Positive electrode optimized for improving high-temperature life characteristics and secondary battery comprising the same

Abstract

In the present invention, the positive electrode comprises a positive electrode composite containing a positive electrode active material formed on a positive electrode current collector, wherein the positive electrode active material comprises a lithium transition metal oxide powder represented by the following chemical formula 1, and LiaNixCoyMzO2-wAw(1) M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, and A is an oxygen-substituted halogen, with 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4, and 0≤w≤0.001. The lithium transition metal oxide powder is composed of primary particles that are aggregated into secondary particles, with an average particle size (D50) of 7㎛ to 17㎛, and small particles that are single-particle and have an average particle size (D50) of 2㎛ to 6㎛. The single-particle small particles have a form in which primary particles with a major axis diameter of 500nm or more exist individually or are aggregated into fewer than 10 particles, and the mixing ratio of the large particles and small particles is 5:5 to 9:1 based on weight.

Description

Technology Field

[0001] The present invention relates to a positive electrode optimized for improving high-temperature life characteristics and a secondary battery including the same. Background Technology

[0002] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative and clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemistry are the most actively researched.

[0003] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is steadily expanding.

[0004] Recently, as technology development and demand for portable devices such as portable computers, mobile phones, and cameras have increased, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been the subject of much research and have been commercialized and widely used.

[0005] Furthermore, as interest in environmental issues grows, extensive research is being conducted on electric vehicles and hybrid electric vehicles to replace fossil fuel-powered vehicles, such as gasoline and diesel cars, which are major causes of air pollution. While nickel-metal hydride batteries are primarily used as the power source for these electric and hybrid vehicles, research utilizing lithium-ion batteries, which offer high energy density and discharge voltage, is actively underway and is already in the commercialization stage.

[0006] Currently, lithium-containing cobalt oxide (LiCoO2) is mainly used as the cathode material for lithium secondary batteries, and in addition, the use of lithium-containing manganese oxides such as layered crystal structure LiMnO2 and spinel crystal structure LiMn2O4, as well as lithium-containing nickel oxide (LiNiO2), is also being considered.

[0007] Among the aforementioned cathode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency; however, it has the disadvantage of having limited price competitiveness due to poor structural stability and high cost resulting from the resource limitations of cobalt used as a raw material, which limits its mass use as a power source in fields such as electric vehicles.

[0008] Although LiNiO2-based cathode active materials are relatively inexpensive and exhibit high discharge capacity battery characteristics, they have problems such as rapid phase transitions in the crystal structure due to volume changes accompanying charge-discharge cycles and a rapid decline in safety when exposed to air and moisture.

[0009] In addition, lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low cost, but they have problems such as low capacity, poor cycle characteristics, and poor high-temperature performance.

[0010] Accordingly, recently, lithium transition metal oxides containing three or more transition metals have been developed by substituting a portion of the above LiNiO2 with Co, Mn, Al, etc.

[0011] These ternary or quaternary lithium transition metal oxides are generally used by converting primary particles into secondary particles.

[0012] However, these secondary particleized lithium transition metal oxides are prone to particle breakage during the electrode rolling process, which increases the specific surface area of ​​the active material and exacerbates the degradation of storage and lifespan performance at high temperatures. This particle breakage of secondary particles occurs more frequently in fine particles with an average particle size (D50) of about 5 μm.

[0013] Therefore, there is a high need to develop a cathode capable of improving lifespan characteristics at high temperatures by minimizing grain breakage during rolling of a cathode containing the above-mentioned lithium transition metal oxide as an active material. The problem to be solved

[0014] The present invention aims to improve the lifespan characteristics at high temperatures of a secondary battery containing the same by minimizing particle breakage of the positive electrode active material through optimizing the composition, mixing conditions, and rolling conditions of the positive electrode active material. means of solving the problem

[0015] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0016] A positive electrode active material according to one embodiment of the present invention, a method for manufacturing the same, and a secondary battery including the same will be described below.

[0018] According to one embodiment of the present invention, the anode comprises an anode composite material including an anode active material formed on an anode current collector, wherein

[0019] The above positive electrode active material comprises a lithium transition metal oxide powder represented by the following chemical formula 1, and

[0020] Li a Ni x Co y M z O 2-w Aw (1)

[0021] M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, and

[0022] A is an oxygen-substituted halogen, and

[0023] 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4, and 0≤w≤0.001,

[0024] The above lithium transition metal oxide powder is,

[0025] Primary particles are aggregated into secondary particles, and the secondary particles have an average particle size (D50) of 7㎛ to 17㎛, and

[0026] It is composed of small particles that are single-particle and have an average particle size (D50) of 2㎛ to 6㎛, and

[0027] The above-mentioned single-particle elementary particles have a primary particle with a long axis diameter of 500 nm or more existing individually or in a form aggregated into fewer than 10 particles, and

[0028] The mixing ratio of the above alleles and subatomic particles is 5:5 to 9:1 based on weight.

[0029] In detail, the average particle size (D50) of the above-mentioned particles may be 9㎛ to 11㎛.

[0030] In addition, specifically, the mixing ratio of the above alleles and subatomic particles may be 6:4 to 8:2 based on weight.

[0031] Specifically, the porosity of the anode composite may be 22% to 30%.

[0032] In addition, specifically, the electrode density of the anode may be 3.2 g / cc to 3.6 g / cc.

[0033] Meanwhile, in the lithium transition metal oxide powder of Formula 1 included as the positive electrode active material, M is Mn b Al cAnd, here, 0≤b≤1 and 0≤c≤1 may be true.

[0034] The above anode composite may further include a binder and a conductive material in addition to the anode active material, wherein the binder is included in an amount of 1 to 5 weight percent based on the total weight of the anode composite, and the conductive material is included in an amount of 0.5 to 5 weight percent based on the total weight of the anode composite.

[0035] According to another embodiment of the present invention, a secondary battery is provided in which an electrode assembly comprising the anode; a cathode; and a separator interposed between the anode and the cathode is embedded in a battery case while impregnated with an electrolyte. Effects of the invention

[0036] The anode according to the present invention comprises an anode active material in which small particles of lithium transition metal oxide powder are formed into single particles, and by configuring the porosity of the anode composite according to the mixing ratio of large particles and small particles and rolling conditions to an optimal range, it has the effect of improving the high-temperature life characteristics of a secondary battery containing the same. Specific details for implementing the invention

[0037] Hereinafter, the positive electrode and secondary battery according to the present invention will be described in more detail.

[0038] According to one embodiment of the present invention,

[0039] A positive electrode having a positive electrode composite containing a positive electrode active material formed on a positive electrode current collector,

[0040] The above positive electrode active material comprises a lithium transition metal oxide powder represented by the following chemical formula 1, and

[0041] Li a Ni x Co y M z O 2-w A w (1)

[0042] M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, and

[0043] A is an oxygen-substituted halogen, and

[0044] 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4, and 0≤w≤0.001.

[0045] The above lithium transition metal oxide powder is,

[0046] Primary particles are aggregated into secondary particles, and the secondary particles have an average particle size (D50) of 7㎛ to 17㎛, and

[0047] It is composed of small particles that are single-particle and have an average particle size (D50) of 2㎛ to 7㎛, and

[0048] The mixing ratio of the above alleles and subatomic particles is 5:5 to 9:1 based on weight, and

[0049] An anode is provided in which the porosity of the above anode composite is 22% to 35%.

[0050] As explained above, the lithium transition metal oxide represented by the above chemical formula 1 is generally used as a positive electrode active material in a secondary particle state.

[0051] In addition, a mixture of large particles with an average particle size (D50) of about 11 μm and small particles with an average particle size (D50) of about 5 μm is used, but there was a problem in that the secondary particleized lithium transition metal oxide powder broke during the rolling process of the electrode.

[0052] In particular, the aforementioned particle breakage mostly occurred in elementary particles, while some particle breakage occurred in alleles.

[0053] Accordingly, the inventors of the present application confirmed that particle breakage can be reduced when the fine particles in the lithium transition metal oxide powder are converted into single particles in order to solve this problem. However, they discovered that when secondary-sized particles and single-sized particles are mixed, depending on the mixing conditions and rolling conditions of the particles and the fine particles, the breakage of the secondary-sized particles may increase compared to the case where the secondary-sized particles and the fine particles are mixed, leading to a greater reduction in lifespan. Consequently, they identified an optimized mixing ratio of particles and fine particles, a porosity according to rolling, and further optimized electrode density in which the breakage of the secondary-sized particles does not increase compared to the existing composition, and thus completed the present invention.

[0054] Accordingly, the anode according to the present invention comprises a lithium transition metal oxide powder of Formula 1, which is included as an anode active material, composed of a mixture of secondary particulates and single particulates.

[0055] Generally, the above single-particle lithium transition metal oxides mostly have an average particle size (D50) of about 5 μm, making it easy to manufacture single-particle small particles, but it is not easy to manufacture single-particle large particles because the heat treatment temperature and time increase too much, and as the single particle size increases, the charge / discharge efficiency and C-rate characteristics decrease rapidly, so it is desirable to use secondary-particle large particles.

[0056] In the present invention, the term "secondary particleized" means a state in which primary particles are aggregated into tens to hundreds of particles, and the term "single particleized" means a state in which primary particles exist individually or are aggregated into fewer than 10 particles.

[0057] At this time, the diameter of the major axis of the primary particle forming the secondary particleized allele may be, for example, 100 nm to 1000 nm, and the diameter of the major axis of the primary particle forming the single particleized elementary particle may be 500 nm to 7000 nm.

[0058] The average particle size (D50) of the secondary particle-formed conglomerates formed by the aggregation of tens to hundreds of these primary particles may be 7㎛ to 17㎛ as defined above, and more specifically, 9㎛ to 11㎛.

[0059] In addition, the average particle size (D50) of the single-particle fine particles formed by the primary particles existing individually or aggregating into fewer than 10 particles may be 2㎛ to 7㎛ as defined above, and more specifically, 4㎛ to 6㎛.

[0060] If the average particle size (D50) of the above-mentioned large particles and the average particle size (D50) of the small particles fall outside the above range, and the average particle size of the large particles is too large, the low efficiency and low C-rate characteristics of the single-particle small particles are exacerbated, which may lead to a decrease in capacity and output. Conversely, if the average particle size of the large particles is too small, electrode rolling performance deteriorates, and in particular, particle breakage of the large particles is intensified by the single-particle small particles during rolling, which may cause deterioration of high-temperature lifespan. Meanwhile, if the average particle size of the single-particle small particles is too small, manufacturing becomes difficult due to reduced processability, and if it is too large, the charge / discharge efficiency and C-rate characteristics deteriorate, which is undesirable.

[0061] Here, the average particle size (D50) refers to the diameter at the 50% point of the cumulative distribution of particle volume according to particle size. This average particle size (D50) can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to particle size as the particles pass through a laser beam, thereby calculating the particle size distribution. D50 can be measured by calculating the particle diameter at the point that is 50% of the cumulative distribution of particle volume according to particle size in the measuring device.

[0062] Meanwhile, according to the present invention, as described above, when mixing single-particle fine particles and secondary-particle coarse particles, particle breakage of the secondary-particle coarse particles may actually increase depending on the mixing conditions and the porosity and electrode density conditions resulting from rolling; therefore, it is very important to control the mixing ratio of coarse particles and fine particles and the porosity resulting from rolling.

[0063] First, the mixture of the above-mentioned allotrope and the subatomic particle may be prepared separately and then mixed. Specifically, the mixing ratio for achieving the effect of the present invention may be 5:5 to 9:1, more specifically 6:4 to 8:2, and even more specifically 7:3.

[0064] If the content of fine particles exceeds the above range, the particle breakage of coarse particles during electrode rolling is exacerbated by fine particles with stronger particle strength, which may worsen high-temperature lifespan; if it is too low, the filling rate by fine particles is low, which is undesirable as it lowers electrode density.

[0065] Secondly, the porosity of the anode composite according to the control of rolling conditions to exert the effects of the present invention may be 22% to 35%, more specifically 24% to 30%, and even more specifically 25% to 28%.

[0066] Here, the above porosity is calculated as follows using the ratio of the electrode density to the true density of the total solid content of the anode mixture.

[0067] (True Density - Electrode Density) / True Density X 100

[0068] Outside the above range, if the porosity is too small, it implies high rolling strength, which consequently leads to an increased problem of particle breakage of secondary granulated afferents; conversely, if the porosity is too large, rolling strength is low, but this results in a decrease in electrode density, which is undesirable in terms of energy density, and there is a problem of reduced output due to loss of inter-particle conduction paths.

[0069] According to the optimization of the porosity based on the mixing ratio of the above-mentioned large and small particles and rolling conditions, the most desirable range of electrode density for exhibiting the effects of the present invention can be determined, and the preferred range of electrode density of the anode according to the present invention may be 3.0 g / cc to 3.6 g / cc, specifically 3.3 g / cc to 3.45 g / cc.

[0070] The above electrode density can be calculated as the weight per unit volume excluding the current collector of the electrode.

[0071] If the electrode density is too low outside the above range, the energy-to-volume ratio decreases, which is undesirable; conversely, if the electrode density is too high, the particle breakage of secondary particle-like particles increases, which leads to a problem where high-temperature lifespan characteristics actually deteriorate.

[0072] Meanwhile, the above-mentioned positive electrode active material may include a lithium transition metal oxide powder represented by the above-mentioned chemical formula 1, and specifically, in the above-mentioned chemical formula 1, M is Mn b Al c And, where 0≤b≤1 and 0≤c≤1 may be possible. In other words, the lithium transition metal oxide powder included as the positive electrode active material may, in detail, include one or more selected from the group consisting of Li-Ni-Co-Mn oxide containing Ni, Co, and Mn as the transition metal, Li-Ni-Co-Al oxide containing Ni, Co, and Al, and Li-Ni-Co-Mn-Al oxide containing Ni, Co, Mn, and Al.

[0073] The term "containing lithium transition metal oxide powder represented by the above chemical formula 1" means that it may include a lithium transition metal oxide having a composition selected from the range of chemical formula 1 alone, but may also be in the form of a mixture of lithium transition metal oxide powders of various compositions within the range of chemical formula 1.

[0074] Furthermore, in addition to the lithium transition metal oxide represented by Chemical Formula 1, the above-mentioned positive electrode active material comprises LiNiO2, LiMnO2, LiMn2O2, and LiCo 1-d Mn d O2, LiNi 1-d Mn d O2(0.2 <d<1), Li(Ni a Co b Mn c )O4(0 <a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn 2-e Ni e O4, LiMn 2-e Co e O4(0 <e<2), LiCoPO4, 또는 LiFePO4등 종래 양극 활물질로서 알려진 화합물들을 더 포함할 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 소량 더 포함될 수 있음은 물론이다.

[0075] However, the lithium transition metal oxide represented by the above chemical formula 1 may be included in at least 60% by weight based on the total weight of the positive electrode active material.

[0076] The above-mentioned anode composite may further include a binder and a conductive material in addition to the anode active material, and optionally, may further include a filler.

[0077] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special restrictions as long as it possesses electronic conductivity without causing chemical changes. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes (SWCNT), and multi-walled carbon nanotubes (MWCNT); graphite such as natural graphite or artificial graphite; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 30% by weight, specifically 0.3% to 10% by weight, and even more specifically 0.5% to 5% by weight based on the total weight of the anode composite.

[0078] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 1% to 30% by weight, more specifically 1% to 10% by weight, and more specifically 1% to 5% by weight, based on the total weight of the anode mixture.

[0079] In addition, the above filler is optionally used as a component to suppress the expansion of the anode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, for example, olifin-based polymers such as polyethylene and polypropylene; or fibrous materials such as glass fibers and carbon fibers are used. At this time, the above filler may be added in an amount of 0.1 to 3 weight percent based on the total weight of the anode mixture.

[0080] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0082] In addition, according to another embodiment of the present invention,

[0083] The above anode;

[0084] cathode; and

[0085] A secondary battery is provided in which an electrode assembly comprising a separator interposed between the anode and the cathode is embedded in a battery case while impregnated with an electrolyte.

[0086] In detail, the above secondary battery may be a lithium secondary battery.

[0087] The above-mentioned cathode may also have a structure in which a cathode composite containing a cathode active material is formed on a cathode current collector, similar to the anode, and the cathode composite may further include a conductive material and a binder as described above, along with the cathode active material, and a filler as necessary.

[0088] The above-mentioned negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ x Examples include metal oxides capable of doping and dedoping lithium, such as (0 < x < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0089] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0090] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0091] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0092] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0093] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0094] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0095] In addition to the above components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

[0096] As described above, the secondary battery according to the present invention can be used as a device power source in fields such as portable devices like mobile phones, laptop computers, and digital cars / cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0098] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0100] <Preparation Example 1> (Secondary particleized allele)

[0101] In a 5L batch-type reactor set at 60°C, a 2M metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in water at a molar ratio of 70:10:20. A container holding the metal salts was connected to the reactor, and a 4M NaOH solution and a 7% concentration aqueous NH4OH solution were prepared and connected to the reactor, respectively. After adding 3 liters of deionized water to a co-precipitation reactor (5L capacity), nitrogen gas was purged into the reactor at a rate of 2 liters / minute to remove dissolved oxygen from the water and create a non-oxidizing atmosphere inside the reactor. Subsequently, 100ml of 4M NaOH was added, and the temperature was maintained at 60°C with a stirring speed of 1200 rpm to maintain a pH of 12.0. Subsequently, the above metal salt solution, NaOH aqueous solution, and NH4OH aqueous solution were added at a rate of 180 ml / hr, 180 ml / hr, and 10 ml / hr, respectively, to co-precipitate Ni for 10 hours. 0.7 Co 0.1 Mn 0.2 (OH)2 nickel-cobalt-manganese complex oxyhydroxide (average particle size (D50): 11㎛) was synthesized.

[0102] The resulting nickel-cobalt-manganese composite metal hydroxide particles were mixed with lithium hydroxide as a lithium raw material at a molar ratio of 1:1.07, and then heat-treated in air at 860°C for 15 hours to obtain large LiNi 0.7 Co 0.1 Mn 0.2 O2 powder (average particle size (D50): 11㎛) was obtained.

[0103] Upon SEM observation, the aforementioned anode powder consisted of primary particles aggregated into more than tens of particles to form secondary particles, and their shape was spherical or elliptical.

[0105] <Preparation Example 2> (Single-particle subatomic particle)

[0106] Except for reducing the co-precipitation reaction time to 3 hours in Preparation Example 1, Ni is prepared in the same manner as in Preparation Example 1. 0.7 Co 0.1 Mn 0.2 (OH)2 nickel-cobalt-manganese complex oxyhydroxide (average particle size (D50): 4.5 μm) was synthesized.

[0108] The resulting nickel-cobalt-manganese composite metal hydroxide particles were mixed with lithium hydroxide as a lithium raw material in a 1:1 molar ratio, and then heat-treated in air at 950°C for 15 hours to produce fine LiNi particles. 0.7 Co 0.1 Mn 0.2 O2 powder (average particle size (D50): 5㎛) was obtained.

[0109] When observing the above-mentioned fine particle anode powder with SEM, the primary particles were found to exist individually or to form single particles aggregated into fewer than 10, and their shape was spherical or elliptical.

[0111] <Preparation Example 3> (Secondary particleized subatomic particles)

[0112] Except for reducing the co-precipitation reaction time to 3 hours in Preparation Example 1, Ni is prepared in the same manner as in Preparation Example 1. 0.7 Co 0.1 Mn 0.2(OH)2 nickel-cobalt-manganese complex oxyhydroxide (average particle size (D50): 4.5 μm) was synthesized.

[0114] The resulting nickel-cobalt-manganese composite metal hydroxide particles were mixed with lithium hydroxide as a lithium raw material at a molar ratio of 1:1.07, and then heat-treated in air at 840°C for 15 hours to produce fine LiNi particles. 0.7 Co 0.1 Mn 0.2 O2 powder (average particle size (D50): 4.5㎛) was obtained.

[0115] Upon SEM observation, the above-mentioned fine particle anode powder consisted of primary particles aggregated into more than tens of particles to form secondary particles, and their shape was spherical or elliptical.

[0117] <Example 1>

[0118] The large-particle anode powder prepared in Preparation Example 1 and the small-particle anode powder prepared in Preparation Example 2 were mixed in a weight ratio of 7:3 and used as the anode active material, and PVdF was used as the binder and carbon black as the conductive material. A slurry (viscosity: 5000 mPa·s) was prepared by thoroughly mixing the anode active material, binder, and conductive material in NMP in a weight ratio of 96:2:2, and coated onto an Al current collector with a thickness of 20 μm. After drying at 130°C, the slurry was rolled under a pressure of 1.7 ton / cm to produce an anode with a thickness of 74.5 μm.

[0120] <Example 2>

[0121] In the above Example 1, an anode was prepared in the same manner as in Example 1, except that the large particle anode powder prepared in Preparation Example 1 and the small particle anode powder prepared in Preparation Example 2 were mixed in a weight ratio of 5:5 and used as the anode active material.

[0123] <Example 3>

[0124] In the above Example 1, an anode was prepared in the same manner as in Example 1, except that the large particle anode powder prepared in Preparation Example 1 and the small particle anode powder prepared in Preparation Example 2 were mixed in a weight ratio of 8:2 and used as the anode active material.

[0126] <Example 4>

[0127] In the above Example 1, the anode was manufactured in the same manner as in Example 1, except that the pressure during rolling was 2.1 ton / cm and the electrode thickness was 73.1 µm.

[0129] <Example 5>

[0130] In the above Example 1, the anode was manufactured in the same manner as in Example 1, except that the pressure during rolling was 1.1 ton / cm and the electrode thickness was 76.8 μm.

[0132] <Example 6>

[0133] In the above Example 1, the anode was manufactured in the same manner as in Example 1, except that the rolling pressure was 0.7 ton / cm to a thickness of 78.4 µm.

[0135] <Comparative Example 1>

[0136] An anode was prepared in the same manner as in Example 1, except that the large particle anode powder prepared in Preparation Example 1 and the small particle anode powder prepared in Preparation Example 3 were mixed in a weight ratio of 7:3.

[0138] <Comparative Example 2>

[0139] In the above Example 1, the anode was prepared in the same manner as in Example 1, except that the large particle anode powder prepared in Preparation Example 1 and the small particle anode powder prepared in Preparation Example 2 were mixed in a weight ratio of 4:6 and used as the anode active material.

[0141] <Comparative Example 3>

[0142] In the above Example 1, the anode was manufactured in the same manner as in Example 1, except that the rolling pressure was 2.5 ton / cm to a thickness of 71.8 µm.

[0144] <Comparative Example 4>

[0145] In the above Example 1, the anode was manufactured in the same manner as in Example 1, except that the rolling pressure was 0.2 ton / cm to a thickness of 82.8 µm.

[0147] <Experimental Example 1>

[0148] The porosity of the anode mixture and the electrode density of the anodes prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were determined as follows, and the results are shown in Table 1.

[0149] The porosity was calculated as follows using the ratio of the electrode density to the true density of the total solid content of the anode mixture.

[0150] (True Density - Electrode Density) / True Density X 100

[0151] The electrode density was calculated as the weight per unit volume excluding the electrode current collector.

[0152] Porosity (%) Electrode density (g / cc) Example 1 25 3.36 Example 2 25 3.36 Example 3 25 3.36 Example 4 23 3.45 Example 5 28 3.21 Example 6 30 3.15 Comparative Example 1 25 3.36 Comparative Example 2 25 3.36 Comparative Example 3 21 3.55 Comparative Example 4 36 2.86

[0153] <Experimental Example 2>

[0154] A half-coin cell was prepared using the anodes prepared in Examples 1 to 6 and Comparative Examples 1 to 4, lithium metal as the cathode, and an electrolyte containing 1M LiPF6 in a solvent with EC : DMC : DEC = 1 : 2 : 1.

[0155] The half coin cell manufactured above was charged at 25°C with a constant current (CC) of 0.1C until it reached 4.25V, and then charged with a constant voltage (CV) of 4.25V until the charging current reached 0.05mAh for the first charge cycle. After leaving it for 20 minutes, it was discharged with a constant current of 0.1C until it reached 3.0V, and the discharge capacity of the first cycle was measured.

[0156] At 45℃, under constant current / constant voltage (CC / CV) conditions, the device was charged at 0.5C to 4.25V and charged until it reached 0.05mAh, then discharged at 1C to 3.0V under constant current (CC) conditions to complete one cycle, and this process was repeated up to 50 cycles. The value calculated as (capacity after 50 cycles / capacity after 1 cycle) × 100 was used as the high temperature life retention rate (%), and the results are shown in Table 2.

[0157] Capacity retention rate (%) at 45℃ Example 1 93 Example 2 89 Example 3 92 Example 4 89 Example 5 94 Example 6 92 Comparative Example 1 88 Comparative Example 2 86 Comparative Example 3 85 Comparative Example 4 85

[0158] By referring to Table 2 above together with Table 1, it can be confirmed that when using an anode satisfying the conditions of the present invention, particle breakage is minimal and high-temperature life characteristics are excellent.

Claims

Claim 1 A positive electrode having a positive electrode composite comprising a positive electrode active material formed on a positive electrode current collector, wherein the positive electrode active material comprises a lithium transition metal oxide powder represented by the following chemical formula 1, and Li a Ni x Co y M z O 2-w A w (1) M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, and A is an oxygen-substituted halogen, with 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4, and 0≤w≤0.

001. The lithium transition metal oxide powder is composed of a primary particle that is aggregated into a secondary particle and has an average particle size (D50) of 7㎛ to 17㎛, and a single particle and a small particle with an average particle size (D50) of 2㎛ to 6㎛. The single particle has a primary particle with a major axis diameter of 500nm or more that exists individually or is aggregated into fewer than 10 particles. The mixing ratio of the primary particle and the small particle is 6:4 to 9:1 based on weight. Claim 2 In claim 1, the anode having an average particle size (D50) of the covalents of 9㎛ to 11㎛. Claim 3 An anode according to claim 1, wherein the mixing ratio of the alleles and the subatomic particles is 6:4 to 8:2 based on weight. Claim 4 An anode according to claim 1, wherein the porosity of the anode composite is 22% to 30%. Claim 5 The anode according to claim 1, wherein the electrode density of the anode is 3.2 g / cc to 3.45 g / cc. Claim 6 In paragraph 1, the above M is Mn b Al c and, where 0≤b≤1 and 0≤c≤1, the positive electrode. Claim 7 In claim 1, the anode composite further comprises a binder and a conductive material. Claim 8 An anode according to claim 7, wherein the binder is included in an amount of 1 to 5 weight percent based on the total weight of the anode mixture, and the conductive material is included in an amount of 0.5 to 5 weight percent based on the total weight of the anode mixture. Claim 9 A secondary battery in which an electrode assembly comprising a positive electrode according to claim 1; a negative electrode; and a separator interposed between the positive electrode and the negative electrode is embedded in a battery case while impregnated with an electrolyte.

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