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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising: a central part comprising a lithium nickel manganese oxide that contains nickel (Ni) and manganese (Mn) and does not contain cobalt (Co); and a surface part, which is disposed on the surface of the central part, contains cobalt (Co) and includes a plurality of contact particles, isolated particles, a contact interface, non-contact interfaces and a coating layer, wherein the contact particles are in contact with the coating layer with the contact interface therebetween, the isolated particles are not in contact with the coating layer, a pair of contact particles adjacent to each other from among the plurality of contact particles are in contact with each other with the non-contact interface therebetween, and relation 1 is satisfied.

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 a minimized cobalt content, a method for producing the same, and a lithium secondary battery comprising the same.

[0002]

[0003] Currently, commercially available cathode active materials for high-energy-density lithium secondary batteries include LCO, NCM, and NCA, all of which contain cobalt. However, the use of cobalt in cathode active materials presents a number of challenges that must be addressed at a commercial level.

[0004] First, cobalt is rare and only found in certain regions. Nearly two-thirds of global cobalt mining takes place in the politically unstable Republic of the Congo, a Central African country. Furthermore, cobalt mining in the Republic of the Congo is often plagued by issues such as non-compliance with environmental protection regulations and child labor exploitation. Meanwhile, the projected production of electric vehicles is expected to increase more than tenfold by 2025, leading to a surge in demand for cobalt over the next decade. Consequently, cobalt price volatility in the market is extremely high. Due to these issues, there is growing consensus in the lithium-ion battery electric vehicle market to reduce the use of cobalt in cathode materials.

[0005] However, cobalt-free cathode materials such as lithium manganese oxide have problems with reduced capacity, output, and lifespan characteristics due to increased instability of the surface structure due to the absence of cobalt.

[0006]

[0007] Accordingly, one task of the present invention is to provide a cathode active material for a lithium secondary battery having excellent capacity, output, and lifespan characteristics while ensuring price competitiveness by minimizing the concentration of cobalt.

[0008] Another object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery having the aforementioned advantages.

[0009]

[0010] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising: a central portion comprising lithium nickel manganese oxide containing nickel (Ni) and manganese (Mn) and not containing cobalt (Co); and a surface portion disposed on a surface of the central portion, the surface portion containing cobalt (Co) and including a plurality of contact particles, isolated particles, a contact interface, a non-contact interface, and a coating layer, wherein the contact particles contact the coating layer with the contact interface interposed therebetween, the isolated particles do not contact the coating layer, and a pair of adjacent contact particles among the plurality of contact particles contact each other with the non-contact interface interposed therebetween, and satisfying the following formula 1.

[0011] <Formula 1>

[0012] Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the non-contact interface > Cobalt concentration (at%) of the contact particle

[0013]

[0014] The above positive electrode active material for a lithium secondary battery can satisfy the following equation 2.

[0015] <Formula 2>

[0016] Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the isolated interface > Cobalt concentration (at%) of the contact particle

[0017]

[0018] The nickel content of the above lithium nickel manganese oxide may be 60 mol% or more based on the total molar number of transition metals excluding lithium.

[0019] The above lithium nickel manganese oxide can be represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li a [Ni x Mn y M z ]O2

[0022] In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, and 0 <y≤0.40이고, 0≤z≤0.3이고, M은 Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo 또는 이들의 조합이다.

[0023] The above contact particles may include lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co), and oxygen (O).

[0024] The thickness of the above surface portion may be 35% or less based on the total length of the average particle diameter (D50) of the positive electrode active material.

[0025] The thickness of the above surface portion may be 1000 nm or less.

[0026] The cobalt concentration of the above coating layer may be 80 to 94 at%.

[0027] The cobalt concentration at the lower portion of the above contact interface may be 55 to 73 at%.

[0028] The cobalt concentration of the non-contact interface may be 40 to 54 at%.

[0029] The cobalt concentration of the above isolated interface may be 15 to 38 at%.

[0030] The cobalt concentration of the above contact particles may be 3 to 12 at%.

[0031] The above coating layer includes cobalt-containing coating particles, and the major axis length of the coating particles may be 50 nm to 1 μm.

[0032] The lithium nickel manganese oxide has a spherical structure in which secondary particles are formed by agglomeration of primary particles, and the average particle diameter (D50) of the secondary particles is 8 to 30 μm.

[0033]

[0034] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, the method comprising: preparing a transition metal hydroxide containing nickel (Ni) and manganese (Mn) and not containing cobalt (Co); forming a mixture containing the transition metal hydroxide and a lithium raw material and calcining the mixture to form a lithium transition metal oxide not containing cobalt; and mixing the lithium transition metal oxide and the cobalt raw material and heat-treating the mixture at a temperature of 570 to 730°C to form a coating layer, wherein the content of the cobalt raw material is 0.8 to 4 mol% based on the total mole number of the lithium transition metal oxide and the cobalt raw material.

[0035] The nickel content of the above transition metal hydroxide may be 60 mol% or more based on the total mole number of transition metals.

[0036] The length of the major axis of the above cobalt raw material particles may be 50 nm to 1 μm.

[0037]

[0038] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode including the positive electrode active material for the aforementioned lithium secondary battery; a negative electrode; and an electrolyte.

[0039]

[0040] A cathode active material for a lithium secondary battery according to one embodiment of the present invention contains a small amount of cobalt in a surface portion, but has a cobalt concentration gradient between each region existing in the surface portion, thereby reducing cost and improving capacity, output, and life characteristics of the battery.

[0041]

[0042] FIG. 1 is a BF-STEM image of a surface portion of a cross-section of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0043] Figure 2 is a schematic diagram showing the surface portion of a cross-section of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0044] FIG. 3 is a BF-STEM image of the entire cross-section of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0045] 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 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0050] 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.

[0051] 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.

[0052]

[0053] 1. Cathode active material for lithium secondary batteries

[0054] The inventors of the present invention have conducted extensive research to address the problem of cobalt-free cathode materials, namely, the deterioration of battery capacity and cycle life due to the unstable surface structure caused by the absence of cobalt. As a result, they discovered that when the active material includes a surface region containing trace amounts of cobalt and a cobalt concentration gradient is formed in the surface region, the cation mixing layer of the excess transition metal present on and within the active material is stabilized, thereby improving battery capacity and cycle life.

[0055] In addition, based on the above-mentioned knowledge, the inventors of the present invention studied the structure of the surface of the positive electrode active material in more detail, and as a result, they found that the capacity and life characteristics of the battery were maximized by optimizing the cobalt concentration relationship between various regions existing in the surface and the cobalt content of each region, thereby completing the present invention.

[0056] In this specification, the term “metal having a concentration gradient” means that the concentration of the metal exists in a concentration distribution that continuously changes in steps throughout the particle or in a specific region.

[0057] Hereinafter, the positive electrode active material for a lithium secondary battery will be described in more detail.

[0058]

[0059] Fig. 1 is a BF-STEM (Bright-field Scanning transmission electron microscopy) image of the surface portion of a cross-section of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention, and Fig. 2 is a schematic diagram schematically showing the surface portion of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention. Fig. 3 is a BF-STEM image of the entire cross-section of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0060] Referring to FIGS. 1 to 3, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a central portion; and a surface portion disposed on a surface of the central portion.

[0061] The central region is a cobalt-free region, and includes lithium nickel manganese oxide containing nickel (Ni) and manganese (Mn), but not cobalt (Co).

[0062] In addition, the surface portion is a region containing cobalt, and includes a plurality of contact particles, isolated particles, a contact interface, a non-contact interface, and a coating layer. In this case, the cobalt contained in the surface portion may be derived from a cobalt raw material, as described in the manufacturing method described below.

[0063] At this time, the contact particles come into contact with the coating layer with a contact interface therebetween. In other words, the positive electrode active material for a lithium secondary battery according to the present invention may be a secondary particle formed by agglomeration of a plurality of primary particles, and at this time, the contact particles may be located at the outer portion of the secondary particles and come into contact with the coating layer with a contact interface therebetween. In other words, the contact interface is a region located between the contact particles and the coating layer. The shape of the contact interface is not particularly limited, except that it may be influenced by the shapes of the contact particles and the coating layer.

[0064] On the other hand, the isolated particle may be located on the outer portion of the secondary particle, but may not come into contact with the coating layer. More specifically, the isolated particle may not come into contact with the coating layer because it is blocked by contact particles that come into contact with the coating layer.

[0065] In addition, among the plurality of contact particles, a pair of adjacent contact particles can contact each other with a non-contact interface therebetween. In other words, the non-contact interface is an interface region located between a pair of adjacent contact particles. The shape of the non-contact interface is not particularly limited, except that it may be influenced by the shapes of the pair of contact particles. In addition, the surface direction of the non-contact interface corresponds to the surface direction of the adjacent pair of contact particles, and the surface direction of the non-contact interface can have various arbitrarily oriented with respect to the outer surface of the secondary particle. Specifically, the surface direction of the non-contact interface may be perpendicular to the outer surface of the secondary particle, may be diagonal, or may be close to parallel.

[0066] In addition, an isolation interface may be located between the contact particle and the isolated particle. That is, the isolation interface is an interface region located between the contact particle and the isolated particle. The shape of the isolation interface is not particularly limited, except that it may be influenced by the shapes of the contact particle and the isolated particle. In addition, the plane direction of the isolation interface corresponds to the plane directions of the adjacent isolated particle and contact particle, and the plane direction of the isolation interface may have various arbitrarily oriented with respect to the outer surface of the secondary particle. Specifically, the plane direction of the isolation interface may be perpendicular to the outer surface of the secondary particle, may be diagonal, or may be close to parallel.

[0067] At this time, the shape of the contact particles and isolated particles is not particularly limited, and the length, width, and thickness can also be adjusted in various ways.

[0068] At this time, the contact particles, isolated particles, contact interface, non-contact interface, and coating layer may each contain cobalt in a predetermined amount. This will be described in more detail later.

[0069]

[0070] Hereinafter, the cobalt concentration gradient in each region existing on the surface of the positive electrode active material according to the present invention will be described.

[0071] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention satisfies the following equation 1.

[0072] <Formula 1>

[0073] Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the non-contact interface > Cobalt concentration (at%) of the contact particle

[0074] In the above equation 1, the “cobalt concentration at the bottom of the contact interface” refers to the cobalt concentration in the region within the contact particle, not the contact interface, and refers to the average cobalt concentration in the region within 50 nm from the contact interface. In this case, the average cobalt concentration refers to the number of cobalt atoms in at% based on the total number of moles of transition metal atoms. Hereinafter, the meaning of the average cobalt concentration in the present specification is the same.

[0075] In addition, the “cobalt concentration of the non-contact interface” refers to the average cobalt concentration in the region existing over a length of 300 nm from the side where the contact particle and the coating layer come into contact among the non-contact interface regions.

[0076] Additionally, “cobalt concentration of contact particles” means the average cobalt concentration over the entire area within one contact particle.

[0077] As the cobalt concentrations at the bottom of the contact interface, the non-contact interface, and the contact particles satisfy the relationship of Equation 1 above, the capacity and life characteristics of the battery can be maximized.

[0078]

[0079] In addition, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can further satisfy the following equation 2.

[0080] <Formula 2>

[0081] Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the isolated interface > Cobalt concentration (at%) of the contact particle

[0082] In the above equation 2, the cobalt concentrations at the bottom of the contact interface and the contact particles are as described above, and the “cobalt concentration at the isolated interface” refers to the average cobalt concentration in the region that exists over a length of 250 nm from the beginning of the isolated interface located closer to the coating layer among the isolated interfaces.

[0083] As the cobalt concentrations at the bottom of the contact interface, the isolated interface, and the contact particles satisfy the relationship of Equation 2 above, the capacity and life characteristics of the battery can be maximized.

[0084]

[0085] In addition, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can additionally satisfy the following equation 3.

[0086] <Formula 3>

[0087] Cobalt concentration (at%) of the coating layer > Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) of the non-contact interface > Cobalt concentration (at%) of the isolated interface > Cobalt concentration (at%) of the contact particle

[0088] In the above formula 3, the cobalt concentrations at the bottom of the contact interface, the non-contact interface, the isolated interface, and the contact particles are as described above, and the “cobalt concentration of the coating layer” means the average cobalt concentration in the entire area within one coating particle existing in the coating layer.

[0089] When the cobalt concentrations of the coating layer, the lower part of the contact interface, the non-contact interface, the isolated interface, and the contact particles satisfy the relationship of the above equation 3, the capacity and life characteristics of the battery can be maximized. This is because the surface of the non-coated lithium transition metal oxide secondary particle and the non-contact interface and isolated interface, which are the interfaces of the primary particles, have an imperfect layered structure, which hinders the movement of lithium during charge and discharge. It is believed that this is because the layered structure is restored by heat-treating it together with cobalt during the formation of the coating layer.

[0090]

[0091] Meanwhile, the nickel content of the lithium nickel manganese oxide included in the central portion may be 60 mol% or more, and more specifically, 80 mol% or more, based on the total moles of transition metals excluding lithium. Accordingly, a sufficient amount of nickel is secured, thereby promoting high capacity of the battery.

[0092] The lithium nickel manganese oxide can be more specifically represented by the following chemical formula 1.

[0093] [Chemical Formula 1]

[0094] Li a [Ni x Mn y M z ]O2

[0095] In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, and 0 <y≤0.40이고, 0≤z≤0.3이고, M은 Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo 또는 이들의 조합이고, x+y+z=1이다.

[0096] In the lithium nickel manganese 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 increase, 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≤p≤1.1 more preferably.

[0097] In the lithium nickel manganese oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, that is, 0.60≤x<1. If x is sufficiently large, such as 0.6 or more, a sufficient amount of nickel is secured to contribute to charge and discharge, thereby achieving high capacity. More specifically, 0.8≤x<1 may be satisfied.

[0098] In the above chemical formula 1, manganese is present in the content corresponding to y, i.e. 0 <y≤0.40로 포함될 수 있다. 망간은 양극 활물질의 안정성을 향상시키고, 결과적으로 전지의 안정성을 개선시킬 수 있다. 상기 망간은 보다 구체적으로는, 0.01≤y≤0.06의 함량으로 포함될 수 있다.

[0099] In the above chemical formula 1, M is a doping element. The doping element M can be included in a content corresponding to z, i.e., 0≤z≤0.3.

[0100]

[0101] The above contact particles may include lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co), and oxygen (O). The contact particles contain not only lithium, nickel, manganese, and oxygen, but also cobalt. This is a result of cobalt contained in the cobalt raw material moving to the contact particles through a direct / indirect reaction between the cobalt raw material and the contact particles during the active material manufacturing process, as described in the manufacturing method described below.

[0102] The thickness of the surface portion may be 35% or less, and more specifically, 20% or 10% or less, based on the total length of the average particle diameter (D50) of the positive electrode active material. In other words, in the positive electrode active material according to the present invention, cobalt may exist only within 35%, 20%, or 10% of the total length of the average particle diameter (D50) of the positive electrode active material from the surface of the positive electrode active material particles toward the particle center. Accordingly, the layered structure of the active material can be formed more easily, so that the surface structure of the active material can be further improved, and the electrochemical characteristics of the battery can be improved.

[0103] More specifically, the thickness of the surface portion may be 1000 nm or less, and more specifically, 800 nm, 600 nm, 400 nm, or 350 nm or less. However, this is only an example, and it is obvious that the thickness may be variously adjusted within the range of the above-mentioned ratio as the average particle diameter (D50) of the positive electrode active material changes.

[0104] In addition, the thickness of the surface portion may be, for example, 1 to 300 times the longitudinal length of the primary particle located on the outer portion of the secondary particle active material having a rod-shaped shape. Accordingly, the layered structure of the active material may be more easily formed, thereby improving the surface structure of the active material and enhancing the electrochemical characteristics of the battery. At this time, the longitudinal length of the primary particle may be, for example, 50 nm to 1000 nm.

[0105]

[0106] Hereinafter, the cobalt concentration contained in each region of the positive electrode active material according to the present invention will be described.

[0107] The cobalt concentration of the above coating layer may be 80 to 94 at%, and more specifically, 85 to 90%.

[0108] The cobalt concentration at the lower portion of the above contact interface may be 55 to 73 at%, and more specifically, 65 to 70 at%.

[0109] The cobalt concentration of the non-contact interface may be 40 to 54 at%, and more specifically, 45 to 50 at%.

[0110] The cobalt concentration of the above isolation interface may be 15 to 38 at%, more specifically 34 to 40.

[0111] The cobalt concentration of the above contact particles may be 3 to 12 at%, more specifically 5 to 10 at%.

[0112] In this specification, “at%” means atomic %.

[0113] If the cobalt concentration of the coating layer, the lower part of the contact interface, the non-contact interface, the isolated interface, and the contact particles is too low, the effect of improving the capacity and life characteristics of the battery may be minimal. On the other hand, if the cobalt concentration of the coating layer, the lower part of the contact interface, the non-contact interface, the isolated interface, and the contact particles is too high, there is a concern about increased cost, a decrease in capacity per weight due to the weight of the coating material, and cobalt may react a lot with the lithium of the positive electrode active material, thereby collapsing the layered structure of the positive electrode active material, which may deteriorate the capacity and life characteristics of the battery.

[0114]

[0115] The above coating layer may include cobalt-containing coating particles. At this time, the major axis length of the coating particles may be 50 nm to 1 μm. If the major axis length of the coating particles is too short, the diffusion of cobalt is too fast, so that it diffuses not only to the lower part of the contact interface or the non-contact interface but also to the isolated particles, thereby reducing the effect of the coating, and the cobalt concentration gradient may not be properly controlled, which may cause a problem of deterioration in battery performance. If the major axis length of the coating particles is too long, the contact with the primary particles of the positive active material deteriorates, so that the cobalt cannot diffuse smoothly, which may lower the effect of the coating and cause a problem of reduced lifespan.

[0116] The major axis length of these coating particles can be obtained to be the same as the major axis length of the cobalt raw material particles when forming the coating layer. This is because the heat treatment temperature when forming the coating layer according to the present invention is a temperature range that does not cause a difference between the major axis length of the cobalt raw material particles and the major axis length of the coating particles.

[0117] The lithium nickel manganese oxide has a spherical structure in which secondary particles are formed by agglomeration of primary particles, and the average particle diameter (D50) of the secondary particles may be 8 to 30 μm. In the present specification, the average particle diameter (D50) may be defined as a particle diameter corresponding to 50% of the volume accumulation amount in a particle diameter distribution curve of particles. The average particle diameter (D50) may be measured using, for example, a laser diffraction method. The laser diffraction method can generally measure particle diameters from a submicron range to several mm, and can obtain results with high reproducibility and high resolution. If the average particle diameter of the secondary particles is too small, the packing density may be lowered, which may cause a problem of low energy density, and if the average particle diameter of the secondary particles is too large, the diffusion distance of lithium during charge and discharge may be long, which may cause a problem of reduced capacity.

[0118]

[0119] 2. Method for manufacturing positive electrode active material for lithium secondary batteries

[0120] Another embodiment of the present invention provides a method for producing a cathode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal hydroxide containing nickel (Ni) and manganese (Mn) and not containing cobalt (Co); forming a mixture containing the transition metal hydroxide and a lithium raw material and firing the mixture to form a lithium transition metal oxide not containing cobalt; and mixing the lithium transition metal oxide and the cobalt raw material and performing a heat treatment to form a coating layer, wherein the content of the cobalt raw material is 4 mol% or less based on the total mole number of the lithium transition metal oxide and the cobalt raw material.

[0121] 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 step by step. However, the method described below is not necessarily limited to this method, and it is obvious that the positive electrode active material may be manufactured according to any method well known in the art.

[0122]

[0123] First, a transition metal hydroxide containing nickel (Ni) and manganese (Mn) and not cobalt (Co) is prepared. The transition metal hydroxide is a precursor for the positive electrode active material.

[0124] At this time, the doping element may be doped in the preparation stage of the positive electrode active material precursor.

[0125] For example, the precursor may be manufactured by a coprecipitation reaction by adding an ammonia solution and a caustic soda solution to a transition metal-containing solution including a nickel raw material, a manganese raw material, and optionally a doping raw material including Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

[0126] 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.

[0127] 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.

[0128] The ammonia solution may include, but is not limited to, a complex forming agent, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. Meanwhile, the ammonia solution may also be used in the form of an aqueous solution, and in this case, a solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0129] The above caustic soda solution may contain an alkali 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, as a precipitant or pH adjuster. The above caustic soda solution may also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used as a solvent.

[0130] The above coprecipitation reaction can be performed under an inert atmosphere such as nitrogen or argon.

[0131] During the above co-precipitation reaction, the temperature inside the reactor may be performed at 30 to 70°C, specifically 40 to 60°C, and more specifically 45 to 55°C.

[0132] Nickel-manganese (doped element) hydroxide particles are generated through the above process and precipitated within the reaction solution. The precipitated precursor particles can be separated and dried using conventional methods to obtain a precursor. The precursor may be a secondary particle formed by agglomeration of primary particles.

[0133] At this time, by adjusting the concentration of the nickel-containing raw material and the manganese-containing raw material, a precursor having a nickel (Ni) content of 60 mol% or more based on the total metal content can be manufactured. In other words, the nickel content of the transition metal hydroxide can be 60 mol% or more based on the total mole number of transition metals, thereby promoting high capacity of the battery.

[0134]

[0135] Next, a mixture containing the above transition metal hydroxide and lithium raw material is formed and calcined to form a lithium transition metal oxide that does not contain cobalt.

[0136] At this time, the mixture may further include a doping raw material including Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo or a combination thereof.

[0137] 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.

[0138] The above firing may be performed at 600 to 900°C, and more specifically, at 600 to 800°C, 700 to 800°C, or 720 to 760°C.

[0139] The above firing can be performed for 5 to 20 hours, more specifically for 5 to 15 hours, or 8 to 12 hours.

[0140] The above firing can be performed by dividing it into first firing and second firing, as needed.

[0141]

[0142] Next, the lithium transition metal oxide and cobalt raw material are mixed and heat-treated to form a coating layer.

[0143] During the above coating layer formation process, cobalt atoms contained in the cobalt raw material diffuse into the contact particles located on the outer surface of the active material, the lower portion of the contact interface, the non-contact interface, and the isolated interface, thereby forming a cobalt concentration in the above regions and causing a cobalt concentration gradient between each region. A detailed description of the cobalt concentration gradient relationship and cobalt concentration is omitted as it is the same as described above.

[0144] The above cobalt raw material may be, for example, Co(OH)2, Co3O4, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4, Co(SO4)2ㆍ7H2O or a combination thereof, but is not limited thereto.

[0145] Preferably, the cobalt raw material may be Co(OH)2.

[0146] At this time, the content of the cobalt raw material is 0.8 to 4 mol% based on the total mole number of the lithium transition metal oxide and the cobalt raw material, and more specifically, it may be 1 to 4 mol% or 1 to 3 mol%. If the content of the cobalt raw material is too high, the cost may increase, and the cobalt concentration of the coating layer, the lower part of the contact interface, the non-contact interface, the isolated interface, and the contact particles may become too large, which may rather deteriorate the capacity and lifespan of the battery as described above. On the other hand, if the content of the cobalt raw material is too low, the cobalt concentration gradient relationship between each region in the active material targeted by the present invention may not be easily obtained, and thus the effect of improving the capacity and lifespan characteristics of the battery may be minimal.

[0147] The above heat treatment is performed at a temperature of 570 to 730°C, and more specifically, may be performed at a temperature of 600 to 720°C, 650 to 700°C, or 660 to 690°C. When the temperature range during the heat treatment satisfies the above range, the cobalt concentration gradient relationship between each region in the active material targeted by the present invention and the cobalt concentration in each region can be easily obtained, so that the battery performance can be preferably implemented.

[0148] In addition, the major axis length of the cobalt raw material particles may be 50 nm to 1 μm. When the major axis length of the cobalt raw material particles satisfies the above range, the cobalt concentration gradient relationship between each region in the active material targeted by the present invention and the cobalt concentration in each region can be easily obtained, so that the battery performance can be preferably implemented.

[0149] The above heat treatment can be performed for 2 to 24 hours, and more specifically, for 3 to 10 hours. As the heat treatment time satisfies the above range, the cobalt concentration gradient relationship between each region in the active material targeted by the present invention and the cobalt concentration in each region can be easily obtained.

[0150]

[0151] 3. Cathode for lithium secondary battery and lithium secondary battery

[0152] Meanwhile, another embodiment of the present invention provides a positive electrode for a lithium secondary battery including the positive electrode active material for a lithium secondary battery described above and a lithium secondary battery including the positive electrode.

[0153]

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163]

[0164] Another embodiment of the present invention provides a lithium secondary battery including the above-described positive electrode.

[0165] 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 of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0166]

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] The above binder and conductive material may be the same as those described above for the positive electrode.

[0172]

[0173] Meanwhile, in the lithium secondary battery, the 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 special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention 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, can 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. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0174]

[0175] 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.

[0176] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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).

[0181] 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.

[0182] 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.

[0183]

[0184] 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.

[0185]

[0186] Example 1

[0187] (1) Manufacturing of positive electrode active material

[0188] (lithium nickel manganese oxide formation) nickel manganese hydroxide [Ni x Mn 1-x Lithium hydroxide (LiOH) was added to [OH2(0.6≤x<1)], mixed in a dry manner at a molar ratio of 1:1, and calcined in an oxygen atmosphere at 760°C for 10 hours to obtain lithium nickel manganese oxide [LiNi x Mn 1-x O2(0.6 ≤ x < 1)] was obtained.

[0189] (Coating layer formation) The lithium nickel manganese oxide [LiNi x Mn 1-x O2(0.6 ≤ x < 1)] and cobalt hydroxide (Co(OH)2) as a cobalt raw material were physically mixed and heat-treated at 680°C for 6 hours to obtain a composite cathode active material having a coating layer containing lithium cobalt oxide. At this time, the major axis length of the cobalt hydroxide particles (cobalt raw material particles) was 200 nm.

[0190] Here, the content of Co(OH)2 was set to 2 mol% based on the total content of lithium nickel manganese oxide and cobalt hydroxide of 100 mol%.

[0191] The average particle diameter (D50) of the final produced positive electrode active material was 10 μm.

[0192] At this time, the above x was set to 0.9.

[0193] (2) Lithium secondary battery manufacturing

[0194] 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) = 96.5:1.5:2 wt%, and NMP (N-Methyl-2-pyrrolidone) was added to adjust the viscosity. The manufactured slurry was coated on a 15 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading amount was 18-20 mg / cm 2 It was.

[0195] The electrolyte was 1M LiPF6 in 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).

[0196]

[0197] Example 2

[0198] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the ratio of nickel manganese hydroxide and lithium hydroxide was set to 1:1.03 when forming lithium nickel manganese oxide.

[0199]

[0200] Example 3

[0201] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment time during the formation of the coating layer was set to 7 hours.

[0202]

[0203] Example 4

[0204] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment time during the formation of the coating layer was set to 5 hours.

[0205]

[0206] Example 5

[0207] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the sintering temperature was set to 740°C when forming lithium nickel manganese oxide.

[0208]

[0209] Comparative Example 1

[0210] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment temperature was set to 750°C when forming the coating layer.

[0211]

[0212] Comparative Example 2

[0213] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the content of Co(OH)2 was set to 0.5 mol% when forming the coating layer.

[0214]

[0215] Comparative Example 3

[0216] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the long axis length of the cobalt raw material particles was 25 nm when forming the coating layer.

[0217]

[0218] Reference Example 1

[0219] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Co3O4 was used instead of Co(OH)2 as the cobalt raw material when forming the coating layer.

[0220]

[0221] Reference Example 2

[0222] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment temperature was set to 850°C when forming the coating layer.

[0223]

[0224] Reference Example 3

[0225] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment temperature was set to 550°C when forming the coating layer.

[0226]

[0227] Reference Example 4

[0228] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the long axis length of the cobalt raw material particles was 25 nm when forming the coating layer and the heat treatment temperature was 750°C.

[0229]

[0230] Reference Example 5

[0231] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Co3O4 was used instead of Co(OH)2 as the cobalt raw material when forming the coating layer and the heat treatment temperature was set to 550°C.

[0232]

[0233] Reference Example 6

[0234] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that CoO was used instead of Co(OH)2 as the cobalt raw material when forming the coating layer.

[0235]

[0236] Tables 1 and 2 below summarize the results of Experimental Examples 1 and 2 described below.

[0237] Coating layer (at%) Contact interface bottom (at%) Non-contact interface (at%) Isolated interface (at%) Contact particle (at%) Example 1886748367 Example 2907051369 Example 38573513810 Example 4916040304 Example 5865844264 Comparative example 1826161115 Comparative example 285574337 Comparative example 3835535406 Reference example 1866645342 Reference example 29370523814 Reference example 3925538152 Reference example 49470603711 Reference example 59369544410 Reference example 687422583

[0238] Initial discharge capacity (mAh / g) High temperature life (%) 2C output (2C / 0.1C, %) DC-IR (Ω) Example 1 206.59 7.18 8.9 15.1 Example 2 205.49 6.88 7.9 16.2 Example 3 203.59 5.98 7.0 17.4 Example 4 202.49 5.48 5.7 19.4 Example 5 204.89 5.88 6.6 17.0 Comparative example 1 198.59 3.28 2.0 28.5 Comparative example 2 201.89 2.67 9.93 5.6 Comparative example 3 197.99 1.98 0.44 0.5 Reference example 1 201.59 3.68 3.0 20.6 Reference example 2191.591.082.217.8Reference Example 3200.693.580.519.1Reference Example 4192.591.583.218.8Reference Example 5193.792.282.817.0Reference Example 6189.487.479.519.5

[0239]

[0240] Experimental Example 1: Measurement of cobalt concentration in each region of the positive electrode active material.

[0241] The cobalt concentration in each region of the positive electrode active materials manufactured according to Examples 1 to 5, Comparative Examples 1 to 3, and Reference Examples 1 to 6 was measured, and the results are shown in Table 1 above.

[0242] Specifically, cobalt concentration was measured using STEM-EDS.

[0243] At this time, the cobalt concentration of the coating layer refers to the average concentration of cobalt in the entire area within one coating particle existing in the coating layer.

[0244] The cobalt concentration at the bottom of the contact interface refers to the cobalt concentration in the region within the contact particle, not at the contact interface, and is the average concentration in the region within 50 nm from the contact interface.

[0245] The cobalt concentration at the non-contact interface refers to the average cobalt concentration in the region that exists over a length of 300 nm from the side where the contact particles and the coating layer come into contact among the non-contact interface regions.

[0246] The cobalt concentration of the isolated interface refers to the average cobalt concentration in the region extending over a length of 250 nm from the beginning of the isolated interface, which is located closer to the coating layer among the isolated interfaces.

[0247] The cobalt concentration of a contact particle means the average concentration of cobalt in the entire area within one contact particle.

[0248]

[0249] Experimental Example 2: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0250] The electrochemical characteristics of lithium secondary batteries manufactured according to Examples 1 to 5, Comparative Examples 1 to 3, and Reference Examples 1 to 6 were evaluated, and the results are shown in Table 1 above. The specific experimental methods are as follows.

[0251] (1) Capacity evaluation

[0252] For a half cell of a lithium secondary battery manufactured by the above method of manufacturing a lithium secondary battery, the capacity was evaluated by charging it with a constant current of 0.1 C in CC-CV mode at 25°C to 4.3 V, switching to constant voltage and charging it until the end current reached 0.05 C, and then discharging it with 0.1 C in CC mode to 2.5 V.

[0253] (2) High temperature life evaluation

[0254] For a half cell of a lithium secondary battery manufactured by the above method of manufacturing a lithium secondary battery, a constant current of 0.1 C was charged to 4.3 V in CC-CV mode at 45°C, then the charge was switched to constant voltage until the end current reached 0.05 C, and a formation cycle was formed by discharging to 2.5 V in CC mode at 0.1 C, and the high-temperature life was evaluated for 30 cycles in the subsequent cycles at 0.33 C in the same temperature and voltage range.

[0255] (3) 2C output characteristics

[0256] For a lithium secondary battery half cell manufactured by the above method of manufacturing a lithium secondary battery, the 2C output capacity at 25°C was divided by the 0.1C output capacity and converted into a percentage (%).

[0257] (4) DC-IR evaluation

[0258] The voltage was measured and calculated 60 seconds after applying a discharge current of 100% at 4.3 V at 25°C to a half cell of a lithium secondary battery manufactured by the above method of manufacturing a lithium secondary battery.

[0259]

[0260] Referring to Tables 1 and 2, it was confirmed that the lithium secondary battery of Example 1, in which the cobalt concentration relationship (concentration gradient) of the coating layer, the lower part of the contact interface, the non-contact interface, the isolated interface, and the contact particles was appropriately controlled to conform to the present invention, and the cobalt concentration of each region was appropriately controlled, had excellent capacity, output, and high-temperature life characteristics.

[0261] On the other hand, in Comparative Example 1 where the cobalt concentration of the non-contact interface was higher than the cobalt concentration at the bottom of the contact interface, in Comparative Example 2 where the cobalt concentration of the contact particles was higher than the cobalt concentration of the isolated interface, and in Comparative Example 3 where the cobalt concentration of the isolated interface was higher than the cobalt concentration of the non-contact interface, it was confirmed that the capacity, output, and high-temperature life characteristics of the battery were inferior.

[0262] Meanwhile, referring to Reference Examples 1 and 2, it was confirmed that even if the cobalt concentration relationship (concentration gradient) in each area is appropriately controlled, if the cobalt concentration of the contact particles is too low or too high, the capacity, output, and high-temperature life characteristics of the battery are somewhat reduced.

[0263] And, referring to Reference Examples 3 and 4, it was confirmed that even if the cobalt concentration relationship (concentration gradient) of each region is appropriately controlled, if the cobalt concentration of the non-contact interface is too low or high, the capacity, output, and high-temperature life characteristics of the battery are somewhat reduced.

[0264] In addition, referring to Reference Examples 5 and 6, it was confirmed that even if the cobalt concentration relationship (concentration gradient) of each region is appropriately controlled, if the cobalt concentration of the isolated interface is too low or too high, the capacity, output, and high-temperature life characteristics of the battery are somewhat reduced.

[0265]

[0266] In summary, the present invention aims to improve battery performance by minimizing the cobalt content of the active material while controlling the cobalt concentration relationship between various regions present on the surface of the active material. By further controlling the cobalt content in each of these regions, battery performance can be further maximized.

[0267]

[0268] 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.

[0269] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A core comprising lithium nickel manganese oxide containing nickel (Ni) and manganese (Mn) and not containing cobalt (Co); and a surface portion disposed on the surface of the core, containing cobalt (Co), and including a plurality of contact particles, isolated particles, a contact interface, a non-contact interface, and a coating layer. The above contact particles contact the coating layer with a contact interface therebetween, the isolated particles do not contact the coating layer, and a pair of adjacent contact particles among the plurality of contact particles contact each other with a non-contact interface therebetween. A cathode active material for a lithium secondary battery satisfying the following equation 1. <Formula 1> Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the non-contact interface > Cobalt concentration (at%) of the contact particle 2. In paragraph 1, A cathode active material for a lithium secondary battery satisfying the following equation 2. <Formula 2> Cobalt concentration (at%) at the bottom of the contact interface > Cobalt concentration (at%) at the isolated interface > Cobalt concentration (at%) of the contact particle 3. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the nickel content of the lithium nickel manganese oxide is 60 mol% or more based on the total molar number of transition metals excluding lithium.

4. In paragraph 1, The above lithium nickel manganese oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Mr y M z ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, and 0 <y≤0.40이고, 0≤z≤0.3이고, M은 Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo 또는 이들의 조합이다.

5. In paragraph 1, The above contact particles are a cathode active material for a lithium secondary battery containing lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co) and oxygen (O).

6. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the thickness of the surface portion is 35% or less of the total length of the average particle diameter (D50) of the positive electrode active material.

7. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the thickness of the surface portion is 1000 nm or less.

8. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the cobalt concentration of the coating layer is 80 to 94 at%.

9. In paragraph 1, A positive electrode active material for a lithium secondary battery having a cobalt concentration of 55 to 73 at% at the lower portion of the above contact interface.

10. In paragraph 1, A positive electrode active material for a lithium secondary battery having a cobalt concentration of 40 to 54 at% at the non-contact interface.

11. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the cobalt concentration of the above-mentioned isolation interface is 15 to 38 at%.

12. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the cobalt concentration of the above contact particles is 3 to 12 at%.

13. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the coating layer comprises cobalt-containing coating particles, and the major axis length of the coating particles is 50 nm to 1 μm.

14. In paragraph 1, The above lithium nickel manganese oxide is a positive electrode active material for a lithium secondary battery, wherein the secondary particles formed by agglomeration of primary particles have a spherical structure, and the average particle diameter (D50) of the secondary particles is 8 to 30 μm.

15. A step of preparing a transition metal hydroxide containing nickel (Ni) and manganese (Mn) and not containing cobalt (Co); A step of forming a mixture containing the above transition metal hydroxide and a lithium raw material and calcining it to form a lithium transition metal oxide that does not contain cobalt; and It includes a step of mixing the lithium transition metal oxide and cobalt raw material and heat-treating at a temperature of 570 to 730°C to form a coating layer. A method for producing a positive electrode active material for a lithium secondary battery, wherein the content of the cobalt raw material is 0.8 to 4 mol% based on the total moles of the lithium transition metal oxide and the cobalt raw material.

16. In paragraph 15, A method for producing a positive electrode active material for a lithium secondary battery, wherein the nickel content of the above transition metal hydroxide is 60 mol% or more based on the total mole number of transition metals.

17. In paragraph 15, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the long axis length of the cobalt raw material particles is 50 nm to 1 μm.

18. A lithium secondary battery comprising a positive electrode including a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 14; a negative electrode; and an electrolyte.

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