Lithium secondary battery positive electrode active material, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material which is improved in ion conductivity and rate characteristics.SOLUTION: The present invention relates to a positive electrode active material including an overlithiated layered oxide. The positive electrode active material includes: an overlithiated layered oxide represented by chemical formula 1 below; and an amorphous glass oxide coating layer of an amorphous glass oxide formed on the surface of the overlithiated layered oxide represented by chemical formula 1. [Chemical formula 1] rLi2MnO3(1-r)LiaNixCoyMnzM11-(x+y+z)O2 (in chemical formula 1, 0<r≤0.6, 0<a≤1, 0≤x≤1, 0≤y<1, 0≤z<1, and 0<x+y+z≤1, and M1 is at least any one 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.)SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cathode active material containing an overlithiated layered oxide (OLO), and more particularly, to a lithium secondary battery cathode active material having an amorphous glass oxide coating layer formed on its surface, a method for manufacturing the same, and a lithium secondary battery including the same.

[0002]

Background Art

[0003] With the development of portable mobile electronic devices such as smartphones, MP3 players, and tablet PCs, the demand for secondary batteries capable of storing electrical energy has increased explosively. In particular, with the emergence of electric vehicles, medium and large-sized energy storage systems, and portable devices that require high energy density, the demand for lithium secondary batteries is increasing.

[0004] In recent years, the most spotlighted material as a cathode active material is lithium nickel manganese cobalt oxide Li(Ni z , x ,

[0005] , y , , Co y Mn z )O2 (where x, y, and z are the atomic fractions of independent oxide composition elements, respectively, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, and 0 < x + y + z ≤ 1). This cathode active material has been actively studied and used as a cathode active material so far, and is used at a higher voltage than LiCoO2, so it has the advantage of showing high capacity, and because the Co content is relatively low, it has the advantage of being low in price. However, it has the disadvantages of poor rate capability and lifespan characteristics at high temperatures.

[0005] Therefore, the existing Li(Ni x Co y Mn zResearch has been conducted to apply lithium-overlithiated layered oxide (OLO), which exhibits higher reversible capacity than O2, to lithium secondary batteries.

[0006] However, such lithium-overlithiated layered oxides (OLOs) present a problem with voltage decay during life cycle cycling. This is due to a phase transition from a spinel-like structure to a cubic structure caused by the movement of transition metals during life cycle cycling. This voltage decay phenomenon in lithium-overlithiated layered oxides (OLOs) is a problem that must be solved for their application in lithium secondary batteries.

[0007] Furthermore, there is a need for solutions that can improve the electrochemical properties of lithium-rich layered oxides.

[0008] [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to improve the lithium ion conductivity of a positive electrode active material containing a lithium-rich layered oxide, thereby reducing resistance, reducing the overvoltage generated during charging and discharging, and improving the rate characteristics.

[0010] Furthermore, the aim is to suppress voltage drop and improve lifespan by suppressing Mn elution from the Mn-rich cathode active material and suppressing the lattice change from the spinel phase to the rock-salt phase that starts from the surface during cycling.

[0011] [Means for solving the problem]

[0012] The positive electrode active material according to an embodiment of the present invention includes an overlithiated layered oxide (OLO) represented by the following Chemical Formula 1.

[0013] [Chemical Formula 1] rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2

[0014] (In Chemical Formula 1, 0 < r ≤ 0.6, 0 < a ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, and 0 < x + y + z ≤ 1, and M1 is at least one 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.)

[0015] The overlithiated layered oxide may be a solid solution phase in which monoclinic Li2MnO3 and rhombohedral LiMO2 are mixed, and M may be at least one selected from Ni, Co, Mn, and M1.

[0016] Also, in the overlithiated layered oxide, a flat section due to Li2MnO3 may appear in the 4.4V region of the initial charge-discharge profile. In the initial charging process of the overlithiated layered oxide according to an embodiment of the present invention, unlike lithium, the Li2MnO3 phase is electrochemically inactive up to the 4.4V region, and reactions in which lithium desorbs and oxygen evolution may occur in the Li2MnO3 phase at 4.4V or higher.

[0017] The ratio (Li / Ni+Co+Mn) of the number of moles of lithium to the total number of moles of metal of Ni, Co, or Mn contained in the lithium-excess layered oxide represented by the chemical formula 1 may be 1.1 to 1.6, 1.2 to 1.6, 1.3 to 1.6, or 1.4 to 1.5.

[0018] In the chemical formula 1, the value of x may be more than 0 and 0.5 or less, more than 0 and 0.4 or less, more than 0 and 0.3 or less, more than 0 and 0.2 or less, or more than 0 and 0.1 or less.

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

[0020] In the chemical formula 1, M1 is at least one substance 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 contained in the lithium-excess layered oxide. More preferably, M1 is at least one selected from Ba, Sr, B, P, Y, Zr, Nb, Mo, Ta, and W that can grow the size of the primary particles and can be appropriately adjusted within a specific range. Most preferably, M1 can be at least one selected from Nb and Ta.

[0021] Also, the ratio (Mn / Ni) of the number of moles of Mn to the number of moles of 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.

[0022] The oxide of the present invention has a layered structure and can have a layered structure in which a lithium atom layer and a metal atom layer of Ni, Co, Mn, or M1 overlap alternately through an oxygen atom layer.

[0023] The layers of the layered structure of the positive electrode active material may have a crystal orientation perpendicular to the C-axis. In this case, the mobility of lithium ions contained in the positive electrode active material is improved, the structural stability of the positive electrode active material is increased, and when applied to a battery, the initial capacity characteristics, output characteristics, resistance characteristics, and long-term life characteristics may be improved.

[0024] The positive electrode active material according to the present invention is an oxide rich in lithium and manganese. By forming an amorphous glass oxide coating layer on the surface, Mn elution is suppressed, and the voltage drop is suppressed and the lifespan is improved by suppressing the lattice change from the spinel phase to the rock-salt phase that starts from the surface during cycling.

[0025] Furthermore, since the amorphous glass oxide coating layer is coated onto the surface of lithium-rich layered oxide particles, the problem of non-uniformity that occurs when coating in a crystalline state can be eliminated, and lithium ion movement can be further improved.

[0026] Furthermore, since the amorphous glass oxide coating layer is coated on the surface of lithium-rich layered oxide particles, the present invention can reduce the overvoltage generated during charging and discharging of lithium-rich layered oxide and improve rate characteristics.

[0027] The amorphous glass oxide coating layer may contain at least one element selected from Si, B, P, and Ge.

[0028] Furthermore, the amorphous glass oxide coating layer may contain a substance represented by the following chemical formula 2.

[0029] [Chemical Formula 2]xLi2O*(1-x)M2 a O b

[0030] For the x value in Chemical Formula 2, 0 < x ≤ 8, more preferably 0.13 ≤ x ≤ 8. Also, for the a value in Chemical Formula 2, 0 < a ≤ 2, more preferably 1 ≤ a ≤ 2. Also, for the b value in Chemical Formula 2, 0 < b ≤ 5, more preferably 2 ≤ b ≤ 5. Also, M2 can be at least one or more selected from Si, B, P, and Ge.

[0031] The amorphous glass oxide coating layer can be contained in the lithium-excess layered oxide in an amount of 0.05 mol% to 5 mol%, or 0.1 mol% to 3 mol%, or 0.1 mol% to 2 mol%.

[0032] The amorphous glass oxide coating layer can be uniformly or non-uniformly contained on the surface of the lithium-excess layered oxide represented by Chemical Formula 1.

[0033] As a more preferred embodiment, the present invention can be embodied in uniformly coating the surface because the amorphous glass oxide coating on the surface of the lithium-excess layered oxide has better ductility than other oxide-based coatings.

[0034] Also, as an example, the amorphous glass oxide coating layer can be formed on the surface of each of the secondary particles or primary particles.

[0035] Also, as an example, in the amorphous glass oxide coating layer on the surface of the secondary particles or primary particles, the elements contained in the amorphous glass oxide coating layer can form a concentration gradient portion.

[0036] In the positive electrode active material according to an embodiment of the present invention, the thickness of the amorphous glass oxide coating layer may be 1 nm to 100 nm, more preferably 10 nm to 100 nm. If the thickness is thinner than the coating layer, the improvement effect may be minimal, while if the thickness is thicker than the coating layer, the resistance to lithium ions may increase. When the amorphous glass oxide coating layer satisfies the above range, it is possible to suppress Mn elution of the Mn-rich positive electrode active material of the present invention, suppress the lattice change from the spinel phase to the rock-salt phase that starts from the surface during cycling, thereby suppressing voltage drop and improving lifespan.

[0037] In the embodiment of the present invention, the positive electrode active material forms secondary particles by aggregation of primary particles, and the amount of primary particles with a size of 300 nm to 10 μm in the primary particles constituting the secondary particles can be adjusted to 50 vol% to 100 vol%, 70 vol% to 100 vol%, or 100 vol%.

[0038] As an example, the positive electrode active material can be adjusted to contain 50 vol% to 100 vol%, 70 vol% to 100 vol%, or 100 vol% primary particles, each having a size greater than 500 nm and less than or equal to 10 μm, within the primary particles that constitute the secondary particles.

[0039] As an example, the positive electrode active material can be adjusted to contain primary particles with a size of 1 μm to 10 μm in the total amount of lithium-rich layered oxide, such as 50 vol% to 100 vol%, 70 vol% to 100 vol%, or 100 vol%.

[0040] As an example, the positive electrode active material can be adjusted to contain primary particles larger than 1 μm in size at a concentration of 50 vol% to 100 vol%, 70 vol% to 100 vol%, or 100 vol% relative to the entire lithium-rich layered oxide.

[0041] As an example, the positive electrode active material can be adjusted so that primary particles with a size of 2 μm or more constitute 50 vol% to 100 vol%, or 50 vol% to less than 70 vol%, relative to the entire lithium-rich layered oxide.

[0042] As an example, the positive electrode active material may have its primary particle size adjusted so that the number of primary particles within the secondary particle is 1 to 1,000, 1 to 100, 1 to 10, or consists of a single primary particle.

[0043] The size of the primary particle refers to the maximum length of the particle.

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

[0045] The lithium-rich layered oxide of the present invention suffers from a voltage decay phenomenon that occurs during life cycling, which is due to a phase transition from a spinel-like structure to a cubic structure caused by the migration of transition metals during life cycling. The present invention solves this problem and allows for adjustment of the size of primary particles to improve the density of the positive electrode active material.

[0046] However, as the primary particles become larger, the lithium ion diffusion distance increases, leading to the problem of overpotential generation due to lithium ion concentration polarization during charging and discharging. Ultimately, this can reduce kinetics and decrease the capacity of the positive electrode active material. However, by forming an amorphous glass oxide coating layer, ionic conductivity increases, which increases lithium ion kinetics, thus increasing capacity and reducing overpotential.

[0047] The average particle size of the secondary particles of the positive electrode active material according to the embodiment of the present invention may be 2 μm to 20 μm, more preferably 10 μm to 20 μm, and more preferably 14 μm to 16 μm. The average particle size can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve. The average particle size can be measured, for example, using the laser diffraction method.

[0048] In the embodiment of the present invention, the size of the primary particles in the positive electrode active material increases from the size of the primary particles in the precursor stage under the manufacturing process conditions of the embodiment described below. Furthermore, under the manufacturing process conditions of the embodiment described below, the ratio of (size of primary particles of the positive electrode active material to which a dopant acting as a flux has been added) / (size of primary particles of the positive electrode active material to which a dopant acting as a flux has not been added) is 1 or more, more preferably 30 or more, and most preferably 50 or more.

[0049] In the aforementioned chemical formula 1, M1 is a dopant that acts as a flux for growing the primary particles and can be doped into the lattice structure. In one embodiment, the size of the primary particles can be adjusted to increase by adding and mixing the flux dopant with the lithium compound during the calcination stage and then heat-treating them together. Acting as a flux means that it can act as a dopant that increases the size of the primary particles through growth between the primary particles.

[0050] In the positive electrode active material according to the present invention, the more parts that correspond to a single crystal structure, that is, the fewer primary particles there are, the more the voltage drop problem that appears in polycrystalline materials can be improved.

[0051] When performing XRD analysis on the positive electrode active material according to an embodiment of the present invention, the half-width (FWHM (deg.)) at I(104) can be 0.1 (deg.) to 0.25 (deg.), but this value can vary depending on the manganese content. Therefore, by adjusting the reduction rate of the half-width through the addition and content adjustment of the dopant M1, problems of lifespan and voltage drop can be solved.

[0052] In the present invention, by adjusting so as to increase the size of the primary particles with lithium-excess layered oxide, when fired under the same conditions, in XRD analysis, the half-width (FWHM (deg.)) at I(104) can be adjusted to decrease by 5% to 50%, 5% to 40%, 5% to 30%, 5% to 20%, 10% to 25%, or 10% to 20% when M1 is included, compared to a comparative example without M1.

[0053] The positive electrode active material according to an embodiment of the present invention can contain a substance represented by the following Chemical Formula 3. The substance represented by the following Chemical Formula 3 can be a substance formed by the reaction of a dopant that acts as a flux for inducing growth between primary particles with lithium.

[0054] [Chemical Formula 3]Li a M3O b

[0055] (where 0 < a ≤ 8, 0 < b ≤ 15, and M3 is at least one 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.)

[0056] The M1 in the aforementioned chemical formula 1 may be present in amounts of 0.001 mol% to 10 mol%, 0.01 mol% to 5 mol%, 0.01 mol% to 3 mol%, 0.1 mol% to 2 mol%, or 0.1 mol% to 1 mol% relative to the total number of moles of metal constituting the positive electrode active material. If the dopant M1 included as a flux to induce primary particle growth exceeds the aforementioned range, an excess of lithium composite oxide may be produced, potentially leading to a decrease in capacity and efficiency. On the other hand, if the dopant M1 is below the aforementioned range, the effect on primary particle growth may be minimal.

[0057] Furthermore, the energy density per unit volume (Wh / L) of the positive electrode active material according to the embodiment of the present invention may be 2.7 (Wh / L) to 4.0 (Wh / L).

[0058] Furthermore, the energy density per unit volume (Wh / L) of the positive electrode active material according to the embodiment of the present invention can be increased by 5% to 30% compared to a material that does not contain M1. The positive electrode active material according to the present invention can be adjusted so that the energy density per unit volume (Wh / L) increases by 5% to 25%, 5% to 20%, 10% to 25%, or 10% to 20% compared to a comparative example that does not contain M1, when M1 is included.

[0059] Furthermore, the packing density (g / cc) of the positive electrode active material, adjusted through the addition and content adjustment of dopant M1, may be between 2.0 (g / cc) and 4.0 (g / cc).

[0060] Furthermore, the specific surface area (BET, m²) of the positive electrode active material adjusted through the addition and content adjustment of dopant M1 is also adjusted. 2 / g) is 0.1 (BET, m 2 / g)~1.5(BET, m 2 It could be / g).

[0061] In the positive electrode active material according to the present invention, the size of the primary particles is adjusted by the lithium-excess layered oxide, thereby increasing the specific surface area (BET, m²).2 The amount ( / g) can be adjusted so that it decreases by 20% to 80% when M1 is included, compared to the comparative example which does not contain M1.

[0062] The present invention increases the energy density per unit volume and reduces the surface area of ​​the positive electrode active material by inducing the growth of the primary particles and adjusting the portion corresponding to the single-crystal structure of the positive electrode active material, thereby reducing the surface area of ​​the positive electrode active material and consequently resolving the problems of lifetime and voltage drop. In the present invention, inducing the growth of the primary particles encompasses all of the concepts of nucleation, ostwald ripening, and particle aggregation.

[0063] A method for producing a positive electrode active material according to an embodiment of the present invention includes a first step of producing a positive electrode active material precursor.

[0064] The precursor can be produced by co-precipitation, spray drying, solid-phase method, wet grinding, fluidized bed drying, or vibration drying, and is not particularly limited thereto.

[0065] Next, the process includes a second step of mixing a lithium compound with the positive electrode active material precursor and calcining it to form a lithium composite oxide.

[0066] The second step involves further mixing and calcining the compound containing M1 of the chemical formula 1.

[0067] The temperature during the firing stage may be 750°C to 950°C, 800°C to 950°C, or 850°C to 950°C.

[0068] Next, the process includes a third step in which the substance formed in the second step is mixed with a coating precursor to form an amorphous glass oxide coating layer.

[0069] The present invention enables the uniform application of an amorphous glass oxide coating layer onto the surface of a lithium-rich layered oxide through the following steps.

[0070] In the third step described above, a dry mixing process can be performed on the coating precursor.

[0071] Furthermore, in the third stage, a wet mixing process can be performed on the coating precursor. For example, the coating precursor can be dispersed or dissolved in water, alcohol, or a dispersion solution, and then mixed with the substance formed in the second stage.

[0072] The third step may include mixing the substance formed in the second step with the coating precursor, maintaining the mixture at 250°C to 700°C for 7 to 12 hours, and then performing furnace cooling. The temperature may vary depending on the type of coating precursor. For example, the temperature may be 250°C to 500°C or 250°C to 400°C when forming a coating layer containing B, and 500°C to 700°C or 550°C to 650°C when forming a coating layer containing P.

[0073] In the method for producing a positive electrode active material according to an embodiment of the present invention, the coating precursor may contain B or P, and may be at least one selected from B2O3, P2O5, H3BO3, NH4HPO4, NH4H2PO4, (NH4)2HPO4, and H3PO4. More preferably, the coating precursor may be H3BO3 or NH4HPO4, but is not particularly limited thereto as long as an amorphous glass oxide coating layer can be formed.

[0074] In the method for producing a positive electrode active material according to an embodiment of the present invention, a step of roasting the precursor produced at 300°C to 600°C may be further included after the first step and before the second step.

[0075] In the method for producing a positive electrode active material according to an embodiment of the present invention, the calcined material may be further washed with water and dried after the first step and before the second step.

[0076] In the method for producing a positive electrode active material according to an embodiment of the present invention, a step of washing and drying the calcined material may be further included after the second step and before the third step.

[0077] The secondary battery according to an embodiment of the present invention includes the positive electrode active material.

[0078] The positive electrode active material is as described above, and the binder, conductive material, and solvent are not particularly limited as long as they can be used on the positive electrode current collector of a secondary battery.

[0079] The lithium secondary battery may specifically include a positive electrode, a negative electrode located opposite the positive electrode, and an electrolyte located between the positive electrode and the negative electrode, but is not particularly limited as long as it can be used as a secondary battery.

[0080] [Effects of the Invention]

[0081] This invention improves lithium ion conductivity and reduces resistance by using a lithium-rich layered oxide, thereby reducing overvoltage generated during charging and discharging and improving rate characteristics.

[0082] Furthermore, by suppressing the elution of Mn from the Mn-rich cathode active material and inhibiting the lattice change from the spinel phase to the rock-salt phase that starts from the surface during cycling, voltage drop is suppressed and the lifespan is improved.

[0083] [Brief explanation of the drawing]

[0084] [Figure 1] This figure shows the SEM measurement results of the positive electrode active material according to the examples and comparative examples of the present invention.

[0085] [Figure 2] This figure shows the EDS measurement results of the positive electrode active material according to an embodiment of the present invention.

[0086] [Figure 3] This figure shows the XRD analysis results of the positive electrode active material according to the examples and comparative examples of the present invention.

[0087] [Figure 4] This figure shows the EDS measurement results of the positive electrode active material according to an embodiment of the present invention.

[0088] [Figure 5] This figure shows the EDS measurement results of the positive electrode active material according to an embodiment of the present invention.

[0089] [Figure 6] This figure shows charge and discharge graphs relating to embodiments and comparative examples of the present invention.

[0090] [Figure 7] This figure shows overvoltage curves relating to embodiments and comparative examples of the present invention.

[0091] [Figure 8] This figure shows rate characteristic curves relating to embodiments and comparative examples of the present invention.

[0092] [Figure 9] This figure shows the life characteristics of embodiments and comparative examples of the present invention.

[0093] [Figure 10] This figure shows the voltage maintenance rate according to the embodiments and comparative examples of the present invention.

[0094] [Modes for carrying out the invention]

[0095] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0096] Expressions such as "include" used herein should be understood as open-ended terms that implicitly include the possibility of other components being included.

[0097] As used herein, "preferred" and "preferred" refer to embodiments of the present invention that can provide certain advantages under certain conditions, and are not intended to exclude other embodiments from the scope of the present invention.

[0098]

[0099] <Example 1> Production of positive electrode active material

[0100] -Synthesis

[0101] Spherical Ni using the co-precipitation method 0.2 Co 0.1 Mn 0.7 A CO3 precursor was synthesized. In a 90L reactor, 25 wt% NaCO3 and 28 wt% NH4OH were added to a 2.5M aqueous solution of complex transition metal sulfuric acid, which was prepared by mixing NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in a molar ratio of 20:10:70. During this time, the pH in the reactor was maintained at 8.0 to 11.0 and the temperature at 45°C to 50°C. In addition, an inert gas, N2, was added to the reactor to prevent oxidation of the produced precursor.

[0102] After synthesis and stirring were completed, washing and dewatering were carried out using a filter press (F / P). Finally, the dewatered product was dried at 120°C for 2 days, filtered through a 75 μm (200 mesh) sieve, and filtered to remove 4 μm to 20 μm Ni particles. 0.17 Co 0.106 Mn 0.719 A CO3 precursor was obtained.

[0103] - Roasting

[0104] The prepared precursor was maintained in a Box calcination furnace in an O2 or air (50 L / min) atmosphere, heated at 2°C per minute, maintained at 550°C for 1 to 6 hours, and then furnace cooled.

[0105] - Firing

[0106] LiOH or Li2CO3 was weighed out so that the Li / (Ni+Co+Mn) ratio to the roasted precursor was 1.45, and 0.6 mol% of Nb2O5 was weighed out as a flux dopant. These were then mixed using a manual mixer (MM).

[0107] The mixture was maintained in a Box firing furnace under an O2 or air (50 L / min) atmosphere, the temperature was increased by 2°C per minute, and the firing temperature was maintained at 900°C for 7 to 12 hours, followed by furnace cooling to produce the cathode active material.

[0108] The composition of the positive electrode active material produced in Example 1 was Li:Ni:Co:Mn:Nb = 15.3:15.1:9.3:59.8:0.4 (wt%).

[0109] -coating

[0110] 1.5 mol% of H3BO3 was weighed out as a surface treatment dopant and mixed using a manual mixer (MM).

[0111] The mixture was maintained in a box firing furnace under an O2 or air (50 L / min) atmosphere, the temperature was increased by 4.4°C per minute, and the firing temperature was maintained at 300°C for 7 to 12 hours, followed by furnace cooling to produce the cathode active material.

[0112]

[0113] <Example 2> Production of positive electrode active material

[0114] The cathode active material was produced in the same manner as in Example 1, except that 0.5 mol% of NH4HPO4 was mixed as a surface treatment dopant during the coating stage of Example 1, and the firing temperature during the coating stage was set to 600°C.

[0115] The composition of the positive electrode active material produced in Example 2 was Li:Ni:Co:Mn:Nb = 15.0:14.8:9.3:60.0:0.8 (wt%).

[0116]

[0117] <Comparative Example 1> Production of Cathode Active Material

[0118] The cathode active material was manufactured in the same manner as in Example 1, except that a flux dopant was not mixed and the coating step was omitted.

[0119]

[0120] <Comparative Example 2> Production of Cathode Active Material

[0121] The positive electrode active material was manufactured in the same manner as in Example 1, except that the coating step was omitted.

[0122]

[0123] <Comparative Example 3> Production of Cathode Active Material

[0124] The positive electrode active material was manufactured in the same manner as in Example 1, except that a flux dopant was not mixed in.

[0125]

[0126] <Manufacturing Example> Manufacturing of lithium-ion secondary batteries

[0127] A cathode slurry was prepared by dispersing 90 wt% of the cathode active material, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder according to the above examples and comparative examples in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was applied to a 15 μm thick aluminum (Al) thin film, which served as the cathode current collector, and dried. The cathode was then manufactured by roll pressing. The loading level of the cathode was 5.5 mg / cm². 2 The electrode density is 2.3 g / cm³. 3 That was the case.

[0128] A metallic lithium was used as the counter electrode to the aforementioned positive electrode, and 1M LiPF6 with an EC / DMC ratio of 1 / 1 (v / v) was used as the electrolyte.

[0129] A lithium secondary battery (coin cell) was manufactured by forming a battery assembly by interposing a separator made of porous polyethylene (PE) film between the positive electrode and the negative electrode, and then injecting the electrolyte.

[0130]

[0131] <Example of experiment>

[0132] Referring to Figure 1, when comparing Comparative Example 2 with Examples 1 and 2, it can be confirmed that there is no change in the size and shape of primary particles due to the B and P coatings. When comparing Comparative Example 1 with Comparative Example 3, it can be confirmed that there is no particle growth due to the amorphous glass oxide coating layer.

[0133] Referring to Figure 2, it can be confirmed that not only Ni, Co, and Mn elements, but also Nb, a flux dopant that induces particle growth, is uniformly distributed within the particles.

[0134] The XRD analysis in Figure 3 was performed using a wavelength of CuK α radiation = 1.5406 Å. Referring to Figure 3, when Nb is added as a flux dopant, the (003) peak shifts, which can be confirmed as evidence that the flux dopant Nb is doped into the lattice of the lithium-rich layered oxide.

[0135] Referring to Figure 4, it can be confirmed that a coating layer containing B is uniformly distributed on the surface of the positive electrode active material according to Example 1.

[0136] Referring to Figure 5, it can be confirmed that a coating layer containing P is uniformly distributed on the surface of the positive electrode active material according to Example 2.

[0137] Referring to Figure 6, in Comparative Example 2, compared to Comparative Example 1, the capacity decreases slightly as the primary particles become larger. This is because the lithium ion diffusion distance increases, resulting in a decrease in kinetics. However, in the example where an amorphous glass oxide coating layer is formed, the ionic conductivity increases, and the kinetics of lithium ions increase, so it can be confirmed that the capacity increases.

[0138] Referring to Figure 7, as the primary particle size increases, the lithium ion diffusion distance increases, which presents a problem of overpotential generation due to lithium ion concentration polarization. However, in the example where an amorphous glass oxide coating layer is formed, the kinetics of lithium ions increase, and it can be confirmed that the overpotential decreases.

[0139] Referring to Figure 8, it can be confirmed that the rate characteristics of the example are improved by approximately 10% or more compared to the comparative example. This is because the resistance is reduced by the amorphous glass oxide coating layer.

[0140] Referring to Figure 9, it can be confirmed that the lifetime characteristics of Comparative Example 3, in which an amorphous glass oxide coating layer was formed, improved by approximately 10% or more compared to Comparative Example 1. Furthermore, in Examples 1 and 2, in which particles were grown and an amorphous glass oxide coating layer was formed, the capacity retention rate by cycling was 80% or more. This is because the amorphous glass oxide coating layer reduced resistance, suppressed Mn elution, and inhibited the phase change from the spinel phase to the rock salt phase that starts from the surface during cycling, thereby improving lifetime.

[0141] Referring to Figure 10, the example showed a voltage maintenance rate of 97%. This is because the amorphous glass oxide coating layer suppressed the phase change of lithium excess layered oxide that occurs during cycling.

[0142]

[0143] The experimental results are shown in Table 1 below.

[0144]

[0145] [Table 1]

Claims

1. Lithium-excess layered oxide (OLO), represented by the following chemical formula 1; and An amorphous glass oxide coating layer formed on the surface of the lithium-rich layered oxide represented by the chemical formula 1; A positive electrode active material for secondary batteries, including: [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, and 0 < x + y + z < 1, and M1 is at least one 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.) The M1 in the aforementioned chemical formula 1 comprises at least one selected from Nb and Ta. The amorphous glass oxide coating layer comprises at least one selected from Si, B, P, and Ge. Cathode active material for secondary batteries.

2. The amorphous glass oxide coating layer comprises a substance represented by the following chemical formula 2, wherein the positive electrode active material for a secondary battery according to claim 1: [Chemical formula 2] xLi ２ O*(1 - x)M2 ａ O ｂ (The above conditions are 0 < x ≤ 0.8, 0 < a ≤ 2, and 0 < b ≤ 5, and M2 is at least one selected from Si, B, P, and Ge.)

3. The amorphous glass oxide coating layer is contained in an amount of 0.05 mol% to 5 mol% relative to the lithium excess layered oxide, as described in claim 1, for a positive electrode active material for a secondary battery.

4. The positive electrode active material for a secondary battery according to claim 1, wherein the thickness of the amorphous glass oxide coating layer is 1 nm to 100 nm.

5. Primary particles aggregate to form secondary particles. The positive electrode active material for a secondary battery according to claim 1, wherein primary particles having a size of 300 nm to 10 μm are adjusted to 50 vol% to 100 vol% in the primary particles constituting the secondary particles.

6. The positive electrode active material for a secondary battery according to claim 1, wherein M1 in the chemical formula 1 is present in an amount of 0.001 mol% to 10 mol% relative to the total number of moles of metal in the lithium-excess layered oxide.

7. The positive electrode active material for a secondary battery according to claim 1, wherein the ratio of the number of moles of lithium to the total number of moles of metal (Li / Ni + Co + Mn) in the lithium-rich layered oxide represented by chemical formula 1 is 1.1 to 1.

6.

8. The positive electrode active material for a secondary battery according to claim 1, wherein in the lithium-rich layered oxide represented by chemical formula 1, the ratio of moles of Mn to the total number of moles of Ni (Mn / Ni) is 1 to 4.

5.

9. In a method for producing a positive electrode active material for a secondary battery according to claim 1, The first step in manufacturing the cathode active material precursor; A second step involves mixing a lithium compound with the positive electrode active material precursor and firing it to form a lithium composite oxide; and A method for producing a positive electrode active material for a secondary battery, comprising: a third step of mixing the material formed in the second step with a coating precursor to form an amorphous glass oxide coating layer;

10. The method for producing a positive electrode active material for a secondary battery according to claim 9, wherein the second step is to further mix and calcine a compound containing M1 of the chemical formula 1.

11. The method for producing a positive electrode active material for a secondary battery according to claim 9, wherein the third step includes mixing the material formed in the second step with a coating precursor, maintaining the mixture at 250°C to 700°C for 7 to 12 hours, and then furnace cooling.

12. The coating precursor is B ２ O ３ , P ２ O ５ , H ３ BO ３ NH ４ HPO ４ NH ４ H ２ PO ４ , (NH ４ ) ２ HPO ４ , and H ３ PO ４ A method for producing a positive electrode active material for a secondary battery according to claim 11, wherein the method is selected from at least one of the following.

13. A method for producing a positive electrode active material for a secondary battery according to claim 9, further comprising the step of roasting a precursor produced at 300°C to 600°C after the first step and before the second step.

14. A method for producing a positive electrode active material for a secondary battery according to claim 9, further comprising the step of washing the calcined material with water after the first step and before the second step.

15. A method for producing a positive electrode active material for a secondary battery according to claim 9, further comprising the step of washing the calcined material with water after the second step and before the third step.

16. A secondary battery comprising the positive electrode active material according to claim 1.

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