Lithium secondary battery

Abstract

A lithium secondary battery according to the present invention includes a positive electrode and a negative electrode disposed opposite the positive electrode. The slip step difference of the positive electrode is 20 nm or less. The slip segment difference is defined in such a manner that, in a line scan pattern obtained by measuring the surface of the positive electrode in a fully discharged state after 500 times of charging and discharging of the battery using an atomic force microscope (AFM), the distance between a pair of parallel lines in which the slope of the observed mountain shape is not zero may include two or more.

Description

Technical Field

[0001] This invention provides a lithium secondary battery. Background Technology

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

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

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

[0005] Because lithium-ion batteries are preferably characterized by high capacity, high stability, and long lifespan, methods have been proposed to introduce single-particle structured positive electrode active materials or to adjust the composition of the positive electrode active material layer. However, with the charging and discharging of the battery, the structure of the positive electrode active material will change, leading to a significant reduction in battery capacity. Therefore, there is a need to develop a high-capacity positive electrode with sufficiently long lifespan. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] One technical problem of the present invention is to provide a lithium secondary battery with improved electrochemical and physical properties.

[0008] (II) Technical Solution

[0009] The lithium secondary battery according to the present invention includes a positive electrode and a negative electrode disposed opposite to the positive electrode. The slip step of the positive electrode is less than 20 nm. The slip step is defined as the distance between a pair of parallel lines with non-zero slopes that may contain two or more observed mountain shapes in a line scan image of the surface of the positive electrode in a fully discharged state after 500 charge-discharge cycles using atomic force microscopy (AFM).

[0010] According to an exemplary implementation, the slip step of the positive electrode can be less than 10 nm.

[0011] According to an exemplary embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on one side of the positive electrode current collector. The positive electrode active material layer may contain coated particles. The coated particles may include a core and at least one metal oxide particle. The core may contain a lithium-nickel metal oxide with a layered structure, and the core may have a single-particle structure. The metal oxide particle may be disposed on the surface of the core.

[0012] According to an exemplary embodiment, the average particle size (D50) of the metal oxide particles can be from 100 nm to 450 nm.

[0013] According to an exemplary embodiment, the average particle size (D50) of the metal oxide particles can be from 220 nm to 300 nm.

[0014] According to an exemplary embodiment, the metal oxide particles may be arranged in an island-like pattern on the surface of the core.

[0015] According to an exemplary embodiment, the metal oxide particles may have a spinel crystal structure, a perovskite crystal structure, a garnet crystal structure, or a sodium superionic conductor crystal structure.

[0016] According to an exemplary embodiment, the metal oxide particles may contain at least one selected from Co, Ba, Ti, Sr, Li, La, Zr, Al, Y, W and P.

[0017] According to an exemplary embodiment, the content of the metal oxide particles in the total weight of the coated particles can be from 500 ppm to 3000 ppm.

[0018] According to an exemplary embodiment, in the lithium-nickel metal oxide, the nickel content can be from 60 mol% to 99 mol% of the total moles of elements other than lithium and oxygen.

[0019] According to an exemplary embodiment, the average particle size (D50) of the nucleus can be from 1 μm to 10 μm.

[0020] According to an exemplary embodiment, the grain size of the core can be from 200 nm to 600 nm.

[0021] According to an exemplary implementation, the 500 charge-discharge cycles can be performed by charging the lithium secondary battery at a voltage of 4.3V to 4.5V and discharging it to a voltage of 3.0V, and repeating the charge-discharge cycle 500 times.

[0022] According to an exemplary embodiment, the lithium secondary battery may have an operating voltage of 4.3V to 4.7V.

[0023] (III) Beneficial Effects

[0024] The lithium secondary battery according to an exemplary embodiment of the present invention exhibits minimal deformation of the crystal structure and shape of the particles even during repeated charge-discharge cycles. Furthermore, it can possess high capacity. Therefore, the lifespan characteristics of high-capacity batteries can be improved.

[0025] The lithium secondary battery according to an exemplary embodiment of the present invention can have a high capacity while exhibiting minimal capacity reduction during repeated charge and discharge.

[0026] The lithium secondary battery of the present invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. Furthermore, the positive electrode for the secondary battery of the present invention, and the lithium secondary battery including the positive electrode, can be used in eco-friendly electric vehicles, hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0027] Figure 1 and Figure 2 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment.

[0028] Figure 3 This is a schematic diagram of the cross-section of coated particles according to an exemplary embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of the cross-section of the existing positive electrode active material particles after charging and discharging.

[0030] Figure 5 This is a cross-sectional schematic diagram of coated particles according to an exemplary embodiment of the present invention after charging and discharging.

[0031] Figure 6 This is a scanning electron microscope (SEM) image of the coated particles from Example 1.

[0032] Figure 7 The image shows a scanning electron microscope (SEM) image of the coated particles of Comparative Example 2.

[0033] Figure 8a This is an AFM image of the positive electrode after repeated charge and discharge in Example 2.

[0034] Figure 8b It is along Figure 8a Example 2 of the dashed line scan shows the positive electrode after repeated charge and discharge based on the line scan step diagram.

[0035] Figure 9a This is the AFM image of the positive electrode after repeated charge and discharge of Comparative Example 2.

[0036] Figure 9b It is along Figure 9a The comparison example 2 shows the positive electrode after repeated charge and discharge based on the step diagram of the dashed line scan.

[0037] Explanation of reference numerals in the attached figures:

[0038] 10: nucleus; 20: metal oxide particles

[0039] 100: Positive electrode; 105: Positive electrode current collector

[0040] 107: Positive electrode lead; 110: Positive electrode active material layer

[0041] 120: Negative electrode active material layer; 125: Negative electrode current collector

[0042] 127: Negative lead; 130: Negative electrode

[0043] 140: Diaphragm; 150: Electrode assembly

[0044] 160: Casing Detailed Implementation

[0045] An exemplary embodiment of the present invention provides a lithium secondary battery.

[0046] According to an exemplary embodiment of the present invention, a lithium secondary battery includes a positive electrode active material for a secondary battery, said positive electrode active material comprising coated particles having metal oxide particles on their core surface. Furthermore, a lithium secondary battery according to an exemplary embodiment of the present invention includes a positive electrode comprising said positive electrode active material for a secondary battery. A lithium secondary battery according to an exemplary embodiment of the present invention includes said positive electrode.

[0047] The term “average particle size (D50)” used in this specification refers to the average particle size of a plurality of particles. D50 may be the average particle size obtained at the point corresponding to 50% of the cumulative volume distribution of the prepared active material particles.

[0048] The method for measuring the cumulative volume distribution of the particles is not particularly limited, but it can be measured using a laser diffraction particle size analyzer, such as a Malvern 3000 device.

[0049] The present invention will now be described in detail with reference to the accompanying drawings. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described herein.

[0050] A lithium secondary battery according to an exemplary embodiment includes the aforementioned positive electrode and a negative electrode disposed opposite to the positive electrode. The lithium secondary battery may include a separator and an electrolyte disposed between the positive electrode and the negative electrode.

[0051] Hereinafter, with reference to the accompanying drawings, a lithium secondary battery according to an exemplary embodiment will be described in more detail. Figure 1 and Figure 2 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment, respectively. For example, Figure 2 It is along Figure 1 A cross-sectional view taken from the I-I' line.

[0052] Reference Figure 1 and Figure 2 The lithium secondary battery may include an electrode assembly comprising a positive electrode 100, a negative electrode 130, and a separator 140 disposed between the positive and negative electrodes. The electrode assembly may be contained in a housing 160 and immersed in the electrolyte.

[0053] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110, and the positive electrode active material layer 110 may contain a positive electrode active material.

[0054] The positive current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, such as aluminum or aluminum alloys.

[0055] The positive electrode active material layer 110 can be disposed on at least one side of the positive electrode current collector 105. For example, the positive electrode active material layer 110 can be disposed on one or both sides of the positive electrode current collector 105.

[0056] The positive electrode active material may contain coated particles.

[0057] Figure 3 This is a schematic diagram of the cross-section of coated particles according to an exemplary embodiment of the present invention.

[0058] Reference Figure 3 The coated particles may include a core 10 and metal oxide particles 20 disposed on the surface of the core 10.

[0059] Core 10 may contain a lithium nickel metal oxide. In addition to nickel, the lithium nickel metal oxide may further contain at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0060] According to an exemplary embodiment, the lithium-nickel metal oxide may contain nickel and manganese. Therefore, while enabling high battery capacity, the battery's lifespan stability can be improved.

[0061] According to an exemplary embodiment, in the lithium-nickel metal oxide, the nickel content can be from 60 mol% to 99 mol% of the total moles of elements other than lithium and oxygen.

[0062] Within the aforementioned range, the increase in internal resistance caused by changes in the crystal structure of the positive electrode active material during rapid charging and discharging of the battery can be reduced without significantly reducing the capacity of the positive electrode.

[0063] According to an exemplary embodiment, the lithium nickel metal oxide may include a layered structure represented by the following chemical formula 1.

[0064] [Chemical Formula 1]

[0065] Li x Ni a M b O 2+z

[0066] In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can include Co, Mn, and / or Al.

[0067] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood as including the introduction and substitution of additional elements.

[0068] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 1.

[0069] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may act as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0070] For example, the lithium nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0071] [Chemical Formula 1-1]

[0072] Li x Ni a M1 b1 M2 b2 O 2+z

[0073] In chemical formula 1-1, M1 may include Co, Mn and / or Al. M2 may include the aforementioned auxiliary elements. In chemical formula 1-1, the elements can be 0.9≤x≤1.2, 0.3≤a≤0.8, 0.01≤b1≤0.4, 0≤b2≤0.1, and -0.5≤z≤0.1.

[0074] The lithium-nickel metal oxide may further comprise coating elements or doping elements. For example, elements substantially the same as or similar to the aforementioned auxiliary elements may be used as coating elements or doping elements. For example, one or more combinations of the aforementioned elements may be used as coating elements or doping elements.

[0075] The coating element or doping element may exist on the surface of the lithium nickel metal oxide particles, or may penetrate through the surface of the lithium nickel metal oxide particles and be contained within the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0076] According to an exemplary embodiment, core 10 may have a single-particle structure. The term "single-particle structure" as used herein is used, for example, to refer to a secondary particle that is substantially composed of multiple primary particles (e.g., more than 10) aggregated to form a single particle.

[0077] For example, core 10 is essentially composed of particles in the form of single particles, excluding secondary particle structures formed by the assembly or aggregation of primary particles. Furthermore, the term "single-particle structure" as used in this specification does not exclude cases where, for example, two to ten single particles are attached or adhered to each other in a monomeric form.

[0078] The single-particle structure can also include multiple primary particles fused together to form a structure that is essentially a single particle.

[0079] For example, core 10 can have a single-particle structure containing fewer than 10 grains.

[0080] For example, core 10 can have a single-crystal structure. The single-crystal structure can include a structure in which a single grain constitutes a particle. For example, the single-crystal structure can be distinguished based on ion images obtained by analyzing the particle cross-section using a focused ion beam (FIB). For example, if the particle has a single-crystal structure, a single crystal can be observed in the FIB analysis image based on differences in crystal orientation.

[0081] According to an exemplary embodiment, the average particle size (D50) of core 10 can be from 1 μm to 10 μm. According to some embodiments, the average particle size (D50) of core 10 can be from 2 μm to 5 μm.

[0082] Within the aforementioned range, the stability of the positive electrode can be improved, and the durability of the positive electrode can be maintained without reducing it during repeated charging and discharging of the battery.

[0083] According to an exemplary embodiment, the grain size of core 10 can be from 200 nm to 600 nm. According to some embodiments, the grain size of core 10 can be from 200 nm to 400 nm.

[0084] For example, the grain size of core 10 can be measured by X-ray diffraction (XRD) analysis. According to an exemplary embodiment, the grain size can be calculated using the full width at half maximum (FWHM) of the peak corresponding to the (104) crystal plane in the XRD pattern obtained from the XRD analysis of core 10, and by Equation 1 below as a Scherrer equation.

[0085] [Formula 1]

[0086]

[0087] In Equation 1, L represents the grain size, λ represents the X-ray wavelength, β represents the full width at half maximum (FWHM) of any peak, and θ represents the diffraction angle.

[0088] For example, the XRD analysis can be performed on dry powder of metal oxide particles using Cu Kα rays as the light source, within a diffraction angle (2θ) range of 10° to 120°, at a scan rate of 0.0065° / step.

[0089] The lithium-nickel metal oxide can have a layered structure. In a layered structure, a large number of lithium ions can be embedded between the two-dimensional layers, thereby increasing the capacity of the cathode.

[0090] Figure 4 This is a schematic diagram of the cross-section of the existing positive electrode active material particles after charging and discharging.

[0091] Reference Figure 4 When a battery containing a positive electrode active material with lithium nickel metal oxide is charged, lithium may be unevenly intercalated between layers. Therefore, interlayer slippage, such as gliding, may occur, which may create unevenness on the surface of the charged positive electrode active material, and the morphology of the positive electrode active material may not be completely and reversibly restored after discharge.

[0092] When the battery is repeatedly charged and discharged, damage such as cracks may occur around the area where slippage occurs. Therefore, the layered structure may irreversibly transform into a rock salt structure. This slippage phenomenon is particularly likely to occur when the positive electrode active material has a single-particle structure.

[0093] Figure 5 This is a cross-sectional schematic diagram of coated particles according to an exemplary embodiment of the present invention after charging and discharging.

[0094] The coated particles according to the present invention may comprise at least one metal oxide particle 20 disposed on the surface of the core 10 comprising the lithium nickel metal oxide having a layered structure. Therefore, the metal oxide particle 20 can suppress the formation of steps caused by slippage, and even during repeated charge and discharge, can prevent cracks and changes in the crystal structure of the positive electrode active material particles caused by slippage.

[0095] The average particle size (D50) of the metal oxide particles 20 can be from 100 nm to 450 nm. According to an exemplary embodiment, the average particle size (D50) of the metal oxide particles 20 can be from 200 nm to 400 nm, from 210 nm to 350 nm, or from 220 nm to 300 nm.

[0096] Within the aforementioned range, slippage caused by the layered structure of lithium nickel metal oxide can be suppressed, thereby improving the durability of the positive electrode active material and enhancing the battery's lifespan characteristics.

[0097] When the average particle size (D50) of the metal oxide particles 20 is less than 100 nm, the particle size of the metal oxide particles 20 is insufficient to exceed the step size at which slippage occurs, and may not be able to suppress the formation of the step size (e.g., referring to...). Figure 4 Therefore, it may degrade the battery's lifespan characteristics.

[0098] When the average particle size (D50) of the metal oxide particles 20 exceeds 450 nm, the volume of the metal oxide particles 20 on the outer surface of the core 10 is relatively large, which may lead to a relative decrease in the density of the positive electrode active material in the positive electrode active material layer. Furthermore, the coating of larger particles may act as a resistor during lithium insertion / extraction. Therefore, it may reduce the energy density and capacity of the positive electrode.

[0099] According to an exemplary embodiment, the metal oxide particles 20 may be disposed in an island-like manner on the surface of the core. The term "island-like" is a concept distinct from a continuous layered coating, and multiple metal oxide particles 20 may not be disposed integrally on the surface of the core 10.

[0100] For example, a plurality of metal oxide particles 20 may be disposed in at least a portion of the surface of the core 10. For example, a plurality of metal oxide particles 20 may be disposed in two or more regions spaced apart from each other on the surface of the core 10.

[0101] Therefore, the migration path of lithium ions can be ensured, allowing lithium ions to be smoothly inserted and extracted between the layered structures.

[0102] According to an exemplary embodiment, the metal oxide particles 20 may have a spinel crystal structure, a perovskite crystal structure, a garnet crystal structure, or a sodium superionic conductor crystal structure. The metal oxide particles 20 may contain an oxide-based solid electrolyte, thus without reducing the lithium-ion conductivity and / or conductivity of the positive electrode containing the coated particles.

[0103] According to an exemplary embodiment, the metal oxide particles 20 may include Co, Ba, Ti, Sr, Li, La, Zr, Al, Y, W, and P, etc. For example, the metal oxide particles 20 may include Co, Ba, Ti, Sr, Li, La, Zr, Al, etc.

[0104] In one embodiment, the metal oxide particles 20 may not contain nickel. Therefore, the metal oxide particles 20 do not function as active materials during battery charging and discharging, thus avoiding volume changes caused by charging and discharging, and more effectively preventing nucleus slippage.

[0105] When the metal oxide particles 20 are simple inorganic materials that do not have lithium-ion conductivity, the portion coated on the surface of the core 10 in the form of a single particle may make it difficult for lithium to pass through, which may reduce the battery capacity or increase the battery's internal resistance.

[0106] In the positive electrode active material of the present invention, the metal oxide particles 20 having a lithium-ion conductive structure can prevent the reduction of battery capacity caused by coating, and can also improve the slippage phenomenon of the core 10 of the single particle structure.

[0107] When the metal oxide particles 20 have a spinel crystal structure, the metal oxide particles 20 are compounds with a spinel crystal structure or a spinel-like crystal structure, such as Co3O4.

[0108] When the metal oxide particles 20 have a garnet crystal structure, the metal oxide particles 20 are compounds with a garnet crystal structure or a garnet-like crystal structure, for example, they may include LLZO-based compounds.

[0109] The LLZO-based compound can be an oxide containing lithium, lanthanum, and zirconium. The LLZO-based compound may further contain Al, Ga, In, Sc, Ba, Nb, etc. For example, it may include Li7La3Zr2O. 12 wait.

[0110] When the metal oxide particles 20 have a sodium superionic conductor crystal structure, the metal oxide particles 20 are compounds with a sodium superionic conductor crystal structure or a sodium-like superionic conductor crystal structure, for example, they may include LATP-based compounds, LYZP-based compounds, LAGP-based compounds, etc.

[0111] The LATP-based compound can be a phosphorus oxide containing lithium, aluminum, and titanium. For example, it can include Li. 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.

[0112] The LYZP-based compound can be a phosphorus oxide containing lithium, yttrium, and zirconium. For example, it can include Li. 1.3 Y 0.3 Zr 1.7 (PO4)3, etc. The LAGP-based compound can be a phosphorus oxide containing lithium, aluminum, and germanium. For example, it can include Li... 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.

[0113] When the metal oxide particles 20 have a perovskite crystal structure, the metal oxide particles 20 are compounds with a perovskite crystal structure or a perovskite-like crystal structure, for example, they may include LLTO-based compounds, BaTiO3, SrTiO3, etc.

[0114] The LLTO-based compound can be an oxide containing lithium, lanthanum, and titanium. For example, it can include Li.0.31 La 0.56 TiO3 and the like.

[0115] According to an exemplary embodiment, in the total weight of the coated particles, the content of the metal oxide particles may be from 500 ppm to 3000 ppm. According to some embodiments, in the total weight of the coated particles, the content of the metal oxide particles may be from 700 ppm to 1500 ppm or from 800 ppm to 1200 ppm.

[0116] Within the above ranges, the slip phenomenon of the layered structure can be further suppressed, and the battery capacity can be not reduced.

[0117] In an exemplary embodiment, in the total weight of the positive electrode active material, the content of the coated particles may be 50% by weight or more. In some embodiments, in the total weight of the positive electrode active material, the content of the coated particles may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. For example, the positive electrode active material may be substantially formed of the coated particles. For example, the positive electrode active material may be formed of the coated particles.

[0118] In some embodiments, the positive electrode active material may further include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, a lithium iron phosphate-based (LFP) active material (e.g., LiFePO4), and the like.

[0119] In some embodiments, the positive electrode active material may include, for example, a Mn-rich-based active material, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO)-based active material, a Co-less-based active material having a chemical structure or crystal structure represented by Chemical Formula 2 below.

[0120] [Chemical Formula 2]

[0121] p[Li2MnO3]·(1-p)[Li q JO2]

[0122] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0123] According to an exemplary embodiment, a method for preparing the positive electrode active material for secondary batteries can be provided. For example, the positive electrode active material for secondary batteries can be prepared by the following method, but is not limited thereto.

[0124] According to an exemplary embodiment, core particles comprising lithium nickel metal oxide with a layered structure can be mixed with metal oxide particles. The mixing can be dry mixing or wet mixing.

[0125] The mixture prepared by the mixing process can be heat-treated to prepare the coated particles. For example, the mixture can be heat-treated at a temperature of 500°C to 750°C to prepare the coated particles.

[0126] For example, the heat treatment can be carried out in an oxygen atmosphere.

[0127] For example, the heat treatment can be carried out for 2 to 5 hours within the above temperature range.

[0128] The positive electrode active material for secondary batteries can be mixed and stirred with binders, conductive materials, and / or dispersing materials in a solvent to prepare a slurry. The slurry can then be coated onto a positive electrode current collector, followed by drying and calendering to manufacture the positive electrode.

[0129] The adhesive may include, for example, organic-based adhesives such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or water-based adhesives such as styrene-butadiene rubber (SBR), and may be used with thickeners such as carboxymethyl cellulose (CMC).

[0130] For example, PVDF-based binders can be used as positive electrode binders. In this case, the amount of binder used to form the positive electrode active material layer can be reduced, and the amount of positive electrode active material can be relatively increased, thus improving the power and capacity of the secondary battery.

[0131] The conductive material may be included to facilitate electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials containing perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0132] The solvent may include, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0133] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed by coating the negative electrode current collector 125 with a negative electrode active material. If necessary, it may also include a negative electrode binder and a conductive material.

[0134] For example, the negative electrode active material can be any material known in the art that enables lithium ion insertion and extraction without particular restriction. For example, the negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon (Si)-based compounds; or tin, etc. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0135] Examples of crystalline carbon include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and other graphite-based carbons. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0136] The silicon-based compound may include, for example, silicon, silicon oxide, or silicon carbide (SiC) and other silicon-carbon composite compounds.

[0137] In some embodiments, the content of silicon active material in the total weight of the negative electrode active material can be from 1% to 20% by weight, from 1% to 15% by weight, or from 1% to 10% by weight.

[0138] The negative electrode active material can be mixed with binders, conductive materials, and / or dispersing materials in a solvent to prepare a slurry. The slurry is then coated onto the negative electrode current collector 125, followed by drying and calendering to prepare the negative electrode active material layer 120.

[0139] For example, the negative electrode active material can be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry is coated / deposited onto a negative electrode current collector, then dried and calendered to prepare the negative electrode active material layer 120. The coating process can be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The negative electrode active material layer 120 may further contain a binder, and optionally may further contain conductive materials, thickeners, etc.

[0140] Non-limiting examples of the solvent may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc.

[0141] The adhesive, conductive material, and thickener may be any of the aforementioned substances that can be used in the manufacture of the positive electrode.

[0142] In some implementations, the negative electrode adhesive may be a styrene-butadiene rubber (SBR) based adhesive, carboxymethyl cellulose (CMC), polyacrylic acid based adhesive, or poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesive, etc.

[0143] The separator 140 may be located between the positive electrode 100 and the negative electrode 130. The separator 140 may comprise a porous polymer membrane prepared from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also comprise a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0144] In some embodiments, the area (e.g., the contact area with the separator 140) and / or volume of the negative electrode 130 can be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 130 without being deposited midway.

[0145] According to an exemplary embodiment, the battery cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150, for example, in a jelly roll form, can be formed by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, lamination, folding, etc., of the separator 140.

[0146] The electrode assembly 150, together with a non-aqueous electrolyte according to the exemplary embodiment described above, is housed in a housing 160, thereby defining a lithium secondary battery. According to the exemplary embodiment, the electrolyte may be a non-aqueous electrolyte.

[0147] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0148] As the aforementioned organic solvents, examples such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran can be used. These can be used alone or in combination of two or more.

[0149] like Figure 1 As shown, the tabs (positive or negative tabs) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one side of the housing 160. The tabs can be fused to said side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0150] The lithium secondary battery can be made in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0151] In the lithium secondary battery of the present invention, the slip range of the positive electrode is less than 20 nm. The slip range can be a value that quantitatively represents the amount of slippage occurring on the surface of the positive electrode after repeated charging and discharging of the lithium secondary battery.

[0152] The slip difference is calculated by using a line scan of the positive electrode surface obtained by atomic force microscopy (AFM) after 500 cycles of repeated charge and discharge of the lithium secondary battery in a fully discharged state.

[0153] For example, the positive electrode can be separated from the lithium secondary battery after repeated charge-discharge cycles in a fully discharged state (e.g., SOC 0%). The surface of the positive electrode after these repeated charge-discharge cycles can be observed and analyzed using atomic force microscopy. Any surface region of the positive electrode active material layer can be observed and analyzed using atomic force microscopy.

[0154] When batteries containing positive electrode active materials with lithium metal oxides are repeatedly charged and discharged, damage such as cracks may occur around the areas where slippage occurs. Therefore, the layered structure may irreversibly transform into a rock salt structure. Furthermore, repeated charging and discharging may lead to an increase in slippage distance and potentially further degrade battery performance.

[0155] The lithium secondary battery according to the present invention can suppress slippage even during repeated charge and discharge cycles. Therefore, the formation of unevenness on the surface of the positive electrode active material layer can be reduced, and the slippage difference can be less than 20 nm. Thus, the battery's lifespan characteristics can be improved.

[0156] According to an exemplary embodiment, the 500 charge-discharge cycles can be performed as follows: charging the lithium secondary battery at a voltage of 4.3V to 4.5V and discharging it to a voltage of 3.0V, repeating this charge-discharge cycle 500 times. For example, the charging can be performed at 0.5C CC / CV (0.05C cutoff) to 4.3V to 4.5V, and the discharging can be performed at 1.0C to a voltage of 3.0V. The 500 charge-discharge cycles can be performed at a temperature of 30°C to 60°C, for example, at a temperature of approximately 45°C.

[0157] The number of formation charge-discharge cycles is not included in the 500 charge-discharge cycles. For example, the slip difference can be calculated for the positive electrode obtained by repeating 500 charge-discharge cycles after the formation charge-discharge of the battery.

[0158] The line scan can be performed in a straight line perpendicular to the slip length direction observed by an atomic force microscope. Therefore, the largest possible convexity or concavity can be observed.

[0159] Based on the line scan, the step difference caused by the unevenness of the positive electrode active material layer surface can be measured. Therefore, a graph of the step difference according to the line scan length can be obtained as a line scan graph.

[0160] Multiple line scan images can be obtained. In any single line scan image, it may be impossible to observe a sufficient number of measurement objects. For data reliability, multiple line scans can be performed in any other region of the positive electrode surface after formation and charging / discharging to obtain multiple line scan images.

[0161] The mountain-like shape can be observed in the line scan image. The mountain-like shape consists of concave and convex convex parts, which may be due to the deformation of the positive electrode active material caused by crystal structure changes resulting from slip phenomena.

[0162] In the line scan diagram, a pair of parallel lines may be shown, which may contain more than two of the mountain shapes. The upper line in the parallel lines may be a line connecting a portion of the vertices of a mountain shape, or it may be any line connecting to the mountain shape.

[0163] The pair of parallel lines may include other lines parallel to the stated line. These other lines may connect to a portion of the valley points within the mountain shape.

[0164] The pair of parallel lines contains more than two of the mountain shapes. For example, at least two of the mountain shapes may be contained between the pair of parallel lines, while the others may extend beyond the pair of parallel lines.

[0165] The slope of the parallel lines is non-zero. For example, the parallel lines are neither perpendicular to nor parallel to the axis.

[0166] The slip step difference is defined as the distance between the pair of parallel lines. Any straight line perpendicular to the pair of parallel lines can be drawn, and the distance between the two points where this line intersects the pair of parallel lines is defined as the slip step difference.

[0167] The slip step of the positive electrode is less than 20 nm. According to some embodiments, the slip step of the positive electrode can be less than 10 nm.

[0168] When the slip difference exceeds 20 nm, excessive irreversible slip may occur during repeated charging and discharging of the battery, thereby reducing the battery's lifespan characteristics. Furthermore, at the slip location, byproducts generated due to excessive side reactions with the electrolyte can act as resistors, potentially increasing the battery's internal resistance.

[0169] According to an exemplary embodiment, the operating voltage of the lithium secondary battery can be from 4.3V to 4.7V. According to some embodiments, the operating voltage of the lithium secondary battery can be from 4.3V to 4.5V. Therefore, the battery can operate in a high-voltage region.

[0170] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which will be obvious to those skilled in the art, and these variations and modifications also fall within the scope of the claims.

[0171] [Example]

[0172] Preparation example: Preparation of primary lithium-nickel metal oxide particles

[0173] NiSO4, CoSO4, and MnSO4 were added to distilled water that had been bubbled with N2 for 24 hours to remove internal dissolved oxygen and mixed in a molar ratio of 88:9:3. The mixture was then added to a reactor at 50°C, and a co-precipitation reaction was carried out for 48 hours using NaOH and NH4OH as precipitating and chelating agents, respectively, to obtain Ni as a transition metal precursor with an average particle size of 3 μm. 0.88 Co 0.09 Mn 0.03(OH)2 precursor. The obtained precursor was dried at 80°C for 12 hours, and then dried at 110°C for another 12 hours.

[0174] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.03:1 and mixed uniformly for 5 minutes. The mixture was then placed in an oxygen-atmospheric calcination furnace and heated to 820°C at a rate of 2°C / min, and subjected to a first calcination at 820°C for 10 hours. During the heating and calcination process, oxygen was continuously introduced at a flow rate of 20 L / min. After calcination, the mixture was allowed to cool naturally to room temperature and then subjected to jet milling and classification to obtain LiNi. 0.88 Co 0.09 Mn 0.03 O2 represents primary lithium-nickel metal oxide particles with a single-particle structure (average particle size (D)). 50 ): 3μm).

[0175] Example 1

[0176] Preparation of positive electrode active material

[0177] A mixture comprising primary lithium-nickel metal oxide particles from the preparation example and spinel-structured Co3O4 particles having an average particle size (D50) of 250 nm was prepared. The mixture was formulated such that the content of Co3O4 particles in the coated particles was 1000 ppm. The mixture was heat-treated at 750 °C under an oxygen atmosphere for 120 minutes to prepare the coated particles.

[0178] Figure 6 This is a scanning electron microscope (SEM) image of the coated particles from Example 1.

[0179] Battery manufacturing

[0180] The coated particles, polyvinylidene fluoride (PVDF) as a binder, and carbon black as a conductive material were mixed in a weight ratio of 96:2:2 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil (12 μm thick), dried, and then calendered to form an areal density of 12 mg / cm³. 2 A positive electrode active material layer with a thickness of 35μm is formed to manufacture the positive electrode.

[0181] Artificial and natural graphite, used as the negative electrode active material, styrene-butadiene rubber, used as a binder, and carboxymethyl cellulose, used as a thickener, were mixed in a weight ratio of 96:2:2 and then dispersed in water to prepare a negative electrode active material slurry. This slurry was coated onto an 8 μm thick copper foil, dried, and then calendered to manufacture the negative electrode.

[0182] A 13 μm thick polyethylene (PE) membrane separator is stacked between the electrodes prepared above, and a cell is constructed using a soft pack with dimensions of 5 mm thickness × 50 mm width × 60 mm length. A non-aqueous electrolyte is injected to manufacture a 2 Ah-level lithium secondary battery. The non-aqueous electrolyte is a 1 M concentration electrolyte containing ethylene carbonate and ethyl methyl carbonate in a mixed solvent at a volume ratio of 25:75.

[0183] Example 2

[0184] The positive electrode active material and battery were prepared using the same method as in Example 1, except that BaTiO3 particles with a perovskite structure having an average particle size (D50) of 230 nm were used instead of Co3O4 particles.

[0185] Example 3

[0186] The positive electrode active material and battery were prepared using the same method as in Example 1, except that BaTiO3 particles with a perovskite structure having an average particle size (D50) of 300 nm were used instead of Co3O4 particles.

[0187] Example 4

[0188] The positive electrode active material and battery were prepared using the same method as in Example 1, except that SrTiO3 particles with a perovskite structure having an average particle size (D50) of 250 nm were used instead of Co3O4 particles.

[0189] Example 5

[0190] The positive electrode active material and battery were prepared using the same method as in Example 1, except that Li7La3Zr2O with a garnet structure and an average particle size (D50) of 220 nm was used. 12 Granules are used to replace Co3O4 granules.

[0191] Example 6

[0192] The positive electrode active material and battery were prepared using the same method as in Example 1, except that Li₂ with a sodium superionic conductor structure having an average particle size (D50) of 250 nm was used. 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were used to replace Co3O4 particles.

[0193] Comparative Example 1

[0194] The battery was manufactured using the same method as in Example 1, except that a LiNi alloy was used. 0.88 Co 0.09Mn 0.03 The core, composed of a single particle structure of O2 (D50: 3μm), serves as the positive electrode active material.

[0195] Comparative Example 2

[0196] The positive electrode active material and battery were prepared using the same method as in Example 1, except that Co3O4 particles with a spinel structure and an average particle size (D50) of 20 nm were used.

[0197] Figure 7 The image shows a scanning electron microscope (SEM) image of the coated particles of Comparative Example 2.

[0198] Comparative Example 3

[0199] The positive electrode active material and battery were prepared using the same method as in Example 1, except that Co3O4 particles with a spinel structure and an average particle size (D50) of 80 nm were used.

[0200] Comparative Example 4

[0201] The positive electrode active material and battery were prepared using the same method as in Example 1, except that Co3O4 particles with a spinel structure and an average particle size (D50) of 500 nm were used.

[0202] Comparative Example 5

[0203] The positive electrode active material was prepared using the same method as in the preparation example, except that, in the process of mixing lithium hydroxide and the transition metal precursor, Li7La3Zr2O with a garnet structure having an average particle size (D50) of 220 nm was further mixed. 12 The particles, with a content of 2000 ppm, are calcined. After calcination of the coated particles, a shell with a thickness of approximately 20 nm is formed on the core surface containing lithium metal oxide.

[0204] The battery was manufactured using the same method as in Example 1, except that the positive electrode active material was used.

[0205] Comparative Example 6

[0206] The positive electrode active material was prepared using the same method as in Comparative Example 5, except that Li7La3Zr2O was formulated as coated particles. 12 The content of the alloy was 5000 ppm, thus preparing a mixture. At this time, a shell with a thickness of about 100 nm was formed on the core surface containing lithium metal oxide.

[0207] The battery was manufactured using the same method as in Example 1, except that the positive electrode active material was used.

[0208] [Table 1]

[0209]

[0210] Reference Figure 6 and Figure 7 It can be confirmed that the coated particles of Example 1 contain large-diameter metal oxide particles arranged in an island-like pattern on the core surface, while the coated particles of Comparative Example 2 contain small-diameter metal oxide particles on the core surface.

[0211] Reference example

[0212] The battery is manufactured using the same method as the battery described above, except that it is mixed with LiNi 0.88 Co 0.09 Mn 0.03 The single-particle structure of lithium nickel metal oxide composed of O2 and BaTiO3 particles with a perovskite structure having an average particle size (D50) of 230 nm were used as positive electrode active material, with a content of 1000 ppm.

[0213] Experimental Example

[0214] For the batteries of the embodiments, comparative examples and reference examples, the electrochemical characteristics and physical properties were evaluated using the following methods and are shown in Table 2.

[0215] (1) Evaluation of the initial discharge capacity of the battery

[0216] For the batteries in the examples, comparative examples, and reference examples, at room temperature (25°C), they were charged at a constant current (CC) of 0.1C until the voltage reached 4.3V, and then charged once at a constant voltage (CV) of 4.3V until the charging current reached 0.05C. After that, they were left to stand for 10 minutes, and then discharged once at a constant current of 0.1C to 3.0V, thereby measuring the discharge capacity.

[0217] (2) Evaluation of battery life characteristics

[0218] For the batteries in the examples, comparative examples, and reference examples, they were charged to 4.3V at a constant current of 0.5C at a high temperature (45°C), and then charged to a constant voltage of 4.3V until the current decreased to 0.05C. They were then discharged to 3.0V at a constant current of 1.0C, and this process was repeated 500 times (cycles). The capacity retention rate at the time of lifetime characteristic evaluation was measured according to the following formula. The capacity retention rate was calculated as the ratio of the discharge capacity after 500 cycles to the initial discharge capacity of (1).

[0219] Capacity retention after 500 cycles (%) = {(Discharge capacity after 500 cycles (mAh / g)) / (Initial discharge capacity (mAh / g))} × 100

[0220] (3) Evaluation of the occurrence of slip phenomenon

[0221] After repeating (1) 500 cycles, the electrode was fully discharged to 3.0V at a constant current of 0.1C. The positive electrode was then separated from the battery, and the surface of the positive electrode active material layer was observed using an atomic force microscope (AFM). Specifically, using an AFM analysis instrument (Bruker, ICON), a probe with a spring constant of 42 N / m was used to capture surface images of a 5 μm × 5 μm region of the positive electrode active material layer at a resolution of 1024 × 1024 and a velocity of 0.5 Hz, and line scans were performed. Parallel lines, which can contain more than two mountain shapes, were shown on the step diagram based on the line scans, and the spacing between the parallel lines was measured.

[0222] Figure 8a This is an AFM image of the positive electrode after repeated charge and discharge in Example 2.

[0223] Figure 8b It is along Figure 8a Example 2 of the dashed line scan shows the positive electrode after repeated charge and discharge based on the line scan step diagram.

[0224] Figure 9a This is the AFM image of the positive electrode after repeated charge and discharge of Comparative Example 2.

[0225] Figure 9b It is along Figure 9a The comparison example 2 shows the positive electrode after repeated charge and discharge based on the step diagram of the dashed line scan.

[0226] [Table 2]

[0227]

[0228] Referring to Table 2, the battery in this embodiment not only exhibits a high initial discharge capacity but also maintains a high capacity after repeated charge-discharge cycles. Furthermore, the slippage phenomenon of the layered structure of the single-particle core is suppressed, resulting in an average step difference of less than 10 nm.

[0229] Reference Figures 8a to 9b In Example 2, the positive electrode active material suppressed slippage even during repeated charge-discharge cycles, resulting in a small step size of approximately 8.3 nm. On the other hand, in Comparative Example 2, the positive electrode active material, due to the metal oxide having a particle size of less than 100 nm, failed to suppress slippage, resulting in a step size of approximately 24 nm.

[0230] On the other hand, in Comparative Example 1 and Reference Example, where a positive electrode was manufactured using a single-particle lithium nickel metal oxide without coating, excessive slippage of the layered structure occurred, with an average step difference exceeding 30 nm, resulting in a significant deterioration in the battery's lifespan characteristics.

[0231] In Comparative Examples 2 and 3, which used positive electrode active materials coated with metal oxide particles having a particle size of less than 100 nm, the slippage phenomenon of the layered structure was not effectively suppressed.

[0232] In Comparative Example 4, which uses a positive electrode active material coated with metal oxide particles having a particle size of more than 450 nm, the density of the positive electrode active material in the positive electrode active material layer may be lower, and the portion coated with large-diameter metal oxide particles may act as a resistor during lithium insertion and / or extraction. As a result, the initial discharge capacity of the battery is slightly reduced, and the battery life characteristics are also partially deteriorated.

[0233] In Comparative Example 5, which used a positive electrode active material with a shell-like coating but without island-shaped particles, the slippage phenomenon of the layered structure was not effectively suppressed. In particular, in Comparative Example 6, which used a positive electrode active material with a thicker shell-like coating, the content of metal oxides was too high, resulting in a relatively lower content of lithium nickel metal oxides, and thus a significant reduction in the initial discharge capacity of the battery.

[0234] The above description is merely an example of applying the principles of the present invention. Other configurations may be included without departing from the scope of the present invention.

Claims

1. A lithium secondary battery, wherein, The lithium secondary battery includes a positive electrode and a negative electrode disposed opposite to the positive electrode. The slip range of the positive electrode is less than 20 nm. The slip difference is defined as the distance between a pair of parallel lines with non-zero slopes that can include two or more observed mountain shapes in a line scan image of the positive electrode surface after 500 charge-discharge cycles of the battery in a fully discharged state.

2. The lithium secondary battery according to claim 1, wherein, The slip range of the positive electrode is less than 10 nm.

3. The lithium secondary battery according to claim 1, wherein, The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on one side of the positive electrode current collector. The positive electrode active material layer comprises coated particles. The coated particles include: A core comprising a lithium-nickel metal oxide having a layered structure, and the core having a single-particle structure; and At least one metal oxide particle is disposed on the surface of the core.

4. The lithium secondary battery according to claim 3, wherein, The average particle size D50 of the metal oxide particles is 100 nm to 450 nm.

5. The lithium secondary battery according to claim 3, wherein, The average particle size D50 of the metal oxide particles is 220 nm to 300 nm.

6. The lithium secondary battery according to claim 3, wherein, The metal oxide particles are arranged in an island-like pattern on the surface of the core.

7. The lithium secondary battery according to claim 3, wherein, The metal oxide particles have a spinel crystal structure, a perovskite crystal structure, a garnet crystal structure, or a sodium superionic conductor crystal structure.

8. The lithium secondary battery according to claim 3, wherein, The metal oxide particles contain at least one selected from Co, Ba, Ti, Sr, Li, La, Zr, Al, Y, W, and P.

9. The lithium secondary battery according to claim 3, wherein, The content of the metal oxide particles in the total weight of the coated particles is between 500 ppm and 3000 ppm.

10. The lithium secondary battery according to claim 3, wherein, In the lithium-nickel metal oxide, the nickel content is 60 mol% to 99 mol% of the total molar amount of elements other than lithium and oxygen.

11. The lithium secondary battery according to claim 3, wherein, The average particle size D50 of the nuclei is 1 μm to 10 μm.

12. The lithium secondary battery according to claim 3, wherein, The core has a grain size of 200 nm to 600 nm.

13. The lithium secondary battery according to claim 1, wherein, The 500 charge-discharge cycles are performed as follows: the lithium secondary battery is charged at a voltage of 4.3V to 4.5V and discharged to a voltage of 4.2V, and the charge-discharge cycle is repeated 500 times.

14. The lithium secondary battery according to claim 1, wherein, The lithium secondary battery has an operating voltage of 4.3V to 4.7V.

Images