KR20240158692A - Method for preparing cathode active material, cathode active material prepared using the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a method for producing a cathode active material for a lithium secondary battery, comprising the steps of: preparing a nickel-containing transition metal precursor; forming a mixture including the transition metal precursor and a lithium raw material and then first firing the mixture to form a first sintered product; crushing the first sintered product; and second firing the crushed first sintered product to form a lithium transition metal oxide in the form of single particles, wherein an absolute value of a difference between the first sintering temperature and the second sintering temperature is 30° C. or less, and the second sintering time is longer than the first sintering time.

Description

Method for preparing cathode active material for lithium secondary battery, cathode active material prepared thereby, and lithium secondary battery comprising same {METHOD FOR PREPARING CATHODE ACTIVE MATERIAL, CATHODE ACTIVE MATERIAL PREPARED USING THE SAME AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a method for producing a cathode active material for a lithium secondary battery, a cathode active material produced thereby, and a lithium secondary battery comprising the same, and more specifically, to a method for producing a cathode active material for a lithium secondary battery in the form of a single particle, a cathode active material produced thereby, and a lithium secondary battery comprising the same.

Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted/deintercalated between the positive and negative electrodes, while charging an organic electrolyte or polymer electrolyte between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _{4 ,} etc.), and lithium iron phosphate compound (LiFePO ₄ ) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide (LiCoO ₂ ) has the advantages of high operating voltage and excellent capacity characteristics, so it is widely used and applied as a high-voltage cathode active material. However, due to the rising price of cobalt (Co) and unstable supply, there are limits to its mass use as a power source in fields such as electric vehicles, and the need for the development of a cathode active material that can replace it has arisen.

Accordingly, nickel-cobalt-manganese lithium composite transition metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") have been developed, in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). However, the NCM-based lithium composite transition metal oxides developed so far are generally in the form of secondary particles in which primary particles are aggregated, and thus have a large specific surface area, low particle strength, and high lithium byproduct content, which results in a large amount of gas generation during cell operation and problems with low lifespan and stability.

Accordingly, development of single particle type cathode active materials, rather than the existing secondary particle type, is underway. In general, single particle type cathode active materials can solve many of the problems of the above-mentioned secondary particle type cathode active materials. However, single particles have an issue in which particle strength is excellent or deteriorated depending on how the sintering process conditions are controlled during manufacturing, so optimization of the sintering process conditions is necessary.

Accordingly, one object of the present invention is to provide a method for producing a cathode active material for a lithium secondary battery having excellent particle strength as a single particle, a cathode active material produced thereby, and a lithium secondary battery including the same.

One embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, comprising the steps of: preparing a nickel-containing transition metal precursor; forming a mixture including the transition metal precursor and a lithium raw material and then first firing the mixture to form a first fired product; crushing the first fired product; and second firing the crushed first fired product to form a lithium transition metal oxide in the form of single particles, wherein an absolute value of a difference between the first firing temperature and the second firing temperature is 30° C. or less, and the second firing time is longer than the first firing time.

The above first firing temperature may be higher than or equal to the above second firing temperature.

The above first firing temperature and the above second firing temperature can each independently be 900 to 950°C.

The sum of the times for performing the first firing and the second firing within the above temperature range may be 13 hours or more.

The sum of the first firing and second firing times performed within the above temperature range can be 13 to 17 hours.

The above first firing time can be 3 to 6 hours.

The content of nickel in the above transition metal precursor may be 50 to 70 mol% based on the total mole number of transition metals.

The content of cobalt in the above transition metal precursor may be 5 to 20 mol% based on the total mole number of transition metals.

The above lithium raw material may be Li ₂ CO ₃ .

Another embodiment of the present invention provides a positive electrode active material for a lithium secondary battery manufactured according to the manufacturing method described above.

The above cathode active material may have a fine particle ratio of 1 μm or less of 1.2% or less after applying a pressure of 9 tons.

The above cathode active material may have a crystallite size of 200 nm or more.

The above positive electrode active material may have an average particle diameter (D50) of 3 μm or more.

The above positive electrode active material may have a maximum particle size (Dmax) of 12 μm or more.

The above positive electrode active material can be represented by the following chemical formula 1.

[Chemical Formula 1]

Li _a [Ni _x Co _y Mn _z M _w ]O ₂

In the chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0.05≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material.

Another embodiment of the present invention provides a lithium secondary battery including the positive electrode.

A method for manufacturing a cathode active material for a lithium secondary battery according to one embodiment of the present invention can manufacture a cathode active material having excellent particle strength as a single particle by controlling the sintering process conditions, thereby improving the life characteristics and safety of the battery.

Figure 1 is a SEM image of a positive electrode active material manufactured according to Example 1.
Figure 2 is a SEM image of a positive electrode active material manufactured according to Comparative Example 1.

The terms first, second, and third, etc. are used to describe, but are not limited to, various parts, components, regions, layers, and/or sections. These terms are only used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms include the plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and/or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and/or components.

When a part is referred to as being "on" or "on" another part, it may be directly on or above the other part, or there may be other parts intervening. In contrast, when a part is referred to as being "directly on" another part, there are no other parts intervening.

Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined.

Also, unless otherwise specified, % means weight%, and 1 ppm is 0.0001 weight%.

In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including at least one selected from the group consisting of said components.

Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

One embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, comprising the steps of: preparing a nickel-containing transition metal precursor; forming a mixture including the transition metal precursor and a lithium raw material and then first firing the mixture to form a first fired product; crushing the first fired product; and second firing the crushed first fired product to form a lithium transition metal oxide in the form of single particles, wherein an absolute value of a difference between the first firing temperature and the second firing temperature is 30° C. or less, and the second firing time is longer than the first firing time.

A method for manufacturing a cathode active material for a lithium secondary battery according to one embodiment of the present invention relates to a method for forming a lithium transition metal oxide in the form of a single particle.

The single particle-type active material has a smaller specific surface area than conventional secondary particles, which reduces the amount of gas generated by side reactions with the electrolyte, and has a large particle strength, which can suppress particle breakage during rolling, and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has the advantage of superior life and safety compared to secondary particles, and can realize high energy density of the electrode.

However, even for the same single particle cathode active material, there may be significant differences in particle strength depending on the sintering process conditions.

According to one embodiment of the present invention, a method for manufacturing a cathode active material for a lithium secondary battery is performed by dividing the sintering into first sintering and second sintering as described above, but the temperature difference between the first sintering temperature and the second sintering temperature is made small, and the second sintering time is controlled to be longer than the first sintering time. Accordingly, uniform growth of particles is induced, thereby improving the particle strength of single particles, and ultimately improving the life characteristics of the battery.

In this specification, the term “single particle” is used to distinguish it from the cathode active material particle in the form of a secondary particle formed by the agglomeration of tens to hundreds of primary particles, which have been generally used in the past, and is a concept that includes a single particle composed of one primary particle and an aggregate particle of 30 or fewer primary particles. The “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by the physical or chemical bonding between tens to hundreds of primary particles without an intentional agglomeration or assembly process for the primary particles.

Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described in detail step by step.

First, a nickel-containing transition metal precursor is prepared.

The above nickel-containing transition metal precursor may be a transition metal hydroxide.

The above transition metal hydroxide may be produced by a coprecipitation reaction by adding a solution containing a complexing agent and a solution containing a pH regulator to a transition metal-containing solution including, for example, a nickel raw material and optionally a cobalt raw material or a manganese raw material.

The above nickel raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be, but is not limited to, NiSO ₄ , NiSO ₄ .6H ₂ O, Ni(OH) 2, NiO, NiOOH, NiCO ₃ .2Ni(OH) ₂ .4H ₂ O, NiC ₂ O ₂ .2H ₂ O, Ni(NO ₃ ) ₂ .6H ₂ O, fatty acid nickel salts, nickel halides or combinations thereof.

The above cobalt raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be CoSO _{4 ,} CoSO ₄ ㆍ7H ₂ O, Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O or a combination thereof, but is not limited thereto.

The above manganese raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, and specifically, may be a manganese salt such as MnSO ₄ , MnCO ₃ , Mn(NO ₃ ) ₂ , manganese acetate, manganese dicarboxylic acid salt, manganese citrate and manganese fatty acid salt, manganese oxide such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ , oxyhydroxide, manganese chloride or a combination thereof, but is not limited thereto.

The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally a cobalt raw material or a manganese raw material to a solvent, specifically, water, or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water.

The above complexing agent-containing solution performs a complex-forming function and may include, but is not limited to, complexing agents such as NH ₃ , NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , NH ₄ CO ₃ or a combination thereof. Meanwhile, the complexing agent-containing solution may be used in the form of an aqueous solution, and at this time, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water may be used as a solvent.

At this time, the content of nickel in the transition metal precursor may be 50 to 70 mol% based on the total mole number of transition metals. Recently, high-nickel active materials having a nickel molar content of 80 mol% or more have been widely used for high-capacity batteries. However, if the nickel content is too high, there may be a thermal propagation issue, that is, a problem with thermal safety, and the cost may increase. Therefore, the transition metal precursor according to the present invention may have a nickel content of 70 mol% or less. However, if the nickel content is too low, the capacity may become too low.

Additionally, the content of cobalt in the transition metal precursor may be 5 to 20 mol% based on the total mole number of transition metals.

Next, a mixture containing the above transition metal precursor and lithium raw material is formed and then subjected to a first calcination to form a first calcined product.

The above lithium raw material is not particularly limited as long as it is commonly used in the art, but more specifically, it may be Li ₂ CO _3. By using Li ₂ CO ₃ , which is inexpensive, instead of LiOH, which is commonly used as a lithium raw material, there may be a cost reduction effect.

Most of the residual lithium (LiOH or Li ₂ CO ₃ ) remaining on the particle surface can be removed through the above first calcination.

There is no particular limitation on the atmosphere during the above first firing. For example, the above first firing can be performed under an oxygen or air atmosphere.

Next, the above primary calcined material is crushed.

Through the above-mentioned disintegration, uniform mixing of the first calcined material and the lithium raw material can be induced in the second calcination process described later. Accordingly, the second calcination reaction can proceed more efficiently, inducing uniform growth of particles, and as a result, the particle strength of the active material can be improved.

The above disintegration can be performed by a method commonly performed in the art.

The above-mentioned disintegration can be performed using, for example, a rotor mill, a ball mill, a pin mill, a jet mill, a bead mill, or a roll mill, but is not limited thereto.

Next, the above-mentioned crushed primary calcined material is subjected to a second calcination to form a lithium transition metal oxide in the form of single particles.

Through the above secondary calcination, a lithium transition metal oxide in the form of a single particle with improved particle strength can be formed.

In particular, at this time, the absolute value of the difference between the first sintering temperature and the second sintering temperature is 30°C or less, and more specifically, may be 20°C or 10°C or less. If the temperature difference between the first sintering temperature and the second sintering temperature is too large, the crystal grains may not grow sufficiently, which may deteriorate the particle strength of the single particle, and thus the life characteristics of the battery may deteriorate.

In addition, the first sintering temperature may be higher than or equal to the second sintering temperature. If the first sintering temperature is lower than the second sintering temperature, the crystal grains may not grow sufficiently, which may deteriorate the particle strength of the single particle and deteriorate the life characteristics of the battery.

Meanwhile, the first sintering temperature and the second sintering temperature may each independently be 900 to 950°C. If the first sintering temperature and the second sintering temperature are too low, the crystal grain size within the single particle may not grow sufficiently, which may deteriorate the particle strength, and the particle diameter of the single particle may not grow sufficiently, which may lower the rolling density and deteriorate the electrode energy density. If the first sintering temperature and the second sintering temperature are too high, oversintering may occur, which may deteriorate the electrochemical characteristics such as capacity and output.

The sum of the first firing and second firing times performed within the above temperature range may be 13 hours or more, and more specifically, 13 to 17 hours. If the time of the firing section within the above temperature range is too short, the crystal grain size within the single particle may not grow sufficiently, which may deteriorate the particle strength, and the particle diameter of the single particle may not grow sufficiently, which may lower the rolling density and deteriorate the electrode energy density. However, if the time of the firing section within the above temperature range is too long, over-firing may occur, which may deteriorate the electrochemical characteristics such as capacity and output.

In addition, the second firing time is longer than the first firing time. More specifically, as time passes during the first firing, residual lithium is gradually removed, and most of the residual lithium is removed by the end of the first firing. At this time, if the first firing time becomes longer than the second firing time, excessive first firing is additionally performed on the fired product from which residual lithium has already been removed, and thus there may be a problem in that the crystal grains do not grow sufficiently during the second firing while having an already stabilized surface. Accordingly, the particle strength and battery life characteristics may deteriorate.

More specifically, the first firing time may be 3 to 6 hours or 3 to 5 hours. Additionally, the second firing time may be 7 to 14 hours or 8 to 12 hours.

According to the above manufacturing method, the positive electrode active material may have a fine particle ratio of 1 μm or less of 1.2% or less after applying a pressure of 9 tons. That is, the positive electrode active material manufactured according to the manufacturing method according to one embodiment of the present invention may have significantly improved particle strength against external pressure, and may improve the life characteristics and safety of the battery.

The above-mentioned manufactured positive electrode active material may have a crystallite size of 200 nm or more, and more specifically, 220 nm, 240 nm, 260 nm or 280 nm or more. When the crystallite size of the positive electrode active material is sufficiently large, particle strength is improved, thereby improving the life characteristics and safety of the battery. In this specification, “crystallite” means a distinct region in which atoms in a primary particle form a lattice structure with a certain direction, and the “crystallite size” can be estimated using peak broadening of XRD data, and can be quantitatively calculated using the Scherr equation.

The above-mentioned manufactured positive electrode active material may have an average particle diameter (D50) of 3 μm or more, and more specifically, may have an average particle diameter of 3.5 μm or 3.8 μm or more. When the average particle diameter of the positive electrode active material is sufficiently large as such, the rolling density is improved, thereby improving the electrode energy density. In the present specification, the average particle diameter (D50) may be defined as a particle diameter corresponding to 50% of the volume accumulation amount in a particle diameter distribution curve of particles. The average particle diameter (D50) may be measured using, for example, a laser diffraction method.

The above-mentioned manufactured positive electrode active material may have a maximum particle size (Dmax) of 12 μm or more, and more specifically, may have a maximum particle size of 12.5 μm or 13.0 μm or more. Since the maximum particle size of the positive electrode active material is sufficiently large, the packing density can be increased during electrode manufacture, thereby improving the electrode energy density. The reason why the maximum particle size of the positive electrode active material is large can be interpreted as a result of good single particle growth occurring as the sintering process according to the present invention is performed. In this specification, the maximum particle size (Dmax) can be defined as a particle size corresponding to 100% of the volume accumulation amount in the particle size distribution curve of the particle. The above-mentioned maximum particle size (Dmax) can be measured using, for example, a laser diffraction method.

The above lithium transition metal oxide can be more specifically represented by the following chemical formula 1.

[Chemical Formula 1]

Li _a [Ni _x Co _y Mn _z M _w ]O ₂

In the chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0.05≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

In the lithium transition metal oxide of the above chemical formula 1, lithium may be included in a content corresponding to a, that is, 0.8≤a≤1.2. If a is too small, the capacity may be reduced, and if a is too large, the strength of the sintered positive electrode active material may be increased, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the lithium content control and the sinterability balance during the manufacture of the active material, the lithium may be included in a content of 0.9≤a≤1.1 more preferably.

In the lithium transition metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, that is, 0.5≤x≤0.7. If the nickel content is too low, it may be difficult to achieve high capacity of the battery, and if the nickel content is too high, the battery life and thermal safety may be reduced due to a decrease in the structural stability of the active material, and the manufacturing cost may increase.

In the lithium transition metal oxide of the above chemical formula 1, cobalt may be included in a content corresponding to y, that is, 0.05≤y≤0.2. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt content is too high, the overall cost of the raw material may increase and the reversible capacity may decrease.

In the lithium transition metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, that is, 0≤z≤0.4. If the manganese content is too low, the production cost may increase and the stability of the active material may deteriorate. If the manganese content is too high, the capacity and output characteristics of the battery may deteriorate.

In the lithium transition metal oxide of the above chemical formula 1, M may be included in a content corresponding to w, that is, 0≤w1≤0.2. At this time, M is a doping element and may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

Another embodiment of the present invention provides a positive electrode active material for a lithium secondary battery manufactured according to the manufacturing method described above.

The above-mentioned positive electrode active material is manufactured according to the manufacturing method described above, so that it can have excellent particle strength and a high degree of single particle formation.

Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material.

Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and including the positive electrode active material described above.

The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The above-described positive electrode active material layer may include a binder and/or a conductive material together with the above-described positive electrode active material.

At this time, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode 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, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one kind alone or a mixture of two or more kinds thereof may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% with respect to the total weight of the positive electrode active material layer.

And, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% with respect to the total weight of the positive electrode active material layer.

The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent or a solvent, on a positive electrode current collector, and then drying and rolling. At this time, the types and contents of the positive electrode active material, the binder and the conductive agent are as described above.

The solvent may be a solvent generally used in the relevant technical field, and may include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive electrode.

Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

Another embodiment of the present invention provides a lithium secondary battery including the positive electrode.

The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

The above lithium secondary battery may optionally further include a battery container that accommodates an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change 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., an aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and, like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. The negative electrode active material layer may be manufactured by, for example, applying a composition for forming a negative electrode active material layer comprising the negative electrode active material, and optionally a binder and a conductive material, onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then peeling the film from the support and laminating the resulting film onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. 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 alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these can be used. In addition, a metallic lithium thin film can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Representative examples of low-crystallization carbon include soft carbon and hard carbon, and representative examples of high-crystallization carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitch microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

The above binder and the conductive material may be the same as those described above for the anode.

The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator that is usually used as a separator in a lithium secondary battery, it can be used without any special restrictions, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, for example, 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, and an ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

The above electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents, such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethyl alcohol and isopropyl alcohol; nitriles, such as R-CN (wherein R represents a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane; and sulfolanes. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of improving the charge/discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. In this case, the cyclic carbonate and the chain carbonate can be mixed and used in a volume ratio of about 1:1 to about 1:9 to exhibit excellent electrolyte performance.

The above lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ . It is preferable to use the concentration of the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. In this case, the additives may be contained in an amount of 0.1 to 5 wt% with respect to the total weight of the electrolyte.

As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The above battery module or battery pack can 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.

Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

Example 1

(1) Manufacturing of positive electrode active material

(Mixed) A precursor having a composition of Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ and LiOH H ₂ O were introduced into a mixer and mechanically mixed so that the molar ratio of lithium to the transition metal of the precursor (Li/M) was 1.04 to 1.08 to form a mixture.

(1st firing) After that, the mixture was heated to 930°C through heat treatment in an air atmosphere, and then fired at a constant temperature of 930°C for 4 hours to form a 1st fired product.

(After crushing), the above primary calcined material was crushed using a rotor mill.

(Secondary calcination) Afterwards, the above-mentioned crushed primary calcined material was subjected to secondary calcination at a constant temperature of 930℃ for 10 hours in an oxygen atmosphere to form a lithium transition metal oxide in the form of single particles.

(2) Lithium secondary battery manufacturing

The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (carbon black, denka black): binder (PVDF, KF9700) = 95.0 : 2.0 : 3.0 wt%, and the viscosity was adjusted so that the solid content was approximately 60% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 20 ㎛ thick Al foil using a doctor blade, and then dry rolled. The electrode loading was 16.0 mg/cm ² , and the rolling density (25 ℃, 20 kN) was 3.5 g/cm ³ .

The electrolyte was 1 M LiPF ₆ in EC:DMC:DEC = 1:2:1 (vol%), with 2.0 vol% VC added to the total amount of the electrolyte. Coin cells were manufactured using a PP separator and a lithium anode (400 μm, Niba metal).

Comparative Example 1

In the manufacture of a cathode active material, a lithium transition metal oxide particle was formed by firing at a constant temperature of 930°C for 14 hours in the first firing step, and the subsequent processes of disintegration and second firing were not performed, except that the cathode active material was manufactured in the same manner as in Example 1. Thereafter, a lithium secondary battery was manufactured in the same manner as in Example 1.

Table 1 below summarizes the sintering process conditions of Example 1 and Comparative Example 1.

1st firing temperature
(℃) 1st firing time
(h) Second firing temperature
(℃) Second firing time
(h) Difference between 1st and 2nd firing temperatures (℃) Example 1 930 4 930 10 0 Comparative Example 1 930 14 - - -

Experimental Example 1: Observation of SEM images

SEM (scanning electron microscope) images of the positive electrode active materials manufactured according to the examples and comparative examples were observed, and are shown in FIGS. 1 and 2.

Referring to FIGS. 1 and 2, it was confirmed that the positive electrode active materials of Example 1 and Comparative Example 1 were in the form of single particles. In addition, it was confirmed that the positive electrode active material of Example 1 had many particles with a diameter of close to 4 um, whereas the positive electrode active material of Comparative Example 1 had few particles with a diameter of close to 4 um. Through this, it was confirmed that the single particle size growth of Example 1 was better than that of Comparative Example 1.

Experimental Example 2: Evaluation of Active Material Properties

The properties of the positive electrode active materials manufactured according to the examples and comparative examples were evaluated and are shown in Table 2 below.

(1) Entry evaluation

For the active material powder, the minimum particle diameter (Dmin), average particle diameter (D50), and maximum particle diameter (Dmax) were measured using the laser diffraction method.

(2) Evaluation of crystal grain size

For the positive electrode active materials manufactured according to the examples and comparative examples, the crystal grain size was measured by quantitative calculation using the Scherr equation, which can be estimated using the peak broadening of XRD data.

(3) Evaluation of the fine particle ratio of particle size less than 1 μm under 9 ton pressure

For the positive electrode active materials manufactured according to the examples and comparative examples, the fine particle ratio of particle diameters of 1 μm or less was evaluated after applying a pressure of 9 tons.

Dmin
(μm) D50
(μm) Dmax
(μm) Grain size
(nm) Differential ratio under 9ton pressure (%) Example 1 1.5 4.0 13.1 288 0.5 Comparative Example 1 1.5 4.0 11.0 288 1.8

Referring to Table 2, in the case of Example 1, where the first and second firings were performed, but the first firing time was shorter than the second firing time and the difference between the first and second firing temperatures was small, it was confirmed that the fine powder ratio under 9 ton pressure was small and thus the particle strength was excellent. In addition, it was confirmed that the Dmax of the active material was large, so that the size growth of the single particles occurred well, and accordingly, an improvement in the electrode energy density was expected.

On the other hand, in the case of Comparative Example 1, which was conducted only with primary firing, it was confirmed that the particle strength was inferior compared to Example 1 because the differential ratio under 9 ton pressure was relatively large. In addition, it was confirmed that the Dmax of the active material was smaller than in Example 1, so that the size growth of single particles was less.

Experimental Example 3: Evaluation of Lithium Secondary Battery Life Characteristics

The life characteristics of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated, and the results are shown in Table 3 below.

Specifically, the life characteristics were measured by performing 50 charge/discharge cycles at 45°C under the conditions of 0.5C charge and 1.0C discharge, and the capacity retention rate of the 50th cycle was measured compared to the first cycle.

Life characteristics (45℃ 50cycle, %) Example 1 94.4 Comparative Example 1 93.9

Referring to Table 3, it was confirmed that in the case of Example 1 with a small differential ratio under 9 ton pressure, the battery life characteristics were superior to those of Comparative Example 1.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications may be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, which also fall within the scope of the present invention.

Accordingly, the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (17)

A step of preparing a nickel-containing transition metal precursor;
A step of forming a mixture including the above transition metal precursor and lithium raw material and then performing a first firing to form a first fired product;
A step of crushing the above primary sintered material; and
Comprising a step of forming a lithium transition metal oxide in the form of single particles by secondary calcining the above-mentioned crushed primary calcined material,
A method for producing a positive electrode active material for a lithium secondary battery, wherein the absolute value of the difference between the first sintering temperature and the second sintering temperature is 30°C or less, and the second sintering time is longer than the first sintering time. In the first paragraph,
A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the first sintering temperature is higher than or equal to the second sintering temperature. In the first paragraph,
A method for producing a positive electrode active material for a lithium secondary battery, wherein the first sintering temperature and the second sintering temperature are each independently 900 to 950°C. In the third paragraph,
A method for manufacturing a cathode active material for a lithium secondary battery, wherein the sum of the first firing and second firing times performed within the above temperature range is 13 hours or longer. In the third paragraph,
A method for manufacturing a cathode active material for a lithium secondary battery, wherein the sum of the first firing and second firing times performed within the above temperature range is 13 to 17 hours. In the first paragraph,
A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the first firing time is 3 to 6 hours. In the first paragraph,
A method for producing a cathode active material for a lithium secondary battery, wherein the content of nickel in the above transition metal precursor is 50 to 70 mol% based on the total mole number of transition metals. In the first paragraph,
A method for producing a cathode active material for a lithium secondary battery, wherein the content of cobalt in the above transition metal precursor is 5 to 20 mol% based on the total mole number of transition metals. In the first paragraph,
The above lithium raw material is a method for manufacturing a cathode active material for a lithium secondary battery, wherein the cathode active material is Li ₂ CO ₃ . A cathode active material for a lithium secondary battery manufactured according to any one of the manufacturing methods of claims 1 to 9. In Article 10,
A cathode active material for a lithium secondary battery having a fine particle size of 1 μm or less of 1.2% or less after applying a pressure of 9 tons. In Article 10,
A cathode active material for a lithium secondary battery having a crystallite size of 200 nm or more. In Article 10,
A cathode active material for a lithium secondary battery having an average particle size (D50) of 3 μm or more. In Article 10,
A cathode active material for a lithium secondary battery having a maximum particle size (Dmax) of 12 μm or more. In Article 10,
A cathode active material for a lithium secondary battery represented by the following chemical formula 1:
[Chemical Formula 1]
Li _a [Ni _x Co _y Mn _z M _w ]O ₂
In the chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0.05≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof. A cathode for a lithium secondary battery comprising the cathode active material of claim 10. A lithium secondary battery comprising the positive electrode for a lithium secondary battery of claim 16.