Positive electrode for lithium secondary battery and lithium secondary battery

Abstract

A positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a positive electrode active material layer having a density of 3 g / cm3 or more and containing a positive electrode active material containing lithium metal oxide particles containing cobalt, and having a density of 3 g / cm3 or more. The content of cobalt in the total number of moles of elements other than lithium and oxygen is more than 0 mol% and 15 mol% or less. The difference between the charge / discharge efficiency of a half-cell including the positive electrode for a lithium secondary battery and the charge / discharge efficiency after 10 times of further charge / discharge is less than 1%.

Description

Technical Field

[0001] This invention provides a positive electrode for lithium secondary batteries and a lithium secondary battery. Background Technology

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

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

[0004] NCM-based active materials containing nickel, cobalt, and manganese are being used as positive electrode active materials for lithium-ion batteries. For example, as the application of lithium-ion batteries expands to large devices such as electric vehicles, high-nickel (High-Ni) based lithium oxides with increased nickel content are known to be used as positive electrode active materials to ensure the high capacity of lithium-ion batteries.

[0005] However, as the nickel content in the positive electrode active material increases, the structural stability of the active material particles may decrease. For example, it may lead to cation mixing, which could cause nickel cations to transfer to lithium sites, thereby potentially reducing the stability and lifespan characteristics of the lithium secondary battery during repeated charge / discharge operations.

[0006] There is a need to realize a battery that contains a high-nickel positive electrode active material, thereby having high capacity and high stability, so as to maintain performance even in extreme environments. Summary of the Invention

[0007] (a) Technical problems to be solved One technical problem of the present invention is to provide a positive electrode for lithium secondary batteries with improved electrochemical properties.

[0008] One technical problem of the present invention is to provide a lithium secondary battery with improved electrochemical properties.

[0009] (II) Technical Solution The positive electrode for a lithium secondary battery according to the present invention comprises a positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material and having a concentration of 3 g / cm³. 3The density is above. The positive electrode active material comprises lithium metal oxide particles, which contain cobalt, wherein the cobalt content is greater than 0 mol% and less than 15 mol% in the total molar number of elements other than lithium and oxygen. The positive electrode for the lithium secondary battery satisfies the following formula 1.

[0010] [Formula 1] (E n -E n+10 <1% In Equation 1, E n E is the charge-discharge efficiency (%) measured after n charge-discharge cycles of a half-cell. The half-cell is a half-cell comprising a negative electrode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte within an outer casing material having a diameter of 20 mm and a height of 1.6 mm. n+10 The charge-discharge efficiency (%) is measured after repeating n+10 charge-discharge cycles of the half-cell. In these cycles, CC-CV charging is performed at 0.5C CC, 4.3V 0.05C CV cutoff, followed by a 10-minute rest period and CC discharge at 0.5C CC. The negative electrode is a lithium foil with a diameter of Φ16 and a thickness of 1.2μm. The positive electrode for the lithium secondary battery is a circular electrode with a diameter of Φ14. The separator is a polyethylene film with a thickness of 13μm disposed between the negative electrode and the positive electrode for the lithium secondary battery. The electrolyte is an electrolyte containing 1M LiPF6 dissolved in a mixed solvent comprising ethylene carbonate and methyl ethyl carbonate at a volume ratio of 3:7. The charge-discharge efficiency is defined as the percentage of charge capacity to discharge capacity measured after repeating a predetermined number of charge-discharge cycles, where n is an integer from 5 to 100.

[0011] The positive electrode for a lithium secondary battery according to the exemplary embodiment can satisfy the following formula 2.

[0012] [Equation 2] (E n -E n+10 ≤0.3% In an exemplary embodiment, the cobalt content may be from 1 mol% to 12 mol% of the total moles of elements other than lithium and oxygen.

[0013] In an exemplary embodiment, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particles can be below 5000 ppm.

[0014] In an exemplary embodiment, the lithium metal oxide particles may further comprise nickel and manganese.

[0015] In an exemplary embodiment, the nickel content may be from 70 mol% to 95 mol% of the total moles of elements other than lithium and oxygen.

[0016] In an exemplary embodiment, the manganese content may be from 5 mol% to 30 mol% of the total moles of elements other than lithium and oxygen.

[0017] In an exemplary embodiment, based on X-ray diffraction (XRD) analysis of the lithium metal oxide particles, no peaks were observed in the 2θ range of 20° to 22°.

[0018] In an exemplary implementation, when n is 5 to 20, E n It can be over 99.7%.

[0019] In an exemplary implementation, when n is 5 to 20, E n+10 It can be over 99%.

[0020] In an exemplary implementation, when n is 45 to 60, E n It can be above 89.5%.

[0021] In an exemplary implementation, when n is 45 to 60, E n+10 It can be above 88.6%.

[0022] In an exemplary embodiment, the density of the positive electrode active material layer can be 3.3 g / cm³. 3 Up to 5g / cm 3 .

[0023] The lithium secondary battery according to the present invention includes: a positive electrode for the lithium secondary battery; and a negative electrode, wherein the negative electrode is disposed opposite to the positive electrode.

[0024] (III) Beneficial Effects The positive electrode for lithium secondary batteries according to an exemplary embodiment of the present invention can have improved high-temperature life characteristics, thus enabling batteries that maintain high capacity even during repeated charge and discharge at high temperatures.

[0025] The positive electrode for a lithium secondary battery according to an exemplary embodiment of the present invention can contain a positive electrode active material that exhibits high stability even after long-term storage at high temperatures. Therefore, side reactions between the positive electrode active material and the electrolyte can be suppressed, and the amount of gas generated inside the battery during storage at high temperatures can be reduced.

[0026] A lithium secondary battery according to an exemplary embodiment of the present invention includes the positive electrode, thereby having improved high-temperature life characteristics and high-temperature storage characteristics. Attached Figure Description

[0027] Figure 1 This is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0028] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0029] According to the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode are provided. The positive electrode for the lithium secondary battery includes a positive electrode active material, the positive electrode active material includes lithium metal oxide particles, the lithium metal oxide particles include cobalt, and the content of cobalt in the total molar number of elements other than lithium and oxygen is greater than 0 mol% and less than 15 mol%.

[0030] The present invention will now be described in detail with reference to the accompanying drawings. However, this is merely an exemplary description, and the present invention is not limited to the specific embodiments described herein.

[0031] Figure 1 This is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0032] Reference Figure 1 The positive electrode for the lithium secondary battery (hereinafter, simply referred to as the positive electrode) may include a positive electrode current collector 105 and a positive electrode active material layer 110. The positive electrode 100 may include the positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one side of the positive electrode current collector 105. The positive electrode active material layer 110 may contain a positive electrode active material.

[0033] The positive electrode active material comprises lithium metal oxide particles. In addition to lithium and oxygen, the lithium metal oxide particles may also contain a metal component, which may contain one or more metals.

[0034] The lithium metal oxide particles contain cobalt. The conductivity of the cobalt is higher than that of other metal components (e.g., nickel and / or manganese) contained in the lithium metal oxide particles, thereby increasing the migration rate of electrons through the lithium metal oxide.

[0035] The cobalt content in the total moles of elements other than lithium and oxygen is greater than 0 mol% and less than 15 mol%. In some embodiments, the cobalt content in the total moles of elements other than lithium and oxygen can be from 1 mol% to 12 mol% or from 1 mol% to 10 mol%.

[0036] When the lithium metal oxide particles do not contain cobalt, the conductivity of the positive electrode active material may be significantly reduced, potentially leading to a slower charge and discharge rate in the lithium secondary battery. Furthermore, it may decrease the stability of the layered structure of the lithium metal oxide particles.

[0037] When the cobalt content in the lithium metal oxide particles exceeds 15 mol%, the content of other metals (e.g., nickel or manganese) decreases relatively, which may lead to a reduction in the capacity or stability of the lithium secondary battery. Furthermore, the unit capacity cost of the positive electrode active material may increase, potentially resulting in reduced productivity.

[0038] In some embodiments, the lithium metal oxide particles may further comprise nickel and manganese. Nickel can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Therefore, due to the high nickel content (high nickel) composition of the lithium metal oxide, a high-capacity cathode and a high-capacity lithium secondary battery can be provided.

[0039] However, with increasing nickel content, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. According to an exemplary embodiment, the lithium metal oxide particles may further contain manganese, thereby improving the battery's lifespan stability.

[0040] In an exemplary embodiment, the nickel content may be from 70 mol% to 95 mol% of the total moles of elements other than lithium and oxygen. In some embodiments, the nickel content may be from 75 mol% to 90 mol% or from 75 mol% to 85 mol% of the total moles of elements other than lithium and oxygen. Within these ranges, capacity can be increased while ensuring the stability of the lithium secondary battery.

[0041] In an exemplary embodiment, the manganese content may be from 5 mol% to 30 mol% of the total moles of elements other than lithium and oxygen. In some embodiments, the manganese content may be from 5 mol% to 25 mol% of the total moles of elements other than lithium and oxygen. Within the above ranges, the long-term stability of lithium metal oxide particles with a high nickel content (high nickel) composition can be improved.

[0042] The lithium metal oxide particles may include a layered structure or a crystal structure containing nickel, cobalt, and manganese. The lithium metal oxide particles may further include auxiliary elements other than nickel, cobalt, and manganese. The auxiliary elements may be included in the lithium metal oxide particles in the form of coating elements and / or doping elements. The auxiliary elements may include, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, Zr, etc.

[0043] When the lithium metal oxide particles include auxiliary elements in the form of coating elements, the auxiliary elements may be present on the surface of the lithium metal oxide particles.

[0044] When the lithium metal oxide particles include auxiliary elements in the form of doping elements, the auxiliary elements may penetrate through the surface of the lithium metal oxide particles and be incorporated into the layered structure / crystal structure together to form a bond.

[0045] The lithium metal oxide particles may include a layered structure or a crystal structure represented by Chemical Formula 1 below.

[0046] [Chemical Formula 1] Li x Ni a Co b Mn c M1 d O 2+z In Chemical Formula 1, 0.9 ≤ x ≤ 1.2, 0.7 ≤ a ≤ 0.95, 0 < b ≤ 0.15, 0.05 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.1, -0.5 ≤ z ≤ 0.1. M1 is an auxiliary element, and M1 may include at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0047] In the total weight of the positive electrode active material, the content of the lithium metal oxide particles may be 50% by weight or more. In some embodiments, in the total weight of the positive electrode active material, the content of the lithium metal oxide particles may be 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 99% by weight or more. For example, the positive electrode active material may consist essentially of the lithium metal oxide particles.

[0048] In some embodiments, the positive electrode active material may also include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0049] The lithium metal oxide particles may contain residual lithium on the particle surface. For example, in the process of preparing the lithium metal oxide particles, an excess of lithium source (lithium salt) may be used to improve yield or the stability of the synthesis process. The residual lithium may be a residue of the lithium source or a by-reaction product of the lithium source. The residual lithium may include lithium carbonate (Li₂CO₃) and / or lithium hydroxide (LiOH).

[0050] According to an exemplary embodiment, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particles can be less than 5000 ppm. According to some embodiments, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particles can be less than 4800 ppm or less than 4600 ppm.

[0051] Within the aforementioned range, the amount of residual lithium that suppresses the conductivity of lithium metal oxide particles is relatively small, thus preventing an increase in battery resistance and a reduction in battery power characteristics.

[0052] In an exemplary embodiment, X-ray diffraction (XRD) analysis of the lithium metal oxide particles showed no peaks observed in the 2θ range of 20° to 22°. Therefore, by incorporating lithium metal oxide particles with a highly stable crystal structure, a cathode with improved lifetime characteristics can be achieved.

[0053] The XRD analysis can be performed as follows: using Cu Kα rays as the light source, the dry powder of lithium metal oxide particles is analyzed within a diffraction angle (2θ) range of 10° to 120° at a scan rate of 0.0065° / step.

[0054] According to an exemplary embodiment, the density of the positive electrode active material layer is 3 g / cm³. 3 The above. According to some embodiments, the density of the positive electrode active material layer can be 3.3 g / cm³. 3 Up to 5g / cm 3 Within the aforementioned range, even during repeated charging and discharging of the battery, high charge-discharge efficiency can be maintained, and battery life characteristics can be improved.

[0055] When the density of the positive electrode active material layer is less than 3 g / cm³ 3When the battery is repeatedly charged and discharged, the structural stability of the positive electrode active material layer may be greatly reduced, which may lead to a significant reduction in the battery's charge and discharge efficiency.

[0056] According to an exemplary embodiment, the positive electrode for the lithium secondary battery satisfies the following formula 1.

[0057] [Formula 1] (E n -E n+10 <1% In Equation 1, E n E is the charge-discharge efficiency (%) measured after n charge-discharge cycles of a half-cell. The half-cell is a half-cell comprising a negative electrode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte within an outer casing material having a diameter of 20 mm and a height of 1.6 mm. n+10 The charge-discharge efficiency (%) is measured after the half-cell has undergone n+10 charge-discharge cycles.

[0058] In the charge-discharge cycle, CC-CV charging is performed under the conditions of 0.5C CC and 4.3V 0.05C CV cutoff, followed by resting for 10 minutes and CC discharging under the condition of 0.5C CC.

[0059] The negative electrode is a lithium foil with a diameter of Φ16 and a thickness of 1.2 μm, and the positive electrode for the lithium secondary battery is a circular electrode with a diameter of Φ14. The separator is a polyethylene film with a thickness of 13 μm disposed between the negative electrode and the positive electrode for the lithium secondary battery. The electrolyte is an electrolyte in which 1 M LiPF6 is dissolved in a mixed solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7.

[0060] The charge-discharge efficiency is defined as the percentage of the charging capacity to the discharging capacity measured after repeating a predetermined number of charge-discharge cycles, where n is an integer from 5 to 100.

[0061] The charge / discharge efficiency of a half-cell comprising the positive electrode and the lithium foil negative electrode for a lithium secondary battery may decrease with repeated charge / discharge cycles. Regarding the charge / discharge efficiency of the half-cell, the difference between the charge / discharge efficiency after n charge / discharge cycles and the charge / discharge efficiency after n+10 charge / discharge cycles can be less than 1%. In some embodiments, E in Formula 1... n -E n+10 The value can be below 0.9%, below 0.8%, below 0.7%, below 0.6%, or below 0.3%.

[0062] When the charge-discharge efficiency difference exceeds 1%, the long-term lifespan characteristics of the positive electrode may decrease, especially under high-temperature environments, where the lifespan of both the positive electrode and the lithium secondary battery may be shortened. Furthermore, when the battery is stored at high temperatures, side reactions between the electrolyte and the positive electrode active material may increase, potentially generating large amounts of gas and increasing the risk of explosion due to battery expansion.

[0063] The positive electrode for a lithium secondary battery according to the exemplary embodiment can satisfy the following formula 2.

[0064] [Equation 2] (E n -E n+10 ≤0.3% In an exemplary implementation, when n is 5 to 20, E n It can be over 99.7%, E n+10 It can be over 99%.

[0065] In an exemplary implementation, when n is 45 to 60, E n It can be above 89.5%, E n+10 It can be above 88.6%.

[0066] Within the aforementioned range, the positive electrode can have improved high-temperature life characteristics and high-temperature storage characteristics, and can realize a lithium secondary battery with high high-temperature capacity retention and reduced internal gas generation during high-temperature storage.

[0067] According to an exemplary embodiment, a method for preparing the lithium metal oxide particles can be provided.

[0068] According to an exemplary embodiment, an active material metal source can be prepared. The active material metal source may include a nickel source and a cobalt source. For example, a manganese source may be used simultaneously.

[0069] Examples of nickel sources include nickel sulfate (NiSO4), nickel hydroxide (Ni(OH)2), nickel nitrate (Ni(NO3)2), nickel acetate (Ni(CH3CO2)2), and their hydrates. Examples of manganese sources include manganese sulfate (MnSO4), manganese hydroxide (Mn(OH)2), manganese nitrate (Mn(NO3)2), manganese acetate (Mn(CH3CO2)2), and their hydrates. Examples of cobalt sources include cobalt sulfate (CoSO4), cobalt hydroxide (Co(OH)2), cobalt nitrate (Co(NO3)2), cobalt carbonate (CoCO3), and their hydrates.

[0070] For example, nickel sulfate, manganese sulfate, and cobalt sulfate can be used as nickel, manganese, and cobalt sources, respectively.

[0071] According to an exemplary embodiment, the above-mentioned active material metal salts can be mixed and reacted, for example, by a co-precipitation method, to obtain an active material precursor. For example, the active material precursor can be prepared in the form of a nickel-manganese-cobalt hydroxide.

[0072] To facilitate the coprecipitation reaction, a precipitant and / or a chelating agent may be used. The precipitant may include alkaline compounds such as sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃). The chelating agent may include, for example, ammonia or ammonium carbonate.

[0073] The active material precursor can be mixed with a lithium source and reacted by heat treatment (calcination) to prepare lithium metal oxide particles. For example, the heat treatment temperature can be adjusted in the range of about 800°C to 1100°C, and the heat treatment time can be adjusted in the range of about 3 hours to 50 hours.

[0074] The lithium source may include, for example, lithium carbonate (Li₂CO₃), lithium nitrate (LiNO₃), lithium acetate (CH₃COOLi), lithium oxide (Li₂O), lithium hydroxide (LiOH), etc. These can be used alone or in combination of two or more. For example, the lithium source can be lithium hydroxide and / or lithium carbonate.

[0075] After the heat treatment, residual lithium, such as unreacted lithium source, remaining on the particle surface can be removed by washing with water-based solvents or organic solvents.

[0076] In one embodiment, a post-calcination process can be performed after the washing process. The post-calcination process can be carried out, for example, at a temperature of about 250°C to 500°C.

[0077] The positive electrode active material can be mixed with binders, conductive materials, and / or dispersing materials in a solvent and stirred to prepare a slurry. The slurry can be coated onto the positive electrode current collector 105 and then dried and calendered to manufacture the positive electrode 100.

[0078] The positive current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, such as aluminum or aluminum alloys.

[0079] The adhesive may include, for example, organic adhesives such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or water-based adhesives such as styrene-butadiene rubber (SBR), and may be used with thickeners such as carboxymethyl cellulose (CMC).

[0080] For example, PVDF-based binders can be used as positive electrode binders. In this case, the amount of binder used to form the positive electrode active material layer can be reduced, and the amount of positive electrode active material can be relatively increased, thereby improving the power and capacity of the secondary battery.

[0081] The conductive material may be included to facilitate electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0082] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 3 It is along Figure 2 A cross-sectional view taken along the thickness direction of the I-I' line.

[0083] The following is for reference Figure 2 and Figure 3 The positive electrode for the lithium secondary battery and the lithium secondary battery including the positive electrode will be described together.

[0084] Reference 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 disposed between the positive and negative electrodes. The electrode assembly may be housed together with an electrolyte in a housing 160 and immersed in the electrolyte.

[0085] Positive electrode 100 is a positive electrode for lithium secondary batteries containing positive electrode active material containing the aforementioned lithium metal oxide particles.

[0086] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, wherein the negative electrode active material layer 120 contains negative electrode active material and is formed on the negative electrode current collector 125.

[0087] According to an exemplary embodiment, the negative electrode 130 may include a carbon-based active material. The carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, and the like.

[0088] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads, mesophase pitch-based carbon fibers, and the like. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbeads (MCMB), graphitized mesophase pitch-based carbon fibers (MPCF), and the like.

[0089] Preferably, the carbon-based active material may use natural graphite and / or artificial graphite.

[0090] In some embodiments, the negative electrode active material may further include a silicon-based active material. For example, the silicon-based active material may include Si, SiO x (0 < x < 2), silicon-carbon composites, metal-doped silicates, and the like.

[0091] For example, compared with the carbon-based material, the silicon-based active material may provide a significantly increased capacity. However, in a high-temperature environment or during repeated charge / discharge, the silicon-based active material may expand excessively, which may lead to deterioration of battery stability.

[0092] Therefore, as the negative electrode active material, the carbon-based active material and the silicon-based active material may be used simultaneously.

[0093] To prevent instability caused by battery expansion, in the total weight of the negative electrode active material, the amount of the carbon-based active material (e.g., graphite-based active material) may be greater than the amount of the silicon-based active material.

[0094] According to an exemplary embodiment, in the total weight of carbon element (C) and silicon element (Si) included in the negative electrode active material, the content of the silicon element may be 1 wt% to 10 wt%. Within the above range, according to the high-capacity / high-stability design in the above positive electrode, a high-capacity / high-stability structure may also be provided in the negative electrode.

[0095] In some embodiments, in the total weight of the negative electrode active material, the content of the silicon element may be 1 wt% to 9 wt%, 1 wt% to 8 wt%, 1 wt% to 7 wt%, 1 wt% to 6 wt%, or 1 wt% to 5 wt%.

[0096] For example, the negative electrode active material may be mixed and stirred together with the above-mentioned binder, conductive material, thickener, etc. in a solvent to prepare a slurry. The slurry may be coated on at least one surface of the negative electrode current collector 125 and then dried and calendered to manufacture the negative electrode 130.

[0097] The adhesive and conductive material may be substantially the same as or similar to the substances used in the positive electrode active material layer 110. In some embodiments, for example, for compatibility with carbon-based active materials, the adhesive used to form the negative electrode may include a water-based adhesive such as styrene-butadiene rubber (SBR) and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0098] A separator 140 can be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may comprise a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also comprise a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0099] In some embodiments, the area (e.g., the area in contact with the separator 140) and / or volume of the negative electrode 130 can be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 130 without, for example, depositing in the middle.

[0100] According to an exemplary embodiment, the battery cell can be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, in the form of a jelly roll, by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, lamination, folding, etc. of the separator 140.

[0101] The electrode assembly 150 can be housed together with the electrolyte within the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0102] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2- (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0103] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0104] like Figure 2 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to a side of the housing 160. The tabs can be fused to said side of the housing 160 and connected to electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0105] The lithium secondary battery can be manufactured in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0106] The embodiments of the present invention described above may include the following aspects, and may be implemented by at least one of the following aspects.

[0107] According to a first aspect of the present invention, a positive electrode for a lithium secondary battery comprises a positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material and having a concentration of 3 g / cm³.3 The density is above. The positive electrode active material comprises lithium metal oxide particles, which contain cobalt, wherein the cobalt content is greater than 0 mol% and less than 15 mol% in the total molar number of elements other than lithium and oxygen. The positive electrode for the lithium secondary battery satisfies the following formula 1.

[0108] [Formula 1] (E n -E n+10 <1% In Equation 1, E n E is the charge-discharge efficiency (%) measured after n charge-discharge cycles of a half-cell. The half-cell is a half-cell comprising a negative electrode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte within an outer casing material having a diameter of 20 mm and a height of 1.6 mm. n+10 The charge-discharge efficiency (%) is measured after repeating n+10 charge-discharge cycles of the half-cell. In these cycles, CC-CV charging is performed at 0.5C CC, 4.3V 0.05C CV cutoff, followed by a 10-minute rest period and CC discharge at 0.5C CC. The negative electrode is a lithium foil with a diameter of Φ16 and a thickness of 1.2μm. The positive electrode for the lithium secondary battery is a circular electrode with a diameter of Φ14. The separator is a polyethylene film with a thickness of 13μm disposed between the negative electrode and the positive electrode for the lithium secondary battery. The electrolyte is an electrolyte containing 1M LiPF6 dissolved in a mixed solvent comprising ethylene carbonate and methyl ethyl carbonate at a volume ratio of 3:7. The charge-discharge efficiency is defined as the percentage of charge capacity to discharge capacity measured after repeating a predetermined number of charge-discharge cycles, where n is an integer from 5 to 100.

[0109] In the first aspect, the positive electrode for a lithium secondary battery according to the second aspect can satisfy the following formula 2.

[0110] [Equation 2] (E n -E n+10 ≤0.3% In either the first or second aspect, according to the third aspect, the cobalt content may be from 1 mol% to 12 mol% of the total number of moles of elements other than lithium and oxygen.

[0111] In any one of the first to the third aspects, according to the fourth aspect, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particles can be less than 5000 ppm.

[0112] In any one of the first to the fourth aspects, according to the fifth aspect, the lithium metal oxide particles may further comprise nickel and manganese.

[0113] In the fifth aspect, according to the sixth aspect, the nickel content may be from 70 mol% to 95 mol% of the total moles of elements other than lithium and oxygen.

[0114] In either the fifth or sixth aspect, according to the seventh aspect, the content of manganese may be from 5 mol% to 30 mol% of the total number of moles of elements other than lithium and oxygen.

[0115] In any one of the first to the seventh aspects, according to the eighth aspect, based on the X-ray diffraction (XRD) analysis results of the lithium metal oxide particles, no peaks can be observed in the 2θ range of 20° to 22°.

[0116] In any of the first to the eighth aspects, according to the ninth aspect, when n is 5 to 20, E n It can be over 99.7%.

[0117] In any one of the first to the ninth aspects, according to the tenth aspect, when n is 5 to 20, E n+10 It can be over 99%.

[0118] In any one of the first to the tenth aspects, according to the eleventh aspect, when n is 45 to 60, E n It can be above 89.5%.

[0119] In any one of the first to the eleventh aspects, according to the twelfth aspect, when n is 45 to 60, E n+10 It can be above 88.6%.

[0120] In any one of the first to the twelfth aspects, according to the thirteenth aspect, the density of the positive electrode active material layer may be 3.3 g / cm³. 3 Up to 5g / cm 3 .

[0121] The lithium secondary battery according to the fourteenth aspect of the present invention comprises: a positive electrode for a lithium secondary battery as described in any one of the first to thirteenth aspects; and a negative electrode disposed opposite to the positive electrode.

[0122] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and do not limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0123] Preparation Example 1 Using distilled water that had been bubbled with N2 for 24 hours to remove internal dissolved oxygen, NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.76:0.01:0.23. The mixed solution was added to a reactor at 50°C, and NaOH and NH3·H2O were added as precipitating and chelating agents, respectively. The co-precipitation reaction was then carried out for 72 hours to obtain Ni as a transition metal precursor. 0.76 Co 0.01 Mn 0.23 (OH)2. The obtained precursor was dried at 100°C for 12 hours, and then dried again at 120°C for 10 hours.

[0124] The transition metal precursor and the mixed lithium raw material (lithium hydroxide and lithium carbonate mixed in a 1:1 ratio) were added to a dry high-speed mixer to achieve a molar ratio of Li to the metal in the transition metal precursor of 1.03:1, and mixed uniformly for 10 minutes. The mixture was then placed in a ceramic crucible and placed in a box-type calcining furnace. The temperature was increased to 780°C at a rate of 2°C / min, and held for 12 hours. The temperature was then increased to 900°C at a rate of 2°C / min, and held for another 12 hours. Finally, the mixture was allowed to cool naturally to 50°C inside the calcining furnace.

[0125] During the heating, holding, and cooling processes, oxygen was continuously introduced at a flow rate of 10 mL / min. After calcination, the calcined material was separated from the ceramic crucible and then pulverized using an air classifier mill (ACM). Following pulverization, it was filtered through a #325 sieve to prepare single-particle lithium metal oxide (LiNi). 0.76 Co 0.01 Mn 0.23 O2.

[0126] Preparation Example 2 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.12:0.08.

[0127] Preparation Example 3 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.85:0.05:0.1, respectively.

[0128] Preparation Example 4 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.15:0.05.

[0129] Preparation Example 5 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4, CoSO4 and MnSO4 were mixed in a ratio of 0.85:0.05:0.1, and the holding time at 780°C was set to 6 hours.

[0130] Preparation Example 6 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that the process of holding at 780°C for 12 hours was omitted.

[0131] Preparation Example 7 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that the mixture containing lithium and transition metal precursors was held once at 780°C for 12 hours and then held a second time at 900°C for 6 hours.

[0132] Preparation Example 8 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.8:0.2.

[0133] Preparation Example 9 Lithium metal oxide particles were prepared using the same method as in Preparation Example 1, except that NiSO4 and MnSO4 were mixed in a ratio of 0.8:0.2.

[0134] Experimental Example 1: Measurement of Residual Lithium Content on Surface Quantitatively add 3g of each of the prepared lithium metal oxide particles to a 250mL flask, along with 150g of deionized water. Then, place a magnetic rod in the flask and stir at 60rpm for 10 minutes. Afterward, filter the solution using a vacuum flask and collect 100g of the solution. Add the collected solution to an automatic titrator container and perform automatic titration with 0.1N HCl according to the Wader method to measure the content of Li₂CO₃ and LiOH in the solution. The measurement results are recorded in Table 2 below.

[0135] Experimental Example 2: XRD Analysis For the lithium metal oxide particles of the preparation examples, XRD analysis was performed using the equipment and conditions shown in Table 1 below. Based on the XRD analysis results of the lithium metal oxide particles of the preparation examples, it was confirmed whether peaks were observed in the 2θ range of 20° to 22°, and the results are recorded in Table 2 below.

[0136] [Table 1] [Table 2] Example 1 (1) Manufacturing of the positive electrode The lithium metal oxide from Preparation Example 1, acetylene black (Denka Black) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 93:5:2 to prepare a positive electrode slurry. The positive electrode slurry was coated onto an aluminum current collector, then dried and calendered to obtain a positive electrode. The calendering was performed to achieve a positive electrode active material layer density of 3.3 g / cm³ (cc).

[0137] (2) Manufacturing of half-cells Lithium foil (1.2 mm thick) was prepared as the negative electrode. The positive and negative electrodes were notched into circular shapes with diameters of Φ14 and Φ16, respectively, and stacked. A separator (polyethylene, 13 μm thick) cut to Φ19 was placed between the positive and negative electrodes to form a battery cell. The battery cell was placed in a coin-shaped battery casing material with a diameter of 20 mm and a height of 1.6 mm, and electrolyte was injected for assembly. The assembly was then aged for at least 12 hours to allow the electrolyte to penetrate the electrodes. The electrolyte used was a 1 M LiPF6 electrolyte dissolved in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0138] (3) Manufacturing of full batteries A negative electrode slurry is prepared, comprising 95% by weight of a natural / artificial graphite mixture as the negative electrode active material, 3% by weight of a flake-type conductive material as the conductive material, 1% by weight of styrene-butadiene rubber (SBR) as the binder, and 1% by weight of carboxymethyl cellulose (CMC) as the thickener. The negative electrode slurry is coated onto a copper substrate and then dried and calendered to obtain the negative electrode.

[0139] The positive and negative electrodes were cut into rectangles of 240mm × 85mm and 245mm × 90mm respectively and stacked. A separator (polyethylene, 13μm thick) was placed between the positive and negative electrodes in a zigzag pattern to form a 20Ah battery cell. The battery cell was placed in a soft package made of external material according to specifications, and three sides were sealed. Electrolyte was then injected through the remaining side for assembly. The cell was then aged for at least 12 hours to allow the electrolyte to penetrate the electrode interior. The electrolyte used was a 1M LiPF6 electrolyte dissolved in a mixed solvent of EC / EMC (20 / 80; volume ratio).

[0140] Examples 2 to 4 and Comparative Examples 1 to 4 Half-cells and full-cells were manufactured using the same method as in Example 1, except that the positive electrode active materials of Preparation Examples 2 to 5 (Examples 2 to 5) and Preparation Examples 6 to 9 (Comparative Examples 1 to 4) were used instead of the positive electrode active material of Preparation Example 1.

[0141] Comparative Example 5 Half-cells and full-cells were manufactured using the same method as in Example 1, except that the density of the positive electrode active material layer was increased to 2.7 g / cm³. 3 The cathode is produced by rolling in a specific manner.

[0142] The half-cells and full-cells of the Examples and Comparative Examples were evaluated as shown in the following experimental examples, and the results are then presented in Table 3.

[0143] Experimental Example 3: Evaluation of the charge and discharge efficiency of a half-cell (1) For the half-cells of the examples and comparative examples, charging (CC-CV 0.5C 4.3V 0.005C cut-off) and discharging (CC 0.5C 3.0V cut-off) are considered as one cycle, and the charge / discharge efficiency (E) is... 10 The value is calculated as the ratio of the charging capacity to the discharging capacity after 10 cycles.

[0144] The half-cells of the examples and comparative examples were further subjected to 10 cycles of charge and discharge, and then the charge and discharge efficiency (E) was calculated using the same method. 20 ).

[0145] (2) For the half-cells of the embodiments and comparative examples, charging (CC-CV 0.5C 4.3V 0.005C cutoff) and discharging (CC 0.5C 3.0V cutoff) are considered as one cycle, and the charge / discharge efficiency (E) is... 50 The value is calculated as the ratio of the charging capacity to the discharging capacity after 50 cycles.

[0146] The half-cells of the examples and comparative examples were further subjected to 10 cycles of charge and discharge, and then the charge and discharge efficiency (E) was calculated using the same method. 60 ).

[0147] Experimental Example 4: Evaluation of High-Temperature Capacity Retention of Full Cells The full cells of the examples and comparative examples were charged (CC-CV 0.1C 4.3V 0.005C cutoff) and discharged (CC 0.1C 3.0V cutoff) in a chamber at 25°C, and the battery capacity (initial discharge capacity) was measured.

[0148] The above charging and discharging were taken as one cycle. The discharge capacity of the full cells of the examples and comparative examples was measured after 100 cycles of charging and discharging at a temperature of 60°C. The high-temperature capacity retention rate was calculated by converting the measured discharge capacity into a percentage (%).

[0149] Experimental Example 5: Evaluation of the High-Temperature Storage Characteristics of Full Batteries The full cells of the examples and comparative examples were placed in a chamber at 60°C for approximately 4 weeks, then left at room temperature for 30 minutes, and then placed in a chamber for measuring gas production. After creating a vacuum in the chamber, nitrogen gas was introduced to create atmospheric pressure. At this time, the volume of injected nitrogen gas (V0) and the internal pressure of the chamber (P0) were measured. After creating a vacuum inside the chamber again, a hole was drilled in the cell, the internal pressure of the chamber (P1) was measured, and the gas production was calculated according to Equation 3 below.

[0150] [Formula 3] Gas production (mL) = (V0 / P0) P1 [Table 3] Referring to Table 3, the lithium secondary battery of the embodiment includes a positive electrode that satisfies Formula 1, thus maintaining high capacity during repeated charge-discharge cycles at high temperatures. Furthermore, the lithium secondary battery of the embodiment produces less gas even when stored for extended periods at high temperatures.

[0151] The lithium secondary batteries of Examples 4 and 5 include a positive electrode containing a relatively high amount of residual lithium active material. Therefore, compared with other examples, the battery life characteristics and high-temperature storage characteristics are slightly reduced.

[0152] E of the comparative example lithium secondary battery 20 -E 10 The value of E 50 -E 60 The value is greater than 1%, so the battery has poor storage characteristics in high-temperature environments, and the high-temperature capacity retention rate of the battery is also reduced.

[0153] The lithium secondary battery of Comparative Example 3 has a positive electrode containing a positive electrode active material with an excessive cobalt content, thus generating excessive gas inside the battery under high temperature conditions.

[0154] The lithium secondary battery of Comparative Example 4 has a positive electrode containing a cobalt-free positive electrode active material, thus the battery capacity retention rate is significantly reduced.

[0155] The lithium secondary battery of Comparative Example 5 has a packing density of less than 3 g / cm³. 3 The positive electrode active material layer is not positive, which leads to a reduction in the contact area between the conductive material and the positive electrode active material particles during repeated charging and discharging of the battery, thus significantly reducing the battery's lifespan characteristics.

[0156] The above description is merely an example of applying the principles of the present invention, and other configurations may be further included without departing from the scope of the present invention.

Claims

1. A positive electrode for a lithium secondary battery, the positive electrode comprising a positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material and having a concentration of 3 g / cm³. 3 The above density refers to a positive electrode active material comprising lithium metal oxide particles, wherein the lithium metal oxide particles contain cobalt, and the cobalt content is greater than 0 mol% and less than 15 mol% in the total molar number of elements other than lithium and oxygen. The positive electrode for the lithium secondary battery satisfies the following formula 1. [Formula 1] (AND n -AND n+10 )<1% In Equation 1, E n E is the charge / discharge efficiency, expressed as a percentage, measured after n charge / discharge cycles of a half-cell. The half-cell is a half-cell comprising a negative electrode, a positive electrode for the lithium secondary battery, a separator, and an electrolyte, housed within an outer casing material with a diameter of 20 mm and a height of 1.6 mm. n+10 The charge / discharge efficiency, expressed as a percentage, is the result of repeating n+10 charge / discharge cycles on the half-cell. In the charge-discharge cycle, CC-CV charging was performed under the conditions of 0.5C CC, 4.3V, and 0.05C CV cutoff, followed by a 10-minute rest period and CC discharging under the condition of 0.5C CC. The negative electrode is a lithium foil with a diameter of Φ16 and a thickness of 1.2 μm; the positive electrode for the lithium secondary battery is a circular electrode with a diameter of Φ14; the separator is a polyethylene film with a thickness of 13 μm disposed between the negative electrode and the positive electrode for the lithium secondary battery; and the electrolyte is an electrolyte in which 1 M LiPF6 is dissolved in a mixed solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:

7. The charge / discharge efficiency is defined as the percentage of the charging capacity to the discharging capacity measured after repeating a predetermined number of charge / discharge cycles, where n is an integer from 5 to 100.

2. The positive electrode for a lithium secondary battery according to claim 1, wherein, The positive electrode for the lithium secondary battery satisfies the following formula 2. [Equation 2] (AND n -AND n+10 )≤0.3%。 3. The positive electrode for a lithium secondary battery according to claim 1, wherein, The cobalt content is between 1 mol% and 12 mol% of the total moles of elements excluding lithium and oxygen.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein, The total content of residual lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) on the surface of the lithium metal oxide particles is less than 5000 ppm.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein, The lithium metal oxide particles further comprise nickel and manganese.

6. The positive electrode for a lithium secondary battery according to claim 5, wherein, The nickel content is between 70 mol% and 95 mol% of the total molar number of elements excluding lithium and oxygen.

7. The positive electrode for a lithium secondary battery according to claim 5, wherein, The manganese content is between 5 mol% and 30 mol% of the total molar number of elements excluding lithium and oxygen.

8. The positive electrode for a lithium secondary battery according to claim 1, wherein, According to the X-ray diffraction (XRD) analysis of the lithium metal oxide particles, no peaks were observed in the 2θ range of 20° to 22°.

9. The positive electrode for a lithium secondary battery according to claim 1, wherein, When n is between 5 and 20, E n It is over 99.7%.

10. The positive electrode for a lithium secondary battery according to claim 1, wherein, When n is between 5 and 20, E n+10 It is over 99%.

11. The positive electrode for a lithium secondary battery according to claim 1, wherein, When n is between 45 and 60, E n It is over 89.5%.

12. The positive electrode for a lithium secondary battery according to claim 1, wherein, When n is between 45 and 60, E n+10 It is over 88.6%.

13. The positive electrode for a lithium secondary battery according to claim 1, wherein, The density of the positive electrode active material layer is 3.3 g / cm³. 3 Up to 5g / cm 3 .

14. A lithium secondary battery, comprising: The positive electrode for a lithium secondary battery as described in claim 1; as well as The negative electrode is positioned opposite to the positive electrode.

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