Positive electrode active material for lithium secondary batteries and its manufacturing method

Abstract

A method for manufacturing a positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes subjecting a first heat treatment of a first mixture of a transition metal precursor and a lithium precursor at a first calcination temperature to obtain primary lithium-transition metal composite oxide particles; and subjecting a second heat treatment of a second mixture obtained by adding a lithium precursor to the primary lithium-transition metal composite oxide particles at a second calcination temperature lower than the first calcination temperature to form lithium-transition metal composite oxide particles.

Description

Cross-references to related applications

[0001] This application is a divisional application of Chinese patent application filed on September 22, 2021, with Chinese patent application number 202111104201.2 and the invention title "Positive electrode active material for lithium secondary batteries and method of manufacturing the same", and this application claims priority to Korean application with application number 10-2020-0124161. Technical Field

[0002] This invention relates to positive electrode active materials for lithium secondary batteries and methods for manufacturing the same, and more specifically, to lithium metal oxide-based positive electrode active materials for lithium secondary batteries and methods for manufacturing the same. Background Technology

[0003] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the rapid development of the information and communication and display industries, rechargeable batteries have been widely used as a power source for various portable telecommunications electronic devices (such as portable camcorders, mobile phones, and laptops). Recently, battery packs incorporating 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 secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries have higher operating voltage and higher energy density per unit weight, and are advantageous in terms of charging speed and light weight. In this respect, 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 (separation membrane); and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include, for example, a pouch-shaped outer case, in which the electrode assembly and electrolyte are housed.

[0006] Lithium metal oxides are traditionally used as the positive electrode active material in lithium-ion batteries, and are manufactured through processes including calcination and washing. However, according to conventional methods for manufacturing positive electrode active materials, the residual metal on the surface of oxide particles increases, which may degrade the life characteristics and operational reliability of lithium-ion batteries.

[0007] For example, Korean patent registration number 10-0548988 discloses a method for manufacturing a positive electrode active material for lithium secondary batteries, but there are limitations in ensuring sufficient lifespan characteristics and operational stability.

[0008] [Existing Technical Documents] [Patent Literature] Korean Patent Publication No. 10-0548988 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, the present invention adopts the following technical solution.

[0012] To achieve the above objectives, according to one aspect of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery is provided, comprising: subjecting a first mixture of a transition metal precursor and a lithium precursor to a first calcination temperature to a first heat treatment to obtain primary lithium-transition metal composite oxide particles; and subjecting a second mixture obtained by adding the lithium precursor to the primary lithium-transition metal composite oxide particles to a second calcination temperature lower than the first calcination temperature to a second heat treatment to form lithium-transition metal composite oxide particles.

[0013] In some embodiments, the lithium-transition metal composite oxide particles may have a composition represented by Formula 1: [Formula 1] Li a Ni x M 1-x O 2+y (In Formula 1, a, x, and y are in the ranges of 0.95≤a≤1.2, 0.6≤x≤0.99, and -0.1≤y≤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).

[0014] In some embodiments, the first calcination temperature may satisfy the following formulas 1 and 2, and the second calcination temperature may satisfy the following formulas 3 and 4: [Formula 1] t1 - 10 ≤ T1(℃) ≤ t1 + 10 (In Formula 1, t1 is the temperature obtained according to Formula 2 below, and T1 is the first calcination temperature).

[0015] [Formula 2] t1(℃) = (-520) x + 1275 (In Formula 2, x is the same as the x defined in Formula 1).

[0016] [Formula 3] t2 - 10 ≤ T2(℃) ≤ t2 + 10 (In Formula 3, t2 is the temperature obtained according to Formula 4 below, and T2 is the second calcination temperature).

[0017] [Formula 4] t2(℃) = (-520) x + 1180 (In Formula 4, x is the same as the x defined in Formula 1).

[0018] In some implementations, x can be 0.8 or higher in Equation 1 above.

[0019] In some embodiments, the lithium precursor may be added in the first mixture at an amount of 80-90 mol% based on the molar number of the added transition metal precursor, and in the second mixture, the lithium precursor may be added at an amount of 10-20 mol% based on the molar number of the added transition metal precursor. In some embodiments, the transition metal precursor may include nickel-containing, cobalt-containing, and manganese-containing compounds.

[0020] In some embodiments, the lithium precursor may include at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium hydroxide.

[0021] In some implementations, washing with water is not included.

[0022] In some implementations, a second heat treatment can be performed immediately after the first heat treatment.

[0023] Furthermore, according to one aspect of the present invention, a positive electrode active material for a lithium secondary battery is provided, comprising: lithium-transition metal composite oxide particles, wherein the crystallite size of the lithium-transition metal composite oxide particles in the (104) plane direction is less than 120 nm, as determined by X-ray diffraction (XRD) analysis, and the ratio of the crystallite size of the lithium-transition metal composite oxide particles in the (104) plane direction to its crystallite size in the (003) plane direction is 1:(2.5 or more), and the crystallite size is measured by the following formula 5: [Formula 5] (In Formula 5, L is the crystallite size (nm), λ is the X-ray wavelength (nm), β is the full width at half maximum (FWHM) of the peak on the (003) or (104) plane (radians (rad)), and θ is the diffraction angle (radians (rad)).

[0024] In some embodiments, the content of lithium carbonate remaining on the surface of lithium-transition metal composite oxide particles may be less than 3000 ppm, and the content of lithium hydroxide remaining on the surface of lithium-transition metal composite oxide particles may be less than 5000 ppm.

[0025] In some implementations, the lithium-transition metal composite oxide particles may have a crystallite size of 80-115 nm in the (104) plane direction.

[0026] In some embodiments, the ratio of the crystallite size of the lithium-transition metal composite oxide particles in the (104) plane direction to its crystallite size in the (003) plane direction can be from 1:2.5 to 1:3.05.

[0027] Furthermore, according to one aspect of the present invention, a lithium secondary battery is provided, comprising: a positive electrode, which may include a positive electrode active material layer containing the above-described positive electrode active material for a lithium secondary battery; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0028] The method for manufacturing the positive electrode active material for a lithium secondary battery according to the above exemplary embodiment may include a two-stage calcination step. Therefore, the content of lithium precursors remaining on the surface of lithium-transition metal composite oxide particles can be reduced, and the lifespan characteristics of the lithium secondary battery can be improved.

[0029] In some implementations, the calcination temperature in each calcination step can be varied according to the molar ratio or concentration of the input Ni. Therefore, the temperature of each calcination step can be appropriately controlled, and the initial capacity and lifetime characteristics of the lithium secondary battery can be improved.

[0030] In some implementations, the input amount of lithium precursor can be controlled for each calcination step based on the number of moles of the added transition metal precursor. Therefore, the number of moles of Ni added in the first calcination step can be reduced, allowing the first calcination step to be performed at a higher temperature than conventional calcination processes. In this case, the amount of lithium precursor remaining on the surface of the lithium-transition metal composite oxide particles can be reduced.

[0031] The lithium-transition metal composite oxide particles prepared according to the method for manufacturing positive electrode active materials can have a crystallite size of less than 120 nm in the (104) plane direction, wherein the ratio of the crystallite size in the (104) plane direction to the crystallite size in the (003) plane direction can be 1:(2.5 or higher). Therefore, the structural stability of the lithium-transition metal composite oxide particles can be increased, and lithium secondary batteries using it can stably adsorb and desorb lithium ions, thereby improving initial capacity efficiency and lifetime characteristics. Attached Figure Description

[0032] The above and other objects, features and 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 A flowchart illustrating a process in a method for manufacturing a positive electrode active material according to an exemplary embodiment; Figure 2 and Figure 3 The figures shown are schematic plan views and cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0033] Embodiments of the present invention provide a method for manufacturing lithium-transition metal composite oxide particles and a positive electrode active material comprising the same, comprising multiple calcination steps. Furthermore, embodiments of the present invention provide a positive electrode active material comprising the lithium-transition metal composite oxide particles and a lithium secondary battery comprising the same.

[0034] In the following, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these embodiments are merely examples, and the present invention is not limited to the specific embodiments described as examples.

[0035] <Method for manufacturing positive electrode active material for lithium secondary batteries> Figure 1 This is a flowchart describing a process in a method for manufacturing a positive electrode active material according to an exemplary embodiment.

[0036] In the following text, reference will be made to Figure 1 A method for manufacturing a positive electrode active material for a lithium secondary battery according to an exemplary embodiment is described.

[0037] refer to Figure 1 The first mixture can be prepared by mixing a transition metal precursor and a lithium precursor (e.g., step S10).

[0038] Transition metal precursors may include nickel-, cobalt-, and manganese-containing compounds. Transition metal precursors may include, for example, nickel-, cobalt-, and manganese-containing hydroxides, sulfates, acetates, nitrates, and their hydrates.

[0039] Transition metal precursors can be prepared by co-precipitation reactions of metal salts. These metal salts can include nickel, manganese, and cobalt salts.

[0040] 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.

[0041] Metal salts can be mixed with precipitants and / or chelating agents, while controlling the content or concentration ratio of each metal, to prepare an aqueous solution. The aqueous solution can then be co-precipitated in a reactor to prepare transition metal precursors.

[0042] 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 carbonate (e.g., NH3HCO3).

[0043] 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 24-72 hours.

[0044] Lithium precursor compounds may include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, etc., as lithium salts. These compounds may be used alone or in combination of two or more.

[0045] In an exemplary embodiment, the obtained first mixture is subjected to a first heat treatment at a first calcination temperature to form primary lithium-transition metal composite oxide particles (e.g., step S20).

[0046] In some implementations, the first calcination temperature can be determined by the molar ratio or concentration of Ni in the final lithium-transition metal composite oxide particles.

[0047] For example, lithium-transition metal composite oxide particles can be represented by the following formula 1.

[0048] [Formula 1] Li a Ni x M 1-x O 2+y In Equation 1, a, x, and y can be in the ranges of 0.95 ≤ a ≤ 1.2, 0.6 ≤ x ≤ 0.99, and -0.1 ≤ y ≤ 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.

[0049] In some embodiments, the molar ratio or concentration x of Ni in Formula 1 can be 0.8 or higher, and in preferred embodiments it exceeds 0.8.

[0050] 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.

[0051] In this respect, as the Ni content increases, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively deteriorate. However, according to an exemplary embodiment, by including Co, lifetime stability and capacity retention characteristics can be improved by using Mn while maintaining conductivity.

[0052] For example, the first calcination temperature can satisfy the range according to the following formulas 1 and 2.

[0053] [Formula 1] t1 - 10 ≤ T1(℃) ≤ t1 + 10 In Formula 1, t1 is the temperature obtained according to Formula 2 below, and T1 is the first calcination temperature.

[0054] [Formula 2] t1(℃) = (-520) x + 1275 In Formula 2, x is the same as the x defined in Formula 1, for example, x is the molar ratio or concentration of Ni in Formula 1.

[0055] For example, in Formula 1, when the first calcination temperature T1 is in the range of t1-10℃ or higher (i.e., t1-10℃≤T1), the content of lithium precursors remaining on the surface of the prepared lithium-transition metal composite oxide particles can be reduced, thereby improving the initial capacity characteristics of the lithium secondary battery.

[0056] For example, in Formula 1, when the first calcination temperature T1 is below t1+10℃ (i.e., T1≤t1+10℃), the ratio of lithium-transition metal composite oxide particles with hexagonal structure can be increased, thereby reducing the specific surface area of ​​lithium-transition metal composite oxide particles to improve the life characteristics of lithium secondary batteries.

[0057] Therefore, when the first calcination temperature meets the temperature range of Formula 1, the output characteristics and lifespan characteristics of lithium secondary batteries, including lithium-transition metal composite oxide particles as positive electrode active materials, can be improved simultaneously.

[0058] In an exemplary embodiment, a second mixture can be prepared by additionally adding a lithium precursor to the obtained primary lithium-transition metal composite oxide particles (e.g., step S30).

[0059] In an exemplary embodiment, the obtained second mixture is subjected to a second heat treatment at a second calcination temperature to form lithium-transition metal composite oxide particles (e.g., step S40).

[0060] In some implementations, the second calcination temperature can be determined by the molar ratio or concentration of Ni in the final lithium-transition metal composite oxide particles.

[0061] For example, the second calcination temperature can meet the range according to the following formulas 3 and 4.

[0062] [Formula 3] t2 - 10 ≤ T2(℃) ≤ t2 + 10 In Formula 3, t2 is the temperature obtained through Formula 4 below, where T2 is the second calcination temperature.

[0063] [Formula 4] t2(℃) = (-520) x + 1180 In Formula 4, x is the same as the x defined in Formula 1, for example, x is the molar ratio or concentration of Ni in Formula 1.

[0064] For example, in Formula 3, when the second calcination temperature T2 is in the range of t2-10℃ or higher (i.e., t2-10℃≤T2), the content of lithium precursors remaining on the surface of the prepared lithium-transition metal composite oxide particles can be reduced, thereby improving the initial capacity characteristics of the lithium secondary battery.

[0065] For example, in Formula 3, when the second calcination temperature T2 is below t2+10℃ (i.e., T2≤t2+10℃), the proportion of lithium-transition metal composite oxide particles with hexagonal structure can be increased, thereby reducing the specific surface area of ​​lithium-transition metal composite oxide particles to improve the life characteristics of lithium secondary batteries.

[0066] Therefore, when the second calcination temperature meets the temperature range of Formula 3, the output characteristics and lifespan characteristics of lithium secondary batteries, including lithium-transition metal composite oxide particles as positive electrode active materials, can be improved simultaneously.

[0067] Typically, in order to give lithium-transition metal composite oxide particles a hexagonal structure during the preparation of lithium-transition metal composite oxide particles, the calcination temperature can be reduced as the amount of Ni input increases.

[0068] In some embodiments, only a portion of the total molar amount of lithium precursor may be added when preparing the first mixture, while the remainder may be added when preparing the second mixture. In this case, the amount of transition metal precursor reacting with the lithium precursor during the first heat treatment can be reduced, thereby also reducing the molar amount of Ni added. Therefore, the first heat treatment process can be carried out at a higher temperature than conventional calcination processes, and the amount of lithium precursor remaining on the surface of the lithium-transition metal composite oxide particles can be reduced.

[0069] For example, based on the number of moles of the transition metal precursor to be added, 80-90 mol% of lithium precursor can be added in the first calcination step, and based on the number of moles of the transition metal precursor to be added, 10-20 mol% of lithium precursor can be added in the second calcination step.

[0070] When the addition ratio of lithium precursor meets the above range, it can prevent the reduction in lifetime characteristics caused by cracks in primary lithium-transition metal composite oxide particles, as well as the reduction in output characteristics caused by lithium precursors remaining on the surface of lithium-transition metal composite oxide particles.

[0071] Conventional processes for manufacturing lithium-transition metal composite oxide particles may also include a water washing process. In this case, at least some particles on the surface and inside the lithium-transition metal composite oxide can change from a hexagonal structure to a cubic structure. This creates voids between the particles, leading to an increase in the specific surface area of ​​the particles, which may degrade capacity and lifetime characteristics at high temperatures.

[0072] However, since the method for manufacturing lithium-transition metal composite oxide particles according to an exemplary embodiment of the present invention includes a first heat treatment process performed at a relatively high temperature, the amount of lithium precursor remaining on the surface of the lithium-transition metal composite oxide particles can be reduced. Therefore, the method of the present invention may not include a water washing process for removing lithium precursor remaining on the surface of the lithium-transition metal composite oxide particles, thereby preventing an increase in the specific surface area of ​​the particles and improving storage performance and stability at high temperatures.

[0073] In an exemplary embodiment, the positive electrode active material may include the aforementioned lithium-transition metal composite oxide particles.

[0074] <Positive electrode active materials for lithium secondary batteries and lithium secondary batteries> According to an embodiment of the present invention, a positive electrode active material prepared by the above-described method for manufacturing a positive electrode active material for a lithium secondary battery can be provided.

[0075] In some embodiments, 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 thereof. Passivation of the positive electrode active material particles by coating elements or doping elements can further improve stability and lifetime against penetration by external objects.

[0076] In some embodiments, the content of lithium carbonate remaining on the surface of the lithium-transition metal composite oxide particles contained in the positive electrode active material may be less than 3000 ppm, and the content of lithium hydroxide remaining on the surface of the lithium-transition metal composite oxide particles may be less than 5000 ppm.

[0077] When the content of residual lithium precursor meets the above range, electron transfer of the positive electrode active material can proceed smoothly, thereby improving the initial capacity characteristics and output characteristics of the lithium secondary battery.

[0078] In some embodiments, the lithium-transition metal composite oxide particles may have a crystallite size (CS) of less than 120 nm in the (104) plane direction.

[0079] When the crystallite size is below 120 nm, the structural stability of lithium-transition metal composite oxide particles can be improved. Lithium secondary batteries using these particles can stably adsorb and desorb lithium ions, thereby improving the capacity retention rate during repeated cycles.

[0080] In some implementations, the crystallite size in the (104) plane direction can be 80-115 nm. Within this range, a composition with high nickel (high Ni) content can effectively maintain thermal stability and lifetime characteristics while fully achieving high output and high capacity.

[0081] In some implementations, as the calcination temperature increases, the crystallites of the lithium-transition metal composite oxide particles on the (003) face can grow faster than those on the (104) face. Therefore, as the calcination temperature increases, the ratio of the crystallite size of the lithium-transition metal composite oxide particles in the (104) face direction to their crystallite size in the (003) face direction can be reduced.

[0082] For example, the ratio of the crystallite size of lithium-transition metal composite oxide particles in the (104) plane direction to their crystallite size in the (003) plane direction can be 1:(2.5 or higher). In this case, the input / output path of Li can be shortened, thereby improving the initial capacity and capacity efficiency.

[0083] In some embodiments, the crystallite size ratio can be from 1:2.5 to 1:3.05. When the above range is met, the crystallite size of the lithium-transition metal composite oxide particles in the (003) plane direction can be suppressed from growing significantly larger than that in the (104) plane direction, thereby preventing the deterioration of structural stability and achieving the aforementioned excellent initial capacity and efficiency, thus simultaneously achieving excellent lifetime characteristics and output characteristics.

[0084] In an exemplary embodiment, the "crystal size" is a value obtained by X-ray diffraction (XRD) analysis. The crystal size can be calculated and obtained using the full width at half maximum (FWHM) obtained by XRD analysis via the Scherrer equation (Equation 5 below).

[0085] [Formula 5] In Formula 5 above, L represents the crystallite 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 full width at half maximum in XRD analysis used to measure the crystallite size can be measured from the peak of the (104) plane when calculating the crystallite size in the (104) plane direction, and from the peak of the (003) plane when calculating the crystallite size in the (003) plane direction.

[0086] In some implementations, β in Equation 5 above can be the full width at half maximum (FWHM) corrected for a value derived from equipment. In one implementation, Si can be used as a standard material reflecting the equipment-derived value. In this case, the equipment-derived FWHM can be expressed as a function of 2θ by plotting a profile of the full width at half maximum (FWHM) over the entire range of 2θ of Si. The corrected value obtained by subtracting the corresponding equipment-derived FWHM from the above function can then be used as β.

[0087] For example, for dry powder of lithium-transition metal composite oxide particles, Cu-Kα rays can be used as the light source to perform XRD analysis at a scan rate of 0.0065° / step within a diffraction angle (2θ) range of 10° to 120°.

[0088] Figure 2 and Figure 3 Schematic plan and cross-sectional views of a lithium secondary battery according to an exemplary embodiment are shown respectively. Referring below... Figure 2 and Figure 3 The description includes the above-mentioned positive electrode active material for lithium secondary batteries.

[0089] refer to Figure 2 and Figure 3 The lithium secondary battery may include an electrode assembly comprising a positive electrode 100, a negative electrode 130, and a separator 140 inserted between the positive and negative electrodes. The electrode assembly may be encapsulated in a housing 160 together with an electrolyte to be impregnated.

[0090] The positive electrode 100 may include a positive electrode active material layer 110 formed by applying the above-mentioned positive electrode active material to the positive electrode current collector 105.

[0091] A slurry can be prepared by mixing and stirring the positive electrode active material containing the above-mentioned lithium-transition metal composite oxide particles with a binder, conductive material and / or dispersant in a solvent. The slurry can be coated onto the positive electrode current collector 105, then dried and pressed to manufacture the positive electrode 100.

[0092] The positive current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, and preferably, aluminum or aluminum alloys.

[0093] The adhesive can be selected from, for example, organic adhesives such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based adhesives such as styrene-butadiene rubber (SBR), and the positive electrode adhesive can be used with a thickener such as carboxymethyl cellulose (CMC)

[0094] 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.

[0095] Conductive materials may be included to facilitate electron transfer between active material particles. For example, conductive materials may include carbon-based conductive materials, such as graphite, carbon black, graphene, or carbon nanotubes, and / or metal-based conductive materials, such as tin, tin oxide, titanium oxide, or perovskite minerals (e.g., LaSrCoO3 or LaSrMnO3).

[0096] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed by coating the negative electrode current collector 125 with a negative electrode active material.

[0097] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, and preferably includes copper or copper alloys.

[0098] The negative electrode active material used in this invention can include any material known in the relevant art, as long as it can adsorb and desorb lithium ions, without 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.

[0099] Examples of crystalline carbon may include graphite-based carbon, such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. Other elements included in lithium alloys may include, for example, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0100] Silicon compounds may include, for example, silicon-carbon composite compounds, such as silicon oxide or silicon carbide (SiC).

[0101] 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 it. The slurry can be coated on at least one surface of the negative electrode current collector 125, then dried and pressed to manufacture the negative electrode 130.

[0102] As the binder and conductive material, materials 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 consistency with the carbon-based active material, and may be used in conjunction with a thickener (e.g., carboxymethyl cellulose (CMC)).

[0103] 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 a polyolefin polymer, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The separator 140 may include a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0104] In some embodiments, the area (e.g., the contact area with the separator 140) and / or volume of the negative electrode 130 may be larger than the area and / or volume of the positive electrode 100. Therefore, for example, lithium ions generated from the positive electrode 100 can move smoothly to the negative electrode 130 without being deposited in the middle.

[0105] According to an exemplary embodiment, the electrode unit is defined by a positive electrode 100, a negative electrode 130, and a separator 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, laminating, folding, etc., the separator 140.

[0106] The electrode assembly 150 may be housed together with the electrolyte within the housing 160 to define the lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used.

[0107] Non-aqueous electrolytes include lithium salt electrolytes and organic solvents, and the lithium salt is, for example, made from Li. + X - This indicates that, and as an anion of lithium salt (X... - Examples include: 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.

[0108] 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.

[0109] like Figure 2 As shown, electrode tabs (positive electrode tab and negative electrode tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each electrode unit, respectively, and can extend to one side of the housing 160. The electrode tabs can be fused together with one side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending or exposed to the outside of the housing 160.

[0110] Lithium-ion batteries can be manufactured in various shapes, such as cylindrical (using cans), square, pouch type, or coin shape.

[0111] In an exemplary embodiment, the aforementioned lithium secondary battery can be manufactured in the shape of a coin.

[0112] For example, the positive and negative electrodes can be notched into circles with diameters of Φ14 or Φ16 and then laminated. For example, a separator can be inserted between the positive and negative electrodes to form an electrode assembly.

[0113] For example, coin-type lithium secondary batteries can be manufactured by placing electrode components in a coin battery casing, then injecting electrolyte and assembling them.

[0114] Specific experimental examples are presented below to facilitate understanding of the invention. However, the following embodiments are merely illustrative, 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 should be included within the appended claims.

[0115] Example 1 Preparation of lithium-transition metal composite oxide particles NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.885:0.09:0.025 using distilled water, which had been bubbled with N2 for 24 hours to remove dissolved oxygen. The solution was then introduced into a reactor at 50°C, and a co-precipitation reaction was carried out for 48 hours using NaOH as a precipitant and NH3H2O ​​as a chelating agent to obtain the transition metal precursor Ni. 0.885 Co 0.09 Mn 0.025 (OH)2. The obtained precursor was dried at 80°C for 12 hours, and then dried at 110°C for 12 hours.

[0116] In the first calcination step, lithium hydroxide and a transition metal precursor were added to a dry high-speed mixer such that the molar percentage of lithium hydroxide was 85 mol% based on the molar percentage of the transition metal precursor. The resulting mixture was then stirred uniformly for 5 minutes. The mixture was placed in a calcination furnace and heated to 805°C (the first calcination temperature) at a heating rate of 2°C / min, and held at 805°C for 5 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, and then pulverized and graded to prepare primary lithium-transition metal composite oxide particles.

[0117] In the second calcination step, lithium hydroxide was added to the primary lithium-transition metal composite oxide particles at a rate of 16 mol% (based on the number of moles of the transition metal precursor added in the first calcination step) in a dry high-speed mixer and then stirred uniformly for 5 minutes. The mixture was placed in a calcination furnace and heated to 710°C (the second calcination temperature) at a heating rate of 2°C / min, and held at 710°C for 5 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 and then pulverized and graded to prepare the positive electrode active material LiNi. 0.885 Co 0.09 Mn 0.025 Lithium-transition metal composite oxide particles in single-particle form of O2.

[0118] Manufacture of lithium secondary batteries The lithium-transition metal composite oxide particles prepared above were used as the positive electrode active material to manufacture secondary batteries. A positive electrode slurry was prepared by mixing the positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder in a mass ratio of 93:5:2. The slurry was then coated onto an aluminum current collector, dried, and pressed to prepare the positive electrode. After pressing, the electrode density of the positive electrode was controlled within the range of 2.9-3.1 g / cc.

[0119] Lithium metal is used as the negative electrode.

[0120] The positive and negative electrodes prepared as described above were cut into circles with diameters of Φ14 and Φ16, respectively, and stacked. Then, an electrode unit was prepared by placing a separator (polyethylene, thickness: 13μm) cut into Φ19 between the positive and negative electrodes. The prepared electrode unit was placed in a coin battery casing with a diameter of 20t and a height of 1.6t, then electrolyte was injected and assembled. The casing was then aged for more than 12 hours to allow the electrolyte to penetrate into the electrode.

[0121] The electrolyte used here is prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0122] The secondary battery manufactured as described above was subjected to chemical charging and discharging (charging conditions: CC-CV 0.1C 4.3 V 0.005C cutoff, discharging conditions: CC 0.1C 3 V cutoff).

[0123] For reference, when substituting the molar ratio of Ni as 0.885 into the calculation, the calcination temperature range of the first calcination step in Formulas 1-4 is 805-825℃, and the calcination temperature range of the second calcination step is 710-730℃.

[0124] Example 2 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the second calcination temperature is set to 720°C.

[0125] Example 3 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the second calcination temperature is set to 730°C.

[0126] Example 4 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the first calcination temperature is set to 815°C.

[0127] Example 5 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 4, except that the second calcination temperature is set to 720°C.

[0128] Example 6 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 4, except that the second calcination temperature is set to 730°C.

[0129] Example 7 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the first calcination temperature is set to 825°C.

[0130] Example 8 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 7, except that the second calcination temperature is set to 720°C.

[0131] Example 9 The lithium-transition metal composite oxide particles and the lithium secondary battery using them as the positive electrode active material are manufactured according to the same steps as described in Example 7, except that the second calcination temperature is set to 730°C.

[0132] Example 10 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 5, except that: based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the first calcination step is 80 mol%, and based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the second calcination step is 21 mol%.

[0133] Example 11 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 5, except that: based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the first calcination step is 90 mol%, and based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the second calcination step is 11 mol%.

[0134] Comparative Example 1 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the second calcination temperature is set to 700°C.

[0135] Comparative Example 2 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that the second calcination temperature is set to 740°C.

[0136] Comparative Example 3 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 4, except that the second calcination temperature is set to 700°C.

[0137] Comparative Example 4 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 4, except that the second calcination temperature is set to 740°C.

[0138] Comparative Example 5 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 7, except that the second calcination temperature is set to 700°C.

[0139] Comparative Example 6 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 7, except that the second calcination temperature is set to 740°C.

[0140] Comparative Example 7 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 2, except that the first calcination temperature is set to 800°C.

[0141] Comparative Example 8 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 2, except that the first calcination temperature is set to 695°C.

[0142] Comparative Example 9 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 2, except that the first calcination temperature is set to 835°C.

[0143] Comparative Example 10 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 10, except that: based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the first calcination step is 75 mol%, and based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the second calcination step is 26 mol%.

[0144] Comparative Example 11 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 10, except that: based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the first calcination step is 95 mol%, and based on the number of moles of the added transition metal precursor, the number of moles of lithium hydroxide added in the second calcination step is 6 mol%.

[0145] Comparative Example 12 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Example 1, except that: a single calcination step is performed; lithium hydroxide and transition metal precursors are added in a ratio of 1.01:1 in the single calcination step; calcination is performed at 710°C in the single calcination step; and water washing is performed after calcination.

[0146] Comparative Example 13 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Comparative Example 12, except that calcination is performed at 720°C in a single calcination step.

[0147] Comparative Example 14 Lithium-transition metal composite oxide particles and lithium secondary batteries using them as positive electrode active materials are manufactured according to the same steps as described in Comparative Example 12, except that calcination is performed at 730°C in a single calcination step.

[0148] In the examples and comparative examples, the calcination temperature (°C) in the first calcination step and the second calcination step, and the amount of lithium hydroxide added (mol%) based on the number of moles of the transition metal precursor are shown in Tables 1 and 2 below.

[0149] [Table 1] [Table 2] Experimental Example (1) Measurement of the content of lithium precursor (LiOH, Li2CO3) remaining on the surface of lithium-transition metal composite oxide particles (2) Measurement of crystallite size and calculation of crystallite size ratio 5.0 g of lithium metal oxide particles from the examples and comparative examples were quantitatively added to a 250 mL flask. 100 g of deionized water was added, and a magnetic rod was placed in the flask. The mixture was stirred at 4 rpm for 10 minutes. Afterward, the mixture was filtered under reduced pressure using a flask, and 50 g of the solution was sampled. The sampled solution was placed in the container of an automatic titrator and automatically titrated with 0.1 N HCl according to Wader's method to determine the LiOH and Li₂CO₃ values ​​in the solution.

[0150] (3) Measurement of initial charge-discharge capacity and calculation of initial capacity efficiency After performing XRD analysis on the lithium-transition metal composite oxide particles used as positive electrode active materials in the above examples and comparative examples according to the XRD analysis equipment / conditions in Table 3 below, the crystallite size (CS(104)) in the (104) plane direction and the crystallite size (CS(003)) in the (003) plane direction were calculated by substituting the measured values ​​into Formula 5, and then divided to obtain the ratio of the two crystallite sizes (CS(003) / CS(104)).

[0151] [Table 3] (4) Measurement of battery life characteristics (capacity retention rate) The lithium secondary batteries manufactured according to the above embodiments and comparative examples were charged in a room at 25°C (CC-CV 0.1C 4.3V 0.005C cutoff), and the battery capacity (initial charge capacity) was measured. After being discharged again (CC 0.1C 3.0V cutoff), the battery capacity (initial discharge capacity) was measured.

[0152] The initial capacity efficiency of each lithium secondary battery is calculated by dividing the measured initial discharge capacity by the measured initial charge capacity and then multiplying by 100.

[0153] ​ After repeatedly charging (CC-CV 0.5C 4.3 V 0.05C cutoff) and discharging (CC 1.0C 3.0 V cutoff) 300 times in a 45°C room, the capacity retention rate after 300 cycles was evaluated by calculating the percentage (%) of the capacity of the 300th discharge cycle based on the capacity of the first discharge cycle.

[0154] The measurement and calculation results are shown in Tables 4 and 5 below.

[0155] [Table 4] [Table 5] Referring to Tables 4 and 5, in the case of the example using lithium-transition metal composite oxide particles prepared by two-step calcination, wherein the two-step calcination is carried out within the temperature range calculated by Formulas 1-4, and the lithium precursor addition ratio of each calcination step is within the specified range, the content of lithium precursor remaining on the surface of lithium-transition metal composite oxide particles is reduced, and compared with the comparative example, excellent initial capacity and capacity retention are ensured overall.

[0156] [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, X-ray diffraction (XRD) analysis revealed that the crystallite size of the lithium-transition metal composite oxide particles in the (104) plane direction is less than 120 nm, and the ratio of the crystallite size in the (104) plane direction to its crystallite size in the (003) plane direction is 1:(2.5 or greater). The crystallite size is measured using the following formula 5: [Formula 5] In Formula 5, L is the crystallite 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) or (104) 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 content of lithium carbonate remaining on the surface of the lithium-transition metal composite oxide particles is less than 3000 ppm, and the content of lithium hydroxide remaining on the surface of the lithium-transition metal composite oxide particles is less than 5000 ppm.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the lithium-transition metal composite oxide particles have a crystallite size of 80-115 nm in the (104) plane direction.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the ratio of the crystallite size of the lithium-transition metal composite oxide particles in the (104) plane direction to its crystallite size in the (003) plane direction is 1:2.5 to 1:3.

05.

5. A lithium secondary battery, comprising: The positive electrode includes a positive electrode active material layer having a positive electrode active material for a lithium secondary battery according to claim 1; Negative electrode; and A diaphragm is disposed between the positive electrode and the negative electrode.

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