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, which is provided in the form of single particles, each comprising a nickel-containing lithium metal oxide core and a nickel-containing surface portion, wherein: the surface portion simultaneously contains nickel having an oxidation state of +2 (Ni2+) and nickel having an oxidation state of +3 (Ni3+); and, within the surface portion, at least one region having a Ni2+ / Ni3+ ratio higher than that at the outermost surface of the particle exists at a location closer to the center of the particle than to the outermost surface thereof.

Description

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

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

[0002]

[0003] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used due to its high operating voltage and excellent capacity characteristics, and is applied as a cathode active material for high voltage. However, due to the rising price of cobalt (Co) and unstable supply, it is difficult to use it in large quantities as a power source in fields such as electric vehicles, and the need for the development of a cathode active material that can replace it has arisen.

[0004] Accordingly, nickel-cobalt-manganese lithium composite transition metal oxides (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxides') have been developed, in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). However, the conventionally developed NCM-based lithium composite transition metal oxides are generally in the form of secondary particles in which primary particles are aggregated, and have a large specific surface area, low particle strength, and a high content of lithium byproducts, which causes a lot of gas generation during cell operation, resulting in low lifespan and stability. Therefore, development of cathode active materials in the form of single particles rather than the conventional secondary particles is being carried out.

[0005] Meanwhile, due to the increasing need for high-capacity batteries and rapid charging, there is a growing trend to use high-capacity SiOx in the anode by mixing it with graphite-based materials at a higher ratio. SiOx has a high capacity of 1,600 mAh / g and has the advantage of being cheaper than other Si-based materials due to its relatively simple manufacturing process. In addition, SiOx can be uniformly distributed in very small nano-sizes of 4 to 6 nm, which minimizes volume expansion of the battery during charge and discharge, making it a very advantageous material for pouch cells. However, it has a low initial efficiency of around 76%, which reduces battery capacity in a full cell when blended in a graphite anode.

[0006]

[0007] Accordingly, one object of the present invention is to provide a positive electrode active material for a lithium secondary battery, which is a lithium metal oxide in the form of a single particle and can improve the capacity characteristics of a full cell to which a Si-based negative electrode active material is applied, a method for producing the same, and a lithium secondary battery including the same.

[0008]

[0009] One embodiment of the present invention is a positive electrode active material particle in the form of a single particle comprising a nickel-containing lithium metal oxide core; and a nickel-containing surface portion, wherein the surface portion is nickel (Ni) having an oxidation number of +2. 2+ ) and nickel (Ni) with oxidation number +3 3+) , and within the surface portion, Ni is higher than the outermost surface of the particle. 2+ / Ni 3+ A cathode active material for a lithium secondary battery is provided, wherein at least one region with a large ratio exists at a position closer to the center of the particle than the outermost surface of the particle.

[0010] The surface portion is Ni as it goes from the outermost surface of the particle toward the center of the particle. 2+ / Ni 3+ There may be at least one nickel oxidation state gradient region with increasing ratio.

[0011] The above positive electrode active material for a lithium secondary battery can satisfy the following equation 1.

[0012] [Formula 1]

[0013] R surface < R 100nm < R 200nm

[0014] In the above equation 1, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ It is molar ratio, and R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0015] The above positive electrode active material for a lithium secondary battery can satisfy the following equation 2.

[0016] [Formula 2]

[0017] 2 ≤ R 100nm - R surface ≤ 15 (%)

[0018] In the above equation 2, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0019] The above positive electrode active material for a lithium secondary battery can satisfy the following equation 3.

[0020] [Formula 3]

[0021] 4 ≤ R 200nm - R 100nm ≤ 25 (%)

[0022] In the above equation 3, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0023] The above positive electrode active material for a lithium secondary battery can satisfy the following equation 4.

[0024] [Formula 4]

[0025] 6 ≤ R 200nm - R surface ≤ 40 (%)

[0026] In the above equation 4, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0027] The content of nickel in the lithium metal oxide core may be 80 mol% or more based on the total mole number of metals excluding lithium.

[0028] The above lithium metal oxide core may have a layered crystal structure.

[0029] The above surface portion may have a layered crystal structure.

[0030] The above surface portion may have a concentration gradient in which the concentration of nickel decreases from the outermost surface of the particle toward the center of the particle.

[0031] The surface portion may have a concentration gradient in which the concentration of at least one metal element other than lithium and nickel increases from the outermost surface of the particle toward the center of the particle.

[0032] The above surface portion contains lithium nickel oxide, and the content of the lithium nickel oxide may be 0.2 to 2.3 wt% based on the total weight of the positive electrode active material.

[0033] The above lithium metal oxide core can be represented by the following chemical formula 1.

[0034] [Chemical Formula 1]

[0035] Li a [Ni x Co y Mn z M W ]O2

[0036] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.1, x+y+z+w=1, and M is another doping element such as Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, Ca, K, Ga, or a combination thereof.

[0037] The above surface portion may contain lithium nickel oxide represented by the following chemical formula 2.

[0038] [Chemical Formula 2]

[0039] Li a Ni b O c

[0040] In the above chemical formula 2, 1.5≤a≤2.5, 0.8≤b≤1.2, 1.5≤c≤2.5.

[0041]

[0042] Another embodiment of the present invention comprises the steps of preparing a nickel-containing lithium metal oxide in the form of a single particle; and the step of mixing the lithium metal oxide and a nickel raw material, followed by heat treatment to form a positive electrode active material particle having a surface portion formed thereon, wherein the surface portion is nickel (Ni) having an oxidation number of +2. 2+ ) and nickel (Ni) with oxidation number +33+ ) and, within the surface portion, Ni is higher than the outermost surface of the particle. 2+ / Ni 3+ A method for manufacturing a positive electrode active material for a lithium secondary battery is provided, wherein at least one region with a large ratio exists at a position closer to the center of the particle than the outermost surface of the particle.

[0043] The amount of the nickel raw material input may be 0.2 to 2.3 wt% based on the total weight of the lithium metal oxide and nickel raw material.

[0044] The above heat treatment can be performed at a temperature of 400 to 600°C.

[0045] The above heat treatment can be performed in a nitrogen (N2) atmosphere.

[0046] The above nitrogen atmosphere may have a nitrogen partial pressure of 95% or more.

[0047]

[0048] Another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including the positive electrode active material described above; a negative electrode including a silicon-based negative electrode active material; and a separator positioned between the positive electrode and the negative electrode.

[0049] The above negative electrode may further include a carbon-based negative electrode active material.

[0050] The above negative electrode may have a content of silicon-based negative electrode active material of 5 wt% or more based on the total weight of the silicon-based negative electrode active material and the carbon-based negative electrode active material.

[0051] The above silicon-based negative electrode active material is Si, SiOx(0 <x<2) 또는 이들의 조합일 수 있다.

[0052]

[0053] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has a single particle form and includes a nickel-containing surface portion having a nickel oxidation number gradient, thereby improving the capacity characteristics of a full cell to which a Si-based negative electrode active material is applied.

[0054]

[0055] Figure 1 is a cross-sectional TEM image after FIB milling of a positive electrode active material manufactured according to Example 3.

[0056] Figure 2 is a TEM image of the surface of a positive electrode active material manufactured according to Example 3.

[0057] Figure 3 is a graph of Ni2p scan XPS depth profile analysis according to surface etching of a positive electrode active material manufactured according to Example 3.

[0058] Figure 4 is a graph of the concentration of Ni, Co, Mn, and O elements when analyzing the element depth profile according to surface etching of a positive electrode active material manufactured according to Example 3.

[0059]

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0065] 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.

[0066] 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.

[0067]

[0068] 1. Positive active material

[0069] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises cathode active material particles in the form of single particles. Compared to conventional secondary particles, the cathode active material in the form of single particles has a smaller specific surface area, which reduces the amount of gas generated by side reactions with the electrolyte. Furthermore, the cathode active material has a larger particle strength, which suppresses particle breakage during rolling, and reduces the occurrence of cracks during repeated charging and discharging. Accordingly, the cathode active material has superior lifespan and safety compared to secondary particles, and has the advantage of being able to realize high energy density of the electrode.

[0070] In this specification, “single particle” is a term used to distinguish it from the secondary particle form of positive electrode active material particles formed by agglomeration of tens to hundreds of primary particles, which have been commonly used in the past, and is a concept that includes a single particle composed of one primary particle and an aggregate particle of 20 or fewer primary particles.

[0071] Additionally, “secondary particle” refers to an aggregate, i.e., a secondary structure, in which tens to hundreds of primary particles are aggregated together by physical or chemical bonding between the primary particles without any intentional aggregation or assembly process for the primary particles.

[0072] In addition, “primary particle” refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be composed of one crystal grain or multiple crystal grains.

[0073] Meanwhile, a cathode active material for a lithium secondary battery according to one embodiment of the present invention includes a nickel-containing lithium metal oxide core. In this case, the lithium metal oxide may have a layered crystal structure and may further contain cobalt and / or manganese.

[0074] At this time, the content of nickel in the lithium metal oxide core may be 80 mol% or more, and more specifically, 85 mol% or 90 mol% or more, based on the total mole number of metals excluding lithium. As such, since the lithium metal oxide core contains a high content of nickel, the capacity and output characteristics may be improved.

[0075]

[0076] In particular, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention further includes a nickel-containing surface portion positioned on the core.

[0077] The nickel-containing surface portion may have a different composition from the lithium metal oxide core. Specifically, the nickel-containing surface portion may be a nickel-rich layer having a higher nickel concentration than the lithium metal oxide core portion.

[0078] Additionally, the nickel-containing surface portion may contain nickel, more specifically in the form of lithium nickel oxide.

[0079] At this time, the surface portion is nickel (Ni) with an oxidation number of +2. 2+ ) and nickel (Ni) with oxidation number +3 3+ ) are simultaneously contained, and at this time, within the surface portion, Ni is higher than the outermost surface of the particle. 2+ / Ni 3+ At least one region with a high ratio exists closer to the center of the particle than to the outermost surface of the particle.

[0080] More specifically, the surface portion is Ni as it goes from the outermost surface of the particle toward the center of the particle. 2+ / Ni 3+ There may be at least one nickel oxidation state gradient region with increasing ratio.

[0081] Typically, single particles use flux or high-temperature calcination technology to increase the primary particle size, and at this time, Ni is generally added to the particle surface in the form of NiO. 2+At this time, Ni exists on the particle surface. 2+ Not only Ni 3+ , and Ni is present as you go from the surface of the particle to the center of the particle. 2+ / Ni 3+ If at least a portion of the nickel oxidation number gradient region with increasing ratio exists, lithium insertion / de-insertion becomes smoother, resistance decreases, and this can be advantageous for capacity development. Consequently, the cathode active material according to the present invention can improve the capacity characteristics of a full cell using a Si-based anode active material.

[0082] However, the surface portion of the positive electrode active material according to the present invention does not necessarily have the nickel oxidation number gradient of the above tendency present in the entire surface portion, and locally, there may be no nickel oxidation number gradient or an irregular nickel oxidation number gradient may exist.

[0083] More specifically, the positive electrode active material according to the present invention can satisfy the following equation 1.

[0084] [Formula 1]

[0085] R surface < R 100nm < R 200nm

[0086] In the above equation 1, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0087] In addition, the positive electrode active material according to the present invention can satisfy the following equation 2.

[0088] [Formula 2]

[0089] 2 ≤ R 100nm - R surface ≤ 15 (%)

[0090] In the above equation 2, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0091] R 100nm - R surface If the value is too small, the degree of nickel oxidation number gradient may be too small, and the effect of improving the capacity characteristics of a full cell using a Si-based negative electrode active material due to nickel oxidation number gradient may be minimal. R 100nm - R surface If the value is too large, the structural stability may deteriorate due to the degree of nickel oxidation number gradient being too large, which may reduce the effect of improving capacity characteristics. Therefore, R 100nm - R surface When the value satisfies the above range, the capacity characteristic improvement effect can be more preferably implemented.

[0092] The above R 100nm - R surface The value may be more specifically 3 to 13% or 3 to 11%.

[0093] In addition, the positive electrode active material according to the present invention can satisfy the following equation 3.

[0094] [Formula 3]

[0095] 4 ≤ R 200nm - R 100nm ≤ 25 (%)

[0096] In the above equation 3, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0097] R 200nm - R 100nm If the value is too small, the degree of nickel oxidation number gradient may be too small, and the effect of improving the capacity characteristics of a full cell using a Si-based negative electrode active material due to nickel oxidation number gradient may be minimal. R 200nm - R 100nm If the value is too large, the structural stability may deteriorate due to the degree of nickel oxidation number gradient being too large, which may reduce the effect of improving capacity characteristics. Therefore, R 200nm - R 100nm When the value satisfies the above range, the capacity characteristic improvement effect can be more preferably implemented.

[0098] The above R 200nm - R 100nm The values ​​may be more specifically 6 to 22% or 9 to 19%.

[0099] In addition, the positive electrode active material according to the present invention can satisfy the following equation 4.

[0100] [Formula 4]

[0101] 6 ≤ R 200nm - R surface ≤ 40 (%)

[0102] In the above equation 4, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0103] R 200nm - R surfaceIf the value is too small, the degree of nickel oxidation number gradient may be too small, and the effect of improving the capacity characteristics of a full cell using a Si-based negative electrode active material due to nickel oxidation number gradient may be minimal. R 200nm - R surface If the value is too large, the structural stability may deteriorate due to the degree of nickel oxidation number gradient being too large, which may reduce the effect of improving capacity characteristics. Therefore, R 200nm - R surface When the value satisfies the above range, the capacity characteristic improvement effect can be more preferably implemented.

[0104] The above R 200nm - R surface The value may be more specifically 10 to 35%, 15 to 30% or 15 to 15%.

[0105] In addition, the positive electrode active material according to the present invention can satisfy the following equation 5.

[0106] [Formula 5]

[0107] R 100nm - R surface < R 200nm - R 100nm

[0108] In the above equation 5, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

[0109]

[0110] Meanwhile, the above R surface The value can be 40 to 90%, more specifically 50 to 90%. In addition, the R100nm The value can be between 42 and 90%, more specifically between 52 and 90%. In addition, the R 200nm The value can be between 46 and 92%, more specifically between 56 and 92%.

[0111] R surface value, R 100nm value or R 200nm When the value satisfies the above range, Ni 2+ Since the content is an appropriate amount capable of implementing a nickel oxidation number gradient on the surface of the positive electrode active material according to the present invention, but not an excessive amount, the capacity and output characteristics of the battery can be implemented more preferably.

[0112] In this specification, R surface The value can be measured by Ni2p scanning XPS (X-ray photoelectron spectroscopy) analysis of the outermost surface of the positive electrode active material particles.

[0113] Also, R 100nm The value can be measured by Ni2p scan XPS (X-ray photoelectron spectroscopy) analysis after etching 100 nm from the outermost surface of the positive electrode active material particle toward the particle center. At this time, etching is performed using Ar + Ions are used, and the etching speed can be 50 nm / min.

[0114] Also, R 200nm The value can be measured by Ni2p scan XPS (X-ray photoelectron spectroscopy) analysis after etching 200 nm from the outermost surface of the positive electrode active material particle toward the particle center. At this time, etching is performed using Ar + Ions are used, and the etching speed can be 50 nm / min.

[0115] Also at this time, Ni 2+ / Ni3+ The ratio was measured by XPS fitting, Ni 2+ Area and Ni 3+ It can be quantified as the ratio of the integrated values ​​over the area.

[0116] Meanwhile, the oxidation number gradient of nickel within the lithium metal oxide core according to the present invention is not particularly limited. For example, the lithium metal oxide core according to the present invention may have no nickel oxidation number gradient throughout the entire region. Or, as another example, the lithium metal oxide core according to the present invention may have no nickel oxidation number gradient in a region close to the center of the particle, while a nickel oxidation number gradient may exist to some extent in a region close to the surface.

[0117] At this time, the average Ni of nickel in the lithium metal oxide core region according to the present invention 2+ / Ni 3+ The ratio can be between 0 and 0.1%.

[0118]

[0119] Meanwhile, the surface portion may have a layered crystal structure. As mentioned above, the lithium metal oxide core according to the present invention may have a layered crystal structure. Since the surface portion also has a layered crystal structure, lithium ion movement may be facilitated, so that the effect of improving capacity characteristics may be more preferably implemented.

[0120] The crystal structure of the above surface portion can be confirmed through TEM (transmission electron microscope) image analysis of the positive electrode active material particles.

[0121]

[0122] Meanwhile, the surface portion may have a concentration gradient in which the nickel concentration decreases from the outermost surface of the particle toward the center of the particle. In this case, the nickel concentration gradient region may exist within a depth of 200 nm or 170 nm from the outermost surface of the particle toward the center of the particle. Accordingly, the capacity characteristics may be improved.

[0123] In addition, the surface portion may have a concentration gradient in which the concentration of at least one metal element excluding lithium and nickel increases from the outermost surface of the particle toward the center of the particle. In this case, the at least one metal element excluding lithium and nickel may be cobalt, manganese, or a combination thereof. In this case, the metal element concentration gradient region may exist within a depth of 200 nm or 170 nm from the outermost surface of the particle toward the center of the particle.

[0124] Meanwhile, the lithium metal oxide core may not have a concentration gradient of nickel, cobalt or manganese.

[0125]

[0126] Meanwhile, the surface portion contains lithium nickel oxide, and the content of the lithium nickel oxide may be 0.2 to 2.3 wt% based on the total weight of the positive electrode active material, and more specifically, may be 0.7 to 2.3 wt%. When the content of the lithium nickel oxide satisfies the above range, the nickel oxidation number concentration gradient within the surface portion can be appropriately controlled within the range according to the present invention, and thus the capacity characteristic improvement effect can be preferably implemented.

[0127] The lithium metal oxide core according to the present invention can be more specifically represented by the following chemical formula 1.

[0128] [Chemical Formula 1]

[0129] Li a [Ni x Co y Mn z M W]O2

[0130] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.1, x+y+z+w=1, and M is another doping element such as Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, Ca, K, Ga, or a combination thereof.

[0131] In the lithium metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to a, that is, 0.8≤a≤1.2. If a is too small, the capacity may be reduced, and if a is too large, the strength of the sintered positive electrode active material may be increased, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the control of the lithium content and the sinterability balance during the production of the active material, the lithium may be included in an amount of 0.9≤a≤1.1 more preferably.

[0132] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 0.8≤x<1 or 0.85≤x≤0.97. If the nickel content is too low, the capacity and output characteristics may deteriorate. If the nickel content is too high, the lifespan and thermal safety may deteriorate due to a decrease in the structural stability of the active material, and the manufacturing cost may increase.

[0133] In the lithium metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.2 or 0.01≤y≤0.15. If the cobalt amount is too low, grain size growth may be inhibited and output characteristics may deteriorate. If the cobalt amount is too high, manufacturing costs may increase and reversible capacity may decrease.

[0134] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0≤z≤0.2 or 0.01≤z≤0.15. If the manganese content is too low, the production cost may increase and the stability of the active material may deteriorate. If the manganese content is too high, the capacity and output characteristics of the battery may deteriorate.

[0135] In the lithium metal oxide of the above chemical formula 1, the doping element M may be included in a content corresponding to w, i.e., 0≤w≤0.1, and may be added and used in an appropriate amount to further improve the electrochemical characteristics of the battery.

[0136]

[0137] In addition, the surface portion according to the present invention may contain lithium nickel oxide represented by the following chemical formula 2 more specifically.

[0138] [Chemical Formula 2]

[0139] Li a Ni b O c

[0140] In the above chemical formula 1, 1.5≤a≤2.5, 0.8≤b≤1.2, 1.5≤c≤2.5.

[0141]

[0142] 2. Method for manufacturing positive electrode active material

[0143] The nickel oxidation number gradient tendency of the surface portion of the positive electrode active material according to the present invention can be more easily obtained by controlling a series of process conditions for forming the surface portion in the manufacturing method. Hereinafter, the manufacturing method of the positive electrode active material according to the present invention will be described.

[0144] Another embodiment of the present invention comprises the steps of preparing a nickel-containing lithium metal oxide in the form of a single particle; and the step of mixing the lithium metal oxide and a nickel raw material, followed by heat treatment to form a positive electrode active material particle having a surface portion formed thereon, wherein the surface portion is nickel (Ni) having an oxidation number of +2. 2+) and nickel (Ni) with oxidation number +3 3+ ) and the surface portion contains Ni as it goes from the outermost surface of the particle toward the center of the particle. 2+ / Ni 3+ A method for producing a positive electrode active material for a lithium secondary battery having a nickel oxidation number gradient with an increasing ratio is provided.

[0145] 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.

[0146]

[0147] First, a nickel-containing lithium metal oxide in the form of single particles is prepared.

[0148] The step of preparing a nickel-containing lithium metal oxide in the form of a single particle can be more specifically prepared by the steps of preparing a nickel-containing metal precursor, mixing the metal precursor and a lithium raw material, and then calcining to form a lithium metal oxide, and pulverizing the lithium metal oxide to form a nickel-containing lithium metal oxide in the form of a single particle.

[0149] First, a metal precursor containing nickel is prepared.

[0150] The nickel content in the above metal precursor may be 80 mol% or more based on the total molar number of the metal. Accordingly, the capacity and output characteristics of the battery can be more preferably implemented.

[0151] The above metal precursor may more specifically be a metal hydroxide.

[0152] The above metal hydroxide may be produced by a coprecipitation reaction by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a metal-containing solution including, for example, a nickel raw material and optionally a cobalt raw material or a manganese raw material.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] The above metal-containing solution may be prepared by adding nickel raw material and optionally cobalt raw material or manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] Through the above process, nickel (cobalt-manganese-doped element) hydroxide particles are generated and precipitated within the reaction solution. The precipitated precursor particles can be separated, washed, and dried using conventional methods to obtain a precursor. The precursor may be a secondary particle formed by the agglomeration of primary particles.

[0161] At this time, the ratio of nickel, cobalt, and manganese in the precursor can be controlled by adjusting the concentration of nickel raw material, cobalt raw material, and manganese raw material.

[0162] Accordingly, the content of nickel in the metal precursor can be controlled to 80 mol% or more based on the total mole number of transition metals. The technical significance of controlling the content of nickel in the transition metal precursor is as described above and therefore is omitted.

[0163] Next, the metal precursor and lithium raw material are mixed and then calcined to form lithium metal oxide.

[0164] At this time, the sintering can be performed at a temperature of 800 to 900°C, more specifically 820 to 890°C or 840 to 890°C. When the sintering temperature satisfies the above range, lithium metal oxide in the form of single particles can be formed, while at the same time, deterioration of electrochemical properties due to oversintering can be prevented.

[0165] In addition, the above-mentioned calcination can be performed in an oxygen atmosphere, and as it is performed in an oxygen atmosphere, the layered structure crystallinity of the lithium metal oxide is improved, so that the electrochemical properties can be preferably implemented.

[0166] Next, the lithium metal oxide is crushed to form a nickel-containing lithium metal oxide in the form of single particles.

[0167] The above-mentioned disintegration method is not particularly limited and can be applied without limitation using methods common in the art.

[0168]

[0169] Next, the lithium metal oxide and nickel raw material are mixed and then heat-treated to form positive electrode active material particles having a surface portion.

[0170] At this time, the nickel raw material may be more specifically lithium nickel oxide, and may be, for example, Li2NiO2 or a compound in which Li2NiO2 is doped with other doping elements, but is not necessarily limited thereto.

[0171] At this time, the amount of nickel raw material input may be 0.2 to 2.3 wt% based on the total weight of the lithium metal oxide and nickel raw material, and more specifically, may be 0.7 to 2.3 wt%. When the amount of nickel raw material input satisfies the above range, the nickel oxidation number concentration gradient within the surface of the positive electrode active material can be appropriately controlled within the range according to the present invention, and thus the effect of improving capacity characteristics can be preferably implemented.

[0172] In addition, the heat treatment can be performed at a temperature of 400 to 600°C, and more specifically, can be performed at a temperature of 420 to 580°C or 430 to 570°C. When the heat treatment temperature satisfies the above range, the nickel oxidation number concentration gradient within the surface of the positive electrode active material can be appropriately controlled within the range according to the present invention, and thus, the effect of improving capacity characteristics can be preferably implemented.

[0173] In addition, the heat treatment can be performed for 2 to 5 hours. When the heat treatment time satisfies the above range, the nickel oxidation number concentration gradient within the surface of the positive electrode active material can be appropriately controlled within the range according to the present invention, and thus the capacity characteristic improvement effect can be preferably implemented.

[0174] Additionally, the heat treatment may be performed in a nitrogen (N2) atmosphere. The nitrogen atmosphere may have a nitrogen partial pressure of 95% or higher. By controlling the heat treatment atmosphere to the above conditions, the nickel oxidation number concentration gradient within the surface of the positive electrode active material can be appropriately controlled within the range of the present invention, thereby achieving a desirable capacity characteristic enhancement effect.

[0175]

[0176] 3. Cathode ray and lithium secondary battery

[0177] Another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including the positive electrode active material described above; a negative electrode including a silicon-based negative electrode active material; and a separator positioned between the positive electrode and the negative electrode.

[0178] Since the positive electrode active material included in the above positive electrode is the same as the positive electrode active material according to the embodiment of the present invention described above, a detailed description thereof is omitted.

[0179] In addition, the negative electrode includes a silicon-based negative electrode active material and may further include a carbon-based negative electrode active material.

[0180] At this time, the content of the silicon-based negative electrode active material may be 5 wt% or more, and more specifically, 8 wt% or 10 wt% or more, based on the total weight of the silicon-based negative electrode active material and the carbon-based negative electrode active material.

[0181] In general, silicon-based negative electrode active materials have a low initial efficiency of around 70%, which causes a problem in that the capacity of a full cell using silicon-based negative electrode active materials deteriorates.

[0182] However, a lithium secondary battery according to another embodiment of the present invention can improve the capacity of a full cell to which a silicon-based negative electrode active material is applied by applying the aforementioned positive electrode active material. In particular, even if the content of the silicon-based negative electrode active material is included at a high content such as the above range (5 wt% or 10 wt% or more based on the total weight of the silicon-based negative electrode active material and the carbon-based negative electrode active material), the problem of initial efficiency decline can be prevented, thereby improving the capacity of the full cell.

[0183] Accordingly, the initial discharge capacity of a silicon-based negative electrode active material full cell to which the positive electrode active material according to the present invention is not applied is at a level of 85 mAh, whereas when the positive electrode active material according to the present invention is applied, the initial discharge capacity can be implemented at a level of 87 mAh or more, more specifically, 88 mAh or more.

[0184] Meanwhile, the above silicon-based negative electrode active material is Si, SiOx(0 <x<2) 또는 이들의 조합일 수 있다.

[0185] Additionally, the carbon-based negative electrode active material may be natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, or a combination thereof.

[0186] The above amorphous carbon may be soft carbon, hard carbon, or a combination thereof.

[0187]

[0188] Hereinafter, the remaining configuration of a lithium secondary battery according to another embodiment of the present invention will be described in more detail.

[0189] The above positive electrode provides a positive electrode for a lithium secondary battery including the positive electrode active material described above.

[0190] More 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199]

[0200] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0201] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] The above binder and conductive material may be the same as those described above for the positive electrode.

[0207]

[0208] 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.

[0209]

[0210] 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.

[0211] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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).

[0216] 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.

[0217] 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 power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0218]

[0219] 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.

[0220]

[0221] Example 1

[0222] (1) Manufacturing of positive electrode active material

[0223] (Preparation of lithium metal oxide in single particle form) Ni 0.93 Co 0.04 Mn 0.03 After mixing a metal precursor of (OH)2 composition and LiOH·H2O, lithium metal oxide was formed by calcining at a temperature of 870°C for 20 hours in an oxygen atmosphere. Thereafter, the lithium metal oxide was pulverized to prepare lithium metal oxide in the form of single particles.

[0224] (Surface portion formation) After mixing the lithium metal oxide and nickel raw material Li2NiO2, the surface portion was formed by heat-treating at a temperature of 500°C for 4 hours in a nitrogen atmosphere with a nitrogen (N2) partial pressure of 95%. At this time, the amount of Li2NiO2 added was set to 0.3 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0225] Meanwhile, the Li2NiO2 was prepared by the following method. LiOH·H2O (Sigma-Aldrich, battery grade) was reacted with hydrogen peroxide (H2O2), vacuum-dried, and then calcined at approximately 900°C for 3 hours under a nitrogen (N2) atmosphere to form a Li2O intermediate. Thereafter, Li2O and NiO were mixed and calcined at approximately 700°C for 12 hours under a nitrogen (N2) atmosphere to prepare Li2NiO2.

[0226] (2) Manufacturing of lithium secondary batteries (full cells)

[0227] The positive electrode plate was prepared by mixing 96 wt% of the above-mentioned manufactured positive electrode active material, 1 wt% of carbon nanotubes (CNTs) as a conductive material, and 3 wt% of PTFE (polytetrafluoroethylene) as a dry binder, and then kneading the mixture at 30 rpm for 5 minutes at a temperature below about 100°C. Afterwards, it was placed in a 3-roll mill and repeated until a uniform positive electrode plate was obtained, ultimately obtaining a positive electrode plate in the form of a sheet. At this time, the temperature of the rolls was maintained at about 60°C, and the gap between each roll was 75 μm. The positive electrode plate thus manufactured was pressed onto an aluminum current collector (15 μm) to prepare a positive electrode.

[0228] The negative electrode plate was manufactured by mixing natural graphite (POSCO Future M) with an initial efficiency of 90.5% and SiOx (POSCO Silicon Solution) with an initial efficiency of 76% in a weight ratio of 90:10, applying the mixture to a copper current collector (10 μm) using a CMC / SBR aqueous binder, drying, and rolling. The N / P ratio of the positive and negative electrodes was designed to be 1.13, and the negative electrode capacity was designed to match the positive electrode capacity.

[0229] The separator used was a polyolefin-based PE separator, and the electrolyte used was EC:DEC=1:1, 1M LiPF6. To manufacture a pouch cell, the separator was placed between the positive and negative plates, the positive and negative tabs were ultrasonically welded with nickel terminals, and this was placed in an aluminum pouch, the electrolyte was injected, and the pouch was sealed to manufacture a full cell in the form of a monocell.

[0230]

[0231] Example 2

[0232] In the surface formation step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of Li2NiO2 added was set to 1 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0233]

[0234] Example 3

[0235] In the surface formation step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of Li2NiO2 added was set to 1.5 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0236]

[0237] Example 4

[0238] In the surface formation step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of Li2NiO2 added was set to 2 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0239]

[0240] Example 5

[0241] In the surface formation step, the amount of Li2NiO2 added was set to 0.5 wt% based on the total weight of lithium metal oxide and Li2NiO2, and heat treatment was performed at a temperature of 450°C, and the same procedure as Example 1 was performed to manufacture a cathode active material and a lithium secondary battery.

[0242]

[0243] Example 6

[0244] In the surface formation step, the amount of Li2NiO2 added was set to 0.5 wt% based on the total weight of lithium metal oxide and Li2NiO2, and heat treatment was performed at a temperature of 550°C, and the same procedure as Example 1 was performed to manufacture a cathode active material and a lithium secondary battery.

[0245]

[0246] Comparative Example 1

[0247] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the surface shaping step was not performed after preparing lithium metal oxide in the form of single particles.

[0248]

[0249] Comparative Example 2

[0250] In the surface formation step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of Li2NiO2 added was set to 0.15 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0251]

[0252] Comparative Example 3

[0253] In the surface formation step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of Li2NiO2 added was set to 2.5 wt% based on the total weight of lithium metal oxide and Li2NiO2.

[0254]

[0255] Comparative Example 4

[0256] In the surface formation step, the amount of Li2NiO2 added was set to 0.5 wt% based on the total weight of lithium metal oxide and Li2NiO2, and heat treatment was performed at a temperature of 380°C, and the same procedure as Example 1 was performed to manufacture a cathode active material and a lithium secondary battery.

[0257]

[0258] Comparative Example 5

[0259] In the surface formation step, the amount of Li2NiO2 added was set to 0.5 wt% based on the total weight of lithium metal oxide and Li2NiO2, and heat treatment was performed at a temperature of 620°C, and the same procedure as Example 1 was performed to manufacture a cathode active material and a lithium secondary battery.

[0260]

[0261] Comparative Example 6

[0262] In the surface formation step, the amount of Li2NiO2 added was set to 0.5 wt% based on the total weight of lithium metal oxide and Li2NiO2, and heat treatment was performed under an air atmosphere with a nitrogen (N2) partial pressure of about 78%, and a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1.

[0263]

[0264] Table 1 below summarizes the process conditions of examples and comparative examples.

[0265] Li2NiO2Dosage (wt%)Heat treatment temperature (℃)Heat treatment atmosphereComparative Example 10--Comparative Example 20.15500N2Example 10.3500N2Example 21500N2Example 31.5500N2Example 42500N2Example 50.5450N2Example 60.5550N2Comparative Example 32.5500N2Comparative Example 40.5380N2Comparative Example 50.5620N2Comparative Example 60.5500Air

[0266]

[0267] Tables 2 and 3 below are tables summarizing the results of evaluating the properties of positive electrode active materials and the capacity characteristics of lithium secondary batteries according to Experimental Examples 3 and 4 described below.

[0268] Ni on the surface 2+ / Ni 3+ Ratio (%)(R surface )Ni at 100 nm depth 2+ / Ni 3+ Ratio (%)(R 100nm )Ni at 200 nm depth 2+ / Ni 3+ Ratio (%)(R 200nm )R 100nm - R surface (%)R 200nm - R 100nm (%)R 200nm - R surface (%)Comparative Example 1100100-90-10-100Comparative Example 2968780-9-7-16Example 165738681321Example 265748591120Example 368778891120Example 470749141721Example 570759051520Example 669748951520Comparative Example 3929189-1-2-3Comparative Example 4979593-2-2-4Comparative Example 5989694-2-2-4Comparative Example 69898950-3-3

[0269] Initial charge capacity (mAh) Initial discharge capacity (mAh) Initial efficiency (%) Comparative example 194.28 5.29 0.4 Comparative example 298.5 85.186.4 Exemplary example 198.8 87.38 8.4 Exemplary example 2100.38 9.38 9.0 Exemplary example 3100.39 1.39 1.0 Exemplary example 499.8 88.5 8.7 Exemplary example 598.6 87.28 8.4 Exemplary example 698.9 87.38 8.3 Comparative example 393.0 84.39 0.6 Comparative example 492.28 3.7 90.8 Comparative example 591.6 83.4 91.0 Comparative example 684.27 6.69 1.0

[0270]

[0271] Experimental Example 1: TEM Image Analysis of the Positive Active Material

[0272] A cross-sectional TEM (transmission electron microscope) image of the positive electrode active material manufactured according to Example 3 after FIB (Focused Ion Beam) milling was observed, and is shown in Fig. 1.

[0273] In addition, the surface of the positive electrode active material manufactured according to Example 3 was observed through a TEM (transmission electron microscope) image, which is shown in Fig. 2.

[0274] Referring to Fig. 1, it was confirmed that the cathode active material of the example had a particle size of about 5 μm and a monolithic particle form consisting of about 8 primary particles.

[0275] Referring to Fig. 2, it was confirmed that the positive electrode active material of the embodiment had a surface portion attached to the surface of the lithium metal oxide core. In addition, the TEM image analysis results confirmed that both the lithium metal oxide core and the surface portion had a layered crystal structure.

[0276]

[0277] Experimental Example 2: Evaluation of the Cathode Active Material Concentration Gradient

[0278] The concentrations of Ni, Co, Mn, and O elements were analyzed through XPS depth profile analysis for the positive electrode active material manufactured according to Example 3, and the results are shown in Fig. 4. In Fig. 4, the right side of the horizontal axis is the direction of the outermost surface of the positive electrode active material particles, the left side is the direction of the center of the positive electrode active material particles, and the rightmost side of the horizontal axis of Fig. 4 is the outermost surface of the positive electrode active material particles.

[0279] Referring to Fig. 4, it was confirmed that the positive electrode active material of the embodiment had a concentration gradient in which nickel concentration decreased from the particle surface toward the center. In contrast, it was confirmed that cobalt and manganese concentrations increased from the particle surface toward the center.

[0280] In addition, it was confirmed that the surface of the positive electrode active material of the example was a nickel-rich layer having a higher nickel concentration than the nickel concentration of the lithium metal oxide core. In addition, it was confirmed that the surface of the positive electrode active material of the example was composed of lithium nickel oxide containing nickel and oxygen as main components.

[0281]

[0282] Experimental Example 3: Evaluation of the oxidation state gradient of nickel, a cathode active material

[0283] For the positive electrode active material powder particles manufactured according to the examples and comparative examples, Ni2p scan XPS (X-ray photoelectron spectroscopy) analysis was performed up to a total depth of 200 nm while etching the particle surface at 20 nm intervals from the particle surface, and through this, Ni at the corresponding location was analyzed. 2+ / Ni 3+ The ratio was measured and shown in Table 2. At this time, etching was done using Ar + Ions were used, and the etching speed was 50 nm / min.

[0284] At this time R surfaceThe values ​​were measured by Ni2p scan XPS analysis at the outermost surface of the positive electrode active material particles. 2+ / Ni 3+ It's a ratio.

[0285] Also, R 100nm The values ​​were measured by Ni2p scan XPS (X-ray photoelectron spectroscopy) analysis after etching 100 nm from the outermost surface of the positive electrode active material particles toward the particle center. 2+ / Ni 3+ It's a ratio.

[0286] Also, R 200nm The values ​​were measured by Ni2p scan XPS (X-ray photoelectron spectroscopy) analysis after etching 200 nm from the outermost surface of the positive electrode active material particles toward the particle center. 2+ / Ni 3+ It's a ratio.

[0287] At this time, Ni 2+ / Ni 3+ The ratio was measured by XPS fitting, Ni 2+ Area and Ni 3+ The area was quantified as the ratio of the integrated values.

[0288] In addition, the XPS analysis depth profile analysis results of the positive electrode active material manufactured according to Example 3 are shown in Fig. 3.

[0289] Referring to Table 2 and Figure 3, the positive electrode active material surface portion according to an embodiment in which the surface portion forming process conditions are appropriately controlled is Ni. 2+ and Ni 3+ Contains Ni at the same time, but as you go from the particle surface to the center, 2+ / Ni 3+ It was confirmed that at least some regions of nickel oxidation state gradient with increasing ratio exist.

[0290] On the other hand, when the surface portion is not formed (Comparative Example 1), the amount of nickel raw material Li2NiO2 is too small or large (Comparative Examples 2 and 3), the heat treatment temperature is too low or high (Comparative Examples 4 and 5), or the heat treatment atmosphere is an air atmosphere (Comparative Example 6), it was confirmed that the surface portion does not have the nickel oxidation number gradient tendency.

[0291]

[0292] Experimental Example 4: Evaluation of Capacity Characteristics of Lithium Secondary Battery (Full Cell)

[0293] After full cell fabrication, the initial formation was performed in the voltage range of 4.25 V to 2.5 V under the charge / discharge conditions of 0.1 C at 25°C (reference capacity 190 mAh / g), and the internal gas was removed. Then, the charge / discharge process was performed again to measure the initial capacity of the full cell, which is shown in Table 3.

[0294] Referring to Table 3, in the case of Examples 1 to 6 where the surface portion has a nickel oxidation number concentration gradient according to the present invention and satisfies Equations 1 to 4, etc., it was confirmed that the initial charge and discharge capacity of the full cell to which the Si-based negative electrode active material was applied was high.

[0295] On the other hand, in the case of Comparative Examples 1 to 6, where there is no nickel oxidation number concentration gradient on the surface and Equations 1 to 4 are not satisfied, it was confirmed that the initial charge and discharge capacity of the full cell to which the Si-based negative electrode active material was applied was significantly deteriorated compared to the examples.

[0296] Meanwhile, when comparing the examples in more detail, it was confirmed that in the case of Examples 2 to 4, where the amount of nickel raw material input (content of lithium nickel oxide in the surface portion) was more appropriately controlled, the effect of improving capacity characteristics was more preferably implemented.

[0297]

[0298] 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.

[0299] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A single particle of positive electrode active material comprising a nickel-containing lithium metal oxide core and a nickel-containing surface portion, The above surface portion is nickel (Ni) with an oxidation number of +2. 2+ ) and nickel (Ni) with oxidation number +3 3+ ) simultaneously, Within the above surface area, Ni is higher than the outermost surface of the particle. 2+ / Ni 3+ A cathode active material for a lithium secondary battery, wherein at least one region with a large ratio exists at a position closer to the center of the particle than the outermost surface of the particle.

2. In paragraph 1, The surface portion is Ni as it goes from the outermost surface of the particle toward the center of the particle. 2+ / Ni 3+ A cathode active material for a lithium secondary battery having at least one nickel oxidation number gradient region with an increasing ratio.

3. In paragraph 1, A cathode active material for a lithium secondary battery satisfying the following equation 1: [Formula 1] R surface < R 100nm < R 200nm In the above equation 1, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

4. In paragraph 1, A cathode active material for a lithium secondary battery satisfying the following equation 2: [Formula 2] 2 ≤ R 100nm - R surface ≤ 15 (%) In the above equation 2, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

5. In paragraph 1, A cathode active material for a lithium secondary battery satisfying the following equation 3: [Formula 3] 4 ≤ R 200nm - R 100nm ≤ 25 (%) In the above equation 3, R 100nm Ni measured at a depth of 100 nm from the particle surface toward the particle center. 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

6. In paragraph 1, A cathode active material for a lithium secondary battery satisfying the following equation 4: [Formula 4] 6 ≤ R 200nm - R surface ≤ 40 (%) In the above equation 4, R surface Ni measured at the outermost surface of the particle 2+ / Ni 3+ is the ratio, R 200nm Ni measured at a depth of 200 nm from the particle surface toward the particle center. 2+ / Ni 3+ It's a ratio.

7. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of nickel in the lithium metal oxide core is 80 mol% or more based on the total mole number of metals excluding lithium.

8. In paragraph 1, The above lithium metal oxide core is a positive electrode active material for a lithium secondary battery having a layered crystal structure.

9. In paragraph 1, The above surface portion is a positive electrode active material for a lithium secondary battery having a layered crystal structure.

10. In paragraph 1, The above surface portion is a positive electrode active material for a lithium secondary battery having a concentration gradient in which the concentration of nickel decreases from the outermost surface of the particle toward the center of the particle.

11. In paragraph 1, A positive electrode active material for a lithium secondary battery having a concentration gradient in which the concentration of at least one metal element other than lithium and nickel increases from the outermost surface of the particle toward the center of the particle.

12. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the surface portion contains lithium nickel oxide, and the content of the lithium nickel oxide is 0.2 to 2.3 wt% based on the total weight of the positive electrode active material.

13. In paragraph 1, The above lithium metal oxide core 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 Co y Mr z M W ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.1, x+y+z+w=1, and M is another doping element such as Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, Ca, K, Ga, or a combination thereof.

14. In paragraph 1, The surface portion is a positive electrode active material for a lithium secondary battery containing lithium nickel oxide represented by the following chemical formula 2: [Chemical Formula 2] Li a Ni b O c In the above chemical formula 1, 1.5≤a≤2.5, 0.8≤b≤1.2, 1.5≤c≤2.

5.

15. A step for preparing a nickel-containing lithium metal oxide in the form of a single particle; and It includes a step of forming positive electrode active material particles having a surface portion formed by mixing the lithium metal oxide and nickel raw material and then performing heat treatment. The above surface portion is nickel (Ni) with an oxidation number of +2. 2+ ) and nickel (Ni) with oxidation number +3 3+ ) and, within the surface portion, Ni is higher than the outermost surface of the particle. 2+ / Ni 3+ A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein at least one region with a large ratio exists at a position closer to the center of the particle than the outermost surface of the particle.

16. In paragraph 15, A method for producing a cathode active material for a lithium secondary battery, wherein the amount of the nickel raw material input is 0.2 to 2.3 wt% based on the total weight of the lithium metal oxide and nickel raw material.

17. In paragraph 15, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above heat treatment is performed at a temperature of 400 to 600°C.

18. In paragraph 15, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above heat treatment is performed in a nitrogen (N2) atmosphere.

19. In paragraph 18, The above nitrogen atmosphere is a method for manufacturing a positive electrode active material for a lithium secondary battery having a nitrogen partial pressure of 95% or more.

20. A positive electrode comprising the positive electrode active material of paragraph 1; A negative electrode comprising a silicon-based negative electrode active material; and A lithium secondary battery comprising a separator positioned between the positive and negative electrodes.

21. In paragraph 20, A lithium secondary battery wherein the negative electrode further comprises a carbon-based negative electrode active material.

22. In paragraph 21, The above negative electrode is a lithium secondary battery in which the content of the silicon-based negative electrode active material is 5 wt% or more based on the total weight of the silicon-based negative electrode active material and the carbon-based negative electrode active material.

23. In paragraph 20, The above silicon-based negative electrode active material is Si, SiOx(0 <x<2) 또는 이들의 조합인 리튬 이차 전지.

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