Positive electrode active material for lithium secondary battery and lithium secondary battery comprising the same

Abstract

A positive electrode active material for a lithium secondary battery includes lithium-transition metal composite oxide particles, a lattice strain (η) of the lithium-transition metal composite oxide particles is 0.18 or less, the lattice strain (η) is calculated by applying a Williamson-Hall method represented by Formula 1 to an XRD pattern measured by XRD analysis, and an XRD peak intensity ratio defined by Formula 2 of the lithium-transition metal composite oxide particles is 8.9% or less. By adjusting the lattice strain and the XRD peak intensity ratio of the lithium-transition metal composite oxide particles, a lithium secondary battery in which life characteristics and power characteristics are simultaneously improved is provided.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202110932057.5, filed on August 13, 2021, entitled "Cathode active material for lithium secondary battery and lithium secondary battery comprising the same", and claims priority to Korean Applications No. 10-2020-0101564 and 10-2020-0150764. TECHNICAL FIELD

[0002] The present application relates to a cathode active material for lithium secondary battery and a lithium secondary battery comprising the same. In more detail, it relates to a cathode active material for lithium secondary battery comprising lithium-transition metal composite oxide particles and a lithium secondary battery comprising the same. BACKGROUND

[0003] Secondary batteries are batteries that can be repeatedly charged and discharged, and are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, notebook computers, etc. as the information communication and display industries develop. In addition, in recent years, battery packs including secondary batteries are being developed and used as power sources for environmentally friendly vehicles such as hybrid electric vehicles.

[0004] Among secondary batteries, for example, lithium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc., lithium secondary batteries have a high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and thus are being actively developed and applied.

[0005] For example, a lithium secondary battery can include an electrode assembly including a cathode, an anode, and a separator film (separator), and an electrolyte impregnating the electrode assembly. The lithium secondary battery can further include an outer material, such as a soft pack type outer material, which accommodates the electrode assembly and the electrolyte.

[0006] Lithium metal oxides are used as cathode active materials for the lithium secondary battery, and are preferred to have high capacity, high power, and high life characteristics. However, when the lithium metal oxides are designed to have high power composition, thermal stability and mechanical stability are reduced, and thus life characteristics and operating reliability of the lithium secondary battery can also be reduced.

[0007] For example, Korean Patent Publication No. 10-2017-0093085 discloses a cathode active material comprising a transition metal compound and an ion-absorbing binder, but has limitations in securing sufficient life characteristics and stability.

[0008] [Prior Art Document]

[0009] [Patent Document]

[0010] Korean Patent Publication No. 10-2017-0093085 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] An object of the present invention is to provide a positive active material for a lithium secondary battery having excellent operational stability and reliability.

[0013] An object of the present invention is to provide a lithium secondary battery comprising a positive active material having excellent operational stability and reliability.

[0014] TECHNICAL SOLUTION

[0015] The positive active material for a lithium secondary battery according to the embodiment of the present invention comprises lithium-transition metal composite oxide particles having a lattice strain (η) of 0.18 or less, the lattice strain (η) being calculated by applying Williamson-Hall method defined by Formula 1 to XRD peaks, and an XRD peak intensity ratio defined by Formula 2 of the lithium-transition metal composite oxide particles being 8.9% or less.

[0016] [Formula 1]

[0017] βcosθ = ηsinθ + λ / D

[0018] (In Formula 1, β is a half-peak width (rad) of a corresponding peak obtained through XRD analysis, θ is a diffraction angle (rad), η is a lattice strain (dimensionless), and λ is an X-ray wavelength D is a crystallite size ).

[0019] [Formula 2]

[0020] XRD peak intensity ratio (%) = 100 x I(110) / {I(110) + I(003)}

[0021] (In Formula 2, I(110) is a maximum height of a peak of a (110) plane through X-ray diffraction (XRD) analysis of the lithium-transition metal composite oxide particles, and I(003) is a maximum height of a peak of a (003) plane through XRD analysis).

[0022] In some embodiments, the lattice strain of the lithium-transition metal composite oxide particles can be a slope of a straight line obtained by obtaining a half-peak width of all peaks shown by the XRD analysis, substituting the obtained half-peak width into Equation 1, and plotting with sinθ as an abscissa and βcosθ as an ordinate.

[0023] In some embodiments, the XRD peak intensity ratio of the lithium-transition metal composite oxide particles can be 4-8.9%.

[0024] In some embodiments, the lithium-transition metal composite oxide particles can include a crystallographically polycrystalline structure.

[0025] In some embodiments, the lithium-transition metal composite oxide particles can have at least one of a morphologically single particle, primary particle, or secondary particle morphology.

[0026] In some embodiments, the lithium-transition metal composite oxide particles can have a composition represented by the following Chemical Formula 1.

[0027] [Chemical Formula 1]

[0028] Li x Ni 1-y M y O 2+z

[0029] (In Chemical Formula 1, 0.9≤x≤1.1, y is 0≤y≤0.7, z is -0.1≤z≤0.1, and M is one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr).

[0030] In some embodiments, in Chemical Formula 1, (1-y) can be 0.8 or more.

[0031] In some embodiments, in Chemical Formula 1, M can include Co and Mn.

[0032] In some embodiments, the lithium-transition metal composite oxide particles can be prepared by reacting a transition metal precursor and a lithium precursor.

[0033] In some embodiments, the transition metal precursor can be a Ni-Co-Mn precursor.

[0034] In some embodiments, the lithium precursor can include lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, or lithium hydroxide.

[0035] The lithium secondary battery according to the embodiment of the present application includes: a positive electrode including a positive electrode active material layer including the positive electrode active material of the above-described embodiment; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0036] Advantageous Effects

[0037] The lithium secondary battery according to the above-described exemplary embodiment can include lithium-transition metal composite oxide particles satisfying the XRD peak intensity ratio of the lattice strain of 0.18 or less and a prescribed value or less as a positive electrode active material. Accordingly, the particle strength can be increased, and the power characteristics can be improved.

[0038] By adjusting the lattice strain to be 0.18 or less, the particle crack phenomenon at the boundary region between the crystal grains or between the particles can be prevented. Accordingly, by preventing the generation of gas in a high-temperature environment and / or the generation of gas at the time of charge and discharge, the life characteristics of the secondary battery can be improved.

[0039] Further, by adjusting the XRD peak intensity ratio to be a prescribed value or less, the diffusion distance of lithium can be shortened, and thus the power characteristics of the battery can be improved. In this case, the relative reduction in the life characteristics due to the shortening of the lithium diffusion distance can be mitigated or compensated for by adjusting the lattice strain to be 0.18 or less.

[0040] Accordingly, the lithium-transition metal composite oxide particles satisfying the above-described lattice strain and XRD peak intensity ratio have the particle strength and power performance as described above, and thus improved operating stability, life characteristics, and power characteristics can be simultaneously provided. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 and Figure 2 are a plan view and a cross-sectional view, respectively, illustrating a lithium secondary battery according to an exemplary embodiment.

[0042] Figure 3 and Figure 4 is a view illustrating a method of applying the Williamson Hall method to values obtained by XRD analysis in an exemplary embodiment.

[0043] EXPLANATION OF REFERENCE NUMERALS

[0044] 100: positive electrode 105: positive electrode current collector

[0045] 107: positive electrode lead 110: positive electrode active material layer

[0046] 120: negative electrode active material layer 125: negative electrode current collector

[0047] 127: negative electrode lead 130: negative electrode

[0048] 140: separator 150: electrode assembly

[0049] 160: case DETAILED DESCRIPTION

[0050] Embodiments of the present application provide a lithium secondary battery including lithium-transition metal complex oxide particles having a lattice strain value and an XRD peak intensity ratio in a prescribed range as a positive electrode active material.

[0051] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings. However, the present application is not limited to the specific embodiments described by way of example.

[0052] Figure 1 and Figure 2 are a plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment. Hereinafter, embodiments of the present application will be described with reference to Figure 1 and Figure 2 A positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same will be described.

[0053] Referring to Figure 1 and Figure 2 , the lithium secondary battery can include an electrode assembly including a positive electrode 100, a negative electrode 130, and a separator 140 interposed between the positive electrode and the negative electrode. The electrode assembly can be accommodated in a case 160 together with an electrolyte, and the electrode assembly can be impregnated with the electrolyte.

[0054] The positive electrode 100 can include a positive electrode active material layer 110 formed by coating a positive electrode active material on a positive electrode current collector 105. The positive electrode active material can include a compound that can reversibly intercalate and deintercalate lithium ions.

[0055] In an exemplary embodiment, the positive electrode active material can include lithium-transition metal complex oxide particles. For example, the lithium-transition metal complex oxide particles include nickel (Ni), and can further include at least one of cobalt (Co) or manganese (Mn).

[0056] For example, the lithium-transition metal complex oxide particles can be represented by the following Chemical Formula 1.

[0057] [Chemical Formula 1]

[0058] Li x Ni 1-y M y O 2+z

[0059] In Chemical Formula 1, 0.9≤x≤1.1, y can be 0≤y≤0.7, and z can be -0.1≤z≤0.1. M can represent one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

[0060] In some embodiments, the molar ratio or concentration of Ni in Chemical Formula 1, (1-y), can be 0.8 or more, and in preferred embodiments, the molar ratio or concentration of Ni in Chemical Formula 1, (1-y), can be more than 0.8.

[0061] Ni can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Accordingly, as described above, a composition with a high Ni content (High-Ni) is employed in the lithium-transition metal composite oxide particles, and thus a positive electrode with high power and a lithium secondary battery with high power can be provided.

[0062] However, as the content of Ni increases, the long-term storage stability and the life stability of the positive electrode or the secondary battery can be relatively reduced. However, according to exemplary embodiments, the life stability and capacity retention characteristics can be improved by Mn while maintaining the electrical conductivity by including Co.

[0063] In some embodiments, the positive active material or the lithium-transition metal composite oxide particles can further include a coating element or a doping element. For example, the coating element or the doping element can include Al, Ti, Ba, Zr, Si, B, Mg, P, or alloys or oxides thereof. They can be used alone or in combination with two or more. The positive active material particles are passivated by the coating element or the doping element, and thus the stability against penetration of external objects and the life can be further improved.

[0064] For example, the lithium-transition metal composite oxide particles can be prepared by wet-mixing or dry-mixing a nickel-manganese-cobalt precursor (e.g., nickel-cobalt-manganese hydroxide) with a lithium precursor (e.g., lithium hydroxide or lithium carbonate) and allowing them to react, and then performing a calcination process on the reaction product.

[0065] The lithium-transition metal composite oxide particles can have a single crystal structure and / or a polycrystal structure in crystallography. In one embodiment, the positive active material can include a mixture or a blend of single crystal particles and polycrystal particles.

[0066] In some embodiments, the lithium-transition metal complex oxide particles can be a polycrystalline structure in terms of crystallography. In this case, the lattice strain described below can occur at the boundary region between the crystal grains, and thus the particle cracking phenomenon can occur at the boundary region.

[0067] According to exemplary embodiments of the present application, the particle cracking at the boundary region is reduced, and thus the generation of gas under repeated charge and discharge and high temperature environments can be reduced, and the life characteristics of the secondary battery can be further improved.

[0068] The lithium-transition metal complex oxide particles can have a single particle, primary particle, or secondary particle morphology in terms of morphology.

[0069] Figure 3 and Figure 4 is a schematic diagram showing a method of applying the Williamson Hall method in the values obtained by XRD analysis in exemplary embodiments.

[0070] Referring to Figure 3 The XRD peak can be obtained by X-ray diffusion (XRD) analysis, and the Williamson Hall method defined by Equation 1 below can be applied in the obtained peak, and thus the lattice strain of the lithium-transition metal complex oxide particles can be obtained.

[0071] [Equation 1]

[0072] βcosθ = ηsinθ + λ / D

[0073] In Equation 1, β denotes the full width at half maximum (FWHM) (rad) of the corresponding peak obtained by XRD analysis, θ denotes the diffraction angle (rad), η denotes the lattice strain (dimensionless), and λ denotes the X-ray wavelength D denotes the crystallite size

[0074] In some embodiments, in Equation 1 above, β can use the half width corrected from the value from the device. In one embodiment, Si can be used as a standard material for reflecting the value from the device. In this case, by drawing the half width profile of the entire range of 2θ of Si, the half width from the device can be expressed as a function of 2θ. Thereafter, the value obtained by deducting and correcting the half width value from the device at the corresponding 2θ obtained from the function can be used as β.

[0075] For example, the XRD analysis can be performed as follows: a dried powder of the lithium-transition metal complex oxide particles is subjected to XRD analysis using CuKα ray as a light source, and in a range of diffraction angles (2θ) of 10° to 120°, at a scan rate of 0.0065° / step.

[0076] Reference Figure 4 The half-peak width of all peaks appearing in the range of diffraction angles is measured, and the obtained measurement value is substituted into Equation 1, and the slope is obtained by linear regression analysis, whereby the lattice strain can be calculated (Williamson Hall method).

[0077] For example, the lattice strain can be defined as the slope of a straight line obtained when plotting sinθ of Equation 1 as the horizontal axis and βcosθ as the vertical axis.

[0078] In an exemplary embodiment, the lattice strain can be 0.18 or less. When the lattice strain is 0.18 or less, the lattice strain can be reduced at the boundary region between the grains or between the particles of the lithium-transition metal complex oxide particles.

[0079] When the lattice strain exceeds 0.18, the lattice strain of the lithium-transition metal complex oxide particles increases, and thus the gas generation amount at high temperature and the capacity retention and the like, which are life characteristics, can be reduced.

[0080] Thus, the particle cracking phenomenon that mainly occurs at the boundary region between the grains during a punching process for forming the positive active material layer 110 or during charging and discharging of the battery can be reduced. Therefore, the particle strength of the lithium-transition metal complex oxide particles can be increased, and a high-density electrode can be achieved. In this case, for example, the gas generation amount at high temperature can be reduced, and the generation of gas due to repeated charging / discharging can be suppressed. Therefore, stable capacity characteristics can be provided even in a high-temperature environment, and the life characteristics of the lithium secondary battery can be improved.

[0081] In some embodiments, the lattice strain can be 0.03 to 0.18. When the lattice strain is 0.03 or more, the strength of the lithium-transition metal complex oxide particles is too high, and thus the reduction in battery impregnability can be prevented, and thus the life characteristics can be improved while preventing the reduction in the power characteristics of the battery.

[0082] According to an exemplary embodiment, the XRD peak intensity ratio of the lithium-transition metal complex oxide particles, which is defined by Equation 2 below, can be 8.9% or less.

[0083] [Equation 2]

[0084] XRD peak intensity ratio (%) = 100 x I(110) / {I(110) + I(003)}

[0085] In Formula 2, I(110) represents a peak intensity of a (110) plane or a maximum height of a peak by X-ray diffraction (XRD) analysis of the lithium-transition metal complex oxide particles, and I(003) represents a peak intensity of a (003) plane or a maximum height of a peak by XRD analysis.

[0086] For example, the XRD analysis can be performed as follows, on a dried powder of the lithium-transition metal complex oxide particles, using Cu Kα rays as a light source, and in a range of diffraction angles (2θ) of 10° to 120°, at a scanning rate of 0.0065° / step.

[0087] Within the above XRD peak intensity ratio range, the ion propagation length and the ion diffusion length of the (110) plane, in which lithium ions diffuse, can be reduced. In addition, the aspect ratio of the particles can be reflected by adjustment of the peak intensity ratio with respect to the (003) plane intersecting the (110) plane. Accordingly, a decrease in power due to an increase in lithium diffusion length or an excessive increase in the aspect ratio of the particles can be prevented.

[0088] For example, since a phenomenon of capacity deterioration occurring due to repeated charge / discharge of a lithium secondary battery is extended from the (110) plane to the inside of the particles, as the diffusion length of lithium ions decreases, the deterioration rate of the battery increases, and thus the life characteristics of the battery can be relatively reduced.

[0089] However, according to an exemplary embodiment, by adopting the lithium-transition metal complex oxide particles having a lattice strain of 0.18 or less to increase the strength of the particles, a decrease in life characteristics at a relatively high temperature due to adjustment of the XRD peak intensity ratio to 8.9% or less can be mitigated or compensated for.

[0090] Accordingly, by adjusting the lattice strain to reduce particle cracking, a high-density electrode can be implemented, and by preventing the generation of gas, life stability at a high-temperature environment can be increased, and by adjusting the XRD peak intensity ratio, lithium ion migration characteristics can be increased, and thus power / capacity can be simultaneously improved.

[0091] In one embodiment, the XRD peak intensity ratio can be 4-8.9%, and preferably can be 5-8.9%. Within the above range, power characteristics can be improved while maintaining surface stability and life characteristics of the lithium-transition metal complex oxide particles.

[0092] For example, a transition metal precursor (e.g., a Ni-Co-Mn precursor) used to prepare the lithium-transition metal complex oxide particles can be prepared through a coprecipitation reaction.

[0093] The transition metal precursor can be prepared by a co-precipitation reaction of metal salts. The metal salts can include nickel salts, manganese salts, and cobalt salts.

[0094] As examples of the nickel salts, nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, their hydrates, and the like can be cited. As examples of the manganese salts, manganese sulfate, manganese acetate, their hydrates, and the like can be cited. As examples of the cobalt salts, cobalt sulfate, cobalt nitrate, cobalt carbonate, their hydrates, and the like can be cited.

[0095] The metal salts can be mixed with a precipitant and / or a chelating agent in a proportion satisfying the content or concentration ratio of each metal explained with reference to Chemical Formula 1 to prepare an aqueous solution. The aqueous solution can be co-precipitated in a reactor to prepare a transition metal precursor.

[0096] The precipitant can include basic compounds such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and the like. The chelating agent can include, for example, aqueous ammonia (e.g., NH3H2O), ammonium carbonate (e.g., NH3HCO3), and the like.

[0097] The temperature of the co-precipitation reaction can be adjusted, for example, in the range of about 40-60°C. The reaction time can be adjusted in the range of about 24-72 hours.

[0098] For example, lithium-transition metal complex oxide particles can be prepared by reacting a transition metal precursor with a lithium precursor. The lithium precursor compound can include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, and the like. They can be used alone or in combination of two or more.

[0099] Thereafter, for example, lithium impurities or unreacted precursors are removed by a water washing process, and the metal particles can be fixed or the crystallinity can be improved by a heat treatment (calcination) process. In one embodiment, the heat treatment temperature can be in the range of about 600-1000°C.

[0100] For example, the heat treatment process can include a first calcination process performed at a high temperature and a second calcination process performed at a relatively low temperature than the high temperature. Specifically, after performing the first calcination process, the second calcination process can be performed at a temperature lower than that of the first calcination process. In this case, the strength and hardness of the lithium-transition metal complex oxide particles formed are improved, and thus the life characteristics and driving stability of the secondary battery can be improved.

[0101] For example, the first calcination process can be performed at 800-1000°C, and the second calcination process can be performed at 600-950°C.

[0102] For example, the lattice strain and the XRD peak intensity ratio described above can vary depending on the co-precipitation reaction time, the reaction temperature, the heat treatment temperature, and the like.

[0103] The positive electrode active material including the lithium-transition metal complex oxide particles described above can be mixed with a binder, a conductive material, and / or a dispersing material, and the like in a solvent and stirred to prepare a slurry. The slurry can be coated on the positive electrode current collector 105, and then dried and pressed to manufacture the positive electrode 100.

[0104] The positive electrode current collector 105 can include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably can include aluminum or an aluminum alloy.

[0105] The binder can include, for example, an organic binder such as a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or the like; or a water-based binder such as styrene butadiene rubber (SBR), and can be used together with a thickening agent such as carboxymethyl cellulose (CMC).

[0106] 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, and thus the power and the capacity of the secondary battery can be improved.

[0107] The conductive material can be included to facilitate electron migration between the active material particles. For example, the conductive material can include a carbon-based conductive material such as graphite, carbon black, graphene, a carbon nanotube, and the like, and / or a metal-based conductive material including a perovskite substance such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, and the like.

[0108] The negative electrode 130 can include a negative electrode current collector 125 and a negative electrode active material layer 120 formed by coating a negative electrode active material on the negative electrode current collector 125.

[0109] The negative electrode active material can be used without particular restriction, as long as it is a known negative electrode active material in the art capable of intercalating and deintercalating lithium ions. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers can be used; 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).

[0110] Examples of crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0111] The silicon-based compound may, for example, comprise a silicon-carbon complex such as silicon oxide or silicon carbide (SiC).

[0112] For example, a slurry can be prepared by mixing and stirring the negative electrode active material with the aforementioned binder, conductive material, thickener, etc. The slurry is then coated onto at least one side of the negative electrode current collector 125, and the negative electrode 130 can be manufactured by drying and pressing.

[0113] The adhesive and the conductive material may be substantially the same as or similar to the substances used in the positive electrode active material layer 110. In some embodiments, for compatibility with the carbon-based active material, the adhesive used to form the negative electrode may, for example, comprise a water-based adhesive such as styrene-butadiene rubber (SBR) and may be used in conjunction with a thickener such as carboxymethyl cellulose (CMC).

[0114] A separator 140 can be inserted between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The separator 140 may also include a nonwoven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0115] In some embodiments, the area (e.g., the area in contact with the separator 140) and / or volume of the negative electrode 130 can be larger than that of the positive electrode 100. Therefore, lithium ions formed on the positive electrode 100 can migrate smoothly to the negative electrode 130 without, for example, depositing in the middle.

[0116] According to an exemplary embodiment, the electrode unit is defined by a positive electrode 100, a negative electrode 130, and a diaphragm 140, and multiple electrode units can be stacked to form an electrode assembly 150, for example, in the form of a jelly roll. For example, the electrode assembly 150 can be formed by winding, lamination, folding, etc., of the diaphragm 140.

[0117] The electrode assembly 150 is housed together with the electrolyte in a housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte can be used.

[0118] The non-aqueous electrolyte comprises a lithium salt as the electrolyte and an organic solvent, the lithium salt being, 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.

[0119] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. They may be used alone or in combination of two or more.

[0120] like Figure 1 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each electrode unit 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.

[0121] The lithium secondary battery can be manufactured in various shapes, such as cylindrical, triangular, pouch, and coin, for use in containers.

[0122] The following specific experimental examples are presented to help understand the present invention. However, these are only for illustrating the present invention and are not intended to limit the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept. This is obvious to those skilled in the art, and it is natural that such modifications and variations fall within the scope of the claims.

[0123] Preparation of lithium-transition metal composite oxide particles

[0124] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.1:0.1 using distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen. The solution was then added to a reactor at 55°C, and a co-precipitation reaction was carried out for 36 hours using NaOH and NH3H2O ​​as precipitating and chelating agents, respectively, to obtain Ni as a transition metal precursor. 0.8 Co 0.1 Mn 0.1 (OH)2. The obtained precursor was dried at 80°C for 12 hours, and then dried again at 110°C for 12 hours.

[0125] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.05:1 and mixed uniformly for 5 minutes. The mixture was then placed in a calcination furnace and heated to 950°C at a rate of 2°C / min, and held at 950°C for 5 hours. It was then allowed to cool naturally to 900°C and held for 5 hours. Oxygen was continuously purged at a flow rate of 10 mL / min during the heating and holding periods. After calcination, the mixture was allowed to cool naturally to room temperature and then pulverized and graded to prepare the positive electrode active material LiNi. 0.8 Co 0.1 Mn 0.1 O2 in single-particle form (including single-crystal and polycrystalline structures) lithium-transition metal composite oxide particles (particle 1).

[0126] By changing the reaction time and temperature in the reactor or the calcination time, calcination temperature, and heating rate in the calcination process, particles 2 through 9 were further prepared. For each of the lithium-transition metal composite oxide particles, the lattice strain calculated using Equation 1 and the XRD peak intensity ratio calculated using Equation 2 were determined by XRD analysis and are shown in Table 2.

[0127] In addition, the specific XRD analysis equipment / conditions are listed in Table 1 below.

[0128] [Table 1]

[0129]

[0130]

[0131] [Table 2]

[0132]

[0133] Example 1

[0134] The aforementioned first particle was used as the positive electrode active material to manufacture a secondary battery. Specifically, the positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder were mixed in a mass ratio of 97:2:1 to prepare a positive electrode mixture, which was then coated onto an aluminum current collector, and the positive electrode was manufactured by drying and pressing. After pressing, the target electrode density of the positive electrode was adjusted to 3.71 g / cc.

[0135] A negative electrode slurry is prepared, comprising 93% by weight of natural graphite as the negative electrode active material, 5% by weight of KS6 as a flake-type 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 onto a copper substrate and then dried and pressed to manufacture the negative electrode.

[0136] The positive and negative electrodes manufactured as described above are notched and stacked according to specifications. A separator (polyethylene, 25 μm thick) is inserted between the positive and negative electrodes to form an electrode unit. Then, the tab portions of the positive and negative electrodes are welded together. The welded positive / separator / negative electrode assembly is placed in a soft package, and the three sides except for the electrolyte injection section are sealed. At this time, the portion with the tabs is contained within the sealed portion. Electrolyte is injected through the remaining sides except for the sealed portion, and the remaining sides are sealed, and then immersed for at least 12 hours.

[0137] The electrolyte was prepared by dissolving 1 M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30, volume ratio) and then adding 1 wt% vinylene carbonate (VC), 0.5 wt% 1,3-propenyl sulfonyl lactone (PRS) and 0.5 wt% lithium bis(oxalato)borate (LiBOB).

[0138] The secondary battery manufactured as described above was then pre-charged for 36 minutes at a current of 0.25C (5A). After 1 hour, degassing was performed, followed by aging for at least 24 hours, and then formation charging and discharging was performed (charging conditions: CC-CV 0.2C 4.2V 0.05C cut-off; discharging conditions: CC 0.2C 2.5V cut-off).

[0139] Example 2

[0140] Except for adjusting the target electrode density of the positive electrode to 3.85 g / cc, the secondary battery was manufactured using the same method as in Example 1.

[0141] Example 3

[0142] Except for using the second particle mentioned above as the positive electrode active material, the secondary battery was manufactured by the same method as in Example 1.

[0143] Example 4

[0144] Except for adjusting the target electrode density of the positive electrode to 3.85 g / cc, the secondary battery was manufactured using the same method as in Example 3.

[0145] Example 5

[0146] Except for using the third particle mentioned above as the positive electrode active material, the secondary battery was manufactured by the same method as in Example 1.

[0147] Comparative Example 1

[0148] Except for using the fourth particle mentioned above as the positive electrode active material, the secondary battery was manufactured by the same method as in Example 1.

[0149] Comparative Example 2

[0150] Except for adjusting the target electrode density of the positive electrode to 3.85 g / cc, the secondary battery was manufactured using the same method as Comparative Example 1.

[0151] Comparative Example 3

[0152] Except for using the fifth particle mentioned above as the positive electrode active material, the secondary battery was manufactured by the same method as in Example 1.

[0153] Comparative Example 4

[0154] Except for using the aforementioned sixth particle as the positive electrode active material, a secondary battery was manufactured using the same method as in Example 1.

[0155] Comparative Example 5

[0156] Except for using the aforementioned 7th particle as the positive electrode active material, a secondary battery was manufactured using the same method as in Example 1.

[0157] Comparative Example 6

[0158] Except for using the aforementioned eighth particle as the positive electrode active material, a secondary battery was manufactured using the same method as in Example 1.

[0159] Comparative Example 7

[0160] Except for using the aforementioned 9th particle as the positive electrode active material, a secondary battery was manufactured using the same method as in Example 1.

[0161] The particle size, lattice strain, XRD peak intensity ratio, and electrode density of the components of the above embodiments and comparative examples are shown in Table 3 below.

[0162] [Table 3]

[0163]

[0164]

[0165] Experimental Example

[0166] (1) Measurement of electrode density (as measured)

[0167] The positive electrode of the lithium secondary battery of the above embodiment and comparative example was coated on both sides and stamped into a size of 12pi (diameter: 12mm), and then the electrode density was measured by the following formula.

[0168] Electrode density (g / cc) = (Weight of electrodes coated on both sides - Weight of foil) / {(Total thickness of electrodes coated on both sides - Thickness of foil) * 12pi area}

[0169] (2) Measurement of gas generation at high temperature

[0170] The lithium secondary batteries of the above embodiments and comparative examples were charged (1C 4.2V 0.1C cutoff) and then stored in a constant temperature chamber at 60°C. The amount of gas generated after 1 week and 4 weeks of storage was confirmed by gas chromatography (GC) analysis. In order to measure the total amount of gas generated, a hole was formed in the chamber under vacuum of a specified volume (V), and the volume of gas generated was calculated by measuring the pressure change.

[0171] (3) Measurement of gas generation amount after repeated charge and discharge

[0172] The lithium secondary batteries of the above embodiments and comparative examples were repeatedly charged (CC-CV 1.0C 4.2V 0.05C cutoff) and discharged (CC 1.0C 2.7V cutoff) 100 times and 300 times respectively in a chamber at 45°C, and then the amount of gas generated was measured by the same method as in (2).

[0173] (4) Measurement of life (capacity retention rate) at 45°C

[0174] The lithium secondary batteries of the above embodiments and comparative examples were charged (1C 4.2V 0.1C cutoff), and then the percentage (%) of the discharge capacity after 4 weeks of storage in a constant temperature chamber at 45°C to the initial discharge capacity was calculated, thereby calculating the capacity retention rate after 4 weeks.

[0175] Furthermore, the lithium secondary batteries of the above embodiments and comparative examples were repeatedly charged (CC-CV 1.0C 4.2V 0.05C cutoff) and discharged (CC 1.0C 2.7V cutoff) 300 times in a chamber at 45°C. Then, the percentage (%) of the discharge capacity at the 300th cycle to the discharge capacity at the 1st cycle was calculated, thereby calculating the capacity retention rate after 300 cycles.

[0176] The evaluation results are shown in Table 4 below.

[0177] [Table 4]

[0178]

[0179] Referring to Table 4, compared with the comparative example, the embodiment using lithium-transition metal composite oxide particles that meet the requirements of lattice strain below 0.18 and XRD peak intensity ratio below 8.9% has a high overall electrode density and ensures good capacity retention while suppressing gas generation.

[0180] Specifically, compared with the comparative examples, Examples 1 to 3, with lattice strain of 0.03-0.18 and XRD peak intensity ratio of 4-8.9%, showed significantly reduced gas generation at high temperatures and during repeated charge and discharge, and exhibited excellent capacity retention.

[0181] However, although Example 5, with an XRD peak intensity ratio of less than 4%, ensured less gas generation and excellent capacity retention compared to the comparative examples, it showed slightly more gas generation and lower capacity retention compared to Examples 1 to 3. Comparative Example 5 had a lattice strain of 0.18 or less but an XRD peak intensity ratio exceeding 8.9%. Comparative Examples 6 and 7 were comparative examples with XRD peak intensity ratios of 8.9% or less but lattice strains exceeding 0.18. Similar to Comparative Examples 1 to 4, Comparative Examples 5 to 7 generally showed more gas generation and lower capacity retention compared to the examples.

Claims

1. A positive electrode active material for lithium secondary batteries, comprising lithium-transition metal composite oxide particles, wherein the lattice strain η of the lithium-transition metal composite oxide particles is in the range of 0.03 to 0.18, the lattice strain η being calculated by applying the Williamson Hall method defined by Equation 1 to XRD peaks measured by XRD analysis, wherein the lithium-transition metal composite oxide particles comprise nickel, cobalt, and manganese, and the XRD peak intensity ratio of the lithium-transition metal composite oxide particles defined by Equation 2 is 3.9-8.9%. [Formula 1] βcosθ=ηsinθ+λ / D In Equation 1, β is the half-width of the corresponding peak obtained through XRD analysis, in radians; θ is the diffraction angle, measured in radians; η is the lattice strain, which is the dimensionless number; λ is the wavelength of X-rays, measured in Å. D is the crystallite size, measured in Å. [Equation 2] XRD peak intensity ratio (%) = 100 × I(110) / {I(110) + I(003)} In Equation 2, I(110) is the maximum height of the peak on the (110) plane of the lithium-transition metal composite oxide particles as analyzed by X-ray diffraction (XRD), and I(003) is the maximum height of the peak on the (003) plane as analyzed by XRD.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lattice strain of the lithium-transition metal composite oxide particles is the slope of a straight line obtained by the following steps: obtaining the full width at half maximum (FWHM) of all peaks shown by the XRD analysis, substituting the obtained FWHM into Equation 1, and plotting the line with sinθ as the horizontal axis and βcosθ as the vertical axis.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The XRD peak intensity ratio of the lithium-transition metal composite oxide particles is 4-8.9%.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles have a polycrystalline structure in terms of crystallography.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles have at least one of the following morphological forms: single particle, primary particle, or secondary particle.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles have a composition represented by the following chemical formula 1: [Chemical Formula 1] Li x Ni 1-y M y O 2+z In chemical formula 1, x is 0.9≤x≤1.1, y is 0≤y≤0.7, z is -0.1≤z≤0.1, and M is one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

7. The positive electrode active material for lithium secondary batteries according to claim 6, wherein, In the chemical formula 1, 0 ≤ y ≤ 0.

2.

8. The positive electrode active material for lithium secondary batteries according to claim 6, wherein, The lithium-transition metal composite oxide particles are prepared by reacting a transition metal precursor with a lithium precursor.

9. The positive electrode active material for lithium secondary batteries according to claim 8, wherein, The transition metal precursor is a Ni-Co-Mn precursor.

10. The positive electrode active material for lithium secondary batteries according to claim 8, wherein, The lithium precursor includes lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, or lithium hydroxide.

11. A lithium secondary battery, comprising: A positive electrode, comprising a positive electrode active material layer containing the positive electrode active material as described in claim 1; negative electrode; and A diaphragm is disposed between the positive electrode and the negative electrode.

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