ni 0.2 Mn 0.6 O2Na2CO3100500Reference Example 1300500Comparative Example 3100100Reference Example 2100650Reference Example 3100Wet Grinding 500

[0187] 1st firing 2nd firing Temperature (℃) Time (h) Temperature (℃) Time (h) Example 15501090010 Example 25001090010 Example 36001090010 Example 47001090010 Example 58001090010 Comparative example 1900 degrees, 10h Comparative example 2900 degrees, 10h Reference example 16001090010 Comparative example 36001090010 Reference example 26001090010 Reference example 36001090010

[0188] Surface Na / Mn molar ratio [Surface Na / Mn molar ratio] / [ICP Na / Mn molar ratio]Average particle size (D50) (μm)Example 10.618365.40.5Example 20.617364.80.5Example 30.602355.90.5Example 40.591344.40.5Example 50.585345.90.5Comparative example 1000.5Comparative example 20.574339.50.5Reference example 10.588347.60.5Comparative example 30.570336.90.5Reference example 20.602354.70.7Reference example 30.592349.90.3

[0189] 45℃ Capacity60℃ CapacityCharge Capacity(mAh / g)Discharge Capacity(mAh / g)Initial Efficiency(%)Charge Capacity(mAh / g)Discharge Capacity(mAh / g)Initial Efficiency(%)Example 13292587835826674Example 237428175---Example 336427074---Example 435625973---Example 536026072---Comparative Example 13402417139624061Comparative Example 23322427335825270Reference Example 135525672---Comparative Example 334424471---Reference Example 235725371---Reference Example 334524872---

[0190] Capacity retention rate (25℃ 50 cycle, %) Rate characteristics 1C / 0.1C(%) 5C / 0.1C(%) 10C / 0.1C(%) Example 192645347 Example 292--- Example 391--- Example 490--- Example 590--- Comparative Example 189574638 Comparative Example 292614738 Reference Example 1----Comparative Example 3----Reference Example 2----Reference Example 3----

[0191]

[0192] Experimental Example 1: Thermogravimetric analysis (TGA)

[0193] Thermogravimetric analysis (TGA) of the pulverized mixture in Example 1 was performed, and the results are shown in Fig. 2.

[0194] Referring to Figure 2, it was confirmed that the melting point of LiOH·H2O, a lithium raw material, is about 420°C, and the melting point of Na2CO3, a sodium raw material, is about 820°C.

[0195]

[0196] Experimental Example 2: Evaluation of X-ray Diffraction Analysis of Primary Calcined Material

[0197] X-ray diffraction analysis was performed on the first fired product of the pulverized and mixed mixture in Example 1, and the results are shown in Fig. 3.

[0198] Referring to Figure 3, the primary sintered product also exhibited a super-structure peak, confirming the formation of lithium-excessive lithium metal oxide, but confirming that the crystallinity was somewhat low.

[0199]

[0200] Experimental Example 3: Evaluation of X-ray Diffraction Analysis of Positive Active Material

[0201] X-ray diffraction analysis of the positive electrode active materials manufactured according to Example 1, Comparative Example 1, and Comparative Example 2 was performed, and the results are shown in Fig. 4.

[0202] Referring to FIG. 4, the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2 all exhibited a very clear super-structure peak between 20 and 30˚, confirming that lithium metal oxide with excess lithium was well formed.

[0203] In addition, it was confirmed that the sodium-doped Example 1 and Comparative Example 2 showed a shift in the (003) plane peak in a lower angle direction compared to Comparative Example 1, and this was a result of the c-axis length being extended because the sodium ion was larger than the lithium ion radius, and it was confirmed that the sodium was well doped into the lattice of the lithium metal oxide in Example 1 and Comparative Example 2.

[0204]

[0205] Experimental Example 4: Evaluation of TEM-EDS elemental mapping images of positive electrode active materials.

[0206] TEM (transmission electron microscope)-EDS (energy-dispersive X-ray spectroscopy) element mapping images of the positive electrode active materials manufactured according to Example 1, Comparative Example 1, and Comparative Example 2 were observed, and these are shown in order in Fig. 5, respectively.

[0207] Referring to FIG. 5, it was confirmed that nickel and manganese were evenly distributed within the particles of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2, and in particular, it was confirmed that Na was doped within the particles of the positive electrode active materials of Example 1 and Comparative Example 2.

[0208]

[0209] Experimental Example 5: Evaluation of positive electrode active material by SEM-EDX line scan concentration analysis

[0210] The SEM (scanning electron microscope)-EDX (energy-dispersive X-ray spectroscopy) line scan concentration analysis of the positive electrode active material manufactured according to Example 1 and Comparative Example 2 was performed, and the results are shown in Fig. 6.

[0211] Referring to Fig. 6, in the case of Example 1, it was confirmed that the sodium concentration was higher at the surface than at the center of the particle, thereby confirming that sodium was concentratedly doped at the surface of the lithium metal oxide particle. On the other hand, in the case of Comparative Example 1, it was confirmed that there was no concentration gradient tendency of sodium.

[0212]

[0213] Experimental Example 6: Evaluation of the properties of positive electrode active materials

[0214] (1) Evaluation of the Na / Mn molar ratio on the outermost surface of lithium metal oxide particles

[0215] The Na / Mn molar ratio at the outermost surface of the lithium metal oxide particles was evaluated by directly dispersing the powder and analyzing it with X-ray photoelectron spectroscopy (XPS). In addition, the concentration of sodium doping on the surface of the lithium metal oxide particles was evaluated by dividing the derived Na / Mn molar ratio at the outermost surface of the lithium metal oxide particles by the Na / Mn molar ratio of the average composition in the lithium metal oxide through ICP component analysis. The XPS analysis results of the positive electrode active materials manufactured according to Example 1, Comparative Example 1, and Comparative Example 2 are shown in Fig. 7.

[0216] (2) Average particle size (D50) evaluation

[0217] For the active material powder, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0218]

[0219] Experimental Example 7: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0220] (1) Initial capacity and initial efficiency evaluation

[0221] After fabricating a half-cell of a lithium secondary battery, it was aged at 25°C for 12 hours and then subjected to charge-discharge tests at 25, 45°C, and 60°C. To evaluate the initial capacity, 200 mAh / g was used as the reference capacity, and the battery was charged to 4.25 V at a constant current of 0.1 C. Then, the battery was switched to a constant voltage and charged until the end current reached 0.05 C. After a 10-minute rest time after charging, the battery was discharged to 2.5 V at a constant current of 0.1 C, using 200 mAh / g as the reference capacity.

[0222] (2) Life characteristics evaluation (25℃, 50 cycles)

[0223] After fabricating a lithium secondary battery half-cell, it was charged to 4.25 V at a constant current of 0.5 C at 25°C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, it was discharged at a constant current of 1.0 C until it reached 2.5 V. Under these charge-discharge cycle conditions, 50 charge-discharge cycles were performed, and the capacity retention rate of the 50th cycle was calculated compared to the first cycle.

[0224] (3) Rate characteristic evaluation

[0225] The output characteristics were evaluated by comparing the initial discharge capacity at 0.1C charge-0.1C discharge and the initial discharge capacity at 0.1C charge-1C / 5C / 10C discharge.

[0226] In relation to this, Fig. 8 is a graph of initial charge and discharge curves at 60°C of lithium secondary batteries manufactured according to Example 1, Comparative Example 1, and Comparative Example 2. Fig. 9 is a graph of initial discharge capacity evaluation results at 45°C of lithium secondary batteries manufactured according to Examples 1 to 2, 4 to 5, and Comparative Examples 1 to 2. Fig. 10 is a graph of life characteristic evaluation results at room temperature 25°C of lithium secondary batteries manufactured according to Examples 1 to 2, 4 to 5, and Comparative Examples 1 to 2. Fig. 11 is a graph of rate characteristic evaluation results of lithium secondary batteries manufactured according to Example 1, Comparative Example 1, and Comparative Example 2.

[0227]

[0228] Referring to Tables 1 to 5 and FIGS. 8 to 11, in the case of Examples 1 to 5 in which the composition of the lithium metal oxide including the sodium doping amount, and the overall process conditions including the first and second firing process conditions were appropriately controlled within the range according to the present invention, it was confirmed that the properties of the positive electrode active material were appropriately obtained within the range according to the present invention, such as the Na / Mn molar ratio at the outermost surface of the lithium metal oxide particles being sufficiently high to realize concentrated doping of sodium on the surface. As a result, it was confirmed that the capacity characteristics, life characteristics, and rate characteristics of the battery were comprehensively excellent.

[0229] Comparing Examples 1 to 5, it was confirmed that in Examples 1 to 3, where the primary sintering temperature was lower, the Na / Mn molar ratio at the outermost surface of the lithium metal oxide particles was higher, so that the surface concentration doping effect of sodium was dominant, and thus the life characteristics were more preferably implemented.

[0230] Meanwhile, in the case of Reference Examples 1 to 3 where the average particle size (D50) of the sodium raw material was somewhat large, the stirring speed was too fast during grinding and mixing, or wet grinding was performed, [top surface Na / Mn molar ratio] / [ICP Na / Mn molar ratio] was somewhat lower than in Examples 1 to 3, and it was confirmed that the surface concentration doping effect of sodium was somewhat deteriorated. In addition, it was confirmed that the capacity characteristics of the battery were somewhat reduced.

[0231] In the case of Comparative Example 1, it was confirmed that the capacity characteristics, life characteristics, and rate characteristics of the battery without sodium doping were significantly deteriorated compared to the example.

[0232] In Comparative Example 2, the composition of the lithium metal oxide, including the sodium doping amount, was appropriate, but as a result of the single-stage sintering process, the Na / Mn molar ratio at the outermost surface of the lithium metal oxide particles was low, which deteriorated the surface concentration doping effect of sodium. As a result, it was confirmed that the capacity characteristics and rate characteristics of the battery were significantly deteriorated compared to the examples.

[0233] In Comparative Example 3, the stirring speed during the grinding and mixing was too slow, which resulted in a low surface Na / Mn molar ratio of the lithium metal oxide particles, thereby deteriorating the concentrated doping effect of sodium on the surface. As a result, it was confirmed that the capacity characteristics of the battery were significantly deteriorated compared to the examples.

[0234]

[0235] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0236] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium metal oxide particle having a lithium and manganese excess composition and doped with sodium, wherein the lithium metal oxide has a structure in which lithium layers and transition metal layers are alternately laminated. The above sodium is more doped into the lithium layer among the lithium layer and the transition metal layer, and the sodium is concentratedly doped on the surface of the lithium metal oxide particles. Cathode active material for lithium secondary batteries.

2. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the molar ratio of sodium to manganese (Na / Mn) on the outermost surface of the lithium metal oxide particles, as analyzed by XPS (X-ray photoelectron spectroscopy), is 342 times or more the average molar ratio of sodium to manganese (Na / Mn) in the lithium metal oxide.

3. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the molar ratio of sodium to manganese (Na / Mn) on the outermost surface of the lithium metal oxide particles is 0.58 or more as analyzed by XPS (X-ray photoelectron spectroscopy).

4. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery having a molar ratio of sodium to lithium metal oxide of 0.01 to 0.

2.

5. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery having a molar ratio of cobalt to lithium metal oxide of 0.05 or less.

6. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery having a molar ratio of lithium to lithium metal oxide of 1.1 to 1.

3.

7. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery having a molar ratio of nickel to lithium metal oxide of 0.1 to 0.

3.

8. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery having a molar ratio of manganese to lithium metal oxide of 0.5 to 0.

7.

9. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the lithium metal oxide particles is 10 μm or less.

10. In paragraph 1, The above lithium metal oxide is a cathode 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 So w1 M w2 )O2 In the chemical formula 1, 0.1≤a≤0.3, 0.1≤x≤0.3, 0≤y≤0.05, 0.5≤z≤0.7, 0.01≤w1≤0.2, 0≤w2≤0.2, and a+x+y+z+w1+w2=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, Ir or a combination thereof.

11. A step of forming a mixture by crushing and mixing lithium raw material, nickel raw material, manganese raw material, and sodium raw material; A step of first calcining the above mixture to form lithium metal oxide particles having an excess composition of lithium and manganese; and It comprises a step of forming lithium metal oxide particles by secondary calcination of the lithium metal oxide particles, wherein sodium is concentratedly doped on the surface. The above first firing temperature is 420 to 800°C, and the above second firing temperature is 820 to 930°C. A method for producing a cathode active material for a lithium secondary battery.

12. In paragraph 11, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the first sintering temperature is 420 to 600°C.

13. In paragraph 11, A method for producing a cathode active material for a lithium secondary battery, wherein the above grinding and mixing is performed by solid-phase grinding and mixing.

14. In paragraph 11, A method for producing a cathode active material for a lithium secondary battery, wherein the above grinding and mixing is performed at a stirring speed of 200 to 600 rpm.

15. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above grinding and mixing is performed for 5 to 15 hours.

16. A cathode for a lithium secondary battery comprising a cathode active material according to Article 1.

17. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to Article 16.

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