Lithium secondary battery

Abstract

The present invention discloses a lithium secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte, wherein the positive electrode active material includes secondary particles formed of agglomerates of a plurality of primary particles made of a lithium composite transition metal oxide having a nickel content of 60 mol % or more in all transition metals, and a boron-containing coating layer formed on a surface of some or all of the plurality of primary particles, and the non-aqueous electrolyte includes boron dissolved therein, and a ratio B / A of a boron content B contained in the non-aqueous electrolyte to a boron content A contained in the positive electrode active material is 0.001 to 5. The lithium secondary battery according to the present invention has improved life characteristics.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery having a positive electrode active material containing a high content of nickel.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0084276, filed on June 28, 2021, and the entire contents disclosed in the specification and drawings of that application are incorporated herein by reference. [Background technology]

[0003] As a positive electrode active material for lithium secondary batteries, a positive electrode active material made of a lithium composite transition metal oxide containing a high content of nickel (Ni-rich) has been attracting attention.

[0004] Typically, a positive electrode active material made of a high-content nickel-based lithium composite transition metal oxide is prepared by mixing a nickel-based composite transition metal precursor synthesized by a coprecipitation method with a lithium source material in a predetermined ratio, followed by firing the mixture in an oxygen atmosphere. The resulting positive electrode active material has the form of secondary particles formed by agglomeration of primary particles, and as the nickel content increases, the lifespan characteristic decreases sharply.

[0005] To solve this problem, a method has been proposed in which, after producing a high-nickel-based lithium positive electrode active material using the above-mentioned method, the surfaces of positive electrode active material particles are coated with a boron precursor and then heat-treated to form a coating layer containing boron, in order to ensure the life characteristics (stability) of the positive electrode active material.

[0006] Meanwhile, in recent years, there has been a demand for the development of lithium secondary batteries with higher energy and rapid charging characteristics. In this context, there is an increasing demand for improving the life characteristics of lithium secondary batteries having a positive electrode active material containing a high content of nickel. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a lithium secondary battery having improved life characteristics by using a positive electrode active material containing a high content of nickel. [Means for solving the problem]

[0008] To achieve the above object, a lithium secondary battery according to a first embodiment of the present invention is a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte solution, the positive electrode active material includes secondary particles formed by agglomerating a plurality of primary particles made of a lithium transition metal oxide having a nickel content of 60 mol% or more in total transition metals, and a boron-containing coating layer formed on a part or all of the surfaces of the plurality of primary particles, the non-aqueous electrolyte solution contains boron dissolved therein, The ratio B / A of the content B of boron contained in the non-aqueous electrolyte to the content A of boron contained in the positive electrode active material is 0.001 to 5.

[0009] According to a second embodiment of the present invention, in the first embodiment, the non-aqueous electrolyte may include a boron-containing lithium salt.

[0010] According to a third embodiment of the present invention, in the first embodiment, the non-aqueous electrolyte may not contain a boron-containing lithium salt.

[0011] According to a fourth embodiment of the present invention, in one or more of the first to third embodiments, the B / A may be 0.005 to 4.

[0012] According to a fifth embodiment of the present invention, in one or more of the first to fourth embodiments, the content A of boron contained in the positive electrode active material may be 100 to 4,000 ppm, and the content B of boron contained in the non-aqueous electrolyte may be 1 to 3,000 ppm. More specifically, the content A of boron contained in the positive electrode active material may be 500 to 2,000 ppm, and the content B of boron contained in the non-aqueous electrolyte may be 10 to 2,000 ppm.

[0013] According to a sixth embodiment of the present invention, in one or more of the first to fifth embodiments, more specifically, the content A of boron contained in the positive electrode active material may be 500 to 2,000 ppm, the content B of boron contained in the non-aqueous electrolyte may be 10 to 2,000 ppm, and the B / A may be 0.005 to 4.

[0014] According to a seventh embodiment of the present invention, in one or more of the first to sixth embodiments, the lithium composite transition metal oxide may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a [Ni x Co y M 1 z M 2 w ]O2 In Chemical Formula 1, M 1 is one or more selected from Mn and Al, M 2 is one or more elements selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y; 0.9≦a≦1.3, 0.6≦x<1.0, 0 <y≦0.4、0<z≦0.4、0≦w≦0.4、x+y+z+w=1である。

[0015] According to an eighth embodiment of the present invention, in one or more of the first to seventh embodiments, the average particle size of the primary particles may be 0.1 to 8 μm, and the D50 of the secondary particles may be 2 to 15 μm, more specifically, the average particle size of the primary particles may be 0.15 to 7 μm, and the D50 of the secondary particles may be 3 to 13 μm.

[0016] According to a ninth embodiment of the present invention, in one or more of the first to eighth embodiments, the coating layer may be one or more selected from the group consisting of lithium boron oxide and boron oxide. [Effects of the Invention]

[0017] In a lithium secondary battery including a positive electrode active material containing a high content of nickel according to the present invention, a boron-containing coating layer is formed on the surface of the positive electrode active material, and the ratio of the content of boron contained in the positive electrode active material to the content of boron contained in the non-aqueous electrolyte is controlled within a predetermined range.

[0018] A lithium secondary battery having such a configuration has improved life characteristics (stability) and can be usefully used in environments where higher energy and rapid charging are required. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below. The terms and phrases used in the specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, but are to be construed as having meanings and concepts that correspond to the technical idea of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0020] A lithium secondary battery according to an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte.

[0021] The present inventors have surprisingly found that in a lithium secondary battery having a positive electrode active material containing a high content of nickel, when a positive electrode active material having a boron-containing coating layer formed on the surface is used and the ratio of the content of boron contained in the positive electrode active material to the content of boron contained in the non-aqueous electrolyte is controlled within a predetermined range, the life characteristics (stability) of the lithium secondary battery is improved, leading to the completion of the present invention.

[0022] The boron contained in the positive electrode active material is added by forming a boron-containing coating layer on particles made of a lithium composite transition metal oxide, and when the boron-containing coating layer is formed, the particles made of a lithium composite transition metal oxide are also partially doped with boron.

[0023] Meanwhile, boron contained in the non-aqueous electrolyte solution is added when boron in the positive electrode active material having the above-mentioned boron-containing coating layer is dissolved into the non-aqueous electrolyte solution due to trace amounts of moisture present in the cell, the activation process during cell production, shipping, etc., or when a boron-containing lithium salt is added to the non-aqueous electrolyte solution as a lithium salt.

[0024] The lithium secondary battery according to the present invention uses a positive electrode active material including secondary particles formed by agglomerating a plurality of primary particles made of a lithium composite transition metal oxide in which the nickel content of all transition metals is 60 mol % or more, and a boron-containing coating layer formed on the surfaces of some or all of the plurality of primary particles, and the non-aqueous electrolyte includes boron dissolved therein. When the ratio B / A of the boron content B contained in the non-aqueous electrolyte to the boron content A contained in the positive electrode active material is controlled to be 0.001 to 5, the life characteristics (stability) of the lithium secondary battery are improved.

[0025] In terms of life characteristics of the lithium secondary battery, the ratio B / A of the boron content B contained in the non-aqueous electrolyte to the boron content A contained in the positive electrode active material may be specifically 0.005 to 4, and more specifically 0.02 to 4. The boron content A contained in the positive electrode active material may be 100 to 4,000 ppm, and the boron content B contained in the non-aqueous electrolyte may be 1 to 3,000 ppm. More specifically, the boron content A contained in the positive electrode active material may be 500 to 2,000 ppm, and the boron content B contained in the non-aqueous electrolyte may be 10 to 2,000 ppm. In particular, the content A of boron contained in the positive electrode active material may be 500 to 2,000 ppm, and the content B of boron contained in the non-aqueous electrolyte may be 10 to 2,000 ppm, and the B / A ratio may be 0.005 to 4, more specifically, 0.02 to 4.

[0026] <Positive electrode> First, the positive electrode active material provided in the lithium secondary battery of the present invention and the positive electrode provided therewith will be described.

[0027] The positive electrode active material comprises secondary particles formed by agglomerating a plurality of primary particles made of a lithium transition metal composite oxide in which the nickel content in all transition metals is 60 mol % or more.

[0028] Although details will be described later, secondary particles formed by agglomerating a plurality of primary particles made of a lithium transition metal oxide in which the nickel content in all transition metals is 60 mol % or more can be easily prepared by a person skilled in the art by a well-known method such as coprecipitation.

[0029] The lithium composite transition metal oxide may be represented by, for example, the following Chemical Formula 1: [Chemical formula 1] Li a [Ni x Co y M 1 z M 2 w ]O2 In Chemical Formula 1, M 1 is one or more selected from Mn and Al, M 2 is one or more elements selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y; 0.9≦a≦1.3, 0.6≦x<1.0, 0 <y≦0.4、0<z≦0.4、0≦w≦0.4、x+y+z+w=1である。

[0030] The average particle size of the primary particles may be 0.1 to 8 μm, and the D50 of the secondary particles may be 8 to 15 μm, more specifically, the average particle size of the primary particles may be 0.15 to 7 μm, and the D50 of the secondary particles may be 3 to 13 μm. Here, the average particle size of the primary particles refers to the average particle size of the primary particles measured by X-ray diffraction, and the D50 of the secondary particles refers to the D50 value of the secondary particles measured by laser diffraction, which is defined as the particle size at 50% of the particle size distribution.

[0031] A boron-containing coating layer is formed on the surfaces of some or all of the primary particles made of a lithium composite transition metal oxide in which the nickel content in all transition metals is 60 mol % or more.

[0032] Here, the primary particle means a single crystal grain (or crystallite).

[0033] Furthermore, the secondary particles refer to aggregates obtained by aggregation of primary particles, and may include voids and boundaries between the primary particles.

[0034] The coating layer may be formed on some or all surfaces of the plurality of primary particles, and may be formed so that the coating layers are connected to each other to fill all gaps between the primary particles. Preferably, the coating layer is formed on all surfaces of the plurality of primary particles to fill all gaps between the primary particles.

[0035] The boron-containing coating layer may be embodied by its constituent element, boron (B). Specifically, the coating layer may contain boron in the form of one or more amorphous boron compounds selected from the group consisting of lithium boron oxide and boron oxide, such as LiBO, LiBO, LiBO, and the like.

[0036] Unlike crystalline compounds, which are in the form of particles and can only be coated discontinuously, amorphous boron compounds can be coated continuously in the form of a film, an island, or a mixture of these.

[0037] The boron-containing coating layer not only improves the lifespan of lithium secondary batteries, but also reduces the barrier energy for Li-ion migration through its constituent element boron. It also improves the stability of the positive electrode active material by preventing direct contact between the secondary particles and the electrolyte.

[0038] The positive electrode active material having the above-described structure may be prepared by the following method, but is not limited thereto.

[0039] First, secondary particles are prepared, which are agglomerates of a plurality of primary particles made of a lithium transition metal composite oxide in which the nickel content in all transition metals is 60 mol % or more.

[0040] These secondary particles may be commercially available or may be directly prepared using a coprecipitation method. More specifically, secondary particles comprising a plurality of high-content nickel-based composite transition metal hydroxide particles are obtained as a precursor using a coprecipitation method commonly known in the art, and then mixed with a lithium source and calcined. Here, the method for controlling the composition of the precursor using the coprecipitation method and the type of lithium source may follow common technical knowledge known in the art. The composition of a lithium composite transition metal oxide having a nickel content of 60 mol% or more of the total transition metals may be represented by Chemical Formula 1 above.

[0041] The secondary particles are then mixed with a boron precursor and then fired in an oxygen atmosphere to form a boron-containing coating layer on some or all surfaces of the plurality of primary particles.

[0042] Here, the oxygen atmosphere includes the air atmosphere and means an atmosphere containing a sufficient amount of oxygen for firing, and it is particularly desirable to perform firing in an atmosphere with a higher oxygen partial pressure than the air atmosphere.

[0043] The boron precursor can be a powder containing amorphous compound particles containing boron (B). For example, it can be a boronic acid (H3BO3) powder, which has a melting point of 170.9°C. When mixed in the solid state and calcined, the boronic acid can be sufficiently melted while the secondary particles maintain their particle state. The calcination temperature can be 150-500°C, more specifically 300-400°C. The boron precursor mixed with the secondary particles can be calcined in an oxygen atmosphere to contain boron in the form of an amorphous boron compound, such as lithium boron oxide (LiBO2), Li2BO7, or LiBO5, or boron oxide.

[0044] The amount of boron precursor mixed can be adjusted to control the amount of boron contained in the resulting positive electrode active material.

[0045] According to the above-described manufacturing method, a positive electrode active material containing a high content of nickel, in which the content of lithium impurities is reduced to preferably 0.6 wt % or less, more preferably 0.5 wt % or less, can be manufactured without an additional water washing process.

[0046] The positive electrode active material thus prepared may be coated on an electrode current collector and used in the following manner.

[0047] For example, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. 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. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0048] The positive electrode active material layer may contain a conductive material and, optionally, a binder in addition to the positive electrode active material. The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically, 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer. When contained in this range, excellent capacity characteristics can be exhibited.

[0049] The conductive material is used to impart conductivity to the electrode and can be any material that is electronically conductive and does not cause chemical changes in the battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0050] The binder functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination. The binder may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0051] The positive electrode for a lithium secondary battery can be manufactured by a conventional method for manufacturing a positive electrode, except for using the above-described positive electrode active material. Specifically, the positive electrode active material and, optionally, a binder and a conductive material are dissolved or dispersed in a solvent to form a composition for forming a positive electrode active material layer, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0052] Alternatively, the positive electrode may be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector. <Nonaqueous electrolyte> The non-aqueous electrolyte will now be described by way of example.

[0053] The non-aqueous electrolyte may include an organic solvent and a lithium salt.

[0054] The organic solvent may be any suitable medium for ion migration in the electrochemical reaction of the battery. Examples of suitable organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are preferably mixed in a volume ratio of about 1:1 to about 1:9, which provides excellent electrolyte performance.

[0055] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O), etc. That is, the lithium salt of the nonaqueous electrolyte may or may not contain a boron-containing lithium salt.

[0056] The lithium salt is preferably used in a concentration range of 0.1 to 2.0 M. When the lithium salt is contained in this concentration range, the non-aqueous electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0057] In addition to the electrolyte components described above, the nonaqueous electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0058] As described above, boron contained in the non-aqueous electrolyte solution is added when boron in the positive electrode active material having the boron-containing coating layer described above is dissolved into the non-aqueous electrolyte solution due to trace amounts of water present in the cell, the activation process during cell manufacturing, shipping, etc., and also when a boron-containing lithium salt is added to the non-aqueous electrolyte solution as a lithium salt.

[0059] <Negative electrode> The positive electrode and non-aqueous electrolyte prepared by the above method can be used together with a conventional negative electrode to manufacture a lithium secondary battery.

[0060] The negative electrode will now be described by way of example.

[0061] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0062] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance adhesion of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0063] The negative electrode active material layer may include a negative electrode active material and, optionally, a binder and a conductive material. For example, the negative electrode active material layer may be fabricated by coating a negative electrode-forming composition including the negative electrode active material and, optionally, the binder and the conductive material on a negative electrode current collector and drying the coating, or by casting the negative electrode-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0064] The negative electrode active material may be a compound capable of reversible lithium intercalation and deintercalation. Specific examples thereof 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, and Al alloys; and SiO. βExamples of suitable materials include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These materials may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. Examples of suitable carbonaceous materials include low-crystalline carbon and high-crystalline carbon. Examples of suitable low-crystalline carbon include soft carbon and hard carbon. Examples of suitable high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitch, and high-temperature-calcined carbon, such as petroleum- or coal-based coke.

[0065] The binder and conductive material are the same as those described above for the positive electrode.

[0066] <Other> A separator may usually be interposed between the positive electrode and the negative electrode.

[0067] In lithium secondary batteries, the separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte impregnation capacity are desirable. Specifically, porous polymer films, such as those made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Separators coated with ceramic components or polymeric materials can also be used to ensure heat resistance or mechanical strength, and can be used in either a single-layer or multi-layer structure.

[0068] Meanwhile, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0069] The lithium secondary battery according to the present invention is useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0070] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0071] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0072] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0073] Secondary particles, which are an aggregate of multiple high-content nickel-based composite transition metal hydroxide particles, are obtained as a precursor using a coprecipitation method well known in the art. The precursor is mixed with a lithium source and then calcined to produce Li a [Ni x Co y M 1 z M 2 w ]O2 (where a=1, x=0.86, y=0.05, z=0.07, w=0.02, M 1 =Mn, M 2 Secondary particles were prepared by agglomerating a plurality of primary particles made of (Al).

[0074] <Production of positive electrode active material> (Production of secondary particles of lithium composite transition metal oxide) Secondary particles, which are an agglomeration of a plurality of high-content nickel-based composite transition metal hydroxide particles, are obtained as a precursor using a coprecipitation method well known in the art. The precursor is mixed with a lithium source and then calcined to prepare a cathode material of secondary particles, which are an agglomeration of a plurality of primary particles made of a lithium composite transition metal oxide represented by the following chemical formula:

[0075] First particle: Li a [Ni x Co y M 1 z ]O2 (where a=1, x=0.60, y=0.20, z=0.20, M 1 =Mn) Second particle: Li a [Ni x Co y M 1 z ]O2 (where a=1.03, x=0.80, y=0.10, z=0.10, M 1 =Mn) Third particle: Li a [Ni x Co y M 1 z M 2 w ]O2 (where a=1.05, x=0.90, y=0.04, z=0.03, w=0.01, M 1 =Mn, M 2 =Al)

[0076] (Formation of a boron-containing coating layer) First cathode active material: 100 g of the first particles and 0.5 g of boronic acid (boric acid HBO3) powder were mixed and fired in a sintering furnace at 300°C for 5 hours under an air atmosphere to form a coating layer, and the sintered body was then crushed and classified to obtain a cathode active material.

[0077] Second positive electrode active material: It was prepared in the same manner as the first positive electrode active material, except that the content of the boronic acid powder was changed to 2 g.

[0078] A third positive electrode active material was prepared in the same manner as the first positive electrode active material, except that the second particles were used instead of the first particles.

[0079] A fourth positive electrode active material was prepared in the same manner as the second positive electrode active material, except that the second particles were used instead of the first particles.

[0080] Fifth positive electrode active material: It was prepared in the same manner as the first positive electrode active material, except that the third particles were used instead of the first particles.

[0081] A sixth positive electrode active material was prepared in the same manner as the second positive electrode active material, except that the third particles were used instead of the first particles.

[0082] Seventh positive electrode active material: It was prepared in the same manner as the second positive electrode active material, except that the baking temperature during the formation of the coating layer was changed to 500° C. and the third particles were used instead of the first particles.

[0083] Example 1 Example 1-1 The first positive electrode active material, carbon black conductive material, and PVdF binder were mixed in a weight ratio of 92.5:3.5:4 to prepare a positive electrode slurry, which was then coated on one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode. Lithium metal was used as the negative electrode.

[0084] An electrode assembly was fabricated by interposing a porous PE separator between the fabricated positive electrode and negative electrode, and the assembly was placed inside a case. A non-aqueous electrolyte (prepared by dissolving 0.1M LiPF6 in an EC / EMC / DEC mixed organic solvent in a volume ratio of 3:4:3) was then injected into the case to fabricate a lithium secondary battery.

[0085] Example 1-2 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that 2 wt % of LiODFB based on the total weight of the electrolyte solution was further added.

[0086] Examples 1-3 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the second positive electrode active material was used instead of the first positive electrode active material.

[0087] Examples 1-4 A lithium secondary battery was manufactured in the same manner as in Example 1-2, except that the second positive electrode active material was used instead of the first positive electrode active material.

[0088] <Example 2> Example 2-1 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the third positive electrode active material was used instead of the first positive electrode active material.

[0089] Example 2-2 A lithium secondary battery was manufactured in the same manner as in Example 1-2, except that the third positive electrode active material was used instead of the first positive electrode active material.

[0090] Example 2-3 A lithium secondary battery was fabricated in the same manner as in Example 1-3, except that the fourth positive electrode active material was used instead of the first positive electrode active material.

[0091] Examples 2-4 A lithium secondary battery was fabricated in the same manner as in Examples 1-4, except that the fourth positive electrode active material was used instead of the first positive electrode active material.

[0092] Example 3 Example 3-1 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the fifth positive electrode active material was used instead of the first positive electrode active material.

[0093] Example 3-2 A lithium secondary battery was manufactured in the same manner as in Example 1-2, except that the fifth positive electrode active material was used instead of the first positive electrode active material.

[0094] Example 3-3 A lithium secondary battery was manufactured in the same manner as in Example 1-3, except that the sixth positive electrode active material was used instead of the first positive electrode active material.

[0095] Examples 3-4 A lithium secondary battery was fabricated in the same manner as in Example 1-4, except that the sixth positive electrode active material was used instead of the first positive electrode active material.

[0096] <Comparative Example 1> Comparative Example 1-1 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that a positive electrode active material prepared by changing the baking temperature during the formation of the coating layer of the first positive electrode active material to 600° C. was used.

[0097] Comparative Example 1-2 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that 3 wt % of LiODFB based on the total weight of the electrolyte solution was further added.

[0098] Comparative Examples 1-3 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that the content of the boronic acid powder was increased by four times when forming the coating layer.

[0099] <Comparative Example 2> Comparative Example 2-1 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that the third positive electrode active material was used instead of the first positive electrode active material.

[0100] Comparative Example 2-2 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-2, except that the third positive electrode active material was used instead of the first positive electrode active material.

[0101] Comparative Example 2-3 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-3, except that the third positive electrode active material was used instead of the first positive electrode active material.

[0102] <Comparative Example 3> Comparative Example 3-1 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that the fifth positive electrode active material was used instead of the first positive electrode active material.

[0103] Comparative Example 3-2 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-2, except that the fifth positive electrode active material was used instead of the first positive electrode active material.

[0104] Comparative Example 3-3 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-3, except that the fifth positive electrode active material was used instead of the first positive electrode active material.

[0105] <Comparative Example 4> A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the seventh positive electrode active material was used instead of the first positive electrode active material.

[0106] <Evaluation of life characteristics of lithium secondary batteries> The fabricated lithium secondary battery cell was initially charged at 25°C in CC (constant current)-CV (constant voltage) mode at 0.1C up to 4.25V, and then discharged at a constant current of 0.1C down to 3.0V.

[0107] For the 100-cycle characteristics, a charge-discharge experiment was carried out by charging at 0.3 C in CC-CV mode at 45°C until the voltage reached 4.2 V, and then discharging at a constant current of 0.3 C until the voltage reached 3.0 V.

[0108] <Measurement of the average particle size of primary particles and D50 of secondary particles> The average particle size of the primary particles of the lithium composite transition metal oxide was measured using XRD, and the D50 of the secondary particles of the reference was measured using a laser diffraction method.

[0109] As a result of the measurement, the average particle size of the primary particles was 0.15 μm, and the D50 of the secondary particles was 10 μm.

[0110] <Measurement of boron content contained in positive electrode active material and non-aqueous electrolyte> a. Measurement of the boron content in the positive electrode active material A small amount of the sample was placed in a Teflon tube and weighed. Then, hydrochloric acid, hydrogen peroxide, and hydrofluoric acid were added to the Teflon tube and heated to completely dissolve the sample. Internal STD (Sc) was then added to the Teflon tube and diluted with ultrapure water. The boron content was measured by ICP-OES.

[0111] b. Measurement of the boron content in the non-aqueous electrolyte The sample was placed in a platinum crucible, and then ultrapure water was added. Concentrated nitric acid was added to the platinum crucible, heated, and then dried. The organic matter was completely decomposed by repeating this process of adding concentrated nitric acid and hydrogen peroxide. Once the organic matter was completely decomposed, the sample was diluted with ultrapure water and analyzed by ICP-OES to measure the boron content.

[0112] The respective contents measured by the above measurement methods, the content ratios calculated therefrom, and the corresponding battery life characteristics are shown in Table 1 below.

[0113] [Table 1]

[0114] Referring to the data in Table 1, it can be seen that the examples in which the ratio B / A of the boron content B contained in the non-aqueous electrolyte to the boron content A contained in the positive electrode active material was controlled within the range of the present invention had better life characteristics than the comparative examples in which the B / A was outside the range of the present invention.

Claims

1. A lithium secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte solution, the positive electrode active material includes secondary particles formed by agglomerating a plurality of primary particles made of a lithium transition metal oxide having a nickel content of 60 mol% or more in total transition metals, and a boron-containing coating layer formed on a part or all of the surfaces of the plurality of primary particles, the non-aqueous electrolyte solution contains boron dissolved therein, a ratio B / A of a boron content B contained in the non-aqueous electrolyte to a boron content A contained in the positive electrode active material is 0.001 to 5; The primary particles have an average particle size of 0.1 to 8 μm, and the secondary particles have a D50 of 2 to 15 μm. The content A of boron contained in the positive electrode active material is 500 to 2,000 ppm; The boron-containing coating layer comprises lithium boron oxide.

2. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte solution contains a boron-containing lithium salt.

3. 2. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte does not contain a boron-containing lithium salt.

4. 2. The lithium secondary battery according to claim 1, wherein the B / A is 0.005 to 4.

5. The lithium secondary battery according to claim 1, wherein the boron content B contained in the non-aqueous electrolyte is 1 to 3,000 ppm.

6. The lithium secondary battery according to claim 1, wherein the boron content B contained in the non-aqueous electrolyte is 10 to 2,000 ppm.

7. The lithium secondary battery according to claim 1, wherein the boron content B contained in the non-aqueous electrolyte is 10 to 2,000 ppm, and the B / A is 0.005 to 4.

8. The lithium composite transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ａ [Ni ｘ Co ｙ M １ ｚ M ２ ｗ ]O ２ In Chemical Formula 1, M １ is one or more selected from Mn and Al, M ２ is one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y; 2. The lithium secondary battery according to claim 1, wherein 0.9≦a≦1.3, 0.6≦x<1.0, 0<y≦0.4, 0<z≦0.4, 0≦w≦0.4, and x+y+z+w=1.

9. 2. The lithium secondary battery according to claim 1, wherein the boron-containing coating layer is lithium boron oxide.

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