Positive electrode active material for lithium secondary batteries, its preparation method, and lithium secondary batteries including the positive electrode active material.

Abstract

This invention provides a positive electrode active material for lithium secondary batteries, a method for preparing the same, and a lithium secondary battery comprising the positive electrode active material. The positive electrode active material for lithium secondary batteries comprises: lithium transition metal oxide particles; and a coating formed on the surface of the lithium transition metal oxide particles, wherein the coating comprises Li3PO4 and an oxide represented by the following chemical formula 1. The content of Li3PO4 in the coating is from 10 mol% to 60 mol%. [Chemical Formula 1] Li w Ti x (PO4)3-(Al2O3) y (0≤w,x≥4 / 3,y>0,0

Description

Technical Field

[0001] This invention relates to a positive electrode active material for lithium secondary batteries, a method for preparing the same, and a lithium secondary battery comprising the same positive electrode active material. More specifically, it relates to a lithium metal oxide series of positive electrode active materials, a method for preparing the same, and a lithium secondary battery comprising the same positive electrode active material. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops (PCs). In addition, in recent years, battery packs that include rechargeable batteries have been developed for use as power sources for environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Secondary batteries can be categorized into lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, so they are being actively developed and applied.

[0004] For example, a lithium secondary battery may include: an electrode assembly comprising a positive electrode, a negative electrode, and a separator; and an electrolyte impregnating the electrode assembly. The lithium secondary battery may also include an outer packaging material housing the electrode assembly and the electrolyte, such as a pouch-type outer packaging material.

[0005] Lithium metal oxides can be used as the positive electrode active material in the lithium secondary battery. When the lithium metal oxide is exposed to air or comes into contact with the electrolyte, lithium or nickel byproducts may be generated on the surface of the lithium metal oxide due to side reactions. Therefore, this may degrade the lifespan and operational stability of the lithium secondary battery.

[0006] In particular, lithium metal oxides containing high nickel content can generate a large number of lithium impurities (LiOH, Li₂CO₃, etc.) on the surface, which may degrade battery performance. During the water washing process to remove these lithium impurities, the specific surface area of ​​the positive electrode active material increases, potentially activating side reactions with the electrolyte. Therefore, this may reduce the stability of the surface structure of the active material. Summary of the Invention

[0007] (a) Technical problems to be solved One technical problem of the present invention is to provide a positive electrode active material for lithium secondary batteries with improved electrochemical and crystallization properties.

[0008] One technical problem of the present invention is to provide a method for preparing a positive electrode active material for lithium secondary batteries with improved electrochemical and crystallinity properties.

[0009] One technical problem of the present invention is to provide a lithium secondary battery including the positive electrode active material.

[0010] (II) Technical solution The positive electrode active material for a lithium secondary battery according to the present invention includes: lithium transition metal oxide particles; and a coating formed on the surface of the lithium transition metal oxide particles, and the coating includes Li3PO4 and an oxide represented by the following Chemical Formula 1. The content of Li3PO4 in the coating is 10 mol% to 60 mol%.

[0011] [Chemical Formula 1] Li w Ti x (PO4)3-(Al2O3) y (0≤w, x≥4 / 3, y>0, 0<x + y≤6 and 0.125≤y / x≤0.5) In some embodiments, the lithium transition metal oxide particles may include lithium transition metal oxide particles in the form of single particles.

[0012] In some embodiments, the content of Li3PO4 in the coating may be 10 mol% to 45 mol%.

[0013] In some embodiments, the oxide of Chemical Formula 1 may include a sodium superionic conductor (NASICON) structure.

[0014] In some embodiments, the total content of Al, Ti, and P in the oxide represented by the Chemical Formula 1 may be 5000 weight ppm (wtppm) or less.

[0015] In some embodiments, the average particle diameter (D50) of the particles of the positive electrode active material may be 2.9 μm to 4.0 μm.

[0016] In some embodiments, the span value of the particles of the positive electrode active material defined by the following Equation 1 may be 1.06 to 1.35.

[0017] [Equation 1] Span value = (D90 - D10) / D50 (In Equation 1, D10, D50, and D90 are the particle diameters at 10%, 50%, and 90% in the volume particle size distribution when measuring the volume particle size distribution of the positive electrode active material by the laser diffraction method (laser diffraction method, Microtrac company, S3500).)

[0018] In some embodiments, the residual lithium content on the surface of the positive electrode active material can be 9500 ppm by weight or less.

[0019] In some embodiments, the residual lithium content on the surface of the positive electrode active material can be 9000 ppm by weight or less.

[0020] In the method for preparing a positive electrode active material for a lithium secondary battery according to the present invention, a transition metal precursor, a lithium source, an Al source, a Ti source, and a P source are mixed to obtain a mixture. The mixture is heat-treated. The P source contains Li3PO4. The prepared positive electrode active material includes: lithium transition metal oxide particles; and a coating formed on the surface of the lithium transition metal oxide particles, and the coating contains Li3PO4 and an oxide represented by the following Chemical Formula 1.

[0021] [Chemical Formula 1] Li w Ti x (PO4)3-(Al2O3) y (0 ≤ w, x ≥ 4 / 3, y > 0, 0 < x + y ≤ 6, and 0.125 ≤ y / x ≤ 0.5).

[0022] In some embodiments, the molar ratio of the Al source, the Ti source, and the P source can be (1 to 4):(1 to 4):(2 to 3).

[0023] In some embodiments, at least one of the formation of the mixture and the heat treatment can be carried out by a dry method.

[0024] The lithium secondary battery according to the present invention includes: a positive electrode including the positive electrode active material for a lithium secondary battery described above; and a negative electrode disposed opposite to the positive electrode.

[0025] (III) Beneficial effects In the positive electrode active material according to the embodiment of the present invention, the amount of residual lithium can be reduced while increasing the ionic conductivity through the coating.

[0026] In the method for preparing a positive electrode active material according to the embodiment of the present invention, Li3PO4 can be used to effectively grow the crystal of the positive electrode active material and reduce the residual lithium content.

[0027] The positive electrode active material and lithium secondary battery of this invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. Furthermore, the positive electrode active material and lithium secondary battery of this invention can be used in eco-friendly electric vehicles and hybrid vehicles, which prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view showing the structure of a positive electrode active material for a lithium secondary battery according to an exemplary embodiment.

[0029] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0030] According to an embodiment of the present invention, a positive electrode active material 10 for lithium secondary batteries comprising lithium transition metal oxide particles 20 and a coating 30 is provided.

[0031] Furthermore, according to an embodiment of the present invention, a lithium secondary battery is provided, the lithium secondary battery comprising: a positive electrode, the positive electrode comprising a positive electrode active material 10 for a lithium secondary battery; and a negative electrode disposed opposite to the positive electrode.

[0032] The present invention will now be described in detail with reference to the accompanying drawings. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0033] Figure 1 This is a schematic cross-sectional view showing the structure of a positive electrode active material for a lithium secondary battery according to an exemplary embodiment.

[0034] Reference Figure 1 The positive electrode active material 10 for lithium secondary batteries (hereinafter referred to as positive electrode active material) comprises: lithium transition metal oxide particles 20; and a coating 30 formed on the surface of the lithium transition metal oxide particles 20.

[0035] The positive electrode active material 10 may contain lithium transition metal oxide particles 20 as the core.

[0036] In some embodiments, the lithium transition metal oxide particles 20 can be in single-particle form. Therefore, the mechanical and chemical stability of the positive electrode active material 10 can be improved. Thus, the lifetime and capacity characteristics of the positive electrode active material 10 can be improved simultaneously.

[0037] The term "single particle" as used in this invention is used to exclude the meaning of a secondary particle structure formed by the aggregation of multiple primary particles (e.g., more than 10, more than 20, more than 30, more than 40, or more than 50) together.

[0038] In some embodiments, the lithium transition metal oxide particles 20 may be in the form of granular or spherical single particles.

[0039] In some embodiments, the positive electrode active material 10 or lithium transition metal oxide particles 20 may contain a layered structure or a crystal structure represented by the following chemical formula 2.

[0040] [Chemical Formula 2] Li x Ni a M b O 2+z In chemical formula 2, the values ​​can be 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, and -0.5≤z≤0.1. M can contain Co, Mn, and / or Al.

[0041] The chemical structure represented by Formula 2 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material 10 or lithium transition metal oxide particles 20, and does not exclude other additional elements. For example, M may contain Co, Mn, and / or Al, and Co, Mn, and / or Al may be provided together with Ni as the main active elements of the positive electrode active material 10. Formula 2 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 2 includes the introduction and substitution of additional elements.

[0042] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material 10 or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure to form a bond, and this should be understood to also include the chemical structures represented by Formula 2.

[0043] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0044] For example, the positive electrode active material 10 or lithium transition metal oxide particles 20 may contain a layered structure or a crystal structure represented by the following chemical formula 2-1.

[0045] [Chemical Formula 2-1] Li x Ni a M1 b1 M2 b2 O 2+z In Chemical Formula 2-1, M1 may include Co, Mn, and / or Al. M2 may include the above auxiliary elements. In Chemical Formula 2-1, 0.9 ≤ x1 ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.5, and -0.5 ≤ z ≤ 0.1.

[0046] In some embodiments, the positive electrode active material 10 may further include a doping element or a coating element. For example, an element substantially the same as or similar to the above auxiliary element may be used as the doping element or the coating element. For example, one or a combination of two or more of the above elements may be used as the doping element or the coating element.

[0047] The doping element or the coating element may be present on the surface of the lithium transition metal oxide particles, or may penetrate through the surface of the lithium transition metal oxide particles and be included in the bonding structure represented by Chemical Formula 2 or Chemical Formula 2-1.

[0048] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0049] The content of Ni in the NCM-based lithium oxide (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) may be 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more. In some embodiments, the content of Ni in the NCM-based lithium oxide may be 80 mol% to 98 mol%, 82 mol% to 98 mol%, 83 mol% to 98 mol%, 84 mol% to 98 mol%, 85 mol% to 98 mol%, 88 mol% to 98 mol%, or 90 mol% to 98 mol%.

[0050] According to an exemplary embodiment, the coating 30 may include Li3PO4 and an oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Li w Ti x (PO4)3-(Al2O3) y (0 ≤ w, x ≥ 4 / 3, y > 0, 0 < x + y ≤ 6, and 0.125 ≤ y / x ≤ 0.5).

[0051] In some embodiments, in Chemical Formula 1, w can be 0 < w ≤ 10, 2 ≤ w ≤ 10, 3 ≤ w ≤ 10, 5 ≤ w ≤ 10, 6 ≤ w ≤ 10, 2 ≤ w ≤ 9, 3 ≤ w ≤ 9, 5 ≤ w ≤ 9, or 6 ≤ w ≤ 9.

[0052] Compared with when forming particles in the form of secondary particles, higher sintering temperature conditions are required to synthesize single particles, because the high sintering temperature may cause problems with residual lithium. Residual lithium may trigger various side reactions such as electrolyte decomposition, thereby reducing battery performance.

[0053] The positive electrode active material 10 according to an exemplary embodiment includes a coating 30 containing Ti, Al, and P elements. Therefore, even through sintering at low temperature, enhanced particle growth can be induced, thereby obtaining a positive electrode active material 10 with reduced residual lithium.

[0054] In one embodiment, the oxide of Chemical Formula 1 may have a sodium superionic conductor structure. In this case, residual lithium can be stored in the coating 30, and the residual lithium can be further reduced.

[0055] According to an embodiment of the present invention, Li3PO4 is included in the coating 30, thereby simultaneously improving the thermal stability and ionic conductivity of the positive electrode active material 10.

[0056] When Li w Ti x (PO4)3 is partially replaced by Al2O3, in order to achieve electrical neutrality, Al 4+ having a lower oxidation number than Ti 3+ can provide positions for lithium to occupy. Therefore, compared with Li w Ti x (PO4)3, Li w Ti x (PO4)3 - Al2O3 has further improved ionic conductivity and can increase the amount of lithium that can be accommodated. Therefore, the amount of residual lithium on the surface of the positive electrode active material 10 can be reduced.

[0057] According to an exemplary embodiment, the content of Li3PO4 in the coating 30 (for example, in the total molar number of the compounds contained in the coating 30, or in the total molar number of the oxide of Chemical Formula 1 and Li3PO4) can be 10 mol% to 60 mol%.

[0058] In some embodiments, the content of Li3PO4 in the coating 30 can be 10 mol% to 45 mol%.

[0059] In some embodiments, the content of Li3PO4 in the coating 30 can be 14 mol% to 35 mol% or 20 mol% to 30 mol%.

[0060] Within the aforementioned range, Li3PO4 can fill the spaces between pores to facilitate mass transfer for crystal growth. Furthermore, even at lower temperatures, the particle size of the positive electrode active material 10 can be effectively increased.

[0061] In addition, it can more effectively reduce residual lithium on the surface of the positive electrode active material 10 and improve the capacity retention rate of lithium secondary batteries.

[0062] For example, when the Li3PO4 content in coating 30 is greater than 60 mol%, it may hinder lithium storage in coating 30 during the sintering process of positive electrode active material 10, thereby increasing residual lithium. Therefore, this may lead to various side reactions, thus reducing the performance of the lithium secondary battery.

[0063] For example, when the Li3PO4 content in coating 30 is less than 10 mol%, the pores of the positive electrode active material 10 may not be sufficiently filled by Li3PO4. Therefore, the particle growth of the positive electrode active material 10 may be delayed. Furthermore, the reduced lithium capacity may lead to a decrease in the ionic conductivity of the secondary battery.

[0064] According to an exemplary embodiment, the oxide of Formula 1 may include a sodium superionic conductor structure. Therefore, oxygen stabilization can be achieved in the positive electrode active material 10, and both thermal stability and ionic conductivity can be improved simultaneously.

[0065] According to an exemplary embodiment, the total content of Al, Ti and P in the oxide represented by chemical formula 1 can be less than 5000 ppm by weight, less than 4000 ppm by weight, less than 3600 ppm by weight, or less than 3200 ppm by weight.

[0066] Within the aforementioned range, the amount of residual lithium can be reduced, and the capacity retention rate of the secondary battery can be further increased.

[0067] According to an exemplary embodiment, the average particle size (D50) of the positive electrode active material 10 can be 2.9 μm to 4.0 μm, 2.95 μm to 3.6 μm, or 3.0 μm to 3.55 μm.

[0068] Within the aforementioned range, the structural stability of the positive electrode active material 10 can be increased, and the power and capacity of the secondary battery can be improved.

[0069] According to an exemplary embodiment, the span value of the positive electrode active material 10, as defined by the following formula 1, can be from 1.06 to 1.35.

[0070] [Formula 1] Span value = (D90 - D10) / D50 In Formula 1, D10, D50, and D90 are the particle diameters at 10%, 50%, and 90% in the volume particle size distribution when measuring the volume particle size distribution of the positive electrode active material 10 using the laser diffraction method (Microtrac Inc., S3500).

[0071] In some embodiments, the span value defined by the following Formula 1 of the positive electrode active material 10 particles can be 1.06 to 1.25 or 1.06 to 1.20.

[0072] According to an exemplary embodiment, the residual lithium content on the surface of the positive electrode active material 10 can be 9500 ppm by weight or less, 9000 ppm by weight or less, 8800 ppm by weight or less, 8700 ppm by weight or less, or 8600 ppm by weight or less.

[0073] Within the above range, side reactions between the residual lithium and the surface of the positive electrode active material 10 can be effectively suppressed, and the performance of the lithium secondary battery can be stably maintained.

[0074] In the method for preparing the positive electrode active material 10 for a secondary battery according to an exemplary embodiment, a transition metal precursor, a lithium source, an Al source, a Ti source, and a P source can be mixed to form a mixture. The mixture can be heat-treated. The P source can include Li3PO4. The formed positive electrode active material 10 can include: lithium transition metal oxide particles 20; and a coating 30, the coating 30 being formed on the surface of the lithium transition metal oxide particles 20, and the coating 30 including Li3PO4 and an oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Li w Ti x (PO4)3-(Al2O3) y (0 ≤ w, x ≥ 4 / 3, y > 0, 0 < x + y ≤ 6, and 0.125 ≤ y / x ≤ 0.5).

[0075] According to an exemplary embodiment, an active material metal salt can be prepared. The active material metal salt can include a nickel salt. The active material metal salt can include a nickel salt, a manganese salt, and a cobalt salt.

[0076] Examples of the nickel salt can include nickel sulfate (NiSO4), nickel hydroxide (Ni(OH)2), nickel nitrate (Ni(NO3)2), nickel acetate (Ni(CH3CO2)2), their hydrates, and the like.

[0077] Examples of manganese salts include manganese sulfate (MnSO4), manganese hydroxide (Mn(OH)2), manganese nitrate (Mn(NO3)2), manganese acetate (Mn(CH3CO2)2), and their hydrates.

[0078] Examples of cobalt salts include cobalt sulfate (CoSO4), cobalt hydroxide (Co(OH)2), cobalt nitrate (Co(NO3)2), cobalt carbonate (CoCO3), and their hydrates.

[0079] In one embodiment, nickel sulfate, manganese sulfate, and cobalt sulfate can be used as nickel salts, manganese salts, and cobalt salts, respectively.

[0080] In some embodiments, a salt, hydroxide, or oxide of at least one of B, Al, Si, Ti, V, Fe, Cu, Zn, Zr, Mo, and W may also be used simultaneously.

[0081] According to an exemplary embodiment, the above-mentioned active metal salts are mixed, for example, by a co-precipitation reaction, to obtain a transition metal precursor. For example, the transition metal precursor can be prepared in the form of nickel manganese cobalt hydroxide.

[0082] To facilitate the co-precipitation reaction described above, a precipitating agent and / or a chelating agent can be used. The precipitating agent may contain alkaline compounds such as sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃). The chelating agent may contain, for example, ammonia or ammonium carbonate.

[0083] The transition metal precursor, lithium source, Al source, Ti source and P source can be mixed to obtain a mixture.

[0084] The lithium source can be lithium carbonate (Li₂CO₃), lithium nitrate (LiNO₃), lithium acetate (CH₃COOLi), lithium oxide (Li₂O), lithium hydroxide (LiOH), etc. These can be used alone or in combination of two or more. In one embodiment, the lithium source can be lithium hydroxide.

[0085] In some implementations, the Ti source may include TiO2, Ti(C4H9O)4, TiO, TiAlN, TiC, Ti, etc. They can be used alone or in combination of two or more.

[0086] In some implementations, the Al source may include Al2O3, Al(OH)3, Al(NO3)3, etc. They can be used alone or in combination of two or more.

[0087] In some implementations, the P source may include Li3PO4.

[0088] Li3PO4 can act as a sintering agent that affects the synthesis and growth of the oxide of Chemical Formula 1. When using Li3PO4 for sintering LATP[Li w Ti x (PO4)3-(Al2O3) y (0 ≤ w, x ≥ 4 / 3, y > 0, 0 < x + y ≤ 6 and 0.125 ≤ y / x ≤ 0.5)], during the sintering process, it may promote the heat conduction and crystal growth between the lithium transition metal oxide particles 20 and the coating 30. In addition, Li3PO4 can be included as a separate component of the coating 30 on the surface of the lithium transition metal oxide particles 20.

[0089] In addition, within the sintering temperature range of the positive electrode, Li3PO4 can be used as a P source for the coating 30 of the positive electrode active material 10. In addition, Li3PO4 can fill the spaces between pores, thereby promoting the mass transfer for crystal growth. Thus, particle growth can be induced even at a lower temperature.

[0090] Therefore, by using Li3PO4 in the sintering process for coating LATP[Li w Ti x (PO4)3-(Al2O3) y (0 ≤ w, x ≥ 4 / 3, y > 0, 0 < x + y ≤ 6 and 0.125 ≤ y / x ≤ 0.5)], the formation of the coating 30 with a sodium superionic conductor structure having improved ionic conductivity and the growth of single particles can be promoted.

[0091] In some embodiments, the P source may further include NH4H2PO4 (DAP), H3PO4, etc.

[0092] According to an exemplary embodiment, the transition metal precursor can be mixed with the lithium source, Al source, Ti source, and P source, and then the positive electrode active material can be prepared by a sintering process. For example, the sintering temperature can be 600°C to 900°C, 700°C to 880°C, or 750°C to 870°C. For example, the sintering time can be 8 hours to 25 hours, 10 hours to 20 hours, or 10 hours to 18 hours.

[0093] According to an exemplary embodiment, the molar ratio of the Al source, the Ti source, and the P source can be (1 to 4):(1 to 4):(2 to 3).

[0094] According to an exemplary embodiment, at least one of the formation of the mixture and the heat treatment can be performed by a dry process.

[0095] Figure 2 and Figure 3These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment.

[0096] The positive electrode 100 includes a positive electrode current collector 105 and a positive electrode active material layer 110 disposed on at least one side of the positive electrode current collector 105.

[0097] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also contain aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector 105 may be, for example, from 10 μm to 50 μm, but is not particularly limited thereto.

[0098] The positive electrode active material layer 110 can also be disposed on both sides (the top and bottom surfaces in the thickness direction) of the positive electrode current collector 105.

[0099] The positive electrode active material layer 110 may contain the positive electrode active material 10 according to the above-described embodiments of the present invention. The positive electrode active material 10 may contain the above-described lithium transition metal oxide.

[0100] In addition to the lithium transition metal oxide, the positive electrode active material layer 110 may further contain other positive electrode active materials. For example, the positive electrode active material 10 may further contain lithium cobalt oxide-based active materials, lithium manganese oxide-based active materials, or lithium iron phosphate (LFP)-based active materials (e.g., LiFePO4), and may also further contain lithium transition metal oxides that do not have a single-particle structure (e.g., a secondary particle structure).

[0101] The positive electrode active material layer 110 may further comprise a conductive material. The conductive material can compensate for the reduced conductivity of the positive electrode active material layer due to the adhesive.

[0102] The conductive material may include, for example, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. For example, the conductive material may include carbon nanotubes.

[0103] The content of the conductive material in the total weight of the positive electrode active material layer 110 can be from 0.01% by weight to 3% by weight. In some embodiments, the content of the conductive material in the total weight of the positive electrode active material layer can be from 0.1% by weight to 1% by weight.

[0104] The positive electrode active material layer may further include an adhesive. The adhesive can increase the adhesion between the positive electrode active material 10 and the conductive material, and also increase the adhesion between the positive electrode active material layer 110 and the positive electrode current collector 105.

[0105] The adhesive may include organic adhesives such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate; or water-based adhesives such as styrene-butadiene rubber (SBR). The adhesive may be used in conjunction with thickeners such as carboxymethyl cellulose (CMC).

[0106] For example, a PVDF-based adhesive can be used as the binder for forming the positive electrode. In this case, the amount of binder used to form the positive electrode active material layer 110 can be reduced, while the amount of positive electrode active material 10 can be relatively increased. As a result, the power and capacity of the secondary battery can be improved.

[0107] The adhesive content can be from 0.5% to 5% of the total weight of the positive electrode active material layer. In some embodiments, the adhesive content can be from 1% to 3% of the total weight of the positive electrode active material layer 110.

[0108] The positive electrode active material layer 110 may further contain thickeners and / or dispersants. For example, the positive electrode active material layer 110 may contain thickeners such as carboxymethyl cellulose (CMC).

[0109] The positive electrode active material layer 110 can be formed from a positive electrode slurry composition comprising positive electrode active material 10 and a binder. For example, a positive electrode slurry composition comprising positive electrode active material 10 and a binder can be coated on the surface of the positive electrode current collector 105 and then dried and calendered to form the positive electrode active material layer 110.

[0110] According to an exemplary embodiment, the positive electrode slurry may further comprise a solvent. As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc., may be used.

[0111] The coating of the positive electrode slurry can be carried out by gravure coating, slot extrusion coating, multi-layer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc., but is not limited to these methods.

[0112] According to an exemplary embodiment, the thickness of the positive electrode active material layer can be, for example, from 5 μm to 200 μm, but is not particularly limited.

[0113] According to some embodiments, the positive electrode active material layer may include two or more layers comprising different positive electrode active materials, conductive materials, and / or binders. For example, the positive electrode active material layer 110 may include a first positive electrode active material layer and a second positive electrode active material layer. The types and / or contents of the active materials, conductive materials, and / or binders in the first positive electrode active material layer may differ from those in the second positive electrode active material layer.

[0114] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, wherein the negative electrode active material layer 120 is formed by coating the negative electrode current collector 125 with a negative electrode active material.

[0115] The negative electrode active material can be any material known in the art that enables lithium ion insertion and extraction without particular restriction. For example, the negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon or tin, etc.

[0116] Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) sintered below 1500°C, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0117] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, preferably copper or copper alloys.

[0118] In some embodiments, the negative electrode active material can be mixed and stirred in a solvent with a binder, conductive material, and / or dispersant to prepare a slurry. The slurry is then coated onto at least one side of the negative electrode current collector 125, followed by drying and calendering to manufacture the negative electrode 130.

[0119] The adhesive and the conductive material may be substantially the same as or similar to the substances used in the positive electrode active material layer 110. In some embodiments, for example, for compatibility with carbon-based active materials, the adhesive used to form the negative electrode may include a water-based adhesive such as styrene-butadiene rubber (SBR) and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0120] The separator 140 can be located between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also include a nonwoven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0121] In some embodiments, the area (e.g., the area in contact with the separator 140) and / or volume of the negative electrode 130 can be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 130 without being deposited in the middle.

[0122] According to an exemplary embodiment, the battery cell can be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, stacking, folding, etc. of the separator 140.

[0123] The electrode assembly 150 can be housed together with the electrolyte in the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0124] Non-aqueous electrolytes may contain lithium salts and organic solvents, the lithium salts being, for example, derived from Li. + X - Indicated. The anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 -(CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - (CF3CF2SO2)2N - wait.

[0125] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in combination of two or more.

[0126] like Figure 2 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one end of the housing 160. The tabs can be fused to said end of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0127] Although Figure 2 The diagram shows the positive electrode lead 107 and the negative electrode lead 127 protruding from the upper side of the housing 160 in the planar direction, but the position of the electrode leads is not limited to this. For example, the electrode leads may also protrude from at least one of the two sides of the housing 160, or from the lower side of the housing 160. Alternatively, the positive electrode lead 107 and the negative electrode lead 127 may be formed to protrude from different sides of the housing 160, respectively.

[0128] The lithium secondary battery can be manufactured in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0129] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0130] Example 1 (1) Preparation of positive electrode active material With 1 mole of Ni 0.88 Co 0.09 Mn 0.03 Based on (OH)₂, 1.01 mol of LiOH·H₂O, 0.2 mol% (0.002 mol) of Al₂O₃, 0.2 mol% (0.002 mol) of TiO₂, and 0.3 mol% (0.003 mol) of Li₃PO₄ were added to a dry high-speed mixer and mixed uniformly for 20 minutes. The mixture was then added to a sintering furnace and heated to 850°C at a rate of 2°C / min, and held at this temperature for 4 hours for a first heat treatment. Subsequently, the temperature was lowered to 720°C and held for 12 hours for a second heat treatment.

[0131] During the heating and holding at the stated temperature, oxygen was continuously introduced at a flow rate of 10 mL / min. After sintering was terminated, the material was allowed to cool naturally to room temperature, and then pulverized and graded to prepare a positive electrode active material comprising a coating represented by Li9Ti2(PO4)3-(Al2O3).

[0132] Examples 2 to 10 The positive electrode active material was prepared using the same method as in Example 1, except that Li3PO4 and (NH4)2HPO4 (DAP) were used as the P source, and the composition of the Al source, Ti source, P source, reactor temperature, and Li were adjusted accordingly. w Ti x (PO4)3-(Al2O3) y The composition adjustment is shown in Table 1.

[0133] Comparative Examples 1 to 11 The positive electrode active material was prepared by the same method as in Example 1, except that Li3PO4 and (NH4)2HPO4 (DAP) were used as the P source, and the composition of the Al source, Ti source, P source and the reactor temperature were adjusted as shown in Table 1.

[0134] [Table 1] Manufacturing of lithium secondary batteries The positive electrode active material, carbon black as a conductive material, and PVDF as a binder were mixed in a weight ratio of 93:5:2 and dispersed in N-methyl-2-pyrrolidone to prepare a slurry. The slurry was coated on one side of an aluminum current collector (20 μm thick) and then dried and rolled to manufacture the positive electrode.

[0135] As the negative electrode, 1.2T of lithium metal is used.

[0136] The positive and negative electrodes are notched to predetermined sizes and stacked, and a separator (polyethylene, 13µm thick) is placed between the positive and negative electrodes. Then, an electrolyte is injected to manufacture the 2016 coin-shaped battery.

[0137] The electrolyte used is a 1M LiPF6 solution containing a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a 1:1 volume ratio.

[0138] Experimental Example (1) Evaluation of positive electrode active material 1) Measurement of the weight ppm of Al, Ti, and P in the coating Take 0.015 g of the positive electrode active material particles from the examples and comparative examples, respectively, and dissolve the particles using 0.1 M hydrochloric acid aqueous solution and 0.1 M hydrogen peroxide. Then, heat the dissolved sample to remove chlorine and hydrogen peroxide, cool the sample to room temperature, and dilute it with ultrapure water.

[0139] The total weight of the transition metal and the individual weights of Al, Ti, and P contained in the metal coating were measured using an inductively coupled plasma emission spectrometer (SPS3000, SII Nanotechnology Co., Ltd.) on the diluted sample.

[0140] The weight ppm of Al, Ti, and P in the positive electrode active material coating is shown in Table 2 below.

[0141] 2) Measurement of particle size and particle size distribution parameters The volumetric particle size distribution of the positive electrode active material was measured using laser diffraction (MT 3000, Macchiato Corporation). The D10, D50, and D90 of the positive electrode active material were calculated based on the particle size at the 10%, 50%, and 90% positions of the volumetric particle size distribution, and the results are shown in Table 2 below.

[0142] [Table 2] (2) Evaluation of secondary batteries 1) Measurement of residual lithium 2.5 g of the positive electrode active material powder from the examples and comparative examples and 100 g of ultrapure water were added to a 100 ml beaker and stirred for 10 minutes. After stirring, the positive electrode active material powder was filtered, and 0.1 mol / L hydrochloric acid was added dropwise to 60 g of the remaining filtrate. The pH of the filtrate was measured using a pH meter at 25°C. The titration volume of hydrochloric acid at pH 8.3 ± 0.1 was set as A ml, and the titration volume of hydrochloric acid at pH 4.5 ± 0.1 was set as B ml. The concentrations of residual Li₂CO₃ and LiOH in the positive electrode active material were calculated using the following formula.

[0143] The concentration of Li₂CO₃ (wt%) = {0.1 × (BA) / 1000} × {73.882 / (20 × 60 / 100)} × 100 The concentration of LiOH (weight %) = {0.1 × (2A - B) / 1000} × {23.941 / (20 × 60 / 100)} × 100 2) Evaluation of C-rate The rate characteristics of the lithium secondary batteries manufactured according to the above embodiments and comparative examples were measured by repeatedly charging (CC-CV 0.5C 4.3V 0.05C cut-off) and discharging (CC 0.5C 3.0V cut-off) in a chamber at 25°C.

[0144] Specifically, two 0.1C charge and 0.1C discharge cycles were performed, and the 0.1C discharge capacity was measured. One 0.5C charge and 4C discharge cycle was performed, and the 4C discharge capacity was measured.

[0145] The rate capability is calculated by dividing the 4C discharge capacity by the 0.1C discharge capacity and then multiplying by 100.

[0146] The results of residual lithium measurement and rate performance evaluation are shown in Table 3 below.

[0147] [Table 3] Referring to Table 2, the particle growth of the positive electrode active material according to the embodiments is improved.

[0148] Referring to Table 3, the residual lithium in the secondary battery according to the embodiment is reduced. Furthermore, in the secondary battery according to the embodiment, the capacity at 4C relative to the 0.1C capacity is increased.

[0149] In Comparative Example 1, which does not include the Li3PO4 coating, particle growth proceeds slowly because the Li3PO4 cannot adequately fill the pores of the positive electrode active material.

[0150] In Comparative Examples 5, 10, and 11, which have a higher Li3PO4 content than the coating, although particle growth is fully achieved due to the presence of Li3PO4, the ionic conductivity is reduced.

[0151] In Comparative Example 3 or Comparative Example 4, where only Ti or Al was used as the coating source, D50 was relatively reduced and residual lithium was increased.

[0152] The above description is merely an example of applying the principles of this invention, and other configurations may be further included without departing from the scope of this invention.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: Lithium transition metal oxide particles; and A coating formed on the surface of the lithium transition metal oxide particles, and the coating contains Li3PO4 and an oxide represented by the following Chemical Formula 1, in, The content of Li3PO4 in the coating is 10 mol% to 60 mol%: [Chemical Formula 1] Yes w Of x (PO4)3-(Al2O3) y 0≤w, x≥4 / 3, y>0, 0<x + y≤6 and 0.125≤y / x≤0.

5.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium transition metal oxide particles include lithium transition metal oxide particles in the form of single particles.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The content of Li3PO4 in the coating is 10 mol% to 45 mol%.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The oxide of Chemical Formula 1 includes a sodium superionic conductor structure.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The total content of Al, Ti and P in the oxide represented by the Chemical Formula 1 is 5000 ppm by weight or less.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The average particle size D50 of the particles of the positive electrode active material is 2.9 μm to 4.0 μm.

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The span value of the particles of the positive electrode active material defined by the following Formula 1 is 1.06 to 1.35: [Formula 1] Span value = (D90 - D10) / D50 In Formula 1, D10, D50 and D90 are the particle diameters at 10%, 50% and 90% in the volume particle size distribution when measuring the volume particle size distribution of the positive electrode active material by the laser diffraction method, respectively.

8. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The residual lithium content on the surface of the positive electrode active material is 9500 ppm by weight or less.

9. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The residual lithium content on the surface of the positive electrode active material is 9000 ppm by weight or less.

10. A method for preparing a positive electrode active material for a lithium secondary battery, comprising the following steps: Mixing a transition metal precursor, a lithium source, an Al source, a Ti source and a P source to obtain a mixture; and Performing heat treatment on the mixture, wherein the P source contains Li3PO4, The prepared positive electrode active material contains: Lithium transition metal oxide particles; and A coating formed on the surface of the lithium transition metal oxide particles, and the coating contains Li3PO4 and an oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Yes w Of x (PO4)3-(Al2O3) y 0≤w, x≥4 / 3, y>0, 0<x + y≤6 and 0.125≤y / x≤0.

5.

11. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 10, wherein, The molar ratio of the Al source, the Ti source and the P source is (1 to 4):(1 to 4):(2 to 3).

12. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 10, wherein, At least one of the step of obtaining the mixture and the step of performing the heat treatment is carried out by a dry method.

13. A lithium secondary battery, comprising: A positive electrode, the positive electrode containing the positive electrode active material for a lithium secondary battery according to claim 1; And A negative electrode, the negative electrode being disposed opposite to the positive electrode.

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