Positive electrode active material and lithium secondary battery comprising same

Abstract

The present specification relates to a positive electrode active material and a lithium secondary battery comprising same, and, more specifically, to a positive electrode active material and a lithium secondary battery comprising same, the positive electrode active material comprising a lithium composite oxide, wherein the lithium composite oxide is in the form of a secondary particle formed by aggregation of a plurality of primary particles, and a concentration gradient of an Al element is formed in a region close to the surface of each of the one or more primary particles such that the structural stability of the particle surface can be improved.

Description

positive electrode active material and lithium secondary battery containing the same

[0001] The present specification relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present specification relates to a positive electrode active material comprising a lithium composite oxide, wherein the lithium composite oxide is in the form of a secondary particle formed by the aggregation of a plurality of primary particles, and wherein it is possible to improve the structural stability of the particle surface by forming a concentration gradient of Al elements in a region close to the surface of one or more primary particles, and to a lithium secondary battery including the same.

[0002]

[0003] A battery stores electrical power by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such a battery is the lithium secondary battery, which stores electrical energy based on the difference in chemical potential when lithium ions intercalate or deintercalate at the positive and negative electrodes.

[0004] The above lithium secondary battery is manufactured by using materials capable of reversible intercalation / deintercalation of lithium ions as positive and negative active materials, and by filling an organic electrolyte or a polymer electrolyte between the positive and negative electrodes.

[0005] Lithium composite oxides are used as cathode active materials for lithium secondary batteries, and examples of such composite oxides being studied include LiCoO2, LiMn2O4, LiNiO2, and LiMnO2.

[0006] Among the above-mentioned cathode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency; however, it has the disadvantage of limited price competitiveness because the cobalt used as a raw material is expensive.

[0007] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low cost, but they have the problem of low capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials have the advantage of exhibiting high discharge capacity, but they are difficult to synthesize due to active cation mixing of Li and Ni, and the rate characteristics and lifespan characteristics of the synthesized cathode active materials are very low.

[0008] Accordingly, in order to improve low rate and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, lithium composite oxides of ternary types such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary types such as NCMA (Ni-Co-Mn-Al) have been developed in which some of the nickel is substituted with cobalt, manganese, and / or aluminum. Since the reversible capacity decreases as the nickel content in these ternary or quaternary type lithium composite oxides decreases, research to increase the nickel content in lithium composite oxides has recently been actively conducted.

[0009] However, as the nickel content in the lithium composite oxide increases, the mixing of cations within the crystal structure increases, leading to a decrease in stability or an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface. As the content of lithium impurities remaining on the surface of the lithium composite oxide increases, gas generation and swelling phenomena may be accelerated in the lithium secondary battery using the lithium composite oxide as a positive electrode active material. Furthermore, as the content of lithium impurities remaining on the surface of the lithium composite oxide increases, there is a problem in that the paste composition becomes gelled due to the lithium impurities when preparing a paste for forming a positive electrode active material layer using the lithium composite oxide.

[0010]

[0011] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is acting as a driving force, and accordingly, the demand for cathode active materials used in lithium secondary batteries is also continuously increasing.

[0012] For example, in the past, lithium secondary batteries using lithium iron phosphate (LFP) were mainly used for reasons such as ensuring safety, but recently, there has been a growing trend of using nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFP (of course, relatively cheaper LFP is still used to reduce costs).

[0013] Accordingly, cathode active materials used in higher-performance lithium secondary batteries need to satisfy both the stability and reliability appropriately expected even under harsher operating conditions.

[0014] Considering these various conditions, the present specification has one objective of providing a positive electrode active material comprising a lithium composite oxide containing at least aluminum and a transition metal, wherein the aluminum is doped into the lithium composite oxide and a concentration gradient is formed on at least a portion of the surface of the primary particles of the lithium composite oxide to improve the structural stability of the surface portion.

[0015] In addition, another objective of this specification is to provide a lithium secondary battery using the positive active material defined herein.

[0016] The purposes of this specification are not limited to those mentioned above, and other purposes and advantages of this specification not mentioned may be understood from the following description and will be more clearly understood by the embodiments of this specification. Furthermore, it will be readily apparent that the purposes and advantages of the invention can be realized by the means and combinations thereof set forth in the claims.

[0017]

[0018] According to one aspect of the present specification, a positive electrode active material is provided, comprising a lithium composite oxide capable of intercalation / deintercalation of lithium, wherein the lithium composite oxide comprises at least lithium, aluminum, and a transition metal, wherein the lithium composite oxide is a secondary particle formed by the aggregation of a plurality of primary particles, and wherein one or more Al elements contained within the primary particles exhibit a concentration gradient that decreases toward the center of the primary particles.

[0019] In one embodiment, at least some of the Al elements in the lithium composite oxide may exist in a doped state within the primary particle.

[0020] Meanwhile, the concentration gradient of the Al element may exist only up to a predetermined depth from the surface of the primary particle. For example, a predetermined depth refers to when the diameter of the primary particle is r, 0.001r, 0.002r, 0.003r, 0.004r, 0.005r, 0.006r, 0.007r, 0.008r, 0.009r, 0.01r, 0.011r, 0.012r, 0.013r, 0.014r, 0.015r, 0.016r, 0.017r, 0.018r, 0.019r, 0.02r, 0.021r, 0.022r, 0.023r, 0.024r, 0.025r, 0.026r, 0.027r, 0.028r, 0.029r, 0.03r, 0.035r, 0.04r, 0.045r, 0.05r, 0.055r, 0.06r, 0.065r, 0.07r, 0.075r, 0.08r, 0.085r, 0.09r, 0.095r, 0.1r, 0.105r, 0.11r, 0.115r, 0.12r, 0.125r, 0.13r, 0.135r, 0.14r, 0.145r, 0.15r, 0.155r, 0.16r, 0.165r, 0.17r, 0.175r, 0.18r, It may be 0.185r, 0.19r, 0.195r, 0.2r, or a range between two of these values, but is not limited thereto.

[0021] Meanwhile, the depth of the Al element concentration gradient formed in the long axis direction of the primary particle and the depth of the Al element concentration gradient formed in the short axis direction of the primary particle may be different or the same.

[0022] In one example, in the primary particle, the thickness of the concentration gradient layer in which a concentration gradient in which the Al element decreases toward the center of the primary particle appears is 0.1 to 200 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm. nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm, 20 nm, 20.5 nm, 21 nm, 21.5 nm, 22 nm, 22.5 nm, 23 nm, 23.5 nm, 24 nm, 24.5 nm, 25 nm, 25.5 nm, 26 nm, 26.5 nm, 27 nm, 27.5 nm, 28 nm, 28.5 nm, 29 nm, 29.5 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm. nm, 190 nm, 200 nm Or it may be a range between two of these values, but is not limited thereto.

[0023] Here, in one or more primary particles, from the surface of the primary particle toward the center of the primary particle, 0.1 to 200 nm, e.g., 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm, 20 nm, 20.5 nm, 21 nm, 21.5 nm, 22 nm, 22.5 nm, 23 nm, 23.5 nm, 24 nm, 24.5 nm, 25 nm, 25.5 nm, 26 nm, 26.5 nm, 27 nm, 27.5 nm, 28 nm, 28.5 nm, 29 nm, 29.5 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm. nm, 200 nm, or between these two values. There may exist regions within the range where Al elements are concentrated.

[0024] In addition, at least one of the transition metal elements, excluding the Al element, in one or more of the primary particles may exhibit a concentration gradient that increases toward the center of the primary particles.

[0025] Meanwhile, the concentration gradient of the transition metal element may exist only up to a predetermined depth from the surface of the primary particle. For example, a predetermined depth refers to when the diameter of the primary particle is r, 0.001r, 0.002r, 0.003r, 0.004r, 0.005r, 0.006r, 0.007r, 0.008r, 0.009r, 0.01r, 0.011r, 0.012r, 0.013r, 0.014r, 0.015r, 0.016r, 0.017r, 0.018r, 0.019r, 0.02r, 0.021r, 0.022r, 0.023r, 0.024r, 0.025r, 0.026r, 0.027r, 0.028r, 0.029r, 0.03r, 0.035r, 0.04r, 0.045r, 0.05r, 0.055r, 0.06r, 0.065r, 0.07r, 0.075r, 0.08r, 0.085r, 0.09r, 0.095r, 0.1r, 0.105r, 0.11r, 0.115r, 0.12r, 0.125r, 0.13r, 0.135r, 0.14r, 0.145r, 0.15r, 0.155r, 0.16r, 0.165r, 0.17r, 0.175r, 0.18r, It may be 0.185r, 0.19r, 0.195r, 0.2r, or a range between two of these values, but is not limited thereto.

[0026] In addition, the average particle size (D) of the primary particle above 50) is 200 nm to 2,000 nm, for example, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 425 nm, 450 nm, 475 nm, 500 nm, 525 nm, 550 nm, 575 nm, 600 nm, 625 nm, 650 nm, 675 nm, 700 nm, 725 nm, 750 nm, 775 nm, 800 nm, 825 nm, 850 nm, 875 nm, 900 nm, 925 nm, 950 nm, 975 nm, 1,000 nm, 1,025 nm, 1,050 nm, 1,075 nm, 1,100 nm, 1,125 nm, 1,150 nm, 1,175 nm, 1,200 nm, 1,225 nm, 1,250 nm, 1,275 nm, 1,300 nm, 1,325 nm, 1,350 nm, 1,375 nm, 1,400 nm, 1,425 nm, 1,450 nm, 1,475 nm, 1,500 nm, 1,525 nm, 1,550 nm, 1,575 nm, 1,600 nm, 1,625 nm, 1,650 nm, 1,675 nm, 1,700 nm, 1,725 ​​nm, 1,750 nm, 1,775 nm, 1,800 nm, 1,825 nm, 1,850 nm nm, 1,875 nm, 1,900 nm, 1,925 nm, 1,950 nm, 1,975 nm, 2,000 nm, or a range between two of these values.

[0027] In one embodiment, the lithium composite oxide may be represented by the following chemical formula 1:

[0028] [Chemical Formula 1]

[0029] Li w Ni 1-(x+y+z) M1 x M2 y Al z O2

[0030] In the above chemical formula 1, M1 is at least one selected from Co and Mn, and M2 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, and 0.5≤w≤1.5, 0 <x≤0.34, 0≤y≤0.20, 0<z≤0.33이다. 여기서 상기 w는 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50 또는 이들 중 두 값의 사이 범위일 수 있고, 상기 x는 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, 0.31, 0.34 또는 이들 중 두 값의 사이 범위일 수 있으며, 상기 y는 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 또는 이들 중 두 값의 사이 범위일 수 있고, 상기 z는 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, 0.31, 0.33 또는 이들 중 두 값의 사이 범위일 수 있다.

[0031] Meanwhile, a coating layer containing lithium and aluminum may be formed on at least a portion of the surface of one or more of the above secondary particles.

[0032] In one example, the coating layer may comprise a lithium-aluminum-based oxide represented by the following chemical formula 2:

[0033] [Chemical Formula 2]

[0034] Li a Al b M3c O d

[0035] In the above chemical formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, W, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, and 0 <a≤10, 0<b≤8, 0≤c≤8, 2≤d≤13이다. 상기 a는 0.01, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 또는 이들 중 두 값의 사이 범위일 수 있고, 상기 b는 0.01, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 또는 이들 중 두 값의 사이 범위일 수 있으며, 상기 c는 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 또는 이들 중 두 값의 사이 범위일 수 있고, 상기 d는 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13 또는 이들 중 두 값의 사이 범위일 수 있다.

[0036] In addition, the lithium-aluminum-based oxide may have a peak detected in at least one region selected from the group consisting of 2θ values ​​of 23.7°±0.2°, 34°±0.2°, and 34.4°±0.2° in XRD analysis.

[0037] According to another aspect of the present specification, a positive electrode comprising the positive electrode active material described above is provided.

[0038] According to another aspect of the present specification, a lithium secondary battery using the anode described above is provided.

[0039]

[0040] According to the present specification, the structural stability of the surface of the lithium composite oxide particles can be improved by forming an Al concentration gradient in a region close to the surface of the primary particles constituting the lithium composite oxide.

[0041] In one example, a lithium-aluminum-based oxide coating layer is formed on at least a portion of the surface of a lithium composite oxide, and residual lithium can be reduced.

[0042] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below.

[0043]

[0044] Figure 1 is the SEM-EDS analysis result of the cathode active material obtained in Preparation Example 1;

[0045] FIGS. 2 to 6 are the TEM-EDS analysis results of the cathode active material obtained in Preparation Example 1;

[0046] Figures 7 to 11 are the XRD analysis results of the cathode active material obtained in Preparation Example 1.

[0047]

[0048] For convenience of understanding this specification, specific terms are defined herein. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings generally understood by those skilled in the art. Furthermore, unless specifically indicated in the context, terms in their singular form shall be understood to include their plural form, and terms in their plural form shall be understood to include their singular form.

[0049]

[0050] positive electrode active material

[0051] A positive electrode active material according to one aspect of the present specification enables reversible intercalation / deintercalation of lithium ions and comprises a lithium composite oxide.

[0052] The above lithium composite oxide is a composite metal oxide capable of lithium ion intercalation / deintercalation and has a layered crystal structure belonging to the R-3m space group. The lithium composite oxide having a layered crystal structure exhibits a specific peak in the region where 2θ is 18° to 20° among the rotation patterns obtained from XRD analysis.

[0053] In one embodiment, the lithium composite oxide comprises at least lithium, aluminum, and a transition metal. The transition metal may comprise at least one, at least two, or all selected from nickel, cobalt, and manganese.

[0054] In a non-limiting example, the lithium composite oxide may be a lithium nickel-based composite oxide containing nickel. Additionally, the lithium composite oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0055] Meanwhile, in order to improve low rate characteristics and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a ternary type lithium composite oxide, such as so-called NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or a quaternary type lithium composite oxide, such as NCMA (Ni-Co-Mn-Al), in which a portion of the nickel is substituted with cobalt, manganese, and / or aluminum. The ternary or quaternary type lithium composite oxide may further include dopants other than nickel, cobalt, manganese, and aluminum. In another embodiment, the lithium nickel-based composite oxide may be a cobalt-free type lithium composite oxide that does not contain cobalt in the bulk particles. The cobalt-free type lithium composite oxide may further include dopants other than nickel, cobalt, manganese, and aluminum.

[0056] Meanwhile, the lithium composite oxide may exist as primary particles, and the primary particles may aggregate to form secondary particles. Here, the primary particle refers to a single grain or crystallite, and the secondary particle refers to an aggregate formed by the aggregation of multiple primary particles.

[0057] Unless otherwise defined, as used herein, the term "surface of the particle" refers to a region relatively close to the "foremost surface" of the particle, and the term "center of the particle" refers to a region relatively closer to the "center" of the particle than the said "surface".

[0058] Accordingly, "the surface portion of the primary particle" refers to an area relatively close to the "foremost surface" of the primary particle, and "the center of the primary particle" refers to an area relatively closer to the "center" of the primary particle than to the "surface portion."

[0059] Likewise, "surface portion of the secondary particle" refers to an area relatively close to the "foremost surface" of the secondary particle, and "center of the secondary particle" refers to an area relatively closer to the "center" of the secondary particle than to the "surface portion."

[0060] In this case, the region within any particle excluding the "surface" can be defined as the "center of the particle."

[0061] The primary particles and the secondary particles may each independently have a rod shape, an elliptical shape, and / or an irregular shape. Additionally, primary particles of various shapes may exist within the same cathode active material unless specifically intended during the manufacturing process. Furthermore, the single particle or the primary particle refers to a particle unit in which no grain boundaries are apparent when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0062] Voids and / or grain boundaries may exist between the primary particles constituting the secondary particles. The primary particles may form internal voids by being spaced apart from neighboring primary particles within the secondary particles. Additionally, the primary particles may form a surface existing within the secondary particles by coming into contact with internal voids rather than coming into contact with neighboring primary particles to form grain boundaries. Meanwhile, the surface of the primary particles existing on the outermost surface of the secondary particles that is exposed to the outside air forms the surface of the secondary particles.

[0063] Here, the average particle size of the primary particle (wherein the average particle size of the primary particle may be the average major axis length of the primary particle) is within the range of 0.1 to 5 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range between two of these values, thereby enabling the realization of the optimal density of the anode manufactured using the anode active material according to various embodiments. The average particle size of the secondary particles, which are aggregated from the primary particles, may vary depending on the number of aggregated primary particles, but generally may be 30 to 40 μm, for example, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, or a range between two of these values. In another embodiment, the positive electrode active material may include a lithium composite compound existing in a single-crystal form having an average particle size of 0.1 μm or more.

[0064] One or more of the primary particles may exhibit a concentration gradient in which the Al element contained within the primary particle decreases toward the center of the primary particle. That is, the concentration gradient of the Al element formed within the primary particle may be in a direction from the surface of the primary particle toward the center of the primary particle.

[0065] This type of concentration gradient can be formed by mixing a lithium composite oxide with a specific aluminum-based compound and then applying a predetermined heat treatment process.

[0066] Separately, at least some of the Al elements in the lithium composite oxide may exist in a doped state within the primary particle in addition to exhibiting the concentration gradient described above. In this specification, simple doping within the particle, forming a concentration gradient within the particle, and existence on the surface of the particle may be mutually distinct concepts.

[0067] The characteristics exhibited by these Al elements can be identified in various ways. For example, there are methods such as verification through TEM-EDS analysis.

[0068] Lithium composite oxides incorporating Al suppress excessive nickel cation mixing, thereby improving electrochemical stability and optimizing electron conduction and ion diffusion pathways.

[0069] Meanwhile, the concentration gradient of the Al element within the primary particle can improve the structural stability of the surface portion of the lithium composite oxide. The lithium composite oxide with improved structural stability can minimize degradation even during repeated charging and discharging.

[0070] That is, the concentration gradient of the Al element may exist only up to a certain depth from the surface of the primary particle. For example, a predetermined depth refers to when the diameter of the primary particle is r, 0.001r, 0.002r, 0.003r, 0.004r, 0.005r, 0.006r, 0.007r, 0.008r, 0.009r, 0.01r, 0.011r, 0.012r, 0.013r, 0.014r, 0.015r, 0.016r, 0.017r, 0.018r, 0.019r, 0.02r, 0.021r, 0.022r, 0.023r, 0.024r, 0.025r, 0.026r, 0.027r, 0.028r, 0.029r, 0.03r, 0.035r, 0.04r, 0.045r, 0.05r, 0.055r, 0.06r, 0.065r, 0.07r, 0.075r, 0.08r, 0.085r, 0.09r, 0.095r, 0.1r, 0.105r, 0.11r, 0.115r, 0.12r, 0.125r, 0.13r, 0.135r, 0.14r, 0.145r, 0.15r, 0.155r, 0.16r, 0.165r, 0.17r, 0.175r, 0.18r, It may be 0.185r, 0.19r, 0.195r, 0.2r, or a range between two of these values, but is not limited thereto.

[0071] In addition, an Al element concentration gradient formed to a certain depth, i.e., a concentration gradient layer, can alleviate structural stress within the particles and improve high-temperature stability.

[0072] The depth of the Al element concentration gradient formed in the long axis direction of the primary particle and the depth of the Al element concentration gradient formed in the short axis direction of the primary particle may be different or the same.

[0073] These characteristics can be controlled according to manufacturing conditions that form an Al element concentration gradient or the composition of the primary particles. Depending on the depth, the ion diffusion path, reaction uniformity within the electrode, etc., may be affected. That is, the lithium composite oxide may have its characteristics adjusted to suit the intended product by making the depth at which the Al element concentration gradient is formed the same or different depending on the direction.

[0074] In one example, the depth D of the Al element concentration gradient formed in the direction of the major axis of the primary particle A and the depth d of the Al element concentration gradient formed in the short axis direction of the primary particle. A It can satisfy the following Equation 1.

[0075] [Equation 1]

[0076] D A >d A

[0077] These primary particles may have a relatively thick concentration gradient layer formed in the long axis direction. These characteristics can be imparted by controlling the arrangement of the primary particles within the secondary particles. For example, these characteristics can be imparted to a positive electrode active material in which the degradation of the primary particles mainly occurs in the long axis direction.

[0078] In another example, the depth D of the Al element concentration gradient formed in the direction of the major axis of the primary particle. A and the depth d of the Al element concentration gradient formed in the short axis direction of the primary particle. A It can satisfy the following Equation 2.

[0079] [Equation 2]

[0080] D A <d A

[0081] These primary particles may have a relatively thick concentration gradient layer formed in the short-axis direction. Likewise, these characteristics can be imparted by controlling the arrangement of the primary particles within the secondary particles. For example, these characteristics can be imparted to a positive electrode active material in which the degradation of the primary particles mainly occurs in the short-axis direction.

[0082] Meanwhile, the thickness of the Al concentration gradient layer may be adjusted according to the position of the primary particle within the secondary particle. That is, the thickness of the concentration gradient layer can be different at a position close to the surface of the secondary particle and at a position close to the center of the secondary particle. For example, the concentration gradient layer may be thicker at a position close to the surface of the secondary particle, or the concentration gradient layer may be thicker at a position close to the center of the secondary particle.

[0083] The thickness of this concentration gradient layer can be controlled by changing the type of aluminum-based compound used to form it or by changing the heat treatment conditions.

[0084] In another example, the thickness of the concentration gradient layer is 0.1 to 200 nm, e.g., 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm. nm, 20 nm, 20.5 nm, 21 nm, 21.5 nm, 22 nm, 22.5 nm, 23 nm, 23.5 nm, 24 nm, 24.5 nm, 25 nm, 25.5 nm, 26 nm, 26.5 nm, 27 nm, 27.5 nm, 28 nm, 28.5 nm, 29 nm, 29.5 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or a range between two of these values, but is not limited thereto.

[0085] Meanwhile, in one or more of the primary particles, from the surface of the primary particle toward the center of the primary particle, 0.1 to 200 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm, 20 nm, 20.5 nm, 21 nm, 21.5 nm, 22 nm, 22.5 nm, 23 nm, 23.5 nm, 24 nm, 24.5 nm, 25 nm, 25.5 nm, 26 nm, 26.5 nm, 27 nm, 27.5 nm, 28 nm, 28.5 nm, 29 nm, 29.5 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm. nm, 200 nm, or between these two values. There may exist regions where Al elements are concentrated at a certain depth within the range.

[0086] Here, the region where Al elements are concentrated may refer to a specific region in the primary particle that exhibits a high Al element content exceeding the measurement error compared to other regions.

[0087] Meanwhile, due to the concentration gradient formed by the Al element, at least one of the transition metal elements constituting the lithium composite oxide may exhibit a concentration gradient that increases from the surface toward the center.

[0088] Therefore, the concentration gradient of the transition metal element may exist only up to a certain depth from the surface of the primary particle. For example, a predetermined depth refers to when the diameter of the primary particle is r, 0.001r, 0.002r, 0.003r, 0.004r, 0.005r, 0.006r, 0.007r, 0.008r, 0.009r, 0.01r, 0.011r, 0.012r, 0.013r, 0.014r, 0.015r, 0.016r, 0.017r, 0.018r, 0.019r, 0.02r, 0.021r, 0.022r, 0.023r, 0.024r, 0.025r, 0.026r, 0.027r, 0.028r, 0.029r, 0.03r, 0.035r, 0.04r, 0.045r, 0.05r, 0.055r, 0.06r, 0.065r, 0.07r, 0.075r, 0.08r, 0.085r, 0.09r, 0.095r, 0.1r, 0.105r, 0.11r, 0.115r, 0.12r, 0.125r, 0.13r, 0.135r, 0.14r, 0.145r, 0.15r, 0.155r, 0.16r, 0.165r, 0.17r, 0.175r, 0.18r, It may be 0.185r, 0.19r, 0.195r, 0.2r, or a range between two of these values, but is not limited thereto.

[0089] Meanwhile, in one example, the average particle size (D) of the primary particle above 50) is 200 nm to 2,000 nm, for example, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 425 nm, 450 nm, 475 nm, 500 nm, 525 nm, 550 nm, 575 nm, 600 nm, 625 nm, 650 nm, 675 nm, 700 nm, 725 nm, 750 nm, 775 nm, 800 nm, 825 nm, 850 nm, 875 nm, 900 nm, 925 nm, 950 nm, 975 nm, 1,000 nm, 1,025 nm, 1,050 nm, 1,075 nm, 1,100 nm, 1,125 nm, 1,150 nm, 1,175 nm, 1,200 nm, 1,225 nm, 1,250 nm, 1,275 nm, 1,300 nm, 1,325 nm, 1,350 nm, 1,375 nm, 1,400 nm, 1,425 nm, 1,450 nm, 1,475 nm, 1,500 nm, 1,525 nm, 1,550 nm, 1,575 nm, 1,600 nm, 1,625 nm, 1,650 nm, 1,675 nm, 1,700 nm, 1,725 ​​nm, 1,750 nm, 1,775 nm, 1,800 nm, 1,825 nm, 1,850 nm nm, 1,875 nm, 1,900 nm, 1,925 nm, 1,950 nm, 1,975 nm, 2,000 nm, or a range between two of these values.

[0090] The average particle size (D) of the above primary particles 50 ) may be the average value of the length in the major axis direction and the length in the minor axis direction of the primary particle ([major axis length + minor axis length] / 2). The average particle size of the primary particle may be calculated as the average value of the particle sizes of all primary particles observed from the surface SEM image and / or cross-sectional SEM image of the lithium composite oxide.

[0091] If the average particle size of the primary particles is too small, the specific surface area of ​​the positive electrode active material becomes excessively large, which may lead to a decrease in stability due to adverse reactions with the electrolyte. On the other hand, if the average particle size of the primary particles is too large, the diffusivity of lithium ions may be reduced.

[0092] In addition, the particle size distribution of the lithium composite oxide among the cathode active materials can be measured using the laser diffraction method. For example, after dispersing secondary particles in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasound at approximately 28 kHz is irradiated at an output of 60 W. After obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount is the average particle size (D 50 It can be defined as ).

[0093] In this document, "particle size" is used with the same meaning as "particle diameter" or "particle size," and unless otherwise defined, all "average particle size" refers to a particle size corresponding to 50% of the volume accumulation determined by the aforementioned laser diffraction method.

[0094] In one embodiment, the lithium composite oxide may be represented by the following chemical formula 1:

[0095] [Chemical Formula 1]

[0096] Li w Ni 1-(x+y+z) M1 x M2 y Al z O2

[0097] In the above chemical formula 1, M1 is at least one selected from Co and Mn, and M2 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, and 0.5≤w≤1.5, 0 <x≤0.34, 0≤y≤0.20, 0<z≤0.33이다.

[0098] Here, w, representing the ratio of lithium to all elements other than lithium in the lithium composite oxide, may be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or a range between two of these values.

[0099] Meanwhile, 1-(x+y+z), representing the ratio of nickel to all elements other than lithium in the lithium composite oxide, may be 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24, 0.27, 0.3, 0.33, 0.36, 0.39, 0.42, 0.45, 0.48, 0.51, 0.54, 0.57, 0.6, 0.63, 0.66, 0.69, 0.72, 0.75, 0.78, 0.81, 0.84, 0.87, 0.9, 0.93, 0.96, 0.99, or a range between two of these values, but is not limited thereto.

[0100] In the above chemical formula 1, M1 represents Co and / or Mn present in the lithium complex oxide. x, representing the ratio of the presence of M1 to the total elements other than lithium in the lithium complex oxide, may be 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, 0.31, 0.34, or a range between two of these values.

[0101] In the above chemical formula 1, M2 represents a dopant other than aluminum doped into the lithium composite oxide. The dopant may exist in a doped state within the crystal lattice (at least one of the lithium layer and / or transition metal layer) of the lithium composite oxide. y, representing the ratio of the presence of M2 to the total elements other than lithium in the lithium composite oxide, may be 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or a range between two of these values.

[0102] When the lithium composite oxide contains a dopant, y in Chemical Formula 1 is greater than 0, and when the lithium composite oxide does not contain a dopant, y in Chemical Formula 1 is 0.

[0103] The z, representing the ratio of aluminum to the total elements other than lithium in the lithium composite oxide, may be 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, 0.31, 0.33, or a range between two of these values.

[0104] The upper and lower limits of the nickel, M1, dopant M2, and aluminum content defined in the above chemical formula 1 can be appropriately selected within a range that satisfies the definitions described above.

[0105] In one example, the lithium composite oxide may have a coating layer containing lithium and aluminum formed on at least a portion of the surface of one or more of the secondary particles.

[0106] The above coating layer can improve structural stability under high temperature conditions by suppressing degradation reactions that may occur at the interface between the electrode and the electrolyte.

[0107] The above coating layer can be defined as a region where aluminum-based oxide and / or lithium aluminum-based oxide exist independently of the lithium composite oxide.

[0108] That is, meanwhile, a thin coating layer containing lithium and aluminum may be formed on at least a portion of the surface of one or more of the secondary particles. That is, aluminum-based oxide and / or lithium aluminum-based oxide may be present on at least a portion of the surface of one or more of the secondary particles. For example, the thickness of the coating layer is 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm, 20 nm, 20.5 nm, 21 nm, 21.5 nm, 22 nm, 22.5 nm, 23 nm, 23.5 nm, 24 nm, 24.5 nm, 25 nm, 27.5 nm, 30 nm, 32.5 nm, 35 nm, 37.5 nm, 40 nm, 42.5 nm, 45 nm, 47.5 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 425 nm, 450 nm, 475 nm, 500 nm, or a range between two of these values, but is not limited thereto.

[0109] The coating layer can improve the interfacial stability of the lithium composite oxide. Under high voltage conditions, the electrolyte can easily oxidize and decompose on the surface of the lithium composite oxide, which can cause an increase in interfacial resistance. The coating layer can suppress such decomposition of the electrolyte by reducing direct contact between the electrolyte and the lithium composite oxide.

[0110] Meanwhile, the coating layer can improve the structural stability of the lithium composite oxide to prevent structural collapse caused by the leaching of constituent elements into the electrolyte.

[0111] Depending on the temperature at which the coating layer is formed, it may include various phases including lithium, aluminum, oxygen, etc. For example, it may include phases such as Li5AlO4, but is not limited thereto.

[0112] Here, the coating layer may comprise a lithium-aluminum-based oxide represented by the following chemical formula 2:

[0113] [Chemical Formula 2]

[0114] Li a Al b M3 c O d

[0115] In the above chemical formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, W, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, and 0 <a≤10, 0<b≤8, 0≤c≤8, 2≤d≤13이다.

[0116] Here, an aluminum-based oxide can react with lithium impurities to form a lithium-aluminum-based oxide, and the above-mentioned a, representing the ratio, may be 0.01, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range between two of these values.

[0117] The above b, representing the aluminum ratio in the coating layer, may be 0.01, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between two of these values.

[0118] The above M3 may refer to other components introduced in addition to aluminum-based oxide when forming the coating layer, and the above c, representing the ratio thereof, may be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between two of these values. If no components introduced in addition to aluminum-based oxide are present, the above c may be 0.

[0119] The above d may be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13 or a range between two of these values, and may be determined according to the stoichiometric ratio of Li, Al, and M3.

[0120] The upper and lower limits of the content of lithium, aluminum, and M3 defined in the above chemical formula 2 can be appropriately selected within a range that satisfies the definitions described above.

[0121] In addition, during the formation process of the coating layer, residual lithium may react with an aluminum-based oxide to form a lithium-aluminum-based oxide. As a result, the content of residual lithium present on the surface of the lithium composite oxide can be reduced.

[0122] In one example, the lithium-aluminum-based oxide may have a peak detected in at least one region selected from the group consisting of 2θ values ​​of 23.7±0.2°, 34°±0.2°, and 34.4°±0.2° in XRD analysis.

[0123] A lithium-aluminum oxide exhibiting at least one of the above peaks can be formed in a heat treatment process of 680 to 900°C to improve the high-temperature life, resistance, and rate characteristics of the cathode active material, but can be easily removed by washing.

[0124] If the above-mentioned positive active material has a primary particle in which Al is doped within the particle and a concentration gradient layer of Al is provided, and a secondary particle having a coating layer including a lithium-aluminum-based oxide, it can suppress excessive mixing of nickel cations, relieve structural stress inside the particle, and suppress degradation reactions at the electrode-electrolyte interface, thereby ensuring structural stability. In addition, electronic conductivity and ion diffusion pathways are optimized, reducing resistance, and as a result, performance under high-power conditions can be improved.

[0125]

[0126] lithium secondary battery

[0127] According to another aspect of the present specification, an anode may be provided comprising an anode current collector and an anode active material layer formed on the anode current collector. Herein, the anode active material layer may include an anode active material according to various embodiments of the present specification. Accordingly, since the anode active material is the same as previously described, a specific description is omitted for convenience, and only the remaining unmentioned components will be described below.

[0128] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes 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 above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0129] The above positive active material layer can be manufactured by applying a positive slurry composition, which includes a conductive material and optionally a binder together with the positive active material, to the positive current collector.

[0130] At this time, the positive active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive active material layer. Excellent capacity characteristics may be exhibited when included within the above-mentioned content range, but it is not necessarily limited thereto.

[0131] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0132] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive active material layer.

[0133] The above-described anode can be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it can be manufactured by applying an anode slurry composition, prepared by dissolving or dispersing the above-described anode active material and optionally a binder and a conductive material in a solvent, onto an anode current collector, and then drying and rolling.

[0134] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0135] In addition, in another embodiment, the anode may be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0136] In addition, according to another aspect of the present invention, an electrochemical device comprising the anode described above may be provided. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0137] Specifically, the above lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is the same as previously described, a detailed description is omitted for convenience, and only the remaining components not previously mentioned are described in detail below.

[0138] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0139] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0140] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0141] The above-mentioned cathode active material layer can be manufactured by applying a cathode slurry composition, which includes a conductive material and optionally a binder together with the above-mentioned cathode active material, to the above-mentioned cathode current collector.

[0142] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples 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 alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, 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.

[0143] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0144] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0145] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0146] In one embodiment, the negative active material layer may be manufactured by applying a negative slurry composition, prepared by dissolving or dispersing a negative active material and optionally a binder and a conductive material in a solvent, onto a negative current collector and drying it, or by casting the negative slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative current collector.

[0147] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0148] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0149] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0150] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0151] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0152] When the electrolyte used in the present invention is a solid electrolyte, for example, solid inorganic electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, halide-based solid electrolytes, etc. may be used, and preferably, sulfide-based solid electrolytes may be used.

[0153] As a material for a sulfide-based solid electrolyte, a solid electrolyte containing Li, an element X (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the above-mentioned sulfide-based solid electrolyte materials include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (Here, m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In) etc.

[0154] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0155] Li7La3Zr2O is a material for oxide-based solid electrolytes. 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO4-x N x (LiPON), Li 2+2x Zn 1-x There are GeO4(LISICON), etc.

[0156] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the anode and the cathode. Additionally, the solid electrolyte may be partially included within the anode active material layer of the anode independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the cathode active material layer of the cathode independently of the solid electrolyte layer.

[0157] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0158] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0159] The external shape of the lithium secondary battery according to the present invention is not subject to any particular limitations, but may be cylindrical, prismatic, pouch, or coin-shaped using a can. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0160] According to another aspect of the present invention, a battery module comprising the lithium secondary battery as a unit cell and / or a battery pack comprising the same may be provided.

[0161] The battery module or the battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0162]

[0163] Preparation Example 1. Preparation of positive electrode active material

[0164] (1) Example 1

[0165] Ni by the co-precipitation method 0.92 Co 0.04 Mn 0.04 (OH)2 hydroxide precursors were synthesized. In a 90L reactor, 25 wt% NaOH and 30 wt% NH4OH were added to a 1.5M complex transition metal sulfuric acid aqueous solution prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 92:4:4. The pH inside the reactor was maintained at 11.5 and the temperature at 60°C, and N2, an inert gas, was introduced into the reactor to prevent oxidation of the prepared precursors. After the synthesis stirring was completed, washing and dehydration were performed using a filter press (F / P) to Ni0.92 Co 0.04 Mn 0.04 (OH)2 hydroxide precursor was obtained.

[0166] LiOH was mixed with a precursor synthesized such that the molar ratio (Li / M) between lithium and the metals other than lithium was 1.065. The mixture was heat-treated for 10 hours in a furnace under an O2 atmosphere at a rate of 1°C / min to a maximum temperature of 720°C, followed by natural cooling to obtain an intermediate product (lithium composite oxide).

[0167] Next, the above intermediate product, Al(OH)3 (weighed such that the aluminum content relative to the total transition metal in the above intermediate product is 2 mol%), was mixed, and heat-treated at 710°C for 10 hours and 35 minutes at a rate of 1°C / min in a kiln under an O2 atmosphere, followed by natural cooling to obtain a final product of an anode active material in which a coating layer containing aluminum was formed on the surface of the secondary particles.

[0168]

[0169] (2) Example 2

[0170] Ni by coprecipitation method 0.92 Co 0.04 Mn 0.04 (OH)2 hydroxide precursors were synthesized. In a 90L reactor, 25 wt% NaOH and 30 wt% NH4OH were added to a 1.5M complex transition metal sulfuric acid aqueous solution prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 92:4:4. The pH inside the reactor was maintained at 11.5 and the temperature at 60°C, and N2, an inert gas, was introduced into the reactor to prevent oxidation of the prepared precursors. After the synthesis stirring was completed, washing and dehydration were performed using a filter press (F / P) to Ni 0.92 Co 0.04 Mn 0.04 (OH)2 hydroxide precursor was obtained.

[0171] LiOH was mixed with a precursor synthesized such that the molar ratio (Li / M) between lithium and the metals other than lithium was 1.065. The mixture was heat-treated for 10 hours in a calcination furnace under an O2 atmosphere at a rate of 1°C / min to a maximum temperature of 720°C, followed by natural cooling to obtain an intermediate product (lithium composite oxide).

[0172] Next, the above intermediate product, Al(OH)3 (weighed so that the aluminum content relative to the total transition metal in the above intermediate product is 4 mol%), was mixed, and heat-treated at 710°C for 10 hours and 35 minutes at a rate of 1°C / mi in a kiln under an O2 atmosphere, followed by natural cooling to obtain a final product of an anode active material in which a coating layer containing aluminum was formed on the surface of the secondary particles.

[0173]

[0174] (3) Comparative Example 1

[0175] A final positive active material product was obtained in the same manner as in Example 1, except that Al(OH)3 was not mixed.

[0176]

[0177] (4) Comparative Example 2

[0178] A final cathode active material was obtained in the same manner as in Example 1, except that Al(OH)3 was weighed so that the aluminum content relative to the total transition metal in the intermediate product was 1 mol%.

[0179]

[0180] (5) Comparative Example 3

[0181] Distilled water was prepared and maintained at a constant temperature of 5 to 40°C. Then, the final product prepared in Example 1 was placed in an equal weight of distilled water and washed for 2 hours while maintaining the temperature. Afterward, the final product of the cathode active material was obtained by drying with a filter press.

[0182]

[0183] Preparation Example 2. Preparation of a lithium secondary battery (half-cell)

[0184] A positive electrode slurry was prepared by dispersing 94 wt% of each positive electrode active material prepared according to Preparation Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated onto an aluminum thin film with a thickness of 15 μm and vacuum dried at 135°C to produce a positive electrode for a lithium secondary battery.

[0185] A half-cell was prepared using a lithium foil as the counter electrode for the above anode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte in which LiPF6 is present at a concentration of 1.15 M in a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0186]

[0187] Experimental Example 1. Analysis of Surface Characteristics of Anode Active Material

[0188] Figure 1 shows a cross-sectional TEM-EDS image obtained after cross-sectionally treating the cathode active material of Example 1 prepared in Preparation Example 1 with a Focused Ion Beam (FIB).

[0189] The results of the SEM-EDS analysis of the cathode active material of Example 1 obtained in Preparation Example 1 are shown in Figures 2 to 6.

[0190] Referring to Figure 1, the EDS analysis results show that the aluminum concentration decreases from the surface towards the center of the particle within the primary particle.

[0191] More specifically, a thin concentration gradient layer was formed on the cathode active material, and some of the aluminum was doped into the lithium composite oxide by diffusion. Referring to Figure 1, it can be seen that a concentration gradient layer of 5.02 nm in the short axis direction and 17.1 nm in the long axis direction of the primary particles was formed.

[0192] Meanwhile, referring to FIGS. 2 to 6, in Comparative Example 1 and Comparative Example 2, in which no aluminum raw material was applied or only a small amount was applied, aluminum was not doped into the lithium composite oxide.

[0193] In Comparative Example 3, where a sufficient amount of aluminum raw material was applied but a washing process was applied, no aluminum coating layer was present. In addition, in Comparative Example 2, aluminum was present only in some areas of the surface of the secondary particles, whereas in the secondary particles of Example 1 and Example 2, an aluminum coating layer was formed on the entire surface.

[0194] These aluminum coating layers are expected to contain compounds formed by the reaction of aluminum raw materials with residual lithium impurities on the surface of secondary particles.

[0195]

[0196] Experimental Example 2. Analysis of Crystallographic Characteristics of Anode Active Material

[0197] X-ray diffraction (XRD) analysis was performed on each positive active material prepared according to Preparation Example 1 to analyze the crystallographic characteristics of the positive active material.

[0198] Specifically, the XRD analysis was performed using a Bruker D8E Endeavor diffractometer with Cu-Kα radiation (1.540598 Å) under conditions of a tube voltage of 45 kV, a tube current of 30 mA, and a step size of 0.02°. The surface crystal phase was defined by referring to the ICDD XRD standard data card from the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-Kα rays for the anode active material. For example, the β-Li5AlO4 phase exhibits diffraction peaks (PDF 00-027-1209) detected at 23.71°±0.2°, 33.97°±0.2°, and 34.40°±0.2°.

[0199] The above XRD analysis results are shown in Table 1 and Figures 7 to 11 below.

[0200] Classification Al Content (mol%) Washing Status Concentration Gradient Thickness (nm) Surface Coating Layer Comparative Example 10 --- Comparative Example 21 -- Li5AlO4 Comparative Example 3 20<100 - Example 12 <100 Li5AlO4 Example 24 <200 Li5AlO4

[0201] Referring to the results in Table 1 above, it can be confirmed that the surface crystal phase changes depending on the content of the Al raw material and whether or not it is washed. In addition, it was confirmed that the thickness of the concentration gradient within the grain varies depending on the content of the Al raw material. For example, in Comparative Example 2, where the Al content used was 1 mol%, a coating layer was formed on the surface of the secondary particle, but a concentration gradient layer was not formed inside the primary particle.

[0202] Meanwhile, it was confirmed from Comparative Example 3 that the β-Li5AlO4 phase formed in the heat treatment process at 680–900°C easily dissolves and disappears upon contact with water. These can improve high-temperature life and output characteristics according to current.

[0203]

[0204] Experimental Example 3. Evaluation of Electrochemical Characteristics of a Lithium Secondary Battery (Half-Cell)

[0205] For the lithium secondary battery (half-cell) prepared in Preparation Example 2, high-temperature life characteristics were confirmed by performing 50 charge / discharge cycles at a constant current of 0.05C at 45℃ within a driving voltage of 2.5~4.25 V using an electrochemical analyzer (Toyo, Toscat-3100). At this time, the ratio of the discharge capacity after 50 cycles to the initial capacity after 50 charge / discharge cycles was defined as the high-temperature cycle capacity retention rate (capacity retention).

[0206] In addition, batteries charged at 0.2C at 25℃ were discharged at 0.2C, 0.5C, 1C, 2C, 3C, and 4C, respectively, to verify the output (rate) characteristics. The 0.2C capacity (C) after the output (rate) characteristic test was completedf ) and initial 0.2C capacity (C i The ratio of ) (C f / C i ×100) was used as the capacity retention rate.

[0207] The above measurement results are shown in Tables 2 and 3 below.

[0208] Classification Initial Discharge Capacity (mAh / g) 50-Cycle Discharge Capacity (mAh / g) High-Temperature Cycle Capacity Retention Rate (%) R ct Resistance (Ω) Example 1 209 1075 112.64 Example 2 208 9847 13.26 Comparative Example 1 201 8040 14.33 Comparative Example 2 209 854 115.42 Comparative Example 3 209 9244 14.03

[0209] Classification 0.2C(mAh / g) 0.5C(mAh / g) 1C(mAh / g) 2C(mAh / g) 3C(mAh / g) 4C(mAh / g) Capacity Retention Rate (%) Example 1 200 195 191 186 184 181 99.5 Example 2 200 194 190 186 183 181 99.6 Comparative Example 1 190 185 180 175 172 170 98.1 Comparative Example 2 200 194 189 185 182 180 99.1 Comparative Example 3 200 191 186 180 178 174 98.6

[0210] Referring to Tables 2 and 3, compared to the examples in which a concentration gradient layer inside the primary particle and a coating layer on the surface of the secondary particle are formed, the comparative examples in which no coating layer exists or an aluminum-based compound exists only inside or on the surface of the particle showed poor high-temperature life, resistance, and rate characteristics.

[0211] Although embodiments of the present invention have been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

1. Includes a lithium composite oxide capable of lithium intercalation / deintercalation, and The above lithium composite oxide comprises at least lithium, aluminum, and a transition metal, and The above lithium composite oxide is a secondary particle formed by the aggregation of a plurality of primary particles, and One or more Al elements contained within the primary particles exhibit a concentration gradient that decreases toward the center of the primary particles, Positive active material.

2. In Paragraph 1, At least some of the Al elements in the lithium composite oxide exist in a doped state within the primary particle, Positive active material.

3. In Paragraph 1, The concentration gradient of the above Al element exists only up to a predetermined depth from the surface of the above primary particle, Positive active material.

4. In Paragraph 3, The depth of the Al element concentration gradient formed in the direction of the major axis of the primary particle and the depth of the Al element concentration gradient formed in the direction of the minor axis of the primary particle are different or the same. Positive active material.

5. In Paragraph 1, In the above primary particle, the thickness of the concentration gradient layer in which a concentration gradient in which the Al element decreases toward the center of the above primary particle appears is 0.1 to 200 nm, Positive active material.

6. In Paragraph 1, In one or more of the primary particles, a region in which Al elements are concentrated exists at a depth of 0.1 to 200 nm from the surface of the primary particles toward the center of the primary particles, Positive active material.

7. In Paragraph 1, In one or more of the primary particles, at least one of the transition metal elements, excluding the Al element, exhibits a concentration gradient that increases toward the center of the primary particles. Positive active material.

8. In Paragraph 7, The concentration gradient of the above transition metal element exists only up to a predetermined depth from the surface of the above primary particle, Positive active material.

9. In Paragraph 1, The average particle size (D) of the above primary particles 50 ) is 200–2,000 nm, Positive active material.

10. In Paragraph 1, The above lithium composite oxide is represented by the following chemical formula 1, Cathode active material: [Chemical Formula 1] Li w Ni 1-(x+y+z) M1 x M2 y Al z O2 In the above chemical formula 1, M1 is at least one selected from Co and Mn, and M2 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Ti, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, and 0.5≤w≤1.5, 0 <x≤0.34, 0≤y≤0.20, 0<z≤0.33이다.

11. In Paragraph 1, A coating layer comprising lithium and aluminum formed on at least a portion of the surface of one or more of the above secondary particles, Positive active material.

12. In Paragraph 11, The above coating layer comprises a lithium-aluminum-based oxide represented by the following chemical formula 2, Cathode active material: [Chemical Formula 2] Li a Al b M3 c O d In the above chemical formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, W, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd, and 0 <a≤10, 0<b≤8, 0≤c≤8, 2≤d≤13이다.

13. In Paragraph 12, The above lithium-aluminum-based oxide is such that a peak is detected in at least one region selected from the group consisting of 2θ values ​​of 23.7°±0.2°, 34°±0.2°, and 34.4°±0.2° in XRD analysis, Positive active material.

14. A positive electrode comprising a positive electrode active material according to any one of paragraphs 1 to 13.

15. A lithium secondary battery using a positive electrode according to Paragraph 13.

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