Positive electrode active material, positive electrode, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material capable of preventing and / or mitigating gas generation and expansion phenomena in a lithium secondary battery caused by a lithium composite oxide used as a positive electrode active material while maintaining the electrochemical characteristics of the lithium secondary battery.SOLUTION: A positive electrode active material includes primary particles capable of intercalating / deintercalating lithium and secondary particles formed by agglomeration of the primary particles, the secondary particles include at least one selected from nickel, cobalt, manganese, and aluminum, and a difference Δd between a maximum value d1 and a minimum value d2 of a d-spacing of a (003) plane within the primary particles in a state charged at 4.3 V based on a half cell is less than 0.019 nm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, the present invention relates to a positive electrode active material, a positive electrode, and a lithium secondary battery including the same, which can suppress excessive growth of primary particles and improve the crystallinity of the primary particles while maintaining electrochemical characteristics of a lithium secondary battery using the lithium composite oxide as a positive electrode active material, and prevent and / or mitigate gas generation and expansion phenomena in the lithium secondary battery caused by the positive electrode active material. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such batteries is a lithium secondary battery, which stores electrical energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at 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 or a polymer electrolyte 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 examples of such composite oxides that have been researched include LiCoO2, LiMn2O4, LiNiO2, and LiMnO2.

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

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of being thermally safe and inexpensive, but have problems with small capacity and poor high-temperature characteristics. LiNiO2-based positive electrode active materials have the advantage of showing high discharge capacity, but are difficult to synthesize due to active cation mixing of Li and Ni, and the rate characteristics and life characteristics of the synthesized positive electrode active materials are very poor.

[0007] As a result, in order to improve the low rate and life characteristics while maintaining the high reversible capacity of LiNiO2, ternary type lithium composite oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary type lithium composite oxides such as NCMA (Ni-Co-Mn-Al) have been developed in which part of the nickel is replaced with cobalt, manganese and / or aluminum. The lower the nickel content in such ternary or quaternary type lithium composite oxides, the lower the reversible capacity, so recently, active research has been conducted to increase the nickel content in lithium composite oxides.

[0008] However, as the nickel content in the lithium composite oxide increases, there are problems in that cation mixing in the crystal structure increases, resulting in a decrease in stability and an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[0009] The greater the change in crystallinity, such as an increase in cation mixing in the crystal structure of the lithium composite oxide, or the greater the content of lithium impurities remaining on the surface of the lithium composite oxide, the greater the gas generation and expansion phenomenon in a lithium secondary battery using the lithium composite oxide as a positive electrode active material.The greater the content of lithium impurities remaining on the surface of the lithium composite oxide, the greater the problem of the lithium impurities causing the paste composition to gel when preparing a paste for forming a positive electrode active material layer using the lithium composite oxide.

[0010] In order to solve the problem of gas generation caused by lithium impurities remaining on the surface of the lithium composite oxide, a method of forming a metal oxide-derived coating layer or a polymer-derived coating layer by reacting the lithium impurities present on the surface of the lithium composite oxide with a coating raw material has been proposed. However, when a coating layer is formed on the surface of the lithium composite oxide, the surface resistance characteristics of the lithium composite oxide are changed, and thus electrochemical characteristics such as charge / discharge capacity and / or rate characteristics of a lithium secondary battery using the lithium composite oxide as a positive electrode active material may be deteriorated.

[0011] Therefore, there is a need to develop a positive electrode active material that can prevent and / or reduce the gas generation and expansion phenomena in a lithium secondary battery caused by the positive electrode active material while maintaining the electrochemical characteristics of the lithium secondary battery using the lithium composite oxide as the positive electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0012] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is playing a leading role in the market, and as a result, the demand for positive electrode active materials used in lithium secondary batteries is also continuously increasing.

[0013] For example, lithium secondary batteries using lithium iron phosphate (LFP) have been mainly used in the past due to safety concerns, but recently there has been a trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP. Of course, relatively cheap LFP is still sometimes used to save costs.

[0014] Recently, nickel-based lithium composite oxides that are mainly used as positive electrode active materials for high-capacity lithium secondary batteries generally have a ternary type composition such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or a quaternary type composition such as NCMA (Ni-Co-Mn-Al).

[0015] As described above, in order to realize a high capacity of such a ternary or quaternary type nickel-based lithium composite oxide, the nickel content in the lithium composite oxide needs to be increased. As the nickel content in the lithium composite oxide increases, the change in crystallinity may become greater, such as an increase in cation mixing in the crystal structure of the lithium composite oxide, or the content of lithium impurities remaining on the surface of the lithium composite oxide may increase.

[0016] Accordingly, the present invention aims to provide a positive electrode active material that can prevent and / or mitigate gas generation and expansion phenomena in a lithium secondary battery caused by the positive electrode active material while maintaining electrochemical characteristics of the lithium secondary battery using the lithium composite oxide as a positive electrode active material by using a dopant that inhibits the growth of primary particles constituting a lithium composite oxide during the calcination process of the positive electrode active material and increasing the calcination temperature to suppress excessive growth of the primary particles and at the same time improve the crystallinity of the primary particles.

[0017] Another object of the present invention is to provide a positive electrode active material that can prevent and / or mitigate the occurrence of cracks due to strain caused by random volumetric contraction / expansion of the primary particles during charge / discharge by reducing crystal defects in the crystal structure of the primary particles constituting the lithium composite oxide.

[0018] It is yet another object of the present invention to provide a lithium secondary battery using the positive electrode active material defined herein.

[0019] The object of the present invention is not limited to the object mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and will be more clearly understood by the embodiments of the present invention. In addition, it will be easily known that the object and advantages of the present invention can be realized by the means and combinations thereof as set forth in the claims. [Means for solving the problem]

[0020] According to one aspect of the present invention, there is provided a positive electrode active material including primary particles capable of intercalating / deintercalating lithium and secondary particles formed by aggregation of the primary particles. The secondary particles may contain at least one selected from nickel, cobalt, manganese and aluminum. Preferably, the secondary particles contain nickel.

[0021] In addition, the d-spacing of the (003) plane in the crystal structure of the primary particles may vary slightly depending on the charged state of the positive active material and the composition of the positive active material (e.g., the mole fraction of nickel).

[0022] For example, the molar fraction of nickel relative to all elements other than lithium in the positive electrode active material may be 70% or more, and the maximum value d1 of the interplanar distance (d-spacing) of (003) planes in the crystal structure of the primary particles when the positive electrode active material is charged at 4.3 V may be less than 0.4794 nm, and the minimum value d2 of the interplanar distance (d-spacing) of (003) planes in the crystal structure of the primary particles present in the secondary particles may be 0.456 nm or more.

[0023] As described above, the maximum value d1 and / or minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles may vary slightly depending on the state of charge of the positive electrode active material and the composition of the positive electrode active material (e.g., the mole fraction of nickel), etc. However, the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles is not significantly affected by changes in the state of charge of the positive electrode active material or the mole fraction of nickel in the positive electrode active material, and can therefore be used as an index indicating crystal defects in the crystal structure of the primary particles.

[0024] Therefore, the smaller the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles, the more the crystal defects in the crystal structure of the primary particles can be reduced, thereby preventing and / or mitigating the occurrence of cracks due to strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging.

[0025] According to the definition in the present application, the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles when the positive electrode active material is charged at 4.3 V may be less than 0.019.

[0026] By making the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles less than 0.019 nm, it is possible to reduce crystal defects (particularly line defects) in the crystal structure of the primary particles constituting the lithium composite oxide, and prevent and / or mitigate the occurrence of cracks due to strain caused by random volume contraction / expansion of the primary particles during charging and discharging.

[0027] The positive electrode active material may have a crystallite size of 70 nm to 130 nm. A dopant that hinders the growth of primary particles during the firing process of the positive electrode active material may be used and the firing temperature may be increased to suppress excessive growth of the primary particles and at the same time improve the crystallinity of the primary particles, so that the positive electrode active material has a crystallite size of 70 nm to 135 nm.

[0028] The secondary particles may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a Ni 1-(b+c+d) Co b M1 c M2 d O2 Here, M1 is at least one selected from Mn and Al, and M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, and M1 and M2 are different from each other, and 0.5≦a≦1.5, 0≦b≦0.20, 0≦c≦0.30, and 0≦d≦0.10. In the secondary particles, the molar fraction of nickel relative to all elements other than lithium may be 70% or more.

[0029] According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material. According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-mentioned positive electrode. Effect of the Invention

[0030] According to the present invention, by using a dopant that inhibits the growth of primary particles constituting a lithium composite oxide during the calcination process of a positive electrode active material and increasing the calcination temperature, it is possible to suppress excessive growth of the primary particles and at the same time improve the crystallinity of the primary particles, thereby preventing and / or mitigating gas generation and expansion phenomena in a lithium secondary battery caused by the positive electrode active material while maintaining the electrochemical characteristics of the lithium secondary battery using the lithium composite oxide as the positive electrode active material.

[0031] In addition, the present invention can reduce crystal defects in the crystal structure of the primary particles constituting the lithium composite oxide, thereby preventing and / or mitigating the occurrence of cracks due to strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging. [Brief description of the drawings]

[0032] [Figure 1] 1 is a cross-sectional SEM image of the positive electrode active material according to Example 1 charged at 4.3 V. [Diagram 2] 1 is a cross-sectional SEM image of the positive electrode active material according to Comparative Example 1 charged at 4.3 V. [Diagram 3] 1 is a cross-sectional SEM image of the positive electrode active material according to Comparative Example 2 charged at 4.3 V. [Figure 4] 1 is a cross-sectional SEM image of the positive electrode active material according to Comparative Example 4 charged at 4.3 V. [Diagram 5] 1 is a cross-sectional SEM image of the positive electrode active material according to Comparative Example 5 charged at 4.3 V. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] In order to make the present invention easier to understand, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used in the present invention shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified by the context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0034] positive electrode active material A positive electrode active material according to an embodiment of the present invention includes primary particles capable of lithium intercalation / deintercalation capable of reversible intercalation / deintercalation of lithium ions, and secondary particles formed by aggregation of the primary particles. For convenience, the primary particles and / or the secondary particles may be referred to as a lithium composite oxide in the present application.

[0035] The lithium composite oxide is a composite metal oxide capable of intercalating / deintercalating lithium ions and has a layered crystal structure belonging to the R-3m space group. The lithium composite oxide having a layered crystal structure exhibits a specific peak in the region of 2θ of 18° to 20° in the rotation pattern obtained by XRD analysis.

[0036] The lithium composite oxide may contain at least one selected from the group consisting of nickel, cobalt, manganese, and aluminum. Preferably, the lithium composite oxide may be a lithium-nickel based composite oxide containing nickel.

[0037] In one embodiment, in order to improve the low rate characteristics and life characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a ternary type lithium composite oxide such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or a quaternary type lithium composite oxide such as NCMA (Ni-Co-Mn-Al), in which part of nickel is replaced with cobalt, manganese and / or aluminum. In another embodiment, the lithium nickel-based composite oxide may be a cobalt-free type lithium composite oxide.

[0038] The primary particles constituting the secondary particles may have a rod shape, an elliptical shape, and / or an irregular shape. Furthermore, primary particles of various shapes may be present in the same positive electrode active material unless otherwise intended in the manufacturing process. Furthermore, the primary particles refer to particle units that do not have grain boundaries in appearance when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0039] The average particle size of the primary particles constituting the lithium composite oxide defined in the present application is preferably 0.04 μm to 2 μm, more preferably 0.06 μm to 2 μm, more preferably 0.08 μm to 2 μm, more preferably 0.1 μm to 2 μm, more preferably 0.25 μm to 2 μm, more preferably 0.04 μm to 1 μm, more preferably 0.06 μm to 1.0 μm, more preferably 0.08 μm to 1 μm, more preferably 0.1 μm to 1 μm, more preferably 0.25 μm to 1 μm, more preferably 0.04 μm to 0.75 μm, more preferably 0.06 μm to 0.75 μm, more preferably 0.08 μm to 0.75 μm, more preferably 0.1 μm to 0.75 μm, and particularly preferably 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated by the average value of the length in the major axis direction and the length in the minor axis direction of the primary particles ([major axis length+minor axis length] / 2).

[0040] The primary particle may be composed of a single crystallite or a plurality of crystallites, and the crystallite size may be calculated from an XRD analysis of the positive active material.

[0041] For example, the crystallite size can be calculated by (1) using all peaks present in the diffraction pattern obtained from the XRD analysis (a method using pattern fitting and Rietveld analysis), or (2) by substituting the half-width of a specific peak (e.g., a peak specific to the crystal plane corresponding to the (003) plane) present in the diffraction pattern obtained from the XRD analysis into the Scherrer equation.

[0042] In the positive electrode active material, the crystallite size present in the lithium composite oxide is preferably 70 nm to 130 nm. The particle size) is preferably 70 nm to 120 nm, more preferably 70 nm to 110 nm, more preferably 70 nm to 105 nm, more preferably 70 nm to 103 nm, more preferably 75 nm to 120 nm, more preferably 75 nm to 110 nm, more preferably 75 nm to 105 nm, more preferably 75 nm to 103 nm, more preferably 80 nm to 120 nm, more preferably 80 nm to 110 nm, more preferably 80 nm to 105 nm, more preferably 80 nm to 103 nm, more preferably 85 nm to 120 nm, more preferably 85 nm to 110 nm, more preferably 85 nm to 105 nm, more preferably 85 nm to 103 nm, more preferably 90 nm to 120 nm, more preferably 90 nm to 110 nm, more preferably 90 nm to 105 nm, or particularly preferably 90 nm to 103 nm. When the crystallite size is less than 70 nm, the crystallite size constituting the positive electrode active material is too small, so that the particle strength of the lithium composite oxide may be reduced. Also, as the crystallite size and the size of the primary particles become too small, the specific surface area increases, which may promote gas generation due to a side reaction with the electrolyte.

[0043] On the other hand, when the crystallite size is larger than 130 nm, the primary particles grow excessively, and thus electrochemical properties such as rate characteristics of a lithium secondary battery using the same as a positive electrode active material may be reduced.

[0044] As described below, according to the present invention, by using a dopant that inhibits the growth of primary particles during the firing process of the positive electrode active material and increasing the firing temperature, the excessive growth of the primary particles is suppressed and at the same time, the crystallinity of the primary particles is improved, so that the positive electrode active material can have a crystallite size of 70 nm to 130 nm.

[0045] As such, the dopant that hinders the growth of primary particles during the firing process of the positive electrode active material can be at least one selected from Al2O3, Al(OH)3, AlPO4, Al(PO3)3, WO3, Nb2O5, TiO2, H3BO3, H2B4O7, B2O3, B2O5, C6H5B(OH)2, (C6H5O)3B, [(CH3(CH2)3O)3B, C3H9B3O6 and (C3H7O3)B.

[0046] If the firing temperature is increased without using a dopant that inhibits the growth of the primary particles during the firing process of the positive electrode active material (i.e., if the material is overfired), the crystallites and the primary particles may grow excessively. In this case, a phase transformation (e.g., layered structure to rock salt structure) may occur on the surfaces of the primary particles and the secondary particles due to a cation mixing phenomenon. Such a change in crystal structure, such as a phase transformation, may cause a change in the surface resistance of the positive electrode active material and a deterioration in its lifespan.

[0047] On the other hand, when the calcination temperature of the positive active material is maintained and a dopant that inhibits the growth of primary particles is used during the calcination process, the growth of the crystallites and the primary particles can be excessively suppressed. In this case, as the crystallite size and the primary particle size become too small, the specific surface area increases, and gas generation due to a side reaction with the electrolyte can be promoted.

[0048] The average particle size of the secondary particles is preferably 0.5 μm to 20 μm, more preferably 2.0 μm to 18 μm, even more preferably 2.0 μm to 15 μm, and particularly preferably 3.0 μm to 12 μm. In addition, when the secondary particles are small particles, the average particle size of the secondary particles is preferably 7 μm or less, more preferably 6.5 μm or less, more preferably 6 μm or less, more preferably 5.5 μm or less, more preferably 5 μm or less, more preferably 4.5 μm or less, more preferably 4 μm or less, more preferably 3.5 μm or less, particularly preferably 3 μm or less, preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 1.5 μm or more, or particularly preferably 2 μm or more. When the secondary particles are small particles, the upper and lower limits of the average particle size of the secondary particles can be appropriately selected within the range that satisfies the above-mentioned definition. When the secondary particles are large particles, the average particle size of the secondary particles is preferably more than 7 μm, more preferably 7.5 μm or more, more preferably 8 μm or more, more preferably 8.5 μm or more, more preferably 9 μm or more, more preferably 9.5 μm or more, more preferably 10 μm or more, more preferably 10.5 μm or more, more preferably 11 μm or more, more preferably 11.5 μm or more, particularly preferably 12 μm or more, preferably 30 μm or less, more preferably 27.5 μm or less, more preferably 25 μm or less, more preferably 22.5 μm or less, more preferably 20 μm or less, more preferably 17.5 μm or less, particularly preferably 15 μm or less. When the secondary particles are large particles, the upper and lower limits of the average particle size of the secondary particles can be appropriately selected within the range that satisfies the above definition.When the positive electrode active material has a bimodal particle size distribution including secondary particles as small particles and secondary particles as large particles, the average particle size of the positive electrode active material is preferably 4 μm to 18 μm, more preferably 6 μm to 16 μm, or even more preferably 8 μm to 14 μm.

[0049] The average particle size of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles. The average particle size (D50) of the secondary particles may be measured using a laser diffraction method. For example, the secondary particles are dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph is obtained, and the particle size corresponding to 50% of the volume cumulative amount is obtained. In other cases, the average particle size of the secondary particles may be calculated as the average value of the particle sizes of the secondary particles confirmed from a SEM image.

[0050] According to the present invention, by using a dopant that hinders the growth of primary particles and increasing the sintering temperature, the excessive growth of the primary particles is suppressed, and at the same time, the crystallinity of the primary particles is improved and crystal defects in the crystal structure of the primary particles are reduced, thereby preventing and / or mitigating the occurrence of cracks due to strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging.

[0051] The crystal defects in the crystal structure of the primary particles may be point defects and / or line defects, and the present invention can reduce line defects among the crystal defects in the crystal structure of the primary particles. The line defects may be present in a form extending in a direction parallel to the (003) plane of the crystal structure of the primary particles.

[0052] In this way, when linear defects exist along a direction parallel to the (003) plane in the crystal structure of the primary particles, cracks may occur in the primary particles along the linear defects due to the accumulation of strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging. In this case, the cracks caused by linear defects in the primary particles are different from cracks formed along the grain boundaries of adjacent primary particles that occur due to the accumulation of strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging.

[0053] The linear defects present in the crystal structure of the primary particles may be caused by dislocations of the layered crystal structure in the primary particles. When dislocations of the layered crystal structure in the primary particles occur, the interplanar distance between some crystal planes may change. The change in interplanar distance may be measured by XRD analysis using Cu-Kα radiation on the positive electrode active material or by other known methods.

[0054] For example, when the diffraction pattern obtained from the XRD analysis using Cu-Kα radiation for the positive electrode active material charged under predetermined conditions shows a splitting of a diffraction peak (2θ=18° to 20°) specific to the (003) plane, it can be expected that crystal defects have occurred on the (003) plane of the primary particles.

[0055] This allows the difference in 2θ between the two peaks split in the 18° to 20° region to be substituted into Bragg's law (interplanar distance d=λ / 2sinθ) to quantify the change in interplanar distance. As another method, a TEM image (e.g., HAADF-STEM) fitted to the (003) plane is obtained from the cross section of the primary particle, and the distance between adjacent (003) planes can then be measured.

[0056] In this case, the charging condition for the positive electrode active material before XRD analysis may be a general formation and / or charging condition for a lithium secondary battery, for example, the positive electrode active material may be charged at 4.3 V before XRD analysis.

[0057] More specifically, a lithium secondary battery (half cell) having the positive electrode active material as a positive electrode and a lithium foil as a negative electrode is charged and discharged twice under conditions of 25° C., a voltage range of 3.0 V to 4.3 V, and 0.05 C / 0.05 C, and then further charged at 4.3 V. The positive electrode active material is then recovered from the half cell and subjected to XRD analysis.

[0058] As described above, in the XRD analysis of the positive electrode active material charged at 4.3 V, no peak splitting occurs in the 2θ region of 18° to 20°, or if peak splitting occurs, the difference in 2θ between the two split peaks is preferably 0.75° or less, more preferably 0.70° or less, even more preferably 0.69° or less, and particularly preferably 0.681° or less.

[0059] As described above, the maximum value d1 and / or minimum value d2 of the d-spacing of the (003) plane in the crystal structure of the primary particles may vary slightly depending on the state of charge of the positive electrode active material and the composition of the positive electrode active material (e.g., the mole fraction of nickel), etc.

[0060] However, the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles is not significantly affected by changes in the state of charge of the positive electrode active material or the mole fraction of nickel in the positive electrode active material, and can therefore be used as an index of crystal defects in the crystal structure of the primary particles.

[0061] Therefore, the smaller the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles, the more the crystal defects in the crystal structure of the primary particles can be reduced, thereby preventing and / or mitigating the occurrence of cracks due to strain caused by random volumetric contraction / expansion of the primary particles during charging and discharging.

[0062] For example, when the molar fraction of nickel relative to all elements other than lithium in the positive electrode active material is 70% or more, and the positive electrode active material is charged at 4.3 V, the maximum value d1 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is preferably less than 0.4794 nm, more preferably 0.4789 nm or less, even more preferably 0.478 nm or less, or particularly preferably 0.4775 nm or less, and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is preferably 0.456 nm or more, more preferably 0.457 nm or more, more preferably 0.458 nm or more, more preferably 0.459 nm or more, or more preferably 0.4598 nm or more, and particularly preferably 0.461 nm or more.

[0063] When the maximum value d1 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is 0.4794 nm or more, the interplanar distance of the other (003) planes adjacent to the (003) plane may be excessively narrow. Also, when the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is 0.456 nm or less, the interplanar distance of the other (003) planes adjacent to the (003) plane may be excessively wide. This results in an imbalance in the interplanar distance between the adjacent (003) planes, and thus line defects are present along a direction parallel to the (003) plane in the crystal structure of the primary particles.

[0064] According to the definition in the present application, the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles when the positive electrode active material is charged at 4.3 V is preferably less than 0.019 nm, more preferably 0.018 nm or less, even more preferably 0.0175 nm or less, and particularly preferably 0.0172 nm or less.

[0065] By making the difference Δd between the maximum value d1 and the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles less than 0.019 nm, it is possible to reduce crystal defects (particularly line defects) in the crystal structure of the primary particles constituting the lithium composite oxide, and prevent and / or mitigate the occurrence of cracks due to strain caused by random volume contraction / expansion of the primary particles during charging and discharging.

[0066] The lithium composite oxide (primary particles and secondary particles) defined in the present application can be represented by the following Chemical Formula 1. [Chemical formula 1] Li a Ni 1-(b+c+d) Co b M1 c M2 d O2 Here, M1 is at least one selected from Mn and Al, M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, M1 and M2 are different from each other, and 0.5≦a≦1.5, 0≦b≦0.20, 0≦c≦0.30, 0≦d≦0.10. It is more preferable that M2 includes at least one selected from B, Al, Nb and W.

[0067] In the lithium composite oxide, a, which indicates the ratio of lithium to all elements other than lithium, is preferably 0.5 or more and 1.5 or less, more preferably 0.75 or more and 1.25 or less, even more preferably 0.90 or more and 1.1 or less, and particularly preferably 0.95 or more and 1.05 or less.

[0068] In one embodiment, the mole fraction of nickel in the lithium composite oxide relative to all elements other than lithium may be 70% or more, in which case b+c+d in Formula 1 is 0.30 or less.

[0069] In another embodiment, the molar fraction of nickel relative to all elements other than lithium in the lithium composite oxide is preferably 75% or more (in this case, b+c+d is 0.25 or less), more preferably 80% or more (in this case, b+c+d is 0.20 or less), even more preferably 85% or more (in this case, b+c+d is 0.15 or less), or particularly preferably 90% or more (in this case, b+c+d is 0.10 or less).

[0070] When the lithium composite oxide contains cobalt, the molar fraction of cobalt relative to all elements other than lithium in the secondary particles is preferably 20% or less (in this case, b is 0.20 or less), more preferably 15% or less (in this case, b is 0.15 or less), even more preferably 10% or less (in this case, b is 0.10 or less), and particularly preferably 5% or less (in this case, b is 0.05 or less). When the secondary particles contain cobalt, b in the chemical formula 1 is greater than 0.

[0071] When the lithium composite oxide contains manganese and / or aluminum, the molar fraction of manganese and / or aluminum relative to all elements other than lithium in the lithium composite oxide is preferably 30% or less (in this case, c is 0.30 or less), more preferably 25% or less (in this case, c is 0.25 or less), more preferably 20% or less (in this case, c is 0.20 or less), more preferably 15% or less (in this case, c is 0.15 or less), more preferably 10% or less (in this case, c is 0.10 or less), and particularly preferably 5% or less (in this case, c is 0.05 or less). When the secondary particles contain manganese and / or aluminum, c in the chemical formula 1 is greater than 0.

[0072] In the formula 1, M2 refers to a dopant present in the secondary particles. The dopant may be present in a doped state in the crystal lattice of the primary particles. In addition, in the formula 1, M2 may selectively include a dopant used to prevent the growth of the primary particles during the sintering process of the positive electrode active material. In addition, the dopant may improve the electrochemical properties of the positive electrode active material by being doped.

[0073] When the secondary particles include a dopant, M2 in Formula 1 is greater than 0. In addition, in the secondary particles, the molar fraction of the dopant relative to all elements other than lithium is preferably 10% or less (in this case, d is 0.10 or less), more preferably 5% or less (in this case, d is 0.05 or less), more preferably 4% or less (in this case, d is 0.04 or less), more preferably 3% or less (in this case, d is 0.03 or less), more preferably 2% or less (in this case, d is 0.02 or less), more preferably 1% or less (in this case, d is 0.01 or less), more preferably 0.5% or less (in this case, d is 0.005 or less), more preferably 0.4% or less (in this case, d is 0.004 or less), more preferably 0.3% or less (in this case, d is 0.003 or less), more preferably 0.2% or less (in this case, d is 0.002 or less), and particularly preferably 0.1% or less (in this case, d is 0.001 or less).

[0074] When the secondary particles selectively contain a dopant, the dopant may include at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, or at least one selected from B, Al, Nb, and W. The type and combination of the dopants may be appropriately selected within a range that does not negatively affect the electrochemical properties and stability of the positive electrode active material.

[0075] Lithium secondary battery The lithium secondary battery of the present invention uses the positive electrode of the present invention. 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 will be omitted for convenience, and only the remaining components not described above will be described below.

[0076] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0077] 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.

[0078] At this time, the positive electrode active material may be included in a content of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the content is within this range, but is not necessarily limited thereto.

[0079] The conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials such as carbon fibers, metal powders or metal fibers 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, and the like, and one or more of these may be used alone or in combination. The conductive material may be contained in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0080] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive strength 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, and among these, one type alone or a mixture of two or more types may be used. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0081] The positive electrode of the present invention includes the positive electrode active material of the present invention. The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent onto a positive electrode current collector, followed by drying and rolling.

[0082] 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 one or more of these may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when applied to manufacture a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0083] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the positive electrode slurry composition from the support, and laminating the resulting film on a positive electrode current collector.

[0084] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-mentioned positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0085] Specifically, the lithium secondary battery may 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 as 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.

[0086] 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. The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0087] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0088] 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.

[0089] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material 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<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, may be used. A metallic lithium thin film may be used as the negative electrode active material. Low-crystalline carbon and high-crystalline carbon may both be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes. 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.

[0090] The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and may be added in an amount of 0.1 wt% 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.

[0091] The conductive material may be added as a component for further improving the conductivity of the negative electrode active material in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and may be, for example, 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 carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives.

[0092] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition 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, and then peeled off from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0093] In another embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition 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, or by casting the negative electrode slurry composition on a separate support and peeling the composition from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0094] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a path for lithium ions to move. Any separator that is generally used as a separator in a lithium secondary battery may be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte humidification ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be selectively used as a single layer or multilayer structure.

[0095] In addition, examples of the electrolyte used in the present application 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. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0096] The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone, an ether solvent such as dibutyl ether or tetrahydrofuran, a ketone solvent such as cyclohexanone, an aromatic hydrocarbon solvent such as benzene or fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that may be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond 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 a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be excellent if the cyclic carbonate and the chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9.

[0097] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

[0098] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-based solid electrolyte may be used, and preferably, a sulfide-based solid electrolyte may be used.

[0099] As the material of the sulfide-based solid electrolyte, a solid electrolyte containing Li, an X element (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S may be used. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (wherein m and n are integers and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(where p, q are integers and M is P, Si, Ge, B, Al, Ga or In).

[0100] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0101] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zinc 1-x Examples include GeO4 (LISICON).

[0102] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. The solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or the solid electrolyte may be partially included in the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0103] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as 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 purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc. 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.

[0104] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0105] The external 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 square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0106] 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.

[0107] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (Electric Vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0108] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0109] Production Example 1. Production of positive electrode active material Example 1 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was synthesized. Specifically, 50 wt% NaOH and 18 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 90:5:5, in a 90L reactor. The pH in the reactor was maintained at 12.0, the temperature of the reactor was maintained at 45°C, and inert gas N2 was added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, washing and dehydration were carried out using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) and H3BO3 (weighed so that the molar fraction of boron among the metal elements is 0.01 based on the total composition of the hydroxide precursor) were mixed, and then heat-treated in an O2 atmosphere at 700°C for 12 hours, vacuum-dried at 120°C, and washed with water to obtain a positive electrode active material.

[0110] Example 2 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was synthesized. Specifically, 50 wt% NaOH and 18 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 90:5:5, in a 90L reactor. The pH in the reactor was maintained at 12.0, the temperature of the reactor was maintained at 45°C, and inert gas N2 was added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, washing and dehydration were carried out using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) and WO3 (weighed so that the molar fraction of tungsten among the metal elements is 0.005 based on the total composition of the hydroxide precursor) were mixed, and then heat-treated in an O2 atmosphere at 700°C for 12 hours, vacuum-dried at 120°C, and washed with water to obtain a positive electrode active material.

[0111] Comparative Example 1 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 The (OH)2 hydroxide precursor was synthesized. Specifically, 50 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 90:5:5, 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 added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, the mixture was washed and dehydrated using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05(OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor and LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) were mixed, and then heat-treated in an O2 atmosphere at 670°C for 12 hours, and then vacuum-dried at 120°C and washed with water to obtain a positive electrode active material.

[0112] Comparative Example 2 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 The (OH)2 hydroxide precursor was synthesized. Specifically, 50 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 90:5:5, 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 added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, the mixture was washed and dehydrated using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor and LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) were mixed, and then heat-treated in an O2 atmosphere at 700°C for 12 hours, and then vacuum-dried at 120°C and washed with water to obtain a positive electrode active material.

[0113] Comparative Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that H3BO3 was used such that the molar fraction of boron among the metal elements was 0.015 based on the total composition of the hydroxide precursor.

[0114] Comparative Example 4 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05The (OH)2 hydroxide precursor was synthesized. Specifically, 50 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 90:5:5, 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 added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, the mixture was washed and dehydrated using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) and H3BO3 (weighed so that the molar fraction of boron among the metal elements is 0.02 based on the total composition of the hydroxide precursor) were mixed, and then heat-treated in an O2 atmosphere at 700°C for 12 hours, vacuum-dried at 120°C, and washed with water to obtain a positive electrode active material.

[0115] Comparative Example 5 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 The (OH)2 hydroxide precursor was synthesized. Specifically, 50 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 90:5:5, 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 added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, the mixture was washed and dehydrated using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05(OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) and H3BO3 (weighed so that the molar fraction of boron among the metal elements is 0.01 based on the total composition of the hydroxide precursor) were mixed, and then heat-treated in an O2 atmosphere at 670°C for 12 hours, vacuum-dried at 120°C, and washed with water to obtain a positive electrode active material.

[0116] Comparative Example 6 Spherical Ni was prepared by the co-precipitation method. 0.90 Co 0.05 Mn 0.05 The (OH)2 hydroxide precursor was synthesized. Specifically, 50 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 90:5:5, 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 added to the reactor to prevent the precursor from being oxidized. After the synthesis and stirring were completed, the mixture was washed and dehydrated using a filter press (F / P) equipment to obtain Ni 0.90 Co 0.05 Mn 0.05 (OH)2 hydroxide precursor was obtained. Next, the hydroxide precursor, LiOH (Li / (Ni+Co+Mn) molar ratio=1.01) and H3BO3 (weighed so that the molar fraction of boron among the metal elements is 0.01 based on the total composition of the hydroxide precursor) were mixed, and then heat-treated in an O2 atmosphere at 730°C for 12 hours, vacuum-dried at 120°C, and washed with water to obtain a positive electrode active material.

[0117] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) A positive electrode slurry was prepared by dispersing 94 wt% of the positive electrode active material prepared in Preparation Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly applied to a thin aluminum film having a thickness of 15 μm and dried in a vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0118] A half cell 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 of LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0119] Manufacturing example 3. Manufacturing of lithium secondary batteries (full cells) 90 wt % of the positive electrode active material prepared in Preparation Example 1, 4.5 wt % of carbon black, and 5.5 wt % of PVDF binder were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry.

[0120] The positive electrode slurry was uniformly applied to a thin aluminum film having a thickness of 15 μm and dried in a vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0121] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 20 μm) as a separator, and an electrolyte solution containing LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0122] Experimental Example 1. XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed to measure the crystallite size and the interplanar distance of the (003) plane of the positive electrode active material. The XRD analysis was performed using a Bruker D8 Endeavor diffractometer using Cu-Kα radiation (1.540598 Å).

[0123] Specifically, the crystallite size of the positive electrode active material was calculated as an Lvol-IB value through Rietveld analysis using TOPAS software from the diffraction pattern obtained by XRD analysis of each positive electrode active material prepared in Preparation Example 1.

[0124] In addition, the lithium secondary battery (half cell) produced in Production Example 2 was charged and discharged twice at 25° C., voltage range of 3.0 V to 4.3 V, and 0.05 C / 0.05 C using an electrochemical analyzer (Toyo, Toscat-3100), and then further charged at 4.3 V. The positive electrode active material was then recovered from the half cell, and XRD analysis was performed to calculate the peak splitting in the region of 2θ of 18° to 20° from the diffraction peak attributable to the (003) plane, and the maximum value d1 and minimum value d2 of the interplanar distance (d-spacing) of the (003) plane. The results of the XRD analysis are shown in Table 1 below.

[0125] [Table 1] *Peak split indicates the difference in 2θ between two peaks split in the 2θ region of 18° to 20°.

[0126] In addition, referring to FIGS. 1 to 5 showing cross-sectional SEM images of the positive electrode active materials (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5) recovered from the half cells, it was confirmed that there were many line defects in the primary particles of the positive electrode active materials according to Comparative Examples 1, 2, 4, and 5, compared to the positive electrode active material according to Example 1.

[0127] Experimental Example 2: Evaluation of the electrochemical characteristics of a lithium secondary battery (half cell) The lithium secondary battery (half cell) manufactured in Manufacturing Example 2 was subjected to a charge-discharge experiment at 25° C., voltage range of 3.0V to 4.3V, and discharge rate of 1.0C / 0.1C using an electrochemical analyzer (Toyo, Toscat-3100) to measure initial charge capacity, initial discharge capacity, initial efficiency, and 1.0C / 0.1C rate characteristics.

[0128] In addition, the same lithium secondary battery (half cell) was charged and discharged 100 times at 25°C, voltage range of 3.0V to 4.3V, and 1C / 1C using an electrochemical analyzer (Toyo, Toscat-3100), and the ratio of the discharge capacity at the 100th cycle to the initial capacity (cycle capacity retention) was measured. The measurement results are shown in Table 2 below.

[0129] [Table 2]

[0130] As can be seen from the crystallite sizes in Table 1, the positive electrode active materials according to Examples 1 and 2 use a dopant that inhibits the growth of primary particles constituting the lithium composite oxide during the sintering process, and increase the sintering temperature to suppress excessive growth of the primary particles and at the same time improve the crystallinity of the primary particles. As a result, electrochemical characteristics including initial efficiency and rate characteristics of a lithium secondary battery using the lithium composite oxide as a positive electrode active material are maintained, while crystal defects in the crystal structure of the primary particles constituting the lithium composite oxide are reduced, thereby improving life characteristics.

[0131] Experimental example 3. Measurement of volume change of a lithium secondary battery (half cell) The lithium secondary battery (full cell) manufactured in Manufacturing Example 3 was subjected to a 3-cycle formation process at 25°C, voltage range of 2.75V to 4.3V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100). Next, the positive electrode charged at 4.3V was collected from the full cell, and a new pouch cell was prepared by injecting an electrolyte. Each pouch cell was stored at 70°C, and the volume change of the initial pouch cell was measured after 14 and 28 days using an electronic specific gravity meter (SID-220W). The measurement results are shown in Table 3 below.

[0132] [Table 3]

[0133] Referring to the results in Table 3, it was found that, among the full cells using positive active materials having similar crystallite sizes, the volume increase rates of the full cells using the positive active materials according to Examples 1 and 2 were lower than the volume increase rates of the full cells using the positive active materials according to Comparative Examples 1, 3, 4, and 5.

[0134] In other words, the positive electrode active material according to the present invention has the advantage that it can prevent and / or mitigate gas generation and expansion phenomena in a lithium secondary battery compared to lithium secondary batteries using other positive electrode active materials having similar particle sizes by suppressing excessive growth of primary particles and improving the crystallinity of the primary particles.

[0135] 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 elements without departing from the concept of the present invention described in the claims, and this may also be considered to be within the scope of the claims of the present invention.

Claims

1. The lithium-intercalation / deintercalation-capable primary particles and secondary particles formed by agglomeration of the primary particles are included, The secondary particles contain at least one selected from the group consisting of nickel, cobalt, manganese, and aluminum, A positive electrode active material, in which a difference Δd between a maximum value d1 and a minimum value d2 of a d-spacing between (003) planes in the primary particles in a state charged at 4.3 V based on a half cell is less than 0.019 nm.

2. 2. The positive electrode active material according to claim 1, wherein the maximum value d1 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is less than 0.4794 nm.

3. 2. The positive electrode active material according to claim 1, wherein the minimum value d2 of the interplanar distance (d-spacing) of the (003) plane in the crystal structure of the primary particles present in the secondary particles is 0.461 nm or more.

4. The positive electrode active material according to claim 1, wherein the positive electrode active material has a crystallite size of 70 nm to 130 nm.

5. The positive electrode active material of claim 1 , wherein the secondary particles are represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni １－（ｂ＋ｃ＋ｄ） Co ｂ M1 ｃ M2 ｄ O ２ (where: M1 is at least one selected from Mn and Al; M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu; M1 and M2 are different from each other, 0.5≦a≦1.5, 0≦b≦0.20, 0≦c≦0.30, 0≦d≦0.10)

6. The positive electrode active material according to claim 5 , wherein a molar fraction of nickel relative to all elements other than lithium in the secondary particles is 70% or more.

7. The positive electrode active material according to claim 5 , wherein M2 includes at least one selected from the group consisting of B, Al, Nb, and W.

8. The positive electrode active material of claim 1, wherein no peak splitting occurs in a 2θ range of 18° to 20° during XRD analysis of the positive electrode active material.

9. 2. The positive electrode active material of claim 1, wherein a difference in 2θ between two peaks split in a 2θ range of 18° to 20° in an XRD analysis of the positive electrode active material is 0.75° or less.

10. A positive electrode comprising the positive electrode active material according to claim 1 .

11. A lithium secondary battery using the positive electrode according to claim 10.

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