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

Abstract

The present invention comprises: an over-lithiated layered oxide represented by the following Chemical Formula 1; and an ion-conductive coating layer on the surface of the over-lithiated layered oxide represented by Chemical Formula 1: rLi2MnO3. (1-r) LiaNixCoyMnzM11-(x + y + z) O2 (in Chemical Formula 1, 0 lt; r is less than or equal to 0.6, 0lt; a < = 1, 0 < = x < = 1, 0 < = y < lt; 1, 0 < = zlt; 1, 0lt; x + y + z < = 1, and M1 is one or more elements selected from the group consisting of Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, and Bi.

Description

[0001] This application is a divisional application of the invention patent application with the application number 202080072959.X. The filing date of the original application is October 19, 2020, and the invention title is "Positive Electrode Active Material for Lithium Secondary Battery, Method for Preparing the Same, and Lithium Secondary Battery Comprising the Same". Technical Field

[0002] The present invention relates to a positive electrode active material comprising a hyperlithiated layered oxide, and more particularly, to a positive electrode active material for a lithium secondary battery having an ion-conductive coating formed on its surface, a method for preparing the same, and a lithium secondary battery comprising the same. Background Art

[0003] With the development of portable mobile electronic devices such as smart phones, MP3 players, and tablet personal computers (PCs), the demand for secondary batteries capable of storing electric energy has increased explosively. In particular, with the emergence of electric vehicles, medium and large-scale energy storage systems, and portable devices requiring high energy density, the demand for lithium secondary batteries is increasing day by day.

[0004] Recently, a highly regarded positive electrode active material is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z )O2 (in this case, x, y, and z are respectively the atomic fractions of the oxide constituent elements, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, 0 < x + y + z ≤ 1). Compared with the positive electrode active material LiCoO2 that has been actively studied heretofore, this positive electrode active material has the advantages of high output capacity because it is used at a high voltage and low cost because the Co content is relatively low. However, it has the disadvantages of poor rate capability and poor life characteristics at high temperatures.

[0005] Therefore, research is being conducted on applying a hyperlithiated layered oxide that exhibits a higher reversible capacity than existing Li(Ni x Co y Mn z )O2 to lithium secondary batteries.

[0006] However, the phenomenon of discharge capacity reduction (cycle life) and voltage decay that occur during the life cycle of such a hyperlithiated layered oxide has become a problem, which is caused by a phase transition from a spinel-like structure to a cubic structure due to the movement of transition metals during the life cycle. In order to be used for the commercialization of lithium secondary batteries, the problems of discharge capacity reduction and voltage decay of the above hyperlithiated layered oxide must be solved.

[0007] Also, a solution capable of improving the electrochemical characteristics of the over-lithiated layered oxide is required. Summary of the Invention

[0009] Technical Problem

[0010] An object of the present invention is to improve the lithium ion conductivity of a positive electrode active material containing an over-lithiated layered oxide, reduce the overpotential occurring during charge and discharge by reducing the resistance, and improve the rate performance.

[0011] Also, an object of the present invention is to suppress the Mn dissolution of a Mn-rich positive electrode active material, suppress the lattice change from the spinel phase to the rock-salt phase starting from the surface phase of the positive electrode active material during cycling, thereby suppressing the reduction of the discharge capacity and the voltage decay and improving the life.

[0012] Technical Solution

[0013] The positive electrode active material according to an embodiment of the present invention includes an over-lithiated layered oxide represented by the following Chemical Formula 1.

[0014] Chemical Formula 1: rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2

[0015] In the above Chemical Formula 1, 0 < r ≤ 0.6, 0 < a ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 < x + y + z ≤ 1, and the above M1 is one or more selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, and Bi.

[0016] The above over-lithiated layered oxide may be a solid solution phase in which monoclinic-structured Li2MnO3 and rhombohedral-structured LiMO2 are mixed, and the above M may be one or more selected from Ni, Co, Mn, and M1.

[0017] Moreover, the over-lithiated layered oxide may have a plateau caused by Li2MnO3 in the 4.4V region of the initial charge-discharge curve. In the over-lithiated layered oxide of the embodiment of the present invention, during the initial charging process, the Li2MnO3 phase is electrochemically inactive relative to lithium up to the 4.4V region, and in the region above 4.4V, lithium may separate from the Li2MnO3 phase and oxygen may evolve.

[0018] In the overlithiated layered oxide represented by the above Chemical Formula 1, a ratio of moles of lithium to total moles of metal Ni, Co or Mn contained (Li / Ni+Co+Mn) may be 1.1 to 1.6, 1.2 to 1.6, 1.3 to 1.6 or 1.4 to 1.5.

[0019] In the chemical formula 1, the value of x may be greater than 0 and less than or equal to 0.5, greater than 0 and less than or equal to 0.4, greater than 0 and less than or equal to 0.3, greater than 0 and less than or equal to 0.2, or greater than 0 and less than or equal to 0.1.

[0020] In the chemical formula 1, the value of y may be greater than 0 and less than or equal to 0.5, greater than 0 and less than or equal to 0.4, greater than 0 and less than or equal to 0.3, greater than 0 and less than or equal to 0.2, or 0.1 to 0.2.

[0021] In the above chemical formula 1, M1 is one or more substances selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Nb, Cu, In, S, B, Ge, Si and Bi, and as an example, it can be a dopant that can be included in the above-mentioned over-lithiated layered oxide. More preferably, it can be one or more selected from Ba, Sr, B, P, Y, Zr, Nb, Mo, Ta and W that can be adjusted to grow the size of the primary particles to a more suitable range, and most preferably, it can be one or more selected from Nb and Ta.

[0022] And, the ratio of the mole number of Mn to the total mole number of Ni (Mn / Ni) may be 1 to 4.5, 1 to 4, 2 to 4.5, 2 to 4, 3 to 4.5, or 3 to 4.

[0023] The oxide of the present invention has a layered structure, which may be a layered structure in which lithium atomic layers and metal atomic layers of Ni, Co, Mn or M1 are alternately stacked via oxygen atomic layers.

[0024] The plane of the layer forming the layered structure of the above-mentioned positive electrode active material may have a crystal orientation in a direction perpendicular to the C axis. In this case, the mobility of lithium ions contained in the above-mentioned positive electrode active material is improved, the structural stability of the above-mentioned positive electrode active material is increased, and the initial capacity characteristics, power output characteristics, resistance characteristics, and long-term life characteristics can be improved when applied to a battery.

[0025] The positive electrode active material of the present invention forms an ion-conductive coating on the surface, inhibits the Mn dissolution of the oxide rich in lithium and manganese, and can inhibit the reduction of the discharge capacity and the voltage decay by suppressing the lattice change from the spinel phase to the rock salt phase mainly starting from the surface phase of the positive electrode active material during cycling.

[0026] Moreover, the present invention coats an ion-conductive coating on the surface of the over-lithiated layered oxide particles, reduces the resistance by increasing the ion conductivity, and thus can inhibit the deterioration of the life and the voltage decay.

[0027] Moreover, the present invention coats an ion-conductive coating on the surface of the over-lithiated layered oxide particles, reduces the overpotential occurring during charge and discharge in the over-lithiated layered oxide, and thus can improve the rate performance.

[0028] To achieve the above effects, more preferably, the ion-conductive coating may contain one or more elements selected from Ti, Al, and Zr.

[0029] Moreover, the ion-conductive coating may contain a substance represented by the following Chemical Formula 2.

[0030] Chemical Formula 2: Li a M2 b O c

[0031] In the above Chemical Formula 2, 0 < a ≤ 4, 0 < b ≤ 5, 0 < c ≤ 12, and M2 may be one or more selected from Ti, Al, and Zr.

[0032] To achieve the above effects, compared with the above over-lithiated layered oxide, the ion-conductive coating may be contained in an amount of 0.05 mol% to 5 mol%, 0.1 mol% to 3 mol%, 0.1 mol% to 2 mol%, or 0.5 to 2 mol%.

[0033] The ion-conductive coating may be uniformly or non-uniformly contained on the surface of the over-lithiated layered oxide represented by the above Chemical Formula 1.

[0034] Moreover, as an example, the ion-conductive coating may be formed on the surface of secondary particles or primary particles, respectively.

[0035] Furthermore, as an example, the element contained in the ion conductive coating layer may form a concentration gradient portion on the surface of the secondary particle or the primary particle.

[0036] In the positive electrode active material of the embodiment of the present invention, the thickness of the above-mentioned ion conductive coating can be 1nm to 100nm, and more preferably, it can be 10nm to 100nm. If it is thinner than the above-mentioned coating, the improvement effect is negligible, and if it is thicker than the above-mentioned thickness, the resistance to lithium ions will increase. When the above-mentioned ion conductive coating meets the above-mentioned range, the Mn dissolution of the manganese-rich positive electrode active material of the present invention can be suppressed, and the lattice change from the spinel type to the rock salt phase starting from the surface phase during the cycle can be suppressed to suppress the reduction of discharge capacity and voltage decay and improve the life.

[0037] In the above-mentioned positive electrode active material of the embodiment of the present invention, secondary particles can be formed by aggregation of primary particles. Among the primary particles constituting the above-mentioned secondary particles, the primary particles with a size of 300nm to 10μm can be adjusted to 50 volume percent to 100 volume percent, 70 volume percent to 100 volume percent or 100 volume percent.

[0038] Furthermore, as an example, among the primary particles constituting the secondary particles, the primary particles in the positive electrode active material having a size greater than 500 nm and less than or equal to 10 μm can be adjusted to 50 volume percent to 100 volume percent, 70 volume percent to 100 volume percent or 100 volume percent.

[0039] Furthermore, as an example, in the above-mentioned positive electrode active material, the primary particles with a size of 1 μm to 10 μm can be adjusted to 50 volume percent to 100 volume percent, 70 volume percent to 100 volume percent or 100 volume percent relative to the total volume of the above-mentioned overlithiated layered oxide.

[0040] Furthermore, as an example, in the above-mentioned positive electrode active material, the primary particles having a size greater than 1 μm can be adjusted to 50 volume percent to 100 volume percent, 70 volume percent to 100 volume percent or 100 volume percent relative to the total volume of the above-mentioned overlithiated layered oxide.

[0041] Furthermore, as an example, in the above-mentioned positive electrode active material, the primary particles with a size of 2 μm or more can be adjusted to 50 volume percent to 100 volume percent, 70 volume percent to 100 volume percent or 100 volume percent relative to the total volume of the above-mentioned overlithiated layered oxide.

[0042] Furthermore, as an example, since the size of the primary particles in the positive electrode active material is adjusted, the number of primary particles in the secondary particles may be 1 to 1000, 1 to 100, 1 to 10, or 1 to 10, or may be formed by one primary particle.

[0043] The above-mentioned size of the primary particle refers to the longest length of the particle.

[0044] Furthermore, as an example, the average particle size of the primary particles of the positive electrode active material may be adjusted to be greater than 500 nm and less than or equal to 10 μm, or to be 1 μm to 10 μm.

[0045] The present invention can solve the problems of reduced discharge capacity and voltage decay occurring in over-lithiated layered oxides by adjusting the size of primary particles and improve the density of positive electrode active materials.

[0046] However, since the primary particles become larger, the diffusion distance of lithium ions increases, so the concentration polarization of lithium ions causes overpotential during charge and discharge. Ultimately, the capacity of the positive electrode active material is reduced due to reduced kinetics. However, since the kinetics of lithium ions are increased by forming the above-mentioned ion conductive coating, the capacity increases and the overpotential decreases.

[0047] The average particle size of the secondary particles of the positive electrode active material of the embodiment of the present invention may be 2 μm to 20 μm.

[0048] The average particle size of the present invention can be defined as a particle size corresponding to 50% of the cumulative volume in a particle size distribution curve of the particles. The above average particle size can be measured by, for example, a laser diffraction method.

[0049] The above-mentioned positive electrode active material of the embodiment of the present invention has a primary particle size in the positive electrode active material stage that is larger than the primary particle size in the precursor stage under the preparation process conditions of the following embodiments. In addition, under the preparation conditions of the following embodiments, the ratio of (the primary particle size of the positive electrode active material with the addition of a dopant that acts as a flux) / (the primary particle size of the positive electrode active material without the addition of a dopant that acts as a flux) is greater than 1, more preferably, greater than 30, and most preferably, greater than 50.

[0050] In the above, M1 in the above Chemical Formula 1 is a dopant that acts as a flux for growing the above primary particles and can be doped into the lattice structure. As an example, it can be adjusted by adding and mixing the above flux dopant during the firing step with the lithium compound and heat-treating them together to increase the size of the primary particles. Acting as a flux can mean acting as a dopant that increases the size of the primary particles through the growth between the primary particles.

[0051] In the cathode active material of the embodiment of the present invention, the more the part equivalent to the single crystal structure, that is, the fewer the number of primary particles, the more the problem of voltage decay exhibited by the polycrystalline structure can be improved.

[0052] When performing X-ray diffraction (XRD) analysis on the above cathode active material of the embodiment of the present invention, although the full width at half maximum (FWHM (deg.)) in I(104) can be 0.1 to 0.25 (deg.), the above value can vary according to the content of manganese. Therefore, the reduction rate of the full width at half maximum can be adjusted by adding and adjusting the content of the above dopant M1, thereby solving the problems of lifespan and voltage decay.

[0053] In the present invention, in the over-lithiated layered oxide, by adjusting to increase the size of the primary particles, when fired under the same conditions, the full width at half maximum (FWHM (deg.)) in I(104) in the case of including M1 in X-ray diffraction analysis can be reduced by 5% to 50% or 5% to 40% or 5% to 30% or 5% to 20%, 10% to 25% or 10% to 20% compared to the comparative example without M1.

[0054] The cathode active material of the embodiment of the present invention may include a substance represented by the following Chemical Formula 3. The substance represented by the following Chemical Formula 3 may be a substance formed by the reaction of a dopant acting as a flux that induces the growth between primary particles with lithium.

[0055] Chemical Formula 3: Li a M3O b

[0056] In the above Chemical Formula 3, 0 < a ≤ 8, 0 < b ≤ 15, and M3 is one or more selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, and Bi.

[0057] The content of M1 in the chemical formula 1 may be 0.001 mol% to 10 mol%, 0.01 mol% to 5.0 mol%, 0.01 mol% to 3.0 mol%, 0.1 mol% to 2.0 mol%, or 0.1 mol% to 1.0 mol% relative to the total molar number of the metal constituting the positive electrode active material. If the dopant M1 included as a flux for inducing the growth of primary particles is greater than the above range, it will cause excess lithium composite oxide and cause a decrease in capacity and efficiency. If it is less than the above range, the effect of primary particle growth will be negligible.

[0058] Furthermore, the volume energy density (Wh / L) of the positive electrode active material according to the embodiment of the present invention may be 2.7Wh / L to 4.0Wh / L.

[0059] Moreover, the volume energy density (Wh / L) of the above-mentioned positive electrode active material of the embodiment of the present invention can be increased by 5% to 30% compared with the material not containing M1. The positive electrode active material of the present invention can increase the size of the primary particles in the over-lithiated layered oxide by adjusting, so that the volume energy density (Wh / L) of the case containing M1 can be increased by 5% to 25%, 5% to 20%, 10% to 25% or 10% to 20% compared with the comparative example not containing M1.

[0060] In addition, the compaction density (g / cc) of the positive electrode active material adjusted by adding the dopant M1 and adjusting the content thereof may be 2.0 g / cc to 4.0 g / cc.

[0061] Furthermore, the specific surface area (BET, m 2 / g) can be 0.1m 2 / g to 1.5m 2 / g.

[0062] The cathode active material of the present invention can be prepared by adjusting the size of the primary particles in the above-mentioned overlithiated layered oxide, thereby adjusting the specific surface area (BET, m 2 / g) was reduced by 20% to 80% compared with the comparative example not containing M1.

[0063] The present invention adjusts the portion of the single crystal structure equivalent to the positive electrode active material by inducing the growth of the primary particles, and reduces the surface portion of the positive electrode active material by increasing the volume energy density and reducing the specific surface area, thereby solving the problems of life and voltage decay. In the present invention, the content of inducing the growth of the primary particles includes all the concepts of nucleation, Ostwald ripening, and particle aggregation.

[0064] As an example, the method for preparing a positive electrode active material according to an embodiment of the present invention includes a first step of preparing a positive electrode active material precursor such as carbonate or hydroxide.

[0065] The average particle size of the precursor particles may be 2 μm to 20 μm.

[0066] The precursor may be prepared by co-precipitation, spray-drying, solid state method, wet pulverization, fluidized bed drying method, or vibration drying method, but the present invention is not limited thereto.

[0067] In the method for preparing the positive electrode active material of the embodiment of the present invention, after the first step and before the second step, a step of calcining the prepared precursor at a temperature of 300° C. to 600° C. or 500° C. to 600° C. may be further included.

[0068] In the method for preparing the positive electrode active material of the embodiment of the present invention, after the first step and before the second step, the steps of washing and drying the sintered material may be further included.

[0069] Next, the method includes a second step of mixing a lithium compound with the positive electrode active material precursor and firing the mixture to form a lithium composite oxide.

[0070] The second step may further include mixing and sintering a compound including M1 of Chemical Formula 1. Compared to the over-lithiated layered oxide particles, 0.1 mol % to 1.0 mol % or 0.3 mol % to 0.8 mol % of M1 may be mixed.

[0071] In order to solve the above problem, the temperature of the sintering step may be 750°C to 950°C or 850°C to 950°C.

[0072] In the method for preparing the positive electrode active material of the embodiment of the present invention, after the second step and before the third step, the steps of washing and drying the sintered material may be further included.

[0073] Next, a third step of mixing the lithium composite oxide formed in the second step with a coating precursor to form an ion conductive coating is included.

[0074] The present invention can uniformly coat the ion conductive coating on the surface of the over-lithiated layered oxide through the following steps.

[0075] In the third step, the coating precursor may be mixed by a dry mixing process.

[0076] Furthermore, in the third step, the coating precursor may be prepared by a wet mixing process. For example, the coating precursor may be dispersed or dissolved in water, alcohol or a dispersion solution and mixed with the substance formed in the second step.

[0077] The third step may include: after mixing the substance formed in the second step with the coating precursor, maintaining the mixture at a temperature of 400° C. to 800° C. or 600° C. to 800° C. for 7 to 12 hours and then performing furnace cooling.

[0078] As an example, when the ion conductive coating includes one or more selected from Ti, Al and Zr, the above-mentioned coating precursor can be one or more selected from TiO2, Al2O3, Al(OH)3, ZrO2 and Zr(OH)4, but is not particularly limited thereto.

[0079] The secondary battery according to the embodiment of the present invention includes the above-mentioned positive electrode active material.

[0080] The positive electrode active material is as described above, and the binder, the conductive material, and the solvent are not particularly limited as long as they can be used on the positive electrode collector of the secondary battery.

[0081] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and an electrolyte between the positive electrode and the negative electrode, but is not particularly limited as long as it can be used in a secondary battery.

[0082] Effects of the Invention

[0083] The present invention improves lithium ion conductivity in a super-lithiated layered oxide, reduces overpotential during charge and discharge by reducing resistance, and improves rate characteristics.

[0084] In addition, the Mn dissolution of the manganese-rich positive electrode active material is suppressed, and the lattice change from the spinel type to the rock salt phase starting from the surface phase during cycling is suppressed, thereby suppressing the reduction in discharge capacity and voltage decay and improving the life. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 This is the EDS test result of the embodiment of the present invention.

[0086] Figure 2 This is the dispersion spectrum detection result of the embodiment of the present invention.

[0087] Figure 3 The scanning electron microscope (SEM) test results of the embodiments and comparative examples of the present invention are shown in FIG.

[0088] Figure 4 The following are the X-ray diffraction (XRD) analysis results of the examples and comparative examples of the present invention.

[0089] Figure 5 The following are the results of X-ray diffraction analysis of the examples and comparative examples of the present invention.

[0090] Figure 6 It is a charge and discharge characteristic curve diagram of the embodiment of the present invention and the comparative example.

[0091] Figure 7 Graphs showing overpotentials of embodiments of the present invention and comparative examples.

[0092] Figure 8 It is a rate characteristic curve diagram of the embodiment of the present invention and the comparative example.

[0093] Fig. 9 The graph is a life characteristic curve of the embodiment of the present invention and the comparative example.

[0094] Fig.10 The graph is a life characteristic curve of the embodiment of the present invention and the comparative example.

[0095] Fig.11 Graphs showing voltage characteristics of the embodiments of the present invention and comparative examples.

[0096] Fig.12 Graphs showing voltage characteristics of the embodiments of the present invention and comparative examples. DETAILED DESCRIPTION

[0097] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0098] Expressions such as “including” and the like used in this specification should be interpreted as open-ended terms including the possibility of further including other embodiments.

[0099] The terms “preferred” and “preferably” used in this specification refer to embodiments of the present invention that can provide specified advantages under specified circumstances, rather than excluding other embodiments from the scope of the present invention.

[0100] Example 1. Preparation of positive electrode active material

[0101] synthesis

[0102] Spherical Ni was synthesized by co-precipitation method. 0.2 Co 0.1 Mn 0.7 CO3 precursor. In a 90L reactor, 25 weight percent NaCO3 and 28 weight percent NH4OH were added to a 2.5M aqueous solution of composite transition metal sulfuric acid in which NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were mixed at a mole ratio of 20:10:70. In this case, the pH in the reactor was maintained at 8.0 to 11.0 and the temperature was maintained at 45°C to 50°C. In addition, inert gas N2 was added to the reactor to prevent the prepared precursor from being oxidized.

[0103] After the synthesis stirring was completed, the mixture was washed and dehydrated using a filter press (F / P) device. Finally, the dehydrated product was dried at 120°C for 2 days and passed through a 75μm (200 mesh) sieve to obtain 18μm and 4μm Ni 0.2 O 0.1 Mn 0.7 CO3 precursor.

[0104] Roasting

[0105] The precursor prepared as above is kept in an O2 or air (Air) (50L / min) atmosphere in a box-type calcining furnace, the temperature is increased at a rate of 2°C per minute and maintained at 550°C for 1 to 6 hours, and then the furnace is cooled.

[0106] Firing

[0107] LiOH or Li2CO3 was weighed so that the Li / (Ni+Co+Mn) ratio of the calcined precursor was 1.45, and 0.6 mol% of Nb2O5 was weighed as a flux dopant, and mixed using a manual mixer (MM).

[0108] The mixture is kept in an O2 or air (50 L / min) atmosphere in a box-type calcining furnace, heated at a rate of 2°C per minute, kept at a sintering temperature of 900°C for 7 to 12 hours, and then furnace-cooled to prepare lithium composite oxide particles.

[0109] Coating

[0110] 1.0 mol % of TiO2 was weighed as a surface treatment dopant and mixed using a hand mixer.

[0111] The above mixture is maintained in an O2 or air (50L / min) atmosphere in a box-type calcining furnace, the temperature is increased at a rate of 4.4°C per minute, and after being maintained at a sintering temperature of 700°C for 7 to 12 hours, the furnace is cooled to prepare the positive electrode active material.

[0112] Example 2. Preparation of positive electrode active material

[0113] A positive electrode active material was prepared in the same manner as in Example 1, except that 1.0 mol % of Al 2 O 3 was mixed as a surface treatment dopant in the coating step of Example 1.

[0114] Example 3. Preparation of positive electrode active material

[0115] A positive electrode active material was prepared in the same manner as in Example 1, except that 1.0 mol % of n-ZrO 2 was mixed as a surface treatment dopant in the coating step of Example 1.

[0116] Example 4. Preparation of positive electrode active material

[0117] A positive electrode active material was prepared in the same manner as in Example 1 above, except that 0.19 mol % of TiO 2 , 0.77 mol % of Al 2 O 3 and 0.04 mol % of n-ZrO 2 were mixed as surface treatment dopants in the coating step of Example 1 above.

[0118] Comparative Example 1. Preparation of positive electrode active material

[0119] A positive electrode active material was prepared in the same manner as in Example 1, except that the flux dopant was not mixed and the coating step was not performed.

[0120] Comparative Example 2. Preparation of positive electrode active material

[0121] A positive electrode active material was prepared in the same manner as in Example 1, except that the coating step was not performed.

[0122] Preparation Example. Preparation of lithium secondary battery

[0123] 90 weight percent of the positive electrode active material of the above-mentioned embodiment and comparative example, 5.5 weight percent of carbon black, and 4.5 weight percent of polyvinylidene fluoride (PVDF) binder were dispersed in 30g of N-methyl-2-pyrrolidone (NMP) to prepare positive electrode slurry. The above positive electrode slurry was applied to a 15μm thick aluminum (Al) film as a positive electrode collector and dried, and then roll pressed to prepare a positive electrode. The filling amount of the positive electrode was 5.5mg / cm 2 , the electrode density is 2.3g / cm 3 .

[0124] With respect to the above-mentioned positive electrode, metallic lithium was used as a counter electrode, 1M LiPF6 was used as an electrolyte, and ethylene carbonate / dimethyl carbonate (EC / DMC)=1 / 1 (v / v).

[0125] A separator formed of a porous polyethylene (PE) film was interposed between the positive electrode and the negative electrode to form a battery assembly, and the electrolyte was injected to prepare a lithium secondary battery (button battery).

[0126] Experimental example

[0127] Reference Figure 1 It can be confirmed that the Ti, Al and Zr coatings are uniformly distributed on the surface of the positive electrode active material of the above-mentioned Examples 1 to 3.

[0128] Reference Figure 2 It can be confirmed that the Ti, Al and Zr coatings are evenly distributed on the surface of the positive electrode active material of the above-mentioned Example 4.

[0129] Reference Figure 3 It can be confirmed that the primary particles are grown by the flux dopant Nb, and Ti, Al and Zr coatings are formed on the grown primary particles.

[0130] Figure 4 and Figure 5 The X-ray diffraction analysis was wavelength. Figure 4 and Figure 5 It can be confirmed that a portion of the surface treatment dopant is doped into the particle surface. In addition, it can be confirmed that the diffusion of lithium ions is facilitated by the interslab expansion effect of a portion of the doping.

[0131] Reference Figure 6 In the case of Comparative Example 2, although there is a problem of slightly reduced capacity due to the decrease in kinetics caused by the increase in the diffusion distance of lithium ions as the primary particles become larger, when the ion conductive coating is formed, it can be confirmed that the capacity increases. This is because the increase in ion conductivity increases the kinetics of lithium ions.

[0132] Reference Figure 7 In the case of Comparative Example 2, since the primary particles become larger and the diffusion distance of lithium ions increases, there is a problem of overpotential caused by concentration polarization of lithium ions, but in the case of the embodiment in which the ion conductive coating is formed, it can be confirmed that the overpotential is reduced. This is because the kinetics of lithium ions increase.

[0133] Reference Figure 8 It can be confirmed that the rate characteristics of the example are improved by about 10% or more compared with the comparative example 2. This is because the resistance is reduced by the ion conductive coating.

[0134] Reference Fig. 9 and Fig.10 Compared with Comparative Example 2, it can be confirmed that the life characteristics of the embodiment are improved, and the capacity retention rate is more than 80%. This is because the ion conductive coating reduces the resistance, suppresses the dissolution of Mn, and suppresses the phase transition from the spinel type to the rock salt phase starting from the surface during the cycle.

[0135] Reference Fig.11 and Fig.12 Compared with Comparative Example 2, it can be confirmed that the voltage holding ratio of the embodiment is improved and the problem of voltage decay is solved. This is because the ion conductive coating suppresses the phase transition of the over-lithiated layered oxide during the cycle.

[0136] The above experimental results are shown in Table 1 below.

[0137] Table 1

[0138]

[0139]

Claims

1. A positive electrode active material for a secondary battery, characterized in that, it comprises: a lithium - over - lithiated layered oxide represented by the following Chemical Formula 1; and an ion - conductive coating located on the surface of the lithium - over - lithiated layered oxide represented by the above Chemical Formula 1, Chemical formula 1: rLi 2 MnO 3 ·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O 2 in the above Chemical Formula 1, 0 < r ≤ 0.6, 0 < a ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 < x + y + z ≤ 1, and the above M1 is one or more selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, and Bi.

2. The positive electrode active material for a secondary battery according to claim 1, characterized in that, the above ion - conductive coating comprises one or more selected from Ti, Al, and Zr.

3. The positive electrode active material for a secondary battery according to claim 1, characterized in that, the above ion - conductive coating comprises a substance represented by the following Chemical Formula 2: Chemical formula 2: Li a M2 b O c in the above Chemical Formula 2, 0 < a ≤ 4, 0 < b ≤ 5, 0 < c ≤ 12, and M2 is one or more selected from Ti, Al, and Zr.

4. The positive electrode active material for a secondary battery according to claim 1, characterized in that, relative to the above lithium - over - lithiated layered oxide, it contains 0.05 mol% to 5.0 mol% of the above ion - conductive coating.

5. The positive electrode active material for a secondary battery according to claim 1, characterized in that, the thickness of the above ion - conductive coating is 1 nm to 100 nm.

6. The positive electrode active material for a secondary battery according to claim 1, characterized in that, in the above positive electrode active material, secondary particles are formed by aggregation of primary particles, among the primary particles constituting the above secondary particles, primary particles with a size of 300 nm to 10 μm are adjusted to 50 vol% to 100 vol%.

7. The positive electrode active material for a secondary battery according to claim 1, characterized in that, the above M1 in the above Chemical Formula 1 is a dopant that acts as a flux for growing the above primary particles.

8. The positive electrode active material for a secondary battery according to claim 1, characterized in that, the above M1 in the above Chemical Formula 1 is one or more selected from Ba, Sr, B, P, Y, Zr, Nb, Mo, Ta, and W.

9. The positive electrode active material for a secondary battery according to claim 1, characterized in that, relative to the total molar number of metals in the above lithium - over - lithiated layered oxide, it contains 0.001 mol% to 10 mol% of the above M1 in the above Chemical Formula 1.

10. The positive electrode active material for a secondary battery according to claim 1, characterized in that, in the lithium - over - lithiated layered oxide represented by the above Chemical Formula 1, the ratio of the molar number of lithium to the total molar number of the included metals Ni, Co, or Mn, i.e., Li / Ni + Co + Mn, is 1.1 to 1.

6.

11. The positive electrode active material for a secondary battery according to claim 1, It is characterized in that In the over-lithiated layered oxide represented by the above Chemical Formula 1, a ratio of the number of moles of Mn to the total number of moles of Ni, ie, Mn / Ni, is 1 to 4.

5.

12. A method for preparing the positive electrode active material for secondary batteries according to claim 1, include: The first step is to prepare a positive electrode active material precursor; The second step is to mix a lithium compound into the positive electrode active material precursor and sinter the mixture to form a lithium composite oxide. as well as In the third step, the lithium composite oxide formed in the second step is mixed with a coating precursor to form an ion conductive coating.

13. The method for preparing a positive electrode active material for a secondary battery according to claim 12, It is characterized in that In the second step, a compound including M1 of the chemical formula 1 is further mixed and fired.

14. The method for preparing a positive electrode active material for a secondary battery according to claim 12, It is characterized in that The coating precursor is selected from TiO 2 、Al 2 O 3 、Al(OH) 3 、ZrO 2 and Zr(OH) 4 One or more of the following.

15. A secondary battery, It is characterized in that Contains the positive electrode active material according to claim 1.

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