Cathode active material and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material and a lithium secondary battery comprising same and, more specifically, to a cathode active material and a lithium secondary battery comprising same, wherein, by adjusting the content of a fine powder within the cathode active material containing a Mid-Ni type lithium transition metal oxide having a relatively low nickel content and controlling the particle size distribution of the lithium transition metal oxide contained in the cathode active material, improved capacity characteristics and lifetime characteristics, and improved driving characteristics at high voltage can be achieved.

Description

Cathode active material and lithium secondary battery containing the same

[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 including a mid-Ni type lithium transition metal oxide having a relatively low nickel content, which controls the content of fine particles in the positive electrode active material and controls the particle size distribution of the lithium transition metal oxide included in the positive electrode active material, thereby improving capacity characteristics and lifespan characteristics and exhibiting improved driving characteristics at high voltage, and a lithium secondary battery including the same.

[0002]

[0003] Batteries store electricity by utilizing materials capable of electrochemical reactions in their anode and cathode. A representative example of such batteries is the lithium secondary battery, which stores electrical energy through the difference in chemical potential resulting from the intercalation / deintercalation of lithium ions between the anode and cathode.

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

[0005] Lithium transition metal oxides are used as positive electrode active materials for lithium secondary batteries, and examples of these include composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2.

[0006] Among the above positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency, but it has the disadvantage of limited price competitiveness because cobalt used as a raw material is expensive.

[0007] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they have the problems of small capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials have the advantage of showing high discharge capacity, but not only is their synthesis difficult due to the active cation mixing of Li and Ni, but the rate characteristics and cycle life characteristics of the synthesized cathode active materials are very low.

[0008] Accordingly, in order to improve the low rate characteristics and cycle life characteristics while maintaining the high reversible capacity of LiNiO2, ternary type lithium transition metal oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary type lithium transition metal oxides such as NCMA (Ni-Co-Mn-Al) have been developed, in which some of the nickel is replaced by cobalt, manganese, and / or aluminum. Since the lower the nickel content in these ternary or quaternary type lithium transition metal oxides, the lower the reversible capacity, recently, active research has been conducted to increase the nickel content in lithium transition metal oxides.

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

[0010] Accordingly, a washing process must be included during the manufacturing process of the positive electrode active material to remove lithium impurities remaining on the surface of the lithium transition metal oxide. However, this washing process may cause damage to the surface of the lithium transition metal oxide, thereby deteriorating the electrochemical characteristics and stability of a lithium secondary battery using the lithium transition metal oxide as a positive electrode active material, and in particular, may cause problems such as premature deterioration of the lifespan.

[0011] Furthermore, with the recent rapid growth in demand for lithium secondary batteries and the increasing cost of raw materials, the lithium secondary battery market is facing strong demands for cost reduction. In particular, cathode active materials account for the largest portion of the cost in lithium secondary batteries. In particular, as the content of nickel, an essential element in ternary or quaternary lithium transition metal oxides, increases, the cost of cathode active materials inevitably increases.

[0012] That is, when the content of nickel in the positive electrode active material increases, the reversible capacity improves, but this causes problems in a trade-off relationship, such as an increase in lithium impurities in the positive electrode active material and an increase in the cost of the positive electrode active material.

[0013] Therefore, it is necessary to develop a Mid-Ni type cathode active material that can achieve the goal of improving the stability and reducing the cost of the cathode active material by reducing the nickel content in the cathode active material, while solving problems such as deterioration of electrochemical characteristics due to a decrease in the nickel content in the cathode active material.

[0014]

[0015] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, and accordingly, demand for cathode active materials used in lithium secondary batteries is also continuously increasing.

[0016] For example, in the past, lithium secondary batteries using lithium iron phosphate (LFP) were mainly used from the perspective of ensuring safety, but recently, the use of nickel-based lithium transition metal oxides, which have a larger energy capacity per weight than LFP, is expanding (of course, relatively inexpensive LFP is still used to reduce costs).

[0017] In addition, nickel-based lithium transition metal oxides, which are mainly used as positive electrode active materials for recent high-capacity lithium secondary batteries, generally have a composition of a ternary type such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or a quaternary type such as NCMA (Ni-Co-Mn-Al).

[0018] However, as previously mentioned, increasing the nickel content in lithium transition metal oxides improves reversible capacity, but this can also lead to increased lithium impurities in the cathode active material or decreased stability of the cathode active material. Furthermore, trade-off issues, such as increased cost of the cathode active material, inevitably arise.

[0019] Conversely, if the nickel content in the lithium transition metal oxide is reduced to achieve the goal of cost-down of the positive electrode active material, this may entail problems such as a decrease in electrochemical characteristics such as capacity or discharge capacity ratio.

[0020] Accordingly, the present invention aims to provide a positive electrode active material comprising a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less), wherein the number of unit particles constituting the lithium transition metal oxide is reduced to improve life characteristics and stability.

[0021] In addition, the present invention aims to provide a positive electrode active material capable of exhibiting improved operating characteristics at high voltage by controlling the content of fine particles in the positive electrode active material through a disintegration process and controlling the particle size distribution of the lithium transition metal oxide included in the positive electrode active material.

[0022] In addition, another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined herein.

[0023] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0024]

[0025] According to one aspect of the present invention, a cathode active material comprising a lithium transition metal oxide capable of lithium intercalation / deintercalation is provided, wherein the content of fine particles in the cathode active material is controlled, and the particle size distribution of the lithium transition metal oxide included in the cathode active material is adjusted, thereby improving capacity characteristics and life characteristics and exhibiting improved driving characteristics at high voltage.

[0026] The above lithium transition metal oxide contains at least lithium and a transition metal, and the content of nickel among the transition metals may be 40 mol% or more and 70 mol% or less, 45 mol% or more and 70 mol% or less, 50 mol% or more and 70 mol% or less, 55 mol% or more and 65 mol% or less, or 60 mol% or more and 65 mol% or less.

[0027] Among the above transition metals, the content of cobalt may be 10 mol% or less, 2.5 mol% or more and 10 mol% or less, or 5 mol% or more and 10 mol% or less. Among the above transition metals, the content of manganese may be 20 mol% or more and 50 mol% or less, 20 mol% or more and 45 mol% or less, 20 mol% or more and 40 mol% or less, 25 mol% or more and 35 mol% or less, or 27 mol% or more and 33 mol% or less.

[0028] In addition, the lithium transition metal oxide further includes cobalt and manganese as transition metals, and the content of manganese in the lithium transition metal oxide may be greater than the content of cobalt.

[0029] The above lithium transition metal oxide may have a composition represented by the following chemical formula 1.

[0030] [Chemical Formula 1]

[0031] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0032] In the above chemical formula 1, M1 is at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and 0.95≤a≤1.15, 0≤b≤0.10, 0.20≤c≤0.50, 0≤d≤0.10, 0.4≤1-(b+c+d)≤0.7.

[0033] As defined herein, as the manganese content in the Mid-Ni type lithium transition metal oxide having a relatively low nickel content increases compared to the cobalt content, the kinetic characteristics such as the conductivity of lithium ions tend to decrease, resulting in a decrease in the rate characteristics.

[0034] Accordingly, in order to improve the efficiency of reversible intercalation / deintercalation of lithium ions by the lithium transition metal oxide, and thereby improve the electrochemical properties which are inferior to those of the high-Ni type lithium transition metal oxide having a relatively high nickel content, the present invention is characterized in that the lithium transition metal oxide has at least one form selected from a single particle form composed of one unit particle and a pseudo-single particle form in which 30 or fewer unit particles are aggregated.

[0035] The average particle diameter (D) of the lithium transition metal oxide existing in the form of single particles 50 ) is 0.5 μm or more and 10.0 μm or less, and the average particle diameter (D) of the lithium transition metal oxide existing in the form of the pseudo-single particle 50 ) may be 3.0 μm or more and 15.0 μm or less. The average particle diameter (D) of the lithium transition metal oxide existing in the form of the pseudo-single particle 50 ) may vary depending on the number and size of unit particles constituting the pseudo-single particle. In addition, the unit particles constituting the pseudo-single particle may have a size comparable to the size of the lithium transition metal oxide existing in the form of the single particle. That is, the average particle diameter (D) of the unit particles constituting the pseudo-single particle 50 ) may be 0.5 μm or more and 10.0 μm or less.

[0036] The particle size distribution of the lithium transition metal oxide included in the positive electrode active material satisfies the following equation 1.

[0037] [Formula 1]

[0038] 0.85 ≤ (D 90 -D 10 ) / D 50 ≤ 1.21

[0039] In the above equation 1, the particle size that is 10% of the volume accumulation amount is D from the volume accumulation particle size distribution graph obtained by laser diffraction particle size distribution measurement. 10, and the particle size that is 50% of the volume accumulation is D 50 , and the particle size that is 90% of the volume accumulation is D 90 am.

[0040] The particle size distribution of the lithium transition metal oxide included in the positive electrode active material satisfies the following equation 2.

[0041] [Formula 2]

[0042] 1.05 ≤ (D max -D 50 ) / (D 50 -D min ) ≤ 2.35

[0043] In the above equation 2, the particle size that becomes 50% of the volume accumulation amount from the volume accumulation particle size distribution graph obtained by laser diffraction particle size distribution measurement is D 50 , and the minimum particle size of the above volume cumulative particle size distribution graph is D min , and the maximum particle size of the above volume cumulative particle size distribution graph is D max am.

[0044] The content of fine particles having a particle size of 1 μm or less among the above positive electrode active materials is 1% by volume or more and 10% by volume or less.

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

[0046] In addition, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

[0047]

[0048] According to the present invention, the number of unit particles constituting a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less) can be reduced, thereby improving the life characteristics and stability of a lithium secondary battery using a positive electrode active material defined herein.

[0049] In addition, according to the present invention, the driving characteristics at high voltage can be improved by controlling the content of fine particles in the positive electrode active material through a disintegration process and adjusting the particle size distribution of the lithium transition metal oxide included in the positive electrode active material.

[0050] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0051]

[0052] Figure 1 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 1.

[0053] Figure 2 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 2.

[0054] Figure 3 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 3.

[0055] Figure 4 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 4.

[0056] Figure 5 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 5.

[0057] Figure 6 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 6.

[0058] Figure 7 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Example 7.

[0059] Figure 8 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Comparative Example 1.

[0060] Figure 9 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Comparative Example 2.

[0061] Figure 10 shows SEM images (high magnification & low magnification) of the positive electrode active material according to Comparative Example 3.

[0062]

[0063] To facilitate a better understanding of 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 specified by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0064]

[0065] positive electrode active material

[0066] A cathode active material according to one aspect of the present invention is capable of reversible intercalation / deintercalation of lithium ions and includes a lithium transition metal oxide.

[0067] The above lithium transition metal oxide is a composite metal oxide capable of lithium ion intercalation / deintercalation and has a layered crystal structure belonging to the R-3m space group. The above lithium transition metal oxide having a layered crystal structure exhibits a specific peak in the region where 2θ is 18° to 20° among the rotation patterns obtained from XRD analysis.

[0068] In one embodiment, the lithium transition metal oxide comprises at least lithium and a transition metal. The transition metal may comprise at least one, at least two, or all selected from nickel, cobalt, and manganese.

[0069] Preferably, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel. In addition, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0070] In one embodiment, to improve the low rate characteristics and cycle life characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a ternary type lithium transition metal oxide such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or a quaternary type lithium transition metal oxide such as NCMA (Ni-Co-Mn-Al), in which some of the nickel is replaced by cobalt, manganese, and / or aluminum. The ternary or quaternary type lithium transition metal oxide may further include a dopant other than nickel, cobalt, and manganese.

[0071] In another embodiment, the lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not include cobalt within the bulk particles. The cobalt-free type lithium transition metal oxide may further include a dopant other than nickel and manganese.

[0072] The lithium transition metal oxide defined herein is a Mid-Ni type lithium transition metal oxide having a relatively low nickel content. In the present invention, a lithium transition metal oxide having a nickel content of 70 mol% or less among the transition metals is defined as a Mid-Ni type lithium transition metal oxide, and a lithium transition metal oxide having a nickel content of more than 70 mol% among the transition metals is defined as a High-Ni type lithium transition metal oxide.

[0073] In one embodiment, the content of nickel among the transition metals (the content of nickel relative to all elements other than lithium among the lithium transition metal oxides) may be 40 mol% or more and 70 mol% or less, 45 mol% or more and 70 mol% or less, 50 mol% or more and 70 mol% or less, 55 mol% or more and 65 mol% or less, or 60 mol% or more and 65 mol% or less.

[0074] When the content of nickel in the lithium transition metal oxide exceeds 70 mol%, the mixing of cations within the crystal structure may increase, resulting in a decrease in stability, or the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface may increase. On the other hand, when the content of nickel in the lithium transition metal oxide is less than 40 mol%, phase separation may be induced by other transition metals (e.g., manganese, etc.) present in excess other than nickel, resulting in the generation of impurity phases belonging to space groups other than the R-3m space group. The impurity phases may directly affect the deterioration of the electrochemical characteristics of the positive electrode active material.

[0075] Among the above transition metals, the content of cobalt may be 10 mol% or less, 2.5 mol% or more and 10 mol% or less, or 5 mol% or more and 10 mol% or less.

[0076] If the content of cobalt in the lithium transition metal oxide exceeds 10 mol%, the goal of cost-down of the positive electrode active material cannot be achieved. In addition, if the content of cobalt in the lithium transition metal oxide becomes excessively high, the operating voltage of the lithium secondary battery using the positive electrode active material may decrease, making it difficult to exhibit high output characteristics at relatively high voltages. In addition, if the content of cobalt in the lithium transition metal oxide becomes excessively high, there is a concern that the stability may be reduced as the amount of gas generated in the lithium secondary battery using the positive electrode active material increases.

[0077] The above lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain cobalt in bulk particles, but it is preferably at least 2.5 mol% or more for smooth formation of a layered crystal structure belonging to the R-3m space group.

[0078] Among the above transition metals, the content of manganese may be 20 mol% or more and 50 mol% or less, 20 mol% or more and 45 mol% or less, 20 mol% or more and 40 mol% or less, 25 mol% or more and 35 mol% or less, or 27 mol% or more and 33 mol% or less.

[0079] When the content of manganese in the lithium transition metal oxide exceeds 50 mol%, it may be difficult to form lithium transition metal oxides in the form of single particles and pseudo-single particles, and phase separation may be caused by manganese existing in excess in the lithium transition metal oxide, resulting in the generation of an impurity phase belonging to a space group other than the R-3m space group. The impurity phase may directly affect the deterioration of the electrochemical characteristics of the positive electrode active material.

[0080] On the other hand, when the content of manganese in the lithium transition metal oxide is less than 20 mol%, the stability of the lithium transition metal oxide having a relatively low content of nickel as defined herein (e.g., about 70 mol% or less or about 65 mol% or less) may be reduced, and the operating voltage of a lithium secondary battery using the positive electrode active material may be lowered, making it difficult to exhibit high output characteristics at relatively high voltages.

[0081] The above lithium transition metal oxide may have a composition represented by the following chemical formula 1.

[0082] [Chemical Formula 1]

[0083] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0084] In the above chemical formula 1, M1 is at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, and 0.95≤a≤1.15, 0≤b≤0.10, 0.20≤c≤0.50, 0≤d≤0.10, 0.4≤1-(b+c+d)≤0.7.

[0085] a, which represents the ratio of lithium to all elements other than lithium among the above lithium transition metal oxides, may be 0.95 or more and 1.15 or less, 0.95 or more and 1.10 or less, 0.98 or more and 1.10 or less, or 1.01 or more and 1.07 or less.

[0086] When a in the above chemical formula 1 is less than 0.95, the capacity of the positive electrode active material including the lithium transition metal oxide represented by the above chemical formula 1 may decrease. On the other hand, when a in the above chemical formula 1 is greater than 1.15, phase separation may occur due to lithium and manganese existing in excess in the lithium transition metal oxide, resulting in the generation of an impurity phase belonging to a space group other than the R-3m space group.

[0087] 1-(b+c+d+e), which represents the ratio of nickel to all elements other than lithium among the above lithium transition metal oxides, may be 0.40 or more and 0.70 or less, 0.45 or more and 0.70 or less, 0.50 or more and 0.70 or less, 0.55 or more and 0.65 or less, or 0.60 or more and 0.65 or less.

[0088] b, which represents the ratio of cobalt to all elements other than lithium among the above lithium transition metal oxides, may be 0 or more and 0.10 or less, 0.025 or more and 0.10 or less, or 0.05 or more and 0.10 or less.

[0089] c, which represents the ratio of manganese to all elements other than lithium among the above lithium transition metal oxides, may be 0.20 or more and 0.50 or less, 0.20 or more and 0.45 or less, 0.20 or more and 0.40 or less, 0.25 or more and 0.35 or less, or 0.27 or more and 0.33 or less.

[0090] When the lithium transition metal oxide contains a dopant, d in the chemical formula 1 is greater than 0. In addition, when the lithium transition metal oxide contains a dopant, d, which represents the mole fraction of the dopant with respect to the total metal elements other than lithium in the lithium transition metal oxide, may be 0.10 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0091] When the lithium transition metal oxide optionally includes a dopant, the dopant may include at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, preferably at least one selected from Mg, Ca, Al, Ti, Zr, Mo, W and P, and more preferably at least one selected from Ca, Al, Ti and Zr. The type and combination of the dopant may be appropriately selected within a range that does not negatively affect the electrochemical characteristics and stability of the positive electrode active material.

[0092] The upper and lower limits of the contents of nickel, cobalt, manganese, and dopant defined in the above chemical formula 1 can be appropriately selected within a range satisfying the above-described definition.

[0093] As described above, the lithium transition metal oxide further includes cobalt and manganese as transition metals, and the content of manganese in the lithium transition metal oxide may be greater than the content of cobalt. However, in the case of conventional Mid-Ni type lithium transition metal oxides, as the content of manganese increases compared to the content of cobalt, kinetic characteristics such as lithium ion conductivity may decrease, resulting in a tendency for rate characteristics to deteriorate.

[0094] Accordingly, the present invention is characterized in that the number of unit particles constituting the lithium transition metal oxide is small in order to improve the efficiency of reversible intercalation / deintercalation of lithium ions by the lithium transition metal oxide and thereby increase the rate characteristics.

[0095] Specifically, the lithium transition metal oxide may have at least one form selected from a single particle form consisting of one unit particle and a pseudo-single particle form in which 30 or fewer unit particles are aggregated. The unit particle may be interpreted in the same sense as a primary particle.

[0096] The above single particle may have a spherical shape, a rod shape, an oval shape, and / or an irregular shape. In addition, unit particles of various shapes may exist within the same positive electrode active material unless specifically intended during the manufacturing process. In addition, the above unit particle refers to a particle unit that does not have a grain boundary when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0097] That is, the single particle form consisting of one unit particle means that the lithium transition metal oxide is composed of only one unit particle, not in the form of secondary particles in which multiple unit particles are aggregated. The average particle diameter (D) of the lithium transition metal oxide existing in the single particle form 50) may be 1.0 μm to 8.0 μm, 1.0 μm to 7.0 μm, 1.0 μm to 6.0 μm, 1.0 μm to 5.0 μm, 2.0 μm to 8.0 μm, 2.0 μm to 7.0 μm, 2.0 μm to 6.0 μm, or 2.0 μm to 5.0 μm.

[0098] The average particle diameter of the above unit particles (D 50 ) may be the average value of the length in the major axis direction and the length in the minor axis direction of the unit particle ([major axis length + minor axis length] / 2). The average particle diameter of the unit particle may be calculated as the average value of the particle diameters of all unit particles observed from the surface SEM image and / or cross-sectional SEM image of the lithium transition metal oxide.

[0099] When the average particle diameter of the unit particle is smaller than 1.0 μm, the lithium transition metal oxide is likely to have a polycrystalline structure in which 50 or more, or 100 or more, unit particles are aggregated, instead of having a single particle form and / or a pseudo-single particle form. In addition, when the average particle diameter of the unit particle is smaller than 1.0 μm, the specific surface area of ​​the positive electrode active material including the lithium transition metal oxide having at least one form selected from a single particle form composed of one unit particle and a pseudo-single particle form in which 30 or fewer unit particles are aggregated may increase, which may cause a decrease in stability due to a side reaction with the electrolyte.

[0100] On the other hand, if the average particle diameter of the unit particle is greater than 8.0 μm, the growth of the unit particle may be excessively induced, which may actually reduce the diffusion of lithium ions through the unit particle. In addition, due to the characteristics of the Mid-Ni type lithium transition metal oxide, which has a relatively large content of transition metals other than nickel, the distribution of the transition metal within the unit particle may become uneven.

[0101] Typically, ternary or quaternary type lithium transition metal oxides have a secondary particle form in which hundreds or thousands of unit particles are aggregated. The lithium transition metal oxide defined herein may have a secondary particle form in which multiple unit particles are aggregated, but has a pseudo-single particle form in which 30 or fewer, 20 or fewer, or 10 or fewer unit particles are aggregated. Hereinafter, in order to distinguish it from secondary particles in which hundreds or thousands of unit particles are aggregated, secondary particles in which 30 or fewer, 20 or fewer, or 10 or fewer unit particles are aggregated may be referred to as pseudo-single particles. In addition, the primary particles constituting the conventional secondary particle form of the ternary or quaternary type lithium transition metal oxide have a particle size smaller than the unit particles defined herein.

[0102] The average particle diameter (D) of the lithium transition metal oxide present in the form of the above pseudo-single particles 50 ) may be 3.0 μm or more and 12.0 μm or less, or 4.0 μm or more and 12.0 μm or less. The average particle diameter (D) of the lithium transition metal oxide existing in the form of the pseudo-single particle 50 ) may vary depending on the number and size of unit particles constituting the above-mentioned pseudo-single particle.

[0103] In addition, the unit particles constituting the pseudo-single particles may have a size comparable to the size of the lithium transition metal oxide existing in the form of the single particles. That is, the average particle diameter (D) of the unit particles constituting the pseudo-single particles 50 ) may be 1.0 μm to 8.0 μm, 1.0 μm to 7.0 μm, 1.0 μm to 6.0 μm, 1.0 μm to 5.0 μm, 2.0 μm to 8.0 μm, 2.0 μm to 7.0 μm, 2.0 μm to 6.0 μm, or 2.0 μm to 5.0 μm.

[0104] The average particle diameter (D) of the lithium transition metal oxide present in the form of the above pseudo-single particles 50) can be calculated as the average value of the particle diameter of the pseudo-single particles confirmed from the SEM image.

[0105] In this application, “particle size” is used interchangeably with “particle diameter” or “particle size”, and unless otherwise defined, all “average particle diameters” mean the particle size corresponding to 50% of the volume accumulation amount determined by the aforementioned laser diffraction method.

[0106] Among the above-mentioned positive electrode active materials, the particle size distribution of the lithium transition metal oxide can be measured using a laser diffraction method. For example, after dispersing secondary particles in a dispersion medium, they are 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, and then a volume-cumulative particle size distribution graph is obtained, and then particle sizes (D) corresponding to 10%, 50%, and 90% of the volume-cumulative amount are measured. 10 , D 50 , D 90 ), the minimum particle size (D) of the above volume cumulative particle size distribution graph min ) and the maximum particle size (D) of the above volume cumulative particle size distribution graph max ) can be produced.

[0107] The above positive electrode active material may include both a lithium transition metal oxide in the form of a single particle and a lithium transition metal oxide in the form of a pseudo-single particle.

[0108] D measured by laser diffraction for the positive electrode active material including the lithium transition metal oxide in the form of single particles and the lithium transition metal oxide in the form of pseudo-single particles 50The positive electrode active material including a Mid-Ni type lithium transition metal oxide in which the content of nickel among the transition metals is 40 mol% or more and 70 mol% or less is D 50 It can represent the optimal energy density per unit volume within the range.

[0109] D measured by laser diffraction for the positive electrode active material including the lithium transition metal oxide in the form of single particles and the lithium transition metal oxide in the form of pseudo-single particles 10 The silver may be 0.3 μm or more and 8.0 μm or less, 0.5 μm to 6.0 μm, 1.0 μm to 5.0 μm, 1.0 μm to 4.0 μm, or 1.0 μm to 3.5 μm.

[0110] D measured by laser diffraction for the above positive electrode active material 10 If it is smaller than 0.3 μm, the content of fine particles having a particle size of 1 μm or less in the positive electrode active material may increase. In addition, the particle size distribution for the lithium transition metal oxide is generally D min As the shift is made laterally, the agglomeration phenomenon between particles increases, which may result in a decrease in the energy density per unit volume.

[0111] D measured by laser diffraction for the positive electrode active material including the lithium transition metal oxide in the form of single particles and the lithium transition metal oxide in the form of pseudo-single particles 90The positive electrode active material including a lithium transition metal oxide of the Mid-Ni type in which the content of nickel among the transition metals is 40 mol% or more and 70 mol% or less is D 90 It can represent the optimal energy density per unit volume within the range.

[0112] D as defined above 10 , D 50 and D 90 The upper and lower limits can be appropriately selected within the range that satisfies the following relationship.

[0113] The particle size distribution of the lithium transition metal oxide included in the positive electrode active material can satisfy the following equation 1.

[0114] [Formula 1]

[0115] 0.85 ≤ (D 90 -D 10 ) / D 50 ≤ 1.21

[0116] In the above equation 1 (D 90 -D 10 ) / D 50 When the value is greater than 1.21, the peak of the particle size distribution of the lithium transition metal oxide included in the positive electrode active material is D, which is the maximum particle size of the peak of the particle size distribution observed in the volume cumulative particle size distribution graph. max It represents a particle size distribution shifted to the side. On the other hand, in the above equation 1 (D 90 -D 10 ) / D 50 When the value is less than 0.85, the peak of the particle size distribution observed in the volume cumulative particle size distribution graph is relatively at the minimum particle size D min It gets closer to the side.

[0117] A positive electrode active material including a Mid-Ni type lithium transition metal oxide having a nickel content of 40 mol% or more and 70 mol% or less among transition metals is represented by the formula 1 above (D 90 -D 10 ) / D 50 When the value has a value of 0.85 to 1.21, it can represent the optimal energy density per unit volume.

[0118] In addition, the particle size distribution of the lithium transition metal oxide included in the positive electrode active material can satisfy the following equation 2.

[0119] [Formula 2]

[0120] 1.05 ≤ (D max -D 50 ) / (D 50 -D min ) ≤ 2.35

[0121] (D max -D 50 ) / (D 50 -D min ) refers to the degree of sharpness of the particle size distribution peak observed in the volume cumulative particle size distribution graph. (D max -D 50 ) / (D 50 -D min ) is less than 1.05, it means that the sharpness of the particle size distribution peak observed in the volume cumulative particle size distribution graph is excessively high. On the other hand, (D max -D 50 ) / (D 50 -D min ) is greater than 2.35, it means that the uniformity of the particle size distribution and the sharpness of the particle size distribution peak observed in the volume cumulative particle size distribution graph are low. If the uniformity of the particle size distribution and the sharpness of the particle size distribution peak are excessively high or low, there is a concern that the energy density per unit volume may decrease.

[0122] A cathode active material including a mid-Ni type lithium transition metal oxide having a nickel content of 40 mol% or more and 70 mol% or less among transition metals can exhibit improved life characteristics and stability and improved operating characteristics at high voltage when it satisfies the particle size distribution according to Equations 1 and 2.

[0123] In addition, in order to improve the uniformity of the particle size distribution of the lithium transition metal oxide included in the positive electrode active material, D observed in the volume cumulative particle size distribution graph max -D 90 It is preferable that the thickness is 0.5 μm or more and 7.5 μm or less, 1.0 μm or more and 7.0 μm or less, or 1.5 μm or more and 6.0 μm or less.

[0124] D max -D 90 When it is smaller than 0.5 μm, the peak of the particle size distribution observed in the volume cumulative particle size distribution graph is the maximum particle size D max It shows a particle size distribution shifted to the side. In this case, it may be difficult for a positive electrode active material including a Mid-Ni type lithium transition metal oxide with a nickel content of 40 mol% or more and 70 mol% or less among transition metals to exhibit an optimal energy density per unit volume. On the other hand, D max -D 90 For larger than 7.5 μm, the peak of the particle size distribution observed in the volume cumulative particle size distribution graph is relatively small, D min The particle size distribution of the lithium transition metal oxide included in the positive electrode active material may become closer to the side or the uniformity may be reduced.

[0125] In order to improve the sharpness of the particle size distribution of the lithium transition metal oxide included in the positive electrode active material, D observed in the volume cumulative particle size distribution graph max -D 50It is preferable that the thickness is 2.0 μm or more and 10.0 μm or less, 2.5 μm or more and 10.0 μm or less, or 3.0 μm or more and 10.0 μm or less.

[0126] D max -D 50 When it is smaller than 2.0 μm, the peak of the particle size distribution observed in the volume cumulative particle size distribution graph is the maximum particle size D max It shows a particle size distribution shifted to the side. In this case, it may be difficult for a positive electrode active material including a Mid-Ni type lithium transition metal oxide with a nickel content of 40 mol% or more and 70 mol% or less among transition metals to exhibit an optimal energy density per unit volume. On the other hand, D max -D 50 For cases larger than 10.0 μm, the peak of the particle size distribution observed in the volume cumulative particle size distribution graph is relatively the minimum particle size D min The particle size distribution of the lithium transition metal oxide included in the positive electrode active material may become closer to the side or the uniformity or sharpness of the particle size distribution may decrease.

[0127] D observed in the volume cumulative particle size distribution graph of the lithium transition metal oxide included in the positive electrode active material max It is desirable that it be 15μm or less.

[0128] The fact that the maximum particle size of the lithium transition metal oxide obtained from the volume cumulative particle size distribution graph for the above-mentioned positive electrode active material exceeds 15 μm means that the growth of the unit particles constituting the lithium transition metal oxide is excessively induced. If the growth of the unit particles is excessively induced, the diffusion of lithium ions through the unit particles may decrease, resulting in the occurrence of a polarization shape, and the possibility of cracks occurring within the unit particles due to the polarization phenomenon increases.

[0129] In addition, when the maximum particle size of the lithium transition metal oxide exceeds 15 μm, there is a concern that the uniformity and sharpness of the particle size distribution observed in the volume cumulative particle size distribution graph may decrease, thereby reducing the energy density per unit volume.

[0130] It is preferable that the content of fine particles having a particle size of 1 μm or less in the positive electrode active material is 1% by volume or more and 10% by volume or less, or 1.5% by volume or more and 10% by volume or less. The fine particles may be the lithium transition metal oxide having a particle size of 1 μm or less. The fine particles may be generated by adjusting the lithium transition metal oxide included in the positive electrode active material to have the above-described particle size distribution through a pulverization process.

[0131] In general, it is known that fine particles observed separately from the main particle size distribution peak obtained from the volume cumulative particle size distribution graph for the positive electrode active material can reduce the energy density per unit volume of the positive electrode active material, and therefore, it is known that it is preferable that the positive electrode active material not include fine particles, if possible. However, when a positive electrode active material including a Mid-Ni type lithium transition metal oxide in which the content of nickel among the transition metals defined herein is 40 mol% or more and 70 mol% or less includes fine particles in a predetermined content (for example, 1 vol% or more), electrochemical characteristics such as life characteristics may be improved. However, when the content of fine particles having a particle size of 1 μm or less in the positive electrode active material exceeds 10 vol%, the capacity characteristics and life characteristics of the positive electrode active material may be deteriorated.

[0132] Similar to the particle size distribution of the lithium transition metal oxide among the positive electrode active materials, the content of fine particles having a particle size of 1 μm or less among the positive electrode active materials can be measured using a laser diffraction method. For example, after dispersing secondary particles in a dispersion medium, they are 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, and then a volume-based cumulative particle size distribution graph is obtained. Then, the volume-based content of fine particles having a particle size of 1 μm or less among the positive electrode active materials can be measured through the volume-based cumulative amount of particles having a particle size of 1 μm or less.

[0133] The average crystallite size of the lithium transition metal oxide defined herein is preferably 145 nm to 185 nm. The average crystallite size can be quantitatively analyzed through X-ray diffraction analysis (XRD) using Cu-Kα X-rays for the lithium transition metal oxide. Specifically, the lithium average crystallite size can be calculated through Rietveld refinement of an X-ray diffraction pattern in the 2θ=10° to 120° region obtained through XRD analysis for a positive electrode active material including the lithium transition metal oxide.

[0134] A positive electrode active material including a mid-Ni type lithium transition metal oxide having a nickel content of 40 mol% or more and 70 mol% or less among transition metals, when satisfying the particle size distribution according to Equations 1 and 2 and having the above-described average crystallite size, can improve the discharge capacity ratio of a lithium secondary battery using the positive electrode active material.

[0135]

[0136] lithium secondary battery

[0137] According to another aspect of the present invention, a positive electrode may be provided, comprising 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 described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described below.

[0138] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0139] The above positive electrode active material layer can be manufactured by applying a positive electrode slurry composition including the positive electrode active material, a conductive material, and optionally a binder as needed, to the positive electrode current collector.

[0140] 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. When included in the content range described above, excellent capacity characteristics may be exhibited, but the present invention is not necessarily limited thereto.

[0141] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0142] The above binder serves to improve the adhesion between 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, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0143] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material described above and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, followed by drying and rolling.

[0144] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0145] Additionally, in another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, and then laminating the resulting film onto a positive electrode current collector by peeling it off from the support.

[0146] In addition, according to another aspect of the present invention, an electrochemical device including the above-described positive electrode may be provided. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0147] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Here, the positive electrode is the same as described above, so a detailed description thereof is omitted for convenience, and only the remaining components not described above will be described in detail below.

[0148] 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.

[0149] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0150] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0151] The above negative electrode active material layer can be manufactured by applying a negative electrode slurry composition including the negative electrode active material, a conductive material, and optionally a binder as needed, to the negative electrode current collector.

[0152] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0153] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0154] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative 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.

[0155] The conductive agent 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 agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or 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 or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0156] In one embodiment, the negative electrode active material layer may be manufactured by applying and drying 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, or by casting the negative electrode slurry composition on a separate support and then laminating the resulting film on a negative electrode current collector by peeling it off from the support.

[0157] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can 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. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0158] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0159] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0160] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0161] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is preferable to use the lithium salt at a concentration within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0162] When the electrolyte used herein 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, a halide-based solid electrolyte, etc. can be used, and preferably, a sulfide-based solid electrolyte can be used.

[0163] As a material of the sulfide-based solid electrolyte, a solid electrolyte containing Li, X element (wherein, X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S can 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-Z m S n (where, m, n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0164] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous, crystalline, or a mixture of amorphous and crystalline.

[0165] Li7La3Zr2O is used as a material for oxide-based solid electrolytes. 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO4-x N x (LiPON), Li 2+2x Zn 1-x There are GeO4 (LISICON), etc.

[0166] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. In addition, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0167] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0168] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0169] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0170] According to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same can be provided.

[0171] The above battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0172]

[0173] Hereinafter, the present invention will be described in more detail through examples. However, these examples are intended solely to illustrate the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0174]

[0175] Manufacturing Example 1. Manufacturing of positive electrode active material

[0176] Example 1

[0177] Ni synthesized by co-precipitation reaction 0.62 Co 0.06 Mn 0.32 (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) were mixed and heat-treated in an air atmosphere at 950°C for 10 hours to obtain a primary intermediate product (lithium transition metal oxide).

[0178] Next, the primary intermediate product was crushed using a jet mill under the conditions of 2 bar and 4,000 rpm to obtain the final product.

[0179]

[0180] Example 2

[0181] A positive electrode active material was manufactured in the same manner as in Example 1, except that the first intermediate product was crushed using a jet mill under the conditions of 2 bar and 6,800 rpm.

[0182]

[0183] Example 3

[0184] A positive electrode active material was manufactured in the same manner as in Example 1, except that the first intermediate product was crushed using a jet mill under the conditions of 2 bar and 9,000 rpm.

[0185]

[0186] Example 4

[0187] A positive electrode active material was manufactured in the same manner as in Example 1, except that the first intermediate product was crushed using a jet mill at 2 bar and 12,000 rpm.

[0188]

[0189] Comparative Example 1

[0190] A positive electrode active material was manufactured in the same manner as in Example 1, except that the lithium transition metal oxide was crushed by hand mixing using a 3L mixer instead of using a jet mill.

[0191]

[0192] Comparative Example 2

[0193] A positive electrode active material was manufactured in the same manner as in Example 1, except that the first intermediate product was crushed using a jet mill at 1.5 bar and 7,500 rpm.

[0194]

[0195] Example 5

[0196] Ni synthesized by co-precipitation reaction 0.62 Co 0.06 Mn 0.32 (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) were mixed and heat-treated in an air atmosphere at 950°C for 10 hours to obtain a primary intermediate product (lithium transition metal oxide).

[0197] Next, the first intermediate product and H3BO3 (weighed so that the content of boron relative to the total transition metal in the first intermediate product is 0.17 mol%) were mixed and heat-treated at 350°C in an O2 atmosphere for 5 hours to obtain a second intermediate product.

[0198] The secondary intermediate product was crushed using a jet mill at 3 bar and 7,000 rpm to obtain the final product.

[0199]

[0200] Example 6

[0201] A positive electrode active material was manufactured in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill at 3 bar and 9,000 rpm.

[0202]

[0203] Example 7

[0204] A positive electrode active material was manufactured in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill at 3 bar and 11,000 rpm.

[0205]

[0206] Example 8

[0207] A positive electrode active material was manufactured in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill at 3 bar and 10,000 rpm.

[0208]

[0209] Comparative Example 3

[0210] A positive electrode active material was manufactured in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill at 3 bar and 18,000 rpm.

[0211]

[0212] Comparative Example 4

[0213] A positive electrode active material was manufactured in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill at 3 bar and 20,000 rpm.

[0214]

[0215] Manufacturing Example 2. Manufacturing of a lithium secondary battery (half-cell)

[0216] A cathode slurry was prepared by dispersing 94 wt% of each cathode active material manufactured according to Manufacturing Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2 pyrrolidone (NMP). The cathode slurry was uniformly applied to a 15 μm thick aluminum film and vacuum-dried at 135°C to prepare a cathode for a lithium secondary battery.

[0217] A half-cell was manufactured using a lithium foil as a counter electrode for the above anode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte containing LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate and ethyl methyl carbonate mixed at a volume ratio of 3:7.

[0218]

[0219] Experimental Example 1. Analysis of the physical properties of the positive electrode active material

[0220] (1) Particle size distribution analysis

[0221] The particle size distribution of the lithium transition metal oxide in each of the positive electrode active materials manufactured according to Manufacturing Example 1 was analyzed using a known laser diffraction method. Specifically, after each positive electrode active material was dispersed in a dispersion medium, ultrasound of approximately 28 kHz was irradiated at an output of 60 W using a laser diffraction particle size measuring device (Microtrac MT 3000), and then a volume-cumulative particle size distribution graph was obtained.

[0222] Next, from the above volume cumulative particle size distribution graph, the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative amount, and the minimum particle size (D) of the above volume cumulative particle size distribution graph min ), the maximum particle size (D) of the above volume cumulative particle size distribution graph max ) and the volume-based content of fine particles having a particle size of 1 μm or less (fine content) was calculated.

[0223]

[0224] (2) XRD analysis

[0225] X-ray diffraction (XRD) analysis was performed on each positive electrode active material manufactured according to Manufacturing Example 1 to calculate the average crystallite size of the lithium transition metal oxide contained in the positive electrode active material.

[0226] XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-kα radiation (1.540598Å). The average crystallite size was calculated from a straight line obtained by plotting the diffraction angle θ (rad) and full width at half maximum β (rad) on a coordinate plane whose horizontal axis is sinθ and whose vertical axis is βcosθ within the range of 2θ = 10° to 120° through Rietveld refinement of the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα radiation for the positive electrode active material.

[0227] The results of the above analysis are shown in Tables 1 and 2 below.

[0228] Differentiated content (volume %)D min (μm)D 10 (μm)D 50 (μm)D 90 (μm)D max (μm)Example 11.570.873.025.409.4615.0Example 22.740.762.874.847.8112.0Example 33.370.772.734.446.8410.0Example 43.400.762.684.216.328.0Comparative Example 10.902.013.376.4811.2715.0Comparative Example 212.10.542.923.825.798.0Example 54.090.422.023.966.8110.0Example 64.960.271.713.205.4610.0Example 79.630.071.102.714.256.0Embodiment 86.320.201.683.185.338.0Comparative Example 310.190.060.192.384.288.0Comparative Example 413.300.050.182.214.188.0

[0229]

[0230] Classification (D 90 -D 10 ) / D 50 (D max -D 50 ) / (D 50 -D min)D max -D 90 D max -D 50 Example 11.192.125.549.60 Example 21.021.754.197.16 Example 30.931.513.165.56 Example 40.861.101.683.79 Comparative Example 11.221.913.738.52 Comparative Example 20.751.272.214.18 Example 51.211.713.196.04 Example 61.172.324.546.80 Example 71.161.251.753.29 Example 81.151.622.674.82 Comparative Example 31.722.423.725.62 Comparative Example 41.812.683.825.79

[0231]

[0232] Experimental Example 2. Evaluation of the Electrochemical Characteristics of a Lithium Secondary Battery (Half-Cell)

[0233] For the lithium secondary battery (half-cell) manufactured in Manufacturing Example 2, an electrochemical analysis device (Toyo, Toscat-3100) was used to measure the initial charge capacity, initial discharge capacity, initial efficiency, and 2.0C / 0.1C rate characteristics through a charge / discharge experiment at 25°C, a voltage range of 3.0 V to 4.4 V, and a discharge rate of 2.0C / 0.1C.

[0234] In addition, for the same lithium secondary battery (half-cell), 50 charge / discharge cycles were performed under the conditions of room temperature (25°C) and high temperature (45°C), voltage range 3.0 V to 4.4 V, and 1C / 1C using an electrochemical analysis device (Toyo, Toscat-3100), and the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0235] The above measurement results are shown in Table 3 below.

[0236] ClassificationCharge capacity (mAh / g)Discharge capacity (mAh / g)Initial efficiency (%)2.0C / 0.1CRate (%)Room temperature life (%)High temperature life (%)Example 1215.1191.388.9484.1090.7091.10Example 2215.9191.688.8483.7091.0090.90Example 3215.7191.388.6984.0091.1090.70Example 4215.1190.988.7584.2091.5091.40Comparative example 1215.6191.088.5983.6090.0090.10Comparative example 2215.5190.988.5883.8089.990.20Example 5216.9192.388.6684.1091.9091.70Example 6216.4191.788.5883.9091.4091.50Example 7215.0191.889.2084.3091.3091.30Example 8216.0191.988.8484.1091.4091.30Comparative Example 3213.9189.488.5584.0090.5090.50Comparative Example 4213.9188.788.2283.4090.0089.90

[0237]

[0238] Comparing the results of Examples 1 to 4 and Comparative Examples 1 and 2, it can be confirmed that the life characteristics of a lithium secondary battery using a positive electrode active material according to Examples 1 to 4, in which the content of fine particles having a particle size of 1 μm or less in the positive electrode active material is 1% by volume or more and 10% by volume or less, are improved at room temperature (25°C) and high temperature (45°C).

[0239] Likewise, when comparing the results of Examples 5 to 8 and Comparative Examples 3 and 4, it can be confirmed that the life characteristics of a lithium secondary battery using a positive electrode active material according to Examples 5 to 8, in which the content of fine particles having a particle size of 1 μm or less in the positive electrode active material is 1% to 10% by volume, are improved at room temperature (25°C) and high temperature (45°C).

[0240] In general, it is known that fine particles observed separately from the main particle size distribution peak obtained from the volume cumulative particle size distribution graph for the positive electrode active material can reduce the energy density per unit volume of the positive electrode active material, and therefore it is desirable for the positive electrode active material not to contain fine particles, if possible. However, a positive electrode active material including a Mid-Ni type lithium transition metal oxide in which the content of nickel among the transition metals defined herein is 40 mol% or more and 70 mol% or less may exhibit improved electrochemical characteristics such as high-temperature life characteristics when it contains fine particles in a predetermined amount or more. However, when the content of fine particles having a particle size of 1 μm or less in the positive electrode active material exceeds 10 vol%, it can be confirmed that the capacity characteristics are deteriorated or the life characteristics at room temperature (25°C) and high temperature (45°C) are deteriorated.

[0241]

[0242] Above, the embodiments of the present invention have been described, but those of ordinary skill in the art will be able to modify and change the present invention in various ways by adding, changing, deleting or adding components, etc., within the scope that does not depart from the spirit of the present invention described in the claims, and this will also be considered to be included within the scope of the rights of the present invention.

Claims

1. Contains a lithium transition metal oxide capable of lithium intercalation / deintercalation, The above lithium transition metal oxide contains at least lithium and a transition metal, Among the above transition metals, the content of nickel is 40 mol% or more and 70 mol% or less, Among the above positive electrode active materials, the content of fine particles having a particle size of 1 μm or less is 1% by volume or more and 10% by volume or less, Positive active material.

2. In paragraph 1, Among the above transition metals, the content of cobalt is 10 mol% or less. Positive active material.

3. In paragraph 1, Among the above transition metals, the content of manganese is 20 mol% or more and 50 mol% or less, Positive active material.

4. In paragraph 1, The above lithium transition metal oxide further contains cobalt and manganese, Among the above transition metals, the content of manganese is greater than that of cobalt. Positive active material.

5. In paragraph 1, The above lithium transition metal oxide is represented by the following chemical formula 1: Cathode active material: [Chemical Formula 1] Li a Ni 1-(b+c+d) Co b Mr c M1 d O2 In the above chemical formula 1, M1 is at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd and Cu, 0.95≤a≤1.15, 0≤b≤0.10, 0.20≤c≤0.50, 0≤d≤0.10, 0.4≤1-(b+c+d)≤0.

7.

6. In paragraph 1, The lithium transition metal oxide has at least one form selected from a single particle form consisting of one unit particle and a pseudo-single particle form in which 30 or fewer unit particles are aggregated. Positive active material.

7. In paragraph 1, The average particle diameter (D) of the lithium transition metal oxide existing in the form of single particles 50 ) is 1.0 μm or more and 8.0 μm or less, Positive active material.

8. In paragraph 1, The average particle diameter (D) of the lithium transition metal oxide present in the form of the above pseudo-single particles 50 ) is 3.0 μm or more and 12.0 μm or less, Positive active material.

9. In paragraph 1, The average crystallite size of the lithium transition metal oxide is 145 nm to 185 nm, Positive active material.

10. In paragraph 1, The particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following equation 1. Cathode active material: [Formula 1] 0.85 ≤ (D 90 -D 10 ) / D 50 ≤ 1.21 In the above equation 1, the particle size that is 10% of the volume accumulation amount is D from the volume accumulation particle size distribution graph obtained by laser diffraction particle size distribution measurement. 10 , and the particle size that is 50% of the volume accumulation is D 50 , and the particle size that is 90% of the volume accumulation is D 90 am.

11. In paragraph 1, The particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following equation 2. Cathode active material: [Formula 2] 1.05 ≤ (D max -D 50 ) / (D 50 -D min ) ≤ 2.35 In the above equation 2, the particle size that becomes 50% of the volume accumulation amount from the volume accumulation particle size distribution graph obtained by laser diffraction particle size distribution measurement is D 50 , and the minimum particle size of the above volume cumulative particle size distribution graph is D min , and the maximum particle size of the above volume cumulative particle size distribution graph is D max am.

12. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 11.

13. A lithium secondary battery using a positive electrode according to Article 12.

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