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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising a layered lithium transition metal oxide that contains an excess of lithium and manganese and consists of secondary particles formed by aggregating a plurality of primary particles, wherein the primary particles include plate-shaped particles and have an average aspect ratio of 5-90.

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 comprising the same, and more specifically, to a positive electrode active material for a lithium secondary battery having an excess of lithium and manganese, a method for producing the same, and a lithium secondary battery comprising the same.

[0002]

[0003] As the scope of application of lithium secondary batteries expands from small electronic devices to electric vehicles and power storage devices, the demand for cathode materials with excellent high energy density and high output characteristics is increasing.

[0004] In this regard, lithium and manganese-rich layered lithium transition metal oxides have a very high capacity of over 240 mAh / g and are attracting attention as candidates for next-generation cathode active materials, and research on them is actively being conducted recently.

[0005] However, lithium and manganese-rich lithium transition metal oxides inherently have a lower true density of the active material itself than conventional cathode materials due to the high lithium content and relatively low transition metal ratio in the structure, and the crystal growth direction varies depending on the composition of the material, so the particle packing is not dense. More specifically, lithium and manganese-rich lithium transition metal oxides have low tap density and electrode density even when secondary particles are formed due to plate-like crystal growth caused by the high manganese content. Therefore, even if the capacity characteristics of the cathode material itself are excellent, there was a limit to increasing the energy density of the electrode when applied to an actual battery.

[0006] Furthermore, lithium- and manganese-rich lithium transition metal oxides utilize oxygen redox reactions in addition to transition metals, making it easy for oxygen on the surface or within the bulk to evolve into oxygen gas. This can easily lead to the formation of dense, non-reactive or low-reactivity spinel / rock salt structures within the particles, which may adversely affect high-power characteristics compared to conventional cathode materials. Furthermore, the surface reactivity in the oxygen redox region is very sensitive to the overall capacity development, so if the particles are made too dense and the tap density becomes excessively high, problems with the power characteristics may occur.

[0007]

[0008] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery, which is a lithium transition metal oxide with an excess of lithium and manganese, capable of improving both battery energy density and output characteristics, a method for producing the same, and a lithium secondary battery including the same.

[0009]

[0010] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a layered lithium transition metal oxide containing an excess of lithium and manganese, wherein the secondary particles are formed by agglomeration of a plurality of primary particles, the primary particles include plate-shaped particles, and have an average aspect ratio of 5 to 90.

[0011] The above lithium transition metal oxide may have a molar ratio of lithium to transition metal (Li / Me) of greater than 1 and a molar ratio of manganese to transition metal (Mn / Me) of 0.55 or more.

[0012] The above lithium transition metal oxide may have a molar ratio of lithium to transition metal (Li / Me) of 1.985 or less.

[0013] The above lithium transition metal oxide may have a molar ratio of nickel to transition metal (Ni / Me) of 0.2 to 0.4.

[0014] The above-mentioned positive electrode active material for a lithium secondary battery may have a tap density of 1.5 to 2.3 g / cc.

[0015] The above-mentioned positive electrode active material for a lithium secondary battery has a BET specific surface area of ​​0.5 to 4 m 2 / g may be.

[0016] The average thickness of the above primary particles may be 500 nm or less.

[0017] The average particle diameter (D50) of the above secondary particles may be 3 to 15 μm.

[0018] The above lithium transition metal oxide can be represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li 1+a (Mn x M y ) 1-a O2

[0021] In the above chemical formula 1, 0 <a≤0.33, 0.55≤x<1, 0<y≤0.45 이고, x+y = 1이고, M은 Ni, Co, V, Cr, Fe, Ru, Ir 또는 이들의 조합이다.

[0022]

[0023] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, the method comprising the steps of: preparing a transition metal hydroxide containing manganese in which a molar ratio of manganese to the transition metal (Mn / Me) is 0.55 or more; forming a mixture including the transition metal hydroxide and a lithium raw material such that a molar ratio of lithium to the transition metal (Li / Me) is 1.3 or more, and then calcining the mixture to form a lithium transition metal oxide, wherein the lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the primary particles include plate-shaped particles and have an average aspect ratio of 10 to 90.

[0024] The step of preparing the above transition metal hydroxide includes: a step of forming a transition metal-containing solution including a manganese raw material and other transition metal raw materials; a step of introducing the transition metal-containing solution, a complexing agent-containing solution, and a pH adjusting agent-containing solution into a reactor to form an initial reaction solution; and a step of performing a co-precipitation reaction on the initial reaction solution to form a transition metal hydroxide. In the step of forming the initial reaction solution, the complexing agent concentration of the complexing agent-containing solution may be 0.4 to 1.6 mol%.

[0025] In the step of forming the initial reaction solution, the pH of the initial reaction solution may be 9.6 to 11.

[0026] In the step of forming the lithium transition metal oxide, the calcination can be performed at a temperature of 700 to 1000°C.

[0027]

[0028] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the positive electrode comprises the positive electrode active material described above.

[0029]

[0030] A cathode active material for a lithium secondary battery according to one embodiment of the present invention contains lithium and manganese in excess, and can satisfactorily improve both battery energy density and output characteristics by controlling the aspect ratio of primary particles.

[0031]

[0032] Figure 1 is a SEM image of a positive electrode active material manufactured according to Example 1.

[0033] Figure 2 is a SEM image of a positive electrode active material manufactured according to Example 2.

[0034] Figure 3 is an SEM image of a positive electrode active material manufactured according to Comparative Example 1.

[0035] Figure 4 is an SEM image of a positive electrode active material manufactured according to Comparative Example 2.

[0036] Figure 5 is an SEM image of a positive electrode active material manufactured according to Comparative Example 3.

[0037] 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 used solely 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0042] 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.

[0043] 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.

[0044]

[0045] 1. Positive active material

[0046] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a layered lithium transition metal oxide containing an excess of lithium and manganese, wherein the secondary particles are formed by agglomeration of a plurality of primary particles, the primary particles include plate-shaped particles, and have an average aspect ratio of 5 to 90.

[0047] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery is a layered lithium transition metal oxide containing excess lithium and manganese. Specifically, the lithium transition metal oxide may have a molar ratio of lithium to transition metal (Li / Me) of greater than 1 and a molar ratio of manganese to transition metal (Mn / Me) of 0.55 or greater.

[0048] As the lithium transition metal oxide contains an excess of lithium and manganese, the initial discharge capacity can be 240 mAh / g or more, and the capacity characteristics can be significantly improved compared to the cathode material of the conventional NCM composition.

[0049] More specifically, the lithium transition metal oxide may have a molar ratio of lithium to transition metal (Li / Me) of greater than 1, more specifically 1.1, 1.2, or 1.3 or greater, and 1.985 or less or 1.6 or less. The larger the molar ratio of lithium to transition metal, the better the capacity characteristics. However, if it is too large, a problem of phase stability due to oxygen oxidation / reduction may occur, which may result in a problem of significantly deteriorating the life characteristics.

[0050]

[0051] However, lithium transition metal oxides containing excessive lithium and manganese generally have primary particle shapes that grow into platelets due to the high manganese content. This shape results in low tap density even when secondary particles are formed, and consequently, low electrode density. If the electrode density is low like this, even if the capacity characteristics of the cathode material itself are excellent, the energy density of the electrode is low.

[0052] In addition, since lithium transition metal oxides containing excess lithium and manganese utilize oxygen redox reactions in addition to transition metals, oxygen on the surface or in the bulk is easily generated as oxygen gas, which can easily form spinel / rock salt structures within the particles, which causes a problem of deterioration in high-power characteristics compared to cathode materials with a typical NCM composition. In addition, when the tap density is increased by making the particles denser in order to increase the energy density of the electrode, the output characteristics may deteriorate due to the surface reaction in the oxygen redox section.

[0053] That is, when lithium and manganese-excess lithium transition metal oxides are applied as cathode materials, the energy density characteristics of the electrode and the battery output characteristics are in a trade-off relationship.

[0054] The inventors of the present invention have completed the present invention by recognizing that it is important to appropriately control the average aspect ratio of primary particles in order to appropriately improve both electrode energy density and battery output characteristics.

[0055]

[0056] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is a secondary particle formed by agglomeration of a plurality of primary particles, wherein the primary particles include plate-shaped particles.

[0057]

[0058] In particular, the average aspect ratio of the primary particles may be 5 to 90, and more specifically, 10 to 80. If the average aspect ratio of the primary particles is too large, the tap density and electrode density of the active material may be too low, resulting in a low battery energy density. If the average aspect ratio of the primary particles is too small, the tap density and battery energy density may be good, but the output characteristics of the battery may deteriorate due to surface reactions in the oxygen oxidation-reduction zone.

[0059] In this specification, “average aspect ratio of primary particles” may be the ratio of the length to the thickness of plate-shaped primary particles (length / ratio), and the length is the diameter of the plane formed by the plate-shaped primary particles, and when the longest and shortest lengths of the plane formed by the primary particles are different, it may mean the longest length.

[0060] And, the above average aspect ratio can be measured by quantifying the SEM image using a segmentation imaging technique.

[0061] In addition, the average thickness of the primary particles may be 500 nm or less, and more specifically, 160 to 500 nm, 180 to 450 nm. If the average thickness of the primary particles is too large, the output characteristics may deteriorate. If the average thickness of the primary particles is too small, the battery energy density may deteriorate. In the present specification, the average thickness of the primary particles can be measured through the same image analysis technique as described above.

[0062]

[0063] The above-described positive electrode active material for a lithium secondary battery may have a tap density of 1.5 to 2.3 g / cc, more specifically, 1.5 to 2.2 g / cc. When the tap density of the active material satisfies the above range, both the energy density of the electrode and the battery output characteristics can be well implemented. More specifically, if the tap density of the active material is too low, the battery energy density may be low, and if the tap density of the active material is too high, the battery output characteristics may deteriorate.

[0064] In this specification, tap density can be measured by a method commonly used in the art for measuring the degree of filling of a sample per unit volume. For example, it can be the density (sample weight / volume) calculated from the change in volume after a measuring container containing a sample is mechanically dropped (tapped) from a fixed height a fixed number of times in accordance with the measuring equipment and method specified in ASTM B527.

[0065]

[0066] The above-mentioned positive electrode active material for a lithium secondary battery has a BET specific surface area of ​​0.5 to 4 m 2 / g may be, more specifically, 2 to 4 m 2 / g or 2.5 to 4 m 2 / g. If the specific surface area of ​​the positive electrode active material is too small, there may be a problem of capacity reduction due to decreased activity of oxygen oxidation / reduction reaction, and if the specific surface area of ​​the positive electrode active material is too large, there may be a problem of reduced output and cycle characteristics due to the formation of a surface spinel structure caused by increased side reactions with the electrolyte at high voltage.

[0067] In this specification, the specific surface area of ​​the active material can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020) for the active material powder.

[0068]

[0069] Meanwhile, the lithium transition metal oxide may have a molar ratio of nickel to transition metal (Ni / Me) of 0.2 to 0.4. When the molar ratio of nickel to transition metal satisfies the above range, the aforementioned battery performance improvement effect can be more preferably implemented.

[0070]

[0071] Additionally, the average particle diameter (D50) of the secondary particles may be 3 to 15 μm.

[0072] In this specification, the average particle diameter (D50) can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter (D50) can be measured using, for example, the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0073]

[0074]

[0075] The lithium transition metal oxide can be more specifically represented by the following chemical formula 1.

[0076] [Chemical Formula 1]

[0077] Li 1+a (Mn x M y ) 1-a O2

[0078] In the above chemical formula 1, 0 <a≤0.33, 0.55≤x<1, 0<y≤0.45 이고, x+y = 1이고, M은 Ti, Nb, Mo, Sn, Ta, W, Ni, Co, V, Cr, Fe, Ru, Ir, Zr, Al, B, Y 또는 이들의 조합이다.

[0079] In the lithium transition metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to 1+a. In this case, a is 0 <a≤0.33 범위를 만족하는데, a가 너무 작으면 용량 특성이 저하될 수 있고, a가 너무 크면 산소 산화 / 환원 이용에 따른 상안정성의 문제가 발생하며, 이로 인해 수명특성이 매우 저하되는 문제가 있을 수 있다.

[0080] In the lithium transition metal oxide of the above chemical formula 1, manganese may be included in an amount corresponding to x, i.e., 0.55≤x<1. When the amount of manganese is sufficiently large, the capacity characteristics may be improved.

[0081] In the lithium transition metal oxide of the above chemical formula 1, the other transition metals have an amount corresponding to y, i.e., 0 <y≤0.45로 포함될 수 있다. 이때, 상기 전이금속은 Ti, Nb, Mo, Sn, Ta, W, Ni, Co, V, Cr, Fe, Ru, Ir, Zr, Al, B, Y 또는 이들의 조합일 수 있다.

[0082]

[0083] 2. Method for manufacturing positive electrode active material

[0084] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, the method comprising the steps of: preparing a transition metal hydroxide containing manganese in which a molar ratio of manganese to the transition metal (Mn / Me) is 0.55 or more; forming a mixture including the transition metal hydroxide and a lithium raw material such that a molar ratio of lithium to the transition metal (Li / Me) is 1.3 or more, and then calcining the mixture to form a lithium transition metal oxide, wherein the lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the primary particles include plate-shaped particles and have an average aspect ratio of 10 to 90.

[0085] Hereinafter, a method for manufacturing a positive electrode active material according to another embodiment of the present invention will be described in detail step by step.

[0086]

[0087] First, prepare a transition metal hydroxide containing manganese having a molar ratio of manganese to transition metal (Mn / Me) of 0.55 or more.

[0088] The step of preparing the above transition metal hydroxide may more specifically include a step of forming a transition metal-containing solution including a manganese raw material and other transition metal raw materials; a step of introducing the transition metal-containing solution, a complexing agent-containing solution, and a pH adjusting agent-containing solution into a reactor to form an initial reaction solution; and a step of performing a coprecipitation reaction on the initial reaction solution to form a transition metal hydroxide.

[0089] In particular, the aspect ratio of the primary particles can be obtained differently by adjusting the amount and concentration of the complexing agent-containing solution and the pH regulator-containing solution and the pH of the initial reaction solution, and through appropriate adjustment of these, the aspect ratio of the primary particles in the lithium transition metal oxide can be easily obtained within the range according to the present invention.

[0090] More specifically, in the step of forming the initial reaction solution, the complexing agent concentration of the complexing agent-containing solution may be 0.4 to 1.6 mol%. In addition, in the step of forming the initial reaction solution, the pH of the initial reaction solution may be 9.6 to 11. By controlling the conditions of the co-precipitation process, the aspect ratio of the primary particles in the lithium transition metal oxide can be appropriately obtained within the range according to the present invention.

[0091] 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.

[0092] The above other transition metal raw materials may include, but are not limited to, nickel raw materials or cobalt raw materials, for example.

[0093] 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.

[0094] 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.

[0095] The above transition metal-containing solution may be prepared by adding manganese raw materials and other transition metal raw materials 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] Through the above process, particles of manganese and other transition metal element hydroxides are generated and precipitated within the reaction solution. The precipitated precursor particles can be separated using conventional methods, washed, and dried to obtain the precursor. The precursor may be a secondary particle formed by the agglomeration of primary particles.

[0100] At this time, the molar ratio of manganese and other transition metals in the precursor can be controlled by controlling the concentration of the manganese raw material and other transition metal raw materials.

[0101]

[0102] Next, a mixture containing the transition metal hydroxide and the lithium raw material is formed so that the molar ratio of lithium to transition metal (Li / Me) is 1.3 or more, and then calcined to form a lithium transition metal oxide.

[0103] By adjusting the molar ratio of lithium to transition metal (Li / Me) to be 1.3 or more, the content of lithium in the final product, lithium transition metal oxide, can be appropriately controlled within the range according to the present invention mentioned above.

[0104] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0105] At this time, the calcination may be performed at a temperature of 700 to 1000°C, and more specifically, may be performed at a temperature of 800 to 900°C. If the calcination temperature is too low, unreacted precursors and residual lithium may remain, which may cause problems with slurry stability during electrode manufacturing, and if the calcination temperature is too high, there may be a problem with particles growing too coarsely.

[0106] The above firing can be performed under an oxygen or air atmosphere. When firing under the above atmosphere, the local oxygen partial pressure increases, which can improve the crystallinity of the positive electrode active material.

[0107] In this way, a lithium transition metal oxide with a lithium and manganese excess can be formed as a secondary particle formed by agglomeration of a plurality of primary particles, wherein the primary particles include plate-shaped particles and have an average aspect ratio of 5 to 90.

[0108]

[0109] 3. Lithium secondary battery

[0110] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the positive electrode comprises the positive electrode active material described above.

[0111] The above lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0112]

[0113] 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.

[0114] 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, calcined 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 μm, 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, sheet, foil, net, porous body, foam, or non-woven fabric.

[0115] 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.

[0116] 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.

[0117] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122]

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] The above binder and conductive material may be the same as those described above for the positive electrode.

[0128]

[0129] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. 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, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0130]

[0131] The above electrolyte may include, but is 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.

[0132] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0133] 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.

[0134] 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.

[0135] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as 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-methoxyethanol, 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. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0136]

[0137] 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).

[0138] 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.

[0139] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0140]

[0141] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0142]

[0143] Example 1: Primary particle average aspect ratio 50

[0144] (1) Manufacturing of positive electrode active material

[0145] (Manufacture of transition metal hydroxides)

[0146] An initial reaction solution with a pH of 10 was formed by adding a transition metal-containing solution, 1.5 M% NH4OH solution, and NaOH solution to a co-precipitation reactor. A co-precipitation reaction was performed to produce a transition metal hydroxide having a composition with a molar ratio of Ni / Mn of 35 / 65.

[0147] (Manufacturing of lithium transition metal oxides)

[0148] Afterwards, LiOH·H2O was mixed so that the molar ratio of lithium to transition metal (Li / Me) of the above transition metal hydroxide was 1.33, and then calcined at a temperature of 850℃ for 10 hours to obtain Li 1.13 Ni 0.3 Mn 0.57 A lithium transition metal oxide with an O2 composition was prepared.

[0149] (2) Lithium secondary battery manufacturing

[0150] 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, KF1100) = 92.5:3.5:4 wt%, and the viscosity was adjusted so that the solid content was approximately 30% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 15 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading was 14.6 mg / cm 2 and the rolling density (25 ℃, 20 kN) was 3.1 g / cm 3 It was.

[0151] The electrolyte was 1M LiPF6in EC:DMC:EMC=3:4:3 (vol%), with 3.0 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 (200 μm, Honzo metal).

[0152]

[0153] Example 2

[0154] A positive electrode active material and a lithium secondary battery having the same composition were manufactured in the same manner as in Example 1, except that the NH4OH solution concentration was set to 0.5 M% and the pH of the initial reaction solution was set to 10.8.

[0155]

[0156] Example 3

[0157] A positive electrode active material and a lithium secondary battery having the same composition were manufactured in the same manner as in Example 1, except that the concentration of the NH4OH solution was set to 1.5 M% and the pH of the initial reaction solution was set to 9.8.

[0158]

[0159] Comparative Example 1

[0160] A positive electrode active material and a lithium secondary battery having the same composition were manufactured in the same manner as in Example 1, except that the NH4OH solution concentration was set to 0.3 M% and the pH of the initial reaction solution was set to 11.3.

[0161]

[0162] Comparative Example 2

[0163] A positive electrode active material and a lithium secondary battery having the same composition were manufactured in the same manner as in Example 1, except that the concentration of the NH4OH solution was set to 1.7 M% and the pH of the initial reaction solution was set to 9.8.

[0164]

[0165] Comparative Example 3

[0166] A positive electrode active material and a lithium secondary battery having the same composition were manufactured in the same manner as in Example 1, except that the NH4OH solution concentration was set to 2.0 M% and the pH of the initial reaction solution was set to 9.8.

[0167]

[0168] Experimental Example 1: SEM image of positive electrode active material

[0169] SEM (scanning electron microscope) images of the positive electrode active materials manufactured according to the examples and comparative examples were observed, and the results are shown in Figs. 1 to 5 (in that order, examples 1 to 2 and comparative examples 1 to 3), respectively.

[0170] Referring to FIGS. 1 to 5, it was confirmed that the positive electrode active materials manufactured according to the examples and comparative examples were secondary particles formed by agglomeration of a plurality of primary particles, and that the primary particles had a plate-like shape and had different aspect ratios, which are the ratio of length to thickness.

[0171]

[0172] Experimental Example 2: Evaluation of the properties of positive electrode active materials

[0173] Various properties of the positive electrode active materials manufactured according to the examples and comparative examples were evaluated, and the results are shown in Table 1 below. The specific experimental methods are as follows.

[0174] (1) Evaluation of the average aspect ratio of primary particles

[0175] The average aspect ratio of primary particles was measured by quantifying SEM images using segmentation imaging techniques.

[0176] (2) Evaluation of the average thickness of primary particles

[0177] The average thickness of the primary particles was measured by quantifying the SEM images using segmentation imaging techniques.

[0178] (3) Tap density evaluation

[0179] Based on ASTM-B527, 15 g of active material powder was placed in a 50 mL container and tapped at 3000 cycles @ 284 cycles / min to measure the packing density.

[0180] (4) BET surface area evaluation

[0181] The specific surface area was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0182] Average aspect ratio of primary particles Average thickness of primary particles (nm) Tap density (g / cc) Specific surface area (m 2 / g)Example 1503001.743.2Example 2104002.182.7Example 3802001.523.8Comparative Example 138002.390.3Comparative Example 21001201.454.2Comparative Example 3150801.224.4

[0183]

[0184] Experimental Example 3: Evaluation of Battery Electrochemical Characteristics

[0185] The electrochemical characteristics of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated, and the results are shown in Table 2 below. The specific experimental methods are as follows.

[0186] (1) Evaluation of initial discharge capacity and initial efficiency

[0187] After fabricating half-cells of lithium secondary batteries, they were aged at 25°C for 12 hours and then subjected to charge-discharge tests. To evaluate the initial capacity, 200 mAh / g was used as the reference capacity, and the cells were charged to 4.25 V at a constant current of 0.1 C. After switching to constant voltage, the cells were charged until the end current reached 0.05 C. After a 10-minute rest period, the cells were discharged to 2.5 V at a constant current of 0.1 C, using 200 mAh / g as the reference capacity.

[0188] (2) Battery energy density evaluation

[0189] A secondary battery was designed using a pouch-type battery design, and the energy density was evaluated by converting the average voltage and capacity, and the battery volume, reflecting the density of electrodes using materials with different aspect ratios. Here, the electrode density was converted using the electrode weight per unit area and the thickness that appears at maximum rolling.

[0190] (3) High-power characteristic evaluation (0.33C / 0.1C)

[0191] High-power characteristics were evaluated by dividing the capacity at 0.33C by the capacity at 0.1C and converting it to a percentage (%).

[0192] (4) Comprehensive performance index evaluation

[0193] The square of the above battery energy density and the weight of the output characteristics were calculated as 1:1 to convert the comprehensive characteristics of the battery, and the comprehensive performance index of Example 2 was set to 100, and then the relative values ​​of other examples and comparative examples were derived.

[0194] Initial discharge capacity (mAh / g) Initial efficiency (%) Battery energy density (wh / L) High power characteristics (%) Comprehensive performance index Example 1279.791.9602.193.7100.0 Example 2277.592.3603.693.2100.0 Example 3280.291.8600.494.3100.1 Comparative example 1265.492.4607.391.097.8 Comparative example 2274.889.7583.395.395.5 Comparative example 3280.290.3573.49793.9

[0195] Referring to Table 2, in the case of Examples 1 to 3 in which the average aspect ratio of the primary particles, the tap density of the active material, and the specific surface area were appropriately controlled, it was confirmed that both the battery energy density and the high-power characteristics of the battery were well improved, resulting in an excellent comprehensive performance index. On the other hand, in the case of Comparative Example 1 in which the average aspect ratio of the primary particles was too small, the tap density of the active material was too large, and the specific surface area was too small, it was confirmed that the battery energy density was good, but the power characteristics deteriorated, resulting in a low comprehensive performance index.

[0196] In addition, in the case of Comparative Examples 2 and 3, where the average aspect ratio of the primary particles was too large, the tap density of the active material was too small, and the specific surface area was too large, it was confirmed that the output characteristics were good, but the battery energy density deteriorated and the comprehensive performance index decreased.

[0197]

[0198] In short, the technical gist of the present invention is that both battery energy density and output characteristics can be improved by appropriately controlling the average aspect ratio of primary particles of lithium and manganese-excess lithium transition metal oxide.

[0199]

[0200] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0201] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A layered lithium transition metal oxide containing excess lithium and manganese, It is a secondary particle formed by the aggregation of multiple primary particles. A positive electrode active material for a lithium secondary battery, wherein the primary particles include plate-shaped particles and have an average aspect ratio of 5 to 90.

2. In paragraph 1, The above lithium transition metal oxide is a cathode active material for a lithium secondary battery, wherein the molar ratio of lithium to the transition metal (Li / Me) is greater than 1 and the molar ratio of manganese to the transition metal (Mn / Me) is 0.55 or more.

3. In paragraph 2, The above lithium transition metal oxide is a positive electrode active material for a lithium secondary battery having a molar ratio of lithium to transition metal (Li / Me) of 1.985 or less.

4. In paragraph 1, The above lithium transition metal oxide is a positive electrode active material for a lithium secondary battery having a molar ratio of nickel to transition metal (Ni / Me) of 0.2 to 0.

4.

5. In paragraph 1, A cathode active material for a lithium secondary battery having a tap density of 1.5 to 2.3 g / cc.

6. In paragraph 1, BET surface area of ​​0.5 to 4 m 2 / g positive electrode active material for lithium secondary batteries.

7. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the primary particles is 500 nm or less.

8. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the above secondary particles is 3 to 15 μm.

9. In paragraph 1, The above lithium transition metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a (Mn x M y ) 1-a O2 In the above chemical formula 1, 0 <a≤0.33, 0.55≤x<1, 0<y≤0.45 이고, x+y = 1이고, M은 Ni, Co, V, Cr, Fe, Ru, Ir 또는 이들의 조합이다.

10. A step for preparing a transition metal hydroxide containing manganese having a molar ratio of manganese to transition metal (Mn / Me) of 0.55 or more; A step of forming a mixture including the transition metal hydroxide and the lithium raw material so that the molar ratio of lithium to the transition metal (Li / Me) is 1.3 or more, and then calcining the mixture to form a lithium transition metal oxide, is included. The lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, wherein the primary particles include plate-shaped particles and have an average aspect ratio of 5 to 90. A method for manufacturing a cathode active material for a lithium secondary battery.

11. In paragraph 10, The step of preparing the above transition metal hydroxide is as follows: A step of forming a transition metal-containing solution including a manganese raw material and other transition metal raw materials; A step of forming an initial reaction solution by introducing the transition metal-containing solution, the complexing agent-containing solution, and the pH regulator-containing solution into the reactor; and A step of forming a transition metal hydroxide by co-precipitation reaction of the above initial reaction solution, A method for producing a positive electrode active material for a lithium secondary battery, wherein, in the step of forming the initial reaction solution, the complexing agent concentration of the complexing agent-containing solution is 0.4 to 1.6 mol%.

12. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein in the step of forming the initial reaction solution, the pH of the initial reaction solution is 9.6 to 11.

13. In paragraph 10, In the step of forming the above lithium transition metal oxide, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above-mentioned sintering is performed at a temperature of 700 to 1000°C.

14. Containing a positive electrode; a negative electrode; a separator; and an electrolyte, A lithium secondary battery comprising the positive electrode active material of any one of claims 1 to 9.

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