Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery containing the same. More specifically, the present invention relates to a positive electrode active material and a lithium secondary battery containing the same, which are capable of improving capacity characteristics and life characteristics and exhibiting improved driving characteristics at high voltages by controlling the content of fine powder in a positive electrode active material containing a Mid-Ni type lithium transition metal oxide with a relatively low nickel content, and by adjusting the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same. More specifically, the present invention relates to a positive electrode active material and a lithium secondary battery containing the same, which are capable of improving capacity characteristics and life characteristics and exhibiting improved driving characteristics at high voltages by controlling the content of fine powder in a positive electrode active material containing a Mid-Ni type lithium transition metal oxide with a relatively low nickel content, and by adjusting the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material. [Background technology]

[0002] Batteries store electricity by using electrochemically reactive materials at the positive and negative electrodes. A typical example of such a battery is the lithium-ion secondary battery, which stores electrical energy through the difference in chemical potential that occurs when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

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

[0004] Lithium transition metal oxides are used as positive electrode active materials in lithium secondary batteries, and composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are being studied as examples.

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

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature performance. LiNiO2-based cathode active materials have the advantage of exhibiting high discharge capacity, but they are difficult to synthesize due to the active cation mixing of Li and Ni, and the synthesized cathode active materials have the problem of very poor rate characteristics and lifetime characteristics.

[0007] As a result, in order to improve the low rate characteristics and lifetime characteristics of LiNiO2 while maintaining its high reversible capacity, ternary lithium transition metal oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary lithium transition metal oxides such as NCMA (Ni-Co-Mn-Al), have been developed in which some of the nickel is replaced with cobalt, manganese, and / or aluminum. Since the reversible capacity decreases as the nickel content in such ternary or quaternary lithium transition metal oxides decreases, research has recently been actively conducted to increase the nickel content in lithium transition metal oxides.

[0008] Incidentally, as the nickel content in lithium transition metal oxides increases, the cation mixing within the crystal structure increases, leading to problems such as decreased stability and an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[0009] The more lithium impurities remain on the surface of the lithium transition metal oxide, the more likely it is to promote gas generation and swelling in lithium secondary batteries using the lithium transition metal oxide as the positive electrode active material. Furthermore, the more lithium impurities remain on the surface of the lithium transition metal oxide, the more likely it is that the paste composition will gel due to the lithium impurities when using the lithium transition metal oxide to produce a paste for forming a positive electrode active material layer.

[0010] Consequently, the manufacturing process of the positive electrode active material must include a water washing step to remove lithium impurities remaining on the surface of the lithium transition metal oxide. However, damage to the surface of the lithium transition metal oxide through such a water washing step can reduce the electrochemical properties and stability of lithium secondary batteries using the lithium transition metal oxide as the positive electrode active material, and in particular, can lead to problems such as premature deterioration of the battery's lifespan.

[0011] Furthermore, with the recent rapid growth in demand for lithium-ion batteries and the increasing cost of raw materials, the lithium-ion battery market has faced a strong demand for cost reduction. In particular, the cathode active material accounts for the largest cost proportion in lithium-ion batteries, and the cost of the cathode active material inevitably rises as the nickel content, an essential element of ternary or quaternary lithium transition metal oxides, increases.

[0012] In other words, increasing the nickel content in the positive electrode active material improves the reversible capacity, but this leads to a trade-off relationship where lithium impurities in the positive electrode active material increase, thus raising the cost of the positive electrode active material.

[0013] Therefore, it is necessary to develop a Mid-Ni type cathode active material that can reduce the nickel content in the cathode active material, thereby achieving the goals of improving the stability and reducing costs of the cathode active material, while simultaneously resolving problems such as the deterioration of electrochemical properties due to the reduced nickel content. [Overview of the project] [Problems that the invention aims to solve]

[0014] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is driving the market, and this is leading to a sustained increase in the demand for positive electrode active materials used in lithium-ion batteries.

[0015] For example, conventionally, lithium-ion batteries using lithium iron phosphate (LFP) have been primarily used due to safety considerations, but recently, there has been a growing trend towards the use of nickel-based lithium transition metal oxides, which have a higher energy capacity per unit weight compared to LFP (of course, relatively inexpensive LFP is still sometimes used to reduce costs).

[0016] Furthermore, nickel-based lithium transition metal oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, generally have ternary compositions such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary compositions such as NCMA (Ni-Co-Mn-Al).

[0017] However, as mentioned above, while increasing the nickel content in lithium transition metal oxides improves reversible capacity, this can lead to problems such as an increase in lithium impurities in the positive electrode active material and a decrease in the stability of the positive electrode active material. In addition, trade-offs inevitably arise, such as an increase in the cost of the positive electrode active material.

[0018] Conversely, reducing the nickel content in lithium transition metal oxides to achieve the goal of lowering the cost of positive electrode active materials can lead to problems such as a decrease in electrochemical properties, including capacity or discharge capacity ratio.

[0019] Therefore, the present invention aims to provide a positive electrode active material comprising a Mid-Ni type lithium transition metal oxide with a relatively low nickel content (for example, 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, thereby improving lifetime characteristics and stability.

[0020] Furthermore, the present invention aims to provide a positive electrode active material that exhibits improved driving characteristics at high voltages by controlling the content of fine powder in the positive electrode active material through a crushing process and adjusting the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material.

[0021] Another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined in this application.

[0022] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and may be more clearly understood from embodiments of the present invention. It can also be readily seen that the objects and advantages of the present invention can be achieved by the means and combinations set forth in the claims. [Means for solving the problem]

[0023] According to one aspect of the present invention, a positive electrode active material is provided that includes a lithium transition metal oxide capable of lithium intercalation / deintercalation, and by controlling the content of fine powder in the positive electrode active material and adjusting the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material, the capacity characteristics and lifetime characteristics are improved, and the positive electrode active material exhibits improved driving characteristics at high voltage.

[0024] The lithium transition metal oxide comprises at least lithium and a transition metal, and the nickel content in the transition metal may be 40 mol% to 70 mol%, 45 mol% to 70 mol%, 50 mol% to 70 mol%, 55 mol% to 65 mol%, or 60 mol% to 65 mol%.

[0025] The cobalt content in the transition metal may be 10 mol% or less, 2.5 mol% to 10 mol%, or 5 mol% to 10 mol%. The manganese content in the transition metal may be 20 mol% to 50 mol%, 20 mol% to 45 mol%, 20 mol% to 40 mol%, 25 mol% to 35 mol%, or 27 mol% to 33 mol%.

[0026] Furthermore, the lithium transition metal oxide may further contain cobalt and manganese as transition metals, and the manganese content in the lithium transition metal oxide may be greater than the cobalt content.

[0027] The lithium transition metal oxide may have a composition represented by the following chemical formula 1. [Chemical formula 1] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2 [Here, 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 the following inequalities are given: 0.95 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.10, 0.20 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.10, and 0.4 ≤ 1 - (b + c + d) ≤ 0.7. As defined in this application, the higher the manganese content in a Mid-Ni type lithium transition metal oxide with a relatively low nickel content compared to the cobalt content, the lower the kinetic properties such as lithium ion conductivity and the lower the rate properties tend to be.

[0028] According to this, in the present application, 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 that are inferior to those of a High-Ni type lithium transition metal oxide with a relatively high nickel content, the lithium transition metal oxide has at least one form selected from a single-particle form composed of one unit particle and a similar single-particle form in which 30 or fewer unit particles are aggregated.

[0029] The average particle size (D 50 ) of the lithium transition metal oxide present in the single-particle form is 0.5 μm or more and 10.0 μm or less, and the average particle size (D 50 ) of the lithium transition metal oxide present in the similar single-particle form can be 3.0 μm or more and 15.0 μm or less. The average particle size (D 50 ) of the lithium transition metal oxide present in the similar single-particle form can vary depending on the number and size of the unit particles constituting the similar single-particle. Further, the unit particles constituting the similar single-particle can have a size corresponding to the size of the lithium transition metal oxide present in the single-particle form. That is, the average particle size (D 50 ) of the unit particles constituting the similar single-particle can be 0.5 μm or more and 10.0 μm or less.

[0030] The particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following formula 1. [Formula 1] 0.85 ≦ (D 90 - D 10 ) / D 50 ≦ 1.21 In the formula 1, the particle size at which the volume cumulative amount becomes 10% from the volume cumulative particle size distribution graph obtained by laser diffraction particle size distribution measurement is D 10 , the particle size at which the volume cumulative amount becomes 50% is D 50 , and the particle size at which the volume cumulative amount becomes 90% is D 90 .

[0031] The particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following equation 2. [Formula 2] 1.05≦(D max -D 50 ) / (D 50 -D min ) ≤ 2.35 In the above equation 2, the particle size that accounts for 50% of the cumulative volume is D, as determined from the volume cumulative particle size distribution graph obtained by laser diffraction particle size distribution measurement. 50 Therefore, the minimum particle size in the volume cumulative particle size distribution graph is D min Therefore, the maximum particle size in the volume cumulative particle size distribution graph is D max That is the case.

[0032] The positive electrode active material contains 1% to 10% by volume of fine particles having a particle size of 1 μm or less.

[0033] Furthermore, according to another aspect of the present invention, a positive electrode containing the aforementioned positive electrode active material is provided.

[0034] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided in which the aforementioned positive electrode is used. [Effects of the Invention]

[0035] According to the present invention, the number of unit particles constituting a Mid-Ni type lithium transition metal oxide with a relatively low nickel content (for example, about 70 mol% or less or about 65 mol% or less) can be reduced, thereby improving the lifespan characteristics and stability of a lithium secondary battery using the positive electrode active material as defined in this application.

[0036] Furthermore, according to the present invention, the driving characteristics at high voltage can be improved by controlling the content of fine powder in the positive electrode active material through a crushing process and adjusting the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material.

[0037] Along with the effects described above, the specific effects of the present invention will be described below while explaining the specific matters for carrying out the invention. [Brief explanation of the drawing]

[0038] [Figure 1] Figure 1 shows SEM images (high and low magnification) of the positive electrode active material according to Example 1. [Figure 2] Figure 2 shows SEM images (high and low magnification) of the positive electrode active material according to Example 2. [Figure 3] Figure 3 shows SEM images (high and low magnification) of the positive electrode active material according to Example 3. [Figure 4] Figure 4 shows SEM images (high and low magnification) of the positive electrode active material according to Example 4. [Figure 5] Figure 5 shows SEM images (high and low magnification) of the positive electrode active material according to Example 5. [Figure 6] Figure 6 shows SEM images (high and low magnification) of the positive electrode active material according to Example 6. [Figure 7] Figure 7 shows SEM images (high and low magnification) of the positive electrode active material according to Example 7. [Figure 8] Figure 8 shows SEM images (high and low magnification) of the positive electrode active material according to Comparative Example 1. [Figure 9] Figure 9 shows SEM images (high and low magnification) of the positive electrode active material according to Comparative Example 2. [Figure 10] Figure 10 shows SEM images (high and low magnification) of the positive electrode active material according to Comparative Example 3. [Modes for carrying out the invention]

[0039] For the convenience of understanding the present invention, certain terms are defined herein. Unless otherwise defined herein, scientific and technical terms used herein have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms to include their singular forms.

[0040] (Cathode active material) A positive electrode active material according to one aspect of the present invention allows for reversible intercalation / deintercalation of lithium ions and includes a lithium transition metal oxide.

[0041] The 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 lithium transition metal oxide having a layered crystal structure shows a specific peak in the region where 2θ is 18° to 20° in the rotation pattern obtained from XRD analysis.

[0042] 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 of nickel, cobalt, and manganese.

[0043] Preferably, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel. Alternatively, the lithium transition metal oxide may be a lithium nickel-based composite oxide containing nickel and cobalt.

[0044] In one embodiment, in order to improve the low rate characteristics and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the lithium nickel-based composite oxide may be a ternary lithium transition metal oxide such as so-called NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), in which part of the nickel is replaced with cobalt, manganese, and / or aluminum, or a quaternary lithium transition metal oxide such as NCMA (Ni-Co-Mn-Al). The ternary or quaternary lithium transition metal oxide may further contain dopants other than nickel, cobalt, and manganese.

[0045] In other embodiments, the lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain bulk particle-containing cobalt. The cobalt-free type lithium transition metal oxide may further contain dopants other than nickel and manganese.

[0046] The lithium transition metal oxide as defined in this application is a Mid-Ni type lithium transition metal oxide with a relatively low nickel content. In this application, a lithium transition metal oxide with a nickel content of 70 mol% or less in the transition metal is called a Mid-Ni type lithium transition metal oxide, and a lithium transition metal oxide with a nickel content of more than 70 mol% in the transition metal is defined as a High-Ni type lithium transition metal oxide.

[0047] In one embodiment, the nickel content in the transition metal (the nickel content relative to all elements other than lithium in the lithium transition metal oxide) may be 40 mol% to 70 mol%, 45 mol% to 70 mol%, 50 mol% to 70 mol%, 55 mol% to 65 mol%, or 60 mol% to 65 mol%.

[0048] If the nickel content in the lithium transition metal oxide exceeds 70 mol%, the cation mixing within the crystal structure increases, which can lead to decreased stability and an increase in the amount of unreacted lithium impurities such as LiOH and Li2CO3 on the surface. On the other hand, if the nickel content in the lithium transition metal oxide is less than 40 mol%, phase separation may occur due to other transition metals present in excess (e.g., manganese), and an impurity phase belonging to a space group other than the R-3m space group may be generated. This impurity phase may have a direct impact on the electrochemical properties of the positive electrode active material.

[0049] The cobalt content in the transition metal may be 10 mol% or less, 2.5 mol% to 10 mol%, or 5 mol% to 10 mol%.

[0050] If the cobalt content in the lithium transition metal oxide exceeds 10 mol%, the goal of reducing the cost of the positive electrode active material cannot be achieved. Furthermore, if the cobalt content in the lithium transition metal oxide is excessive, the driving voltage of the lithium secondary battery using the positive electrode active material will be lower, making it difficult to exhibit high output characteristics at relatively high voltages. In addition, if the cobalt content in the lithium transition metal oxide is excessive, the amount of gas generated inside the lithium secondary battery using the positive electrode active material will increase, which may reduce stability.

[0051] The lithium transition metal oxide may be a cobalt-free lithium transition metal oxide that does not contain cobalt in the bulk particles, but it is preferable that it contains at least 2.5 mol% or more in order to smoothly form a layered crystal structure belonging to the R-3m space group.

[0052] When the manganese content in the transition metal exceeds 50 mol%, it may be difficult to form lithium transition metal oxides in single-particle and similar single-particle forms. Excess manganese in the lithium transition metal oxide can cause phase separation, leading to the generation of impurity phases belonging to space groups other than the R-3m space group. These impurity phases may have a direct impact on the electrochemical properties of the positive electrode active material.

[0053] On the other hand, if the manganese content in the lithium transition metal oxide is less than 20 mol%, the stability of the lithium transition metal oxide with a relatively low nickel content (for example, about 70 mol% or less or about 65 mol% or less) as defined in this application may decrease, resulting in a lower drive voltage for the lithium secondary battery using the positive electrode active material, making it difficult to exhibit high output characteristics at relatively high voltages.

[0054] The manganese content may be 20 mol% to 50 mol%, 20 mol% to 45 mol%, 20 mol% to 40 mol%, 25 mol% to 35 mol%, or 27 mol% to 33 mol%.

[0055] The lithium transition metal oxide may have a composition represented by the following chemical formula 1. [Chemical formula 1] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2 [Here, 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 the following inequalities are given: 0.95 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.10, 0.20 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.10, and 0.4 ≤ 1 - (b + c + d) ≤ 0.7.

[0056] The ratio of lithium to all elements other than lithium in the lithium transition metal oxide, a, 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.

[0057] In the aforementioned chemical formula 1, if a is less than 0.95, the capacity of the positive electrode active material containing the lithium transition metal oxide represented by the aforementioned chemical formula 1 may decrease. On the other hand, in the aforementioned chemical formula 1, if a is greater than 1.15, phase separation may be caused by the excess lithium and manganese present in the lithium transition metal oxide, and an impurity phase belonging to a space group other than the R-3m space group may be generated.

[0058] The ratio 1-(b+c+d), which represents the proportion of nickel to all elements other than lithium in the lithium transition metal oxide, 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.

[0059] The ratio b, which represents the proportion of cobalt to all elements other than lithium in the lithium transition metal oxide, 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.

[0060] c, which represents the ratio of manganese to all elements other than lithium in the lithium transition metal oxide, 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.

[0061] If the lithium transition metal oxide contains a dopant, then in chemical formula 1, d is greater than 0. Also, if the lithium transition metal oxide contains a dopant, d, which represents the mole fraction of the dopant relative 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.

[0062] If the lithium transition metal oxide selectively contains 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 can be appropriately selected within a range that does not negatively affect the electrochemical properties and stability of the positive electrode active material.

[0063] The upper and lower limits of the nickel, cobalt, manganese, and dopant content defined in the above chemical formula 1 can be appropriately selected within the range that satisfies the above definition.

[0064] As mentioned above, the lithium transition metal oxide further contains cobalt and manganese as transition metals, and the manganese content in the lithium transition metal oxide may be greater than the cobalt content. However, in conventional Mid-Ni type lithium transition metal oxides, as the manganese content increases compared to the cobalt content, kinetic properties such as lithium ion conductivity tend to decrease, and rate properties tend to decline.

[0065] Accordingly, the present invention is characterized by a small number of unit particles constituting the lithium transition metal oxide in order to improve the efficiency of reversible intercalation / deintercalation of lithium ions by the lithium transition metal oxide and thereby enhance the rate characteristics.

[0066] 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 similar 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.

[0067] The unit particles may have spherical, rod-shaped, elliptical, and / or amorphous shapes. Furthermore, unless specifically intended in the manufacturing process, unit particles of various shapes may exist within the same positive electrode active material. The unit particles refer to particle units that, when observed at a magnification of 5,000x to 20,000x using a scanning electron microscope, appear to have no grain boundaries.

[0068] In other words, the single-particle form consisting of one unit particle means that the lithium transition metal oxide consists of only one unit particle and not in the form of secondary particles formed by the aggregation of multiple unit particles. The average particle size (D) of the lithium transition metal oxide present in the single-particle form is... 50 The particle size can 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.

[0069] The average particle size (D) of the aforementioned unit particle 50 The particle size can be the average of the length in the long axis direction and the length in the short axis direction of the unit particle ([length in the long axis direction + length in the short axis direction] / 2). The average particle size of the unit particle can be calculated as the average of the particle sizes of all unit particles observed from the surface SEM image and / or cross-sectional SEM image of the lithium transition metal oxide.

[0070] If the average particle size of the unit particles is less 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 similar single-particle form. Furthermore, if the average particle size of the unit particles is less than 1.0 μm, the specific surface area of ​​the positive electrode active material containing the lithium transition metal oxide having at least one form selected from the single-particle form consisting of one unit particle and the similar single-particle form in which 30 or fewer unit particles are aggregated becomes larger, which may lead to a decrease in stability due to side reactions with the electrolyte.

[0071] On the other hand, if the average particle size of the unit particles is greater than 8.0 μm, the growth of the unit particles may be excessively induced, which may actually reduce the diffusivity of lithium ions mediated by the unit particles. Furthermore, the distribution of transition metals within the unit particles may become non-uniform due to the characteristics of Mid-Ni type lithium transition metal oxides, which have a relatively large content of transition metals other than nickel.

[0072] Generally, ternary or quaternary lithium transition metal oxides have a secondary particle form in which hundreds or thousands of unit particles are aggregated. The lithium transition metal oxides defined in this application may have a secondary particle form in which multiple unit particles are aggregated, but they also have a similar single particle form in which 30 or fewer, 20 or fewer, or 10 or fewer unit particles are aggregated. Hereinafter, in order to distinguish them 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 similar single particles. Furthermore, the primary particles constituting ternary or quaternary lithium transition metal oxides, which have a conventional secondary particle form, have a smaller particle size than the unit particles defined in this application.

[0073] The average particle size (D) of the lithium transition metal oxide present in the aforementioned similar single-particle form. 50 The average particle size (D) of the lithium transition metal oxide present in the same single-particle form 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. 50 ) can vary depending on the number and size of the unit particles that make up the aforementioned similar single particle.

[0074] Furthermore, the unit particles constituting the similar single particle may have a size corresponding to the size of the lithium transition metal oxide existing in the single particle form. That is, the average particle size (D) of the unit particles constituting the similar single particle. 50The particle size can 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.

[0075] The average particle size (D) of the lithium transition metal oxide present in the aforementioned similar single-particle form. 50 This can be calculated as the average value of the particle sizes of the similar single particles identified from the SEM image.

[0076] In this application, "particle size" is used interchangeably with "particle diameter" or "particle size," and unless otherwise defined, all "average particle size" refers to the particle size corresponding to 50% of the cumulative volume determined by the laser diffraction method described above.

[0077] The particle size distribution of the lithium transition metal oxide among the positive electrode active material can be measured using the laser diffraction method. For example, after dispersing secondary particles in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and after irradiating with ultrasound at approximately 28 kHz with an output of 60 W, a volume cumulative particle size distribution graph is obtained, and the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative amount (D 10 , D 50 , D 90 ), the minimum particle size (D) of the volume cumulative particle size distribution graph. min ) and the maximum particle size (D) in the volume cumulative particle size distribution graph. max It is possible to calculate ).

[0078] The positive electrode active material may include all lithium transition metal oxides in single-particle form and lithium transition metal oxides in similar single-particle form.

[0079] D measured by laser diffraction for the positive electrode active material comprising the lithium transition metal oxide in single-particle form and the lithium transition metal oxide in similar single-particle form. 50The diameters may be 1.0 μm to 12.0 μm, 1.0 μm to 10.0 μm, 1.0 μm to 8.0 μm, 1.0 μm to 7.0 μm, 2.0 μm to 8.0 μm, 2.0 μm to 7.0 μm, 2.0 μm to 6.0 μm, 2.5 μm to 5.5 μm, or 2.7 μm to 5.4 μm. The positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal is 40 mol% or more and 70 mol% or less is the D 50 Within this range, it is possible to achieve the optimal energy density per unit volume.

[0080] D measured by laser diffraction for the positive electrode active material comprising the lithium transition metal oxide in single-particle form and the lithium transition metal oxide in similar single-particle form. 10 The particle size can be between 0.3 μm and 8.0 μm, 0.5 μm and 6.0 μm, 1.0 μm and 5.0 μm, 1.0 μm and 4.0 μm, or 1.0 μm and 3.5 μm.

[0081] D measured for the positive electrode active material by laser diffraction 10 If the particle size is smaller than 0.3 μm, the content of fine particles with a particle size of 1 μm or less in the positive electrode active material may increase. Also, if the particle size distribution for the lithium transition metal oxide is generally D min Shifting to one side can increase the aggregation phenomenon between particles, which can lead to a decrease in energy density per unit volume.

[0082] D measured by laser diffraction for the positive electrode active material comprising the lithium transition metal oxide in single-particle form and the lithium transition metal oxide in similar single-particle form. 90 The diameter may be 1.0 μm to 15.0 μm, 2.0 μm to 12.0 μm, 3.0 μm to 12.0 μm, 4.0 μm to 10.0 μm, or 4.2 μm to 9.5 μm. A positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal is 40 mol% to 70 mol% is the same as described above. 90 Within this range, it is possible to achieve the optimal energy density per unit volume.

[0083] 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.

[0084] The particle size distribution of the lithium transition metal oxide contained in the positive electrode active material can satisfy the following equation 1.

[0085] [Formula 1] 0.85≦(D 90 -D 10 ) / D 50 ≤1.21 In the above formula 1, (D 90 -D 10 ) / D 50 If the value is greater than 1.21, the particle size distribution peak of the lithium transition metal oxide contained in the positive electrode active material is the peak of the particle size distribution observed from the volume cumulative particle size distribution graph, which corresponds to the maximum particle size D max This shows a particle size distribution that has been 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 in the particle size distribution observed from the volume cumulative particle size distribution graph corresponds to the relatively smallest particle size D. min Approaching.

[0086] A positive electrode active material containing a Mid-Ni type lithium transition metal oxide having a nickel content of 40 mol% or more and 70 mol% or less in the transition metal is, in formula 1 above, (D 90 -D 10 ) / D 50 When the value is between 0.85 and 1.21, it can be said that the optimal energy density per unit volume can be achieved.

[0087] Furthermore, the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material can satisfy the following equation 2. [Formula 2] 1.05≦(D max -D 50 ) / (D50 -D min ) ≤ 2.35

[0088] (D max -D 50 ) / (D 50 -D min ) refers to the degree of sharpness of the particle size distribution peak observed from the volume cumulative particle size distribution graph. (D max -D 50 ) / (D 50 -D min If (D) is less than 1.05, it means that the sharpness of the particle size distribution peak observed from the volume cumulative particle size distribution graph is too high. On the other hand, (D max -D 50 ) / (D 50 -D min If the value is greater than 2.35, it means that the uniformity of the particle size distribution and the sharpness of the particle size distribution peaks observed from 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 peaks are too high or too low, there is a risk that the energy density per unit volume will decrease.

[0089] A positive electrode active material containing a Mid-Ni type lithium transition metal oxide with a nickel content of 40 mol% to 70 mol% in the transition metal can exhibit improved lifetime characteristics and stability, as well as enhanced driving characteristics at high voltages, when it satisfies the particle size distributions given by Equations 1 and 2.

[0090] Furthermore, in order to improve the uniformity of the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material, D observed from the volume cumulative particle size distribution graph max -D 90 Preferably, 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.

[0091] D max -D 90 If the particle size is smaller than 0.5 μm, the peak of the particle size distribution observed from the volume cumulative particle size distribution graph is the maximum particle size D. maxShows a particle size distribution shifted to the side. In this case, a positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal is 40 mol% or more and 70 mol% or less may not easily exhibit an optimal energy density per unit volume. On the other hand, D max -D 90 When it is larger than 7.5 μm, the peak of the particle size distribution observed from the volume cumulative particle size distribution graph approaches the relatively minimum particle size D min side, or the uniformity of the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material may decrease.

[0092] To improve the sharpness of the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material, D max -D 50 is preferably 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.

[0093] D max -D 50 When it is smaller than 2.0 μm, the peak of the particle size distribution observed from the volume cumulative particle size distribution graph shows a particle size distribution shifted to the maximum particle size D max side. In this case, a positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal is 40 mol% or more and 70 mol% or less may not easily exhibit an optimal energy density per unit volume. On the other hand, D max -D 50 When it is larger than 10.0 μm, the peak of the particle size distribution observed from the volume cumulative particle size distribution graph approaches the relatively minimum particle size D min side, or the uniformity and sharpness of the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material may decrease.

[0094] D max observed from the volume cumulative particle size distribution graph of the lithium transition metal oxide contained in the positive electrode active material is preferably 15 μm or less.

[0095] The fact that the maximum particle size of the lithium transition metal oxide obtained from the volume cumulative particle size distribution graph for the positive electrode active material exceeds 15 μm means that the growth of the unit particles constituting the lithium transition metal oxide has been excessively induced. When the growth of the unit particles is excessively induced, the diffusivity of lithium ions mediated by the unit particles decreases, which can cause polarization, and the possibility of cracks occurring within the unit particles due to this polarization increases.

[0096] Furthermore, if the maximum particle size of the lithium transition metal oxide exceeds 15 μm, the uniformity and sharpness of the particle size distribution observed from the volume cumulative particle size distribution graph may decrease, potentially leading to a decrease in energy density per unit volume.

[0097] Preferably, 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 1.5% by volume or more and 10% by volume. The fine particles may be the lithium transition metal oxide having a particle size of 1 μm or less. The fine particles can be produced by adjusting the lithium transition metal oxide contained in the positive electrode active material through a crushing process so that it has the particle size distribution described above.

[0098] Generally, 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 preferable for the positive electrode active material to contain as few fine particles as possible. However, in the case of a positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal as defined in this application is 40 mol% or more and 70 mol% or less, the electrochemical properties such as lifetime characteristics can actually be improved when fine particles are included in a predetermined content (e.g., 1 volume% or more). However, if the content of fine particles with a particle size of 1 μm or less in the positive electrode active material exceeds 10 volume%, the capacity characteristics and lifetime characteristics of the positive electrode active material may decrease.

[0099] Similar to the particle size distribution of the lithium transition metal oxide in the positive electrode active material, the content of fine particles with a particle size of 1 μm or less in the positive electrode active material can be measured using the laser diffraction method. For example, after dispersing secondary particles in a dispersion medium, they can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a volume cumulative particle size distribution graph, the volume-based content of fine particles with a particle size of 1 μm or less in the positive electrode active material can be measured by the volume cumulative amount of particles with a particle size of 1 μm or less.

[0100] The average crystallite size of the lithium transition metal oxide as defined in this application is preferably 145 nm to 185 nm. The average crystallite size can be quantitatively analyzed by X-ray diffraction (XRD) analysis using Cu-Kα X-rays on the lithium transition metal oxide. Specifically, the average crystallite size can be calculated by Rietveld refinement on the X-ray diffraction pattern in the 2θ = 10° to 120° region obtained through XRD analysis of the positive electrode active material containing the lithium transition metal oxide.

[0101] A positive electrode active material containing a Mid-Ni type lithium transition metal oxide having a nickel content of 40 mol% to 70 mol% in the transition metal satisfies the particle size distribution according to Equations 1 and 2 and has the average crystallite size described above, and can improve the discharge capacity ratio of a lithium secondary battery using the positive electrode active material.

[0102] (Lithium-ion secondary battery) According to another aspect of the present invention, a positive electrode can be provided that includes 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 positive electrode active materials according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as that described above, for convenience, a detailed explanation will be omitted, and only the remaining undescribed components will be described below.

[0103] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric, etc.

[0104] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0105] In this case, the positive electrode active material may be present in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When present within this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0106] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal 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, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the positive electrode active material layer.

[0107] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15 wt% relative to the total weight of the positive electrode active material layer.

[0108] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except for the use of the positive electrode active material. Specifically, it may be manufactured by coating a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0109] The solvent may be any 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 individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0110] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0111] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0112] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0113] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0114] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0115] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0116] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0117] 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 alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0118] The aforementioned negative electrode active material may be present in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0119] The binder 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, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0120] The conductive material may be added as a component to further improve 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 for example, 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 fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0121] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0122] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0123] Furthermore, the electrolytes 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.

[0124] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0125] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate 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 and discharge performance of the 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 electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0126] The lithium salt may be used without 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, etc. The concentration of the lithium salt is preferably used 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 has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0127] When the electrolyte used in the present application is a solid electrolyte, for example, solid inorganic electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, and halide-based solid electrolytes may be used, and preferably, sulfide-based solid electrolytes may be used.

[0128] As the material of the sulfide-based solid electrolyte, a solid electrolyte containing Li, X element (where 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 (where 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 (where m and n are integers and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In.)

[0129] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or a mixture of amorphous and crystalline materials.

[0130] As a material for oxide-based solid electrolytes, 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 Zn 1-x Examples include GeO4 (LISICON).

[0131] The aforementioned solid electrolyte may be arranged as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Furthermore, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0132] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 wt% to 5 wt% relative to the total weight of the electrolyte.

[0133] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0134] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0135] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0136] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems. [Examples]

[0137] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0138] (Manufacturing Example 1: Manufacturing of Cathode Active Material) (Example 1) Ni synthesized by coprecipitation reaction 0.62 Co 0.06 Mn 0.32 A (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn)molar ratio=1.03) were mixed and heat-treated at 950°C for 10 hours in an air atmosphere to obtain a primary intermediate product (lithium transition metal oxide). Next, the primary intermediate product was crushed using a jet mill at 2 bar and 4,000 rpm to obtain the final product.

[0139] (Example 2) The cathode active material was produced in the same manner as in Example 1, except that the primary intermediate product was crushed using a jet mill at 2 bar and 6,800 rpm.

[0140] (Example 3) The positive electrode active material was produced in the same manner as in Example 1, except that the primary intermediate product was crushed using a jet mill at 2 bar and 9,000 rpm.

[0141] (Example 4) The positive electrode active material was produced in the same manner as in Example 1, except that the primary intermediate product was crushed using a jet mill at 2 bar and 12,000 rpm.

[0142] (Comparative Example 1) The cathode active material was produced in the same manner as in Example 1, except that the lithium transition metal oxide was crushed by a hand-mixing method using a 3L mixer instead of using a jet mill.

[0143] (Comparative Example 2) The cathode active material was produced in the same manner as in Example 1, except that the primary intermediate product was crushed using a jet mill at 1.5 bar and 7,500 rpm.

[0144] (Example 5) Ni synthesized by coprecipitation reaction 0.62 Co 0.06 Mn 0.32 A (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn)molar ratio=1.03) were mixed and heat-treated at 950°C for 10 hours in an air atmosphere to obtain a primary intermediate product (lithium transition metal oxide).

[0145] Next, the primary intermediate product and H3BO3 (weighed out so that the boron content relative to the total transition metals in the primary intermediate product is 0.17 mol%) were mixed and heat-treated at 350°C for 5 hours in an O2 atmosphere to obtain a secondary intermediate product.

[0146] The secondary intermediate product was crushed using a jet mill at 3 bar and 7,000 rpm to obtain the final product.

[0147] (Example 6) The cathode active material was produced 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.

[0148] (Example 7) The cathode active material was prepared 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.

[0149] (Example 8) The positive electrode active material was produced in the same manner as in Example 5, except that the secondary intermediate product was crushed using a jet mill under conditions of 3 bar and 10,000 rpm.

[0150] (Comparative Example 3) The cathode active material was prepared 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.

[0151] (Comparative Example 4) The cathode active material was prepared 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.

[0152] (Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries (Half-Cells)) A cathode slurry was prepared by dispersing 94 wt% of each cathode active material, 3 wt% of carbon black, and 3 wt% of PVDF binder, produced according to Production Example 1, in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0153] A half-cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.15 M.

[0154] (Experimental Example 1: Analysis of the physical properties of the positive electrode active material) (1) Analysis of particle size distribution The particle size distribution of lithium transition metal oxides among the positive electrode active materials produced according to Production Example 1 was analyzed using a known laser diffraction method. Specifically, after dispersing each positive electrode active material in a dispersion medium, an ultrasonic wave of approximately 28 kHz was irradiated at an output of 60 W using a laser diffraction particle size analyzer (Microtrac MT 3000), and a volume cumulative particle size distribution graph was obtained.

[0155] Next, from the 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 volume cumulative particle size distribution graph are determined. min ), the maximum particle size (D) in the volume cumulative particle size distribution graph. max The volume-based content (fine powder content) of fine powder particles with a particle size of 1 μm or less was calculated.

[0156] (2)XRD analysis X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials produced according to Production Example 1, and the average crystallite size of the lithium transition metal oxide contained in the positive electrode active material was calculated.

[0157] XRD analysis was performed using a Bruker D8 Advance diffractometer employing Cu-Kα radiation (1.540598 Å). 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) within the region 2θ = 10° to 120° on a coordinate plane with sinθ on the horizontal axis and βcosθ on the vertical axis, using the Rietveld Refinement method on the diffraction spectrum obtained through X-ray diffraction (XRD) analysis of the positive electrode active material using Cu-Kα radiation.

[0158] The results of the above analysis are shown in Tables 1 and 2 below.

[0159] [Table 1]

[0160] [Table 2]

[0161] (Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries (half-cells)) For lithium secondary batteries (half-cells) manufactured in Manufacturing Example 2, the initial charge capacity, initial discharge capacity, initial efficiency, and 2.0C / 0.1C rate characteristics were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.4V, and a discharge rate of 2.0C / 0.1C.

[0162] Furthermore, the same lithium secondary battery (half-cell) was subjected to 50 charge-discharge cycles using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C and 45°C, with a voltage range of 3.0V to 4.4V and a 1C / 1C current. The ratio of the discharged capacity at the 50th cycle to the initial capacity (cycle capacity retention) was then measured.

[0163] The measurement results are shown in Table 3 below.

[0164] [Table 3]

[0165] Comparing the results of Examples 1 to 4 with those of Comparative Examples 1 and 2, it can be confirmed that the life characteristics of lithium secondary batteries using the positive electrode active materials of Examples 1 to 4, in which the content of fine particles with a particle size of 1 μm or less is 1% to 10% by volume, are improved at room temperature (25°C) and high temperature (45°C).

[0166] Similarly, comparing the results of Examples 5 to 8 with those of Comparative Examples 3 and 4, it can be confirmed that the life characteristics of lithium secondary batteries using the positive electrode active materials of Examples 5 to 8, in which the content of fine particles with a particle size of 1 μm or less is 1% to 10% by volume, are improved at room temperature (25°C) and high temperature (45°C).

[0167] Generally, 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 preferable for the positive electrode active material to contain as few fine particles as possible. However, in the case of a positive electrode active material containing a Mid-Ni type lithium transition metal oxide in which the nickel content in the transition metal as defined in this application is 40 mol% or more and 70 mol% or less, if fine particles are present in a predetermined amount or more, electrochemical properties such as high-temperature lifetime characteristics may actually improve. However, it can be confirmed that if the content of fine particles with a particle size of 1 μm or less in the positive electrode active material exceeds 10 volume%, the capacity characteristics may decrease, and the lifetime characteristics at room temperature (25°C) and high temperature (45°C) may decrease.

[0168] Although embodiments of the present invention have been described above, any person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. It contains lithium transition metal oxides that allow for lithium intercalation / deintercalation, The lithium transition metal oxide comprises at least lithium and a transition metal. The nickel content in the transition metal is 40 mol% or more and 70 mol% or less. A positive electrode active material in which 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.

2. The positive electrode active material according to claim 1, wherein the cobalt content in the transition metal is 10 mol% or less.

3. The positive electrode active material according to claim 1, wherein the manganese content in the transition metal is 20 mol% or more and 50 mol% or less.

4. The lithium transition metal oxide further comprises cobalt and manganese, The positive electrode active material according to claim 1, wherein the manganese content in the transition metal is greater than the cobalt content.

5. The lithium transition metal oxide is represented by the following chemical formula 1, the positive electrode active material according to claim 1. [Chemical formula 1] Li ａ Ni １－（ｂ＋ｃ＋ｄ） Co ｂ Mn ｃ M1 ｄ O ２ [Here, in the 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, and 0.4 ≤ 1 - (b + c + d) ≤ 0.

7.

6. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide has at least one form selected from a single-particle form consisting of one unit particle and a similar single-particle form in which 30 or fewer unit particles are aggregated.

7. The average particle size (D) of the lithium transition metal oxide present in the single-particle form. ５０ The positive electrode active material according to claim 1, wherein the particle size is 1.0 μm or more and 8.0 μm or less.

8. The average particle size (D) of the lithium transition metal oxide present in the aforementioned similar single-particle form. ５０ The positive electrode active material according to claim 1, wherein the particle size is 3.0 μm or more and 12.0 μm or less.

9. The positive electrode active material according to claim 1, wherein the average crystallite size of the lithium transition metal oxide is 145 nm to 185 nm.

10. The positive electrode active material according to claim 1, wherein the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following formula 1. [Formula 1] 0.85≦(D ９０ -D １０ ) / D ５０ ≦1.21 [Here, In the above equation 1, the particle size that represents 10% of the cumulative volume is obtained from the volume cumulative particle size distribution graph obtained by laser diffraction particle size distribution measurement. １０ Therefore, the particle size that accounts for 50% of the cumulative volume is D. ５０ Therefore, the particle size that accounts for 90% of the cumulative volume is D. ９０ That is the case.

11. The positive electrode active material according to claim 1, wherein the particle size distribution of the lithium transition metal oxide contained in the positive electrode active material satisfies the following formula 2. [Formula 2] 1.05≦(D ｍａｘ -D ５０ ) / (D ５０ -D ｍｉｎ )≦2.35 [Here, in Equation 2, the particle size that is 50% of the cumulative volume is obtained from the volume cumulative particle size distribution graph obtained by laser diffraction particle size distribution measurement is D. ５０ Therefore, the minimum particle size in the volume cumulative particle size distribution graph is D ｍｉｎ Therefore, the maximum particle size in the volume cumulative particle size distribution graph is D ｍａｘ That is the case.

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

13. A lithium secondary battery using the positive electrode described in claim 12.

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