Positive electrode for lithium secondary battery, and lithium secondary battery

Abstract

A positive electrode for a lithium secondary battery according to embodiments of the present disclosure comprises a positive electrode active material layer containing a positive electrode active material and having a density of 3 g / cm3 or more, wherein the positive electrode active material includes lithium metal oxide particles containing cobalt, the content of cobalt being 0 mol% (exclusive) to 15 mol% (inclusive) relative to the total number of moles of elements excluding lithium and oxygen. The difference between the charge / discharge efficiency and the charge / discharge efficiency after 10 additional charge / discharge cycles in a half-cell comprising the positive electrode for a lithium secondary battery is less than 1%.

Description

Cathode for lithium secondary batteries and lithium secondary batteries

[0001] The present disclosure provides a positive electrode for a lithium secondary battery and a lithium secondary battery.

[0002] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are actively being researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0004] Nickel-containing nickel-cobalt (NCM)-based active materials, containing nickel, cobalt, and manganese, are used as cathode active materials in lithium secondary batteries. For example, as the application scope of lithium secondary batteries expands to large devices such as electric vehicles, high-nickel (High-Ni) lithium oxides with increased nickel content are becoming known as cathode active materials for securing high capacity in lithium secondary batteries.

[0005] However, as the nickel content in the cathode active material increases, the structural stability of the active material particles may deteriorate. For example, this may lead to cation mixing, where nickel cations are transferred to lithium sites, which may deteriorate the stability and lifespan characteristics of lithium secondary batteries during repeated charge / discharge operations.

[0006] There is a need to develop a battery that has high capacity, including a high nickel cathode active material, and high stability, so that it can maintain its performance even in extreme environments.

[0007]

[0008] An object of the present disclosure is to provide a positive electrode for a lithium secondary battery having improved electrochemical properties.

[0009] An object of the present disclosure is to provide a lithium secondary battery with improved electrochemical characteristics.

[0010]

[0011] The positive electrode for a lithium secondary battery according to the present disclosure comprises a positive electrode active material and has a density of 3 g / cm 3 A positive electrode active material layer having a density above is included. The positive electrode active material includes lithium metal oxide particles containing cobalt and having a cobalt content of more than 0 and less than 15 mol% among the total moles of elements excluding lithium and oxygen. The positive electrode for a lithium secondary battery satisfies the following equation 1.

[0012] [Formula 1]

[0013] (E n -E n+10 ) < 1 %

[0014] In the above equation 1, E n is the charge-discharge efficiency (%) measured after repeating n charge-discharge cycles of a half-cell containing a cathode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte inside an outer shell with a diameter of 20 mm and a height of 1.6 mm, and E n+10is the charge-discharge efficiency (%) measured after repeating the charge-discharge cycle of the half-cell n+10 times, and the charge-discharge cycle is a CC-CV charge under the condition of 0.5C CC, 4.3V 0.05C CV cut, followed by a 10-minute rest and a CC discharge under the condition of 0.5C CC, and the negative electrode is a lithium foil having a circular shape with a diameter of Φ16 and a thickness of 1.2 ㎛, the positive electrode for a lithium secondary battery is a circular shape with a diameter of Φ14, the separator is a polyethylene film interposed between the negative electrode and the positive electrode for a lithium secondary battery and having a thickness of 13 ㎛, and the electrolyte is a mixture of ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and the charge-discharge efficiency is defined as a percentage of the charge capacity compared to the discharge capacity measured after repeating a predetermined number of charge-discharge cycles, and n is 5 to It is an integer of 100.

[0015] A positive electrode for a lithium secondary battery according to exemplary embodiments may satisfy the following equation 2.

[0016] [Formula 2]

[0017] (E n -E n+10 ) ≤ 0.3%

[0018] In exemplary embodiments, the content of cobalt may be from 1 mol% to 12 mol% of the total moles of elements excluding lithium and oxygen.

[0019] In exemplary embodiments, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the particle surface of the lithium metal oxide may be 5000 ppm or less.

[0020] In exemplary embodiments, the lithium metal oxide particles may further include nickel and manganese.

[0021] In exemplary embodiments, the nickel content may be 70 mol% to 95 mol% of the total moles of elements excluding lithium and oxygen.

[0022] In exemplary embodiments, the manganese content may be 5 mol% to 30 mol% of the total moles of elements excluding lithium and oxygen.

[0023] In exemplary embodiments, the X-ray diffraction (XRD) analysis results of the lithium metal oxide particles may show that no peak is observed within a 2θ range of 20° to 22°.

[0024] In exemplary embodiments, when n is 5 to 20, E n can be over 99.7%.

[0025] In exemplary embodiments, when n is 5 to 20, E n+10 can be over 99%.

[0026] In exemplary embodiments, when n is 45 to 60, E n can be more than 89.5%.

[0027] In exemplary embodiments, when n is 45 to 60, E n+10 can be more than 88.6%.

[0028] In exemplary embodiments, the density of the positive electrode active material layer is 3.3 g / cm 3 5 g / cm 3 It could be.

[0029] A lithium secondary battery according to the present disclosure includes a positive electrode for the lithium secondary battery and a negative electrode opposite to the positive electrode.

[0030]

[0031] The cathode for a lithium secondary battery according to exemplary embodiments of the present disclosure can have improved high-temperature life characteristics, and thus a battery can be implemented in which a high capacity is maintained even when charging and discharging is repeated at high temperatures.

[0032] The cathode for a lithium secondary battery according to exemplary embodiments of the present disclosure may include a cathode active material that exhibits high stability even when stored at high temperatures for extended periods of time. Accordingly, side reactions between the cathode active material and the electrolyte can be suppressed, and the amount of gas generated within the battery when stored at high temperatures can be reduced.

[0033] A lithium secondary battery according to exemplary embodiments of the present disclosure may have improved high-temperature lifespan characteristics and high-temperature storage characteristics by including the positive electrode.

[0034]

[0035] FIG. 1 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to exemplary embodiments.

[0036] FIGS. 2 and 3 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0037]

[0038] According to the present disclosure, a positive electrode for a lithium secondary battery and a lithium secondary battery including the same are provided, including a positive electrode active material including lithium metal oxide particles containing cobalt and having a cobalt content of more than 0 and less than 15 mol% among the total moles of elements excluding lithium and oxygen.

[0039] Hereinafter, the present disclosure will be described in detail with reference to the attached drawings. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0040] FIG. 1 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to exemplary embodiments.

[0041] Referring to FIG. 1, the positive electrode for the lithium secondary battery (hereinafter, abbreviated as positive electrode) may include a positive electrode current collector (105) and a positive electrode active material layer (110). The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed on at least one surface of the positive electrode current collector (105). The positive electrode active material layer (110) may include a positive electrode active material.

[0042] The above positive electrode active material includes lithium metal oxide particles. The lithium metal oxide particles may include a metal component including one or more metals in addition to lithium and oxygen.

[0043] The lithium metal oxide particles include cobalt. The cobalt has higher electrical conductivity than other metal components included in the lithium metal oxide particles, such as nickel and / or manganese, and thus can increase the rate of electron movement through the lithium metal oxide.

[0044] The cobalt content is greater than 0 and less than or equal to 15 mol% of the total moles of elements excluding lithium and oxygen. In some embodiments, the cobalt content may be from 1 mol% to 12 mol% or from 1 mol% to 10 mol% of the total moles of elements excluding lithium and oxygen.

[0045] If the lithium metal oxide particles do not contain cobalt, the electrical conductivity of the positive electrode active material may be significantly reduced, which may slow down the charge / discharge speed of the lithium secondary battery. In addition, the stability of the layered structure of the lithium metal oxide particles may be reduced.

[0046] When the lithium metal oxide particles contain cobalt in an amount exceeding 15 mol%, the content of other metals (e.g., nickel or manganese) may be relatively reduced, which may result in a decrease in the capacity of the lithium secondary battery or a decrease in stability. In addition, the unit cost per capacity of the positive electrode active material may increase, which may result in a decrease in productivity.

[0047] In some embodiments, the lithium metal oxide particles may further include nickel and manganese. Nickel may serve as a transition metal associated with the output and capacity of a lithium secondary battery. Accordingly, since the lithium metal oxide has a high nickel (High-Ni) content, a high-capacity cathode and a high-capacity lithium secondary battery can be provided.

[0048] However, as the nickel content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. According to exemplary embodiments, the lithium metal oxide particles may further include manganese to improve the lifespan stability of the battery.

[0049] In exemplary embodiments, the nickel content may be 70 mol% to 95 mol% of the total moles of elements excluding lithium and oxygen. In some embodiments, the nickel content may be 75 mol% to 90 mol% or 75 mol% to 85 mol% of the total moles of elements excluding lithium and oxygen. Within this range, the capacity of the lithium secondary battery can be increased while ensuring the stability of the lithium secondary battery.

[0050] In exemplary embodiments, the manganese content may be 5 mol% to 30 mol% of the total moles of elements excluding lithium and oxygen. In some embodiments, the manganese content may be 5 mol% to 25 mol% of the total moles of elements excluding lithium and oxygen. Within this range, the long-term stability of lithium metal oxide particles having a high nickel (High-Ni) composition can be improved.

[0051] The lithium metal oxide particles may include a layered structure or crystal structure including 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, and the like.

[0052] When the lithium metal oxide particles include an auxiliary element in the form of a coating element, the auxiliary element may be present on the surface of the lithium metal oxide particles.

[0053] When the lithium metal oxide particles contain auxiliary elements in the form of doping elements, the auxiliary elements can penetrate through the surface of the lithium metal oxide particles and be incorporated into the layered structure / crystal structure to form bonds.

[0054] The above lithium metal oxide particles may include a layered structure or crystal structure represented by the following chemical formula 1.

[0055] [Chemical Formula 1]

[0056] Li x Ni a Co b Mn c M1 d O 2+z

[0057] 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≤0.1일 수 있다. M1은 보조 원소로서, 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 및 Zr 중 적어도 하나를 포함할 수 있다.

[0058] The content of the lithium metal oxide particles in the total weight of the positive electrode active material may be 50 wt% or more. In some embodiments, the content of the lithium metal oxide particles in the total weight of the positive electrode active material may be 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 99 wt% or more. For example, the positive electrode active material may be substantially composed of the lithium metal oxide particles.

[0059] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0060] The lithium metal oxide particles may include residual lithium on the particle surface. For example, in the process of manufacturing the lithium metal oxide particles, a lithium source (lithium salt) may be used in excess to improve yield or ensure stability of the synthesis process. The residual lithium may be a residue of the lithium source or a side reaction product of the lithium source. The residual lithium may include lithium carbonate (Li2CO3) and / or lithium hydroxide (LiOH).

[0061] According to exemplary embodiments, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particle may be 5000 ppm or less. According to some embodiments, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the surface of the lithium metal oxide particle may be 4800 ppm or less or 4600 ppm or less.

[0062] Within the above range, the amount of residual lithium that inhibits the electrical conductivity of the lithium metal oxide particles is small, so that the battery resistance may not increase, and a decrease in the output characteristics of the battery may be prevented.

[0063] In exemplary embodiments, the X-ray diffraction (XRD) analysis results of the lithium metal oxide particles may not show a peak within a 2θ range of 20° to 22°. Accordingly, a positive electrode having improved life characteristics can be realized by including lithium metal oxide particles having a highly stable crystal structure.

[0064] The above XRD analysis can be performed on dried powder of lithium metal oxide particles using Cu Kα rays as a light source, at a diffraction angle (2θ) range of 10° to 120°, and at a scan rate of 0.0065° / step.

[0065] According to exemplary embodiments, the density of the positive electrode active material layer is 3 g / cm 3 According to some embodiments, the density of the positive electrode active material layer is 3.3 g / cm 3 5 g / cm 3 It can be ideal. Within the above range, the charge / discharge efficiency can be maintained high even when the battery is repeatedly charged / discharged, and the life characteristics of the battery can be improved.

[0066] The density of the above positive electrode active material layer is 3 g / cm 3If it is less than this, the structural stability of the positive electrode active material layer may be significantly reduced when the battery is repeatedly charged and discharged, and thus the charge and discharge efficiency of the battery may be significantly reduced.

[0067] According to exemplary embodiments, the positive electrode for the lithium secondary battery satisfies the following equation 1.

[0068] [Formula 1]

[0069] (E n -E n+10 ) < 1 %

[0070] In the above equation 1, E n is the charge-discharge efficiency (%) measured after repeating n charge-discharge cycles of a half-cell containing a cathode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte inside an outer shell with a diameter of 20 mm and a height of 1.6 mm, and E n+10 is the charge-discharge efficiency (%) measured after repeating the charge-discharge cycle of the above half-cell n+10 times.

[0071] The above charge / discharge cycle is CC-CV charging under 0.5C CC, 4.3V 0.05C CV cut conditions, followed by 10 minutes of rest and CC discharge under 0.5C CC conditions.

[0072] The negative electrode is a lithium foil having a circular shape with a diameter of Φ16 and a thickness of 1.2 ㎛, and the positive electrode for a lithium secondary battery is a circular shape with a diameter of Φ14. The separator is interposed between the negative electrode and the positive electrode for a lithium secondary battery, and is a polyethylene film having a thickness of 13 ㎛. The electrolyte is a solution of 1 M LiPF6 in a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0073] Charge-discharge efficiency is defined as the percentage of charge capacity compared to discharge capacity measured after a predetermined number of charge-discharge cycles, where n is an integer from 5 to 100.

[0074] The charge / discharge efficiency of a half-cell including the positive electrode and the negative electrode of a lithium secondary battery may decrease as the charge / discharge is repeated. The charge / discharge efficiency of the half-cell may be such that the difference between the charge / discharge efficiency after n charge / discharge cycles and the charge / discharge efficiency after n+10 charge / discharge cycles is less than 1%. In some embodiments, E of the above formula 1 n -E n+10 The value may be less than or equal to 0.9%, less than or equal to 0.8%, less than or equal to 0.7%, less than or equal to 0.6%, or less than or equal to 0.3%.

[0075] If the charge-discharge efficiency difference is greater than 1%, the long-term life characteristics of the positive electrode may deteriorate, and the lifespan of the positive electrode and lithium secondary battery may be shortened, especially in high-temperature environments. Furthermore, when the battery is stored in a high-temperature environment, side reactions between the electrolyte and the positive electrode active material may increase, generating large amounts of gas, and increasing the risk of explosion due to battery expansion.

[0076] A positive electrode for a lithium secondary battery according to exemplary embodiments may satisfy the following equation 2.

[0077] [Formula 2]

[0078] (E n -E n+10 ) ≤ 0.3%

[0079] In exemplary embodiments, when n is 5 to 20, E n can be more than 99.7%, E n+10 can be over 99%.

[0080] In exemplary embodiments, when n is 45 to 60, E n can be more than 89.5%, E n+10 can be more than 88.6%.

[0081] Within the above range, the positive electrode can have improved high-temperature life characteristics and high-temperature storage characteristics, and a lithium secondary battery having a high high-temperature capacity retention rate and a reduced amount of gas generated inside the battery during high-temperature storage can be implemented.

[0082] According to exemplary embodiments, a method for producing the lithium metal oxide particles may be provided.

[0083] According to exemplary embodiments, an active metal source may be prepared. The active metal source may include a nickel source and a cobalt source. For example, a manganese source may additionally be used.

[0084] Examples of the nickel source include nickel sulfate (NiSO4), nickel hydroxide (Ni(OH)2), nickel nitrate (Ni(NO3)2), nickel acetate (Ni(CH3CO2)2), and hydrates thereof. Examples of the manganese source include manganese sulfate (MnSO4), manganese hydroxide (Mn(OH)2), manganese nitrate (Mn(NO3)2), manganese acetate (Mn(CH3CO2)2), and hydrates thereof. Examples of the cobalt source include cobalt sulfate (CoSO4), cobalt hydroxide (Co(OH)2), cobalt nitrate (Co(NO3)2), cobalt carbonate (CoCO3), and hydrates thereof.

[0085] For example, nickel sulfate, manganese sulfate and cobalt sulfate can be used as nickel sources, manganese sources and cobalt sources, respectively.

[0086] According to exemplary embodiments, the above-described active material metal salts can be mixed and reacted, for example, through a co-precipitation method, to obtain an active material precursor. For example, the active material precursor can be prepared in the form of nickel-manganese-cobalt hydroxide.

[0087] A precipitating agent and / or a chelating agent may be used to promote the above-described coprecipitation reaction. The precipitating agent may include an alkaline compound such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), etc. The chelating agent may include, for example, ammonia water, ammonium carbonate, etc.

[0088] The above active material precursor can be mixed with a lithium source and reacted through heat treatment (sintering) to produce lithium-metal oxide particles. For example, the heat treatment temperature is about 800 o C to 1100 o The temperature can be controlled in the C range, and the heat treatment time can be controlled in the range of about 3 hours to 50 hours.

[0089] The lithium source may include, for example, lithium carbonate (Li2CO3), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxide (Li2O), lithium hydroxide (LiOH), etc. These may be used alone or in combination of two or more. For example, lithium hydroxide and / or lithium carbonate may be used as the lithium source.

[0090] After the above heat treatment, residual lithium such as unreacted lithium source remaining on the particle surface can be removed by washing with an aqueous solvent or organic solvent.

[0091] In one embodiment, a post-firing process may be further performed after the washing process. The post-firing process may be performed at a temperature of, for example, about 250 to 500°C.

[0092] The above-mentioned positive electrode active material can be mixed and stirred with a binder, a conductive agent, and / or a dispersing agent in a solvent to prepare a slurry. After coating the slurry on a positive electrode current collector (105), the slurry can be dried and rolled to prepare a positive electrode (100).

[0093] The cathode current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and may include, for example, aluminum or an aluminum alloy.

[0094] The binder may include, for example, an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0095] For example, a PVDF-based binder can be used as a positive electrode binder. In this case, the amount of binder required to form the positive electrode active material layer can be reduced, while the amount of positive electrode active material can be relatively increased, thereby improving the output and capacity of the secondary battery.

[0096] The conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0097] Figures 2 and 3 are schematic plan views and cross-sectional views, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, Figure 3 is a cross-sectional view taken along line II' of Figure 2 in the thickness direction.

[0098] Hereinafter, the positive electrode for the lithium secondary battery and the lithium secondary battery including the same will be described together with reference to FIGS. 2 and 3.

[0099] Referring to FIGS. 2 and 3, a lithium secondary battery may include an electrode assembly including a positive electrode (100), a negative electrode (130), and a separator (140) interposed between the positive electrode and the negative electrode. The electrode assembly may be contained and impregnated with an electrolyte within a case (160).

[0100] The positive electrode (100) is a positive electrode for a lithium secondary battery that includes a positive electrode active material including the lithium metal oxide particles described above.

[0101] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material, and may include a negative electrode active material layer (120) formed on the negative electrode current collector (125).

[0102] According to exemplary embodiments, the negative electrode (130) may include a carbon-based active material. The carbon-based active material may include crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, or the like.

[0103] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads, mesophase pitch-based carbon fibers, etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0104] Preferably, natural graphite and / or artificial graphite can be used as the carbon-based active material.

[0105] In some embodiments, the negative active material may further include a silicon-based active material. For example, the silicon-based active material may be Si, SiO. x (0 <x<2), 실리콘-탄소 복합체, 금속 도핑된 실리케이트 등을 포함할 수 있다.

[0106] The silicon-based active material can provide significantly increased capacity compared to, for example, carbon-based materials. However, the silicon-based active material can expand excessively in high-temperature environments or during repeated charge / discharge cycles, thereby deteriorating battery stability.

[0107] Accordingly, a carbon-based active material can be used together with the silicon-based active material as the negative electrode active material.

[0108] To prevent instability due to battery expansion, the amount of the carbon-based active material (e.g., graphite-based active material) among the total weight of the negative electrode active material may be greater than the amount of the silicon-based active material.

[0109] According to exemplary embodiments, among the total weight of carbon element (C) and silicon element (Si) included in the negative electrode active material, the content of silicon element may be 1 wt% to 10 wt%. Within the above range, a high-capacity / high-stability structure can be provided in the negative electrode as well, according to the high-capacity / high-stability design of the positive electrode described above.

[0110] In some embodiments, the content of elemental silicon in the total weight of the negative electrode active material 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%.

[0111] For example, a slurry can be prepared by mixing and stirring the above-described negative electrode active material with the above-described binder, conductive agent, thickener, etc. in a solvent. After coating the slurry on at least one surface of a negative electrode current collector (125), drying and compressing can be performed to prepare a negative electrode (130).

[0112] Materials substantially identical to or similar to the above-described materials used in the positive electrode active material layer (110) as the binder and conductive agent may be used. In some embodiments, the binder for forming the negative electrode may include, for example, an aqueous binder such as styrene-butadiene rubber (SBR) for compatibility with the carbon-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0113] A separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). The separator (140) may include a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0114] In some embodiments, the area (e.g., contact area with the separator (140)) and / or volume of the negative electrode (130) may be larger than that of the positive electrode (100). Accordingly, lithium ions generated from the positive electrode (100) may smoothly move to the negative electrode (130) without being precipitated in the middle, for example.

[0115] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode cells may be stacked to form an electrode assembly (150) in the form of, for example, a jelly roll. For example, the electrode assembly (150) may be formed by winding, lamination, folding, or the like of the separator (140).

[0116] An electrode assembly (150) may be housed together with an electrolyte within a case (160) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0117] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as 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 - Examples include:

[0118] Examples of the organic solvent that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0119] As illustrated in FIG. 2, electrode tabs (positive electrode tab and negative electrode tab) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form a connection with electrode leads (positive electrode lead (107) and negative electrode lead (127)) that extend or are exposed to the outside of the case (160).

[0120] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0121] The embodiments of the present disclosure described above include the following aspects and can be implemented through at least one of the following aspects.

[0122] A positive electrode for a lithium secondary battery according to the first aspect of the present disclosure comprises a positive electrode active material and has a density of 3 g / cm 3 A positive electrode active material layer having a density above is included. The positive electrode active material includes lithium metal oxide particles containing cobalt and having a cobalt content of more than 0 and less than 15 mol% among the total moles of elements excluding lithium and oxygen. The positive electrode for a lithium secondary battery satisfies the following equation 1.

[0123] [Formula 1]

[0124] (E n -E n+10 ) < 1 %

[0125] In the above equation 1, E n is the charge-discharge efficiency (%) measured after repeating n charge-discharge cycles of a half-cell containing a cathode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte inside an outer shell with a diameter of 20 mm and a height of 1.6 mm, and E n+10 is the charge-discharge efficiency (%) measured after repeating the charge-discharge cycle of the half-cell n+10 times, and the charge-discharge cycle is a CC-CV charge under the condition of 0.5C CC, 4.3V 0.05C CV cut, followed by a 10-minute rest and a CC discharge under the condition of 0.5C CC, and the negative electrode is a lithium foil having a circular shape with a diameter of Φ16 and a thickness of 1.2 ㎛, the positive electrode for a lithium secondary battery is a circular shape with a diameter of Φ14, the separator is a polyethylene film interposed between the negative electrode and the positive electrode for a lithium secondary battery and having a thickness of 13 ㎛, and the electrolyte is a mixture of ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and the charge-discharge efficiency is defined as a percentage of the charge capacity compared to the discharge capacity measured after repeating a predetermined number of charge-discharge cycles, and n is 5 to It is an integer of 100.

[0126] In the first aspect, the positive electrode for a lithium secondary battery according to the second aspect can satisfy the following equation 2.

[0127] [Formula 2]

[0128] (E n -E n+10 ) ≤ 0.3%

[0129] In the first aspect or the second aspect, according to the third aspect, the content of cobalt may be 1 mol% to 12 mol% of the total moles of elements excluding lithium and oxygen.

[0130] In any one of the first to third aspects, according to the fourth aspect, the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the particle surface of the lithium metal oxide may be 5000 ppm or less.

[0131] In any one of the first to fourth aspects, according to the fifth aspect, the lithium metal oxide particles may further include nickel and manganese.

[0132] In the fifth aspect, according to the sixth aspect, the content of nickel may be 70 mol% to 95 mol% of the total moles of elements excluding lithium and oxygen.

[0133] In the fifth or sixth aspect, according to the seventh aspect, the content of the manganese may be 5 mol% to 30 mol% of the total moles of elements excluding lithium and oxygen.

[0134] In any one of the first to seventh aspects, according to the eighth aspect, no peak may be observed within a 2θ range of 20° to 22° in the X-ray diffraction (XRD) analysis results of the lithium metal oxide particles.

[0135] In any one of the first to eighth aspects, according to the ninth aspect, when n is 5 to 20, E n can be over 99.7%.

[0136] In any one of the first to ninth aspects, according to the tenth aspect, when n is 5 to 20, E n+10 can be over 99%.

[0137] In any one of the first to tenth aspects, according to the eleventh aspect, when n is 45 to 60, E n can be more than 89.5%.

[0138] In any one of the first to eleventh aspects, when n is 45 to 60 according to the twelfth aspect, E n+10 can be more than 88.6%.

[0139] In any one of the first to twelfth aspects, according to the thirteenth aspect, the density of the positive electrode active material layer is 3.3 g / cm 3 5 g / cm 3 It could be.

[0140] A lithium secondary battery according to a 14th aspect of the present disclosure includes a positive electrode for a lithium secondary battery according to any one of the first to 13th aspects and a negative electrode opposite to the positive electrode.

[0141] Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various modifications and variations of the examples are possible within the scope and technical spirit of the present invention, and it is also natural that such modifications and variations fall within the scope of the appended claims.

[0142]

[0143] Manufacturing Example 1

[0144] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.76:0.01:0.23 using distilled water that had been bubbled with N2 for 24 hours to remove internal dissolved oxygen. The mixed solution was put into a reactor at 50°C, and NaOH and NH3H2O ​​were added as precipitants and chelating agents. After that, a coprecipitation reaction was performed for 72 hours to obtain Ni as a transition metal precursor. 0.76 Co 0.01 Mn 0.23 (OH)2 was obtained. The obtained precursor was dried at 100°C for 12 hours and then re-dried at 120°C for 10 hours.

[0145] Lithium hydroxide and lithium carbonate were mixed in a 1:1 ratio to form a mixed lithium raw material, and the molar ratio of Li to the transition metal precursor was 1.03:1, which was added to a dry high-speed mixer and mixed uniformly for 10 minutes. The mixture was placed in a ceramic crucible and placed in a box-type sintering furnace, and the temperature was increased to 780°C at a heating rate of 2°C / min, and maintained for 12 hours. Then, the temperature was increased to 900°C at a heating rate of 2°C / min, and maintained for 12 hours. After that, the mixture was left inside the sintering furnace to cool naturally to 50°C.

[0146] Oxygen was continuously passed at a flow rate of 10 mL / min during heating, maintenance, and cooling. After the firing was completed, the fired product was separated from the ceramic crucible and ground using an ACM (Air Classifier Mill) equipment, and then filtered through a #325 mesh to obtain LiNi. 0.76 Co 0.01 Mn 0.23 A lithium metal oxide with a single particle structure of O2 was prepared.

[0147]

[0148] Manufacturing Example 2

[0149] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.12:0.08, respectively.

[0150]

[0151] Manufacturing Example 3

[0152] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.85:0.05:0.1, respectively.

[0153]

[0154] Manufacturing Example 4

[0155] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.8:0.15:0.05, respectively.

[0156]

[0157] Manufacturing Example 5

[0158] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.85:0.05:0.1, respectively, and the primary holding time at 780°C was set to 6 hours.

[0159]

[0160] Manufacturing Example 6

[0161] Lithium metal oxide particles were manufactured using the same method as Manufacturing Example 1, except that the first process of maintaining at 780℃ for 12 hours was omitted.

[0162]

[0163] Manufacturing Example 7

[0164] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that the mixture containing lithium and a transition metal precursor was first maintained at 780°C for 12 hours and then secondarily maintained at 900°C for 6 hours.

[0165]

[0166] Manufacturing Example 8

[0167] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.8:0.2, respectively.

[0168]

[0169] Manufacturing Example 9

[0170] Lithium metal oxide particles were manufactured in the same manner as in Manufacturing Example 1, except that NiSO4 and MnSO4 were mixed in a ratio of 0.8:0.2, respectively.

[0171]

[0172] Experimental Example 1: Measurement of surface residual lithium content

[0173] 3g of lithium metal oxide particles of the manufacturing examples were each weighed and placed in a 250mL flask, 150g of deionized water was added, and a magnetic bar was added and stirred at 60 rpm for 10 minutes. Afterwards, 100g was aliquoted after filtering using a reduced pressure flask. The aliquoted solution was placed in an autotitrator container and automatically titrated with 0.1N HCl referring to the Wader Method to measure the Li2CO3 and LiOH contents in the solution. The measurement results are shown in Table 2 below.

[0174]

[0175] Experimental Example 2: XRD Analysis

[0176] XRD analysis was performed on the lithium metal oxide particles of the manufacturing examples using the equipment and conditions shown in Table 1 below. As a result of the XRD analysis of the lithium metal oxide particles of the manufacturing examples, it was confirmed whether a peak was observed within the 2θ range of 20° to 22°, and this was recorded in Table 2 below.

[0177] MakerPANalyticalAnode materialCuK-Alpha1 wavelength1.540598 ÅGenerator voltage45 kVTube current40 mAScan Range10-120 °Scan step size0.0065°Divergence slit1 / 4°Antiscatter slit1 / 2°

[0178] Residual lithium content (ppm) XRD 20-22° peak observation status Manufacturing example 14507X Manufacturing example 24216X Manufacturing example 34378X Manufacturing example 46211X Manufacturing example 510127X Manufacturing example 643918O Manufacturing example 78762X Manufacturing example 85214X Manufacturing example 94995X

[0179]

[0180] Example 1

[0181] (1) Positive electrode manufacturing

[0182] A positive electrode slurry was prepared by mixing the lithium metal oxide of Manufacturing Example 1, Denka Black as a conductive agent, and PVDF as a binder in a mass ratio of 93:5:2. The positive electrode slurry was coated on an aluminum current collector, followed by drying and pressing to prepare a positive electrode. The pressing was performed so that the density of the positive electrode active material layer reached 3.3 g / cc.

[0183] (2) Half-cell manufacturing

[0184] Lithium foil (thickness 1.2 mm) was prepared as a negative electrode, and the positive and negative electrodes were laminated by notching them into circular shapes with diameters of Φ14 and Φ16, respectively, and a separator (polyethylene, thickness 13 μm) notched into Φ19 was interposed between the positive and negative electrodes to form an electrode cell. The electrode cell was placed in a coin cell outer case with a diameter of 20 mm and a height of 1.6 mm, and the electrolyte was injected to assemble it, and the electrode was aged for more than 12 hours so that the electrolyte could be impregnated into the electrode. The electrolyte used was 1 M LiPF6 dissolved in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0185] (3) Full cell manufacturing

[0186] An anode slurry was prepared containing 95 wt% of a natural / artificial graphite mixture as an anode active material, 3 wt% of a flake-type conductive material as an anode active material, 1 wt% of styrene-butadiene rubber (SBR) as a binder, and 1 wt% of carboxymethyl cellulose (CMC) as a thickener. The anode slurry was coated, dried, and pressed onto a copper substrate to prepare an anode.

[0187] The positive and negative electrodes were notched into rectangular shapes measuring 240 mm X 85 mm and 245 mm X 90 mm, respectively, and laminated, and a separator (polyethylene, thickness 13 μm) was interposed in a zigzag shape between the positive and negative electrodes to form a 20 Ah electrode cell. The electrode cell was placed in an outer pouch formed according to the specifications, sealed on three sides, and then assembled by pouring the electrolyte into the remaining side, and aging was performed for more than 12 hours so that the electrolyte could be impregnated into the inside of the electrode. The electrolyte used was 1 M LiPF6 dissolved in a mixed solvent of EC / EMC (20 / 80; volume ratio).

[0188]

[0189] Examples 2 to 4 and Comparative Examples 1 to 4

[0190] Half cells and full cells were manufactured in the same manner as in Example 1, except that the positive electrode active materials of Manufacturing Examples 2 to 5 (Examples 2 to 5) and Manufacturing Examples 6 to 9 (Comparative Examples 1 to 4) were used instead of the positive electrode active material of Manufacturing Example 1.

[0191]

[0192] Comparative Example 5

[0193] The density of the positive electrode active material layer is 2.7 g / cm 3 Half cells and full cells were manufactured in the same manner as in Example 1, except that the positive electrode was manufactured by performing a press to reach .

[0194]

[0195] After evaluating the half-cells and full-cells of the examples and comparative examples as in the experimental examples below, the results are shown in Table 3.

[0196]

[0197] Experimental Example 3: Evaluation of Half-Cell Charge-Discharge Efficiency

[0198] (1) In the half-cells of the examples and comparative examples, charging (CC-CV 0.5 C 4.3 V 0.005 C CUT-OFF) and discharging (CC 0.5 C 3.0 V CUT-OFF) are considered as one cycle, and the charge-discharge efficiency (E) is defined as the ratio of the charge capacity to the discharge capacity after 10 cycles are repeated. 10 ) was calculated.

[0199] After repeating the charge / discharge cycle of the half-cells of the examples and comparative examples for 10 more cycles, the charge / discharge efficiency (E) was measured using the same method. 20 ) was calculated.

[0200] (2) In the half-cells of the examples and comparative examples, charging (CC-CV 0.5 C 4.3 V 0.005 C CUT-OFF) and discharging (CC 0.5 C 3.0 V CUT-OFF) are considered as one cycle, and the charge-discharge efficiency (E) is the ratio of the charge capacity to the discharge capacity after 50 cycles are repeated. 50 ) was calculated.

[0201] After repeating the charge / discharge cycle of the half-cells of the examples and comparative examples for 10 more cycles, the charge / discharge efficiency (E) was measured using the same method. 60 ) was calculated.

[0202]

[0203] Experimental Example 4: Evaluation of Full-Cell High-Temperature Capacity Retention Rate

[0204] The full cells of the examples and comparative examples were charged (CC-CV 0.1 C 4.3 V 0.005 C CUT-OFF) and discharged (CC 0.1 C 3.0 V CUT-OFF) in a 25°C chamber, respectively, and then the battery capacity (initial discharge capacity) was measured.

[0205] The above charging and discharging was considered as one cycle, and the discharge capacity after repeating 100 cycles of charging and discharging of the full cells of the examples and comparative examples at a temperature of 60°C was measured, and the high-temperature capacity retention rate was calculated by dividing the measured discharge capacity by the initial discharge capacity and converting the value into a percentage (%).

[0206]

[0207] Experimental Example 5: Evaluation of Full-Cell High-Temperature Storage Characteristics

[0208] The full cells of the examples and comparative examples were left in a 60°C chamber for about 4 weeks, then left at room temperature for 30 minutes and placed in a chamber for measuring the amount of gas generated. After forming a vacuum in the chamber, nitrogen gas was filled to form atmospheric pressure. At this time, the volume of nitrogen injected (V0) and the pressure inside the chamber (P0) were measured. After forming a vacuum again inside the chamber, a hole was made in the cell and the pressure inside the chamber (P1) was measured, and the amount of gas generated was calculated according to Equation 3 below.

[0209] [Formula 3]

[0210] Gas generation (mL) = (V0 / P0)*P1

[0211] Half-cell charge / discharge efficiency evaluation (%) High-temperature capacity retention (%) Gas generation (ml) E10 E20 E10-E20 E50 E60 E50-E60 Example 199.9 199.66 0.25 98.89 98.66 0.23 97 34.1 Example 299.74 99.50 0.24 98.78 98.55 0.23 95 42.3 Example 399.76 99.49 0.27 98.69 98.41 0.28 96 43.2 Example 499.67 99.16 0.5 197.5 997.07 0.5 294 48.9 Example 599.698.770.8396.2995.440.858961.7Comparative Example 199.6298.381.2494.6193.351.2683104.0Comparative Example 299.5198.31.2194.5293.291.238459.1Comparative Example 399.6498.561.0895.3994.351.0496101Comparative Example 499.397.961.3493.1891.761.427639.8Comparative Example 599.8399.570.2698.6698.340.327736.6

[0212] Referring to Table 3, the lithium secondary batteries of the examples contained a positive electrode satisfying Equation 1, and thus maintained a high capacity during repeated charge and discharge cycles in a high-temperature environment. In addition, the lithium secondary batteries of the examples generated less gas even when stored for a long period of time in a high-temperature environment.

[0213] The lithium secondary batteries of Examples 4 and 5 included a cathode active material having a relatively large amount of residual lithium. Accordingly, the battery's life characteristics and high-temperature storage characteristics were slightly lower than those of the other examples.

[0214] The lithium secondary batteries of the comparative examples are E 20 -E 10 The value of and E 50 -E 60 The value exceeded 1%, which resulted in poor storage characteristics in a high-temperature environment of the battery, and the high-temperature capacity retention rate of the battery also decreased.

[0215] The lithium secondary battery of Comparative Example 3 had a cathode containing a cathode active material with an excessively high cobalt content, and thus excessive gas was generated inside the battery in a high-temperature environment.

[0216] The lithium secondary battery of Comparative Example 4 had a positive electrode including a positive electrode active material that did not contain cobalt, and thus the capacity retention rate of the battery was significantly reduced.

[0217] The lithium secondary battery of Comparative Example 5 has a density of 3 g / cm 3 When a positive electrode including a positive electrode active material layer having a density of less than 10 μm is repeatedly charged and discharged, the contact area between the conductive material and the positive electrode active material particles decreases, and accordingly, the life characteristics of the battery are significantly deteriorated.

[0218] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

Claims

1. A cathode active material comprising lithium metal oxide particles containing cobalt and having a cobalt content of more than 0 and less than or equal to 15 mol% of the total moles of elements excluding lithium and oxygen, and 3 g / cm 3 It comprises a positive electrode active material layer having a density above, A cathode for a lithium secondary battery satisfying the following equation 1: [Formula 1] (AND n -AND n+10 ) < 1 % (In the above equation 1, E n is the charge-discharge efficiency (%) measured after repeating n charge-discharge cycles of a half-cell containing a cathode, a positive electrode for a lithium secondary battery, a separator, and an electrolyte inside an outer shell with a diameter of 20 mm and a height of 1.6 mm, and E n+10 is the charge-discharge efficiency (%) measured after repeating the charge-discharge cycle of the above half-cell n+10 times, The above charge / discharge cycle is CC-CV charging under 0.5C CC, 4.3V 0.05C CV cut conditions, then resting for 10 minutes and CC discharging under 0.5C CC conditions. The negative electrode is a lithium foil having a circular shape with a diameter of Φ16 and a thickness of 1.2 ㎛, the positive electrode for a lithium secondary battery is a circular shape with a diameter of Φ14, the separator is interposed between the negative electrode and the positive electrode for a lithium secondary battery and is a polyethylene film having a thickness of 13 ㎛, and the electrolyte is a mixture of ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and 1M LiPF6 is dissolved in a mixed solvent. Charge-discharge efficiency is defined as the percentage of charge capacity compared to discharge capacity measured after a predetermined number of charge-discharge cycles, where n is an integer from 5 to 100.

2. In the first paragraph, a positive electrode for a lithium secondary battery satisfying the following formula 2: [Formula 2] (AND n -AND n+10 ) ≤ 0.3% 3. A positive electrode for a lithium secondary battery, wherein the content of cobalt in the first paragraph is 1 mol% to 12 mol% of the total moles of elements excluding lithium and oxygen.

4. A positive electrode for a lithium secondary battery, wherein the total content of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) remaining on the particle surface of the lithium metal oxide in the first paragraph is 5000 ppm or less.

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

6. A positive electrode for a lithium secondary battery, wherein the content of nickel in the fifth paragraph is 70 mol% to 95 mol% of the total moles of elements excluding lithium and oxygen.

7. A positive electrode for a lithium secondary battery, wherein the content of manganese in the fifth paragraph is 5 mol% to 30 mol% of the total moles of elements excluding lithium and oxygen.

8. In the first paragraph, the X-ray diffraction (XRD) analysis result of the lithium metal oxide particles is 20 o 22 inland o A cathode for a lithium secondary battery, in which no peak is observed within the 2θ range.

9. In paragraph 1, if n is 5 to 20, E n A cathode for lithium secondary batteries with a purity of 99.7% or higher.

10. In the first paragraph, if n is 5 to 20, E n+10 A cathode for lithium secondary batteries with a purity of 99% or more.

11. In the first paragraph, if n is 45 to 60, E n A cathode for a lithium secondary battery having a silver content of 89.5% or more.

12. In the first paragraph, if n is 45 to 60, E n+10 A cathode for a lithium secondary battery having a purity of 88.6% or higher.

13. In the first paragraph, the density of the positive electrode active material layer is 3.3 g / cm 3 5 g / cm 3 Anode for lithium secondary batteries.

14. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to paragraph 1; and a negative electrode facing the positive electrode.

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