Cathode active material for lithium secondary battery, method for manufacturing same and lithium secondary battery comprising same

Abstract

A cathode active material for a lithium secondary battery according to the present invention comprises: a lithium metal oxide in the form of a single particle; and a coating layer positioned on the surface of the lithium metal oxide, wherein the coating layer may comprise Al and W, and the cathode active material for a lithium secondary battery has excellent electrochemical performance due to improved discharge capacity and high-temperature lifespan.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same.

[0002] Driven by the recent explosive demand for electric vehicles and the need to increase driving range, the development of high-capacity, high-energy-density secondary batteries to meet these demands is actively underway worldwide.

[0003] To meet these demands, a technology utilizing a high-nickel NCM (nickel cobalt manganese) cathode material with a high nickel content has been proposed. Furthermore, to enhance the plate density of the electrode, a cell component, the material should be composed of a bimodal structure, blending large and small particles in a certain ratio.

[0004] However, the cathode material, which is composed of secondary particles in the form of aggregates of primary particles of sizes ranging from several tens of nm to several micrometers, has a large specific surface area of ​​the powder, resulting in a large area in contact with the electrolyte, which increases the possibility of gas generation and deteriorates the life characteristics.

[0005] To address this issue, a method has been proposed to manufacture cathode materials in the form of single particles with the primary particles maximized in size, rather than in the form of secondary particles formed by agglomeration of primary particles, i.e., multiparticles. Specifically, a method has been proposed to increase the size of the primary particles using a sintering agent or flux. However, this method has the problem of creating a rocksalt structure on the particle surface, which degrades the electrochemical performance of the cathode active material.

[0006] Therefore, there is a need to develop a cathode active material that can solve the problem of life degradation that occurs in high-nickel NCM cathode active materials by increasing the size of the primary particles, reducing the specific surface area, and increasing the strength of the particles.

[0007]

[0008] The present invention aims to provide a positive electrode active material for a lithium secondary battery having a single particle form and improved discharge capacity and high-temperature lifespan.

[0009] In addition, the present invention seeks to provide a lithium secondary battery with improved discharge capacity and high-temperature lifespan.

[0010]

[0011] A cathode active material for a lithium secondary battery according to one embodiment of the present invention may include a lithium metal oxide in the form of a single particle; and a coating layer positioned on the surface of the lithium metal oxide.

[0012] The above coating layer may include Al and W, and the content ratio of W to the Al content (W / Al) may be 1.5 or less (excluding 0), and the content ratio of W to the Al content (W / Al) may be 1.0 or less (excluding 0).

[0013] The content of each coating element included in the above coating layer may be 2000 ppm or less (excluding 0 ppm), and the content of each coating element included in the above coating layer may be 1500 ppm or less (excluding 0 ppm).

[0014] The above lithium metal compound may not have a titration equivalence point detected between pH 6.5 and 9.0 when neutralization titration is detected using a potentiometric titrator.

[0015] The above lithium metal oxide may contain 50 to 70 mol% of nickel based on the total mole number of transition metals.

[0016] A method for manufacturing a cathode active material for a lithium secondary battery according to one embodiment of the present invention may include the steps of: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; mixing the transition metal precursor and a lithium raw material and then calcining to obtain a lithium metal oxide; crushing the lithium metal oxide to obtain a lithium metal oxide in the form of single particles; and mixing the lithium metal oxide in the form of single particles and a coating raw material and then heat-treating to obtain a lithium metal oxide having a coating layer formed thereon.

[0017] The above coating raw material may include two or more selected from Al, W, Co, V, Ti, Nb, Ce, B, and P.

[0018] In the step of obtaining lithium metal oxide by mixing the lithium metal oxide in the form of single particles and the coating raw material and then performing heat treatment to form a coating layer, the heat treatment can be performed at a temperature of 350 to 450°C.

[0019] In the step of mixing the above transition metal precursor and lithium raw material and then calcining to obtain lithium metal oxide, the calcination can be performed at a temperature of 900 to 960°C.

[0020] After the step of mixing the lithium metal oxide in the form of single particles and the coating raw material and then heat-treating the mixture to obtain a lithium metal oxide with a coating layer formed, the step of crushing the obtained lithium metal oxide may be further included.

[0021] Another embodiment of the present invention can provide a positive electrode for a lithium secondary battery including the positive electrode active material for a lithium secondary battery.

[0022] Another embodiment of the present invention can provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0023]

[0024] The cathode active material for a lithium secondary battery according to the present invention has the advantage of having a single particle form, while improving the discharge capacity of a battery using the cathode active material, thereby exhibiting excellent electrochemical performance.

[0025] The cathode active material for a lithium secondary battery according to the present invention has the advantage of excellent electrochemical performance due to improved high-temperature lifespan of a battery using the cathode active material while having a single particle form.

[0026] In addition, the lithium secondary battery according to the present invention has the advantage of excellent electrochemical performance due to improved discharge capacity and high-temperature lifespan.

[0027]

[0028] In this specification, the terms first, second, and third, etc. are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, 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.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0030] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0031] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0032] 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 any one or more selected from the group consisting of said components.

[0033] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0034]

[0035] <Cathode active material for lithium secondary batteries>

[0036] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium metal oxide in the form of a single particle. Compared to conventional secondary particles, the single particle active material has a smaller specific surface area, which reduces the amount of gas generated by side reactions with the electrolyte. Furthermore, the single particle active material has a higher particle strength, which suppresses particle breakage during rolling, and reduces the occurrence of cracks during repeated charging and discharging. Accordingly, the single particle active material has superior lifespan and safety compared to secondary particles, and has the advantage of being able to realize a high energy density of the electrode.

[0037] In this specification, the term “single particle” is used to distinguish it from the secondary particle type positive electrode active material particle formed by the agglomeration of tens to hundreds of primary particles, which has been commonly 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. In addition, “secondary particle” means 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.

[0038] A cathode active material for a lithium secondary battery according to one embodiment of the present invention may include a lithium metal oxide in the form of a single particle; and a coating layer positioned on the surface of the lithium metal oxide.

[0039] The positive electrode active material for a lithium secondary battery according to the present invention may include two or more types of coating elements on the surface, and the coating elements may be two or more types selected from among Al, W, Co, V, Ti, Nb, Ce, B, and P.

[0040] By providing a coating layer including two or more types of coating elements as described above, there is an advantage in that the charge / discharge capacity of the battery can be improved and higher electrochemical stability, electrolyte resistance, and capacity retention can be provided.

[0041] The content of each coating element included in the above coating layer may be 2500 ppm or less, specifically 2000 ppm or less, more specifically 1500 ppm or less, and even more specifically 1400 ppm or less.

[0042] When the content of the element included in the coating layer satisfies the above range, there is an advantage in that both discharge capacity and high-temperature lifespan can be improved simultaneously. When the content is less than the above range, the effect of improving battery discharge capacity is minimal, and when the content exceeds the above range, there is a problem in that the effect of improving high-temperature lifespan is minimal.

[0043]

[0044] Meanwhile, the coating layer may include Al and W. The content ratio of W to the Al content (W / Al) may be less than 2.0, specifically 1.5 or less (excluding 0), and more specifically 1.0 or less (excluding 0).

[0045] When the value of the W content ratio (W / Al) to the above Al content satisfies the above range, there is an advantage in that the effects of improved discharge capacity and improved high-temperature lifespan can be obtained. When the above content ratio is exceeded, there is a problem in that the effect of improving high-temperature lifespan is reduced due to the formation of unstable LiWOx at the interface.

[0046]

[0047] The cathode active material for a lithium secondary battery according to the present invention may not detect a titration point within a pH range of 6.5 to 9.0 when detecting neutralization titration using a potentiometric titrator. Specifically, the titration point may be detected only at a pH of 9.0 or higher and less than 6.5. More specifically, the titration point may not be detected within a pH range of 6.5 to 8.5.

[0048] From this, it can be seen that most of the residual lithium (Li) on the surface of the positive electrode active material for a lithium secondary battery according to the present invention exists as LiOH or Li2CO3.

[0049]

[0050] Meanwhile, the lithium metal oxide according to one embodiment of the present invention contains 50 to 70 mol% of nickel based on the total mole number of transition metals. Conventional NCM (nickel-cobalt-manganese ternary) cathode active materials have attempted to implement high capacity of batteries by increasing the nickel content, but if the nickel content is too high, there may be a thermal propagation issue, i.e., a thermal safety problem, and the high nickel price may increase the manufacturing cost. Therefore, the lithium metal oxide according to the present invention has the nickel content adjusted to the above range in order to secure appropriate capacity and thermal safety characteristics while implementing economic feasibility.

[0051] However, in order to manufacture lithium metal oxide in the form of single particles, the sintering temperature is higher than that in the case of secondary particles, so there is a problem that the capacity characteristics are inherently lower than those of secondary particles.

[0052] The above lithium metal oxide can be more specifically represented by the following chemical formula 1.

[0053] [Chemical Formula 1]

[0054] Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2

[0055] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.2, 0≤z≤0.4, 0 <w1<0.03, 0<w2<0.03이고, x+y+z+w1+w2=1이고, M1 및 M2는 상이한 원소이고, M1 및 M2는 Al, W, Co, V, Ti, Nb, Ce, B 및 P 중 선택되는 1종 이상을 포함할 수 있다.

[0056] In the lithium metal oxide of the above chemical formula 1, lithium may be included in an amount 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 control of the lithium content and the sinterability balance during the production of the active material, the lithium may be included in an amount of 0.9≤a≤1.1 more preferably.

[0057] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 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.

[0058] In the lithium metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.2 or 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.

[0059] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0≤z≤0.4 or 0.1≤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.

[0060] In the lithium metal oxide of the above chemical formula 1, M1 and M2 correspond to contents corresponding to w1 and w2, respectively, i.e., 0 <w<0.03으로 포함될 수 있다.

[0061]

[0062] <Method for manufacturing positive electrode active material for lithium secondary batteries>

[0063] A method for manufacturing a cathode active material for a lithium secondary battery according to another embodiment of the present invention may include the steps of: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; mixing the transition metal precursor and a lithium raw material and then calcining to obtain a lithium metal oxide; crushing the lithium metal oxide to obtain a lithium metal oxide in the form of single particles; and mixing the lithium metal oxide in the form of single particles and a coating raw material and then heat-treating to obtain a lithium metal oxide having a coating layer formed thereon.

[0064] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described in detail.

[0065] First, a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals is prepared.

[0066] The above transition metal precursor may be a transition metal hydroxide.

[0067] The above transition metal hydroxide may be manufactured by, for example, adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution including a nickel raw material and optionally a cobalt raw material or a manganese raw material, and performing a co-precipitation reaction.

[0068] 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 NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide or a combination thereof, but is not limited thereto.

[0069] 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, CoSO 4, It may be, but is not limited to, CoSO4ㆍ7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O or a combination thereof.

[0070] The manganese raw material is not particularly limited as long as it is used in the art for manufacturing a precursor of a cathode active material. 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 MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylic acid salt, manganese citrate, and manganese fatty acid salt, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0071] 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.

[0072] The above complexing agent-containing solution performs the function of forming a complex, and may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof as the complexing agent. 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 the solvent.

[0073] The above pH adjusting agent-containing solution acts as a precipitant or pH adjusting agent, and may include an alkaline compound such as a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. Meanwhile, the pH adjusting agent-containing solution may also 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 the solvent. At this time, the pH adjusting agent-containing solution may be added in an amount such that the pH of the reaction solution becomes 11 to 13.

[0074] The above coprecipitation reaction can be performed under an inert atmosphere such as nitrogen or argon, can be performed at a temperature of 30 to 70°C, and can be performed at a pH of 11 to 13.

[0075] Through the above process, nickel-cobalt-manganese (doped element) hydroxide particles are generated and precipitated within the reaction solution. The precipitated precursor particles can be separated, washed, and dried using conventional methods to obtain the precursor. The precursor may be a secondary particle formed by the agglomeration of primary particles.

[0076] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by controlling the concentration of nickel raw material, cobalt raw material, and manganese raw material.

[0077] Accordingly, the content of nickel in the transition metal precursor may be 50 to 70 mol% based on the total mole number of transition metals. The technical significance of controlling the content of nickel in the transition metal precursor is as described above and therefore is omitted.

[0078]

[0079] Next, the above transition metal precursor and lithium raw material are mixed and then calcined to obtain lithium metal oxide. Specifically, lithium metal oxide can be obtained through primary calcination and secondary calcination.

[0080] In the past, the formation of lithium metal oxide in the form of single particles was achieved by only performing a primary calcination at high temperature for a long time. However, this method had problems such as a decrease in the electrochemical properties of the active material due to nickel cation mixing and the formation of rock salt impurities caused by over-calcination. On the other hand, the manufacturing method according to the present invention can prevent the above problems by performing the calcination in two stages, and has the advantage of increasing particle strength and increasing production volume.

[0081] At this time, the atmosphere during the first firing is not particularly limited. For example, it can be performed in an air or oxygen (O2) atmosphere, but more specifically, it can be performed in an air atmosphere. Since the layered crystal structure of a high-nickel cathode active material does not form well when performed in an air atmosphere, a significant deterioration in electrochemical characteristics occurs, so it is generally performed in an oxygen atmosphere. On the other hand, when the nickel content is relatively low as in the present invention, even if the firing is performed in an air atmosphere, a significant deterioration in electrochemical characteristics does not occur, and the process cost can be reduced.

[0082] In particular, the secondary firing is performed in an air atmosphere. The primary firing and the secondary firing may each be independently performed at a temperature of 900 to 960°C. If the primary firing and secondary firing temperatures are too low, lithium metal oxide in the form of single particles may not be easily formed. If the primary firing and secondary firing temperatures are too high, over-firing may occur, which may deteriorate electrochemical characteristics such as capacity.

[0083] The above first firing can be performed for 2 to 6 hours. If the first firing time is too short, there may be a problem in which lithium ions are not fully inserted into the precursor, and if the first firing time is too long, there may be a problem in which productivity is reduced due to difficulty in disintegration due to over-firing.

[0084] The above secondary firing can be performed for 7 to 14 hours. If the secondary firing time is too short, the shape of a single particle may not be completely formed, and there may be a problem of poor electrochemical performance due to insufficient annealing time for a layered structure. If the secondary firing time is too long, the problem of capacity reduction due to over-firing may occur.

[0085] When the secondary firing is performed within the temperature and time ranges described above, it is preferable because the crystal structure of the positive electrode active material can be stabilized. In addition, the lithium byproduct remaining on the surface of the metal oxide is decomposed by heat and diffuses into the metal oxide, thereby reducing the amount of lithium remaining on the surface. In addition, the lithium ions react with the surface of the metal oxide to form a stable layered structure, thereby stabilizing the surface structure of the metal oxide surface, thereby improving the resistance characteristics and life characteristics of the battery, which is preferable.

[0086] A method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention includes a step of crushing a lithium metal oxide to obtain a lithium metal oxide in the form of single particles.

[0087] The above-mentioned disintegration can be performed after cooling the calcined lithium metal oxide to 50 to 200°C. Cooling to the above-mentioned cooling temperature can suppress the reaction between external moisture and the calcined material and suppress the increase of residual lithium.

[0088] The above disintegration can be performed by a method commonly performed in the art.

[0089] The above-mentioned disintegration can be performed using, for example, a rotor mill, a jet mill, a ball mill, a pin mill, a jet mill, a bead mill, or a roll mill, but is not limited thereto.

[0090]

[0091] A method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention includes a step of mixing the obtained lithium metal oxide with a coating raw material and performing heat treatment to form a coating layer.

[0092] The step of mixing the lithium metal oxide with a coating raw material and performing heat treatment to form a coating layer may specifically use a coating raw material including two or more selected from Al, W, Co, V, Ti, Nb, Ce, B, and P. The coating raw material may specifically be two or more coating raw materials each including different types of coating elements. More specifically, it may be a coating raw material including Al and W, and even more specifically, it may be a mixture of an Al coating raw material including Al and a W coating raw material including W. The coating raw material is not particularly limited as long as it can form the desired coating layer in the present invention.

[0093] The above coating raw material can be mixed in an amount and a mixing ratio depending on the positive electrode active material desired in the present invention. Since the content and ratio of the coating element have been specifically described above, they are omitted here.

[0094] The step of mixing the lithium metal oxide with the coating raw material and heat-treating it to form a coating layer can be performed at a temperature of 350 to 450°C and can be performed for 1 to 12 hours, but is not limited thereto.

[0095] When a coating layer is formed within the above heat treatment temperature range, there is an advantage in that the coating layer can be formed stably while controlling the occurrence of side reactions of surface residual lithium, thereby realizing excellent discharge capacity and high-temperature lifespan.

[0096] After forming the above coating layer, a further step of crushing may be included.

[0097] The above dissolution may be applied to the aforementioned contents.

[0098] According to another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery can be used to manufacture the positive electrode active material for a lithium secondary battery.

[0099] The cathode active material for the manufactured lithium secondary battery has been described in detail above, so it is omitted here.

[0100]

[0101] Bipolar

[0102] In another embodiment of the present invention, a positive electrode is provided, which includes a current collector and a positive electrode active material layer positioned on at least one surface of the current collector.

[0103] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as described above. Therefore, a detailed description of the positive electrode active material will be omitted.

[0104] The above-mentioned collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0105] Meanwhile, the positive electrode active material layer may include a binder and a conductive material.

[0106] At this time, the binder plays a role of improving 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% based on the total weight of the positive electrode active material layer.

[0107] 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 any 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. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0108] 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.

[0109] 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, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0110] The solvent may be a solvent generally used in the relevant technical field, such as 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 when applied thereafter for manufacturing the positive electrode.

[0111] 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.

[0112] The structure and manufacturing method of the positive electrode are not limited in the present invention.

[0113]

[0114] Lithium secondary battery

[0115] In another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

[0116] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0117] In the above lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0118] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., 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, a non-woven fabric, etc.

[0119] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by 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 laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0120] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may 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 comprising 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 may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0121] The above binder and conductive material may be the same as those described above for the positive electrode.

[0122] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, and mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0123] In addition, in the lithium secondary battery, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0124] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0125] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. 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; 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 is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. 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 that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0126] The lithium salt may 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 LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0127] The structure and manufacturing method of the battery are not limited in the present invention.

[0128]

[0129] 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).

[0130]

[0131] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0132] Example 1

[0133] (Manufacturing of positive electrode active materials)

[0134] (Mixed) Ni 0.6 Co 0.1 Mn 0.3 Li2CO3 was introduced into a mixer and mechanically mixed to form a mixture so that the molar ratio of lithium to the precursor of (OH)2 composition and the transition metal of the precursor (Li / M) was 1.07.

[0135] (Sintering and crushing) After that, the mixture was heated to 940℃ through heat treatment in an air atmosphere, and then first fired at a constant temperature of 940℃ for 4 hours, and then naturally cooled. Thereafter, the first fired product was crushed using a rotor mill. Then, the crushed first fired product was secondarily fired at a constant temperature of 940℃ for 10 hours in an air atmosphere, and then naturally cooled to form lithium metal oxide. The lithium metal oxide was crushed using a Jet-Mill to form lithium metal oxide in the form of single particles.

[0136] The composition of the finally obtained lithium metal oxide in the form of single particles is Li 1.07 Ni 0.6 Co 0.1 Mn 0.3 It was O2.

[0137] (Coating) Al(OH)3 (or Al2O3) and WO3 were uniformly mixed with the lithium metal oxide in the single particle form at the equivalent ratio of Al and W described in Example 1 in Table 1 below, and placed in a crucible, followed by heat treatment at 400°C for 6 hours in an RHK kiln with oxygen flowing in, to produce a cathode active material coated with Al and W. Thereafter, the cathode active material in the single particle form was pulverized using ACM to produce a cathode active material having an Al and W coating layer formed thereon.

[0138]

[0139] (Lithium secondary battery manufacturing)

[0140] 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 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading was 16.0 mg / cm 2 and the rolling density (25 ℃, 20 kN) was 3.5 g / cm 3 It was.

[0141] The electrolyte was 1M LiPF6in EC:DMC:DEC=1:2:1 (vol%), with 2.0 vol% VC added to the total amount of the electrolyte, and a coin cell was manufactured using a PP separator and a lithium negative electrode (400 μm, Niba metal).

[0142]

[0143] (2) Comparative examples 1 to 4

[0144] A positive electrode active material and a coin cell were manufactured in the same manner as in Example 1, except that the coating element content was adjusted as shown in Table 1 below.

[0145]

[0146] Experimental Example 1: SEM image of positive electrode active material

[0147] SEM images of the positive electrode active materials manufactured according to the examples and comparative examples were observed and are shown in Figs. 1 to 5, respectively.

[0148] Referring to FIGS. 1 to 5, it was confirmed that the positive electrode active materials of the examples and comparative examples had a single particle form.

[0149]

[0150] Experimental Example 2: Equivalence Point (EP) of Positive Electrode Active Material

[0151] The appropriate equivalence point (EP) was confirmed from the differential curve (dpH / Dv) of the positive electrode active material manufactured according to the examples and comparative examples.

[0152] Specifically, potentiometric titration was performed using (Mettler Toledo equipment).

[0153] 0.1 M HCl was added dropwise at a rate of 0.05 mL / sec until the added 0.1 M HCl solution reached 15 mL. The equivalence point (EP) of the cathode active material for a lithium secondary battery according to the present invention was determined using a differential curve (dpH / dV, where V is the volume of the 0.1 M HCl solution).

[0154] Table 1 below summarizes the content and equivalence point of each coating element in the above examples and comparative examples.

[0155] Coating element titration equivalence point (EP)Al (ppm)W (ppm)W / AlInitial pH1st peak pH2nd peak pH3rd peakpHComparative example 114000-11.5 8.9-5.7Comparative example 21400 2800 2.01 1.49 77.45.1Comparative example 31400 4200 3.01 1.49 87.64.8Comparative example 40 2800-11.6 9.07.25.1Example 11400 1400 1.01 1.7 9.7-5.5

[0156] Refer to Table 1 above

[0157] In the case of Example 1, Al and W are each included as coating elements at 1400 ppm, the content ratio of W to Al (W / Al) is 1, and the pH is 2 between pH 6.5 and 9.0. nd It was confirmed that no peak (equivalence point) occurred. On the other hand, Comparative Examples 2 to 4 showed 2 peaks between pH 6.5 and 9.0. nd It can be confirmed that a peak (titration equivalence point) is observed.

[0158]

[0159] Experimental Example 3: Coin Cell Manufacturing and Capacity Evaluation

[0160] (Evaluation of initial capacity and initial efficiency)

[0161] After fabricating a lithium secondary battery half-cell, it was aged at 25°C for 12 hours and then subjected to a charge-discharge test at 25°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.4 V at a constant current of 0.1 C. After switching to a constant voltage, the battery was charged until the end current reached 0.05 C. After a 10-minute rest period, the battery was discharged at a constant current of 0.1 C, using the reference capacity of 200 mAh / g, until the battery reached 2.5 V.

[0162]

[0163] (Evaluation of high-temperature life characteristics (high-temperature capacity retention rate) (45℃, 50 cycles))

[0164] After fabricating a lithium secondary battery half-cell, it was charged to 4.4 V at a constant current of 0.5 C at 45°C, then switched to constant voltage and charged until the end current reached 0.05 C. After a 10-minute rest period after charging, it was discharged at a constant current of 1.0 C until the voltage reached 2.5 V. Under these charge-discharge cycle conditions, 50 charge-discharge cycles were performed, and the capacity retention rate of the 50th cycle was calculated compared to the first cycle.

[0165] 0.1C / 0.1C Initial Cycle Discharge(mAh / g)high temperature (45℃)test,(Retention @50 소 ) Comparative Example 1194.595.70% Comparative Example 2195.794.80% Comparative Example 3195.294.80% Comparative Example 4195.694.30% Example 1195.395.54%

[0166] Referring to Table 2 above, it can be seen that when the positive electrode active material for a lithium secondary battery according to Example 1, which satisfies the conditions such as the content and ratio of the coating elements of the present invention, is used, both the initial discharge capacity and high-temperature life characteristics are excellent.

[0167] On the other hand, it can be confirmed that Comparative Examples 1 to 4, in which the content and ratio of coating elements are outside the scope of the present invention, have lower initial discharge capacity or high-temperature life characteristics compared to the examples.

[0168]

[0169] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Lithium metal oxide in the form of single particles; and A coating layer positioned on the surface of the lithium metal oxide; The above coating layer contains Al and W, Cathode active material for lithium secondary batteries.

2. In paragraph 1, The W content ratio (W / Al) to the above Al content is 1.5 or less (excluding 0). Cathode active material for lithium secondary batteries.

3. In paragraph 2, The content ratio of W to the above Al content (W / Al) is 1.0 or less (excluding 0). Cathode active material for lithium secondary batteries.

4. In paragraph 1, The content of each coating element included in the above coating layer is 2000 ppm or less (excluding 0 ppm). Cathode active material for lithium secondary batteries.

5. In paragraph 4, The content of each coating element included in the above coating layer is 1500 ppm or less (excluding 0 ppm). Cathode active material for lithium secondary batteries.

6. In paragraph 1, The lithium metal oxide is such that the titration equivalence point is not detected between pH 6.5 and 9.0 when neutralization titration is detected using a potentiometric titrator. Cathode active material for lithium secondary batteries.

7. In paragraph 1, The above lithium metal oxide contains 50 to 70 mol% of nickel based on the total mole number of transition metals. Cathode active material for lithium secondary batteries.

8. A step of preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; A step of mixing the above transition metal precursor and lithium raw material and then calcining to obtain lithium metal oxide; A step of crushing the lithium metal oxide to obtain a lithium metal oxide in the form of single particles; and A step of mixing the lithium metal oxide in the form of single particles and the coating raw material, and then performing heat treatment to obtain a lithium metal oxide having a coating layer formed thereon; The above coating raw material contains two or more selected from Al, W, Co, V, Ti, Nb, Ce, B and P. A method for manufacturing a cathode active material for a lithium secondary battery.

9. In paragraph 8, In the step of obtaining lithium metal oxide by mixing the lithium metal oxide and coating raw materials in the form of single particles and then heat-treating them to form a coating layer, The above heat treatment is performed at a temperature of 350 to 450°C. A method for manufacturing a cathode active material for a lithium secondary battery.

10. In paragraph 8, In the step of mixing the above transition metal precursor and lithium raw material and then calcining to obtain lithium metal oxide, The above firing is performed at a temperature of 900 to 960°C. A method for producing a positive electrode active material for a lithium secondary battery.

11. In paragraph 8, After mixing the lithium metal oxide and coating raw material in the form of single particles and performing heat treatment to form a coating layer, a step of obtaining lithium metal oxide is performed. It further comprises a step of crushing the lithium metal oxide obtained above. A method for producing a positive electrode active material for a lithium secondary battery.

12. A lithium secondary battery comprising a positive electrode active material according to any one of claims 1 to 7. Cathode for lithium secondary batteries.

13. Containing the positive electrode for a lithium secondary battery of Article 12, Lithium secondary battery.