Positive active material for lithium secondary battery and lithium secondary battery including same

Abstract

A positive electrode active material for a lithium secondary battery includes lithium-transition metal composite oxide particles having a grain size of less than 300 nm as measured by XRD analysis and an XRD peak intensity ratio of 7% or more. The present invention provides a lithium secondary battery having improved life performance and output performance by controlling the grain size and XRD peak intensity ratio of lithium-transition metal composite oxide particles.

Description

[0001] This application is a divisional application of Chinese patent application No. 2021113214244, filed on November 9, 2021, entitled "Positive electrode active material for lithium secondary batteries and lithium secondary batteries including the same", and claims priority to KR10-2020-0148777. Technical Field

[0002] The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the positive electrode active material, and more specifically, to a positive electrode active material for a lithium secondary battery including a lithium-transition metal composite oxide and a lithium secondary battery including the positive electrode active material. Background Technology

[0003] Rechargeable batteries are batteries that can be recharged and discharged repeatedly. With the rapid development of the information communication and display industries, rechargeable batteries have been widely used as a power source for various portable communication electronic devices such as portable cameras, mobile phones, and laptops. Recently, battery packs that include rechargeable batteries have also been developed and are being used as a power source for environmentally friendly vehicles, such as hybrid vehicles.

[0004] Examples of rechargeable batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries offer advantages in terms of high operating voltage and energy density per unit weight, as well as fast charging speed and light weight. In this regard, lithium-ion batteries have been actively developed and are being used as power sources.

[0005] For example, a lithium secondary battery may include: an electrode assembly comprising a positive electrode, a negative electrode, and a separator; and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include, for example, a pouch-shaped housing in which the electrode assembly and electrolyte are contained.

[0006] In lithium-ion batteries, lithium metal oxides, which possess high capacity, high output, and long lifespan characteristics, are preferably used as the positive electrode active material. However, designing lithium metal oxides for high-output compositions may degrade thermal and mechanical stability, potentially leading to a decline in the lifespan and operational reliability of the lithium-ion battery.

[0007] For example, Korean Patent Publication No. 10-2017-0093085 discloses a positive electrode active material including a transition metal compound and an ion adsorption binder, but there are limitations in ensuring sufficient lifetime characteristics and stability.

[0008] [Existing Technical Documents] [Patent Literature] Korean Patent Publication No. 10-2017-0093085 Summary of the Invention

[0009] One object of the present invention is to provide a positive electrode active material for lithium secondary batteries with excellent operational stability and reliability.

[0010] Another object of the present invention is to provide a lithium secondary battery comprising a positive electrode active material having excellent operational stability and reliability.

[0011] To achieve the above objectives, according to one aspect of the present invention, a positive electrode active material for lithium secondary batteries comprising lithium-transition metal composite oxide particles is provided, the particles having a grain size of less than 300 nm as measured by X-ray diffraction (XRD) analysis, and having an XRD peak intensity ratio of more than 7% as defined by Equation 2 below: [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) surface of the lithium-transition metal composite oxide particles obtained by XRD analysis, and I(003) is the maximum height of the peak on the (003) surface of the lithium-transition metal composite oxide particles obtained by XRD analysis).

[0012] In some implementations, grain size can be measured using the following Equation 1: [Equation 1] (In Equation 1, L is the grain size (nm), λ is the X-ray wavelength (nm), β is the full width at half maximum (in radians) of the peak on the (003) plane, and θ is the diffraction angle (in radians).)

[0013] In some implementations, the crystal grain size of the lithium-transition metal composite oxide particles can be greater than 100 nm and less than 300 nm.

[0014] In some implementations, the grain size of the lithium-transition metal composite oxide particles can be from 150 nm to 265 nm.

[0015] In some implementations, the XRD peak intensity ratio of lithium-transition metal composite oxide particles can be 7% to 12%.

[0016] In some implementations, the XRD peak intensity ratio of lithium-transition metal composite oxide particles can be 9% to 11%.

[0017] In some implementations, the XRD peak area ratio of the lithium-transition metal composite oxide particles, as defined by Equation 3, can be 16% or higher: [Equation 3] XRD peak area ratio (%) = 100 × A(110) / {A(110) + A(003)} (In Equation 3, A(110) is the peak area of ​​the (110) plane obtained by X-ray diffraction (XRD) analysis of lithium-transition metal composite oxide particles, and A(003) is the peak area of ​​the (003) plane obtained by XRD analysis).

[0018] In some implementations, the XRD peak area ratio of lithium-transition metal composite oxide particles can be 16% to 19%.

[0019] In some implementations, the particle size (D) of the lithium-transition metal composite oxide particles is... 50 The diameter can range from 3μm to 16μm.

[0020] In some implementations, the particle size of the lithium-transition metal composite oxide particles can be from 10 μm to 15 μm.

[0021] In some implementations, the lithium-transition metal composite oxide particles may have a composition represented by Formula 1: [Formula 1] Li x Ni 1-y M y O 2+z (In Equation 1, x, y, and z are in the ranges of 0.9≤x≤1.2, 0≤y≤0.7, and -0.1≤z≤0.1, respectively, and M is at least one element 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, and Zr).

[0022] In some implementations, lithium-transition metal composite oxide particles can be prepared by reacting a transition metal precursor with a lithium precursor.

[0023] In some implementations, the transition metal precursor may be a Ni-Co-Mn precursor.

[0024] In some implementations, y in Equation 1 can be less than 0.2.

[0025] In some implementations, y in Equation 1 can be less than 0.1.

[0026] In some embodiments, the lithium-transition metal composite oxide particles may have a coating element, which may include at least one element selected from Al, Ti, Ba, Zr, Si, B, Mg and P.

[0027] In some embodiments, the lithium-transition metal composite oxide particles may have doping elements, which may include at least one element selected from Al, Ti, Ba, Zr, Si, B, Mg and P.

[0028] According to another aspect of the present invention, a lithium secondary battery is provided comprising a positive electrode including a positive electrode active material layer and a negative electrode opposite to the positive electrode, the positive electrode active material layer comprising a positive electrode active material according to the above embodiment.

[0029] The lithium secondary battery according to the above exemplary embodiment may include lithium-transition metal composite oxide particles with a grain size of less than 300 nm and an X-ray diffraction (XRD) peak intensity ratio of more than 7% as the positive electrode active material. Therefore, battery degradation can be prevented by improving lifespan performance while preventing a decrease in output performance.

[0030] In an exemplary embodiment, by reducing the grain size of the aforementioned particles to less than 300 nm, it is possible to prevent the degradation of the battery's output performance due to an excessive increase in the migration distance of lithium ions inserted / extracted during the charging and discharging of the secondary battery.

[0031] In an exemplary embodiment, by adjusting the XRD peak intensity ratio to above 7%, the lithium-ion diffusion distance can be increased, and in this case, the cation mixing phenomenon that leads to battery degradation can be reduced. Therefore, the battery deterioration rate can be reduced, thereby reducing gas generation amount and enhancing lifetime stability.

[0032] Therefore, lithium-transition metal composite oxide particles that meet the above-mentioned grain size range and XRD peak intensity ratio range can provide improved operational stability and lifetime performance while maintaining the desired output performance. Attached Figure Description

[0033] The above and other objects, features, and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, wherein: Figure 1 and Figure 2 These are schematic plan views and cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0034] An embodiment of the present invention provides a lithium secondary battery comprising lithium-transition metal composite oxide particles having grain size and XRD peak intensity ratio within a predetermined range as positive electrode active material.

[0035] In the following, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings. However, these embodiments are merely examples, and the invention is not limited to the specific embodiments described as examples.

[0036] Figure 1 and Figure 2 These are schematic plan views and cross-sectional views of a lithium secondary battery according to an exemplary embodiment, respectively. In the following text, reference will be made to... Figure 1 and Figure 2 Together, we describe a positive electrode active material for lithium secondary batteries and a lithium secondary battery including the positive electrode active material.

[0037] 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 between the positive and negative electrodes. The electrode assembly may be housed together with an electrolyte impregnating the electrode assembly in a housing 160.

[0038] The positive electrode 100 may include a positive electrode active material layer 110 formed by coating a positive electrode active material onto the positive electrode current collector 105. The positive electrode active material may include a compound capable of reversibly inserting and deintercalating lithium ions.

[0039] In an exemplary embodiment, the positive electrode active material may include lithium-transition metal composite oxide particles. For example, the lithium-transition metal composite oxide particles include nickel (Ni) and may further include at least one of cobalt (Co) and manganese (Mn).

[0040] For example, lithium-transition metal composite oxide particles can be represented by the following formula 1.

[0041] [Formula 1] Li x Ni 1-y M y O 2+z In Equation 1, x, y, and z can be in the ranges of 0.9 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.7, and -0.1 ≤ z ≤ 0.1, respectively. M can represent at least one element 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, and Zr.

[0042] In some embodiments, the molar ratio or concentration (1-y) of Ni in Formula 1 can be 0.8 or higher, and in preferred embodiments it can exceed 0.8. For example, the molar ratio or concentration (1-y) of Ni can be 0.9 or higher. In this case, the output performance of the secondary battery can be improved because the positive electrode active material includes a high content of nickel.

[0043] Ni can be provided as a transition metal related to the output and capacity of lithium secondary batteries. Therefore, as described above, by employing a composition with a high nickel (high-Ni) content in lithium-transition metal composite oxide particles, a high-power cathode and a high-power lithium secondary battery can be provided.

[0044] In this respect, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively deteriorate with increasing Ni content. However, according to an exemplary embodiment, lifetime stability and capacity retention characteristics can be improved by using Mn while maintaining conductivity through the inclusion of Co.

[0045] In some implementations, the positive electrode active material or lithium-transition metal composite oxide particles may further include coating elements or doping elements. For example, coating elements or doping elements may include Al, Ti, Ba, Zr, Si, B, Mg, P, or alloys thereof or oxides thereof. These elements may be used alone or in combination of two or more of them. Passivation of the positive electrode active material particles by coating elements or doping elements can thereby improve stability and lifetime against penetration by external objects.

[0046] In an example implementation, the grain size of the lithium-transition metal composite oxide particles can be less than 300 nm.

[0047] Typically, as the grain size of the particles increases, the propagation length required for lithium-ion insertion / extraction during battery charging and discharging may increase, thus potentially degrading initial output performance.

[0048] However, according to an exemplary embodiment, by employing lithium-transition metal composite oxide particles with a grain size of less than 300 nm, the degradation of battery output performance due to excessive increase in the migration distance of lithium ions during the charging and discharging of the secondary battery can be prevented when the grain size increases.

[0049] In an exemplary embodiment, the "crystal grain size" is a value obtained by X-ray diffraction (XRD) analysis. The grain size can be calculated and obtained using the full width at half maximum (FWHM) obtained by XRD analysis via the Scherrer equation (Equation 1 below).

[0050] [Equation 1] In Equation 1 above, L represents the grain size (nm), λ represents the X-ray wavelength (nm), β represents the full width at half maximum (FWHM) of the corresponding peak (radians), and θ represents the diffraction angle (radians). According to an exemplary embodiment, the FWHM in XRD analysis used to measure grain size can be measured from the peak of the (003) plane.

[0051] In some implementations, β in Equation 1 above can be the corrected full width at half maximum (FWHM) of the equipment-derived value. In one implementation, Si can be used as a standard substance reflecting the equipment-derived value. In this case, the equipment-derived FWHM can be expressed as a function of 2θ by plotting the full width at half maximum (FWHM) profile of Si over the full 2θ range. The corrected value obtained by subtracting the corresponding equipment-derived FWHM at 2θ from the above function can then be used as β.

[0052] When the grain size is reduced excessively, the particle strength decreases in a high-Ni environment, which may lead to particle breakage during the pressing process used to form the positive electrode active material layer 110. Consequently, electrolyte may penetrate the particles, resulting in gas generation due to side reactions, and the lifetime performance of the lithium-transition metal composite oxide particles may deteriorate.

[0053] In some embodiments, the grain size of the particles can be greater than 100 nm and less than 300 nm, preferably 150 nm to 265 nm. Within this range, thermal stability and lifetime characteristics can be effectively maintained, while high output and high capacity can be fully achieved through the composition with high Ni content.

[0054] For example, lithium-transition metal composite oxide particles can be prepared by wet or dry mixing of a Ni-Co-Mn precursor (e.g., Ni-Co-Mn hydroxide) with a lithium precursor (e.g., lithium hydroxide or lithium carbonate) and reacting them, followed by calcination of the reactants.

[0055] In one implementation, the grain size of lithium-transition metal composite oxide particles can be controlled by adjusting the calcination temperature.

[0056] Lithium-transition metal composite oxide particles can have a crystallographic single-crystal structure and / or a polycrystalline structure. In one embodiment, the positive electrode active material may include a mixture or blend of single-crystal particles and polycrystalline particles having the above-described grain size.

[0057] Lithium-transition metal composite oxide particles can take the form of single particles, primary particles, or secondary particles in terms of morphology.

[0058] In an exemplary embodiment, the XRD peak intensity ratio of the lithium-transition metal composite oxide particles can be above 7%, as defined by Equation 2 below.

[0059] [Equation 2] XRD peak intensity ratio (%) = 100 × I(110) / {I(110) + I(003)} In Equation 2, I(110) represents the peak intensity or maximum height of the (110) plane obtained by X-ray diffraction (XRD) analysis of lithium-transition metal composite oxide particles, and I(003) represents the peak intensity or maximum height of the (003) plane obtained by XRD analysis.

[0060] For example, dry powder of lithium-transition metal composite oxide particles can be analyzed by using Cu-Kα rays as a light source and scanning at a rate of 0.0065° / step within a diffraction angle (2θ) range of 10° to 120°.

[0061] In high-Ni lithium-transition metal composite oxide particles, for example, lithium ions (Li) in the lithium layer + ) and nickel ions (Ni 2+ At high temperatures, the ions irreversibly substitute for each other, leading to cation mixing that degrades the battery. The cation mixing phenomenon propagates from the surface of the (110) facet inwards. As the diffusion length of lithium ions increases, the substitution of lithium ions with nickel ions decreases, thereby reducing structural degradation caused by cation mixing.

[0062] Within the aforementioned range of XRD peak intensity ratios, the ion propagation length and ion diffusion length at the (110) plane through which lithium ions diffuse can be increased. Furthermore, by adjusting the ratio of peak intensities at the (003) plane intersecting the (110) plane, the aspect ratio of the particles can be controlled. In this case, cation mixing can be reduced, thereby reducing the degradation area of ​​the lithium-transition metal composite oxide particles. Therefore, lifetime characteristics at high temperatures and during charge / discharge can be improved, and gas production can be reduced.

[0063] Furthermore, for example, as described above, by adjusting the XRD peak intensity ratio, the reduction in relative lifetime performance caused by reducing the grain size to less than 300 nm can be mitigated or compensated.

[0064] Therefore, output / capacity can be increased by controlling the grain size to enhance lithium-ion migration performance, and lifetime stability can be improved by controlling the XRD peak intensity ratio to prevent cation mixing.

[0065] In some embodiments, the lithium-transition metal composite oxide particles may have an XRD peak intensity ratio of 7% to 12%, preferably 9% to 11%. Within this range, it is possible to prevent the output characteristics from deteriorating due to an excessive increase in the longer migration path of lithium ions, while maintaining the surface stability and lifetime characteristics of the lithium-transition metal composite oxide particles.

[0066] In some implementations, the XRD peak intensity ratio of lithium-transition metal composite oxide particles can be above 16%, as defined by Equation 3 below.

[0067] [Equation 3] XRD peak area ratio (%) = 100 × A(110) / {A(110) + A(003)} In Equation 3, A(110) represents the peak area of ​​the (110) plane obtained by X-ray diffraction (XRD) analysis of lithium-transition metal composite oxide particles, and A(003) represents the peak area of ​​the (003) plane obtained by XRD analysis.

[0068] By adjusting the peak area ratio and the aforementioned peak intensity ratio, the effect of controlling the lithium-ion diffusion length and aspect ratio through XRD values ​​can be better achieved.

[0069] In a preferred embodiment, the XRD peak area ratio can be 16% to 19%.

[0070] In some implementations, the average particle size (D) of the lithium-transition metal composite oxide particles is... 50The particle size can range from 3 μm to 16 μm. In this case, the reduction in mechanical strength and chemical stability of the positive electrode active material due to excessive particle size reduction can be prevented, thereby preventing gas generation due to particle breakage during the pressing process used to form the positive electrode active material layer 110. Furthermore, particle breakage of the high-Ni positive electrode active material can be reduced, which may be caused, for example, by the repeated shrinkage / expansion of the positive electrode active material volume during repeated charging and discharging.

[0071] In this invention, "particle diameter" or "D" refers to the particle size. 50 "It can refer to the particle size when the cumulative percentage of volume in the particle size distribution obtained from the particle volume reaches 50%."

[0072] In some implementations, the particle size of the lithium-transition metal composite oxide particles can be from 10 μm to 15 μm. In this case, gas production can be reduced and lifetime performance can be improved, while preventing output performance from deteriorating due to excessive increase in particle size.

[0073] For example, transition metal precursors (e.g., Ni-Co-Mn precursors) for preparing lithium-transition metal composite oxide particles can be prepared by co-precipitation reactions.

[0074] The aforementioned transition metal precursors can be prepared by co-precipitation reactions of metal salts. These metal salts can include nickel, manganese, and cobalt salts.

[0075] Examples of nickel salts may include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, and their hydrates. Examples of manganese salts may include manganese sulfate, manganese acetate, and their hydrates. Examples of cobalt salts may include cobalt sulfate, cobalt nitrate, cobalt carbonate, and their hydrates.

[0076] Metal salts can be mixed with precipitants and / or chelating agents in proportions satisfying the content or concentration ratios of each metal as described in Formula 1 to prepare aqueous solutions. The aqueous solutions can be co-precipitated in a reactor to prepare transition metal precursors.

[0077] Precipitating agents may include basic compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). Chelating agents may include, for example, ammonia (e.g., NH3H2O) and ammonium carbonates (e.g., NH3HCO3).

[0078] The temperature of the coprecipitation reaction can be controlled, for example, within the range of about 40°C to 60°C. The reaction time can be controlled within the range of about 24 hours to 72 hours.

[0079] For example, transition metal precursors can be reacted with lithium precursors to prepare lithium-transition metal composite oxide particles. Lithium precursor compounds can include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, etc. These compounds can be used alone or in combination of two or more of them.

[0080] Subsequently, lithium impurities or unreacted precursors can be removed, for example, by a washing process, and metal particles can be fixed or crystallinity can be increased by a heat treatment (calcination) process. In one embodiment, the heat treatment can be carried out at a temperature of about 600°C to 1000°C.

[0081] For example, the above-mentioned grid deformation, XRD peak intensity ratio, and XRD peak area ratio can be changed according to the reaction time, reaction temperature, heat treatment temperature, etc. of the coprecipitation reaction.

[0082] A slurry can be prepared by mixing and stirring the positive electrode active material, including the aforementioned lithium-transition metal composite oxide particles, with a binder, a conductive material, and / or a dispersant in a solvent. The slurry can be coated onto the positive electrode current collector 105, followed by drying and pressing to manufacture the positive electrode 100.

[0083] The positive current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, and preferably aluminum or aluminum alloys.

[0084] The adhesive may include, for example, organic adhesives such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or aqueous adhesives such as styrene-butadiene rubber (SBR) that can be used with thickeners such as carboxymethyl cellulose (CMC).

[0085] For example, PVDF-based binders can be used as positive electrode forming 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, thereby improving the output and capacity of the secondary battery.

[0086] Conductive materials may be included to facilitate electron migration between active material particles. For example, conductive materials may include carbon-based materials such as graphite, carbon black, graphene, or carbon nanotubes, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, perovskite minerals such as LaSrCoO3 or LaSrMnO3, etc.

[0087] 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 active material onto the negative electrode current collector 125.

[0088] The negative electrode active material used in this invention can include any material known in the relevant art, as long as it enables lithium ion insertion and extraction, without any particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium alloys; silicon compounds or tin can be used. Examples of amorphous carbon can include hard carbon, coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers (MPCF), etc.

[0089] Examples of crystalline carbon can include graphite-based carbon, such as natural graphite, artificial graphite, graphite coke, graphitized MCMB, graphitized MPCF, etc. Other elements included in lithium alloys can include, for example, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0090] Silicon compounds may include, for example, silicon-carbon composite compounds, such as silicon oxide or silicon carbide (SiC).

[0091] For example, a slurry can be prepared by mixing the negative electrode active material with a binder, a conductive material, and / or a thickener in a solvent and then stirring. The slurry can be coated onto at least one surface of the negative electrode current collector 125, followed by drying and pressing to manufacture the negative electrode 130.

[0092] As the binder and conductive material, substances substantially the same as or similar to those used in the positive electrode active material layer 110 can be used. In some embodiments, the binder used to form the negative electrode may include, for example, an aqueous binder, such as styrene-butadiene rubber (SBR), to maintain compatibility with the carbon-based active material, and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0093] 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 made of a polyolefin polymer, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The separator 140 may also comprise a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like.

[0094] In some embodiments, the negative electrode 130 may have a larger area (e.g., contact area with the separator 140) and / or volume than the positive electrode 100. Therefore, for example, lithium ions generated from the positive electrode 100 can be readily transferred to the negative electrode 130 without precipitation in between.

[0095] 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, for example, a jelly roll type electrode assembly 150. For example, the electrode assembly 150 can be formed by winding, stacking, folding, etc., of the diaphragm 140.

[0096] The electrode assembly 150 and the electrolyte can be housed together in the housing 160 to define a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0097] Non-aqueous electrolytes include lithium salt electrolytes and organic solvents, and the lithium salt is made of, for example, Li. + X - This indicates that, and as an anion of lithium salt (X... - ), for example 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.

[0098] As organic solvents, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc., can be used. These compounds can be used alone or in combination of two or more of them.

[0099] like Figure 1 As shown, the tabs (positive tab and negative tab) may protrude from the positive current collector 105 and negative current collector 125 belonging to each electrode cell, respectively, and may extend to one side of the housing 160. The tabs may be fused to one side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending or exposed outside the housing 160.

[0100] Lithium-ion batteries can be manufactured in shapes such as cylindrical (canned), square, pouch, or coin.

[0101] Specific experimental examples are presented below to illustrate the invention. However, the following embodiments are given merely to explain the invention, and those skilled in the art will clearly understand that various changes and modifications can be made within the scope and spirit of the invention. Such changes and modifications are suitably included within the appended claims.

[0102] Preparation of lithium-transition metal composite oxide particles Using distilled water that has been bubbled with N2 for 24 hours to remove dissolved oxygen, NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.1:0.1, respectively. This solution was introduced into a reactor at 50°C, and a co-precipitation reaction was carried out for 72 hours using sodium hydroxide as a precipitant and NH3H2O ​​as a chelating agent to obtain Ni as a transition metal precursor. 0.8 C 0.1 MN 0.1 (OH)2. The obtained precursor was dried at 100°C for 12 hours, and then dried again at 120°C for 10 hours.

[0103] Then, lithium hydroxide and the transition metal precursor were added in a dry high-speed mixer at a ratio of 1.03:1, followed by uniform stirring and mixing for 5 minutes. The mixture was then placed in a calcination furnace and heated to 950°C at a heating rate of 2°C / min, and held at 950°C for 12 hours. During heating and holding, oxygen was continuously passed through at a flow rate of 10 mL / min. After calcination, the mixture was allowed to cool naturally to room temperature, followed by grinding and classification to prepare lithium-transition metal composite oxide LiNi in single-particle (including single-crystal and polycrystalline structures) form as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2 particles (first particle).

[0104] Second to tenth particles were prepared by changing the reaction time and temperature in the reactor, or the calcination time, calcination temperature, and heating rate during the calcination process. XRD analysis of each lithium-transition metal composite oxide particle yielded the grain size calculated using Equation 1 and the XRD peak intensity ratio calculated using Equations 2 and 3.

[0105] Meanwhile, the specific XRD analysis equipment / conditions are described in Table 1 below.

[0106] [Table 1] Example 1 The aforementioned first particle was used as the positive electrode active material to manufacture a secondary battery. Specifically, the positive electrode active material, Denka Black as a conductive material, and polyvinylidene fluoride as a binder were mixed in a mass ratio of 97:2:1 to prepare a positive electrode slurry. This slurry was then coated onto an aluminum current collector, and the positive electrode was prepared by drying and pressing. After pressing, the target electrode density of the positive electrode was controlled at 3.55 g / cc (grams per cubic centimeter).

[0107] A negative electrode slurry was prepared comprising 93% by weight ('wt%) natural graphite as the negative electrode active material, 5% by weight KS6 as the sheet conductive material, 1% by weight styrene-butadiene rubber (SBR) as a binder, and 1% by weight carboxymethyl cellulose (CMC) as a thickener. The negative electrode slurry was coated onto a copper substrate, followed by drying and pressing to prepare the negative electrode.

[0108] The positive and negative electrodes, prepared as described above, are cut (notched) and stacked to predetermined dimensions. A separator (polyethylene, thickness: 25µm) is then inserted between the positive and negative electrodes to fabricate an electrode cell. Subsequently, the tab portions of the positive and negative electrodes are welded together. The welded positive / separator / negative electrode assembly is placed in a pouch, and then the three sides of the pouch, except for the electrolyte injection side, are sealed. At this point, the portion with the tabs is included in the sealed portion. After injecting electrolyte through the remaining side (excluding the sealed portion), the remaining side is also sealed, and then the cell is immersed for 12 hours or longer.

[0109] The electrolyte used in this paper was prepared by dissolving LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio) to obtain a 1M LiPF6 solution, and adding 1 wt% vinylene carbonate (VC), 0.5 wt% 1,3-propenyl sulfonyl lactone and 0.5 wt% lithium bis(oxalate)borate (LiBOB).

[0110] Then, the secondary battery prepared as described above was precharged for 36 minutes at a current equivalent to 0.25C (5A). After 1 hour, it was degassed and then aged for 24 hours or longer, followed by formation charging-discharging (charging conditions: CC-CV 0.2C 4.2 V 0.05C cutoff; discharging conditions: CC 0.2C 2.5 V cutoff).

[0111] Example 2 Except for using the second particle mentioned above as the positive electrode active material, the secondary battery is manufactured according to the same steps as described in Example 1.

[0112] Example 3 Except for using the aforementioned third particle as the positive electrode active material, the secondary battery is manufactured according to the same steps as described in Example 1.

[0113] Example 4 Except for using a fourth particle as the positive electrode active material, the secondary battery is manufactured according to the same steps as described in Example 1.

[0114] Example 5 Except for using the fifth particle mentioned above as the positive electrode active material, the secondary battery is manufactured according to the same steps as described in Example 1.

[0115] Example 6 Except for using the sixth particle mentioned above as the positive electrode active material, the secondary battery was manufactured according to the same steps as described in Example 1.

[0116] Example 7 Except for using the seventh particle mentioned above as the positive electrode active material, the secondary battery was manufactured according to the same steps as described in Example 1.

[0117] Comparative Example 1 Except for using the eighth particle mentioned above as the positive electrode active material, the secondary battery was manufactured according to the same steps as described in Example 1.

[0118] Comparative Example 2 Except for using the aforementioned ninth particle as the positive electrode active material, the secondary battery was manufactured according to the same steps as described in Example 1.

[0119] Comparative Example 3 Except for using the aforementioned tenth particle as the positive electrode active material, the secondary battery was manufactured according to the same steps as described in Example 1.

[0120] The XRD analysis values ​​and particle sizes of the lithium-transition metal composite oxide particles of the above embodiments and comparative examples are shown in Table 2 below.

[0121] [Table 2] Experimental Example (1) Measurement of gas production at high temperature After charging the lithium secondary batteries of the above embodiments and comparative examples (1C 4.2V 0.1C cutoff), the gas production after storage in a thermostatic chamber at 60°C for 1 week and 4 weeks was confirmed by gas chromatography (GC) analysis. To measure the total gas production, a hole was formed in the battery in a chamber under vacuum conditions of a predetermined volume (V), and the pressure change was measured to calculate the gas production.

[0122] (2) Measure lifetime (capacity retention) at 45°C. After repeatedly charging (CC-CV 1.0C 4.2V 0.05C cutoff) and discharging (CC 1.0C 2.7V cutoff) the lithium secondary batteries of the above embodiments and comparative examples 100 times and 300 times respectively in a chamber at 45°C, the capacity retention rate after 100 cycles was evaluated by calculating the percentage (%) of the discharge capacity of the 100th cycle to the discharge capacity of the first cycle, and the capacity retention rate after 300 cycles was evaluated by calculating the percentage (%) of the discharge capacity of the 300th cycle to the discharge capacity of the first cycle.

[0123] (3) Measure the rate of increase in internal resistance at room temperature (DC internal resistance (DCIR)) The lithium secondary batteries of the above-described examples and comparative examples were charged (CC-CV 0.5C, SOC 100%) and discharged twice at 25°C. Then, the lithium secondary batteries were charged again (CC-CV 0.5C, SOC 100%), and then discharged until SOC 50% was reached. Afterward, the voltage (first voltage) was measured after 30 minutes of inactivity.

[0124] Then, after performing the following steps, measure the voltage (second voltage): i) discharge at 1C for 10 seconds, then place for 40 seconds, and ii) charge at 0.75C for 10 seconds, then place for 40 seconds. Use the difference between the first and second voltages to measure DCIR.

[0125] The evaluation results are shown in Table 3 below.

[0126] [Table 3] Referring to Table 3, in general, in the case of using lithium-transition metal composite oxide particles with a grain size of less than 300 nm and an XRD peak intensity ratio that meets or exceeds a predetermined value, compared with the comparative example, good capacity retention and DCIR characteristics at room temperature are ensured while suppressing gas production.

[0127] Specifically, Examples 1 to 5, which use particles with a grain size of 100 nm or more and less than 300 nm and an XRD peak intensity ratio of 7% to 12%, exhibit relatively high capacity retention and low resistance, thereby ensuring excellent lifetime performance and output performance.

[0128] However, in Example 6, which uses particles with an XRD peak intensity ratio exceeding 12%, the migration length of lithium ions increases compared to Examples 1 to 5, and a slightly increased DCIR value is observed, resulting in some degradation in output performance.

[0129] Furthermore, in Example 7, which uses particles with a grain size of less than 100 nm, the particle strength is reduced and the possibility of particle breakage during repeated charging and discharging is increased, resulting in a decrease in capacity retention rate based on repeated cycles compared to Examples 1 to 5.

[0130] Comparative Examples 1 and 2, which use particles with a grain size exceeding 300 nm, exhibited high resistance values ​​because the migration length of lithium ions was excessively increased compared to the Examples, resulting in a decrease in the output performance of the secondary battery compared to the Examples.

[0131] In Comparative Example 3, which uses particles with an XRD peak intensity ratio of less than 7%, the lithium-ion migration path is shortened and battery degradation occurs due to cation mixing, resulting in a decrease in capacity retention based on repeated cycles compared to the Examples.

[0132] [Explanation of reference numerals in the attached figures] 100: Positive electrode 105: Positive current collector 110: Positive electrode active material layer 120: Negative electrode active material layer 125: Negative electrode current collector 130: Negative electrode 140: Diaphragm 160: Outer shell 107: Positive lead 127: Negative lead 150: Electrode assembly

Claims

1. A positive electrode active material for lithium secondary batteries, comprising lithium-transition metal composite oxide particles having a grain size of less than 300 nm as determined by X-ray diffraction (XRD) analysis, and having an XRD peak intensity ratio of more than 7% as defined by Equation 2 below, the grain size being measured by Equation 1 below. [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) surface of the lithium-transition metal composite oxide particles obtained by XRD analysis, and I(003) is the maximum height of the peak on the (003) surface obtained by XRD analysis. [Equation 1] ， In Equation 1, L is the grain size in nm, λ is the X-ray wavelength in nm, β is the full width at half maximum (FWHM) of the peak on the (003) plane in radians, and θ is the diffraction angle in radians.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The grain size of the lithium-transition metal composite oxide particles is greater than 100 nm and less than 300 nm.

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 7% to 12%.

4. 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 9% to 11%.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The XRD peak area ratio of the lithium-transition metal composite oxide particles, as defined by Equation 3, is above 16%. [Equation 3] XRD peak area ratio (%) = 100 × A(110) / {A(110) + A(003)} In Equation 3, A(110) is the peak area of ​​the (110) surface obtained by X-ray diffraction (XRD) analysis of the lithium-transition metal composite oxide particles, and A(003) is the peak area of ​​the (003) surface obtained by XRD analysis.

6. The positive electrode active material for lithium secondary batteries according to claim 5, wherein, The XRD peak area ratio of the lithium-transition metal composite oxide particles, as defined by Equation 3, is 16% to 19%.

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The particle size D50 of the lithium-transition metal composite oxide particles is 3 μm to 16 μm.

8. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles have the following composition represented by 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≤1.2, 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, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

9. The positive electrode active material for lithium secondary batteries according to claim 8, wherein, In the chemical formula 1, y is less than 0.

2.

10. The positive electrode active material for lithium secondary batteries according to claim 9, wherein, The grain size of the lithium-transition metal composite oxide particles is from 150 nm to 265 nm.

11. The positive electrode active material for lithium secondary batteries according to claim 10, wherein, The particle size D50 of the lithium-transition metal composite oxide particles is 10 μm to 15 μm.

12. The positive electrode active material for lithium secondary batteries according to claim 9, wherein, In the chemical formula 1, y is less than 0.

1.

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

14. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles contain coating elements. The coating elements include at least one element selected from Al, Ti, Ba, Zr, Si, B, Mg and P.

15. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal composite oxide particles contain doping elements. The doping element includes at least one element selected from Al, Ti, Ba, Zr, Si, B, Mg and P.

16. A lithium secondary battery, comprising: Positive electrode, wherein the positive electrode comprises a positive electrode active material layer containing the positive electrode active material as described in claim 1; as well as The negative electrode opposite to the positive electrode.

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