Positive electrode active material, its manufacturing method, and lithium secondary battery including positive electrode containing the same

Abstract

The present invention relates to a positive electrode active material containing a lithium transition metal oxide in which the molar ratio of Mn element is 0.5 or more and the sum of the molar ratios of sodium (Na) element and sulfur (S) element satisfies 0 < Na + S < 0.025, a method for producing the same, and a lithium secondary battery including the same.

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material having a new composition, a method for producing the same, and a lithium secondary battery provided with a positive electrode containing the same. [Background technology]

[0002] Since being commercialized by Sony in 1991, lithium secondary batteries have seen a rapid increase in demand in a variety of fields, from small home appliances such as mobile IT (information technology) products to medium- and large-sized electric vehicles and energy storage systems. In particular, low-cost, high-energy positive electrode materials are essential for medium- and large-sized electric vehicles and energy storage systems, and the currently commercially available positive electrode active material, single-crystal LiCoO 2 Cobalt, the main raw material for (LCO), is expensive.

[0003] Recently, LiNi, which has a structure similar to LCO, has been used as a positive electrode active material for medium- to large-sized secondary batteries. x Co y Mn z O2(NCM) and LiNi x Co y Al z Ni-based positive electrode materials such as O2(NCA) are used because nickel, which is a raw material, is inexpensive compared to cobalt and has a high reversible capacity. However, Ni-based positive electrode active materials have a maximum reversible capacity of about 240 mAh / g, and there is a limit to the increase in reversible capacity due to an increase in Ni content, and they have a high residual lithium content, which can cause a stability problem. The residual lithium in the positive electrode active material is electrochemically decomposed during continuous charging and discharging to generate gas, and reacts with the electrolyte to generate a resistance layer on the surface of the positive electrode active material, thereby reducing the life characteristics. That is, in order to increase the energy density of lithium secondary batteries, it is necessary to develop a next-generation positive electrode active material that can realize a high reversible capacity and a low residual lithium content compared to Ni-based positive electrode active materials.

[0004] Li / Mn-rich (LMR) positive electrode active material is Li2 MnO 3 and LiMO 2 (where M is a transition metal), in a solid solution in which the structures are mixed, has the property of realizing a high reversible capacity of 250 mAh / g or more at a high operating voltage. This is because lithium exists not only in the lithium layer within the layered structure different from the Ni-based cathode active material, but also in the transition metal layer, so a high reversible capacity can be realized compared with the Ni-based cathode active material. In addition, compared with the Ni-based cathode active material due to the reduction of the Ni content in the cathode active material, it has a low residual lithium content, which can bring about an improvement in the stability of the lithium secondary battery.

[0005] However, the secondary particle-shaped LMR cathode active material has a porous morphology compared with the secondary particle-shaped Ni-based cathode active material, and it is difficult to realize a high electrode density, and there is still a limit point in increasing the energy density per volume of the lithium secondary battery. Moreover, the LMR cathode active material has a characteristic of low output characteristics due to low electrical conductivity compared with the Ni-based cathode active material, and thus has a limit point of being disadvantageous for high-rate charge and discharge.

[0006] Therefore, there is still a market demand for an LMR cathode active material having a high electrode density and high output characteristics. Summary of the Invention Problems to be Solved by the Invention

[0007] According to one aspect, a lithium manganese-rich (LMR) cathode active material with improved life characteristics is provided. Means for Solving the Problems

[0008] According to one aspect, a cathode active material containing a lithium transition metal oxide in which the molar ratio of the Mn element is 0.5 or more and the sum of the molar ratios of the sodium (Na) element and the sulfur (S) element (Na + S) satisfies 0 < Na + S < 0.025 is provided.

[0009] According to another aspect, there is provided a method for producing a positive electrode active material, the method including the steps of: preparing a lithium transition metal oxide precursor compound having a molar ratio of Mn element of 0.5 or more; mixing the transition metal oxide precursor with a Li precursor compound, a Na precursor compound, and a S precursor compound to obtain a lithium transition metal oxide precursor; and calcining the lithium transition metal oxide precursor to obtain lithium transition metal oxide particles.

[0010] In still another embodiment, there is provided a lithium secondary battery including a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. Effect of the Invention

[0011] The positive electrode active material according to one embodiment of the present invention has a single particle shape consisting of a single particle of several μm in size, not a secondary particle shape formed by agglomeration of small primary particles of several hundred nm in size, and can improve the electrode density of the LMR positive electrode active material through shape change.Furthermore, it has an effect of improving the output characteristics through substitution of Na element at the lithium site and S element at the oxygen site in the LMR positive electrode active material. [Brief description of the drawings]

[0012] [Figure 1A] 1 is a scanning electron microscope (SEM) image of the positive electrode active materials of Examples 1 to 6. [Figure 1B] 1 shows scanning electron microscope (SEM) images of the positive electrode active materials of Comparative Examples 1 to 11. [Diagram 2] 1 is an XRD (X-ray diffraction) graph of lithium transition metal oxide particles of Example 1 and Comparative Examples 1, 3, and 7. [Diagram 3] FIG. 3 is an enlarged view of the XRD graph in FIG. 2 at 2θ=20° to 26°. [Figure 4] 1 is a schematic diagram of a lithium battery according to an illustrative embodiment; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present inventive concept described below can be modified in various ways and can have various embodiments, but specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, they do not limit the present inventive concept to the specific embodiments, and should be understood to include all modifications, equivalents, or alternatives that fall within the technical scope of the present inventive concept.

[0014] The terms used below are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless otherwise clearly indicated in the context. In the following, terms such as "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, ingredient, material, or combination thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, ingredients, materials, or combinations thereof. In the following, " / " can be interpreted as "and" or "or" depending on the context.

[0015] In the drawings, the various layers and regions are shown exaggerated or reduced in thickness for clarity. Similar parts are designated by the same reference numerals throughout the specification. Throughout the specification, when a part, such as a layer, film, region, or plate, is referred to as being "on" or "above" another part, this includes not only when it is directly on top of the other part, but also when there is another part between them. Throughout the specification, terms such as first and second may be used to describe various components, but the components are not limited by these terms. These terms are used only to distinguish one component from another.

[0016] Hereinafter, a positive electrode active material, a manufacturing method thereof, and a lithium secondary battery including a positive electrode including the same according to example embodiments will be described in more detail.

[0017] The positive electrode active material according to an embodiment also includes a lithium transition metal oxide in which the molar ratio of the Mn element is 0.5 or more, and the sum of the molar ratios of the sodium (Na) element and the sulfur (S) element is 0 < Na + S < 0.025.

[0018] Recently, research on single-particle form lithium manganese-rich (LMR) positive electrode active materials has been actively conducted in order to achieve a high electrode density and suppress the formation of internal cracks in particles. However, for the development of LMR positive electrode active materials for high-energy lithium secondary batteries, it is essential to stabilize the unstable structure inside the particles along with the change in particle morphology. The LMR positive electrode active material generally consists of a LiMO 2 compound with an R-3m crystal structure and a Li 2 MnO 3 compound with a monoclinic crystal structure. The Li 2 MnO 3 structure helps to achieve a high capacity through activation in the first cycle. However, in order to activate the Li 2 MnO 3 structure, a high voltage of 4.4 V or more is required, which causes the desorption of Li ions and oxygen in the crystal structure, forms an electrochemically inactive phase, and induces a rapid reduction in lifespan and energy density. Therefore, there is still a need to obtain a single-particle type LMR positive electrode active material in which the structure is stabilized during charge and discharge by causing a bond with oxygen or lithium through doping or coating in the structure.

[0019] According to one aspect of the present invention, the positive electrode active material has a single particle shape instead of the shape of secondary particles formed by aggregation of conventional LMR positive electrode active material primary particles. Therefore, in the electrode formation process, there is no particle breakage due to rolling, and it is possible to form a high-density active material layer and achieve a high electrode density. Furthermore, by stabilizing unstable Mn ions inside the particles through Na element substitution at lithium sites and S element substitution at oxygen sites in the LMR positive electrode active material, it has the effects of increasing the capacity per unit volume and improving the output characteristics. Specifically, when the sum of the molar ratios of sodium (Na) element and sulfur (S) element is 0 < Na + S < 0.025, the crystal stability is improved and the cycle characteristics are improved during the charge and discharge process of the secondary battery.

[0020] According to one embodiment, the X-ray diffraction (XRD) spectrum of the lithium transition metal oxide can satisfy the following mathematical formula 1:

[0021] (Mathematical formula 1) 10 ≤ Grain size (020) / Grain size (110) ≤ 15 Here, the grain size (110) means the grain size on the crystal plane 110, and the grain size (020) means the grain size on the crystal plane 020.

[0022] The grain size was calculated through quantitative analysis using the Scherrer equation. Specifically, the analysis of the grain size was carried out using the full width at half maximum (FWHM). In FWHM = Kλ / LcosΘ, the FWHM is the half width of a specific peak, K is the shape factor constant, λ is the wavelength used in the X-ray diffraction analysis, and Θ is the number representing the peak position in radians. Also, L is the grain size, and the grain size can be expressed by the mathematical formula L = Kλ / (cosΘ * FWHM).

[0023] The lithium transition metal oxide according to an embodiment of the present invention satisfies the above formula 1, and the value of the crystal grain (020) / crystal grain (110) in the formula 1 has a low value of less than 10 in polycrystalline or amorphous particles. However, like the lithium transition metal oxide of the present invention, Na and S are doped in the structure within a specific content range, and Li 2 MnO 3 This is believed to be due to the high grain size of the 020 peak, which is caused by the crystal phase growing with structural stability. 2 MnO 3 The lithium transition metal oxide of the present invention containing this phase is electrochemically stable during charging and discharging, and has brought about an improvement in life characteristics.

[0024] According to an embodiment, the lithium transition metal oxide has a molar ratio of Co element of 0.01 or less. For example, the lithium transition metal oxide has a molar ratio of Co element of 0.009 or less, 0.008 or less, 0.007 or less, 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, 0.001 or less, or 0. Here, when the molar ratio of Co element is 0, it means that the lithium transition metal oxide does not contain Co element.

[0025] According to an embodiment, the lithium transition metal oxide has a molar ratio of Mn element exceeding 0.5. For example, the lithium transition metal oxide has a molar ratio of Mn element of 0.55 or more, 0.6 or more, or 0.65 or more.

[0026] In the lithium transition metal oxide, when the molar ratio of Mn element satisfies the above range, the structure is stable and the lithium transition metal oxide can be used for producing a high-capacity secondary battery.

[0027] According to an embodiment, the lithium transition metal oxide further includes Ni element, for example, the lithium transition metal oxide includes Ni element in a molar ratio of less than 0.5, 0.45 or less, 0.4 or less, or 0.35 or less.

[0028] According to an embodiment, the lithium transition metal oxide further includes Li element, and the molar ratio of the Li element is greater than 1.

[0029] For example, the lithium transition metal oxide contains Li element in a molar ratio of 1.1 or more, 1.2 or more, 1.3 or more, or 1.4 or more. The lithium transition metal oxide also contains Li element in a molar ratio of more than 1 and less than 1.5, 1.1 or more and less than 1.5, 1.2 or more and less than 1.5, 1.3 or more and less than 1.5, or 1.4 or more and less than 1.5.

[0030] In the lithium transition metal oxide, when the molar ratio of Li element satisfies the above range, structural stability can be achieved and sufficient lithium ions can be supplied.

[0031] According to an embodiment, the lithium transition metal oxide may be represented by Formula 1: (chemical formula 1) Li x Na y Ni 1-a-b Mn a M b O 2+α-β S β In the above Chemical Formula 1, M is one or more elements selected from B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, and Co; 1.3 <x<1.5、0<y<0.015、0.5≦a<1、0≦b<0.1、0<α<0.5、0<β≦0.01である。

[0032] According to an embodiment, in Formula 1, M can be B, Zr, Sr, Y, Ba, W, Ti, Mg, Al or Co.

[0033] According to an embodiment, x is 1.35≦x<1.5 or 1.35≦x≦1.49.

[0034] According to one embodiment, y is also in the range of 0.001≦y<0.015.

[0035] According to an embodiment, the a is 0.55≦a<1, 0.6≦a<1, or 0.65≦a<1.

[0036] According to an embodiment, the α may be 0<α≦0.49, 0<α≦0.48, or 0<α≦0.47.

[0037] According to an embodiment, the formula 1 may be represented by any one of the following formulas 1-1 to 1-10:

[0038] (Chemical formula 1-1) Li x Na y Ni 1-a-b Mn a B b O 2+α-β S β

[0039] (Chemical formula 1-2) Li x Na y Ni 1-a-b Mn a Zr b O 2+α-β S β

[0040] (Chemical formula 1-3) Li x Na y Ni 1-a-b Mn a Y b O 2+α-β S β

[0041] (Chemical formula 1-4) Li x Na y Ni 1-a-b Mn a Mg b O 2+α-β S β

[0042] (Chemical formula 1-5) Li x Na y Ni 1-a-b Mn aAl b O 2+α-β S β

[0043] (Chemical formula 1-6) Li x Na y Ni 1-a-b Mn a Co b O 2+α-β S β

[0044] (Chemical formula 1-7) Li x Na y Ni 1-a-b Mn a Sr b O 2+α-β S β

[0045] (Chemical formula 1-8) Li x Na y Ni 1-a-b Mn a Ba b O 2+α-β S β

[0046] (Chemical formula 1-9) Li x Na y Ni 1-a-b Mn a W b O 2+α-β S β

[0047] (Chemical formula 1-10) Li x Na y Ni 1-a-b Mn a Ti b O 2+α-β S β

[0048] In the above Chemical Formulas 1-1 to 1-10, the contents of x, y, a, b, α, and β are as described above.

[0049] According to an embodiment, the lithium transition metal oxide may be represented by Formula 2: (Chemical formula 2) TLi 2 MnO 3 (1-T)LiNa y Ni 1-a-b Mn a M b O 2-β S β

[0050] In the above Chemical Formula 2, M is one or more elements selected from B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, and Co; 0.3 <T<0.6、0<y<0.015、0.3<a<1、0<b≦0.25、0<β≦0.025である。

[0051] According to an embodiment, the lithium transition metal oxide may be a single particle.

[0052] The single particle is a concept that is different from a secondary particle formed by agglomeration of a plurality of particles, or a particle formed by agglomeration of a plurality of particles and coating the periphery of the agglomerate. Since the lithium transition metal oxide has a single particle form, particle collapse can be prevented even at high electrode density. Therefore, a high energy density can be realized for a positive electrode active material including a lithium transition metal oxide. In addition, compared to secondary particles formed by agglomeration of a plurality of single particles, collapse during rolling is suppressed, making it possible to realize a high energy density and prevent deterioration of life due to particle collapse.

[0053] According to an embodiment, the lithium transition metal oxide may include R-3m crystals and monoclinic crystals.

[0054] For example, the lithium transition metal oxide may have a layered crystal structure.

[0055] According to an embodiment, the positive electrode active material may include a single-particle lithium transition metal oxide particle and a secondary particle formed by agglomeration of a plurality of the single-particle lithium transition metal oxide particles.

[0056] According to an embodiment, in the secondary particles, a surface of the lithium transition metal oxide particle or an interface between a plurality of lithium transition metal oxide particles may include a coating layer containing Na, S, or Na and S.

[0057] For example, the interface between the primary particles may include a coating layer containing Na element, S element, or Na and S element. For example, the coating layer may be crystalline, quasi-crystalline, or amorphous.

[0058] According to one embodiment, the average particle size (D 50 ) is 0.1 μm to 20 μm. For example, 50 ) may be 0.1 μm to 20 μm, 1.5 μm to 15 μm, 2 μm to 15 μm, 2.5 μm to 15 μm, 2.5 μm to 10 μm, 3 μm to 10 μm, 3.5 μm to 10 μm, or 4 μm to 10 μm. When the average particle diameter of the lithium transition metal oxide falls within the above range, a desired energy density per volume can be realized. When the average particle diameter of the lithium transition metal oxide exceeds 20 μm, a rapid decrease in charge / discharge capacity occurs, and when it is 0.1 μm or less, it is difficult to obtain a desired energy density per volume.

[0059] Hereinafter, a method for producing a positive electrode active material according to one embodiment will be described in detail.

[0060] According to an embodiment, a method for producing a positive electrode active material includes the steps of: preparing a lithium transition metal oxide precursor compound having a molar ratio of Mn element of 0.5 or more; mixing the transition metal oxide precursor compound with a Li precursor compound, a Na precursor compound and a S precursor compound to obtain a lithium transition metal oxide precursor; calcining the lithium transition metal oxide precursor to obtain lithium transition metal oxide particles.

[0061] The lithium transition metal oxide particles may be a compound represented by any one selected from the above-mentioned Chemical Formulas 1, 1-1 to 1-10, and Chemical Formula 2, and the details thereof are described above.

[0062] The mixing step includes mechanically mixing the specific element-containing compound. The mechanical mixing is performed by a dry method. The mechanical mixing is performed by applying a mechanical force to pulverize and mix the materials to be mixed to form a uniform mixture. The mechanical mixing may be performed using a mixing device such as a ball mill, a planetary mill, a stirred ball mill, or a vibrating mill using chemically inert beads. At this time, in order to maximize the mixing effect, a small amount of alcohol such as ethanol or a higher fatty acid such as stearic acid may be selectively added.

[0063] The mechanical mixing is carried out in an oxidizing atmosphere in order to prevent reduction of the transition metal in the transition metal source (eg, Ni compound) and to realize structural stability of the active material.

[0064] The Li precursor compound may include, but is not limited to, lithium hydroxide hydrate, lithium hydroxide, lithium oxide, lithium nitride, lithium carbonate, or a combination thereof. For example, the lithium precursor compound may be LiOH·H 2 O or Li 2 CO 3 It is also.

[0065] The Na precursor compounds may include, but are not limited to, Na hydroxides, oxides, nitrides, carbonates, or combinations thereof. For example, NaOH, Na2 CO 3 or a combination thereof.

[0066] The S precursor compound may include, but is not limited to, ammonium sulfate, hydroxide of S, oxide, nitride, carbonate, ammonium compound, or a combination thereof. For example, (NH 4 ) 2 SO 4 is also one.

[0067] The lithium transition metal oxide precursor compound may include, but is not limited to, hydroxide, oxide, nitride, carbonate, or a combination thereof containing Ni element and Mn element. For example, Ni z1 Mn z2 M z3 (OH) 2 (0 < Z1 ≤ 0.5, 0.5 ≤ Z2 < 1, 0 ≤ Z3 < 0.1, M is one or more elements selected from B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, and Co) is also one.

[0068] According to one embodiment, the lithium transition metal oxide precursor compound may be provided from a compound containing Ni element, Mn element, and M element obtained by pre-mixing the aforementioned Ni element, Mn element, and M element.

[0069] According to another embodiment, the lithium transition metal oxide precursor compound is provided from a compound containing Ni element and Mn element obtained by pre-mixing the aforementioned Ni element and Mn element, and the M element may be provided from a separate M element-containing compound.

[0070] The firing step may be performed by heat treatment at 900 °C to 1,100 °C for 8 to 12 hours.

[0071] For example, the firing temperature may be 910°C to 1,090°C, 920°C to 1,080°C, 930°C to 1,070°C, 940°C to 1,060°C, 950°C to 1,050°C, 960°C to 1,040°C, or 970°C to 1,030°C, but is not limited thereto, and includes any range formed by selecting any two points within the above range.

[0072] For example, the firing time may be 9 to 11 hours, or 10 hours.

[0073] According to an embodiment, the method further includes a separate heat treatment step after the firing step, which may be performed in the same chamber as the firing step or in a different chamber.

[0074] According to an embodiment, the heat treatment step may be performed at a temperature lower than the firing temperature, for example, 700° C. to 800° C. The heat treatment temperature may be, but is not limited to, 710° C. to 800° C., 720° C. to 800° C., 730° C. to 800° C., 740° C. to 800° C., 750° C. to 800° C., 700° C. to 780° C., 700° C. to 760° C., 700° C. to 750° C., or 700° C. to 730° C., and includes any range formed by selecting any two points within the above ranges.

[0075] According to an embodiment, the heat treatment time is longer than the firing time, for example, the heat treatment time is 10 to 20 hours, or 10 to 15 hours, but is not limited thereto, and includes any range formed by selecting any two points within the above ranges.

[0076] The calcination step forms a crystal structure of the lithium transition metal oxide particles and induces particle growth to form a single particle shape, and then, if necessary, an additional heat treatment can be performed to increase the crystallinity and obtain lithium transition metal oxide particles with improved particle stability.

[0077] According to an embodiment, the lithium transition metal oxide particles prepared by the method are single particles, and the average particle size of the lithium transition metal oxide is 0.1 μm to 20 μm.

[0078] In addition, the lithium transition metal oxide particles produced by the method for producing the positive electrode active material have a single particle shape, so that there is no particle collapse due to rolling during the electrode formation process, making it possible to form a high-density active material layer, and not only can the electrode density be improved, but also the cycle characteristics are improved through the substitution of Na element at the lithium site and S element at the oxygen site in the LMR positive electrode active material.

[0079] According to another aspect, a positive electrode is provided that includes the positive electrode active material described above.

[0080] According to yet another aspect, there is provided a lithium secondary battery including the positive electrode, the negative electrode, and an electrolyte.

[0081] According to an embodiment, the electrolyte may be a liquid electrolyte, a semi-solid electrolyte or a solid electrolyte, as described below.

[0082] The positive electrode and the lithium secondary battery including the positive electrode may be manufactured by the following method.

[0083] First, the positive electrode is prepared.

[0084] For example, a positive electrode active material composition is prepared by mixing the positive electrode active material, conductive material, binder, and solvent. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and the film peeled off from the support may be laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the forms listed above, and may be in other forms.

[0085] Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbons, zinc oxide, and potassium titanate; and conductive metal oxides such as titanium oxide. However, the conductive material is not limited to these, and any material that can be used as a conductive material in the relevant technical field can be used.

[0086] The binder may be, but is not limited to, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, or a mixture thereof, a metal salt, or a styrene butadiene rubber-based polymer, etc. Any binder known in the art may be used. Other examples of binders include lithium salts, sodium salts, or calcium salts of the aforementioned polymers.

[0087] The solvent may be, but is not limited to, N-methylpyrrolidone, acetone, water, or the like, and any solvent that can be used in the art may be used.

[0088] The contents of the positive electrode active material, conductive material, binder, and solvent are at levels generally used in lithium batteries, and one or more of the conductive material, binder, and solvent may be omitted depending on the application and configuration of the lithium battery.

[0089] Next, the negative electrode is prepared.

[0090] For example, a negative active material, a conductive material, a binder, and a solvent are mixed to prepare a negative active material composition. The negative active material composition is directly coated on a metal current collector having a thickness of 3 μm to 500 μm and dried to manufacture a negative plate. Alternatively, the negative active material composition may be cast on a separate support, and the film peeled off from the support may be laminated on a metal current collector to manufacture a negative plate.

[0091] The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, copper, nickel, or copper surface-treated with carbon may be used.

[0092] The negative electrode active material may be any material that can be used as a negative electrode active material for lithium batteries in the art, for example, at least one selected from the group consisting of lithium metal, metals that can be alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0093] For example, the metal capable of being alloyed with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Si), or a Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Sn). The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, R Also u, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se or Te.

[0094] For example, the transition metal oxide can be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0095] For example, the non-transition metal oxide is SnO 2 , SiO x (0 <x<2)などでもある。

[0096] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature sintered carbon), hard carbon, mesophase pitch carbide, sintered coke, etc.

[0097] In the negative electrode active material composition, the conductive material, binder, and solvent may be the same as those in the positive electrode active material composition.

[0098] The contents of the negative active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries. Depending on the application and configuration of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0099] Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

[0100] The separator may be any separator that is generally used in lithium batteries. A separator that has low resistance to ion migration of the electrolyte and has excellent electrolyte wettability may be used. The separator may be a single membrane or a multi-layer membrane, and may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. A mixed multi-layer membrane such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used. For example, a separator that can be wound such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator that has excellent organic electrolyte wettability may be used for a lithium ion polymer battery. For example, the separator may be manufactured by the following method.

[0101] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated on the top of an electrode and dried to form a separator. Alternatively, the separator composition may be cast on a support and dried, and the separator film may be peeled off from the support and laminated on the top of an electrode to form a separator.

[0102] The polymer resin used to manufacture the separator is not particularly limited, and any material used as a binder for an electrode plate may be used, such as vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof.

[0103] Next, the electrolyte is prepared.

[0104] For example, the electrolyte may be an organic electrolyte solution. The electrolyte may also be a solid. For example, the electrolyte may be boron oxide, lithium oxynitride, etc., but is not limited thereto. Any electrolyte that is used as a solid electrolyte in the art may be used. The solid electrolyte may be formed on the negative electrode by a method such as a sputtering method.

[0105] For example, the organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

[0106] The organic solvent may be any that can be used as an organic solvent in the technical field. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, and dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. They may be used alone or in combination. For example, a solvent in which a cyclic carbonate and a chain carbonate are mixed can be used.

[0107] In addition, gel-type polymer electrolytes, which are polymer electrolytes such as polyethylene oxide and polyacrylonitrile impregnated with electrolyte, and LiI, Li 3 N, Li x Ge y P z S α , Li x Ge y P z S α Xδ Inorganic solid electrolytes such as (X is F, Cl, Br) can be used.

[0108] The lithium salt may be any lithium salt that can be used in the art. For example, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , Li(CF 3 SO 2 ) 2 N, LiC 4 F 9 SO 3 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

[0109] As can be seen from FIG. 4, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 are wound or folded and accommodated in a battery case 5. An organic electrolyte is then injected into the battery case 5, and the battery case 5 is sealed with a cap assembly 6 to complete the lithium battery 1. The battery case 5 may be cylindrical, rectangular, pouch-shaped, coin-shaped, or thin-film-shaped. For example, the lithium battery 1 may be a thin-film battery. The lithium battery 1 may be a lithium-ion battery.

[0110] A separator may be disposed between the positive electrode and the negative electrode to form a battery structure, which may then be stacked in a bi-cell structure and then immersed in an organic electrolyte. The resulting structure may then be placed in a pouch and sealed to complete a lithium ion polymer battery.

[0111] In addition, a plurality of the battery structures may be stacked to form a battery pack, which may be used in any device requiring high capacity and high output, such as a notebook computer, a smartphone, or an electric vehicle (EV).

[0112] In addition, the lithium battery has excellent life characteristics and high rate characteristics, and therefore can be used in electric vehicles (EVs), for example, hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs), and in fields requiring large amounts of power storage, for example, electric bicycles, power tools, power storage systems, and the like.

[0113] The present invention will be described in more detail with reference to the following Production Examples, Examples and Comparative Examples. However, the Examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0114] (Production of positive electrode active material)

[0115] Example 1 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 13.76g Na 2 CO 3 , and 1.44 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0116] Example 2 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 13.76g Na 2 CO3 , and 2.88 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0117] Example 3 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 27.52g Na 2 CO 3 , and 1.44 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0118] Example 4 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 27.52g Na 2 CO 3 , and 2.88 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0119] Example 5 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 820.3 g LiOH H 2 O, 13.76g Na 2 CO 3 , and 1.44 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0120] Example 6 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 820.3 g LiOH H 2 O, 27.52g Na 2 CO 3 , and 1.44 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0121] Comparative Example 1 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 13.76g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0122] Comparative Example 2 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 820.3 g LiOH H 2 O, 13.76g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0123] Comparative Example 3 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 27.52g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0124] Comparative Example 4 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 55.04g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0125] Comparative Example 5 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 137.6g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0126] Comparative Example 6 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 275.2g Na 2 CO 3 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0127] Comparative Example 7 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 55.04g Na 2 CO 3 , and 2.88 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0128] Comparative Example 8 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 137.6g Na 2 CO 3 , and 2.88 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0129] Comparative Example 9 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 275.2g Na 2 CO 3 , and 1.44 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0130] Comparative Example 10 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 792 g LiOH H 2 O, 275.2g Na 2 CO 3 , and 2.88 g of (NH 4 ) 2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0131] Comparative Example 11 1,000g of Ni 0.35 Mn 0.65 (OH) 2 , 820.3 g LiOH H 2 O, 550.4g Na 2 CO 3 , and 2.88 g of (NH 4 )2 SO 4 The mixture was mechanically mixed for about 15 minutes, and the mixed powder was synthesized through sintering at 980° C. for 10 hours.

[0132] (Half-cell manufacturing) Example 7 A slurry was prepared by mixing the positive electrode active material obtained in Example 1, the conductive material, and the binder in a weight ratio of 97:1:2. Here, carbon nanotubes (CNTs) were used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in an N-methyl-2-pyrrolidone solvent and used as the binder. The slurry was uniformly applied to an Al current collector and dried at 110° C. for 2 hours to prepare a positive electrode. The loading level of the electrode plate was 11.0 mg / cm 2 and the electrode density was 3.20 g / cc. The prepared positive electrode was used as a working electrode, lithium foil was used as a counter electrode, and 5% by weight of fluoroethylene carbonate (FEC) and 0.5% by weight of vinylene carbonate (VC) were added to a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 2 / 5 / 3, and then mixed. LiPF 6 A liquid electrolyte containing 1.3M of EDTA was used to prepare a CR2032 half cell by a commonly known process.

[0133] Examples 8 to 12 A half cell was prepared in the same manner as in Example 7, except that the positive electrode active material obtained in Examples 2 to 6 was used instead of the positive electrode active material obtained in Example 1.

[0134] Comparative Examples 12 to 22 Half cells were prepared in the same manner as in Example 7, except that the positive electrode active material obtained in Example 1 was replaced with the positive electrode active materials obtained in Comparative Examples 1 to 11.

[0135] [Table 1]

[0136] Evaluation example 1: Evaluation of the composition of positive electrode active material The positive electrode active materials synthesized in Examples 1 to 6 and Comparative Examples 1 to 11 were subjected to inductively coupled plasma (ICP) analysis using a 700-ES (Varian) instrument, and the results are shown in Table 2 below.

[0137] Referring to Table 2, the ICP analysis results of Comparative Examples 1 to 11 and Examples 1 to 6 show that the introduction of Na and S doping materials into the single particle type LMR positive electrode active material causes substitution with lithium and oxygen in the active material, increasing the Na content and S content in the active material and decreasing the mole number of lithium and oxygen. Even if the ICP analysis is performed in a vacuum, it is difficult to analyze the stoichiometric value of oxygen contained in the material due to the inflow of trace amounts of oxygen and carbon dioxide in the air.

[0138] [Table 2]

[0139] Evaluation example 2: Appearance evaluation of positive electrode active material In order to evaluate the appearance of the positive electrode active materials obtained in Examples 1 to 6 and Comparative Examples 1 to 11, SEM (scanning electron microscope) photographs were taken, and the results are shown in Figures 1A and 1B. Referring to Figure 1A, it was confirmed that the active materials of Examples 1 to 6 have a single particle shape, and there is no significant difference in the sample surface or size even when Na and S doping agents are introduced.

[0140] Evaluation example 3: XRD evaluation of positive electrode active material For the positive electrode active materials synthesized in Example 1 and Comparative Examples 1, 3 and 7, X-ray diffraction spectrum graphs were obtained using a D / MAX 2500 V / PC (Rigaku Co., Ltd.) using Cu-Ka radiation in the range of 2θ=10° to 80°, and the results are shown in FIG. 2. Referring to FIG. 2, no significant difference is observed between Comparative Examples 1, 3, and 7 and Example 1. However, a characteristic peak is observed in Example 1 in the range of 2θ=20° to 25°. In order to quantitatively analyze this, an enlarged view of the X-ray diffraction spectrum in the range of 2θ=20° to 25° is shown in FIG. 3.

[0141] 3, differences were observed in the half-width sizes of the (020) peak and the (110) peak between Comparative Examples 1, 3, and 7 and Example 1. The grain size ratio of the (020) peak / (110) peak was calculated based on the contents described herein, and is shown in Table 3.

[0142] [Table 3]

[0143] Comparative Examples 1, 3, and 7 are L (020)ピークにおける微結晶サイズ / L (110)ピークにおける微結晶サイズ While Example 1 shows a low value of less than 10, Example 2 shows a high value of 11.58. This is due to the large grain size of the (020) peak, and while Na and S are doped in the structure, Li 2 MnO 3 This appears to contribute to the structural stability of the phase, and the relatively stable Li 2 MnO 3 Positive electrode active materials having this phase within their positive electrode active material structure positively affect electrochemical performance.

[0144] Evaluation example 4: High temperature life evaluation The half cells prepared in Examples 7 to 12 and Comparative Examples 12 to 22 were rested for 10 hours, then charged in CC mode at 0.1 C to 4.7 V, and then charged in CV mode to a current corresponding to 0.05 C. Next, the half cells were discharged in CC mode at 0.1 C to 2.5 V to complete the formation process.

[0145] Subsequently, the battery was charged in CC mode at a high temperature (45° C.) to 4.6 V at 0.33 C, and then charged in CV mode to a current corresponding to 0.05 C. It was then discharged in CC mode at 0.33 C to 2.5 V, and this process was repeated a total of 50 times.

[0146] The initial charge capacity and the initial discharge capacity were measured, and the initial efficiency was calculated based on the results. The capacity retention rate after 50 charge and discharge cycles relative to the initial discharge capacity was calculated and is shown in Table 4 below.

[0147] [Table 4]

[0148] The cells of Examples 7 to 12 were confirmed to have high initial efficiency and high discharge capacity compared to Comparative Examples 12 to 17 in which S doping was not performed. Also, the cells of Examples 7 to 12 in which Na and S were doped at a molar ratio of less than 0.025 were confirmed to have high initial charge capacity, high initial discharge capacity, and high capacity retention rate compared to Comparative Examples 18 to 22 in which Na and S were doped at a molar ratio of 0.025 or more. Therefore, when an LMR-based lithium transition metal oxide is doped with an appropriate amount of Na and S (a molar ratio of less than 0.025), the initial charge / discharge capacity is increased and the life characteristics are improved.

[0149] Although the preferred embodiment of the present invention has been described above with reference to the drawings and examples, it is understood that the present invention is not limited to the above-mentioned embodiments, and that various modifications and equivalent embodiments are possible. Therefore, the scope of the present invention is defined by the following claims.

Claims

1. The molar ratio of Mn element is 0.5 or more, the sum of the molar ratios of sodium (Na) element and sulfur (S) element is 0<Na+S<0.025, and the lithium transition metal oxide contains sodium (Na) element and sulfur (S) element as essential components, The X-ray diffraction spectrum of the lithium transition metal oxide satisfies the following formula 1: Cathode active material. (Formula 1) 10≦grain (020) / grain (110)≦15 Here, grain (110) means the grain size in the 110 crystal plane, and grain (020) means the grain size in the 020 crystal plane.

2. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide has a molar ratio of Co element of 0.01 or less.

3. The positive electrode active material according to claim 1 , wherein the molar ratio of Mn element is more than 0.

5.

4. The positive electrode active material according to claim 1 , further comprising a Ni element.

5. Further containing Li element, The positive electrode active material according to claim 1 , wherein the molar ratio of the Li element is greater than 1.

6. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide is represented by the following Chemical Formula 1: (Chemical formula 1) Li ｘ Na ｙ Ni １－ａ－ｂ Mn ａ M ｂ O ２＋α－β S β In the above Chemical Formula 1, M is one or more elements selected from B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, and Co; 1.3<x<1.5, 0<y<0.015, 0.5≦a<1, 0≦b<0.1, 0<α<0.5, and 0<β≦0.

01.

7. 7. The positive electrode active material of claim 6, wherein in Formula 1, M is B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, or Co.

8. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide is represented by the following formula 2: (Chemical formula 2) TLi ２ Mnｯ ３ ・(1-T)L-Na ｙ Ni １－ａ－ｂ Mn ａ M ｂ O ２－β S β In the above Chemical Formula 2, M is one or more elements selected from B, Zr, Sr, Y, Ba, W, Ti, Mg, Al, and Co; 0.3<T<0.6, 0<y<0.015, 0.3<a<1, 0<b≦0.25, and 0<β≦0.

025.

9. The positive electrode active material of claim 1 , wherein the lithium transition metal oxide is a single particle.

10. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide comprises an R-3m crystal and a monoclinic crystal.

11. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide has a layered crystal structure.

12. The positive electrode active material according to claim 1 , comprising: a single-particle lithium transition metal oxide particle; and a secondary particle formed by agglomeration of a plurality of the single-particle lithium transition metal oxide particles.

13. 13. The positive electrode active material according to claim 12, wherein in the secondary particles, a surface of a lithium transition metal oxide particle or an interface between a plurality of lithium transition metal oxide particles includes a coating layer containing a Na element, a S element, or Na and S elements.

14. The positive electrode active material according to claim 1 , wherein the positive electrode active material has an average particle size of 0.1 μm to 20 μm.

15. preparing a transition metal oxide precursor having a molar ratio of Mn element of 0.5 or more; mixing the transition metal oxide precursor with a Li precursor, a Na precursor and a S precursor to obtain a lithium transition metal oxide precursor; calcining the lithium transition metal oxide precursor to obtain lithium transition metal oxide particles; The X-ray diffraction spectrum of the lithium transition metal oxide particles satisfies the following formula 1: A method for producing a positive electrode active material. (Formula 1) 10≦grain (020) / grain (110)≦15 Here, grain (110) means the grain size in the 110 crystal plane, and grain (020) means the grain size in the 020 crystal plane.

16. The method for producing a positive electrode active material according to claim 15 , wherein the mixing is mechanical mixing in a solid phase.

17. The method for producing a positive electrode active material according to claim 15, wherein the calcination is a heat treatment at 900° C. to 1,100° C. for 8 to 12 hours.

18. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 14; A negative electrode; and an electrolyte.

19. 20. The lithium secondary battery according to claim 18, wherein the electrolyte is a liquid electrolyte, a semi-solid electrolyte, or a solid electrolyte.

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