Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery

Abstract

According to an embodiment of the present invention, the positive electrode active material for a lithium secondary battery has a lithium transition metal oxide structure, the ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material for a lithium secondary battery measured by XRD analysis is 0.7 to 2.0, and the ratio of the crystallite size of the (003) plane to the crystallite size of the (104) plane is 0.7 to 2.0. A positive electrode for a lithium secondary battery and a lithium secondary battery include a positive electrode active material for a lithium secondary battery.

Description

Technical Field

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

[0002] A secondary battery is a battery that can be repeatedly charged and discharged. With the development of the information communication and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. In addition, in recent years, battery packs including secondary batteries are being developed and used as power sources for eco-friendly vehicles such as hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, calcium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. Among them, lithium secondary batteries have a high operating voltage and energy density per unit weight, and can be beneficial for charging speed and weight reduction.

[0004] For example, a lithium secondary battery may include an electrode assembly and an electrolyte impregnating the electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator (separating membrane). The lithium secondary battery may further include an exterior material that houses the electrode assembly and the electrolyte, such as an exterior material in the form of a pouch.

[0005] As the positive electrode active material of the lithium secondary battery, a lithium metal oxide is used, and preferably has characteristics of high capacity, high power, and high life. However, when the lithium metal oxide is designed to have a high-power composition, the uniformity, thermal stability, and mechanical stability of the particles may be reduced, thereby possibly reducing the life characteristics and operating reliability of the lithium secondary battery. Summary of the Invention

[0006] (I) Technical Problems to be Solved

[0007] One technical problem of the present invention is to provide a positive electrode active material for a lithium secondary battery having improved charge and discharge characteristics and reliability.

[0008] One technical problem of the present invention is to provide a positive electrode for a lithium secondary battery including the positive electrode active material for a lithium secondary battery.

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

[0010] (II) Technical Solutions

[0011] According to an embodiment of the present invention, the positive electrode active material for a lithium secondary battery has a lithium transition metal oxide structure, and the ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material for the lithium secondary battery measured by XRD analysis is 0.7 to 2.0, and the ratio of the crystallite size of the (003) plane to the crystallite size of the (104) plane is 0.7 to 2.0.

[0012] In some embodiments, the crystallite size of the (003) plane of the positive electrode active material measured by XRD may be 350 nm or more.

[0013] In some embodiments, the crystallite size of the (003) plane of the positive electrode active material measured by XRD may be 350 nm to 700 nm.

[0014] In some embodiments, the positive electrode active material may have a single crystal form.

[0015] In some embodiments, the positive electrode active material may have a layered structure.

[0016] In some embodiments, the ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material measured by XRD may be 0.7 to 1.7.

[0017] In some embodiments, the ratio of the crystallite size of the (003) plane to the crystallite size of the (104) plane of the positive electrode active material measured by XRD may be 0.7 to 1.7.

[0018] In some embodiments, the crystallite size of the (104) plane of the positive electrode active material measured by XRD may be 300 nm to 760 nm.

[0019] In some embodiments, the crystallite size of the (110) plane of the positive electrode active material measured by XRD may be 300 nm to 700 nm.

[0020] In some embodiments, the lithium transition metal oxide may contain nickel.

[0021] In some embodiments, in 100 mol% of the total metal elements other than lithium in the lithium transition metal oxide, the content of nickel may be 60 mol% or more.

[0022] In some embodiments, the lithium transition metal oxide may further contain manganese.

[0023] In some embodiments, the lithium transition metal oxide may be represented by the following Chemical Formula 1.

[0024] [Chemical Formula 1]

[0025] Li a Ni x Mn y M 1-x-y O2

[0026] In Chemical Formula 1, M may include at least one of Co, Mg, Sr, Ba, B, Al, Zr, Ti, Y, and W, and may be 0.95 ≤ a ≤ 1.1, 0.6 ≤ x < 0.9, 0.04 ≤ y ≤ 0.3.

[0027] According to an embodiment of the present invention, a positive electrode for a lithium secondary battery may include: a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer contains a positive electrode active material for a lithium secondary battery according to the above embodiment.

[0028] According to an embodiment of the present invention, a lithium secondary battery may include: a positive electrode containing a positive electrode active material for a lithium secondary battery according to the above embodiment; and a negative electrode disposed opposite to the positive electrode.

[0029] (III) Beneficial Effects

[0030] In the positive electrode active material for a lithium secondary battery according to an embodiment of the present invention, the ratio of the crystallite size of the (110) plane measured by XRD analysis to the crystallite size of the (003) plane may be maintained within an appropriate range. Therefore, a change in the crystal structure of the positive electrode active material for a lithium secondary battery can be suppressed, and the migration distance of lithium ions can be appropriately adjusted.

[0031] In the positive electrode active material for a lithium secondary battery, the ratio of the crystallite size of the (104) plane measured by XRD analysis to the crystallite size of the (003) plane may be maintained within an appropriate range. The crystal structure stability of the positive electrode active material for a lithium secondary battery can be further enhanced. For example, even if the positive electrode active material contains a high content of nickel, improved structural stability can be maintained, and power and capacity can be increased without reducing operating stability and life characteristics.

[0032] The lithium secondary battery according to an embodiment of the present invention can be widely applied to green technology fields such as electric vehicles, battery charging stations, other battery-utilizing solar power generation, and wind power generation. In addition, the lithium secondary battery according to an embodiment of the present invention can be used for eco-friendly electric vehicles (EVs) and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 and Figure 2 are a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment, respectively. Detailed Description

[0034] According to an embodiment of the present invention, a positive electrode active material for a lithium secondary battery having predetermined crystal characteristics is provided.

[0035] According to an embodiment of the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode active material are provided.

[0036] Terms such as "upper surface" and "bottom surface" used in the present invention represent the relative positions of the respective components, rather than specifying absolute positions.

[0037] Hereinafter, the present invention will be described in detail. However, this is merely an exemplary description, and the present invention is not limited to the specific embodiments described exemplarily.

[0038] According to an embodiment of the present invention, a positive electrode active material for a lithium secondary battery (hereinafter, may be simply referred to as "positive electrode active material") may include a lithium transition metal oxide. For example, the lithium transition metal oxide may include nickel (Ni). For example, the positive electrode active material may include a lithium nickel-based oxide.

[0039] According to an exemplary embodiment, among the metal elements other than lithium contained in the lithium transition metal oxide, the content (mole% or atomic%) of nickel (Ni) may be the highest.

[0040] In some embodiments, the content of nickel in the lithium transition metal oxide may be 60 mole% or more based on 100 mole% of the total metal elements other than lithium. For example, the content of nickel in the lithium transition metal oxide may be 60 mole% or more and less than 100 mole%, 60 mole% to 98 mole%, 60 mole% or more and less than 90 mole%, 60 mole% to 80 mole% of the total metal elements other than lithium.

[0041] Nickel can be provided as a transition metal related to the power and capacity of the lithium secondary battery. Therefore, since the positive electrode active material includes a high nickel (High-Ni) composition, for example, including 60 mole% or more of nickel, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0042] According to an exemplary embodiment, the lithium transition metal oxide may further include other transition metals other than nickel, such as manganese (Mn), etc. For example, when the content of nickel increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may be relatively reduced. By means of transition metals such as manganese, the life stability, capacity retention characteristics, and through-stability of the positive electrode active material can be further improved.

[0043] According to an exemplary embodiment, the positive electrode active material may have a layered structure. For example, the lithium transition metal oxide may include a lithium layer and a transition metal layer within the crystal structure.

[0044] According to an exemplary embodiment, the positive electrode active material may have a crystallographically single crystal structure. The single crystal may refer to a crystal structure in which grains or grain boundaries are not included inside the particles. For example, the single crystal structure can be distinguished from the polycrystalline structure having multiple crystals inside the particles.

[0045] In one embodiment, the single crystal structure can be confirmed by a Scanning Electron Microscope (SEM), a Transmission Electron Microscope (TEM), an Electron-Back Scattered Diffraction (EBSD), etc. For example, through Electron-Back Scattered Diffraction (EBSD), the grain orientation information of the particles can be measured, and the single crystal structure and the polycrystalline structure can be distinguished by the grain orientation distribution of the particles.

[0046] The positive electrode active material has a single crystal structure, so that it can have improved structural stability. Therefore, the generation of cracks inside the particles can be suppressed, and the propagation of heat and shock caused by the cracks can be reduced. Therefore, for example, even if the calendering strength is increased to manufacture a high-density positive electrode, the structural damage and the increase in resistance of the positive electrode active material can be suppressed.

[0047] According to an embodiment of the present invention, the ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material measured by X-ray diffraction (XRD) analysis may be 0.7 to 2.0.

[0048] The microcrystalline size can be calculated using the Scherrer equation with the full width at half maximum (FWHM) obtained from XRD analysis according to Equation 1 below.

[0049] [Equation 1]

[0050]

[0051] In Equation 1, L is the grain size, λ is the X-ray wavelength, β is the full width at half maximum of the peak corresponding to each crystal plane, and θ is the diffraction angle (in radians (rad)) of the peak corresponding to each crystal plane.

[0052] For example, the XRD analysis can be performed on the dry powder of lithium transition metal oxide particles using Cu-Kα rays as the light source and at a scanning speed of 0.0065° / step within a diffraction angle (2θ) range of 10° to 120°.

[0053] The (110) plane of the positive electrode active material can act as a factor related to the migration of ions. For example, lithium ions can diffuse through the (110) plane within the particles. The (003) plane of the positive electrode active material can be the reference microcrystalline size.

[0054] By controlling the microcrystalline size of the (110) plane of the positive electrode active material relative to the microcrystalline size of the (003) plane within the above range, the stability of the crystal structure can be improved, and at the same time, the migration of lithium ions can be promoted.

[0055] For example, when the microcrystalline size of the (003) plane increases excessively relative to the microcrystalline size of the (110) plane, lithium ions may migrate through the (003) plane, which may hinder the migration of lithium ions.

[0056] In addition, in a layered positive electrode active material with a high nickel content composition, a cation mixing phenomenon may occur, such as the irreversible replacement of lithium ions in the lithium layer with nickel ions in the transition metal layer. In this case, the cation mixing phenomenon may spread from the (110) plane to the inside of the particles. Therefore, when the microcrystalline size of the (110) plane decreases excessively, the replacement of lithium ions with nickel ions may increase, and thus the crystal structure may deteriorate.

[0057] In one example, when the microcrystalline size of the (110) plane increases excessively relative to the microcrystalline size of the (003) plane, the migration distance of lithium ions through the (110) plane may increase, resulting in a possible decrease in capacity and efficiency.

[0058] In some embodiments, the ratio of the microcrystalline size of the (003) plane to the microcrystalline size of the (110) plane of the positive electrode active material may be 0.7 to 1.7, 0.7 to 1.6, 0.8 to 1.6, 0.9 to 1.6, or 1.0 to 1.6. Within the above range, the stability of the crystal structure, the life characteristics, and the capacity characteristics of the lithium secondary battery can be further improved.

[0059] According to an embodiment of the present invention, the ratio of the microcrystalline size of the (003) plane to the microcrystalline size of the (104) plane of the positive electrode active material measured by XRD analysis may be 0.7 to 2.0. The microcrystalline size of the (104) plane can also be obtained by calculation using the Scherrer equation (the formula 1) using the full width at half maximum (FWHM) obtained by XRD analysis.

[0060] By controlling the crystal growth of the (104) plane and the (003) plane of the positive electrode active material within the above range, the migration characteristics and diffusion characteristics of lithium ions can be enhanced, and at the same time, the particle strength and the stability of the crystal structure can be improved.

[0061] For example, when the ratio of the microcrystalline size of the (003) plane to the microcrystalline size of the (104) plane exceeds 2.0, the change in the crystal structure during charge and discharge may increase. In this case, the stress caused by the change in the crystal structure may act on the positive electrode active material particles, thereby possibly reducing the life characteristics.

[0062] For example, when the ratio of the microcrystalline size of the (003) plane to the microcrystalline size of the (104) plane is less than 0.7, the migration distance and diffusion distance of lithium ions may increase, and the particle strength may decrease.

[0063] In some embodiments, the ratio of the microcrystalline size of the (003) plane to the microcrystalline size of the (104) plane of the positive electrode active material may be 0.7 to 1.7, 0.7 to 1.6, 0.8 to 1.6, or 0.9 to 1.6. Within the above range, the life characteristics, capacity characteristics, and efficiency of the positive electrode active material can be further improved.

[0064] According to an exemplary embodiment, the microcrystalline size of the (003) plane of the positive electrode active material measured by XRD may be 350 nm or more. Therefore, the particle strength of the positive electrode active material can be increased, and the positive electrode active material can have an ideal single crystal structure, thereby reducing the cracks of the particles.

[0065] In some embodiments, the microcrystalline size of the (003) plane of the positive electrode active material may be 700 nm or less. Therefore, the change in the crystal structure due to repeated charge / discharge can be reduced, and the generation of cracks and the increase in resistance can be suppressed, thereby improving the capacity characteristics and life characteristics even in a high-temperature environment.

[0066] For example, the crystallite size of the (003) plane of the positive electrode active material may be 350 nm to 700 nm, 400 nm to 700 nm, 450 nm to 700 nm, or 450 nm to 650 nm. Within the above range, the high-temperature life characteristics and capacity characteristics can be further improved.

[0067] In some embodiments, the crystallite size of the (110) plane of the positive electrode active material measured by XRD may be 300 nm to 700 nm. Within the above range, the migration distance and diffusion distance of lithium ions can be more appropriately adjusted, and changes in the crystal structure, generation of cracks, and increase in resistance can be suppressed.

[0068] In one embodiment, the crystallite size of the (110) plane of the positive electrode active material may be more than 300 nm and 700 nm or less, 320 nm to 700 nm, 320 nm to 650 nm, or 320 nm to 500 nm.

[0069] In some embodiments, the crystallite size of the (104) plane of the positive electrode active material measured by XRD may be 300 nm to 760 nm. Within the above range, the aspect ratio of the positive electrode active material can be controlled within an appropriate range, and the structural stability, capacity characteristics, and power characteristics can be further improved. Therefore, generation of gas and crack phenomena can be suppressed even in a high-temperature environment, and stable capacity characteristics can be provided.

[0070] In one embodiment, the crystallite size of the (104) plane of the positive electrode active material may be 300 nm to 750 nm, 300 nm to 700 nm, 320 nm to 550 nm, or 320 nm to 400 nm.

[0071] By controlling each value of the crystallite size of the (003) plane, (110) plane, and / or (104) plane while controlling the above-mentioned crystallite size ratio, the crystal growth direction of the positive electrode active material, the migration characteristics and diffusion characteristics of lithium ions, and the stability of the crystal structure can be further enhanced.

[0072] In one embodiment, the lithium transition metal oxide may be represented by Chemical Formula 1.

[0073] [Chemical Formula 1]

[0074] Li a Ni x Mn y M 1-x-y O2

[0075] In Chemical Formula 1, M may include at least one of Co, Mg, Sr, Ba, B, Al, Zr, Ti, Y, and W, and may be 0.95 ≤ a ≤ 1.1, 0.6 ≤ x < 0.9, 0.04 ≤ y ≤ 0.3.

[0076] In some embodiments, the positive electrode active material may further include sulfur (S). For example, some oxygen element sites in the crystal lattice of the lithium transition metal oxide may be replaced by sulfur elements. By introducing sulfur elements into the crystal structure, the crystal structure can be made more stable, thereby suppressing crystal collapse caused by cation mixing and lithium insertion / extraction, and thus the capacity / power characteristics and life characteristics can be further improved.

[0077] In some embodiments, in the lithium transition metal oxide, the content of sulfur may be 600 ppm to 2000 ppm of the total weight of the lithium transition metal oxide. The content of sulfur can be detected by Inductively Coupled Plasma (ICP). Within the above range, the crystal stability, life characteristics, and capacity characteristics of the positive electrode active material can be further enhanced.

[0078] In one embodiment, in the lithium transition metal oxide, the content of sulfur may be 600 ppm to 1800 ppm, 700 ppm to 1600 ppm, or 750 ppm to 1500 ppm.

[0079] In one embodiment, the lithium transition metal oxide may be represented by Chemical Formula 2.

[0080] [Chemical Formula 2]

[0081] Li a Ni x Mn y M 1-x-y O 2-z S z

[0082] In Chemical Formula 2, M may include at least one of Co, Mg, Sr, Ba, B, Al, Zr, Ti, Y, and W, and may be 0.95 ≤ a ≤ 1.1, 0.6 ≤ x < 0.9, 0.04 ≤ y ≤ 0.3, 0 < z ≤ 0.1.

[0083] In some embodiments, in Chemical Formula 1 and Chemical Formula 2, M may include Co and may further include at least one of Al, Zr, Ti, Y, and W. The above metal elements can promote the crystal growth of the (104) plane and the (110) plane during the preparation of the positive electrode active material. Therefore, the microcrystal size ratio of the positive electrode active material can be easily adjusted to an appropriate range.

[0084] According to an exemplary embodiment, the above positive electrode active material can be prepared by the following process.

[0085] According to an exemplary embodiment, a metal source for the active material can be prepared. The metal source for the active material may include a nickel source, a manganese source, a cobalt source, etc.

[0086] As an example of the nickel source, nickel sulfate (NiSO4), nickel hydroxide (Ni(OH)2), nickel nitrate (Ni(NO3)2), nickel acetate (Ni(CH3CO2)2), or their hydrates, etc. can be cited.

[0087] As an example of the manganese source, manganese sulfate (MnSO4), manganese hydroxide (Mn(OH)2), manganese nitrate (Mn(NO3)2), manganese acetate (Mn(CH3CO2)2), or their hydrates, etc. can be cited.

[0088] As an example of the cobalt source, cobalt sulfate (CoSO4), cobalt hydroxide (Co(OH)2), cobalt nitrate (Co(NO3)2), cobalt carbonate (CoCO3), or their hydrates, etc. can be cited.

[0089] In some embodiments, nickel sulfate, manganese sulfate, and cobalt sulfate can be used as the nickel source, the manganese source, and the cobalt source, respectively. Therefore, sulfur (S) elements can remain in the active material precursor.

[0090] The above metal source for the active material can be added to distilled water and mixed to form a transition metal solution. According to an exemplary embodiment, the metal source for the active material can be reacted by a co-precipitation method to obtain an active material precursor. For example, the active material precursor can be made in the form of nickel-manganese-cobalt hydroxide.

[0091] In one embodiment, a precipitating agent and / or a chelating agent can be used to promote the co-precipitation reaction.

[0092] The precipitating agent may include, for example, alkaline compounds such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), etc. The chelating agent may include, for example, ammonia water, ammonium carbonate, etc.

[0093] For example, the precipitating agent can be added to the transition metal solution and reacted at a temperature in the range of about 50°C to 70°C. In one embodiment, the molar ratio of the precipitating agent (e.g., NaOH) contained in the transition metal solution to the transition metal can be more than 1 and less than 3, for example, it can be 1.4 to 2.5.

[0094] In some embodiments, the precipitated product can be heat-treated to obtain a cathode active material precursor. For example, the heat treatment can be carried out at the above reaction temperature for 35 hours to 60 hours to form the active material precursor.

[0095] In one embodiment, the active material precursor can be washed with distilled water. By this washing, the sulfur (S) content of the active material precursor can be adjusted to 1000 ppm to 3000 ppm. Since the sulfur (S) content in the active material precursor is within the above range, even at a relatively low temperature, microcrystals of the (104) plane and microcrystals of the (110) plane can easily grow.

[0096] The active material precursor can be reacted with a lithium source to prepare a lithium transition metal oxide. The lithium source can include, for example, 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.

[0097] For example, the active material precursor can be mixed with the lithium source, and then lithium transition metal oxide particles can be prepared as the cathode active material through a calcination process.

[0098] In some embodiments, a compound containing Mg, Sr, Ba, B, Al, Si, Ti, Zr, Y, or W can be used together with the lithium source. For example, salts (such as carbonates) of the above metal elements, hydroxides, or oxides can be reacted with the lithium source.

[0099] The metal element can promote the crystal growth of the (104) plane and the (110) plane of the active material precursor, and can promote the doping of sulfur elements. For example, a compound containing the metal element can be used as a crystal growth promoter. Through metal element sources such as Al, Zr, and W, the microcrystal sizes of the (104) plane and the (110) plane can be easily adjusted to the desired range.

[0100] In some embodiments, the crystal growth promoter can include a compound containing Zr or W and a compound containing Al. For example, the crystal growth promoter can include a mixture of at least one of Zr oxide or W oxide and Al oxide. Therefore, the microcrystal sizes of each crystal plane of the cathode active material can be easily adjusted to the desired range.

[0101] In one embodiment, the metal element can be consumed by the crystal growth of the active material precursor, and thus may not be included in the calcined cathode active material.

[0102] In one embodiment, the metal element may be present as a dopant of the positive electrode active material to replace a part of Ni, Co, and Mn inside the particles, and may also be present as a surface coating agent on the surface of the active material particles.

[0103] In some embodiments, the calcination temperature may be about 700 °C to 1000 °C, 800 °C to 1000 °C, or 850 °C to 980 °C. Within the above calcination temperature range, a lithium metal oxide in single crystal form can be easily formed, and at the same time, the growth of crystal planes can be promoted.

[0104] In some embodiments, the heating rate of the calcination process may be 0.5 °C / minute to 4 °C / minute or 1 °C / minute to 3 °C / minute.

[0105] In some embodiments, the calcination time may be 5 hours to 24 hours or 10 hours to 20 hours.

[0106] The sulfur element contained in the active material precursor can promote the growth of (104) and (110) planes, and can control the crystal growth direction, so that the microcrystal size ratio can be maintained within an appropriate range.

[0107] According to some embodiments, the lithium transition metal oxide particles formed as the positive electrode active material can be further subjected to a cleaning process. The cleaning process may include washing with an aqueous solvent or an organic solvent. Through the cleaning process, lithium impurities (such as Li2O, Li2CO3, LiOH, etc.) remaining on the surface of the lithium transition metal oxide particles can be removed.

[0108] Figure 1 and Figure 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Hereinafter, with reference to Figure 1 and Figure 2 , the positive electrode for a lithium secondary battery and the lithium secondary battery will be described together.

[0109] Referring to Figure 1 and Figure 2 , the lithium secondary battery may include a positive electrode 100 and a negative electrode 130, and the negative electrode 130 is disposed opposite to the positive electrode 100.

[0110] The positive electrode 100 may include a positive electrode active material layer 110, and the positive electrode active material layer 110 is formed by coating the above positive electrode active material on a positive electrode current collector 105.

[0111] For example, the above-mentioned positive electrode active material can be mixed and stirred with a binder, a conductive material, and / or a dispersing material, etc. in a solvent to prepare a slurry. The slurry can be coated on the positive electrode current collector 105 and then calendered and dried to manufacture the positive electrode 100.

[0112] The positive electrode current collector 105 can include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector 105 can also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0113] The binder can include, for example, organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc. or water-based binders such as styrene-butadiene rubber (SBR), and can be used together with thickeners such as carboxymethyl cellulose (CMC).

[0114] For example, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of the binder used to form the positive electrode active material layer can be reduced, and the amount of the positive electrode active material can be relatively increased, so the power and capacity of the secondary battery can be improved.

[0115] The conductive material can be included to promote electron migration between the active material particles. For example, the conductive material can include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, etc. and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0116] The negative electrode 130 can include a negative electrode current collector 125 and a negative electrode active material layer 120, and the negative electrode active material layer 120 is formed by coating a negative electrode active material on the negative electrode current collector 125.

[0117] The negative electrode active material can be a material known in the art that allows lithium ions to be intercalated and deintercalated without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium alloys; silicon (Si)-based compounds or tin, etc. As examples of the amorphous carbon, hard carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. can be cited.

[0118] Examples of the crystalline carbon may include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Examples of the elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0119] The silicon-based compound may include, for example, a silicon-carbon composite compound such as silicon oxide or silicon carbide (SiC).

[0120] For example, the negative electrode active material may be mixed and stirred together with the above-mentioned binder, conductive material, thickener, etc. in a solvent to form a slurry. The slurry may be coated on at least one surface of the negative electrode current collector 125 and then calendered and dried to manufacture the negative electrode 130.

[0121] The binder and the conductive material may use substances that are substantially the same as or similar to the above-mentioned substances used in the positive electrode active material layer 110. In some embodiments, for compatibility with the carbon-based active material, the binder used to form the negative electrode may include, for example, a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0122] In some embodiments, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer membrane made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also include a non-woven fabric formed of glass fibers with a high melting point, polyethylene terephthalate fibers, etc.

[0123] According to an exemplary embodiment, the battery cell is defined by the positive electrode 100, the negative electrode 130, and the separator 140, and a plurality of the battery cells may be repeatedly arranged to form an electrode assembly 150. In some embodiments, the electrode assembly 150 may be of a winding type, a stacking type, a z-folding type, and a stack-folding type.

[0124] The electrode assembly 150 may be accommodated in the housing 160 together with the above-mentioned electrolyte, thereby defining a lithium secondary battery. For example, the above-mentioned electrolyte may impregnate the electrode assembly 150.

[0125] As Figure 1As shown, the tabs (the positive tab and the negative tab) can respectively protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the housing 160. The tabs can be fused to the one side of the housing 160 to form electrode leads (the positive lead 107 and the negative lead 127) extending to the outside of the housing 160 or exposed to the outside of the housing 160).

[0126] The lithium secondary battery can be made into, for example, a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin shape, etc.

[0127] Hereinafter, preferred embodiments are presented to help understand the present invention, but these embodiments are only for illustrating the present invention and not for limiting the claims. Various changes and modifications can be made to the embodiments within the scope and technical concept of the present invention, which is obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0128] Experimental Example

[0129] Example 1

[0130] (1) Preparation of the positive electrode active material

[0131] Using distilled water that has been bubbled with N2 for 24 hours to remove dissolved oxygen inside, NiSO4, CoSO4, and MnSO4 were mixed in a molar ratio of 60:10:30 to prepare a transition metal solution. The transition metal solution was added to a reactor at 60 °C, and NaOH and NH3·H2O were added. NaOH was added to the reactor at a constant rate such that the molar ratio of the transition metal in the transition metal solution to NaOH was 1:2, and NH3·H2O was added. The addition amount of NH3·H2O was more than 4 times the addition amount of the transition metal, and a coprecipitation reaction was carried out for 48 hours.

[0132] The reaction precipitate was separated using a centrifuge, and the reaction precipitate was washed with distilled water to obtain an active material precursor with the sulfur element content adjusted to be in the range of 1000 ppm to 3000 ppm.

[0133] The active material precursor, Li2CO3 as a lithium source, Al2O3 and ZrO2 as crystal growth promoters were mixed evenly. The mixture was placed in a calcination furnace and heated to 980 °C at a heating rate of 2 °C / minute, held at 980 °C for 10 hours, and then held at 800 °C for 2 hours. During the heating process and the holding process, oxygen was continuously introduced at a flow rate of 10 mL / minute.

[0134] After the calcination was completed, it was naturally cooled to room temperature and classified to obtain a positive electrode active material in single crystal form.

[0135] (2) Manufacture of secondary battery

[0136] The positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder are mixed in a mass ratio of 94:3:3 respectively to obtain a positive electrode mixture. Then, the positive electrode mixture is coated on an aluminum current collector and dried and calendered to obtain a positive electrode. After the calendering, the electrode density of the positive electrode is adjusted to 3.5 g / cm³ (cc) or more.

[0137] Prepare a negative electrode slurry, which contains 93% by weight of natural graphite as a negative electrode active material, 5% by weight of flake type conductive material KS6 as a conductive material, 1% by weight of styrene-butadiene rubber (SBR) as a binder, and 1% by weight of carboxymethyl cellulose (CMC) as a thickener. The negative electrode slurry is coated on a copper substrate and dried and calendered to obtain a negative electrode.

[0138] The positive electrode and negative electrode prepared as described above are respectively cut (notching) into specified sizes, and then a separator (polyethylene, thickness 25 μm) is provided between the positive electrode and the negative electrode and laminated. Then, the tab portions of the positive electrode and the negative electrode are welded respectively. The welded positive electrode / separator / negative electrode assembly is placed in a soft package, and three sides except the electrolyte injection surface are sealed. At this time, the portion having the tab is included in the sealed portion. Inject electrolyte through the electrolyte injection surface, seal the electrolyte injection surface, and then immerse for 12 hours or more.

[0139] The electrolyte is prepared by adding 1% by weight of vinylene carbonate (VC), 0.5% by weight of 1,3 - propanesultone (PRS), and 0.5% by weight of lithium bis(oxalato)borate (LiBOB) to a 1 M LiPF6 solution using a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio).

[0140] (3) Measurement of crystallite size

[0141] Measure the crystallite sizes of the (003) plane, (104) plane, and (110) plane of the positive electrode active material by XRD analysis and the Scherrer equation of Equation 1, and calculate the crystallite size ratio. The measurement results are shown in Table 2 below.

[0142] The specific XRD analysis equipment and conditions are shown in Table 1 below.

[0143] [Table 1]

[0144]

[0145] Example 2

[0146] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 1, except that in the preparation process of the positive electrode active material, the mixture of the active material precursor and Li2CO3 is put into a calcination furnace, heated to 980 °C at a heating rate of 2 °C per minute, maintained at 980 °C for 10 hours, and then cooled.

[0147] Example 3

[0148] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 2, except that in the preparation process of the positive electrode active material, the molar ratio of NiSO4, CoSO4, and MnSO4 is changed to 75:0:25, and the calcination temperature of the mixture is changed from 980 °C to 850 °C.

[0149] Example 4

[0150] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 1, except that in the preparation process of the positive electrode active material, the molar ratio of NiSO4, CoSO4, and MnSO4 is changed to 75:0:25, and the calcination temperature of the mixture is changed from 980 °C to 850 °C.

[0151] Example 5

[0152] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 1, except that in the preparation process of the positive electrode active material, the molar ratio of NiSO4, CoSO4, and MnSO4 is changed to 80:8:12, and the calcination temperature of the mixture is changed from 980 °C to 800 °C.

[0153] Example 6

[0154] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 2, except that in the preparation process of the positive electrode active material, the molar ratio of NiSO4, CoSO4, and MnSO4 is changed to 90:4:6, and the calcination temperature of the mixture is changed from 980 °C to 750 °C.

[0155] Comparative Example 1

[0156] The positive electrode active material and the secondary battery are manufactured by the same method as in Example 2, except that in the preparation process of the positive electrode active material, the mixture does not contain a crystal growth promoter, and the calcination temperature is changed from 980 °C to 850 °C.

[0157] Comparative Example 2

[0158] The positive electrode active material and the secondary battery were fabricated in the same manner as in Comparative Example 1, except that in the preparation process of the positive electrode active material, the molar ratio of NiSO4, CoSO4, and MnSO4 was changed to 75:0:25, and the calcination temperature was changed to 750 °C.

[0159] Comparative Example 3

[0160] The positive electrode active material and the secondary battery were fabricated in the same manner as in Example 4, except that in the preparation process of the positive electrode active material, the calcination temperature of the mixture was changed from 850 °C to 700 °C.

[0161] Comparative Example 4

[0162] The positive electrode active material and the secondary battery were fabricated in the same manner as in Example 6, except that in the preparation process of the positive electrode active material, the calcination temperature of the mixture was changed from 750 °C to 680 °C.

[0163] Comparative Example 5

[0164] The positive electrode active material and the secondary battery were fabricated in the same manner as in Example 1, except that in the preparation process of the positive electrode active material, the mixture was placed in a calcination furnace and heated to 980 °C at a heating rate of 5 °C / minute, held at 980 °C for 5 hours, and then held at 800 °C for 2 hours.

[0165] Comparative Example 6

[0166] The positive electrode active material and the secondary battery were fabricated in the same manner as in Comparative Example 5, except that in the preparation process of the positive electrode active material, only Al2O3 was added as a crystal growth promoter.

[0167] Comparative Example 7

[0168] The positive electrode active material and the secondary battery were fabricated in the same manner as in Example 1, except that in the preparation process of the positive electrode active material, the calcination temperature was changed from 980 °C to 850 °C, and only Al2O3 was added as a crystal growth promoter.

[0169] Comparative Example 8

[0170] The positive electrode active material and the secondary battery were fabricated in the same manner as in Example 1, except that in the preparation process of the positive electrode active material, the calcination temperature was changed from 980 °C to 850 °C, and only ZrO2 was added as a crystal growth promoter.

[0171] [Table 2]

[0172]

[0173] Experimental Example

[0174] (1) Evaluation of High - Temperature Life Retention Rate

[0175] The lithium secondary batteries of the examples and comparative examples were repeatedly charged by CC / CV (0.1C 4.3V, 0.05C cut - off) and discharged by CC (0.1C cut - off at 3.0V) twice at 25°C, and the discharge capacity C1 of the second time was measured. Then the lithium secondary batteries were charged by CC / CV (0.1C 4.3V, 0.05C cut - off).

[0176] The charged lithium secondary batteries were stored at 60°C for 3 weeks, then further left at room temperature for 30 minutes, and then discharged by CC (0.5C cut - off at 3.0V), and the discharge capacity C2 was measured.

[0177] The capacity retention rate after high - temperature storage was calculated as follows.

[0178] Capacity retention rate after high - temperature storage (%) = C2 / C1×100%

[0179] (2) Evaluation of High - Temperature Resistance Increase Rate

[0180] The lithium secondary batteries of the examples and comparative examples were charged by CC / CV (0.1C, 0.05C) at 25°C to set the SOC to 50%. Then the lithium secondary batteries were discharged at a current of 1C, and the voltage before discharge (V0) and the voltage during discharge 10 seconds later (V1) were measured, and the room - temperature resistance was calculated as follows.

[0181] Room - temperature resistance=(V1 - V0) / 1C

[0182] The lithium secondary batteries of the examples and comparative examples were charged by CC / CV (0.1C, 0.05C) at 60°C to adjust the SOC to 50%. Then the lithium secondary batteries were discharged at a current of 1C, and the voltage before discharge (V2) and the voltage during discharge 10 seconds later (V3) were measured, and the high - temperature resistance was calculated as follows.

[0183] High - temperature resistance=(V3 - V2) / 1C

[0184] The high - temperature resistance increase rate was evaluated by calculating the percentage of the ratio of the high - temperature resistance to the room - temperature resistance.

[0185] (3) Measurement of Microcrystalline Size Retention Rate

[0186] After evaluating the high - temperature life retention rate, the microcrystalline sizes (A2) of the (003), (104), and (110) planes of the positive - electrode active material were measured, and the retention rate relative to the initial microcrystalline size (A1) was measured.

[0187] The microcrystalline size retention rate is calculated as follows.

[0188] Microcrystalline size retention rate = {1 - (|A2 - A1| / A1)} × 100%

[0189] The evaluation results are shown in Table 3 below.

[0190] [Table 3]

[0191]

[0192] Referring to Table 3, in the examples, the high-temperature life characteristics and high-temperature resistance characteristics of the lithium secondary battery are improved. In addition, even when the nickel content of the positive electrode active material increases, the high-temperature life retention rate is improved. In the examples, the microcrystalline size change rate of the positive electrode active material after high-temperature cycling is smaller than that of the positive electrode active material in the comparative examples.

[0193] In the comparative examples, when the lithium secondary battery is charged and discharged at high temperature, the life retention rate of the lithium secondary battery is significantly reduced, or the resistance increases significantly compared with the initial stage. In addition, the resistance increases at high temperature. In the comparative examples, the microcrystalline size of the positive electrode active material after high-temperature cycling increases significantly.

Claims

1. A positive electrode active material for a lithium secondary battery, the positive electrode active material for a lithium secondary battery having a lithium transition metal oxide structure, The ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material for lithium secondary batteries measured by XRD analysis is 0.7 to 2.0, and the ratio of the crystallite size of the (003) plane to the crystallite size of the (104) plane is 0.7 to 2.

0.

2. The positive electrode active material for lithium secondary battery according to claim 1, wherein The crystallite size of the (003) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 350 nm or more.

3. The positive electrode active material for lithium secondary battery according to claim 2, wherein The crystallite size of the (003) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 350 nm to 700 nm.

4. The positive electrode active material for lithium secondary battery according to claim 1, wherein The positive electrode active material for a lithium secondary battery has a single crystal form.

5. The positive electrode active material for lithium secondary battery according to claim 1, wherein The positive electrode active material for a lithium secondary battery has a layered structure.

6. The positive electrode active material for lithium secondary battery according to claim 1, wherein The ratio of the crystallite size of the (003) plane to the crystallite size of the (110) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 0.7 to 1.

7.

7. The positive electrode active material for lithium secondary battery according to claim 1, wherein The ratio of the crystallite size of the (003) plane to the crystallite size of the (104) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 0.7 to 1.

7.

8. The positive electrode active material for lithium secondary battery according to claim 1, wherein The crystallite size of the (104) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 300 nm to 760 nm.

9. The positive electrode active material for lithium secondary battery according to claim 1, wherein The crystallite size of the (110) plane of the positive electrode active material for a lithium secondary battery measured by XRD is 300 nm to 700 nm.

10. The positive electrode active material for lithium secondary battery according to claim 1, wherein The lithium transition metal oxide contains nickel.

11. The positive electrode active material for lithium secondary battery according to claim 10, wherein The content of nickel in 100 mol % of the total metal elements excluding lithium in the lithium transition metal oxide is 60 mol % or more.

12. The positive electrode active material for lithium secondary battery according to claim 10, wherein The lithium transition metal oxide further contains manganese.

13. The positive electrode active material for lithium secondary battery according to claim 12, wherein The lithium transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li a Ni x Mr y M 1-x-y O2 In Chemical Formula 1, M includes at least one of Co, Mg, Sr, Ba, B, Al, Zr, Ti, Y, and W, 0.95≤a≤1.1, 0.6≤x<0.9, and 0.04≤y≤0.

3.

14. A positive electrode for a lithium secondary battery, comprising: Positive electrode current collector; as well as A positive electrode active material layer is provided on at least one side of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material for a lithium secondary battery according to claim 1.

15. A lithium secondary battery comprising: A positive electrode, the positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 1; as well as A negative electrode is arranged opposite to the positive electrode.

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