Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material improved in electrochemical characteristics and stability, and a lithium secondary battery using a positive electrode including the positive electrode active material, and more particularly, to provide a positive electrode active material which may prevent in advance decreases in electrochemical characteristics and stability of the positive electrode active material, the decreases being caused by Li impurities, by controlling the content of the Li impurities remaining on the surface of the positive electrode active material without a washing process, to reduce the amount of residual lithium present on the surface thereof, and a lithium secondary battery using a positive electrode including the positive electrode active material.SOLUTION: According to one aspect of the present invention, there is provided a positive electrode active material which includes a first compound enabling lithium intercalation / deintercalation and a coating layer present on at least a part of the surface of the first compound, the coating layer including a second compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cathode active material having improved electrochemical properties and stability, and a lithium secondary battery using a cathode including the cathode active material. More specifically, the present invention relates to a cathode active material that can prevent deterioration in the electrochemical properties and stability of the cathode active material due to Li impurities by controlling the content of Li impurities remaining on the surface without performing a water washing process to reduce the amount of residual lithium present on the surface of the cathode active material, and a lithium secondary battery using a cathode including the cathode active material. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A typical example of such batteries is a lithium secondary battery, which stores electrical energy by utilizing the difference in chemical potential when lithium ions are intercalated / deintercalated between the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode.

[0004] Lithium composite oxides are used as the positive electrode active material of lithium secondary batteries, and composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are being researched as examples.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but suffer from low capacity and poor high-temperature characteristics. LiNiO2-based positive electrode active materials exhibit high discharge capacity, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, resulting in significant problems with rate characteristics.

[0007] Furthermore, as the degree of cation mixing deepens, a large amount of Li by-products is generated, and most of these Li by-products consist of compounds of LiOH and Li2CO3, which cause gelation during the manufacture of the positive electrode paste and gas generation during charge and discharge after electrode manufacture. The remaining Li2CO3 increases the swelling phenomenon of the cell, reducing cycle life and causing the battery to swell.

[0008] Meanwhile, the content of Li impurities present on the surface of the positive electrode active material tends to increase in proportion to the content of Ni in the positive electrode active material.

[0009] Therefore, in the case of high-Ni type cathode active materials, which have recently been introduced to improve the capacity characteristics of cathode active materials, a water washing process is essential to remove excess Li impurities present on the surface.

[0010] However, although the water washing process can reduce residual lithium present on the surface of the positive electrode active material, it can also damage the surface of the positive electrode active material. If the surface of the positive electrode active material is damaged by the water washing process, the electrochemical properties and stability of the positive electrode active material may be reduced. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2016-0112622 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to provide a cathode active material with improved electrochemical properties and stability that overcomes various problems associated with conventional cathode active materials for lithium secondary batteries. In particular, the present invention aims to provide a cathode active material that can prevent deterioration of the electrochemical properties and stability of the cathode active material due to Li impurities by controlling the content of Li impurities remaining on the surface without requiring a water washing process to reduce the amount of residual lithium present on the surface of the cathode active material.

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

[0014] It is yet another object of the present invention to provide a lithium secondary battery using the positive electrode defined herein. [Means for solving the problem]

[0015] According to one aspect of the present invention, there is provided a positive electrode active material including: a first compound capable of lithium intercalation / deintercalation; and a coating layer present on at least a portion of a surface of the first compound, the coating layer including a second compound.

[0016] In this case, the second compound may be an oxide containing 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.

[0017] Here, the first compound may be represented by the following Chemical Formula 1:

[0018] [Chemical formula 1] Li w Ni 1-(x+y+z) Co x M1y M2 z O 2+α (where, M1 is at least one selected from Mn and 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, W, 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≦α≦0.02)

[0019] The second compound may be represented by the following Chemical Formula 2:

[0020] [Chemical formula 2] Li a Co b M3 c (P β O γ ) d (where, M3 is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦a≦10, 0≦b≦8, 0≦c≦8, 0 <d≦13、0 ≦ β≦4, 0<γ≦10)

[0021] In this case, 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.

[0022] [Chemical formula 3] Li a′ Co b′ M3′ c′ (P β′ O γ′ ) d′ (where, M3′ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0 <a′≦10、0≦b′≦8、0≦c′≦8、0<d′≦13、0≦β′≦4、0<γ′≦10である)

[0023] [Chemical formula 4] Co b″ M3″ c″ (P β″ O γ″ ) d″ (where, M3″ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦b″≦8, 0≦c″≦8, 0 <d″≦13、0≦β″≦4、0<γ″≦10である)

[0024] In another embodiment, the first compound may further include a third compound represented by the following Chemical Formula 5 on at least a portion of the surface thereof:

[0025] [Chemical formula 5] Li e W f M4 g O h (where, M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦e≦10, 0 <f≦8、0≦g≦8、 0< h≦13)

[0026] According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material.

[0027] According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-described positive electrode. [Effects of the Invention]

[0028] The cathode active materials according to various embodiments of the present invention can control the amount of Li impurities remaining on the surface by forming lithium metal oxide and / or lithium metal phosphate on the surface without a water washing process for reducing the amount of residual lithium present on the surface of the cathode active material.

[0029] This makes it possible to prevent in advance the deterioration of the electrochemical properties and stability of the positive electrode active material caused by Li impurities remaining on the surface of the positive electrode active material.

[0030] Thus, by using the positive electrode active materials according to various embodiments of the present invention, the lithium secondary battery can improve various electrochemical characteristics such as capacity characteristics, life characteristics, rate characteristics, etc., which are important indicators for evaluating the performance of the lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to more readily understand the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise required by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0032] Hereinafter, the cathode active material according to the present invention, the cathode including the cathode active material, and the lithium secondary battery using the cathode will be described in more detail.

[0033] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material including a first compound capable of lithium intercalation / deintercalation and a coating layer present on at least a portion of a surface of the first compound.

[0034] The first compound may be a lithium composite oxide in a single crystal or polycrystalline form, and is preferably a lithium composite oxide in a polycrystalline form. The polycrystalline lithium composite oxide refers to an aggregate including primary particles and secondary particles formed by agglomerating a plurality of the primary particles.

[0035] The primary particle refers to a single crystal grain (grain or crystallite), and the secondary particle refers to an aggregate formed by the aggregation of a plurality of primary particles. Voids and / or grain boundaries may exist between the primary particles constituting the secondary particle.

[0036] For example, the primary particles may be separated from adjacent primary particles within the secondary particle to form internal voids. Also, the primary particles may contact the internal voids rather than contact adjacent primary particles to form grain boundaries, thereby forming surfaces present within the secondary particle.

[0037] On the other hand, the surfaces of the primary particles present on the outermost surfaces of the secondary particles, which are exposed to the outside air, form the surfaces of the secondary particles.

[0038] The average particle size of the primary particles is in the range of 0.1 μm to 5 μm, preferably 0.1 μm to 3 μm, so that the optimum density of the cathode manufactured using the cathode active material according to various embodiments of the present invention can be realized. Also, 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.

[0039] Additionally, the primary particles and / or the secondary particles may have a rod-like, elliptical and / or irregular shape.

[0040] Here, the first compound is a lithium composite oxide represented by the following Chemical Formula 1:

[0041] [Chemical formula 1] Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α (where, M1 is at least one selected from Mn and 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, W, 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≦α≦0.02)

[0042] In this case, the first compound may be a lithium composite oxide having a layered crystal structure containing at least Ni and Co. In addition, the first compound is preferably a high-Ni type lithium composite oxide in which x+y+z in Chemical Formula 1 is 0.20 or less.

[0043] As previously explained, in the case of a lithium composite oxide containing Ni, as the mixing of Li and Ni cations becomes more intense, a large amount of residual lithium, i.e., Li impurities, may form on the surface of the lithium composite oxide. The Li impurities mainly include LiOH and Li2CO3, and these Li impurities may cause gelation during the preparation of a paste for manufacturing a positive electrode or may cause swelling in the cell.

[0044] The content of the Li impurity increases proportionally with the Ni content in the lithium composite oxide, and in the case of a high-Ni type positive electrode active material (lithium composite oxide) having a Ni content of 80 mol% or more, a water washing process is required to remove the Li impurities from the surface. However, the water washing process may partially damage the surface of the lithium composite oxide, which may cause deterioration in the electrochemical properties and stability of the lithium composite oxide.

[0045] Meanwhile, the lithium composite oxides according to various embodiments of the present invention and the cathode active materials including the lithium composite oxides can effectively reduce the content of Li impurities remaining on the surface of the lithium composite oxide without a water washing process by forming lithium metal oxide and / or lithium metal phosphate, which will be described later, on the lithium composite oxide.

[0046] Also, the first compound may be doped with a metal element represented by M1 as shown in Chemical Formula 1, and preferably, M1 may include tungsten (W).

[0047] In this case, the tungsten may be present in the crystal lattice of the first compound, i.e., the tungsten may be present in the first compound in a state of substituting Ni inserted into at least one of the Li 3a site and 3b site.

[0048] On the other hand, when the tungsten is doped into the first compound, the ratio of Ni inserted into the Li 3a site is determined by Rietveld analysis of the X-ray diffraction pattern. occ The ratio of Ni inserted into the Li 3a site can be improved, thereby improving the electrochemical properties and stability of the positive electrode active material. occThis may be due to an increase in the amount of Ni inserted into the Li 3a site due to the doping of tungsten, but may also increase as W is inserted into the Li 3a site. Preferably, when 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, which can contribute to improving the electrochemical properties and stability of the first compound.

[0049] In this case, the first compound may be represented by the following Chemical Formula 1-1.

[0050] [Chemical formula 1-1] Li w Ni 1-(x+y+z) Co x M1 y M2 z W z′ O 2+δ (where, M1 is at least one selected from Mn and 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)

[0051] Additionally, M1 present in the lithium composite oxide may exhibit a concentration gradient that decreases from the surface portion toward the center portion of the secondary particle.

[0052] The concentration gradient means that there is a negative gradient 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.

[0053] As a result of the existence of a concentration gradient of M1, preferably tungsten (W), within the secondary particles, a migration path (lithium ion diffusion path) of lithium ions within the secondary particles and the primary particles constituting the secondary particles can be formed in a direction from the surface of the secondary particles toward the center.

[0054] The positive electrode active materials according to various embodiments of the present invention are characterized in that a coating layer including a second compound is provided on the surface of the first compound to reduce the amount of residual Li, i.e., Li impurities, present on the surface of the first compound.

[0055] In this case, the second compound may be present at least part of the interfaces between primary particles of the first compound and the surfaces of secondary particles formed by aggregation of the primary particles, and 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.

[0056] The coating layer can contain the second compound, which is an oxide containing 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.

[0057] The second compound may be represented by the following Chemical Formula 2:

[0058] [Chemical formula 2] Li a Co b M2 c (P β O γ ) d (where, M2 is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦a≦10, 0≦b≦8, 0≦c≦8, 0 <d≦13、0 ≦ β≦4, 0<γ≦10)

[0059] In this case, the second compound may be a single crystalline or amorphous oxide, but is not necessarily limited thereto, and may be a collection of at least one crystalline and / or amorphous heterogeneous oxide.

[0060] If at least one of the second compounds is an oxide having a crystalline structure, the second compound may have a crystalline structure belonging to the space group Fd-3m, Pnma, P* / n, R3c, or R-3m, and the crystalline structure may be a monoclinic, cubic, orthorhombic, or rhombohedral crystalline structure.

[0061] In a preferred case, in order to effectively remove residual Li 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 may be 13 mol% or less, more preferably 10 mol% or less, and more preferably 5 mol% or less. In the second compound, the crystal structure belonging to the space group Fd-3m, R3c, or R-3m may be a cubic or rhombohedral crystal structure.

[0062] Representative examples of the oxide having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m in the second compound include Co3O4, LiCoO2, and P2O5, and the second compound may further include oxides that may act as impurities similar to residual Li when present on the surface of the first compound.

[0063] If the proportion of the compound having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m in the second compound exceeds 13 mol % in order to effectively remove residual Li present on the surface of the first compound, the effect of the second compound in improving the electrochemical properties and stability of the positive electrode active material may be very small, or the electrochemical properties and stability of the positive electrode active material may be reduced.

[0064] In addition, 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.

[0065] [Chemical formula 3] Li a′ Co b′ M3′ c′ (P β′ O γ′ ) d′ (where, M3′ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0 <a′≦10、0≦b′≦8、0≦c′≦8、0<d′≦13、0≦β′≦4、0<γ′≦10である)

[0066] [Chemical formula 4] Co b″ M3″ c″ (P β″ O γ″ ) d″ (where, M3″ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦b″≦8, 0≦c″≦8, 0 <d″≦13、0≦β″≦4、0<γ″≦10である)

[0067] For example, the first oxide may be lithium phosphate, lithium cobalt phosphate, lithium metal (cobalt-excluded) phosphate, lithium metal (cobalt-excluded)-cobalt phosphate, lithium cobalt oxide, and / or lithium metal (cobalt-excluded) oxide, and the second oxide may be phosphorus pentoxide, cobalt phosphate, metal (cobalt-excluded) phosphate, metal (cobalt-excluded)-cobalt phosphate, cobalt oxide, and / or metal (cobalt-excluded) oxide.

[0068] Additionally, in the second compound present in the coating layer, the ratio of the first oxide to the second oxide (first oxide / second oxide) as defined above is preferably 0.87 or more.

[0069] When the ratio of the first oxide to the second oxide (first oxide / second oxide) in the second compound present in the coating layer is less than 0.87 (i.e., when the ratio of metal oxide to lithium phosphate is high), the effect of the second compound in improving the electrochemical properties and stability of the positive electrode active material is extremely small, or the second compound may actually deteriorate the electrochemical properties and stability of the positive electrode active material.

[0070] On the other hand, among the first oxides (e.g., LiCo(PO4), LiPO3, and LiCoO2) in the second compound, it is preferable that the ratio r1 / r2 (e.g., LiCoO2 (mol%) / LiCo(PO4) (mol%) + LiPO3 (mol%)) of compound r1 (e.g., LiCoO2) having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m to compound r2 (e.g., LiCo(PO4) and LiPO3) having a crystal structure belonging to a space group other than Fd-3m, R3c, or R-3m is 0.03 or less.

[0071] Furthermore, among the second oxides (e.g., Co3(PO4)2, Co3O4, and PO5), it is preferable that the ratio s1 / s2 (e.g., Co3O4 and PO5) of compounds s1 (e.g., Co3O4 and PO5) having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m to compounds s2 (e.g., Co3(PO4)2) having a crystal structure belonging to a space group other than Fd-3m, R3c, or R-3m) (e.g., Co3O4 (mol%) + PO5 (mol%) / Co3(PO4)2 (mol%)) is 0.24 or less.

[0072] In the second compound, when the ratio of the compound having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m contained in the first oxide and the second oxide to the compound having a crystal structure belonging to a space group other than Fd-3m, R3c, or R-3m is within the above-mentioned range, it is possible to minimize deterioration in the electrochemical properties and stability of the positive electrode active material.

[0073] Furthermore, as described above, the first oxide and the second oxide can exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle, and as a result, the Co concentration in the lithium composite oxide can also exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0074] In another embodiment, the first compound may further include a third compound represented by the following Chemical Formula 5 on at least a portion of the surface thereof:

[0075] [Chemical formula 5] Li e W f M4 g O h (where, M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦e≦10, 0 <f≦8、0≦g≦8、 0< h≦13)

[0076] The third compound may be present in the coating layer containing the second compound or may exist independently of the coating layer. The third compound may be present at the interface between primary particles of the first compound and at least a portion of the surface of secondary particles formed by aggregation of the primary particles. The concentration of the third compound may exhibit a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles.

[0077] In yet 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.

[0078] 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 in which the fourth compound represented by the following Chemical Formula 4 exists.

[0079] [Chemical formula 4] Li j M4 k O l (Here, M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W 、V , Ba, Ta, Sn, Hf, Ce, Gd, and Nd; (0≦j≦10, 0≦k≦8, ​​2≦l≦13)

[0080] In addition, the shell layer may be in a form in which different types of fourth compounds are present simultaneously in one layer, or different types of fourth compounds represented by Formula 4 are present in separate layers.

[0081] 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, and may also exist in a state of forming a solid solution with the first compound, the second compound, and / or the third compound.

[0082] The fourth compound is an oxide in which lithium and an element represented by M4 are combined, or as an oxide of M4, the oxide is, for example, 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 merely given for the sake of convenience to facilitate understanding, and the oxides defined in the present application are not limited to the above examples.

[0083] In another embodiment, the fourth compound may be an oxide of lithium and at least two elements represented by M4, or may further include an oxide of lithium and at least two elements represented by A. The oxide of lithium and at least two elements represented by A may be, for example, 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 It may be, but is not necessarily limited to, the above.

[0084] Here, the fourth compound may exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle, so that the concentration of the fourth compound may decrease from the outermost surface of the secondary particle toward the center portion of the secondary particle.

[0085] As described above, the fourth compound exhibits a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles, thereby further reducing residual Li present on the surface of the first compound. Furthermore, the fourth compound can prevent a decrease in crystallinity in the inner surface region of the first compound. Furthermore, the fourth compound can prevent the overall structure of the positive electrode active material from being destroyed during an electrochemical reaction.

[0086] Additionally, the shell layer may include a first shell layer including at least one fourth compound represented by Chemical Formula 4, and a second shell layer including at least one fourth compound represented by Chemical Formula 4 and an oxide different from the oxide included in the first shell layer.

[0087] Lithium secondary battery According to another aspect of the present invention, a positive electrode may be provided, including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include a positive electrode active material according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as that described above, detailed description thereof will be omitted for brevity, and only the remaining components not described above will be described below.

[0088] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0089] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0090] In this case, the positive electrode active material may be contained in an amount of 80 to 99 wt%, more specifically, 85 to 98.5 wt%, based on the total weight of the positive electrode active material layer. When contained in the above content range, excellent capacity characteristics can be exhibited, but the amount is not necessarily limited thereto.

[0091] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. 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, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0092] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt% of the total weight of the positive electrode active material layer.

[0093] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material described above and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0094] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the production yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for the production of a positive electrode.

[0095] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off from the support, and laminating the resulting film onto a positive electrode current collector.

[0096] According to yet another aspect of the present invention, there is provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

[0097] The lithium secondary battery may specifically include a positive electrode, a negative electrode facing 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 that described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0098] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0099] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0100] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0101] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0102] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β (0 ≦ Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0103] The negative electrode active material may be included in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer.

[0104] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0105] The 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. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0106] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0107] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular limitations. It is particularly preferable that the separator has low resistance to electrolyte ion movement and excellent electrolyte impregnation capacity. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymer materials can also be used, and they can be used in either a single-layer or multi-layer structure.

[0108] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0109] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0110] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC) and polycarbonate; alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which can result in excellent electrolyte performance.

[0111] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without any particular limitations. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0112] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0113] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0114] The shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery may be used as a battery cell used as a power source for a small device, and may also be preferably used as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0115] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0116] The battery module or the battery pack is used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0117] The present invention will be described in more detail below through examples. However, these examples are merely for the purpose of illustrating the present invention, and it should be understood that the scope of the present invention is not limited to these examples.

[0118] Experimental example 1. Production Example 1: Production of positive electrode active material (1) Example 1 Spherical Ni was prepared by the co-precipitation method. 0.91 Co 0.08 Mn 0.01(OH)2 hydroxide precursor was synthesized. Specifically, 25 wt% NaOH and 30 wt% NH4OH were added to a 1.5M composite transition metal sulfate aqueous solution, which was a mixture of nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 91:8:1, in a 90L reactor. The pH in the reactor was maintained at 11.5, the temperature of the reactor was maintained at 60°C, and inert gas N2 was introduced into the reactor to prevent the precursor from oxidizing. After the synthesis and stirring were completed, washing and dehydration were carried out using a filter press (F / P) equipment, and Ni 0.91 Co 0.08 Mn 0.01 (OH)2 hydroxide precursor was obtained.

[0119] Next, the synthesized precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.01), and then heated to 700°C at a rate of 2°C per minute while maintaining an O2 atmosphere in a calciner, and heat-treated for 10 hours to obtain a lithium composite oxide.

[0120] Next, the lithium composite oxide was mixed with a Co-containing raw material (Co3(PO4)2) and a W-containing raw material (WO3), and then calcined to finally produce a cathode active material. Specifically, the lithium composite oxide was mixed with the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3), and then the mixture was heated to 400°C at a rate of 2°C per minute while maintaining an O2 atmosphere in a calcination furnace, and then heat-treated for 5 hours, followed by natural cooling to obtain a cathode active material.

[0121] The Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3) were mixed so that each amount was 0.3 mol % relative to the mixture of the lithium composite oxide, the Co-containing raw material (Co3(PO4)2), and the W-containing raw material (WO3).

[0122] The ICP analysis results for the composition of the positive electrode active material are shown in Table 1 below.

[0123] [Table 1]

[0124] (2) Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the Co-containing raw material (Co3(PO4)2) was mixed at 0.5 mol % with respect to the mixture of the lithium composite oxide, the Co-containing raw material (Co3(PO4)2), and the W-containing raw material (WO3). The ICP analysis results for the composition of the positive electrode active material are shown in Table 2 below.

[0125] [Table 2]

[0126] (3) Example 3 A cathode active material was prepared in the same manner as in Example 1, except that the W-containing raw material (WO3) was mixed at 1.0 mol% with respect to the mixture of the lithium composite oxide, the Co-containing raw material (Co3(PO4)2), and the W-containing raw material (WO3). The ICP analysis results for the composition of the cathode active material are shown in Table 3 below.

[0127] [Table 3]

[0128] (4) Example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that 0.05 mol% of a Zr-containing compound (ZrO2) was added to the synthesized precursor. The ICP analysis results for the composition of the positive electrode active material are shown in Table 4 below.

[0129] [Table 4]

[0130] (5) Example 5 A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium composite oxide was mixed with a Co-containing raw material (Co3(PO4)2) and a W-containing raw material (WO3), followed by heat treatment, and then 0.2 mol% of a Ti-containing compound (TiO2) was added to the same firing furnace, and the mixture was heated to 400°C at a rate of 2°C per minute while maintaining an O2 atmosphere, and heat-treated for 5 hours. The ICP analysis results for the composition of the positive electrode active material are shown in Table 5 below.

[0131] [Table 5]

[0132] (6) Comparative Example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium composite oxide was not mixed with the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3), and the temperature was increased to 400°C at a rate of 2°C per minute and heat-treated for 5 hours. The ICP analysis results for the composition of the positive electrode active material are shown in Table 6 below.

[0133] [Table 6]

[0134] (7) Comparative Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that only the W-containing raw material (WO) was mixed with the lithium composite oxide and then calcined. The ICP analysis results for the composition of the positive electrode active material are shown in Table 7 below.

[0135] [Table 7]

[0136] (8) Comparative Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that only the Co-containing raw material (Co3(PO4)2) was mixed with the lithium composite oxide and then calcined. The ICP analysis results for the composition of the positive electrode active material are shown in Table 8 below.

[0137] [Table 8]

[0138] (9) Comparative Example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium composite oxide was not mixed with the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3), and the temperature was increased to 700°C at a rate of 2°C per minute and heat-treated for 5 hours. The ICP analysis results for the composition of the positive electrode active material are shown in Table 9 below.

[0139] [Table 9]

[0140] (10) Comparative Example 5 A cathode active material was prepared in the same manner as in Example 1, except that only the W-containing raw material (WO) was mixed with the lithium composite oxide and then the temperature was increased to 700°C at a rate of 2°C per minute and heat-treated for 5 hours. The ICP analysis results for the composition of the cathode active material are shown in Table 10 below.

[0141] [Table 10]

[0142] (11) Comparative Example 6 A positive electrode active material was prepared in the same manner as in Example 1, except that only the Co-containing raw material (Co3(PO4)2) was mixed with the lithium composite oxide and then the temperature was increased to 700°C at a rate of 2°C per minute and heat-treated for 5 hours. The ICP analysis results for the composition of the positive electrode active material are shown in Table 11 below.

[0143] [Table 11]

[0144] (12) Comparative Example 7 A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium composite oxide was mixed with a Co-containing raw material (Co3(PO4)2) and a W-containing raw material (WO3), and then the temperature was increased to 700°C at a rate of 2°C per minute and heat-treated for 5 hours. The ICP analysis results for the composition of the positive electrode active material are shown in Table 12 below.

[0145] [Table 12]

[0146] Manufacturing Example 2: Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 92 wt% of the positive electrode active material prepared in Preparation Example 1, 4 wt% of artificial graphite, and 4 wt% of a PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0147] A coin battery was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0148] Experimental Example 1: XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed on the positive electrode active material prepared in Preparation Example 1 to determine the Ni content of the positive electrode active material. occ The coating material was confirmed on the surface of the positive electrode active material. XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu Kα radiation (1.540598 Å).

[0149] (1) Ni as the positive electrode active material occ measurement The occupancy of Ni metal inserted into the Li 3a site of the positive electrode active material prepared in Preparation Example 1 was measured by Rietveld refinement of the X-ray diffraction pattern. The measurement results are shown in Table 13 below.

[0150] [Table 13]

[0151] Referring to the results in Table 13, it can be seen that when the lithium composite oxide is mixed with the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3), the occupancy rate of Ni inserted into the Li3a site is increased compared to when only the Co-containing raw material (Co3(PO4)2) or the W-containing raw material (WO3) is mixed with the lithium composite oxide. Furthermore, referring to Example 1 and Comparative Example 7, the occupancy rate of Ni inserted into the Li3a site can be improved by mixing the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3) with the lithium composite oxide and then heat-treating the mixture at a relatively low temperature.

[0152] Thus, by mixing the lithium composite oxide with the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3) and then heat-treating at a relatively low temperature, the occupancy rate of Ni inserted into the Li 3a site increased compared to when the lithium composite oxide was mixed with only the Co-containing raw material (Co3(PO4)2) or the W-containing raw material (WO3) alone and then heat-treated, or when the Co-containing raw material (Co3(PO4)2) and the W-containing raw material (WO3) were mixed and then heat-treated at a relatively high temperature. This may be due to the insertion of W into the Li 3a site as a result of tungsten being doped into the crystal lattice of the lithium composite oxide.

[0153] (2) Analysis of coating materials on the surface of the positive electrode active material The content of the coating material (i.e., second compound) on the surface of the cathode active material prepared according to Preparation Example 1 was quantitatively analyzed by screening the oxides listed in Tables 14 and 15 below from XRD raw data measured using Bruker's EVA program.

[0154] The analysis results of the coating material on the surface of the positive electrode active material analyzed by the above method are shown in Tables 14 to 16 below.

[0155] [Table 14]

[0156] [Table 15]

[0157] [Table 16]

[0158] Referring to the results in Table 14, it can be seen that the second compound present as a coating layer on at least a portion of the surface of the first compound, which is a lithium composite oxide, and having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m has a cubic or rhombohedral crystal structure.

[0159] Referring to the results in Tables 14 to 16, it was confirmed that, unlike the cathode active materials of Comparative Examples 6 and 7, in the cathode active materials of Examples 1 to 5, the lithium composite oxide was mixed with a Co-containing raw material (Co3(PO4)2) and a W-containing raw material (WO3), and then heat-treated at a relatively low temperature. As a result, the proportion of compounds (Co3O4, LiCoO2, and P2O5) having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m in the oxides defined as the second compound in the present application was 13 mol% or less.

[0160] Furthermore, unlike the positive electrode active materials of Comparative Examples 6 and 7, in the positive electrode active materials of Examples 1 to 5, it can be confirmed that the ratio of LiCoO2, which is the compound (r1) having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m among the first oxides LiCo(PO4), LiPO3, and LiCoO2 in the second compound, to LiCo(PO4) and LiPO3, which are the compounds (r2) having a crystal structure belonging to a space group other than Fd-3m, R3c, or R-3m (r1 / r2 = LiCoO2 (mol%) / LiCo(PO4) (mol%) + LiPO3 (mol%)) is 0.03 or less.

[0161] Furthermore, unlike the cathode active materials of Comparative Examples 6 and 7, in the cathode active materials of Examples 1 to 5, it was confirmed that the ratio of Co3O4 and P2O5, which are compounds (s1) having a crystal structure belonging to the space group Fd-3m, R3c, or R-3m among the second oxides Co3(PO4)2, Co3O4, and P2O5, to Co3(PO4)2, which is a compound (s2) having a crystal structure belonging to a space group other than Fd-3m, R3c, or R-3m (s1 / s2 = Co3O4 (mol%) + P2O5 (mol%) / Co3(PO4)2 (mol%)) in the second compound was 0.24 or less.

[0162] Meanwhile, in the case of the cathode active material according to Comparative Example 3, it was prepared in the same manner as the cathode active material according to Example 1, except that the heat treatment was carried out without mixing the W-containing raw material (WO), and it was confirmed that the oxide defined as the second compound was present in a similar composition.

[0163] Experimental Example 2: Measurement of unreacted lithium in the positive electrode active material The amount of unreacted lithium in the positive electrode active material prepared according to Preparation Example 1 was measured by pH titration using the amount of 0.1 M HCl used until the pH reached 4. First, 5 g of each positive electrode active material prepared according to Preparation Example 1 was placed in 100 ml of DIW, stirred for 15 minutes, and filtered. 50 ml of the filtered solution was taken, to which 0.1 M HCl was added. The amount of HCl consumed according to the change in pH was measured to determine Q1 and Q2, from which the content of unreacted LiOH was calculated.

[0164] M1=23.95(LiOH Molecular weight) M2=73.89(Li2CO3Molecular weight) SPL Size=(Sample weight×Solution Weight) / Water Weight LiOH(wt%)=[(Q1-Q2)×C×M1×100] / (SPL Size×1000)

[0165] The results of measuring the content of lithium impurities present in the positive electrode active material using the above formula are shown in Table 17 below.

[0166] [Table 17]

[0167] (2) Evaluation of the electrochemical properties of lithium secondary batteries The lithium secondary battery prepared according to Preparation Example 2 was subjected to a charge-discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and a discharge rate of 0.1C to 5.0C, to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and discharge capacity ratio (C-rate).

[0168] In addition, the lithium secondary battery manufactured by the above method was charged and discharged 50 times at a temperature of 25°C and a driving voltage range of 3.0V to 4.4V at 1C / 1C, and then the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0169] Meanwhile, the initial resistance of the lithium secondary battery manufactured in Manufacturing Example 2 was measured within a frequency range (10 kHz to 0.01 Hz) using electrochemical impedance spectroscopy (EIS).

[0170] The measurement results are shown in Table 18 below.

[0171] [Table 18]

[0172] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. A first compound represented by the following chemical formula 1 and capable of lithium intercalation / deintercalation; a second compound represented by the following chemical formula 2; Including, [Chemical formula 1] Li ｗ Ni １－（ｘ＋ｙ＋ｚ） Co ｘ M1 ｙ M2 ｚ O ２＋α (where, M1 is at least one selected from Mn and 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, W, 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≦α≦0.02) [Chemical formula 2] Li ａ Co ｂ M3 ｃ (P β O γ ) ｄ (where, 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, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦a≦10, 0≦b≦8, 0≦c≦8, 0<d≦13, 0<β≦4, 0<γ≦10) the second compound has a crystal structure selected from monoclinic and orthorhombic; a coating layer made of the second compound formed on at least a portion of a surface of the first compound;

2. The positive electrode active material of claim 1 , wherein the second compound includes an oxide having a monoclinic crystal structure and an oxide having an orthorhombic crystal structure.

3. 2. The positive electrode active material of claim 1, wherein the second compound includes at least one selected from a first oxide represented by the following Chemical Formula 3 and a second oxide represented by the following Chemical Formula 4, and the first oxide and the second oxide each independently include an oxide having a monoclinic crystal structure and an oxide having an orthorhombic crystal structure: [Chemical formula 3] Li ａ′ Co ｂ′ M3′ ｃ′ (P β′ O γ′ ) ｄ′ (where, 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, V, Ba, Ta, Sn, Hf, Ce, 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″ (where, 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, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦b″≦8, 0≦c″≦8, 0<d″≦13, 0<β″≦4, 0<γ″≦10)

4. 4. The positive electrode active material according to claim 3, wherein at least one selected from the first oxide and the second oxide includes an oxide having a monoclinic crystal structure and an oxide having an orthorhombic crystal structure.

5. The first oxide is LiCo(PO ４ ) and LiPO ３ The positive electrode active material according to claim 3 , comprising at least one selected from the group consisting of:

6. The second oxide is Co ３ (P.O. ４ ) ２ The positive electrode active material according to claim 3 , comprising:

7. The positive electrode active material according to claim 3 , wherein in the second compound, a ratio of the first oxide to the second oxide (first oxide / second oxide) is 0.87 or more.

8. the first compound is a lithium composite oxide in a single crystal or polycrystalline form, The positive electrode active material according to claim 1 , wherein the coating layer containing the second compound is formed on at least a portion of a surface of the lithium composite oxide.

9. the first compound is a secondary particle formed by aggregation of a plurality of primary particles, The positive electrode active material according to claim 1 , wherein the second compound is present at least partially at interfaces between primary particles and on surfaces of secondary particles.

10. The positive electrode active material according to claim 9 , wherein the second compound exhibits a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

11. The positive electrode active material according to claim 8 , wherein a third compound represented by the following chemical formula 5 is present on at least a part of the surface of the lithium composite oxide: [Chemical formula 5] Li ｅ W ｆ M4 ｇ O ｈ (where, 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, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦e≦10, 0<f≦8, 0≦g≦8, 0<h≦13)

12. The positive electrode active material of claim 11 , wherein the third compound is present within a coating layer or is present independently of a coating layer.

13. the first compound is a secondary particle formed by aggregation of a plurality of primary particles, The positive electrode active material according to claim 11 , wherein the third compound is present at least partially at interfaces between primary particles and on surfaces of secondary particles.

14. The positive electrode active material according to claim 13 , wherein the third compound exhibits a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

15. The positive electrode active material according to claim 1 , wherein in Chemical Formula 1, x + y + z is 0.20 or less.

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