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

Abstract

The positive electrode active material according to embodiments of the present disclosure comprises: a lithium metal oxide particle; and a conductive coating partially covering the surface of the lithium metal oxide particle and including a plurality of conductive particles. The conductive coating includes a first pattern having an island shape and a second pattern having a chain shape. According to embodiments of the present disclosure, the positive electrode active material can be formed by stirring lithium metal oxide particles and conductive particles with a resonance mixer. According to embodiments of the present disclosure, a lithium secondary battery including the above-described positive electrode active material can be provided.

Description

Cathode active material, lithium secondary battery containing same, and method for producing the cathode active material

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

[0002] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are actively being researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] Secondary batteries may further include a liquid electrolyte. For example, an electrode assembly may be manufactured by interposing a separator between the positive and negative electrodes, and the electrode assembly may be housed in an outer case. A liquid electrolyte may be injected into the outer case to impregnate the positive and negative electrodes.

[0005] Additionally, the secondary battery may include a solid electrolyte. The solid electrolyte may be used in place of the liquid electrolyte described above. For example, the electrode assembly may include a positive electrode, a negative electrode, and an intermediate electrolyte layer. Additionally, the solid electrolyte may be included in either the positive electrode or the negative electrode.

[0006] One object of the present disclosure is to provide a cathode active material with improved electrochemical properties.

[0007] One object of the present disclosure is to provide a method for manufacturing a cathode active material with improved electrochemical properties.

[0008] An object of the present disclosure is to provide a lithium secondary battery.

[0009] According to embodiments of the present disclosure, the positive electrode active material may include lithium metal oxide particles and a conductive coating that partially covers the surfaces of the lithium metal oxide particles and includes a plurality of conductive particles. The conductive coating may include a first pattern having an island shape and a second pattern having a chain shape.

[0010] In some embodiments, the diameter of the first pattern may be greater than or equal to 0.03 μm and less than or equal to 1.0 μm.

[0011] In some embodiments, the length of the second pattern may be 1.0 μm to 10.0 μm.

[0012] In some embodiments, the conductive coating may further include a third pattern having a web shape formed by connecting a plurality of the second patterns.

[0013] In some embodiments, the content of the conductive coating may be 0.1 part by weight to 1 part by weight per 100 parts by weight of the lithium metal oxide particles.

[0014] In some embodiments, the conductive particles may include at least one of carbon black and carbon nanotubes.

[0015] In some embodiments, the conductive coating may cover less than 70% of the surface of the lithium metal oxide particle.

[0016] In some embodiments, the average particle diameter (D) of the lithium metal oxide particles 50 ) can be 1㎛ to 15㎛.

[0017] According to embodiments of the present disclosure, a lithium secondary battery may include a positive electrode including a positive electrode active material according to the embodiments described above and a negative electrode opposite to the positive electrode.

[0018] In some embodiments, the positive electrode may further comprise a solid electrolyte.

[0019] In the method for manufacturing a positive electrode active material according to embodiments of the present disclosure, a mixture of lithium metal oxide particles and conductive particles can be manufactured. The mixture can be stirred using a resonance mixer. The content of the conductive particles in the mixture can be 0.1 to 1 part by weight based on 100 parts by weight of the lithium metal oxide particles.

[0020] In some embodiments, the conductive particles may be coated on the surface of the lithium metal oxide particles by stirring the mixture with a resonance mixer.

[0021] In some embodiments, the conductive particle may partially cover the surface of the lithium metal oxide particle.

[0022] In some embodiments, some of the conductive particles may be aggregated together in an island shape, and other some of the conductive particles may be connected to each other in a chain shape.

[0023] In some embodiments, the conductive particles may include at least one of carbon black and carbon nanotubes.

[0024] In some embodiments, the specific surface area of ​​the carbon black is 65 m 2 / g to 120m 2 / g may be.

[0025] In some embodiments, the specific surface area of ​​the carbon nanotube is 250 m 2 / g to 700m 2 / g may be.

[0026] In some embodiments, the resonant mixer may be an acoustic resonant mixer.

[0027] In some embodiments, the mixture may be stirred at a frequency of 58 Hz to 62 Hz.

[0028] In some embodiments, the mixture may be stirred at an acceleration greater than 40 G and less than 75 G.

[0029] According to embodiments of the present disclosure, the positive electrode active material may include a conductive coating having an island shape and a chain shape. The stability, lithium ion conductivity, and electronic conductivity of the positive electrode active material may be improved. A lithium secondary battery having high output and high energy density may be provided.

[0030] According to embodiments of the present disclosure, a conductive material can be coated onto lithium metal oxide particles using an acoustic resonance mixer. The conductive material partially covers the lithium metal oxide particles, and the contact between the lithium metal oxide particles and the solid electrolyte can also be increased. Accordingly, the electronic conductivity and lithium ion conductivity of the positive electrode active material can be improved simultaneously.

[0031] FIG. 1 and FIG. 2 are schematic drawings showing positive electrode active materials according to exemplary embodiments, respectively.

[0032] Figure 3 is a process flow diagram illustrating a method for manufacturing a positive electrode active material according to exemplary embodiments.

[0033] Figures 4 to 7 are SEM images of some of the positive electrode active materials manufactured sequentially in Examples 1 to 4.

[0034] Figures 8 and 9 are SEM images of a portion of the surface of the positive electrode active material manufactured in Comparative Example 1 and Comparative Example 2, respectively.

[0035] Figures 10 and 11 are SEM images of a portion of the surface of the positive electrode active material manufactured in Comparative Example 4.

[0036] Figure 12 is an SEM image of a portion of the surface of the positive electrode active material manufactured in Comparative Example 5.

[0037] According to embodiments of the present disclosure, a positive electrode active material including a lithium metal oxide and a lithium secondary battery including the same are provided.

[0038] According to embodiments of the present disclosure, a method for manufacturing a positive electrode active material is provided.

[0039] Lithium secondary batteries according to embodiments of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, lithium secondary batteries according to embodiments of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0040] Hereinafter, the present disclosure will be described in detail with reference to the drawings. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0041] Figure 1 is a schematic diagram showing a positive electrode active material according to exemplary embodiments.

[0042] Referring to FIG. 1, the positive electrode active material (50) may include a core particle (10) and a conductive coating covering the surface of the core particle (10).

[0043] The core particle (10) can reversibly intercalate and deintercalate lithium ions and provide positive electrode activity. For example, the core particle (10) may include lithium metal oxide particles.

[0044] The core particle (10) may include one or more compounds selected from lithium iron phosphate compounds, lithium cobalt oxides, lithium manganese oxides, lithium nickel oxides, or lithium composite oxides. For example, the core particle (10) may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); LiV3O8, LiFe3O4, V2O 5　 It may include vanadium oxides such as Cu2VO7, lithium iron phosphate oxides such as LiFePO4, etc.

[0045] In some embodiments, the core particle (10) may include a compound represented by the following chemical formula 1.

[0046] [Chemical Formula 1]

[0047] Li a Ni b M 1-b O2

[0048] In chemical formula 1, 0.95≤a≤1.08, b≥0.5, and M may be at least one element among Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0049] In one embodiment, the core particle (10) includes nickel (Ni) and may further include at least one of cobalt (Co) or manganese (Mn). For example, a nickel-cobalt-manganese (NCM) based lithium oxide may be used as the positive electrode active material.

[0050] For example, nickel (Ni) can be provided as a metal associated with the capacity of lithium secondary batteries. While a higher nickel content can improve the capacity and output of a lithium secondary battery, excessive nickel content can shorten its lifespan and compromise mechanical and electrical stability.

[0051] In one embodiment, the conductivity or resistance of a lithium secondary battery can be improved by cobalt (Co), and the mechanical and electrical stability of a lithium secondary battery can be improved by manganese (Mn).

[0052] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the lattice structure or crystal structure of the core particle (10) and does not exclude other additional elements. For example, M may be provided as the main active element of the core particle (10). Chemical Formula 1 is provided to express the bonding relationship of the main active element and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0053] In one embodiment, in addition to the main active element, auxiliary elements may be further included to enhance the chemical stability of the core particle (10) or the crystal structure. The auxiliary elements may be incorporated into the crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0054] In some embodiments, the core particle (10) may have a single particle form, or may have a secondary particle form in which a plurality of primary particles are assembled.

[0055] The conductive coating may include conductive particles. For example, the conductive particles may be attached to the surface of the core particle (10) to form a conductive coating.

[0056] A conductive coating may be formed on the surface of the core particle (10) to provide an additional electron transfer path. Therefore, for example, electrons transferred from the electrode current collector can smoothly move through the positive electrode active material (50). In addition, an increase in interfacial resistance due to contact between core particles can be prevented.

[0057] In one embodiment, the electronic conductivity of the positive electrode active material layer can be increased even when the conductive material content within the positive electrode active material layer is reduced by the conductive coating. Therefore, the amount of conductive material used can be reduced, and the overall contact area between the conductive material and the electrolyte can be reduced, thereby suppressing side reactions.

[0058] The conductive coating may partially cover the surface of the core particle (10). For example, the conductive coating may not be formed on at least some area of ​​the surface of the core particle (10).

[0059] If the conductive coating uniformly covers the entire surface of the lithium metal oxide particles, the movement of lithium ions on the surface of the lithium metal oxide particles may be reduced. Consequently, the ionic conductivity of the positive electrode active material may be reduced, and the capacity and output of the lithium secondary battery may be reduced.

[0060] However, according to exemplary embodiments, the conductive coating is formed only on a portion of the surface of the core particle (10), so that the lithium ion conductivity can be improved while securing electronic conductivity through the conductive coating.

[0061] In one embodiment, the conductive coating may cover at least 10%, at least 20%, or at least 30% of the surface of the core particle (10). In one embodiment, the conductive coating may cover at most 80%, at most 70%, at most 60%, or at most 50% of the surface of the core particle (10).

[0062] Within the above range, the electronic conductivity and stability of the positive electrode active material can be improved, thereby enabling the positive electrode active material to have high ionic conductivity. Accordingly, the output, capacity, and lifespan characteristics of the lithium secondary battery can be further improved.

[0063] According to exemplary embodiments, the conductive coating may include a first pattern (22) and a second pattern (24) having different shapes.

[0064] The first pattern (22) may have an island shape. For example, the first pattern (22) may be formed by dispersing each of the conductive particles on the surface of the core particle (10), or some of the conductive particles may be formed by agglomerating with each other.

[0065] The island shape can mean a shape in which the challenging particles are distributed in a discontinuous manner, and can be a sphere, hemisphere, cylinder, ellipse, or irregular shape.

[0066] By including the first pattern (22) having an island shape in the conductive coating, ion conductivity on the surface of the positive electrode active material can be improved. Therefore, for example, the movement of lithium ions between the positive electrode active material and the electrolyte can be facilitated, thereby improving the capacity characteristics of the lithium secondary battery.

[0067] The second pattern (24) may have a chain shape. For example, the second pattern (24) may be formed by continuously connecting some of the conductive particles.

[0068] The chain shape may refer to a chain shape in which multiple conductive particles are connected and extended. For example, the second pattern (24) may have a straight line shape, a curved shape, a broken line shape, a zigzag shape, a wave shape, an arc shape, etc., and may further include multiple branches branching off from these.

[0069] By including a second pattern (24) having a chain shape as a conductive coating, conductivity between positive electrode active material particles can be improved and the internal resistance of the positive electrode can be reduced. Accordingly, the rate characteristics of a lithium secondary battery can be improved.

[0070] The conductive coating can improve both the ion conductivity and electron transport of the positive electrode active material (50) by including both the first pattern (22) and the second pattern (24). For example, if the conductive coating has only an island-shaped pattern, electrons can be isolated within the island pattern. For example, if the conductive coating has only a chain-shaped pattern, lithium ions can be isolated in the area surrounded by the chain-shaped pattern.

[0071] In one embodiment, the diameter (W1) of the first pattern (22) may be 0.03 μm or more and less than 1.0 μm. For example, the diameter may refer to the length of the longest portion of the first pattern (22).

[0072] Within the above range, the ionic conductivity and electronic conductivity of the positive electrode active material can be improved. For example, if the diameter of the first pattern (22) is excessively large, the ionic conductivity of the first pattern (22) may be relatively low, and electron transfer may be hindered due to agglomeration of the conductive material.

[0073] In one embodiment, the diameter (W1) of the first pattern (22) may be 0.03 μm to 0.5 μm, 0.05 μm to 0.5 μm, or 0.1 μm to 0.3 μm.

[0074] In one embodiment, the length (W2) of the second pattern (24) may be 1.0 μm to 10.0 μm. For example, the length (W2) may be the length of the longest portion of the second pattern (24). If the second pattern (24) further includes a plurality of branches branching off from one branch, the length (W2) may be the length of the longest branch of the second pattern (24).

[0075] Within the above range, the electronic and ionic conductivity of the positive electrode active material can be further improved. For example, if the length of the second pattern (24) is excessively short, the coating coverage may be reduced, thereby reducing the electron transfer path. If the length of the second pattern (24) is excessively long, the movement of lithium ions may not be smooth.

[0076] In one embodiment, the length (W2) of the second pattern (24) may be 1.0 μm to 7 μm, 1.0 μm to 5.0 μm, or 1.0 μm to 3.5 μm.

[0077] In one embodiment, the second pattern may have a length greater than the diameter of the first pattern.

[0078] In some embodiments, some of the second patterns of the conductive coating may be interconnected.

[0079] Figure 2 is a schematic diagram showing a positive electrode active material according to exemplary embodiments.

[0080] Referring to FIG. 2, the conductive coating may further include a third pattern (26) formed by connecting a plurality of second patterns. The third pattern (26) may have a web shape.

[0081] A web-like structure may refer to a mesh structure formed by interconnecting multiple chain-like structures. For example, at least two second patterns may be interconnected and intersecting to form a third pattern (26), and the third pattern (26) may include chains extending in multiple directions.

[0082] Since the conductive coating includes a third pattern (26) having a web shape, a continuous electron movement path can be additionally provided through the third pattern (26) on the surface of the core particle (10). Accordingly, the electronic conductivity of the positive electrode active material (50) can be further improved, and the output characteristics of the lithium secondary battery can be improved.

[0083] According to exemplary embodiments, the conductive coating may include carbon black and / or carbon nanotubes.

[0084] In some embodiments, the carbon black may include acetylene black, furnace black, ketjen black, channel black, etc. These may be included alone or in combination of two or more.

[0085] In one embodiment, the carbon black may have the form of an aggregate or secondary structure of primary particles.

[0086] In some embodiments, the carbon nanotubes may include single-walled nanotubes (SWCNTs), double-walled nanotubes (DWCNTs), and / or multi-walled nanotubes (MWCNTs). These may be used alone or in combination of two or more.

[0087] In one embodiment, the conductive coating may include carbon black, for example, acetylene black. Acetylene black has high electronic conductivity, chemical stability, and mechanical strength, and thus, the output characteristics and stability of the lithium secondary battery may be further improved.

[0088] In one embodiment, the diameter of the carbon black may be 10 nm to 100 nm, 20 nm to 50 nm, or 25 nm to 30 nm. When the conductive particles have the form of aggregates or secondary structures of primary particles, the diameter may refer to the diameter of the primary particles.

[0089] In one embodiment, the diameter of the carbon nanotube may be 10 nm or less. For example, the diameter of the carbon nanotube may be 1 nm to 10 nm, 2 nm to 10 nm, 4 nm to 9 nm, or 6 nm to 9 nm. In one embodiment, the diameter of the carbon nanotube refers to the length in the short axis direction.

[0090] Within the above diameter range, the bonding force to the core particles can be further improved, and a thin conductive coating can be formed.

[0091] In one embodiment, the specific surface area of ​​the carbon black is 65 m 2 / g to 120m 2 / g, 70m 2 / g to 120m 2 / g, or 80m 2 / g to 110m 2 / g can be measured. The specific surface area can be measured by the BET (Brunaucer-Emmett-Teller) method.

[0092] In one embodiment, the specific surface area of ​​the carbon nanotube is 250 m 2 / g to 700m 2 / g, 300m 2 / g to 700m 2 / g, or 400m 2 / g to 600m 2 / g can be measured. The specific surface area can be measured by the BET (Brunaucer-Emmett-Teller) method.

[0093] Within the above specific surface area range, aggregation of conductive particles can be suppressed, and a thin coating layer can be formed. In addition, the coverage ratio for core particles can be adjusted to an appropriate range.

[0094] In one embodiment, the oil absorption number (OAN) of the conductive particles may be 100 ml / 100 g to 600 ml / 100 g, 150 ml / 100 g to 500 ml / 100 g, or 200 ml / 100 g to 400 ml / 100 g. Within this range, the secondary structure of the conductive particles may be appropriately developed, thereby further improving the electronic conductivity of the conductive coating.

[0095] In some embodiments, the content of the conductive coating may be 0.1 to 1 part by weight based on 100 parts by weight of the core particles (10). Within the above range, the coverage of the conductive coating can be adjusted to an appropriate range, and the electronic conductivity and ionic conductivity of the positive electrode active material can be improved together.

[0096] For example, when the content of the conductive coating exceeds 1 part by weight, the conductive coating may cover the entire surface of the core particle (10) or the coating thickness may increase.

[0097] In one embodiment, the content of the conductive coating may be 0.1 part by weight or more and less than 1 part by weight, 0.1 part by weight to 0.9 part by weight, 0.2 part by weight to 0.8 part by weight, or 0.3 part by weight to 0.7 part by weight, based on 100 parts by weight of the core particles (10).

[0098] In some embodiments, the average particle diameter (D) of the core particles (10) 50 ) can be 1㎛ to 15㎛. "The average particle diameter (D 50 )" may be the particle size at a volume fraction of 50% among the volume particle size distribution obtained by accumulating particles in order of smallest particle size.

[0099] For example, when the average particle diameter of the core particles (10) is less than 1 ㎛, the specific surface area of ​​the particles may increase excessively, which may increase side reactions with the electrolyte, and the electrode density and energy density may decrease as the number of fine particles increases.

[0100] For example, when the average particle diameter of the core particles (10) exceeds 15 μm, as the particle size increases, the movement distance of lithium ions may become longer, and the capacity characteristics and output characteristics of the lithium secondary battery may deteriorate.

[0101] In one embodiment, the average particle diameter of the core particles (10) may be 2 μm to 12 μm, or 5 μm to 10 μm.

[0102] FIG. 3 is a process flow diagram illustrating a method for manufacturing a positive electrode active material according to exemplary embodiments. Hereinafter, the method for manufacturing the positive electrode active material described above will be described with reference to FIG. 3.

[0103] Referring to FIG. 3, a mixture of lithium metal oxide particles and conductive particles can be prepared (e.g., step S10).

[0104] For example, lithium metal oxide particles and conductive particles can be introduced together into a resonance mixer.

[0105] The lithium metal oxide particles and conductive particles may use the materials described above. For example, the conductive particles may include carbon black and / or carbon nanotubes. The carbon black and / or carbon nanotubes may each have the diameter, specific surface area, and / or oil absorption value described above.

[0106] In one embodiment, when the conductive particles include carbon nanotubes, the length of the carbon nanotubes may be 50 μm to 250 μm, 100 μm to 250 μm, or 100 μm to 200 μm. The length of the carbon nanotubes refers to the length in the major axis direction.

[0107] In one embodiment, the conductive particles may include carbon black, for example, acetylene black.

[0108] In one embodiment, the content of the conductive particles in the mixture may be 0.1 part by weight to 1 part by weight, 0.1 part by weight or more and less than 1 part by weight, 0.1 part by weight to 0.9 part by weight, 0.2 part by weight to 0.8 part by weight, or 0.3 part by weight to 0.7 part by weight, based on 100 parts by weight of the lithium metal oxide particles.

[0109] A mixture of lithium metal oxide particles and conductive particles can be stirred using a resonance mixer (e.g., step S20).

[0110] An acoustic resonance mixer may be used as the above resonance mixer. Examples of acoustic resonance mixers include the LabRAM series from Resodyn.

[0111] In some embodiments, the mixing and stirring may be performed under dry conditions. For example, the lithium metal oxide particles and the conductive particles may be mixed and stirred without a solvent.

[0112] As lithium metal oxide particles and conductive particles are stirred with an acoustic resonance mixer, strong shear and collision forces induced from acoustic energy and vibration energy act on the particles, so that the conductive particles can be attached to the surface of the lithium metal oxide particles.

[0113] For example, during the process of stirring the mixture using an acoustic resonance mixer, the surfaces of the lithium metal oxide particles may be partially covered by conductive particles. Some of the conductive particles may aggregate together in an island shape, and other conductive particles may be connected together in a chain shape.

[0114] In some embodiments, the mixture may be stirred at a frequency of 58 Hz to 62 Hz. Within this range, patterns having an island shape and patterns having a chain shape may be formed on the surface of the lithium metal oxide particles.

[0115] For example, when the frequency of the acoustic resonance mixer is less than 58 Hz, the conductive particles can completely cover the surface of the lithium metal oxide particles. Therefore, a conductive coating can be formed on the entire surface of the lithium metal oxide particles. When the frequency of the acoustic resonance mixer exceeds 62 Hz, the lithium metal oxide particles may break, and a chain-shaped or web-shaped coating may not be formed.

[0116] In one embodiment, the frequency of the acoustic resonance mixer may be 58.5 Hz to 61 Hz, or 59 Hz to 61 Hz.

[0117] In some embodiments, the mixture may be stirred at an acceleration greater than 40 G and less than 75 G. Within this range, the shape, coverage, and thickness of the conductive coating may be appropriately controlled.

[0118] In one embodiment, the acceleration of the acoustic resonance mixer may be from 50G to 70G, from 50G to 65G, or from 55G to 65G.

[0119] In some embodiments, the stirring time of the mixture may be from 1 minute to 50 minutes, from 5 minutes to 40 minutes, or from 10 minutes to 30 minutes. Within this range, the conductive particles may be partially bonded to the surface of the lithium metal oxide particles, and a conductive coating having an island shape and a chain shape may be more easily formed.

[0120] A positive electrode active material can be obtained from a resonance mixer (e.g., step S30).

[0121] The positive electrode active material may include a core particle comprising lithium metal oxide particles and a conductive coating partially formed on the core particle and comprising conductive particles.

[0122] A lithium secondary battery according to embodiments of the present disclosure may include the positive electrode active material described above. The lithium secondary battery may include a positive electrode including the positive electrode active material and a negative electrode facing the positive electrode.

[0123] According to exemplary embodiments, the positive electrode may include a positive electrode active material, a conductive agent, and / or a binder. For example, a positive electrode slurry may be prepared by mixing and stirring the positive electrode active material with a conductive agent and / or a binder in a solvent. The positive electrode slurry may be dried and pressurized to form the positive electrode.

[0124] In one embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. For example, the positive electrode slurry may be coated on at least one surface of the positive electrode current collector, followed by drying and rolling to manufacture the positive electrode.

[0125] The positive electrode current collector may comprise stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0126] The above binder may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, nitrile butadiene rubber, and the like.

[0127] The conductive material may be included to promote electron transport. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0128] In one embodiment, the positive electrode may further include a solid electrolyte. The solid electrolyte may provide an additional ion transport path in the positive electrode, thereby improving the capacity of the lithium secondary battery.

[0129] As the conductive coating partially covers the surface of the lithium metal oxide particles, sufficient ion transfer paths between the solid electrolyte and the positive electrode active material can be secured. Therefore, ion isolation within the positive electrode active material can be prevented.

[0130] The solid electrolyte may include a sulfide-based electrolyte, an oxide-based electrolyte, or a polymer electrolyte. The polymer electrolyte may include an ion-conducting polymer or a gel polymer electrolyte.

[0131] In one embodiment, the sulfide-based electrolyte may be represented by the following chemical formula 2.

[0132] [Chemical Formula 2]

[0133] Li e Y f P g S h Z i

[0134] In chemical formula 2, 0<e<12, 0≤f≤6, 0≤g≤6, 0<h≤12, 0≤i≤9, Y is at least one element selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, Bi, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, and W, and Z may be at least one element selected from the group consisting of F, Cl, Br, and I.

[0135] For example, the sulfide-based electrolyte may be an LPS-based solid electrolyte containing Li, P, and S, an LGPS-based solid electrolyte containing Li, P, Ge, and S, or an LSiPSCl-based solid electrolyte containing Li, Si, P, S, and Cl.

[0136] For example, as the sulfide-based electrolyte, Li2S-P2S5, Li 10 GeP2S 12 , Li 10 SnP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 10 (Si 0.5 Ge 0.5 )P2S 12 , Li 10 (Ge 0.5 Sn 0.5 )P2S 12 , Li 10 (Si 0.5 Sn 0.5 )P2S 12 , Li 10 GeP2S 11.7 O 0.3 , Li 9.6 P3S 12 , Li9P3S9O3, Li 10.35 Ge 1.35 P 1.65 S 12 , Li 10.35 Si 1.35 P 1.65S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 , Li6PS5Cl, etc. can be used.

[0137] In one embodiment, the oxide-based electrolyte may include a metal oxide or an ion-conducting compound containing oxygen. For example, examples of the oxide-based electrolyte include Al2O3, ZnO2, Ce2O3, TiO2, ZrO2, HfO2, MnO2, MgO, WO 2, Metal oxides such as V2O5, LLTO compounds, LLZO compounds, Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO4)3(0≤x≤1, 0≤y≤1), LiTi x Zr 2-x (PO4)3 (wherein, 0≤x≤1, 0≤y≤1), LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, etc. can be mentioned.

[0138] In one embodiment, the solid electrolyte may include a sulfide-based electrolyte. The sulfide-based electrolyte has high compatibility and stability with the positive electrode active material, thereby further improving the electrochemical characteristics of the lithium secondary battery.

[0139] In some embodiments, the content of the solid electrolyte may be 5 to 80 parts by weight, 10 to 70 parts by weight, or 15 to 60 parts by weight, based on 100 parts by weight of the positive electrode active material. Within this range, the capacity and output characteristics of the lithium secondary battery may be improved together.

[0140] For example, if the content of the solid electrolyte exceeds 80 parts by weight, the energy density of the positive electrode may be relatively low. If the content of the solid electrolyte is less than 5 parts by weight, the ionic conductivity of the positive electrode may be relatively low.

[0141] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector.

[0142] The negative electrode current collector may comprise, for example, gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, for example, copper or a copper alloy.

[0143] The negative electrode active material layer may include a negative electrode active material. The negative electrode active material can be any material known in the art capable of absorbing and desorbing lithium ions without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon, tin, etc. may be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1,500°C or lower, and mesophase pitch-based carbon fibers (MPCF). Examples of the crystalline carbon include graphite-based carbons 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, and indium.

[0144] In some embodiments, the negative electrode slurry may be prepared by mixing and stirring the negative electrode active material with a binder, a conductive agent, and / or a dispersing agent in a solvent. The negative electrode slurry may be coated on the negative electrode current collector, followed by drying and compression to prepare the negative electrode.

[0145] Materials substantially identical to or similar to the above-described binder and conductive agent may be used. In some embodiments, the binder for forming the negative electrode may include, for example, an aqueous binder such as styrene-butadiene rubber (SBR) for compatibility with the carbon-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0146] In some embodiments, a separator may be interposed between the positive and negative electrodes. The separator may include a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The separator may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0147] According to exemplary embodiments, an electrode assembly may be formed by repeatedly arranging a positive electrode, a negative electrode, and a separator. In some embodiments, the electrode assembly may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0148] An electrode assembly may be housed within a case to define a lithium secondary battery. The lithium secondary battery may be manufactured in a cylindrical, square, pouch, or coin shape using, for example, a can.

[0149] According to exemplary embodiments, an electrolyte may be housed within a case together with an electrode assembly. A non-aqueous electrolyte may be used as the electrolyte.

[0150] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as 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 - or (CF3CF2SO2)2N - Examples include:

[0151] Examples of the organic solvent that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0152] In some embodiments, a solid electrolyte layer may be interposed between the positive and negative electrodes. The solid electrolyte layer may include a sulfide-based electrolyte, an oxide-based electrolyte, or a polymer electrolyte.

[0153] In this case, the lithium secondary battery may not include a separator or electrolyte. The solid electrolyte layer substantially functions as a separator and can prevent short circuits between the positive and negative electrodes. Furthermore, the solid electrolyte layer allows lithium ions to move between the positive and negative electrodes.

[0154] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0155] Manufacturing example

[0156] (1) Manufacturing of core particles

[0157] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 88:9:3 using distilled water that had been bubbled with N2 for 24 hours to remove internal dissolved oxygen. The solution was put into a reactor at 50°C, and a coprecipitation reaction was performed for 48 hours using NaOH and NH3H2O ​​as precipitants and chelating agents to obtain Ni as a transition metal precursor. 0.88 Co 0.09 Mn 0.03 (OH)2 was obtained. The obtained precursor was dried at 80°C for 12 hours and then re-dried at 110°C for 12 hours.

[0158] Lithium hydroxide and the above transition metal precursor were added to a dry high-speed mixer at a ratio of 1.01:1 to 1.025:1 and uniformly mixed for 5 minutes. The mixture was placed in a calcination furnace, heated to 730 to 750°C at a heating rate of 2°C / min, and maintained at 730 to 750°C for 10 hours. Oxygen was continuously passed at a flow rate of 10 mL / min during the heating and maintenance. After the calcination, the mixture was naturally cooled to room temperature, and then pulverized and classified to obtain LiNi. 0.88 Co 0.09 Mn 0.03 O2(D 50 : Core particles of 10㎛ were obtained.

[0159] (2) Manufacturing of positive electrode active material

[0160] Example 1

[0161] 100 parts by weight of the core particles manufactured above and acetylene black (diameter: 25 to 30 nm, OAN: 200 ml / 100 g, specific surface area: 100 m) were added to an acoustic resonance mixer (LabRAMⅡ, Resodyn). 2 / g) 0.5 parts by weight was added.

[0162] The acoustic resonance mixer was stirred for 20 minutes at a frequency of 60 Hz and an acceleration of 60 G. After this, the positive electrode active material was obtained from the acoustic resonance mixer.

[0163] Example 2

[0164] A positive electrode active material was manufactured in the same manner as in Example 1, except that 0.1 part by weight of acetylene black was added to the acoustic resonance mixer.

[0165] Example 3

[0166] A positive electrode active material was manufactured in the same manner as in Example 1, except that 1 part by weight of acetylene black was added to the acoustic resonance mixer.

[0167] Example 4

[0168] Carbon nanotubes (diameter: 6 nm to 9 nm, length: 100 μm to 200 μm, specific surface area: 400 m) were used instead of acetylene black in the acoustic resonance mixer. 2 / g to 600m 2 / g) A positive electrode active material was manufactured in the same manner as in Example 1, except that 0.5 parts by weight of the active material was added.

[0169] Comparative Example 1

[0170] A positive electrode active material was manufactured in the same manner as in Example 1, except that the acceleration of the acoustic resonance mixer was changed to 75 G.

[0171] Comparative Example 2

[0172] A positive electrode active material was manufactured in the same manner as in Example 1, except that the acceleration of the acoustic resonance mixer was changed to 40 G.

[0173] Comparative Example 3

[0174] The core particles manufactured above were used as a positive electrode active material without forming a conductive coating.

[0175] Comparative Example 4

[0176] A positive electrode active material was manufactured in the same manner as in Example 1, except that 0.05 parts by weight of acetylene black was added.

[0177] Comparative Example 5

[0178] A positive electrode active material was manufactured in the same manner as in Example 1, except that acetylene black was added in an amount of 3 parts by weight.

[0179] (3) Manufacturing of lithium secondary batteries

[0180] A secondary battery was manufactured using the positive electrode active material manufactured above. Specifically, the positive electrode active material, solid electrolyte (Li6PS5Cl), binder (PVdF), and conductive agent (Super P) of the examples and comparative examples were mixed in a mass ratio of 68:28:2:2, respectively, to manufacture a positive electrode slurry.

[0181] The above positive electrode slurry was uniformly applied onto an aluminum foil (15 μm thick), dried, and then rolled to manufacture a positive electrode.

[0182] Density 10mg / cm in SUS circular mold with Φ13 diameter 2 Solid electrolyte (Li6PS5Cl) was added and solid electrolyte pellets were manufactured by uniaxial cold isostatic pressing (CIP) molding at 80 MPa. The positive electrode was applied to one side of the solid electrolyte pellet at 10 mg / cm 2 After being placed on one side and pressed at 350 MPa to pelletize, an In foil was placed on the other side and pressed at 50 MPa to manufacture an electrode cell having a structure of a cathode composite-solid electrolyte-In cathode. The electrode cell was assembled into a coin cell outer case with a diameter of Φ20.

[0183] Experimental example

[0184] (1) Coating shape measurement

[0185] Figures 4 to 7 are scanning electron microscope (SEM) images of the positive electrode active materials manufactured sequentially in Examples 1 to 4.

[0186] Referring to Fig. 4, in Example 1, island-shaped and web-shaped coatings were formed on the surface of the core particles. Referring to Fig. 5, in Example 2, island-shaped and web-shaped coatings were formed on the surface of the core particles. Referring to Fig. 6, in Example 3, island-shaped and web-shaped coatings were formed on the surface of the core particles. Referring to Fig. 7, in Example 4, island-shaped and web-shaped coatings were formed on the surface of the core particles.

[0187] Figures 8 and 9 are SEM images of the positive electrode active materials manufactured in Comparative Example 1 and Comparative Example 2, respectively.

[0188] Referring to Fig. 8, in Comparative Example 1, only a web-shaped coating was formed on the surface of the core particle. Referring to Fig. 9, in Comparative Example 2, only an island-shaped coating was formed on the surface of the core particle.

[0189] Fig. 10 is an SEM image of the positive electrode active material manufactured in Comparative Example 4. Fig. 11 is an enlarged view of Fig. 10. Fig. 12 is an SEM image of the positive electrode active material manufactured in Comparative Example 5.

[0190] Referring to FIGS. 10 and 11, in Comparative Example 4, only an island-shaped coating was formed on the surface of the core particle. Referring to FIG. 12, in Comparative Example 5, a film-shaped coating was formed on the surface of the core particle.

[0191] (2) Capacity evaluation

[0192] The fabricated coin cell was charged and discharged at 0.1C for the first three cycles at a temperature of 30℃ with a cut-off charge of 4.3V and a discharge of 2.5V, and the discharge capacity (B1) in the first cycle was measured. Thereafter, two cycles of charge and discharge were performed at a rate of 0.2C, and two cycles of charge and discharge were performed at a rate of 0.5C. Thereafter, charge and discharge were performed at 1C, and the discharge capacity (B2) was measured.

[0193] The high-rate characteristics were evaluated as the percentage of the discharge capacity (B2) at high rate (1C) to the discharge capacity (B1) at low rate (0.1C), as shown in Equation 1 below.

[0194] [Formula 1]

[0195] High-rate capacity characteristic (%) = B2 / B1 × 100%

[0196] (3) Initial efficiency

[0197] The above-mentioned manufactured coin cell was charged (CC-CV 0.1C, 4.3V, 0.01C cut-off) and discharged (CC 0.1C, 2.5V cut-off) at 30°C to measure the initial charge and discharge capacities. The initial efficiency was evaluated as the percentage of the initial discharge capacity (A2) to the initial charge capacity (A1) as shown in Equation 2 below.

[0198] [Formula 2]

[0199] Initial efficiency (%) = A2 / A1 × 100%

[0200] The evaluation results are shown in Table 1 below.

[0201] High-rate capacity characteristics (%) Initial efficiency characteristics (%) Example 1 85.5 80.5 Example 2 82.0 7 4.1 Example 3 83.9 7 6.4 Example 4 85.7 82.5 Comparative example 1 78.1 6 3.7 Comparative example 2 77.5 6 1.8 Comparative example 3 75.1 5 8.3 Comparative example 4 75.3 5 9.0 Comparative example 5 70.1 5 2.4

[0202] The cathode active materials manufactured in the examples had coatings having web shapes and island shapes partially formed on the surface of the core particles, and the lithium secondary batteries had high capacity and initial efficiency.

[0203] The lithium secondary batteries manufactured in the comparative examples had lower capacity characteristics and initial efficiency compared to the examples.

Claims

1. Lithium metal oxide particles; and A conductive coating partially covering the surface of the lithium metal oxide particles and including a plurality of conductive particles, A positive electrode active material, wherein the conductive coating comprises a first pattern having an island shape and a second pattern having a chain shape.

2. A positive electrode active material according to claim 1, wherein the diameter of the first pattern is 0.03 μm or more and less than 1.0 μm.

3. A positive electrode active material according to claim 1, wherein the length of the second pattern is 1.0 μm to 10.0 μm.

4. A positive electrode active material according to claim 1, wherein the conductive coating further includes a third pattern having a web shape formed by connecting a plurality of the second patterns.

5. A positive electrode active material according to claim 1, wherein the content of the conductive coating is 0.1 to 1 part by weight based on 100 parts by weight of the lithium metal oxide particles.

6. A positive electrode active material according to claim 1, wherein the conductive particles include at least one of carbon black and carbon nanotubes.

7. In claim 1, the average particle diameter (D) of the lithium metal oxide particles 50 ) is a positive electrode active material having a diameter of 1㎛ to 15㎛.

8. A positive electrode comprising the positive electrode active material of claim 1; and A lithium secondary battery comprising a cathode opposite to the positive electrode.

9. A lithium secondary battery according to claim 8, wherein the positive electrode further comprises a solid electrolyte.

10. A step of preparing a mixture of lithium metal oxide particles and conductive particles; and A step of stirring the above mixture with a resonance mixer is included, A method for producing a positive electrode active material, wherein the content of the conductive particles in the mixture is 0.1 to 1 part by weight based on 100 parts by weight of the lithium metal oxide particles.

11. A method for producing a positive electrode active material according to claim 10, wherein the step of stirring the mixture with a resonance mixer includes coating the conductive particles on the surface of the lithium metal oxide particles.

12. A method for producing a positive electrode active material according to claim 11, wherein the conductive particles partially cover the surface of the lithium metal oxide particles.

13. A method for producing a positive electrode active material according to claim 11, wherein some of the conductive particles are aggregated together in an island shape, and other parts of the conductive particles are connected together in a chain shape.

14. A method for producing a positive electrode active material according to claim 10, wherein the conductive particles include at least one of carbon black and carbon nanotubes.

15. In claim 14, the specific surface area of ​​the carbon black is 65 m 2 / g to 120m 2 / g, a method for manufacturing a positive electrode active material.

16. In claim 14, the specific surface area of ​​the carbon nanotube is 250 m 2 / g to 700m 2 / g, a method for manufacturing a positive electrode active material.

17. A method for producing a positive electrode active material according to claim 10, wherein the resonance mixer is an acoustic resonance mixer.

18. A method for producing a positive electrode active material according to claim 10, wherein the mixture is stirred at a frequency of 58 Hz to 62 Hz.

19. A method for producing a positive electrode active material according to claim 10, wherein the mixture is stirred at an acceleration of more than 40G and less than 75G.

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