Positive electrode active material and lithium secondary battery comprising the same

Abstract

The present invention relates to a positive electrode active material with improved electrochemical performance and stability and a lithium secondary battery using a positive electrode containing the above-mentioned positive electrode active material. More specifically, the present invention relates to a positive electrode active material that controls the content of lithium impurities remaining on the surface of the positive electrode active material without undergoing a water washing process in order to reduce the amount of residual lithium remaining on the surface of the positive electrode active material, so as to prevent in advance the reduction in the electrochemical performance and stability of the positive electrode active material caused by the above-mentioned lithium impurities and a lithium secondary battery using a positive electrode containing the above-mentioned positive electrode active material.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material with improved electrochemical performance and stability and a lithium secondary battery using a positive electrode containing the above-mentioned positive electrode active material. More specifically, the present invention relates to a positive electrode active material that controls the content of lithium impurities remaining on the surface of the positive electrode active material without undergoing a water washing process in order to reduce the amount of residual lithium remaining on the surface of the positive electrode active material, so as to prevent in advance the reduction in the electrochemical performance and stability of the positive electrode active material caused by the above-mentioned lithium impurities and a lithium secondary battery using a positive electrode containing the above-mentioned positive electrode active material. Background Art

[0002] Batteries use electrochemically reactive materials at the positive and negative electrodes to store electricity. A representative example of such batteries is a lithium secondary battery that stores electrical energy through changes in chemical potential during the insertion and extraction of lithium ions at the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using materials that can reversibly intercalate or deintercalate lithium ions as positive electrode active materials and negative electrode active materials, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

[0004] As a positive electrode active material of a lithium secondary battery, lithium composite oxides have been used, and for example, composite oxides of LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiMnO 2 , etc. are being studied.

[0005] Among the above-mentioned positive electrode active materials, although LiCoO 2 having excellent lifespan and charge-discharge efficiency is widely used, the above-mentioned material has limitations in price competitiveness due to the high price of cobalt used as a raw material due to limited resources.

[0006] While lithium manganese oxides such as LiMnO2 and LiMn2O4 offer advantages such as good thermal stability and low cost, they suffer from low capacity and poor high-temperature performance. Furthermore, while LiNiO2-based cathode active materials offer battery characteristics with high discharge capacity, their synthesis is extremely difficult due to cation mixing between lithium and transition metals, resulting in significant issues with rate performance.

[0007] In addition, depending on the degree of cation mixing, a large amount of lithium by-products is generated. Since most of the lithium by-products are composed of LiOH and Li2CO3 compounds, there are problems such as gelation during the production of positive electrode slurry and gas generation during charge and discharge after electrode production. Residual Li2CO3 increases battery expansion, not only reducing cycle life, but also causing battery expansion.

[0008] On the other hand, the content of lithium impurities present on the surface of the positive electrode active material tends to increase in proportion to the content of nickel in the above-mentioned positive electrode active material.

[0009] Therefore, in the case of a high-nickel type positive electrode active material recently introduced to improve the capacity characteristics of the positive electrode active material, an excessive amount of lithium impurities are present on the surface, and therefore a water washing process for removing the impurities is necessary.

[0010] While the above-described water washing process can reduce the residual lithium on the surface of the positive electrode active material, it has the disadvantage of potentially damaging the surface of the positive electrode active material. Damage to the surface of the positive electrode active material by the water washing process may deteriorate the electrochemical performance and stability of the positive electrode active material. Summary of the Invention

[0011] Technical issues

[0012] To address various issues with existing positive electrode active materials for lithium secondary batteries, the present invention aims to provide a positive electrode active material with improved electrochemical performance and stability. In particular, the present invention aims to reduce the amount of residual lithium remaining on the surface of the positive electrode active material by controlling the content of lithium impurities remaining on the surface without undergoing a water washing step, thereby preventing the degradation of the electrochemical performance and stability of the positive electrode active material caused by these lithium impurities.

[0013] Furthermore, another object of the present invention is to provide a positive electrode comprising the positive electrode active material defined herein.

[0014] In addition, another object of the present invention is to provide a lithium secondary battery using the positive electrode defined herein.

[0015] The purpose of the present invention is not limited to the purpose mentioned above. Other purposes and advantages of the present invention that are not mentioned here will be understood through the following description and will be more clearly understood through the embodiments of the present invention. In addition, it is easy to understand that the purposes and advantages of the present invention can be achieved by the means and combinations thereof in the claims.

[0016] Solutions to the Problem

[0017] According to one aspect of the present invention, there is provided a positive electrode active material including: a first compound capable of inserting and extracting lithium; and a second compound present on at least a portion of a surface of the first compound.

[0018] In this case, the second compound may be an oxide including at least one first element selected from Group 1A elements, Group 3A elements, and Group 5A elements and at least one second element selected from Group 8 elements.

[0019] The first compound can be represented by the following chemical formula 1:

[0020] [Chemical Formula 1]

[0021] Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α

[0022] (wherein, M1 is at least one selected from Mn or Al,

[0023] M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu,

[0024] M1 and M2 are different elements,

[0025] 0.5≤w≤1.5,0≤x≤0.50,0≤y≤0.20,0≤z≤0.20,0≤α≤0.02)

[0026] The second compound may be represented by the following Chemical Formula 2.

[0027] [Chemical Formula 2]

[0028] Li a Co b M3 c (P β O γ ) d

[0029] (Wherein, M3 is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0030] 0≤a≤10,0≤b≤8,0≤c≤8,0 <d≤13,0<β≤4,0<γ≤10)

[0031] Here, the second compound may include a first oxide represented by the following Chemical Formula 3 and a second oxide represented by the following Chemical Formula 4.

[0032] [Chemical Formula 3]

[0033] Li a' Co b' M3' c' (P β' O γ' ) d'

[0034] (Wherein, M3' is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0035] 0 <a'≤10,0≤b'≤8,0≤c'≤8,0<d'≤13,0≤β'≤4,0<γ'≤10)

[0036] [Chemical Formula 4]

[0037] Co b" M3" c" (P β" O γ" ) d"

[0038] (Wherein, M3" is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0039] 0≤b"≤8,0≤c"≤8,0 <d"≤13,0≤β"≤4,0<γ"≤10)

[0040] In another embodiment, at least a portion of the surface of the first compound may further include a third compound represented by the following Chemical Formula 5.

[0041] [Chemical Formula 5]

[0042] Li e W f M4 g O h

[0043] (Wherein, M4 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd,

[0044] 0≤e≤10,0 <f≤8,0≤g≤8,2≤h≤13)

[0045] Furthermore, according to another aspect of the present invention, a positive electrode including the positive electrode active material is provided.

[0046] According to another aspect of the present invention, there is provided a lithium secondary battery using the positive electrode.

[0047] Effects of the Invention

[0048] According to the positive electrode active materials of various embodiments of the present invention, there is no need to perform a water washing process for reducing the amount of residual lithium present on the surface of the above-mentioned positive electrode active materials. Instead, the content of lithium impurities remaining on the surface can be controlled by forming lithium metal oxide and / or lithium metal phosphate within the surface.

[0049] Thus, it is possible to prevent in advance the degradation of the electrochemical performance and stability of the positive electrode active material due to lithium impurities remaining on the surface of the positive electrode active material.

[0050] Thus, the lithium secondary battery uses the positive electrode active material according to various embodiments of the present invention, and thus can improve various electrochemical characteristics such as capacity characteristics, life characteristics, rate characteristics, etc., which are important indicators in evaluating the performance of the lithium secondary battery.

[0051] Hereinafter, specific matters for implementing the invention will be described, and specific effects of the present invention and the above-mentioned effects will be described. DETAILED DESCRIPTION

[0052] In order to facilitate the understanding of the present invention, specific terms are appropriately defined in this application. Unless otherwise defined herein, the scientific terms and technical terms used in the present invention have the meanings commonly understood by those skilled in the art to which the present invention belongs. In addition, unless the context requires otherwise, terms in the singular shall include the plural form and terms in the plural form shall include the singular form.

[0053] Hereinafter, the positive electrode active material according to the present invention, the positive electrode including the positive electrode active material, and the lithium secondary battery using the positive electrode will be described in further detail.

[0054] positive electrode active material

[0055] According to one aspect of the present invention, a positive electrode active material is provided, including a first compound capable of inserting and extracting lithium and a coating layer, wherein the coating layer is present on at least a portion of a surface of the first compound.

[0056] The first compound may be a single crystal or polycrystalline lithium composite oxide, but is preferably a polycrystalline lithium composite oxide. The polycrystalline lithium composite oxide refers to an aggregate including primary particles and secondary particles formed by agglomerating a plurality of the primary particles.

[0057] The primary particle is a single crystal grain (grain or crystallite), and the secondary particle is an aggregate formed by agglomeration of a plurality of primary particles. Spaces and / or grain boundaries may exist between the primary particles constituting the secondary particle.

[0058] For example, the primary particles may be spaced apart from adjacent primary particles within the secondary particles to form internal voids. Alternatively, the primary particles may form surfaces within the secondary particles by contacting the internal voids, rather than forming grain boundaries by contacting adjacent primary particles.

[0059] On the other hand, the surface of the primary particle present on the outermost surface of the secondary particle, which is exposed to the outside air, forms the surface of the secondary particle.

[0060] The average particle size of the primary particles is in the range of 0.01 μm to 5 μm, preferably 0.01 μm to 3 μm, thereby achieving the optimal density of the positive electrode prepared using the positive electrode active material of various embodiments of the present invention. In addition, the average particle size of the secondary particles may vary depending on the number of agglomerated primary particles, but may be in the range of 3 μm to 20 μm.

[0061] Furthermore, the primary particles and / or the secondary particles may have a rod-like, elliptical, and / or irregular shape.

[0062] The first compound is a lithium composite oxide represented by the following Chemical Formula 1.

[0063] [Chemical Formula 1]

[0064] Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α

[0065] (wherein, M1 is at least one selected from Mn or Al,

[0066] M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu,

[0067] M1 and M2 are different elements,

[0068] 0.5≤w≤1.5,0≤x≤0.50,0≤y≤0.20,0≤z≤0.20,0≤α≤0.02)

[0069] In this case, the first compound may be a lithium composite oxide having a layered crystal structure containing at least nickel and cobalt. In addition, the first compound is preferably a high-nickel lithium composite oxide in which x+y+z in the chemical formula 1 is 0.20 or less.

[0070] As described above, in the case of nickel-containing lithium composite oxides, as the mixing of lithium and nickel cations becomes more severe, a large amount of residual lithium, i.e., lithium impurities, may form on the surface of the lithium composite oxide. These lithium impurities mainly include LiOH and Li2CO3, and these lithium impurities may cause gelation during the preparation of the paste for manufacturing the positive electrode or cause battery swelling.

[0071] As the nickel content in the lithium composite oxide increases, the content of the lithium impurities also increases proportionally. Generally, in the case of high-nickel positive electrode active materials (lithium composite oxides) with a nickel content of 80 mol% or more, a water washing step is required to remove lithium impurities on the surface. However, this water washing step can cause partial surface damage to the lithium composite oxide, potentially reducing the electrochemical performance and stability of the lithium composite oxide.

[0072] On the other hand, the lithium composite oxide and the positive electrode active material including the lithium composite oxide according to various embodiments of the present invention can effectively reduce the lithium impurity content remaining on the surface of the lithium composite oxide by forming lithium metal oxide and / or lithium metal phosphate described below on the lithium composite oxide without the need for a water washing process.

[0073] In addition, the first compound may be doped with a metal element represented by M1 as shown in the above Chemical Formula 1. Preferably, M1 may include tungsten (W).

[0074] In this case, the tungsten may be present in the crystal lattice of the first compound. That is, the tungsten may be present in a state of being substituted by nickel inserted into at least one of the Li 3a position and the Li 3b position in the first compound.

[0075] On the other hand, when the tungsten is doped into the first compound, the ratio of nickel inserted into the Li 3a site (Ni occ ), thereby improving the electrochemical performance and stability of the positive electrode active material. At this time, the ratio of nickel inserted into the Li 3a position (Ni occ) may be due to an increase in the amount of nickel inserted into the Li 3a site due to the tungsten doping, but may also be due to the insertion of tungsten into the Li 3a site. Preferably, when the tungsten is doped into the first compound, at least a portion of the tungsten doped into the first compound is inserted into the Li 3a site, thereby helping to improve the electrochemical performance and stability of the first compound.

[0076] In this case, the first compound may be represented by the following Chemical Formula 1-1.

[0077] [Chemical Formula 1-1]

[0078] Li w Ni 1-(x+y+z) Co x M1 y M2 z W z' O 2+δ

[0079] (wherein, M1 is at least one selected from Mn or Al, M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, and Cu, M1 and M2 are different elements, 0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.20, 0≤z≤0.20, 0≤z'≤0.20, 0≤δ≤0.02)

[0080] Furthermore, M1 present in the lithium composite oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0081] The concentration gradient means that there is a negative (-) slope between the concentration of M1 at any point on the surface of the secondary particle and the concentration of M1 at any point in the center of the secondary particle.

[0082] As described above, there is a concentration gradient of M1 in the above-mentioned secondary particles, preferably, there is a concentration gradient of tungsten (W), so that the movement path of lithium ions in the above-mentioned secondary particles and the above-mentioned primary particles constituting the above-mentioned secondary particles (diffusion path of lithium ions) can be formed from the surface part of the above-mentioned secondary particles toward the center part.

[0083] The positive electrode active material according to various embodiments of the present invention is characterized in that a coating layer including a second compound is formed on the surface in order to reduce the content of residual lithium, ie, lithium impurities, present on the surface of the first compound.

[0084] In this case, the second compound may be present at least partially at the interface between primary particles of the first compound and at the surface of secondary particles formed by agglomeration of the primary particles. Furthermore, the concentration of the second compound may exhibit a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles.

[0085] The coating layer may include the second compound, which is an oxide including at least one first element selected from Group 1A elements, Group 3A elements, and Group 5A elements and at least one second element selected from Group 8 elements.

[0086] The second compound may be represented by the following Chemical Formula 2.

[0087] [Chemical Formula 2]

[0088] Li a Co b M2 c (P β O γ ) d

[0089] (Wherein, M2 is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0090] 0≤a≤10,0≤b≤8,0≤c≤8,0 <d≤13,0<β≤4,0<γ≤10)

[0091] At this time, the second compound may be a single crystal structure or an amorphous oxide, but is not limited thereto and may be a collection of at least one crystal structure and / or amorphous heterogeneous oxide.

[0092] If at least one of the second compounds is an oxide having a crystal structure, the second compound may have a crystal structure belonging to space group Fd-3m, Pnma, P* / n, R3c, or R-3m. In this case, the crystal structure may be a monoclinic, cubic, orthorhombic, or rhombohedral crystal structure.

[0093] In order to effectively remove residual lithium present on the surface of the first compound, the proportion of the compound having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m in the second compound is preferably 13 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less. The crystal structure belonging to the space group Fd-3m, R3c, or R-3m in the second compound may be a cubic or rhombohedral crystal structure.

[0094] Representative examples of oxides having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the above-mentioned second compound are Co3O4, LiCoO2 and P2O5, etc. In addition, oxides that act as impurities similar to residual lithium due to their presence on the surface of the above-mentioned first compound may also be included.

[0095] When the ratio of the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the second compound is greater than 13 mol% in order to effectively remove the residual lithium present on the surface of the first compound, the improvement of the electrochemical properties and stability of the positive electrode active material by the second compound is minimal, or may even reduce the electrochemical properties and stability of the positive electrode active material.

[0096] Also, the second compound may include a first oxide represented by the following Chemical Formula 3 and a second oxide represented by the following Chemical Formula 4.

[0097] [Chemical Formula 3]

[0098] Li a' Co b' M3' c' (P β' O γ' ) d'

[0099] (Wherein, M3' is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0100] 0 <a'≤10,0≤b'≤8,0≤c'≤8,0<d'≤13,0≤β'≤4,0<γ'≤10)

[0101] [Chemical Formula 4]

[0102] Co b" M3" c" (P β" Oγ" ) d"

[0103] (Wherein, M3" is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd,

[0104] 0≤b"≤8,0≤c"≤8,0 <d"≤13,0≤β"≤4,0<γ"≤10)

[0105] For example, the first oxide may be lithium phosphate, lithium cobalt phosphate, lithium metal (except cobalt) phosphate, lithium metal (except cobalt)-cobalt phosphate, lithium cobalt oxide and / or lithium metal (except cobalt) oxide, and the second oxide may be phosphorus pentoxide, cobalt phosphate, metal (except cobalt) phosphate, metal (except cobalt)-cobalt phosphate, cobalt oxide and / or metal (except cobalt) oxide.

[0106] Furthermore, the ratio of the first oxide to the second oxide defined above in the second compound present in the coating layer (first oxide / second oxide) is preferably 0.87 or more.

[0107] When the ratio of the first oxide to the second oxide (first oxide / second oxide) in the second compound present in the coating is less than 0.87 (i.e., when the proportion of the metal oxide relative to lithium phosphate increases), the effect of improving the electrochemical properties and stability of the positive electrode active material by the second compound is minimal, or may even reduce the electrochemical properties and stability of the positive electrode active material.

[0108] On the other hand, in the above-mentioned second compound, the ratio r1 / r2 (for example, LiCoO2 (mol %) / LiCo(PO4) (mol %) + LiPO3 (mol %)) of the compound r1 (for example, LiCoO2) having a crystal structure belonging to the space group Fd-3m, R3c or R-3m and the compound r2 (for example, LiCo(PO4) and LiPO3) having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m in the above-mentioned first oxide (for example, LiCo(PO4), LiPO3 and LiCoO2) is preferably less than 0.03.

[0109] Furthermore, the ratio s1 / s2 (e.g., Co3O4 (mol %) + P2O5 (mol %) / Co3(PO4)2 (mol %)) of the compound s1 (e.g., Co3O4 and P2O5) having a crystal structure belonging to the space group Fd-3m, R3c or R-3m and the compound s2 (e.g., Co3(PO4)2) having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m in the above-mentioned second oxide (e.g., Co3(PO4)2, Co3O4 and P2O5) in the above-mentioned second compound is preferably less than 0.24.

[0110] When the ratio of the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m and the compound having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m contained in the above-mentioned first oxide and the above-mentioned second oxide in the above-mentioned second compound is within the above-mentioned range, the reduction in the electrochemical performance and stability of the above-mentioned positive electrode active material can be minimized.

[0111] Furthermore, as described above, the first oxide and the second oxide may present a concentration gradient that decreases from the surface of the secondary particle toward the center of the secondary particle, and thus, the cobalt concentration in the lithium composite oxide may also present a concentration gradient that decreases from the surface of the secondary particle toward the center of the secondary particle.

[0112] In another embodiment, at least a portion of the surface of the first compound may further include a third compound represented by the following Chemical Formula 5.

[0113] [Chemical Formula 5]

[0114] Li e W f M4 g O h

[0115] (Wherein, M4 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd,

[0116] 0≤e≤10,0 <f≤8,0≤g≤8,2≤h≤13)

[0117] The third compound may be present in the coating layer containing the second compound or independently of the coating layer. Furthermore, the third compound may be present at least partially at the interface between primary particles of the first compound and at the surface of secondary particles formed by agglomerating the primary particles. Furthermore, the concentration of the third compound may form a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles.

[0118] In another embodiment, the positive electrode active material may further include a shell layer covering at least a portion of a surface of the first compound (a surface not covered by the coating layer) and a surface of the coating layer.

[0119] In this case, the shell layer may include a fourth compound represented by the following Chemical Formula 4. That is, the shell layer may be defined as a region where the fourth compound represented by the following Chemical Formula 4 exists.

[0120] [Chemical Formula 4]

[0121] Li j M4 k O l

[0122] (Wherein, M4 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd,

[0123] 0≤j≤10,0≤k≤8,2≤l≤13)

[0124] In addition, the shell layer may have a form in which different types of fourth compounds exist simultaneously in the same layer, or different types of fourth compounds represented by the above Chemical Formula 4 exist respectively in separate layers.

[0125] The fourth compound represented by Chemical Formula 4 may be physically and / or chemically bonded to the first compound, the second compound, and / or the third compound. Furthermore, the fourth compound may exist in a solid solution with the first compound, the second compound, and / or the third compound.

[0126] The fourth compound is an oxide formed by combining lithium and an element represented by M4 or an oxide of M4. An example of the oxide is Li a W b O c 、Li a Zr b O c、Li a Ti b O c 、Li a Ni b O c 、Li a B b O c 、W b O c 、Zr b O c 、Ti b O c or B b O c However, the above examples are only described for ease of understanding, and the above oxides defined in this article are not limited to the above examples.

[0127] In another embodiment, the fourth compound may be an oxide formed by combining lithium with at least two elements represented by M4, or further includes an oxide formed by combining lithium with at least two elements represented by M4. Examples of oxides formed by combining lithium with at least two elements represented by M4 may be Li a (W / Ti) b O c 、Li a (W / Zr) b O c 、Li a (W / Ti / Zr) b O c 、Li a (W / Ti / B) b O c etc., but the present invention is not limited thereto.

[0128] The fourth compound may have a concentration gradient that decreases from the surface of the secondary particle toward the center of the secondary particle. Thus, the concentration of the fourth compound may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

[0129] As described above, the fourth compound exhibits a concentration gradient that decreases from the surface of the secondary particle toward the center of the secondary particle, thereby further reducing residual lithium on the surface of the first compound. Furthermore, the fourth compound can prevent the crystallinity of the inner region of the surface of the first compound from being reduced. Furthermore, the fourth compound can prevent the overall structure of the positive electrode active material from being disrupted by the fourth compound during the electrochemical reaction.

[0130] Furthermore, the shell layer may include a first shell layer and a second shell layer, wherein the first shell layer includes at least one fourth compound represented by Chemical Formula 4, and the second shell layer includes at least one fourth compound represented by Chemical Formula 4 and includes an oxide different from the oxide included in the first shell layer.

[0131] lithium secondary batteries

[0132] According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. The positive electrode active material layer can include the positive electrode active material according to various embodiments of the present invention. Since the details regarding the positive electrode active material are the same as those described above, a detailed description will be omitted for convenience. The following will only describe the remaining components not described above.

[0133] There are no particular limitations on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Examples include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surfaces have been treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, or may have microscopic irregularities formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, various forms such as films, sheets, foils, meshes, porous materials, foams, and non-woven fabrics may be used.

[0134] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition on the positive electrode current collector. The positive electrode slurry composition includes the positive electrode active material and a conductive material, and optionally includes a binder as needed.

[0135] At this time, the content of the positive electrode active material can be 80% to 99% by weight, more specifically 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be achieved, but the present invention is not necessarily limited thereto.

[0136] The conductive material is used to provide conductivity to the electrode and can be used without limitation, as long as it has electronic conductivity and does not cause chemical changes in the assembled battery. Specific examples include: graphite such as natural graphite or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. These materials can be used alone or as a mixture of two or more. The content of the conductive material can be 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0137] The above-mentioned binder serves to adhere the positive electrode active material particles to each other and to improve the adhesion of the positive electrode active material and the collector. Specific examples thereof may include: polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers, and these substances can be used as a single or as a mixture of two or more. The content of the above-mentioned binder can be 0.1 wt % to 15 wt % relative to the total weight of the positive electrode active material layer.

[0138] In addition to using the above-mentioned positive electrode active material, the above-mentioned positive electrode can be prepared using a common positive electrode preparation method. Specifically, the above-mentioned positive electrode can be prepared by applying a positive electrode slurry composition prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder and a conductive material in a solvent onto a positive electrode current collector, and then drying and rolling the resultant.

[0139] The above-mentioned solvent can be a solvent commonly used in the art, and can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, water, etc., and these substances can be used alone as a substance, or as a mixture of two or more. Considering the coating thickness and preparation yield of the slurry, as long as the above-mentioned solvent can dissolve or disperse the above-mentioned positive electrode active material, conductive material and binder and has a viscosity sufficient to obtain excellent thickness uniformity when it is subsequently used to prepare the positive electrode coating, the amount of the solvent used is sufficient.

[0140] Furthermore, in another embodiment, the positive electrode may be prepared by casting the positive electrode slurry composition on a separate support, and then laminating the film obtained by peeling the film from the support on a positive electrode current collector.

[0141] According to another aspect of the present invention, an electrochemical device comprising the positive electrode is provided. The electrochemical device may be specifically a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0142] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as the positive electrode described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0143] The lithium secondary battery may optionally further include a battery container for housing an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0144] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0145] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. Examples include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. Furthermore, the negative electrode current collector can typically have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, the negative electrode current collector surface can be formed with microscopic irregularities to enhance adhesion of the negative electrode active material. For example, various forms such as films, sheets, foils, meshes, porous materials, foams, and non-woven fabrics can be used.

[0146] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition on the negative electrode current collector. The negative electrode slurry composition includes the negative electrode active material and a conductive material, and optionally includes a binder as needed.

[0147] The above-mentioned negative electrode active material can use a compound that can reversibly intercalate and deintercalate lithium. Specific examples thereof may include: carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds that can alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides that can be doped and dedoped with lithium such as SiO β(0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite comprising a metal compound and a carbon material such as a Si-C composite or a Sn-C composite, and any one of these substances or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as the above-mentioned negative electrode active material. In addition, the carbon material can use both low-crystalline carbon and high-crystalline carbon. Low-crystalline carbon generally includes soft carbon and hard carbon, and high-crystalline carbon generally includes: amorphous, plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, and high-temperature sintered carbon such as floating graphite (Kish graphite), pyrolytic carbon (pyrolytic carbon), mesophase pitch based carbon fiber (mesophase pitch based carbon fiber), mesophase carbon microbeads (meso-carbon microbeads), mesophase pitch (Mesophase pitches) and petroleum or coal tar pitch derived coke (petroleum or coal tar pitch derived cokes).

[0148] The 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.

[0149] The binder is a component that helps to bind the conductive material, the active material, and the current collector, and its content is generally 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile butadiene rubber, fluororubber, and various copolymers thereof.

[0150] The conductive material is a component used to further improve the conductivity of the negative electrode active material. The content of the conductive material can be 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. The conductive material is not limited as long as it has conductivity and does not cause chemical changes in the battery. Conductive materials such as graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorocarbons, aluminum, or nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives can be used.

[0151] In one embodiment, the negative electrode active material layer can be prepared by: applying a negative electrode slurry composition prepared by dissolving or dispersing the negative electrode active material and an optional binder and a conductive material in a solvent on a negative electrode collector and drying the resultant; or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling off the support on the negative electrode collector.

[0152] On the other hand, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration channel for lithium ions, and is not particularly limited as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having low resistance to electrolyte ion migration and excellent ability to contain electrolyte liquid moisture is preferred. Specifically, it is possible to use: a porous polymer film, for example, a porous polymer film prepared from 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. In addition, a commonly used porous non-woven fabric such as a non-woven fabric made of high melting point glass fiber or polyethylene terephthalate fiber can be used. In addition, in order to ensure heat resistance and mechanical strength, a coated separator comprising a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multilayer structure.

[0153] In addition, the electrolyte used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the preparation of lithium secondary batteries, but the present invention is not limited thereto.

[0154] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0155] The above-mentioned organic solvent can be used without particular limitation, as long as it can act as a medium for the migration of ions participating in the electrochemical reaction of the battery. Specific examples of the above-mentioned organic solvent may include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (EPC). Carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, which can enhance the charge and discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of approximately 1:1 to 1:9 can produce excellent electrolyte performance.

[0156] The above-mentioned lithium salt can be used without particular limitation, as long as it is a compound capable of providing lithium ions in a lithium secondary battery. Specific examples of the above-mentioned lithium salts may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt can be advantageously used in a concentration range of 0.1M to 2.0M. When the lithium salt concentration is included in the above range, the electrolyte has appropriate conductivity and viscosity, thereby being able to exhibit excellent electrolyte performance, and lithium ions can be effectively migrated.

[0157] In the above electrolyte, in order to increase the battery life properties, suppress the decline of battery capacity, improve the battery discharge capacity, etc., in addition to the above electrolyte forming components, one or more additives may be further included, including, for example: halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol or aluminum chloride. The content of the above additives may be 0.1 wt % to 5 wt % relative to the total weight of the electrolyte.

[0158] The lithium secondary battery containing the positive electrode active material according to the present invention as described above stably exhibits excellent discharge capacity, output characteristics and life characteristics, and is therefore used in the following fields: the field of portable devices such as mobile phones, laptop computers and digital cameras; and the field of electric vehicles such as hybrid electric vehicles (HEV) and the like.

[0159] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may have a cylindrical shape, an angular shape, a pouch shape, or a coin shape, such as a can shape. Furthermore, the lithium secondary battery may be used as a battery cell for a power source of a small device, or as a unit cell of a medium-sized or large-sized battery module including a plurality of battery cells.

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

[0161] The battery module or the battery pack can be used as a power source for power tools; electric vehicles including electric vehicles (EV), hybrid vehicles and plug-in hybrid electric vehicles (PHEV); or one or more medium and large devices in a system for storing electricity.

[0162] Hereinafter, the present invention will be described in more detail with reference to Examples. However, it should be understood that these Examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0163] Experimental Example 1.

[0164] Preparation Example 1. Preparation of positive electrode active material

[0165] (1) Example 1

[0166] Spherical Ni was synthesized by co-precipitation method. 0.91 Co 0.08 Mn 0.01 (OH)2 hydroxide precursor. Specifically, in a 90L reactor, 25 wt% of NaOH and 30 wt% of NH4OH are added to a 1.5M composite transition metal sulfuric acid aqueous solution, which is mixed with nickel sulfate, cobalt sulfate and manganese sulfate in a molar ratio of 91:8:1. The pH in the reactor is maintained at 11.5, the reactor temperature at this time is maintained at 60°C, and N2 as an inert gas is introduced into the reactor to prevent the prepared precursor from being oxidized. After the synthesis stirring is completed, a filter press (F / P) device is used for washing and dehydration to obtain Ni 0.91 Co 0.08 Mn 0.01 (OH)2 hydroxide precursor.

[0167] Next, LiOH (Li / (Ni+Co+Mn) molar ratio = 1.01) was mixed into the synthesized precursor, and then the temperature was raised to 700° C. at 2° C. per minute in a sintering furnace while maintaining an O 2 atmosphere, and heat-treated for 10 hours to obtain a lithium composite oxide.

[0168] Next, the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2), and the tungsten-containing raw material (WO3) are mixed and then sintered to prepare a positive electrode active material. Specifically, the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2), and the tungsten-containing raw material (WO3) are mixed and then heated in a sintering furnace maintained at an O2 atmosphere. The temperature is raised at 2°C per minute to 400°C, and the mixture is heat treated for 5 hours, followed by natural cooling to obtain the positive electrode active material.

[0169] The cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) are mixed so that the content of each of the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) is 0.3 mol % relative to the mixture of the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3).

[0170] The ICP analysis results of the composition of the positive electrode active material are shown in Table 1 below.

[0171] Table 1

[0172] element Ni Co Mn W P Content (mol%) 90.35 8.22 0.99 0.31 0.13

[0173] (2) Example 2

[0174] A positive electrode active material was prepared in the same manner as in Example 1, except that the cobalt-containing raw material (Co3(PO4)2) was mixed so that the ratio of the cobalt-containing raw material to the mixture of the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2), and the tungsten-containing raw material (WO3) was 0.5 mol %. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 2 below.

[0175] Table 2

[0176] element Ni Co Mn W P Content (mol%) 90.08 8.21 0.99 0.50 0.22

[0177] (3) Example 3

[0178] A positive electrode active material was prepared in the same manner as in Example 1, except that the tungsten-containing raw material (WO3) was mixed so that the ratio of the tungsten-containing raw material to the mixture of the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2), and the tungsten-containing raw material (WO3) was 1.0 mol%. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 3 below.

[0179] Table 3

[0180] element Ni Co Mn W P Content (mol%) 89.33 8.31 0.98 0.97 0.41

[0181] (4) Example 4

[0182] A positive electrode active material was prepared in the same manner as in Example 1, except that 0.05 mol % of a zirconium-containing compound (ZrO 2 ) was further mixed into the synthesized precursor. The ICP analysis results of the composition of the positive electrode active material are shown in Table 4 below.

[0183] Table 4

[0184] element Ni Co Mn Zr W P Content (mol%) 90.34 8.20 0.99 0.05 0.30 0.12

[0185] (5) Example 5

[0186] A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium composite oxide, the cobalt-containing raw material (Co3(PO4)2), and the tungsten-containing raw material (WO3) were mixed and then heat-treated. 0.2 mol% of a titanium-containing compound (TiO2) was further mixed in the same sintering furnace. The sintering furnace maintained an O2 atmosphere, the temperature was raised at 2°C per minute to 400°C, and the heat treatment was continued for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 5 below.

[0187] Table 5

[0188] element Ni Co Mn Ti W P Content (mol%) 90.28 8.18 0.99 0.18 0.25 0.12

[0189] (6) Comparative Example 1

[0190] A positive electrode active material was prepared in the same manner as in Example 1, except that the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) were not mixed with the lithium composite oxide, and the temperature was raised to 400°C at 2°C per minute and heat treated for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 6 below.

[0191] Table 6

[0192] element Ni Co Mn W P Content (mol%) 91.01 7.93 1.06 - -

[0193] (7) Comparative Example 2

[0194] A positive electrode active material was prepared in the same manner as in Example 1, except that only the tungsten-containing raw material (WO 3 ) was mixed with the lithium composite oxide and then calcined. The ICP analysis results of the composition of the positive electrode active material are shown in Table 7 below.

[0195] Table 7

[0196] element Ni Co Mn W P Content (mol%) 90.78 7.90 1.01 0.31 -

[0197] (8) Comparative Example 3

[0198] A positive electrode active material was prepared in the same manner as in Example 1, except that only the cobalt-containing raw material (Co3(PO4)2) was mixed with the lithium composite oxide and then calcined. The ICP analysis results of the composition of the positive electrode active material are shown in Table 8 below.

[0199] Table 8

[0200] element Ni Co Mn W P Content (mol%) 90.57 8.28 1.01 - 0.14

[0201] (9) Comparative Example 4

[0202] A positive electrode active material was prepared in the same manner as in Example 1, except that the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) were not mixed with the lithium composite oxide, and the temperature was increased to 700°C at 2°C per minute and heat treated for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 9 below.

[0203] Table 9

[0204] element Ni Co Mn W P Content (mol%) 91.09 7.91 1.00 - -

[0205] (10) Comparative Example 5

[0206] A positive electrode active material was prepared in the same manner as in Example 1, except that only the tungsten-containing raw material (WO3) was mixed with the lithium composite oxide, the temperature was raised to 700°C at 2°C per minute, and the heat treatment was performed for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 10 below.

[0207] Table 10

[0208] element Ni Co Mn W P Content (mol%) 90.74 7.96 1.00 0.30 -

[0209] (11) Comparative Example 6

[0210] A positive electrode active material was prepared in the same manner as in Example 1, except that only the cobalt-containing raw material (Co3(PO4)2) was mixed with the lithium composite oxide, the temperature was raised to 700°C at 2°C per minute, and the heat treatment was performed for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 11 below.

[0211] Table 11

[0212] element Ni Co Mn W P Content (mol%) 90.60 8.24 1.01 - 0.15

[0213] (12) Comparative Example 7

[0214] A positive electrode active material was prepared in the same manner as in Example 1, except that the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) were mixed with the lithium composite oxide, and then the temperature was raised to 700°C at 2°C per minute and heat treated for 5 hours. The results of ICP analysis of the composition of the positive electrode active material are shown in Table 12 below.

[0215] Table 12

[0216] element Ni Co Mn W P Content (mol%) 90.27 8.34 0.94 0.30 0.15

[0217] Preparation Example 2. Preparation of lithium secondary battery

[0218] A positive electrode slurry was prepared by dispersing 92 wt% of the positive electrode active material prepared according to Preparation Example 1, 4 wt% of artificial carbon black, and 4 wt% of a PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on an aluminum film having a thickness of 15 μm and vacuum-dried at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0219] A button cell was prepared using lithium foil as the counter electrode of the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte containing LiPF6 at a concentration of 1.15 M in a solvent prepared by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0220] Experimental Example 1. XRD analysis of positive electrode active materials

[0221] X-ray diffraction (XRD) analysis was performed on the positive electrode active material prepared according to Preparation Example 1 to confirm the Ni occ and the coating on the surface of the above-mentioned positive electrode active material. By using Cu Kα radiation ( XRD analysis was performed on a Bruker D8 Advance diffractometer.

[0222] (1) Ni of positive electrode active material occ Determination

[0223] The occupancy of nickel metal inserted into the Li 3a position of the positive electrode active material prepared according to Preparation Example 1 was determined by Reitveld analysis (Reitveld refinement) of the X-ray diffraction pattern. The results are shown in Table 13 below.

[0224] Table 13

[0225] Classification c / a ratio <![CDATA[Ni at the 3a position occ (%)]]> Example 1 4.940 2.41 Example 2 4.940 2.47 Example 3 4.940 2.52 Example 4 4.940 2.23 Example 5 4.940 2.10 Comparative Example 1 4.940 2.27 Comparative Example 2 4.940 2.39 Comparative Example 3 4.940 2.30 Comparative Example 4 4.940 1.62 Comparative Example 5 4.940 2.09 Comparative Example 6 4.940 1.68 Comparative Example 7 4.940 2.29

[0226] Referring to the results in Table 13, it can be confirmed that when a cobalt-containing raw material (Co3(PO4)2) and a tungsten-containing raw material (WO3) are mixed with the lithium composite oxide, the nickel occupancy rate at the Li 3a site increases compared to when only the cobalt-containing raw material (Co3(PO4)2) or the tungsten-containing raw material (WO3) is mixed with the lithium composite oxide. Furthermore, referring to Example 1 and Comparative Example 7, after mixing the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) with the lithium composite oxide, heat treatment at a relatively low temperature can increase the nickel occupancy rate at the Li 3a site.

[0227] As described above, after mixing the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) in the above-mentioned lithium composite oxide, heat treatment is performed at a relatively low temperature. Thus, compared with the case where heat treatment is performed after mixing the cobalt-containing raw material (Co3(PO4)2) or the tungsten-containing raw material (WO3) alone in the above-mentioned lithium composite oxide, or heat treatment is performed at a relatively high temperature after mixing the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3), the increase in the nickel occupancy rate inserted into the above-mentioned Li 3a position may be because when tungsten is doped into the crystal lattice of the above-mentioned lithium composite oxide, tungsten is inserted into the Li 3a position.

[0228] (2) Analysis of coating content on the surface of positive electrode active materials

[0229] From the XRD raw data measured using Bruker's EVA program, the oxides shown in Tables 14 and 15 below were screened to quantitatively analyze the content of the coating (ie, the second compound) on the surface of the positive electrode active material prepared according to Preparation Example 1.

[0230] The analysis results of the coating material in the surface of the positive electrode active material analyzed according to the above method are shown in Tables 14 to 16 below.

[0231] Table 14

[0232] Classification Space group Crystal structure <![CDATA[Co3(PO4)2]]> <![CDATA[P21 / c]]> Monoclinic <![CDATA[LiCo(PO4)]]> Pnma Orthogonal <![CDATA[Co3O4]]> Fd-3m cube <![CDATA[LiPO3]]> P* / n Monoclinic <![CDATA[P2O5]]> R3c diamond <![CDATA[LiCoO2]]> R-3m diamond

[0233] Table 15

[0234]

[0235] Table 16

[0236]

[0237] Referring to the results in Table 14 above, it can be confirmed that the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the above-mentioned second compound present as a coating on at least a part of the surface of the above-mentioned first compound as a lithium composite oxide has a cubic or rhombohedral crystal structure.

[0238] Referring to the results of Tables 14 to 16 above, it can be confirmed that, unlike the positive electrode active materials according to Comparative Examples 6 and 7, in the case of the positive electrode active materials according to Examples 1 to 5, after mixing the cobalt-containing raw material (Co3(PO4)2) and the tungsten-containing raw material (WO3) in the above-mentioned lithium composite oxide, heat treatment is performed at a relatively low temperature, so that the ratio of the compound (Co3O4, LiCoO2 and P2O5) having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the oxide defined as the second compound herein is less than 13 mol%.

[0239] In addition, unlike the positive electrode active materials according to Comparative Examples 6 and 7, in the case of the positive electrode active materials according to Examples 1 to 5, it can be confirmed that the ratio of the compound r1 having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the first oxide in the above-mentioned second compound, i.e., LiCo(PO4), LiPO3 and LiCoO2, i.e., LiCoO2 and the compound r2 having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m, i.e., LiCo(PO4) and LiPO3 (r1 / r2=LiCoO2 (mol%) / LiCo(PO4) (mol%)+LiPO3 (mol%)) is 0.03 or less.

[0240] Furthermore, unlike the positive electrode active materials according to Comparative Examples 6 and 7, in the case of the positive electrode active materials according to Examples 1 to 5, it can be confirmed that the ratio of the second oxide in the above-mentioned second compound, i.e., compound s1 having a crystal structure belonging to space group Fd-3m, R3c or R-3m, i.e., Co3O4 and P2O5 and compound s2 having a crystal structure belonging to a space group other than space group Fd-3m, R3c or R-3m, i.e., Co3(PO4)2 (s1 / s2=Co3O4 (mol%)+P2O5 (mol%) / Co3(PO4)2 (mol%), is less than 0.24.

[0241] On the other hand, it can be confirmed that in the case of the positive electrode active material according to Comparative Example 3, except that the tungsten-containing raw material (WO3) is not mixed and heat-treated, the rest is prepared in the same method as the positive electrode active material according to Example 1, so that it exists in a composition similar to the oxide defined as the second compound.

[0242] Experimental Example 2. Determination of Unreacted Lithium in Positive Electrode Active Materials

[0243] The unreacted lithium content of the positive electrode active material prepared according to Preparation Example 1 was measured by pH titration using 0.1 M HCl until the pH reached 4. First, 5 g of each positive electrode active material prepared according to Preparation Example 1 was added to 100 ml of DIW, stirred for 15 minutes, and filtered. 50 ml of the filtrate was collected and 0.1 M HCl was added thereto. The HCl consumption according to the change in pH was measured to determine Q1 and Q2, thereby calculating the content of unreacted LiOH.

[0244] M1 = 23.95 (LiOH molecular weight)

[0245] M2 = 73.89 (Li2CO3 molecular weight)

[0246] SPL size = (sample weight x solution weight) / water weight

[0247] LiOH (wt%) = [(Q1-Q2) × C × M1 × 100] / (SPL size × 1000)

[0248] The results of the lithium impurity content in the positive electrode active material determined by the above calculation formula are shown in Table 17 below.

[0249] Table 17

[0250] Classification LiOH (ppm) Example 1 2,378 Example 2 2,090 Example 3 1,789 Example 4 2,423 Example 5 2,892 Comparative Example 1 4,432 Comparative Example 2 2,911 Comparative Example 3 3,059 Comparative Example 4 5,503 Comparative Example 5 7,148 Comparative Example 6 5,020 Comparative Example 7 6,363

[0251] (2) Electrochemical performance evaluation of lithium secondary batteries

[0252] The initial charge capacity, initial discharge capacity, initial reversible efficiency and discharge capacity ratio (C-rate) were determined by performing a charge / discharge experiment on the lithium secondary battery prepared according to Preparation Example 2 at a discharge rate of 0.1C to 5.0C at 3.0V to 4.3V at 25°C using an electrochemical analyzer (Toyo, Toscat-3100).

[0253] Furthermore, the lithium secondary battery prepared by the above method was charged / discharged 50 times at 1C / 1C in the driving voltage range of 3.0V to 4.4V at a temperature of 25°C, and then the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0254] On the other hand, the initial impedance of the lithium secondary battery prepared according to Preparation Example 2 was measured using electrochemical impedance spectroscopy (EIS) in a frequency range of 10 kHz to 0.01 Hz.

[0255] The above measurement results are shown in Table 18 below.

[0256] Table 18

[0257]

[0258]

[0259] Although the embodiments of the present invention are described above, those skilled in the art will understand that various modifications and changes can be made to the present invention by adding, modifying, deleting, increasing, etc. the constituent elements without departing from the scope of the concept of the present invention as described in the claims, and these also fall within the scope of the rights of the present invention.

Claims

1. A positive electrode active material, characterized in that include: A first compound represented by the following chemical formula 1 and capable of intercalating and deintercalating lithium; and The second compound is represented by the following chemical formula 2: [Chemical Formula 1] Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α Where, M1 is Mn, M2 is at least one selected from P, Sr, Ba, B, Ti, Zr, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu, 0.5≤w≤1.5,0≤x≤0.50,0≤y≤0.20,0≤z≤0.20,0≤α≤0.02, [Chemical Formula 2] Li a Co b M3 c (P β O γ ) d Wherein, M3 is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤a≤10,0≤b≤8,0≤c≤8,0 <d≤13,0<β≤4,0<γ≤10, The second compound includes Co3(PO4)2, LiCo(PO4)4, and LiPO3 as compounds having a crystal structure belonging to a space group other than the space group Fd-3m, R3c, or R-3m, and does not include Co3O4, LiCoO2, and P2O5 as compounds having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m. The second compound includes a first oxide represented by the following Chemical Formula 3 and a second oxide represented by the following Chemical Formula 4: [Chemical Formula 3] Li a' Co b' M3' c' (P β' O γ' ) d' wherein M3′ is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd; 0 <a'≤10,0≤b'≤8,0≤c'≤8,0<d'≤13,0≤β'≤4,0<γ'≤10, [Chemical Formula 4] Co b" M3" c" (P β" O γ" ) d" Wherein, M3" is at least one selected from Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤b"≤8,0≤c"≤8,0 <d"≤13,0≤β"≤4,0<γ"≤10, The second compound is contained in a coating layer, and the coating layer is present on at least a portion of the surface of the first compound.

2. The positive electrode active material according to claim 1, characterized in that Among the second compounds, the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m has a cubic or rhombohedral crystal structure.

3. The positive electrode active material according to claim 1, characterized in that The second compound is an oxide including at least one first element selected from Group 1A elements, Group 3A elements, and Group 5A elements and at least one second element selected from Group 8 elements.

4. The positive electrode active material according to claim 1, characterized in that The ratio r1 / r2 of the compound r1 having a crystal structure belonging to the space group Fd-3m, R3c or R-3m and the compound r2 having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m in the first oxide is 0.03 or less, The unit of compounds r1 and r2 is mol %.

5. The positive electrode active material according to claim 1, characterized in that The ratio s1 / s2 of the compound s1 having a crystal structure belonging to the space group Fd-3m, R3c or R-3m and the compound s2 having a crystal structure belonging to a space group other than the space group Fd-3m, R3c or R-3m in the second oxide is 0.24 or less, The unit of compounds s1 and s2 is mol %.

6. The positive electrode active material according to claim 1, characterized in that In the above Chemical Formula 1, x+y+z is 0.20 or less.

7. The positive electrode active material according to claim 1, characterized in that Tungsten exists in the crystal lattice of the first compound.

8. The positive electrode active material according to claim 1, characterized in that At least a portion of the surface of the first compound further includes a third compound represented by the following Chemical Formula 5: [Chemical Formula 5] Li e W f M4 g O h Wherein, M4 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd and Nd, 0≤e≤10,0 <f≤8,0≤g≤8,2≤h≤13。 9. A positive electrode, characterized in that The positive electrode active material according to claim 1 is included.

10. A lithium secondary battery, characterized in that: The positive electrode according to claim 9 is used.

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