Positive electrode active material for lithium secondary battery, method for producing same, and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, which comprises a single crystal containing a lithium nickel composite oxide and a coating portion containing S and Si located on the surface of the single crystal, a method for producing the same, and a lithium secondary battery containing the same.

Description

[Technical field]

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

[0002] Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as the driving power source for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted on using high-energy-density lithium secondary batteries as driving power sources or power storage sources for hybrid and electric vehicles.

[0003] In order to realize a lithium secondary battery suitable for such applications, various positive electrode active materials have been investigated. Among them, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, lithium cobalt oxide, etc. are mainly used as positive electrode active materials. However, such positive electrode active materials have problems such as the structure collapsing or cracking as charging and discharging are repeated, which reduces the long-term life of the lithium secondary battery and increases the resistance, making it impossible to show satisfactory capacity characteristics. Therefore, there is a need to develop a new positive electrode active material that can achieve high capacity and high energy density while ensuring long-term life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0004] Provided are a positive electrode active material for a lithium secondary battery that is structurally stable, suppresses side reactions with an electrolyte, realizes low interfacial resistance and high capacity, and has improved normal temperature and high temperature life characteristics; a method for producing the same; and a lithium secondary battery including the same. [Means for solving the problem]

[0005] In one embodiment, a positive electrode active material for a lithium secondary battery is provided, which includes a single crystal including a lithium nickel-based composite oxide and a coating portion containing S and Si located on the surface of the single crystal.

[0006] In another embodiment, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method comprising: (i) mixing a precursor including a nickel-based transition metal hydroxide, a nickel-based transition metal oxide, or a combination thereof; a lithium raw material; a flux agent including an alkali metal sulfate; and silica; and subjecting the mixture to a primary heat treatment; and (ii) obtaining a positive electrode active material including a single crystal including a lithium nickel-based composite oxide and a coating portion located on the surface of the single crystal and containing S and Si.

[0007] In yet another embodiment, a lithium secondary battery is provided that includes a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. Effect of the Invention

[0008] The positive electrode active material for a lithium secondary battery manufactured according to an embodiment has a stable structure and a suppressed side reaction with an electrolyte, resulting in low interfacial resistance. A lithium secondary battery including the positive electrode active material can achieve high capacity and high energy density while exhibiting excellent room temperature and high temperature life characteristics. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Diagram 2] 1 is a scanning electron microscope photograph of the positive electrode active material produced in Example 1. [Diagram 3] 2 is a scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS) image of the positive electrode active material prepared in Example 1. [Figure 4] 1 is a scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS) image of the positive electrode active material prepared in Example 2. [Diagram 5]1 is a Nyquist plot measured at the time of initial charging for batteries produced in Example 1 and Comparative Example 1. [Figure 6] 1 is a Nyquist plot measured after 25 cycles for the batteries produced in Example 1 and Comparative Example 1. [Figure 7] 1 is a Nyquist plot measured after 25 cycles for the batteries produced in Example 2 and Comparative Example 1. [Figure 8] 1 shows Nyquist plots measured after 25 cycles for the batteries produced in Example 1, Example 3, and Comparative Example 1. [Figure 9] 1 is a graph showing lithium ion diffusion rates during initial charging of batteries manufactured in Comparative Example 1 and Comparative Example 2. [Figure 10] 1 is a graph showing lithium ion diffusion rates during initial discharge of batteries produced in Comparative Example 1 and Comparative Example 2. [Figure 11] 1 is a graph showing the lithium ion diffusion rate during initial charging of the batteries produced in Comparative Example 1, Example 1, and Example 2. [Figure 12] 1 is a graph showing the lithium ion diffusion rates during initial discharge of the batteries produced in Comparative Example 1, Example 1, and Example 2. [Figure 13] 1 is a DC-IR graph of the batteries of Example 1, Comparative Example 1, and Comparative Example 2 before / after 50 cycles at 25° C. [Figure 14] 1 is a DC-IR graph of the batteries of Example 1, Comparative Example 1, and Comparative Example 2 before / after 50 cycles at 45° C. [Figure 15] 1 is a graph showing the life characteristics of the batteries produced in Examples 1, 6, and 7. [Figure 16] 1 is an X-ray photoelectron spectroscopy analysis graph of the surface of the positive electrode active material of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. [Figure 17] 1 is an X-ray photoelectron spectroscopy analysis graph showing a profile according to depth of the positive electrode active material of Example 1. [Figure 18] 1 is an X-ray photoelectron spectroscopy analysis graph showing a profile according to depth of the positive electrode active material of Example 2. [Figure 19]1 is a graph showing the lithium ion diffusion rates during initial charging in Comparative Example 1, Example 2, and Example 5. [Figure 20] 1 is a graph showing the initial discharge capacities of Comparative Example 1, Comparative Example 2, Example 1, Example 4, and Example 5. [Figure 21] 1 is a scanning electron microscope photograph of the positive electrode active material produced in Comparative Example 1. [Figure 22] 1 is a scanning electron microscope photograph of the positive electrode active material produced in Comparative Example 2. [Diagram 23] 1 is a graph showing the self-discharge behavior of the batteries of Example 2, Comparative Example 1, and Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is not limited to the embodiments described herein, but may be embodied in many different forms, and should not be construed as limited to the embodiments described herein.

[0011] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless otherwise clearly indicated in the context.

[0012] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0013] It should be understood that the terms "including," "comprising," or "having" are intended to specify the presence of embodied features, numerals, steps, components, or combinations thereof, and do not preclude the presence or additional possibility of one or more other features, numerals, steps, components, or combinations thereof.

[0014] In the drawings, the thickness of the various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0015] In addition, the terms "coating portion", "protective layer", "protective film", and the like herein include shapes formed on not only the entire surface but also a shape formed on a portion of the surface when observed in a plan view.

[0016] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope or a scanning electron microscope. Alternatively, the average particle size can be calculated by measuring the number of particles in each particle size range using a dynamic light scattering method and performing data analysis. Unless otherwise defined, the average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0017] Method for producing positive electrode active material In one embodiment, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method comprising: (i) mixing a precursor including a nickel-based transition metal hydroxide, a nickel-based transition metal oxide, or a combination thereof; a lithium raw material; a flux agent including an alkali metal sulfate; and silica; and subjecting the mixture to a primary heat treatment to obtain (ii) a positive electrode active material including a single crystal including a lithium nickel-based composite oxide and a coating portion located on the surface of the single crystal and containing S and Si.

[0018] In general, high-nickel-based positive electrode active materials have a capacity-increasing effect due to their high nickel concentration, and attempts are being made to apply them to fields such as electric vehicles that require high energy density. Such high-nickel-based positive electrode active materials usually have a poly-crystal structure, and as charging and discharging continues, structural degradation occurs due to stress between the poly-crystal interfaces, resulting in a decrease in life characteristics. On the other hand, single-crystal high-nickel-based positive electrode active materials can eliminate the disadvantages caused by such structural bonds, and are being actively developed in the industry.

[0019] In one embodiment, in manufacturing a single-crystal high-nickel-based positive electrode active material, a sulfate-based flux agent is used to form a silicon-based protective film on the surface of the single crystal, thereby providing a positive electrode active material that is structurally stable and has high lithium conductivity while suppressing side reactions between the active material and the electrolyte, thereby achieving high capacity and improving life characteristics.

[0020] In the method for producing a positive electrode active material, the precursor may be a nickel-based transition metal hydroxide, or may be a material obtained by subjecting a nickel-based transition metal hydroxide to an oxidative heat treatment. For example, the precursor may be obtained by subjecting a nickel-based transition metal hydroxide to an oxidative heat treatment at a temperature of 400°C to 600°C for 0.1 to 3 hours. Therefore, the precursor may be a nickel-based transition metal hydroxide, a nickel-based transition metal oxide, or a mixture thereof.

[0021] The average particle size (D50) of the precursor may be 1 μm to 20 μm, for example, 1 μm to 15 μm, 1 μm to 10 μm, or 1 μm to 6 μm. The precursor may be a single crystal.

[0022] In the precursor, nickel may be contained in an amount of 60 mol% or more, for example, 70 mol% or more, 80 mol% or more, or 90 mol% or more, based on the total transition metal content. The higher the nickel content, the higher the capacity of the positive electrode active material produced from the precursor. As an example, the nickel-based transition metal oxide may be represented by the following formula 21.

[0023] [Chemical formula 21] Ni x21 M 21 y21 M 22 1-x21-y21 O2

[0024] In the above formula 21, 0.6≦x21≦1, 0≦y21≦0.4, and M 21 and M. 22 are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0025] In the above formula 21, 0.7≦x21≦1, 0≦y21≦0.3, or 0.8≦x21≦1, 0≦y21≦0.2, or 0.9≦x21≦1, 0≦y21≦0.1.

[0026] The nickel-based transition metal hydroxide may be, for example, one represented by the following chemical formula 31.

[0027] [Chemical formula 31] Ni x31 M 31 y31 M 32 1-x31-y31 (OH)2

[0028] In the above formula 31, 0.6≦x31≦1, 0≦y31≦0.4, M 31 and M. 32are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0029] Similarly, in the formula 31, x31 and y31 may be, for example, 0.7≦x31≦1, 0≦y31≦0.3, or 0.8≦x31≦1, 0≦y31≦0.2, or 0.9≦x31≦1, 0≦y31≦0.1.

[0030] In the above-mentioned manufacturing method, the lithium raw material may be, for example, Li2CO3, LiOH, a hydrate thereof, or a combination thereof. The lithium raw material may be mixed in an amount of 100 to 130 parts by mol, for example, 110 to 120 parts by mol, when the total content of the transition metals including nickel is taken as 100 parts by mol. In this case, an active material having a stable structure and a high capacity can be obtained.

[0031] In the manufacturing method, the flux agent is known to be a material involved in the growth of a single crystal, and in one embodiment, a sulfate-based flux agent is used, specifically, an alkali metal sulfate is used. The alkali metal sulfate can be represented by A2SO4 (A is an alkali metal), and may be, for example, lithium sulfate, sodium sulfate, or a combination thereof. Here, the alkali metal includes lithium, sodium, potassium, rubidium, cesium, and francium. That is, the manufacturing method of a positive electrode active material according to one embodiment can be said to be a method of synthesizing a single crystal using a flux agent. The flux agent including the alkali metal sulfate may be mixed in an amount of 0.1 to 10 molar parts, for example, 0.5 to 5 molar parts, 0.5 to 3 molar parts, or 0.5 to 2 molar parts, when the total content of the transition metals including nickel is 100 molar parts. In this case, a single crystal of an appropriate size can be successfully synthesized, and a positive electrode active material that is structurally stable and achieves high capacity can be obtained.

[0032] On the other hand, when only a sulfate-based fluxing agent is used to synthesize a single crystal positive active material, there is a problem that no sulfur or sulfur oxide remains on the surface of the single crystal, and there is no separate protective film on the surface, resulting in structural collapse during charging and discharging, or side reactions between the active material and the electrolyte. On the other hand, when a sulfate-based fluxing agent and silica are used together according to one embodiment, sulfur and silicon are both present on the surface of the single crystal, forming a stable protective film on the surface of the single crystal, and a single crystal that has grown larger and harder can be obtained.

[0033] In the preparation method, the silica may be mixed in an amount of 0.05 to 5 molar parts, for example, 0.05 to 3 molar parts, or 0.1 to 2 molar parts, when the total content of the transition metals including nickel is 100 molar parts. In this case, the surface of the single crystal is stably coated with a silicon-based material, and the lithium ion conductivity is improved, and the structure of the single crystal is stabilized, and the capacity is increased by the silicon.

[0034] The silica may include hydrophobic silica (hydrophobic SiO2), hydrophilic silica (hydrophilic SiO2), or a combination thereof. The hydrophobic silica may be silica particles having an aliphatic hydrocarbon bonded to the surface thereof, and the hydrophilic silica may be silica particles having a hydroxyl group bonded to the surface thereof. The aliphatic hydrocarbon may be, for example, an aliphatic hydrocarbon having 1 to 10 carbon atoms, or an aliphatic hydrocarbon having 1 to 6 carbon atoms, or may be a chain aliphatic hydrocarbon. Both hydrophobic silica and hydrophilic silica can form a stable silicon-based protective film on the surface of the single crystal. However, it has been confirmed that the use of hydrophobic silica is more advantageous in terms of the capacity characteristics and life characteristics of the battery (see Evaluation Example 6 described later).

[0035] Meanwhile, in the above preparation method, an alkali metal phosphate may be further mixed and the first heat treatment may be performed. The alkali metal phosphate may be represented by A3PO4 (A is an alkali metal), and may be, for example, lithium phosphate, sodium phosphate, or a combination thereof. When a single crystal active material is prepared by mixing a sulfate-based fluxing agent, silica, and an alkali metal phosphate together, the P component is present on the surface of the single crystal, and such an active material has improved lithium ion conductivity and reduced interface resistance, leading to improved capacity characteristics and life characteristics.

[0036] The primary heat treatment can be carried out at 750° C. to 900° C., for example, 750° C. to 850° C., for 10 to 20 hours.

[0037] The method may further include washing the product after the first heat treatment and performing a second heat treatment. The washing may include mixing the product in distilled water and drying it, and residual lithium may be removed through this process. The second heat treatment may be performed at, for example, 600°C to 780°C or 650°C to 750°C for 10 to 20 hours. By performing the second heat treatment, a positive electrode active material having a stable structure, high lithium ion conductivity, low interfacial resistance, and high capacity and long life can be obtained.

[0038] The method may further include, after the first heat treatment, washing the product, adding a cobalt compound to perform cobalt coating, and then performing a second heat treatment. The cobalt coating may be performed by coating 1 to 10 mol parts or 1 to 5 mol parts of cobalt with respect to 100 mol parts of transition metals including nickel. The cobalt compound may be, for example, cobalt sulfate. The second heat treatment may also be performed at 600°C to 780°C or 650°C to 750°C for 10 to 20 hours. When the surface of the single crystal is coated with cobalt in this manner, the single crystal positive electrode active material has a more stable structure and can achieve a longer life characteristic.

[0039] In addition, the manufacturing method may further include, after the first heat treatment, mixing the obtained product with a zirconium compound to perform zirconium coating, and performing a second heat treatment. The zirconium coating may be performed by coating 0.001 to 0.5 mol parts, 0.005 to 0.3 mol parts, or 0.01 to 0.1 mol parts of zirconium with respect to 100 mol parts of transition metals including nickel. The zirconium compound may be, for example, zirconium oxide, which may be mixed in a dry manner. The second heat treatment may also be performed at 600°C to 780°C, or 650°C to 750°C, for 10 to 20 hours.

[0040] Meanwhile, the method may further include, after the first heat treatment, washing the obtained material, adding a cobalt compound to perform cobalt coating, drying the obtained material, mixing a zirconium compound to perform zirconium coating, and performing a second heat treatment. In this case, the coating portion on the surface of the single crystal may contain S and Si, and optionally P, and may further contain Co and Zr. In this case, the positive electrode active material may exhibit excellent capacity characteristics and life characteristics.

[0041] positive electrode active material In one embodiment, a positive electrode active material for a lithium secondary battery is provided, which is a positive electrode active material produced by the above-mentioned method, and includes a single crystal containing a lithium nickel-based composite oxide and a coating portion containing S and Si and located on the surface of the single crystal.

[0042] The positive electrode active material for a lithium secondary battery has, first, a low interface resistance (R ct , charge-transfer resistance), which facilitates lithium insertion / desertion during charging / discharging and maintains a constant charge / discharge efficiency, thereby significantly improving the battery's life characteristics. Secondly, the single crystalline positive electrode active material exhibits an improved lithium diffusivity, i.e., lithium ion conductivity is significantly improved. Thirdly, the positive electrode active material has a stable protective film formed on its surface, which effectively suppresses side reactions between the active material and the electrolyte, and a battery including the same has low resistance at the interface between the positive electrode and the electrolyte, thereby exhibiting excellent output characteristics and high-temperature life characteristics.

[0043] In the positive electrode active material, the single crystal means a single particle that exists independently without a grain boundary within the particle, and may mean a monolith structure or a single body structure in which particles exist as an independent phase that is not coagulated with each other in terms of morphology, and may also be expressed as a single crystal particle.

[0044] In the positive electrode active material, the coating portion can be expressed as a kind of protective layer or protective film, and the lithium ion conductive layer (Li +The coating may be formed on the entire surface of the single crystal or on a part of the surface. The coating may have a thickness of about 1 nm to 50 nm, for example, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 20 nm, 1 nm to 10 nm, or 1 nm to 5 nm. When the coating has a thickness in this range, the coating can improve the lithium ion conductivity while suppressing a side reaction between the active material and the electrolyte, thereby improving the capacity and improving the life characteristics.

[0045] The coating portion contains elemental sulfur (S) and elemental silicon (Si) at the same time. The elemental sulfur may be due to a sulfate-based flux agent in the above-mentioned manufacturing method, or may be seen as a sulfate-based flux agent chemisorbed onto the surface of the single crystal. The elemental sulfur may be in the form of sulfur oxide, lithium-sulfur, lithium-sulfur oxide, lithium-silicon-sulfur oxide, or a form in which an aliphatic hydrocarbon group is bonded to any of these.

[0046] The silicon element may originate from the silica produced by the above-mentioned production method, and may be present on the surface of the single crystal in the form of silicon oxide, lithium-silicon, lithium-silicon oxide, lithium-silicon-sulfur oxide, or in the form of any of these bonded with an aliphatic hydrocarbon group.

[0047] On the surface of the single crystal, i.e., in the coating portion, the sulfur-containing compound such as elemental sulfur or sulfur oxide and the silicon-containing compound such as silicon oxide may be chemically bonded to each other through covalent bonds, ionic bonds, etc. It is understood that such chemical bonds occur because the precursor, the lithium source, the sulfate-based flux agent, and the silica are mixed and then a first heat treatment is performed at a high temperature and a second heat treatment is performed selectively during the synthesis process. Also, in the coating portion, the sulfur-containing compound and the silicon-containing compound may have a relationship of mutual attraction between molecules such as van der Waals forces or electrostatic interactions. In other words, it is understood that the sulfur-containing compound and the silicon-containing compound are not separated from each other on the surface of the single crystal, but are chemically bonded, have mutual attraction between molecules, or both are present.

[0048] In one embodiment, when the sulfur-containing compound or the silicon-containing compound is present on the surface of the single crystal in a form having mutual attraction, as compared with the case where only the sulfur-containing compound or only the silicon-containing compound is present, or the compounds are separated without any interaction, a significant increase in the interface resistance, lithium ion conductivity, DC resistance, initial capacity, room temperature life, and high temperature life was observed, and it was also confirmed that the single crystal itself grew larger and stronger.

[0049] Specifically, the coating portion may include a sulfur-containing compound represented by the following Chemical Formula 1 and a silicon-containing compound represented by the following Chemical Formula 2.

[0050] [Chemical formula 1] A a1 SO z1

[0051] In the above Chemical Formula 1, A is an alkali metal, 0≦a1≦2, and 0≦z1≦4.

[0052] [Chemical formula 2] A a2 S x2 O z2

[0053] In Chemical Formula 2 above, A is an alkali metal, 0 ≦ a2 ≦ 5, 1 ≦ x2 ≦ 2, and 0 ≦ z2 ≦ 4.

[0054] In the synthesis process, through the process of mixing a precursor, a lithium raw material, a sulfate-based flux agent, and silica and performing a primary heat treatment, and selectively performing a secondary heat treatment, a sulfur-containing compound is distributed on the surface of a single crystal containing a lithium nickel-based transition metal oxide, where the sulfur-containing compound can have various compositions. For example, the sulfur-containing compound represented by Chemical Formula 1 above may include an alkali metal sulfate (e.g., Li2SO4, Na2SO4) or an alkali metal sulfur oxide containing a modification thereof; an alkali metal sulfide such as lithium sulfide (Li2S); or a combination thereof. It is understood that sulfur-containing compounds with various compositions exist alone or in combination.

[0055] Here, A, which is an alkali metal, may be lithium, sodium, potassium, rubidium, cesium, francium, or a combination thereof. For example, it may be lithium or sodium.

[0056] In Chemical Formula 1, 0 ≦ a1 ≦ 2, 0 < a1 ≦ 2, 0.5 ≦ a1 ≦ 2, 1 ≦ a1 ≦ 2, or 1.5 ≦ a1 ≦ 2 may be satisfied, and 0 ≦ z1 ≦ 4, 0 < z1 ≦ 4, 1 ≦ z1 ≦ 4, 2 ≦ z1 ≦ 4, or 3 ≦ z1 ≦ 4 may be satisfied. Sulfur-containing compounds having various oxidation numbers can coexist in the coating portion.

[0057] The silicon-containing compound represented by Chemical Formula 2 above may include, for example, silicon oxide containing silica (SiO2) or a modification thereof; alkali metal silicate (e.g., Li2SiO3, Li4SiO4) or alkali metal silicon oxide containing a modification thereof; alkali metal silicide (e.g., Li x Si, 1 ≦ x ≦ 5); etc., and these can exist alone or in combination in the coating portion.

[0058] In the formula (2), 0 ≦ a2 ≦ 5, 0 < a2 ≦ 5, 1 ≦ a2 ≦ 5, 2 ≦ a2 ≦ 5, 3 ≦ a2 ≦ 5, 3 ≦ a2 ≦ 4, 0 ≦ a2 ≦ 2, 0 < a2 ≦ 5, or 1 ≦ a2 ≦ 2 may be satisfied, and 0 ≦ z2 ≦ 4, 0 < z2 ≦ 4, 1 ≦ z2 ≦ 4, or 2 ≦ z2 ≦ 4 may be satisfied. In the coating portion, silicon-containing compounds having various oxidation numbers may coexist.

[0059] It is understood that the sulfur-containing compound represented by the formula (1) and the silicon-containing compound represented by the formula (2) do not exist separately from each other and have an intermolecular attractive force such as van der Waals force and electrostatic interaction.

[0060] Further, the sulfur-containing compound and the silicon-containing compound may form a chemical bond. Specifically, the coating portion may include a sulfur-silicon-containing compound represented by the following formula (3), that is, a compound containing both sulfur and silicon.

[0061] [Chemical formula 3] A a3 Si x3 S y3 O z3

[0062] In the above formula (3), A is an alkali metal, and 0 ≦ a3 ≦ 5, 0 < x3 ≦ 2, 0 < y3 ≦ 5, and 0 ≦ z3 ≦ 10.

[0063] The sulfur-silicon-containing compound represented by the formula (3) may be, for example, an alkali metal silicon sulfide such as lithium silicon sulfide (e.g., Li2SiS3); silicon sulfide (e.g., SiS, SiS2); silicon sulfate (e.g., Si(SO4)2); an alkali metal silicon sulfur oxide; or a combination thereof.

[0064] In the formula (3), 0 < a3 ≤ 5, 1 ≤ a3 ≤ 5, 2 ≤ a3 ≤ 5, 3 ≤ a3 ≤ 5, 0 ≤ a3 ≤ 4, 0 ≤ a3 ≤ 3, or 0 ≤ a3 ≤ 2 may be applicable; 0.1 ≤ x3 ≤ 2, 0.5 ≤ x3 ≤ 2, or 1 ≤ x3 ≤ 2 may be applicable; 0.1 ≤ y3 ≤ 5, 0.5 ≤ y3 ≤ 5, 1 ≤ y3 ≤ 4, 1 ≤ y3 ≤ 3, or 1 ≤ y3 ≤ 2 may be applicable; 0 < z3 ≤ 10, 0 ≤ z3 ≤ 9, 0 ≤ z3 ≤ 8, 1 ≤ z3 ≤ 10, or 2 ≤ z3 ≤ 10 may be applicable. It is considered that sulfur-silicon-containing compounds with various compositions are formed on the surface of the single crystal as it undergoes a primary heat treatment and selectively a secondary heat treatment during the synthesis process.

[0065] The sulfur-containing compound represented by the formula (1) and the sulfur-silicon-containing compound represented by the formula (3) may be distributed on the surface of the single crystal. FIG. 3 is an energy-dispersive X-ray spectroscopy (EDS) photograph of the positive electrode active material manufactured in Example 1 described later. Referring to FIG. 3, it can be confirmed that the sulfur element displayed in blue is distributed over the entire surface of the single crystal.

[0066] The silicon-containing compound represented by the formula (2) or the sulfur-silicon-containing compound represented by the formula (3) may be distributed on the surface of the single crystal and may also exist in the form of island-shaped coatings with a thickness of 1 nm to 50 nm. Referring to FIG. 3, it can be confirmed that the silicon element displayed in pink is distributed over the entire surface of the single crystal and is simultaneously coated in an island form in the near-surface area. Also, the silicon-containing compound or the sulfur-silicon-containing compound may exist in the crack portions inside the single crystal. FIG. 4 is an EDS analysis photograph of the positive electrode active material of Example 2 described later. Referring to FIG. 4, it can be confirmed that the silicon element displayed in pink is also observed in the crack region inside the single crystal. Thus, by coating the silicon-containing compound on the surface, near the surface, and in the internal crack region of the single crystal, it is confirmed that the positive electrode active material containing this can exhibit high lithium ion conductivity while effectively suppressing side reactions with the electrolyte and can show high high-temperature life characteristics while achieving high capacity.

[0067] Here, the coating portion may be a concept including the surface and the vicinity of the surface.

[0068] For example, the sulfur-containing compound may be present on the single crystal surface in a thickness range of 1 nm to 20 nm, or in a thickness range of 1 nm to 10 nm, and the silicon-containing compound may be present on the single crystal surface in a thickness range of 1 nm to 50 nm, or in a thickness range of 1 nm to 30 nm. In the coating portion, the sulfur (S) content may be 0.01 atomic % to 5 atomic %, or 0.01 atomic % to 3 atomic %, or 0.01 atomic % to 1 atomic %, and the silicon (Si) content may be 0.001 atomic % to 3 atomic %, or 0.005 atomic % to 2 atomic %, or 0.01 atomic % to 1 atomic %, based on the entire positive electrode active material. In this case, the positive electrode active material exhibits excellent lithium ion conductivity while effectively suppressing side reactions with the electrolyte, thereby reducing electrode resistance, and exhibiting high initial capacity and excellent room temperature / high temperature life characteristics.

[0069] Meanwhile, the coating portion may further include a carbon atom (C). Specifically, the coating portion may further include an aliphatic hydrocarbon. The aliphatic hydrocarbon may be, for example, a chain aliphatic hydrocarbon having 1 to 10 carbon atoms or a chain aliphatic hydrocarbon having 1 to 6 carbon atoms. This may be due to an aliphatic hydrocarbon group bonded to the surface of the silica when hydrophobic silica is used in the synthesis process, or may be generated when the positive electrode active material is exposed to air (or oxygen) as it undergoes a first heat treatment and an optional second heat treatment.

[0070] Specifically, the coating portion may further include at least one of a sulfur-containing compound represented by the following Chemical Formula 1-1, a silicon-containing compound represented by the following Chemical Formula 2-1, and a sulfur-silicon-containing compound represented by the following Chemical Formula 3-1.

[0071] [Chemical formula 1-1] A a1 SOz1 -(CH2) n1 CH3

[0072] In the above formula 1-1, A is an alkali metal, 0≦a1≦2, 0≦z1≦4, and 0≦n1≦5;

[0073] [Chemical formula 2-1] A a2 S x2 O z2 -(CH2) n2 CH3

[0074] In the above chemical formula 2-1, A is an alkali metal, and 0≦a2≦2, 1≦x2≦2, 0≦z2≦4, and 0≦n2≦5.

[0075] [Chemical formula 3-1] A a3 S x3 S y3 O z3 -(CH2) n3 CH3

[0076] In the above chemical formula 3-1, A is an alkali metal, 0≦a3≦5, 0 <x3≦2、0<y3≦5、0≦z3≦10、および0≦n3≦5である。

[0077] For example, the coating portion may include a silicon-containing compound represented by Chemical Formula 2-1, and may optionally further include a sulfur-containing compound represented by Chemical Formula 1-1, and / or a sulfur-silicon-containing compound represented by Chemical Formula 3-1.

[0078] In the above formulas 1-1, 2-1, and 3-1, the alkyl group (-(CH2) nCH3) may be bonded to a portion of the chemical formula, or may be connected to the surface of a particle composed of the chemical formula. The alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or a combination thereof. When the coating portion further includes an aliphatic hydrocarbon group, the positive electrode active material including the coating portion may exhibit better capacity characteristics and life characteristics.

[0079] In addition, the coating portion may further include phosphorus (P). When an alkali metal phosphate is used together with a sulfate-based flux agent and silica in the synthesis process, a phosphorus-containing compound may be formed on the surface of the single crystal. When the coating portion further includes P, the positive electrode active material may have a lower interface resistance and exhibit better capacity characteristics and high-temperature life characteristics.

[0080] The coating portion may include, for example, a phosphorus-containing compound represented by Formula 4 below.

[0081] [Chemical formula 4] A a4 PO z4

[0082] In the above chemical formula 4, A is an alkali metal, and 0≦a4≦3 and 0≦z4≦4.

[0083] In the above Chemical Formula 4, 0 <a4≦3、1≦a4≦3、または2≦a4≦3であってもよく、0<z4≦4、1≦z4≦4、2≦z4≦4、または3≦z4≦4であってもよい。

[0084] In the coating portion, the phosphorus-containing compound may be chemically bonded to the sulfur-containing compound and / or the silicon-containing compound, or may have an intermolecular mutual attractive effect. The phosphorus-containing compound may further include the above-mentioned aliphatic hydrocarbon group.

[0085] As an example, the coating portion can contain a sulfur-silicon-phosphorus-containing compound represented by the following Chemical Formula 5.

[0086] [Chemical Formula 5] A a5 Si x5 S y5 P p5 O z5

[0087] In Chemical Formula 5 above, A is an alkali metal, 0 ≦ a5 ≦ 5, 0 < x5 ≦ 2, 0 < y5 ≦ 5, 0 < p5 ≦ 3, and 0 ≦ z5 ≦ 10.

[0088] In Chemical Formula 5, 0 < a5 ≦ 5, 1 ≦ a5 ≦ 5, 2 ≦ a5 ≦ 5, 3 ≦ a5 ≦ 5, 0 ≦ a5 ≦ 4, 0 ≦ a5 ≦ 3, or 0 ≦ a5 ≦ 2 etc. may be possible, 0.1 ≦ x5 ≦ 2, 0.5 ≦ x5 ≦ 2, or 1 ≦ x5 ≦ 2 may be possible, 0.1 ≦ y5 ≦ 5, 0.5 ≦ y5 ≦ 5, 1 ≦ y5 ≦ 4, 1 ≦ y5 ≦ 3, or 1 ≦ y5 ≦ 2 etc. may be possible, 0.1 ≦ p5 ≦ 3, 0.5 ≦ p5 ≦ 3, or 1 ≦ p5 ≦ 2 may be possible, 0 < z5 ≦ 10, 0 ≦ z5 ≦ 9, 0 ≦ z5 ≦ 8, 1 ≦ z5 ≦ 10, or 2 ≦ z5 ≦ 10 etc. may be possible. It is considered that sulfur-silicon-phosphorus-containing compounds with various compositions are formed on the single crystal surface as the first heat treatment and optionally the second heat treatment are carried out during the synthesis process.

[0089] The content of the phosphorus element (P) may be 0.001 atomic % to 3 atomic %, or 0.005 atomic % to 2 atomic %, or 0.01 atomic % to 1 atomic % with respect to the entire positive electrode active material. In this case, the positive electrode active material can have a very low interfacial resistance and exhibit a high initial capacity and improved room temperature / high temperature life characteristics.

[0090] Meanwhile, the coating portion may further include at least one selected from Co and Zr. In the synthesis process, a cobalt and / or zirconium coating process may be further performed after the first heat treatment. In this case, the positive electrode active material may have a more stable structure and may exhibit more excellent room temperature and high temperature life characteristics. For example, the thickness of the cobalt coating portion may be 1 nm to 50 nm, or 1 nm to 30 nm, and the thickness of the zirconium coating portion may be 1 nm to 20 nm, or 1 nm to 10 nm.

[0091] The coating portion may further include Al, B, Ca, Ce, Cr, Cu, F, Fe, Mg, Nb, Sr, Ti, W, Y, or a combination thereof for structural stability of the positive electrode active material or for improving the life characteristics of the battery.

[0092] The lithium nickel-based composite oxide may be expressed as a lithium nickel transition metal composite oxide, and may be an oxide containing lithium, nickel, and other transition metals. In the lithium nickel-based composite oxide, nickel may be contained in an amount of 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, or 100 mol% or less, 99 mol% or less, 98 mol% or less, or 96 mol% or less, based on the total content of transition metals excluding lithium. In the case of a high nickel-based oxide having a high nickel content, a high capacity can be realized, but a single crystal high nickel-based oxide is difficult to synthesize and difficult to grow into particles having an appropriate particle size, and even if synthesized, there are problems such as not being able to express a desired level of capacity. On the other hand, the positive electrode active material according to an embodiment is a single crystal form containing a high nickel-based oxide, but the particles can be grown to an appropriate size, and the structure is stable, so that it can exhibit high capacity and excellent room temperature and high temperature life characteristics.

[0093] The lithium nickel-based composite oxide can be represented, for example, by the following chemical formula 11.

[0094] [Chemical formula 11] Li a11 Ni x11 M 1 y11 M 2 1-x11-y11 O2

[0095] In the above formula 11, 0.9≦a11≦1.8, 0.6≦x11≦1, and 0≦y11≦0.4; M 1 and M. 2 are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0096] In the above chemical formula 11, 0.9≦a11≦1.5, or 0.9≦a11≦1.2, or 0.95≦a11≦1.10, and 0.7≦x11≦1 and 0≦y11≦0.3, or 0.8≦x11≦1 and 0≦y11≦0.2, or 0.9≦x11≦1 and 0≦y11≦0.1.

[0097] The lithium nickel-based composite oxide can be represented, for example, by the following chemical formula 12.

[0098] [Chemical formula 12] Li a12 Ni x12 Co y12 M 3 1-x12-y12 O2

[0099] In the above chemical formula 12, 0.9≦a12≦1.8, 0.6≦x12<1, 0 <y12≦0.4であり、M 3 is selected from the group consisting of Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0100] In the formula 12, 0.9≦a12≦1.5, or 0.9≦a12≦1.2, or 0.95≦a12≦1.10; <y12≦0.3、または0.8≦x12<1および0<y12≦0.2、または0.9≦x12≦0.99および0.01≦y12≦0.1であってもよい。

[0101] The lithium nickel-based composite oxide can be represented, for example, by the following chemical formula 13.

[0102] [Chemical formula 13] Li a13 Ni x13 Co y13 Al z13 M 4 1-x13-y13-z13 O2

[0103] In the above chemical formula 13, 0.9≦a13≦1.8, 0.6≦x13<1, 0 <y13<0.4、0<z13<0.4であり、M 4 is selected from the group consisting of B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0104] In the formula 13, 0.9≦a13≦1.5, or 0.9≦a13≦1.2, or 0.95≦a13≦1.10; <y13≦0.3および0<z13≦0.3、または0.8≦x13<1、0<y13≦0.2および0<z13≦0.2、または0.9≦x13≦0.98、0.01≦y13≦0.1および0.01≦z13≦0.1であってもよい。

[0105] The positive electrode active material may have an average particle size (D50) of 1 μm to 20 μm, for example, 1 μm to 15 μm, 1 μm to 10 μm, 1 μm to 8 μm, or 2 μm to 6 μm. When the positive electrode active material has such a particle size range while being a single crystal, excellent capacity characteristics and life characteristics can be achieved.

[0106] The positive electrode active material can have a full width at half maximum (FWHM) in the range of 0.1 to 0.2 in X-ray diffraction analysis (XRD). Further, in the X-ray diffraction analysis of the positive electrode active material, the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane, that is, I(003) / I(104), can have a value of 1 to 1.5, for example, 1 < I(003) / I(104) < 1.5 may also be acceptable. When the positive electrode active material has such a crystal structure, excellent capacity characteristics and life characteristics can be exhibited.

[0107] Also, the residual lithium in the positive electrode active material may be 3000 ppm or less, for example, 2000 ppm or less. When manufacturing a high-nickel-based positive electrode active material, an excessive amount of lithium can be used, which may result in an excessive amount of residual lithium in the final positive electrode active material and a decrease in battery performance. On the contrary, the positive electrode active material according to one embodiment has a residual lithium of 3000 ppm or less and can maintain excellent battery performance.

[0108] positive electrode The positive electrode for a lithium secondary battery can include a current collector and a positive electrode active material layer located on the current collector. The positive electrode active material layer contains a positive electrode active material and can further contain a binder and / or a conductive material.

[0109] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0110] The positive electrode active material layer may have a binder content of about 1 wt % to about 5 wt % based on the total weight of the positive electrode active material layer.

[0111] The conductive material is used to impart conductivity to the electrodes, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of the conductive material that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0112] The positive electrode active material layer may have a conductive material content of 1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0113] The current collector may be, but is not limited to, an aluminum foil.

[0114] negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material, and may further include a binder and / or a conductive material.

[0115] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0116] As a substance capable of reversibly intercalating / deintercalating the lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0117] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0118] As the substance capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiO x (0 < x < 2), an Si-Q alloy (wherein Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof and is not Si), and as the Sn-based negative electrode active material, Sn, SnO2, an Sn-R alloy (wherein R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof and is not Sn), and the like can be mentioned. Also, at least one of these can be mixed with SiO2 and used. As the elements Q and R, those selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a combination thereof can be used.

[0119] The silicon-carbon composite may be, for example, a silicon-carbon composite including a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resin such as phenol resin, furan resin, or polyimide resin. In this case, the content of silicon may be 10% by weight to 50% by weight based on the total weight of the silicon-carbon composite. The content of the crystalline carbon may be 10% by weight to 70% by weight based on the total weight of the silicon-carbon composite, and the content of the amorphous carbon may be 20% by weight to 40% by weight based on the total weight of the silicon-carbon composite. The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D50) of the silicon particles may be 10 nm to 20 μm. The average particle size (D50) of the silicon particles may be preferably 10 nm to 200 nm. The silicon particles are present in an oxidized form, and at this time, the atomic ratio of Si:O in the silicon particles, which indicates the degree of oxidation, may be 99:1 to 33:66 by weight. x In this case, SiO x In the above, x may range from more than 0 to less than 2. Unless otherwise defined herein, the average particle size (D50) refers to the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution.

[0120] The Si-based or Sn-based negative electrode active material may be mixed with a carbon-based negative electrode active material. When the Si-based or Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material, the mixing ratio by weight may be 1:99 to 90:10.

[0121] The negative active material layer may have a negative active material content of 95 wt % to 99 wt % based on the total weight of the negative active material layer.

[0122] In one embodiment, the negative active material layer may further include a binder and may optionally further include a conductive material. The content of the binder in the negative active material layer may be 1 wt% to 5 wt% based on the total weight of the negative active material layer. In addition, when the negative active material layer further includes a conductive material, the negative active material layer may include 90 wt% to 98 wt% of the negative active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0123] The binder serves to adhere the negative active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0124] The non-water-soluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0125] The water-soluble binder may be a rubber-based binder or a polymeric resin binder. The rubber-based binder may be selected from styrene butadiene rubber, acrylated styrene butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymeric resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0126] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li. The amount of the thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0127] The conductive material is used to impart conductivity to the electrodes, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of the conductive material that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials including mixtures thereof.

[0128] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0129] Lithium secondary battery Another embodiment provides a lithium secondary battery including a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the electrodes may be the positive electrode and / or the negative electrode.

[0130] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment. Referring to FIG 1, a lithium secondary battery 100 according to an embodiment of the present invention includes a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a lithium secondary battery electrolyte impregnated in the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 in which the battery cell is housed, and a sealing member 140 for sealing the battery container 120.

[0131] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0132] The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent. The carbonate-based solvent may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. The ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. The ether solvent may be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the ketone solvent may be cyclohexanone, etc. In addition, examples of the alcohol solvent include ethyl alcohol and isopropyl alcohol, and examples of the aprotic solvent include nitriles such as R-CN (wherein R is a hydrocarbon group having a linear, branched, or cyclic structure with 2 to 20 carbon atoms and may contain a double bond oriented ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0133] The non-aqueous organic solvent may be used alone or in combination of two or more thereof. When two or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which should be widely understood by those skilled in the art.

[0134] In addition, in the case of the carbonate-based solvent, a cyclic carbonate and a chain carbonate can be mixed and used. In this case, the performance of the electrolyte is shown to be excellent when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9.

[0135] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0136] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula I:

[0137] [Chemical formula I] [ka]

[0138] In the above formula I, R 4 ~R 9 are the same or different and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

[0139] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene ... and combinations thereof. The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of the following formula II as a life-improving additive in order to improve the battery life.

[0140] [Chemical formula II] [ka]

[0141] In the above formula II, R 10 and R 11 are the same or different and are selected from the group consisting of hydrogen, a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, 10 and R 11At least one of R is selected from the group consisting of a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, with the proviso that 10 and R 11 But it's not all hydrogen.

[0142] Representative examples of the ethylene carbonate compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life-improving additive is further used, the amount of the additive used can be appropriately adjusted.

[0143] The lithium salt is a material that is dissolved in a non-aqueous organic solvent and acts as a source of lithium ions in a battery to enable basic operation of a lithium secondary battery and to promote the movement of lithium ions between a positive electrode and a negative electrode.

[0144] Representative examples of lithium salts are LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1and lithium difluoro(oxalato)borate (LiDFOB).

[0145] The lithium salt is preferably used at a concentration within the range of 0.1 M to 2.0 M. If the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can be effectively transferred.

[0146] The separator 113, also called a separator membrane, separates the positive electrode 114 and the negative electrode 112 and provides a passage for lithium ions to move, and can be any material that is commonly used in lithium ion batteries. That is, a material that has low resistance to the movement of electrolyte ions and has excellent electrolyte humidification ability can be used. For example, the material can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and can be in the form of a non-woven fabric or a woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used in lithium ion batteries, and coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0147] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, into cylindrical, square, coin, pouch, etc. types depending on the shape, and into bulk and thin film types depending on the size. The structure and manufacturing method of these batteries are widely known in this field, so a detailed description will be omitted.

[0148] The lithium secondary battery according to an embodiment has a high capacity and is excellent in storage stability, life characteristics, and high rate characteristics at high temperatures, and can be used in electric vehicles (EVs) and hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

[0149] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples. EXAMPLES

[0150] Example 1 Manufacture of positive electrode active material Precursor Ni with an average particle size (D50) of 3.5 μm 0.946 Co 0.039 Al 0.015 (OH)2 is oxidized and heat-treated at 500°C for 0.5 hours. To the oxidized and heat-treated material, 112 mol% hydrous lithium hydroxide (LiOH), 1.0 mol% flux agent Li2SO4, 0.5 mol% hydrophobic silica (SiO2), and 0.5 mol% Li3PO4 are added relative to the total amount of Ni and Co, and mixed in a mixer. The mixed material is subjected to primary firing at 800°C for 15 hours in an O2 atmosphere. The obtained active material is then pulverized in a jet mill at a pressure of 3 bar to remove fine powder.

[0151] The crushed active material is coated with cobalt and washed with water to remove residual lithium. The active material powder is added to distilled water and washed while mixing. Cobalt nitrate hexahydrate (Co(NO3)26H2O) is added at a constant rate, which is equivalent to 3 mol% of the total amount of Ni and Co in the active material, and ammonium hydroxide (NH4OH) and sodium hydroxide (NaOH) are gradually added as pH adjusters to perform cobalt coating. The resulting material is then dried at 150°C for 12 hours, sieved through a 45μm sieve, and subjected to a secondary firing at 700°C in an O2 atmosphere for 15 hours. The active material after the secondary firing is sieved through a 45μm sieve. A scanning electron microscope image of the final active material is shown in Figure 2.

[0152] Cathode manufacturing 97.7% by weight of the obtained positive electrode active material, 1.3% by weight of polyvinylidene fluoride binder, and 1% by weight of carbon nanotube (CNT) conductive material are mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry is applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0153] Manufacture of lithium secondary batteries A coin half cell is manufactured by using the prepared positive electrode and lithium metal counter electrode, placing a polyethylene polypropylene multilayer separator between them, and injecting an electrolyte solution of 1.15 M LiPF6 lithium salt added to a solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40.

[0154] Example 2 The positive electrode active material, the positive electrode, and the battery were prepared in the same manner as in Example 1, except that 0.5 mol % of Li3PO4 was not added.

[0155] Example 3 The positive electrode active material, the positive electrode, and the battery were prepared in the same manner as in Example 1, except that Na2SO4 was used instead of Li2SO4 as the flux agent.

[0156] Example 4 A positive electrode active material, a positive electrode, and a battery were prepared in the same manner as in Example 1, except that hydrophilic silica (hydrophilic SiO2) was used instead of hydrophobic silica in the preparation of the positive electrode active material in Example 1.

[0157] Example 5 A positive electrode active material, a positive electrode, and a battery were prepared in the same manner as in Example 2, except that hydrophilic silica was used instead of hydrophobic silica in the preparation of the positive electrode active material of Example 2.

[0158] Example 6 A positive electrode active material, a positive electrode, and a battery were prepared in the same manner as in Example 1, except that the primary sintering was performed at 825° C. for 25 hours.

[0159] Example 7 A positive electrode active material, a positive electrode, and a battery were prepared in the same manner as in Example 1, except that the primary sintering was performed at 850° C. for 25 hours.

[0160] Comparative Example 1 A positive electrode active material, a positive electrode, and a battery were prepared in the same manner as in Example 1, except that in the preparation of the positive electrode active material of Example 1, no flux agent, hydrophobic silica, and Li3PO4 were used, and only 112 mol% of hydrous lithium hydroxide was added and the primary firing was performed.

[0161] Comparative Example 2 A positive electrode active material, a positive electrode, and a battery were manufactured in the same manner as in Example 1, except that in the preparation of the positive electrode active material of Example 1, hydrophobic silica and Li3PO4 were not used, and only 112 mol % of hydrous lithium hydroxide and 1 mol % of a flux agent Li2SO4 were added and the primary sintering was performed.

[0162] Comparative Example 3 A positive electrode active material, a positive electrode, and a battery were manufactured in the same manner as in Example 1, except that in the preparation of the positive electrode active material of Example 1, no flux agent and Li3PO4 were used, and only 112 mol % of hydrous lithium hydroxide and 0.5 mol % of hydrophilic silica were added and the primary firing was performed.

[0163] Evaluation example 1: Elemental analysis (STEM-EDS) The positive electrode active materials prepared in Examples 1 and 2 were photographed using a scanning transmission electron microscope (STEM) and subjected to energy dispersive X-ray spectroscopy (EDS) to analyze the elements on the surface of the active materials. The results of Example 1 are shown in FIG. 3, and the results of Example 2 are shown in FIG. 4.

[0164] Referring to FIG. 3, it can be seen that cobalt is coated on the surface of the single crystal, silicon is observed on the surface of the single crystal and even near the surface, and sulfur is distributed over the entire surface of the single crystal.

[0165] Referring to FIG. 4, it can be seen that silicon components are observed not only on and near the surface of the single crystal grains but also in the internal crack regions.

[0166] Evaluation example 2: Interface resistance evaluation The lithium secondary batteries fabricated in Examples 1, 2, 3, and Comparative Example 2 were measured for the degree of resistance formed at the electrode interface using an electrochemical impedance analyzer (EIS). The amplitude was ±10 mV, and the frequency range was 10 mHz to 1 MHz. The resistance was measured by charging the batteries to a maximum voltage of 4.25 V based on the Li negative electrode at a constant current of 0.1 C rate, and then cutting off the current at a 0.05 C rate while maintaining a constant voltage of 4.25 V and leaving a pause for 1 hour. Thereafter, the resistance was measured by a 2-probe method using an impedance analyzer at an equilibrium voltage.

[0167] Fig. 5 shows Nyquist plots measured at the initial charge of Example 1 and Comparative Example 1, Fig. 6 shows Nyquist plots measured after 25 cycles of Example 1 and Comparative Example 1, and Fig. 7 shows Nyquist plots measured after 25 cycles of Example 2 and Comparative Example 1. Referring to Figs. 5 to 7, it can be seen that Example 1 and Example 2 have lower interface resistance than Comparative Example 1.

[0168] 8 is a Nyquist plot of Example 1, Comparative Example 1, and Example 3 using sodium sulfate as a fluxing agent after 25 cycles. Referring to FIG. 8, it can be seen that both Example 1 and Example 3 have lower interfacial resistance than Comparative Example 1.

[0169] Low interface resistance (R ct , charge-transfer resistance, facilitates the insertion / extraction reaction of lithium ions during charging / discharging, thereby maintaining a constant charge / discharge efficiency and significantly improving the life characteristics of the battery.

[0170] Evaluation example 3: Lithium ion diffusion rate evaluation The batteries prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were charged at room temperature (25° C.) with a constant current / constant voltage pattern of 0.1 C to an upper voltage of 4.25 V, and then a 0.05 C current cut-off was performed in the constant voltage state. After a 10-minute rest period, the cells were discharged at a constant current of 0.1 C to a discharge end voltage of 3.0 V to confirm the initial charge / discharge capacity. The cells were then charged at a constant current of 0.1 C for 20 minutes at 25° C., rested for 1 hour to stabilize the cells in an equilibrium voltage state, and charged again for 20 minutes to an upper voltage of 4.3 V, and then discharged at a constant current of 0.1 C to a discharge end voltage of 3.0 V for 20 minutes in the same pattern to measure the diffusion rate of lithium ions (Li + Evaluate the diffraction grating (diffusivity).

[0171] Fig. 9 is a graph showing the lithium ion diffusivity measured during initial charging at 25°C for the batteries produced in Comparative Example 1 and Comparative Example 2, and Fig. 10 is a graph showing the lithium ion diffusivity measured during initial discharging at 25°C for the batteries produced in Comparative Example 1 and Comparative Example 2. Fig. 11 is a graph showing the lithium ion diffusivity measured during initial charging at 25°C for the batteries produced in Comparative Example 1, Example 1, and Example 2, and Fig. 12 is a graph showing the lithium ion diffusivity measured during initial discharging at 25°C for the batteries produced in Comparative Example 1, Example 1, and Example 2. 9 to 12, the lithium ion diffusivity of Examples 1 and 2 was improved compared to Comparative Examples 1 and 2, and Examples 1 and 2 exhibited lithium ion diffusivities that were approximately 1.5 times higher than Comparative Example 1. Such high lithium ion conductivity characteristics can be said to be an index of the stability of the active material structure.

[0172] Evaluation example 4: DC-IR evaluation The batteries of Example 1, Comparative Example 1, and Comparative Example 2 were charged at room temperature (25° C.) with a constant current / constant voltage pattern of 0.1 C to an upper limit voltage of 4.25 V, then a 0.05 C current cutoff was performed in the constant voltage state, and after a 10-minute rest period, an initial charge / discharge was performed by constant current discharge at 0.1 C to a discharge end voltage of 3.0 V. In the case of room temperature evaluation, 50 charge / discharge cycles were then performed at 1 C, and in the case of high temperature (45° C.) evaluation, charging and discharging were performed in the same manner as above, except that charging and discharging were performed up to an upper limit voltage of 4.30 V for accelerated evaluation.

[0173] Resistance (DC-IR) was measured before and after 50 cycles at room temperature and high temperature for the batteries of Example 1, Comparative Example 1, and Comparative Example 2. FIG. 13 is a DC-IR graph before and after 50 cycles at 25° C., and FIG. 14 is a DC-IR graph before and after 50 cycles at 45° C. Referring to FIG. 13, it can be seen that the cell deviation is larger in Comparative Examples 1 and 2 than in Example 1 in the graph after cycling. Referring to FIG. 14, it can be seen that the cell deviation is larger in Comparative Examples 1 and 2 than in Example 1 in the graph after cycling, and the battery of Example 1 shows the lowest DC resistance characteristics at high temperature.

[0174] In the single crystal active material according to the embodiment, a silicon-based protective film is stably formed by surface chemisorption of a lithium sulfate flux agent, and such a structure controls the irreversible characteristics of the cathode electrolyte layer (CEI) generated by charging and discharging the battery, and reduces the DC resistance, thereby improving the high-temperature life characteristics, which are the output characteristics of the battery.

[0175] Evaluation example 5: Battery life characteristic evaluation The batteries of Example 1, Example 6, Example 7, and Comparative Example 1 were charged at 25° C. with a constant current / constant voltage pattern of 0.1 C to an upper limit voltage of 4.25 V, then a 0.05 C current cutoff was performed in a constant voltage state, and after a 10-minute rest period, the batteries were discharged at 0.1 C to a discharge end voltage of 3.0 V to perform initial charge / discharge and measure the initial discharge capacity, and then 50 charge / discharge cycles were repeated at 1 C to measure the discharge capacity at 50 cycles, and the ratio (%) of the 50th discharge capacity to the initial discharge capacity is shown as the capacity retention rate, i.e., life characteristics. The 50th capacity retention rates of Example 1 and Comparative Example 2 are shown in Table 1, and the life characteristics of Example 1, Example 6, and Example 7 are shown in FIG.

[0176] [Table 1]

[0177] 15, it can be seen that the life characteristics of Examples 1, 6, and 7 are significantly improved compared to Comparative Example 1, and the capacity retention rate of Example 6 is 92.7%, and the capacity retention rate of Example 7 is 96.7%, which is a significant improvement.

[0178] Evaluation example 6: XPS evaluation The positive electrode active materials prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were analyzed by X-ray photoelectron spectroscopy (XPS).

[0179] 16 is a graph showing the Ni2p peak and the S2p peak on the surface of the positive electrode active material of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. Referring to FIG. 16, Ni2p shown in purple in relation to the Ni2p peak 1 / 2 Peaks and Ni2p shown in red 3 / 2It can be seen that the peaks of Examples 1 and 2 were reduced compared to Comparative Examples 1 and 2. The reduction in the Ni2p peak is evidence that a protective film mainly consisting of Li-Si was formed on the surface, and it can be seen that a synergistic effect was achieved in Examples 1 and 2 in which a flux agent and silica were applied compared to Comparative Example 2 in which a flux agent was used alone. In addition, with regard to the S2p peak, it can be seen that the S2p peak was formed only in Examples 1 and 2. The formation of the S2p peak can be seen as evidence that a Li-Si-based protective film was well formed using a lithium sulfate flux agent as a seed.

[0180] 17 and 18 are XPS analysis graphs showing the depth profiles of the positive electrode active materials of Examples 1 and 2, respectively. Referring to FIGS. 17 and 18, it can be understood that the S2p peak is formed only on the surface (0 sec etching) in the sky blue graph, which means that the sulfate-based flux agent seeds are only present on the surface. Also, the Si2p peak is formed in the sky blue and orange graphs, which means that the Si2p peak is formed even to a depth below the surface after 500 sec etching, which means that silicon-based components are distributed not only on the surface of the single crystal positive electrode active material but also near the surface.

[0181] For reference, the unit of the horizontal axis in FIGS. 16 to 18 is eV, and in FIGS. 17 and 18, sky blue is the XPS graph after etching for 0 seconds, maroon is the XPS graph after etching for 500 seconds, yellow is the XPS graph after etching for 1500 seconds, and light green is the XPS graph after etching for 3000 seconds.

[0182] Evaluation Example 7: Lithium ion diffusion rate and initial discharge capacity For Examples 4 and 5 using hydrophilic silica, the lithium ion diffusion rate and initial discharge capacity are measured in the same manner as in Evaluation Example 3. FIG. 19 is a graph showing the lithium ion diffusion rate at the time of initial charging for Comparative Example 1, Example 2, and Example 5, and FIG. 20 is a graph showing the initial discharge capacity for Comparative Example 1, Comparative Example 2, Example 1, Example 4, and Example 5. Referring to FIG. 19, it can be understood that in the case of Example 5, the lithium ion conductivity is improved and structural stability is ensured, as in Example 2. However, referring to FIG. 20, in terms of initial discharge capacity, Example 1 using hydrophobic silica was more superior to Example 4 using hydrophilic silica.

[0183] Evaluation example 8: SEM image analysis 21 and 22 show scanning electron microscope images of the positive electrode active materials prepared in Comparative Examples 1 and 2, respectively. When compared with the scanning electron microscope image of the positive electrode active material of Example 1 shown in FIG. 2, it can be seen that the single crystal particles in Example 1 grew larger than those in Comparative Examples 1 and 2.

[0184] Evaluation Example 9: Self-discharge evaluation related to Comparative Example 3 The batteries prepared in Example 2, Comparative Example 1, and Comparative Example 3 were charged at 25° C. with a constant current / constant voltage pattern of 0.1 C to an upper limit voltage of 4.25 V, and then a 0.05 C current cut-off was performed under a constant voltage condition, and the open circuit voltage (OCV) behavior was monitored for 3 hours to analyze the self-discharge behavior, and the results are shown in FIG. 23. Referring to FIG. 23, it can be seen that Example 2 has better self-discharge characteristics than Comparative Example 1 as well as Comparative Example 3, which uses only silica without a flux agent. This is understood to be because the surface of the single crystal is stabilized by using a sulfate-based flux agent and silica at the same time, and side reactions with the electrolyte are controlled, improving the self-discharge characteristics.

[0185] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0186] 100: Lithium secondary battery 112: Negative electrode 113: Separation membrane 114: Positive electrode 120:Battery container 140: Encapsulating material

Claims

1. A positive electrode active material for a lithium secondary battery, comprising a single crystal containing a lithium nickel-based composite oxide, and a coating portion containing S and Si and disposed on a surface of the single crystal, The coating portion further contains at least one element selected from Co and Zr, The coating portion is a positive electrode active material for a lithium secondary battery, the positive electrode active material including at least one of a sulfur-containing compound represented by the following Chemical Formula 1-1 and a silicon-containing compound represented by the following Chemical Formula 2-1: [Chemical formula 1-1] A a1 SO z1 -(CH 2 ) n1 CH 3 In the above chemical formula 1-1, A is an alkali metal, 0≦a1≦2, 0≦z1≦4, and 0≦n1≦5; [Chemical formula 2-1] A a2 Si x2 O z2 -(CH 2 ) n2 CH 3 In the above chemical formula 2-1, A is an alkali metal, and 0≦a2≦2, 1≦x2≦2, 0≦z2≦4, and 0≦n2≦5.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating portion further comprises a sulfur-containing compound represented by the following Chemical Formula 1 and a silicon-containing compound represented by the following Chemical Formula 2: [Chemical formula 1] A ａ１ SO ｚ１ In the above formula 1, A is an alkali metal, 0≦a1≦2, and 0≦z1≦4; [Chemical formula 2] A ａ２ Yes ｘ２ O ｚ２ In the above formula 2, A is an alkali metal, and 0≦a2≦5, 1≦x2≦2, and 0≦z2≦4.

3. The silicon-containing compound represented by Chemical Formula 2 is distributed on the surface of the single crystal, The positive electrode active material for a lithium secondary battery according to claim 2, wherein the single crystal exists in the form of islands having a thickness of 1 nm to 50 nm and / or exists in cracks inside the single crystal.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating portion further comprises a sulfur-silicon-containing compound represented by the following Chemical Formula 3: [Chemical formula 3] A ａ３ Yes ｘ３ S ｙ３ O ｚ３ In the above formula 3, A is an alkali metal, and 0≦a3≦5, 0<x3≦2, 0<y3≦5, and 0≦z3≦10.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating portion further comprises a sulfur-silicon-containing compound represented by the following Chemical Formula 3-1: [Chemical formula 3-1] A ａ３ Si ｘ３ S ｙ３ O ｚ３ -(CH ２ ) ｎ３ CH ３ In the above chemical formula 3-1, A is an alkali metal, and 0≦a3≦5, 0<x3≦2, 0<y3≦5, 0≦z3≦10, and 0≦n3≦5.

6. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the coating portion further comprises a P element.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating portion further comprises a phosphorus-containing compound represented by the following Chemical Formula 4: [Chemical formula 4] A ａ４ PO ｚ４ In the above formula 4, A is an alkali metal, and 0≦a4≦3 and 0≦z4≦4.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium nickel-based composite oxide is represented by the following chemical formula 11: [Chemical formula 11] Li ａ１１ Ni ｘ１１ M １ ｙ１１ M ２ １－ｘ１１－ｙ１１ O ２ In the above formula 11, 0.9≦a11≦1.8, 0.6≦x11≦1, 0≦y11≦0.4, and M １ and M. ２ are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

9. A precursor including a nickel-based transition metal hydroxide, a nickel-based transition metal oxide, or a combination thereof; a lithium source; a flux agent including an alkali metal sulfate; and silica are mixed and subjected to a first heat treatment; After the first heat treatment, the product is washed and then coated with cobalt and / or zirconium by adding a cobalt compound and / or a zirconium compound, and then subjected to a second heat treatment. A method for producing a positive electrode active material for a lithium secondary battery, comprising obtaining a positive electrode active material comprising a single crystal containing a lithium nickel-based composite oxide and a coating portion located on a surface of the single crystal and containing S and Si, the coating portion further containing at least one element selected from Co and Zr.

10. 100 moles of the transition metal containing nickel as a precursor are mixed with 100 to 130 moles of the lithium raw material, 0.1 to 10 moles of the flux agent, and 0.05 to 5 moles of silica. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9.

11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the first heat treatment is performed at 750°C to 900°C.

12. The silica is hydrophobic silica (hydrophobic SiO ２ 10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9,

13. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 9, further comprising mixing an alkali metal phosphate and carrying out a first heat treatment.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the second heat treatment is performed at 600°C to 780°C.

15. 10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the nickel-based transition metal oxide in the precursor is represented by the following Chemical Formula 21, and the nickel-based transition metal hydroxide is represented by the following Chemical Formula 31: [Chemical formula 21] Yes ｘ２１ M ２１ ｙ２１ M ２２ １－ｘ２１－ｙ２１ Oh ２ In the above formula 21, 0.6≦x21≦1, 0≦y21≦0.4, and M ２１ and M. ２２ are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof; [Chemical formula 31] Ni ｘ３１ M ３１ ｙ３１ M ３２ １－ｘ３１－ｙ３１ (OH) ２ In the above formula 31, 0.6≦x31≦1, 0≦y31≦0.4, and M ３１ and M. ３２ are each independently selected from the group consisting of Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

16. A positive electrode comprising the positive electrode active material according to claim 1. negative electrode, and an electrolyte.

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