Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material with improved discharge capacity and rate characteristics. [Solution] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a positive electrode active material capable of exhibiting improved driving characteristics in a high-voltage operating environment through surface modification of a Mid-Ni type lithium transition metal oxide with a relatively low nickel content, and a lithium secondary battery containing the same.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a positive electrode active material capable of exhibiting improved driving characteristics in a high-voltage operating environment through surface modification of a Mid-Ni type lithium transition metal oxide with a relatively low nickel content, and a lithium secondary battery containing the same. [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 have problems such as 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 synthesis difficult due to the active cation mixing of Li and Ni, but there is also a problem that the rate characteristics and life characteristics of the synthesized cathode active material are very low.

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

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

[0009] The higher the content of lithium impurities remaining on the surface of the lithium transition metal oxide, the more likely it is to promote gas generation and swelling phenomena in a lithium secondary battery using the lithium transition metal oxide as a cathode active material. In addition, the higher the content of lithium impurities remaining on the surface of the lithium transition metal oxide, when manufacturing a paste for forming a cathode active material layer using the lithium transition metal oxide, there is a problem that the paste composition gels due to the lithium impurities.

[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, while lithium-ion batteries using lithium iron phosphate (LFP) have traditionally been the primary choice due to safety considerations, there is 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. Furthermore, 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 is accompanied by problems such as a decrease in electrochemical properties, particularly low-temperature power characteristics, making it unsuitable for exhibiting appropriate driving characteristics in high-voltage operating environments.

[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), which improves the electrochemical properties that are inferior to those of High-Ni type lithium transition metal oxides with a relatively high nickel content through surface modification of the lithium transition metal oxide.

[0020] In particular, the present invention aims to provide a positive electrode active material with improved discharge capacity and rate characteristics by forming a tungsten-containing coating layer on the surface of the lithium transition metal oxide.

[0021] Furthermore, 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), which reduces surface residual lithium through surface modification of the lithium transition metal oxide and suppresses surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, thereby improving stability.

[0022] Another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined in this application.

[0023] 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]

[0024] According to one aspect of the present invention, a positive electrode active material is provided that reduces surface residual lithium, suppresses surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, and improves stability by comprising: a lithium transition metal oxide having a crystal structure belonging to the R-3m space group and having a nickel content of 40 mol% or more and 70 mol% or less in the transition metal; and a tungsten-containing coating layer located on the surface of the lithium transition metal oxide.

[0025] Furthermore, according to the present invention, a positive electrode active material is provided in which the discharge capacity and rate characteristics are improved through surface modification of the lithium transition metal oxide.

[0026] The positive electrode active material as defined in this application can have a lattice strain of 0.00025 or less, calculated by Rietveld refinement on the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material, by forming a tungsten-containing coating layer on the surface of the lithium transition metal oxide.

[0027] 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%.

[0028] 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%.

[0029] 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.

[0030] 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 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.

[0031] As defined in this application, the rate characteristics tend to decrease as the manganese content in a Mid-Ni type lithium transition metal oxide with a relatively low nickel content increases compared to the cobalt content, due to a decrease in surface kinetic properties such as lithium ion conductivity.

[0032] In this invention, by forming a tungsten-containing coating layer on the surface of the lithium transition metal oxide, the efficiency of reversible intercalation / deintercalation of lithium ions by the lithium transition metal oxide can be improved, thereby improving the electrochemical properties which are inferior to those of high-Ni type lithium transition metal oxides with a relatively high nickel content.

[0033] Furthermore, 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 high-Ni type lithium transition metal oxides with a relatively high nickel content, 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.

[0034] The average particle size (D) of the lithium transition metal oxide present in the single-particle form. 50 ) is 0.5 μm or more and 10.0 μm or less, and the average particle size (D) of the lithium transition metal oxide present in the similar single-particle form is 0.5 μm or more and 10.0 μm or less. 50) 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.

[0035] Further, the lithium transition metal oxide having at least one form selected from the single particle form composed of one unit particle and the similar single particle form in which 30 or less unit particles are aggregated can have a larger average crystallite size than the lithium transition metal oxide in the multi-particle form.

[0036] The average crystallite size can be calculated through Rietveld refinement for the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays for the positive electrode active material. The average crystallite size of the lithium transition metal oxide defined in the present application can be 160 nm to 200 nm.

[0037] The coating layer can be formed in an island form that discontinuously occupies the surface of the lithium transition metal oxide.

[0038] Further, according to another aspect of the present invention, a positive electrode including the above-described positive electrode active material is provided.

[0039] Further, according to still another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

Advantages of the Invention

[0040] 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.

[0041] Furthermore, according to the present invention, surface residual lithium can be reduced through surface modification of 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), suppress surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, and suppress and / or mitigate the swelling phenomenon of lithium secondary batteries caused by gas generation.

[0042] Generally, compared to positive electrode active materials containing high-Ni type lithium transition metal oxides with a nickel content exceeding 70 mol%, positive electrode active materials containing mid-Ni type lithium transition metal oxides with a relatively low nickel content (e.g., approximately 70 mol% or less, or approximately 65 mol% or less) suffer from problems with reduced electrochemical properties related to the output of lithium secondary batteries, such as capacity characteristics and rate characteristics. Therefore, they are not suitable for exhibiting appropriate driving characteristics in high-voltage operating environments.

[0043] Furthermore, in Mid-Ni type lithium transition metal oxides with relatively low nickel content, the manganese content increases compared to the cobalt content, and the kinetic properties such as lithium ion conductivity tend to decrease, while the capacity and rate characteristics also tend to decline.

[0044] According to the present invention, a positive electrode active material with particularly improved discharge capacity and rate characteristics can be provided by forming a tungsten-containing coating layer on the surface of a Mid-Ni type lithium transition metal oxide having a relatively low nickel content (for example, about 70 mol% or less or about 65 mol% or less) through low-temperature heat treatment.

[0045] 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]

[0046] [Figure 1] Figure 1 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 1. [Figure 2] Figure 2 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 2. [Figure 3] Figure 3 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 3. [Figure 4] Figure 4 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 4. [Figure 5] Figure 5 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 1. [Figure 6] Figure 6 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 2. [Figure 7] Figure 7 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 3. [Figure 8] Figure 8 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 4. [Figure 9] Figure 9 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 5. [Figure 10] Figure 10 shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 6. [Figure 11] Figure 11 shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 2. [Figure 12] Figure 12 shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 3. [Figure 13]Figure 13 shows a surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 2. [Figure 14] Figure 14 shows the surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 2. [Figure 15] Figure 15 shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 3. [Figure 16] Figure 16 shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 4. [Modes for carrying out the invention]

[0047] 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.

[0048] (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.

[0049] 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 diffraction pattern obtained from XRD analysis.

[0050] 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.

[0051] 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.

[0052] 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) or a quaternary lithium transition metal oxide such as NCMA (Ni-Co-Mn-Al), in which a portion of the nickel is replaced with cobalt, manganese, and / or aluminum. The ternary or quaternary lithium transition metal oxide may further contain dopants other than nickel, cobalt, manganese, and aluminum.

[0053] In other embodiments, the lithium transition metal oxide may be a cobalt-free type lithium transition metal oxide that does not contain cobalt in the bulk particles. The cobalt-free type lithium transition metal oxide may further contain dopants other than nickel, cobalt, and manganese.

[0054] 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.

[0055] 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%.

[0056] When 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 content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface. In particular, the higher the nickel content in the lithium transition metal oxide, the more rapidly the stability may decrease in high-voltage operating environments. On the other hand, when 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 of nickel (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 deterioration of the electrochemical properties of the positive electrode active material.

[0057] 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%.

[0058] 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, structural instability may occur at high charge levels, leading to reduced stability in high-voltage operating environments.

[0059] The lithium transition metal oxide may be a cobalt-free type 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.

[0060] 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%. The difference between the manganese content and the cobalt content in the transition metal is preferably 10 mol% or more.

[0061] If the manganese content in the lithium transition metal oxide exceeds 50 mol%, the charge / discharge capacity and energy density of the positive electrode active material may decrease. Furthermore, since manganese is easily dissolved at high voltage, if the manganese content in the lithium transition metal oxide becomes excessive, the amount of manganese leached from the positive electrode in a high-voltage operating environment will increase, which may cause a long-term deterioration in the performance and lifespan characteristics of the lithium secondary battery.

[0062] Furthermore, if the manganese content in the lithium transition metal oxide exceeds 50 mol%, it may be difficult to form single-particle and similar single-particle forms of lithium transition metal oxide. The excess manganese present in the lithium transition metal oxide may cause phase separation, resulting in 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 degradation of the electrochemical properties of the positive electrode active material.

[0063] 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.

[0064] 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 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 apply: 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.

[0065] The molar ratio of lithium to all other elements in the lithium transition metal oxide, a, can 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.

[0066] If a in the aforementioned chemical formula 1 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, if a in the aforementioned chemical formula 1 is greater than 1.15, phase separation may occur due to 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.

[0067] In the aforementioned chemical formula 1, 1-(b+c+d), which represents the molar ratio 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.

[0068] In the aforementioned chemical formula 1, b, which represents the molar ratio 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.

[0069] In the aforementioned chemical formula 1, c, which represents the molar 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.

[0070] In the above chemical formula 1, M1 represents a dopant doped into the lithium transition metal oxide. The lithium transition metal oxide has a layered crystalline structure in which lithium layers containing lithium and transition metal layers containing transition metals are arranged alternately, and the dopant may exist in a doped state within the crystal lattice of the lithium transition metal oxide (at least one of the lithium layers and / or transition metal layers).

[0071] When the lithium transition metal oxide contains a dopant, the molar ratio d in chemical formula 1, which represents the ratio of the dopant to all elements other than lithium in the lithium transition metal oxide, is greater than 0.

[0072] If the lithium transition metal oxide contains a dopant, d, which represents the mole fraction of the dopant relative to all metal elements other than lithium in the lithium transition metal oxide in chemical formula 1, 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.

[0073] Furthermore, as will be described later, a coating layer exists on the surface of the lithium transition metal oxide. The coating layer contains tungsten. If the tungsten contained in the coating layer formed on the surface of the lithium transition metal oxide diffuses into the unit particles constituting the lithium transition metal oxide and dops them, then in the chemical formula 1, d, which represents the molar ratio of the dopant to all elements other than lithium in the lithium transition metal oxide, is greater than 0, and M1 contains tungsten.

[0074] 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, W, and Zr. The type, combination, and content 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.

[0075] The upper and lower limits of the content (molar ratio) of nickel, cobalt, manganese, and dopant as defined in Chemical Formula 1 can be appropriately selected within the range that satisfies the aforementioned definition.

[0076] 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, the kinetic properties such as lithium ion conductivity tend to decrease, and the rate properties tend to decline.

[0077] 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.

[0078] Furthermore, the fewer the number of unit particles constituting the lithium transition metal oxide, the lower the specific surface area of ​​the positive electrode active material containing the lithium transition metal oxide, which reduces surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, thereby improving the lifespan characteristics of the lithium secondary battery using the positive electrode active material containing the lithium transition metal oxide.

[0079] Specifically, the lithium transition metal oxide can 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 can be interpreted in the same sense as a primary particle.

[0080] The single particle may have a spherical, rod-shaped, elliptical, and / or amorphous shape. Furthermore, unless specifically intended in the manufacturing process, unit particles of various shapes may exist within the same cathode active material. The unit particle refers to a particle unit that, when observed at a magnification of 5,000x to 20,000x using a scanning electron microscope, appears to have no grain boundaries.

[0081] 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 a secondary particle form in which multiple unit particles are aggregated. 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.

[0082] 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.

[0083] 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.

[0084] 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 can 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.

[0085] Generally, ternary or quaternary lithium transition metal oxides have a secondary particle morphology in which hundreds or thousands of unit particles are aggregated. The lithium transition metal oxides defined in this application may have a secondary particle morphology in which multiple unit particles are aggregated, but they also have a similar single-particle morphology 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 can be called similar single particles. Furthermore, the primary particles constituting ternary or quaternary lithium transition metal oxides, which have a conventional secondary particle morphology, have a smaller particle size than the unit particles defined in this application.

[0086] 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.

[0087] 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. 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.

[0088] 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.

[0089] 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.

[0090] 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 ).

[0091] The positive electrode active material may contain all of the lithium transition metal oxides in single-particle form and lithium transition metal oxides in similar single-particle form.

[0092] D measured by laser diffraction for the cathode active material comprising the lithium transition metal oxide in single-particle form and the lithium transition metal oxide in similar single-particle form. 50 The 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.

[0093] Generally, compared to cathode active materials containing high-Ni lithium transition metal oxides with a nickel content exceeding 70 mol%, cathode active materials containing mid-Ni lithium transition metal oxides with a relatively low nickel content (e.g., approximately 70 mol% or less, or approximately 65 mol% or less) are not suitable for exhibiting appropriate driving characteristics in high-voltage operating environments because they suffer from a decrease in electrochemical properties related to the output of lithium secondary batteries, such as capacity characteristics and rate characteristics.

[0094] Furthermore, in Mid-Ni type lithium transition metal oxides with relatively low nickel content, the manganese content increases compared to the cobalt content, and the kinetic properties such as lithium ion conductivity tend to decrease, while the capacity and rate characteristics also tend to decline.

[0095] Accordingly, according to the present invention, discharge capacity and rate characteristics can be improved by forming a tungsten-containing coating layer through surface modification of 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).

[0096] Furthermore, according to the present invention, surface residual lithium can be reduced through surface modification of 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), suppress surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, and suppress and / or mitigate the swelling phenomenon of lithium secondary batteries caused by gas generation.

[0097] The tungsten-containing coating layer may also contain lithium-tungsten oxide represented by the following chemical formula 2. [Chemical formula 2] Li e W f O g In Chemical Formula 2, 0 < e ≦ 8, 0 < f ≦ 15, and 0 < g ≦ 20, where e, f, and g represent numbers determined from the stoichiometric ratio based on the valence (oxidation number) and equivalent weight of tungsten. Non-limiting examples of the lithium tungsten-containing oxide include LiWO3, Li2WO4, Li3WO4, Li3WO6, Li4WO5, Li6WO6, Li8WO6, and the like.

[0098] The tungsten-containing coating layer can be formed by the reaction of residual lithium present on the surface of the lithium transition metal oxide with the tungsten-containing raw material substance through heat treatment of a mixture of a tungsten-containing raw material substance such as WO3 or W2O5 and the lithium transition metal oxide.

[0099] When the heat treatment temperature for a mixture of 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) and the tungsten-containing raw material substance is excessively high (for example, 500 °C or higher), the tungsten contained in the tungsten-containing raw material substance may diffuse and dope into the lithium transition metal oxide, making it difficult to form a tungsten-containing coating layer on the surface of the lithium transition metal oxide. On the other hand, when the heat treatment temperature for a mixture of 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) and the tungsten-containing raw material substance is excessively low (for example, less than 300 °C), the residual lithium present on the surface of the lithium transition metal oxide and the tungsten-containing raw material substance do not react sufficiently, not only resulting in an insufficient effect of reducing surface residual lithium but also allowing the tungsten-containing raw material substance to exist as an impurity on the surface.

[0100] The tungsten content, calculated based on all metallic elements excluding lithium present in the positive electrode active material, may be greater than 0.1 mol% and less than 0.5 mol%, 0.15 mol% or more and 0.45 mol%, 0.2 mol% or more and 0.4 mol%, or 0.2 mol% or more and 0.3 mol%. The tungsten content present in the tungsten-containing coating layer can be calculated through ICP analysis of the positive electrode active material.

[0101] Specifically, the ICP analysis method is a method for measuring the elemental content contained in the positive electrode active material by a known method using an inductively coupled plasma spectrometer (ICP). The tungsten content measured through the ICP analysis method reflects the tungsten content (design composition) used in the manufacturing process of the positive electrode active material, even considering the margin of error.

[0102] When the tungsten content, calculated based on all metal elements excluding lithium present in the positive electrode active material, is 0.1 mol% or less, not only is the effect of reducing surface residual lithium insufficient, but a sufficient tungsten-containing coating layer is not formed on the surface, resulting in insufficient improvement in the capacity characteristics and rate characteristics of Mid-Ni type lithium transition metal oxides with relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less).

[0103] On the other hand, if the tungsten content, calculated based on all metal elements excluding lithium present in the positive electrode active material, is 0.5 mol% or more, the surface kinetic properties of the Mid-Ni type lithium transition metal oxide with a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less) may change. For example, the ionic conductivity or electrical conductivity of the lithium transition metal oxide may decrease, suppressing the interaction between the lithium transition metal oxide and the electrolyte, which can make it difficult to achieve sufficient activation during initial charging.

[0104] The coating layer may be formed continuously and / or discontinuously on the surface of the lithium transition metal oxide. For example, the coating layer may be formed in an island form that discontinuously occupies the surface of the lithium transition metal oxide.

[0105] If the lithium transition metal oxide has a secondary particle morphology in which at least two unit particles are aggregated, the coating layer may be formed in the gaps between adjacent unit particles and / or at grain boundaries corresponding to the contact surfaces of adjacent unit particles. The presence of the coating layer in the gaps between adjacent unit particles means that the oxide and / or lithium composite oxide constituting the coating layer exist in a form that fills the gaps between adjacent unit particles.

[0106] Furthermore, if the lithium transition metal oxide has a secondary particle morphology in which at least two unit particles are aggregated, the coating layer can diffuse in a direction toward the center of the secondary particles along the gaps between adjacent unit particles and / or grain boundaries corresponding to the contact surfaces of adjacent unit particles. In this case, the tungsten contained in the coating layer can exhibit a concentration gradient that decreases in the direction toward the center of the secondary particles from the surface of the secondary particles.

[0107] Furthermore, in Mid-Ni type lithium transition metal oxides defined in this application, the nickel content is relatively low (for example, about 70 mol% or less or about 65 mol% or less), and the manganese content is greater than the cobalt content (in particular, the difference between the manganese content and the cobalt content among the transition metals is 10 mol% or more), and the lattice strain may increase to the extent that the distribution of transition metals within the composition becomes non-uniform or the stability of the crystal structure decreases.

[0108] The less stable the crystal structure of the lithium transition metal oxide, the more irregular the crystallite size or the distance between adjacent crystallites constituting the lithium transition metal oxide may become. The lattice strain is one indicator of the regularity of the crystallites, and the greater the irregularity of the crystallites, the greater the lattice strain may become.

[0109] For example, if the heat treatment temperature for a mixture of a Mid-Ni type lithium transition metal oxide with a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less) and the tungsten-containing raw material is excessively high (e.g., 500°C or higher), the tungsten contained in the tungsten-containing raw material may diffuse and dope into the lithium transition metal oxide, potentially increasing the lattice strain.

[0110] The lattice strain ε can be calculated from the diffraction spectrum obtained through Cu-kα X-ray diffraction (XRD) analysis of the positive electrode active material using a variety of known methods. For example, the lattice strain ε can be calculated from the diffraction spectrum obtained through Cu-kα X-ray diffraction (XRD) analysis of the positive electrode active material using Rietveld refinement or the Williamson-Hall method. The lattice strain is expressed as Δd / d, and as the lattice strain ε increases, it can cause structural displacement of atoms and induce broadening of the diffraction peak. The Williamson-Hall method proposes a method for extracting information about crystallite size and lattice strain from the integrated width of the diffraction peak.

[0111] The lattice strain ε, expressed as Δd / d, can be expressed as 1 / 4 of the gradient of a straight line obtained by plotting the diffraction angle θ (rad) and half-width β (rad) within the region 2θ = 10° to 120° on a coordinate plane where the horizontal axis is sinθ and the vertical axis is βcosθ (or it can be expressed as β / 4tanθ).

[0112] Furthermore, the lattice strain ε can be calculated using the following formula. βcosθ = 4εsinθ + 0.9λ / D

[0113] In the above formula, β is the full width at half maximum, θ is the diffraction angle, λ is the X-ray wavelength (Å) used for XRD analysis, and D is the crystallite size of the lithium transition metal oxide. The lattice strain ε can be calculated from the intercept and slope of the straight line obtained by plotting the values ​​calculated by the above formula.

[0114] The lattice strain of Mid-Ni type lithium transition metal oxides, defined in this application, having a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less) and a manganese content greater than the cobalt content, can be reduced through surface modification performed under predetermined conditions.

[0115] Preferably, the lattice strain calculated by Rietveld refinement on the diffraction spectrum obtained by X-ray diffraction (XRD) analysis using Cu-kα rays for the positive electrode active material containing a Mid-Ni type lithium transition metal oxide, which has a relatively low nickel content (e.g., about 70 mol% or less or about 65 mol% or less) and a manganese content greater than the cobalt content, is 0.00025 or less.

[0116] Furthermore, the average crystallite size of the lithium transition metal oxide calculated using the method described above may be between 160 nm and 200 nm.

[0117] If the average crystallite size is less than 160 nm or greater than 200 nm, the improvement in electrochemical properties such as capacity characteristics and rate characteristics of a lithium secondary battery using the lithium transition metal oxide as the positive electrode active material is extremely small. If the growth of the unit particles constituting the lithium transition metal oxide is insufficient, the average crystallite size may be less than 160 nm. If the average crystallite size is greater than 200 nm, the resistance may increase, causing polarization, which may lead to the occurrence of intraparticle cracks, ultimately resulting in a reduction in the lifespan of the positive electrode active material.

[0118] The average Ni occupancy within the Li3a site, calculated by Rietveld refinement on the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material, may be less than 3.5%, 3.4% or less, 3.35% or less, or 3.34% or less.

[0119] In this application, the average Ni occupancy within the Li3a site can be varied by the growth of the unit particles constituting the lithium transition metal oxide or by the results of surface modification of the lithium transition metal oxide.

[0120] The average Ni occupancy within the Li3a site is an indicator of the degree of cation mixing (cation mixing of lithium and nickel) between the lithium layer and the transition metal layer. The larger the average Ni occupancy within the Li3a site, the greater the lattice strain can be.

[0121] (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 configurations will be described below.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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 drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0141] 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.

[0142] 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.

[0143] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0144] 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, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent electrolyte performance.

[0145] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. 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 within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0146] In the present invention, when the electrolyte used is a solid electrolyte, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, oxide-based solid electrolyte, nitride-based solid electrolyte, or halogen-based solid electrolyte may be used, and preferably a sulfide-based solid electrolyte may be used.

[0147] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (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, and Li2S-P2S5-Z. m S n (Here, 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.)

[0148] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or a mixture of amorphous and crystalline materials.

[0149] 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).

[0150] 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 partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0151] 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 like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate 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.

[0152] 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).

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] (Manufacturing Example 1: Manufacturing of Cathode Active Material) (Example 1) Ni synthesized by coprecipitation reaction 0.62 Co 0.07 Mn 0.31 A (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn)molar ratio=1.04) were mixed and heat-treated in a furnace under an air atmosphere at 950°C for 10 hours to obtain an intermediate product (lithium transition metal oxide).

[0158] Next, the intermediate product and WO3 (weighed out so that the tungsten content relative to the total transition metal in the intermediate product is 0.3 mol%) were mixed, and the mixture was heat-treated in a furnace in an air atmosphere at 350°C for 8 hours to obtain a final product in which a tungsten-containing coating layer was formed on the surface of the lithium transition metal oxide.

[0159] As can be seen from the surface SEM image in Figure 1, the positive electrode active material according to Example 1 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0160] (Example 2) The cathode active material was produced in the same manner as in Example 1, except that the heat treatment temperature for the mixture of the intermediate product and WO3 was set to 375°C.

[0161] As can be seen from the surface SEM image in Figure 2, the positive electrode active material according to Example 2 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0162] (Example 3) The positive electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature for the mixture of the intermediate product and WO3 was set to 400°C.

[0163] As can be seen from the surface SEM image in Figure 3, the positive electrode active material according to Example 3 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0164] (Example 4) A positive electrode active material was produced in the same manner as in Example 1, except that the intermediate product was mixed with WO3 so that the tungsten content relative to the total transition metals in the intermediate product was 0.2 mol%.

[0165] As can be seen from the surface SEM image in Figure 4, the positive electrode active material according to Example 4 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0166] (Comparative Example 1) Ni synthesized by coprecipitation reaction 0.62 Co 0.07 Mn 0.31The (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn)molar ratio=1.04) were mixed and heat-treated at 950°C for 10 hours in an air atmosphere to obtain the final product.

[0167] As can be seen from the surface SEM image in Figure 5, the positive electrode active material according to Comparative Example 1 includes lithium transition metal oxides in single-particle form and similar single-particle form.

[0168] (Comparative Example 2) Ni synthesized by coprecipitation reaction 0.62 Co 0.07 Mn 0.31 A (OH)2 hydroxide precursor and LiOH (Li / (Ni+Co+Mn)molar ratio=1.04) were mixed and heat-treated at 850°C for 10 hours in an air atmosphere to obtain an intermediate product (lithium transition metal oxide).

[0169] Next, the intermediate product and WO3 (weighed so that the tungsten content relative to the total transition metal in the intermediate product is 0.3 mol%) were mixed and heat-treated in a furnace in an air atmosphere at 375°C for 8 hours to obtain a final product in which a tungsten-containing coating layer was formed on the surface of the lithium transition metal oxide.

[0170] As can be seen from the surface SEM image in Figure 6, the positive electrode active material in Comparative Example 2 contains a lithium transition metal oxide in a multi-particle form with more than 30 unit particles. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0171] (Comparative Example 3) The positive electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature for the mixture of the intermediate product and WO3 was set to 250°C.

[0172] As can be seen from the surface SEM image in Figure 7, the positive electrode active material in Comparative Example 3 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0173] (Comparative Example 4) The cathode active material was produced in the same manner as in Example 1, except that the heat treatment temperature for the mixture of the intermediate product and WO3 was set to 650°C.

[0174] As can be seen from the surface SEM image in Figure 8, the positive electrode active material in Comparative Example 4 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0175] (Comparative Example 5) A positive electrode active material was produced in the same manner as in Example 1, except that the intermediate product was mixed with WO3 so that the tungsten content relative to the total transition metals in the intermediate product was 0.1 mol%.

[0176] As can be seen from the surface SEM image in Figure 9, the positive electrode active material in Comparative Example 5 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0177] (Comparative Example 6) A positive electrode active material was produced in the same manner as in Example 1, except that the intermediate product was mixed with WO3 so that the tungsten content relative to the total transition metals in the intermediate product was 0.5 mol%.

[0178] As can be seen from the surface SEM image in Figure 10, the positive electrode active material in Comparative Example 6 contains lithium transition metal oxides in single-particle and similar single-particle forms. ICP analysis of the final product confirmed that the tungsten content in the final product was consistent with the designed composition.

[0179] (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.

[0180] 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.

[0181] (Experimental Example 1. Analysis of surface-modified positive electrode active material) Referring to Figures 1 to 10, which show surface SEM images of the positive electrode active material (lithium transition metal oxide) from the examples and comparative examples manufactured in Manufacturing Example 1, it can be confirmed that a coating layer formed in an island form exists on the surface of the surface-modified lithium transition metal oxide. Furthermore, referring to Figure 6, it can be confirmed that the positive electrode active material from Comparative Example 2 has a multi-particle form with more than 30 unit particles, unlike the other examples and comparative examples.

[0182] SEM / EDS analysis was performed using the following method. First, the lithium transition metal oxides contained in each cathode active material produced by Production Example 1 were sorted. Then, the lithium transition metal oxides were cross-sectionally treated using a FIB (Ga-ion source), and cross-sectional FE-SEM images were taken with a scanning electron microscope. Next, the target element, tungsten (W), was mapped to the cross-sectional FE-SEM images using EDS mapping, and the distribution of tungsten within the particles was analyzed.

[0183] Referring to Figures 11 and 12, which show cross-sectional SEM / EDS images of the positive electrode active material (lithium transition metal oxide in a similar single-particle form) according to Example 2 and Example 3, it can be confirmed that a tungsten-containing coating layer was uniformly formed at the interface or gap between unit particles. Furthermore, referring to Figure 13, which shows a surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide in a similar single-particle form) according to Example 2, it can be confirmed that tungsten is uniformly distributed on the surface of the unit particles, and through this, it can be seen that a tungsten-containing coating layer was uniformly formed on the surface of the unit particles.

[0184] On the other hand, referring to Figure 14, which shows a surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide in a similar single-particle form) according to Comparative Example 2, it can be confirmed that aggregation of the coating material (tungsten) occurred on the surface of the unit particles. Furthermore, referring to Figure 15, which shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide in a similar single-particle form) according to Comparative Example 3, it can be confirmed that aggregation of the coating material occurred at the interface or gaps between unit particles. This is presumed to be because, when forming the tungsten-containing coating layer on the surface of the lithium transition metal oxide, the amount of heat supplied was insufficient, resulting in insufficient diffusion of the coating material and conversion to the coating layer.

[0185] Referring to Figure 16, which shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide in a similar single-particle form) according to Comparative Example 4, it can be confirmed that although there is no aggregation of the coating material at the interface or gaps between unit particles, a large amount of the coating material has diffused into the unit particles. Thus, when tungsten introduced as a coating material diffuses into and dops the unit particles constituting the lithium transition metal oxide, the lattice strain of the lithium transition metal oxide changes.

[0186] (Experimental Example 2. XRD Analysis of Cathode Active Material) X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials manufactured according to Manufacturing Example 1 to analyze the crystallographic properties of the lithium transition metal oxide and tungsten-containing coating layer contained in the positive electrode active material.

[0187] Specifically, the XRD analysis was performed using a Bruker D8E Endeavor diffractometer with Cu-kα radiation (1.540598 Å). The presence or absence of a phase corresponding to lithium-tungsten oxide (Li2WO4) in the region of 2θ = 20.0° to 22.0° and a phase corresponding to tungsten oxide (WO3) in the region of 2θ = 22.5° to 25.0° was confirmed from the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material.

[0188] Furthermore, lattice strain and average crystallite size were calculated from the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material. The lattice strain and average crystallite size were calculated from a straight line obtained by plotting the diffraction angle θ (rad) and full width at half maximum β (rad) in the region 2θ = 10° to 120° on a coordinate plane with sinθ on the horizontal axis and βcosθ on the vertical axis, using Rietveld refinement on the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material. The lattice strain ε, expressed as Δd / d, was calculated as 1 / 4 of the slope of the straight line (or can be expressed as β / 4tanθ).

[0189] Similarly, the average Ni occupancy within the Li3a site was calculated by Rietveld refinement of the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material.

[0190] The results of the aforementioned XRD analysis are shown in Table 1 below. [Table 1]

[0191] "O" indicates that the corresponding diffraction peak was clearly detected, "△" indicates that the corresponding diffraction peak was weakly detected, and "X" indicates that no diffraction peak was detected.

[0192] Referring to the results in Table 1, it can be confirmed that the positive electrode active materials from Examples 1 to 4 do not contain the phase corresponding to WO3, but do contain the phase corresponding to Li2WO4. That is, it can be expected that there is no unreacted WO3 in the positive electrode active materials from Examples 1 to 4, and that a Li2WO4-containing coating layer is formed. The lattice strain (ε) measured from the positive electrode active materials from Examples 1 to 4 is 0.00025 or less, the average crystallite size is 160 to 200 nm, and the Ni occupancy is less than 3.5%.

[0193] Considering that the lattice strain (ε) measured from the positive electrode active material of Comparative Example 1, which was not surface modified, was 0.00041 or less, and the Ni occupancy was 4.86%, it can be confirmed that the lattice strain of the lithium transition metal oxide can be relaxed and the Ni occupancy reduced through the surface modification presented in this application.

[0194] Unlike the positive electrode active materials of Examples 1 to 4, the lattice strain (ε) measured from the positive electrode active material of Comparative Example 2, which has a multi-particle morphology, was 0.00035, the average crystallite size was 147.51 nm, and the Ni occupancy was 4.75%.

[0195] It can be confirmed that the positive electrode active material in Comparative Example 3 does not contain the phase corresponding to Li2WO4, but does contain the phase corresponding to WO3. This is presumed to be because, when forming the tungsten-containing coating layer on the surface of the lithium transition metal oxide, the amount of heat supplied was insufficient, preventing WO3 from reacting sufficiently with lithium. The lattice strain (ε) measured from the positive electrode active material in Comparative Example 3 was 0.00030, and the Ni occupancy was 3.67%.

[0196] The positive electrode active material of Comparative Example 4, like the positive electrode active material of Comparative Example 1, did not contain phases corresponding to WO3 and Li2WO4. This is presumably because the tungsten introduced as a coating material diffused into the unit particles and doped them, rather than forming a coating layer on the surface of the lithium transition metal oxide. As previously predicted, the lattice strain (ε) measured from the positive electrode active material of Comparative Example 4 was 0.00040 due to the diffusion of tungsten within the unit particles, and the Ni occupancy was 4.04%.

[0197] Furthermore, in the positive electrode active material of Comparative Example 5, the intensity of the peaks corresponding to the WO3 phase and the Li2WO4 phase were both detected as very weak. This is presumed to be because the amount of tungsten (WO3) introduced as a coating material was excessively low, resulting in the inability to properly form a Li2WO4-containing coating layer. In the positive electrode active material of Comparative Example 6, the amount of tungsten (WO3) introduced as a coating material was excessively high, and it can be confirmed that unreacted WO3 was present.

[0198] The lattice strain (ε) measured from the positive electrode active material in Comparative Example 5 was 0.00029, and the lattice strain (ε) measured from the positive electrode active material in Comparative Example 6 was 0.00027. This confirms that the tungsten content used to coat the surface of the lithium transition metal oxide can affect the lattice strain of the lithium transition metal oxide.

[0199] (Experimental Example 3. 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.

[0200] The measurement results are shown in Table 2 below. [Table 2]

[0201] Referring to the results in Table 2 above, it can be confirmed that the discharge capacity and rate characteristics of lithium secondary batteries using the positive electrode active materials of Examples 1 to 4 were particularly improved. Furthermore, compared to Comparative Example 2, which contains a multi-particle form of lithium transition metal oxide, it can be confirmed that the capacity characteristics, initial efficiency, and rate characteristics of lithium secondary batteries using the positive electrode active materials of Examples 1 to 4 did not decrease, or were even improved.

[0202] (Experimental Example 4. Analysis of Residual Lithium in the Cathode Active Material) The residual lithium content in each cathode active material produced according to Production Example 1 was quantitatively analyzed using a known method. Specifically, 5 g of each cathode active material produced according to Production Example 1 and 100 g of deionized water were placed in a 300 mL beaker, and then stirred at a speed of 300 rpm for 15 minutes using a magnetic bar.

[0203] After filtering using a vacuum flask, 50 g was taken out. The taken solution was placed in an auto titrator container and automatically titrated with 0.1 N HCl, following the Wader Method, to measure the LiOH and Li2CO3 levels in the solution.

[0204] The results of the residual lithium analysis are shown in Table 3 below. [Table 3]

[0205] Compared to the results of Comparative Example 1, which was not surface-modified, it can be confirmed that the positive electrode active materials of Examples 1 to 4 showed a reduction in residual lithium content through surface modification. Furthermore, it can be confirmed that the positive electrode active materials of Examples 1 to 4, which include lithium transition metal oxides in single-particle and similar single-particle forms, showed an even further reduction in residual lithium content compared to Comparative Example 2, which includes lithium transition metal oxides in multi-particle form. As a result, it is expected that using the positive electrode active materials of Examples 1 to 4 instead of the positive electrode active material of Comparative Example 2 will reduce gas generation and swelling phenomena within lithium secondary batteries, thereby improving long-term life characteristics.

[0206] 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. A lithium transition metal oxide having a crystal structure belonging to the R-3m space group and a nickel content of 40 mol% to 70 mol% in the transition metal; A tungsten-containing coating layer located on the surface of the lithium transition metal oxide; Includes, The lattice strain of the positive electrode active material, calculated by Rietveld Refinement on the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays, is 0.00025 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, and is 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 In the aforementioned 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 coating layer comprises a lithium-tungsten oxide represented by the following chemical formula 2, wherein the positive electrode active material is as described in claim 1: [Chemical formula 2] Li ｅ W ｆ O ｇ In the above chemical formula 2, 0 < e ≤ 8, 0 < f ≤ 15, and 0 < g ≤ 20.

10. The positive electrode active material according to claim 1, wherein the average Ni occupancy within the Li 3a site, calculated by Rietveld refinement of the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material, is less than 3.5%.

11. The positive electrode active material according to claim 1, wherein the average crystallite size of the lithium transition metal oxide, calculated by Rietveld refinement of the diffraction spectrum obtained through X-ray diffraction (XRD) analysis using Cu-kα rays on the positive electrode active material, is 160 nm to 200 nm.

12. The positive electrode active material according to claim 1, wherein the coating layer is formed in an island form that discontinuously occupies the surface of the lithium transition metal oxide.

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

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

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