Positive electrode active material and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery comprising the same, and more specifically, to a positive electrode active material for a lithium secondary battery, which is obtained by modifying the surface of a medium nickel (Mid-Ni) type lithium transition metal oxide having a relatively low nickel content, the present invention relates to a positive electrode active material capable of exhibiting improved driving characteristics in a high-voltage operating environment and a lithium secondary battery including the same.

Description

Technical Field

[0001] This invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a positive electrode active material that exhibits improved driving characteristics under high-voltage operating conditions by modifying the surface of a mid-Ni type lithium transition metal oxide with a relatively low nickel content, and a lithium secondary battery including the same. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. As a representative example of such batteries, there are lithium-ion secondary batteries that store electrical energy through the difference in chemical potential during the insertion / extraction of lithium ions at the positive and negative electrodes.

[0003] The aforementioned lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative electrode active materials, and filling the space between the positive and negative electrodes with organic or polymer electrolytes.

[0004] Lithium composite oxides are used as positive electrode active materials for lithium secondary batteries. For example, composite oxides of LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are currently under investigation.

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

[0006] Lithium manganese-based oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they suffer from small capacity and poor high-temperature performance. In addition, LiNiO2-type cathode active materials exhibit high discharge capacity battery characteristics, but due to the active cation mixing between lithium and nickel, they are not only difficult to synthesize, but also have the problems of very low rate capability and lifetime characteristics of the synthesized cathode active materials.

[0007] Accordingly, in order to improve low-rate and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, so-called ternary lithium composite oxides, such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary lithium composite oxides such as NCMA (Ni-Co-Mn-Al), have been developed, in which a portion of the nickel is replaced by cobalt, manganese, and / or aluminum. Since the lower the nickel content in the ternary or quaternary lithium composite oxides mentioned above, the lower the reversible capacity, recent research has focused on increasing the nickel content in lithium composite oxides.

[0008] However, as the nickel content in lithium composite oxides increases, the mixing of cations in the crystal structure also increases, leading to decreased stability or an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface.

[0009] As the content of lithium impurities remaining on the surface of the aforementioned lithium composite oxide increases, gas generation and bulging phenomena in lithium secondary batteries using the aforementioned lithium composite oxide as the positive electrode active material may intensify. Furthermore, as the content of lithium impurities remaining on the surface of the aforementioned lithium composite oxide increases, when preparing a paste for forming the positive electrode active material layer using the aforementioned lithium composite oxide, there is a problem of the paste composition gelling due to lithium impurities.

[0010] Therefore, a water washing process is necessary in the preparation of the positive electrode active material to remove lithium impurities remaining on the surface of the aforementioned lithium composite oxide. However, because this water washing process damages the surface of the lithium composite oxide, the electrochemical characteristics and stability of lithium secondary batteries using the aforementioned lithium composite oxide as the positive electrode active material decrease, and it may even lead to premature failure.

[0011] Furthermore, in recent years, with the rapid growth in demand for lithium-ion batteries, raw material costs have also increased, leading to a strong demand for cost reduction in the lithium-ion battery market. In particular, the positive electrode active material accounts for the highest proportion of cost in lithium-ion batteries. Among them, the higher the content of nickel, an essential element in ternary or quaternary lithium transition metal oxides, the higher the cost of the positive electrode active material will inevitably be.

[0012] That is, as the nickel content in the positive electrode active material increases, the reversible capacity improves, but at the same time, it also leads to an increase in lithium impurities in the positive electrode active material and an increase in the cost of the positive electrode active material, presenting a trade-off problem.

[0013] Therefore, it is necessary to develop a medium-nickel type positive electrode active material that can improve the stability and reduce the cost of the positive electrode active material by reducing the nickel content, and also solve the problem of decreased electrochemical characteristics caused by the reduction of nickel content. Summary of the Invention

[0014] Technical issues

[0015] In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles plays a leading role, the demand for positive electrode active materials used in lithium secondary batteries is also constantly increasing.

[0016] For example, in the prior art, from the point of view of ensuring safety, lithium secondary batteries using lithium iron phosphate (LFP) are mainly used. However, recently, the use of nickel-based lithium transition metal oxides with a larger energy capacity per unit weight compared to LFP is expanding (of course, at present, the relatively inexpensive LFP is still used to reduce costs).

[0017] In addition, nickel-based lithium metal oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, usually have ternary types such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary types such as NCMA (Ni-Co-Mn-Al).

[0018] However, as mentioned earlier, while increasing the nickel content in lithium transition metal oxides can improve reversible capacity, it may also lead to problems such as increased lithium impurities in the positive electrode active material or decreased stability of the positive electrode active material. Furthermore, trade-offs such as increased cost of the positive electrode active material are unavoidable.

[0019] Conversely, in order to reduce the cost of the positive electrode active material, reducing the nickel content in lithium transition metal oxides will, in particular, lead to a decline in electrochemical characteristics such as low-temperature output characteristics, and may therefore be unsuitable for exhibiting good driving characteristics in high-voltage operating environments.

[0020] Therefore, the object of the present invention is to provide a positive electrode active material comprising a medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than about 70 mol% or less, or less than about 65 mol%), wherein the positive electrode active material improves the insufficient electrochemical properties of the lithium transition metal oxide compared with high-nickel lithium transition metal oxides by modifying the surface of the lithium transition metal oxide.

[0021] In particular, the present invention aims to provide a positive electrode active material that significantly improves the discharge capacity and rate performance by forming a tungsten-containing coating on the surface of the aforementioned lithium transition metal oxide.

[0022] Furthermore, another object of the present invention is to provide a positive electrode active material comprising a medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than about 70 mol% or less, or less than about 65 mol%), wherein the amount of residual lithium on the surface is reduced by modifying the surface of the lithium transition metal oxide, and surface side reactions between the lithium transition metal oxide and the electrolyte are suppressed during charge and discharge, thereby improving the stability of the positive electrode active material.

[0023] Furthermore, another object of the present invention is to provide a lithium secondary battery using a positive electrode active material as defined herein.

[0024] The objectives of this invention are not limited to those stated above. Other objectives and advantages of this invention not mentioned above can be understood through the following description and through embodiments of this invention. Furthermore, it will be readily understood that the objectives and advantages of this invention can be achieved by the means and combinations thereof described in the claims.

[0025] Solution to the problem

[0026] According to one aspect of the present invention, a positive electrode active material is provided, comprising: a lithium transition metal oxide having a crystal structure belonging to the R-3m space group, wherein the nickel content in the transition metal is 40 mol% or more and 70 mol% or less; and a tungsten-containing coating located on the surface of the lithium transition metal oxide; thereby reducing the amount of residual lithium on the surface and suppressing surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, thereby improving its stability.

[0027] Furthermore, according to the present invention, a positive electrode active material having improved discharge capacity and rate performance characteristics by surface modification of the above-mentioned lithium transition metal oxide is provided.

[0028] The positive electrode active material defined in this paper forms a tungsten-containing coating on the surface of the lithium transition metal oxide, so that the lattice strain calculated by Rietveld Refinement can be less than 0.00025 for the diffraction spectrum obtained by X-ray diffraction (XRD) analysis of the positive electrode active material using Cu-kα rays.

[0029] The aforementioned lithium transition metal oxide contains at least lithium and a transition metal, wherein the nickel content in the transition metal can be 40 mol% or more and 70 mol% or less, 45 mol% or more and 70 mol% or less, 50 mol% or more and 70 mol% or less, 55 mol% or more and 65 mol% or less, or 60 mol% or more and 65 mol% or less.

[0030] The cobalt content in the aforementioned transition metals can be less than 10 mol%, more than 2.5 mol% and less than 10 mol%, or more than 5 mol% and less than 10 mol%. The manganese content in the aforementioned transition metals can be more than 20 mol% and less than 50 mol%, more than 20 mol% and less than 45 mol%, more than 20 mol% and less than 40 mol%, more than 25 mol% and less than 35 mol%, or more than 27 mol% and less than 33 mol%.

[0031] In addition, the aforementioned lithium transition metal oxides also include cobalt and manganese as transition metals, and the content of manganese in the aforementioned lithium transition metal oxides can be greater than the content of cobalt.

[0032] The aforementioned lithium transition metal oxides may have a composition represented by the following chemical formula 1.

[0033] [Chemical Formula 1]

[0034] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0035] 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, with 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.

[0036] As defined in this paper, in medium-nickel lithium transition metal oxides with relatively low nickel content, the surface kinetic properties such as lithium-ion conductivity tend to decrease as the manganese content increases relative to the cobalt content, leading to a deterioration in rate performance.

[0037] In this paper, by forming a tungsten-containing coating on the surface of the aforementioned lithium transition metal oxide, the reversible intercalation / deintercalation efficiency of lithium ions achieved by the aforementioned lithium transition metal oxide can be improved, thereby improving its insufficient electrochemical characteristics compared with high-nickel lithium transition metal oxides with relatively high nickel content.

[0038] Therefore, in this paper, in order to improve the relatively insufficient electrochemical properties compared with high-nickel lithium transition metal oxides with relatively high nickel content by improving the reversible insertion / extraction efficiency of lithium ions achieved by the above-mentioned lithium transition metal oxides, the above-mentioned lithium transition metal oxides may have at least one of the following forms: a single-particle form composed of a single unit particle and a pseudo-single-particle form composed of 30 or fewer unit particles.

[0039] The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned single-particle form 50 The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned pseudo-single-particle morphology can be 0.5 μm or larger and 10.0 μm or smaller. 50The particle size can be greater than 3.0 μm and less than 15.0 μm. The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned pseudo-single-particle morphology is... 50 The size of the unit particles constituting the pseudo-single particle may vary depending on the number and size of the unit particles. Furthermore, the unit particles constituting the pseudo-single particle may have a size comparable to that 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 pseudo-single particle... 50 The size can be greater than 0.5μm and less than 10.0μm.

[0040] In addition, lithium transition metal oxides having at least one of the following forms: a single-particle form composed of a single unit particle and a pseudo-single-particle form composed of 30 or fewer unit particles, can have a larger average grain size than lithium transition metal oxides with multi-particle forms.

[0041] The average grain size mentioned above can be calculated by Rietveld refinement of the diffraction spectrum obtained by X-ray diffraction (XRD) analysis of the above positive electrode active material using Cu-kα rays. The average grain size of the above lithium transition metal oxide as defined in this paper can be from 160 nm to 200 nm.

[0042] The coating can be formed in the form of islands that discontinuously occupy the surface of the lithium transition metal oxide.

[0043] Furthermore, according to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material is provided.

[0044] Furthermore, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

[0045] The effects of the invention

[0046] According to the present invention, by reducing the number of unit particles constituting a medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than about 70 mol% or less than about 65 mol%), the lifetime characteristics and stability of lithium secondary batteries made using the positive electrode active material as defined herein can be improved.

[0047] Furthermore, according to the present invention, by modifying the surface of a medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than about 70 mol% or less than about 65 mol%), the amount of residual lithium on the surface can be reduced, and the surface side reactions between the lithium transition metal oxide and the electrolyte can be suppressed during charging and discharging, thereby suppressing and / or alleviating the swelling phenomenon of lithium secondary batteries caused by gas generation.

[0048] On the other hand, generally speaking, compared with high-nickel lithium transition metal oxides containing more than 70 mol% nickel, medium-nickel lithium transition metal oxides containing relatively low nickel content (e.g., less than 70 mol% or less than 65 mol%) are accompanied by a decline in electrochemical characteristics related to lithium secondary battery output, such as capacity characteristics and rate characteristics, and therefore may not be suitable for exhibiting appropriate driving characteristics under high-voltage operating conditions.

[0049] Furthermore, in medium-nickel lithium transition metal oxides with relatively low nickel content, the higher the manganese content compared to the cobalt content, the lower the kinetic characteristics such as lithium-ion conductivity, leading to a downward trend in capacity and rate performance.

[0050] According to the present invention, a positive electrode active material can be provided, which is formed by low-temperature heat treatment on the surface of a medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than about 70 mol% or less or less than about 65 mol%) to form a tungsten-containing coating, thereby particularly improving the discharge capacity and rate characteristics.

[0051] In addition to the effects described above, the specific effects of the invention will be described while explaining the specific details of implementing the invention. Attached Figure Description

[0052] Figure 1 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 1.

[0053] Figure 2 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 2.

[0054] Figure 3 This is a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 3.

[0055] Figure 4 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Example 4.

[0056] Figure 5 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 1.

[0057] Figure 6 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 2.

[0058] Figure 7 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) based on Comparative Example 3.

[0059] Figure 8 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 4.

[0060] Figure 9 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 5.

[0061] Figure 10 The image shows a surface SEM image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 6.

[0062] Figure 11 This is a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 2.

[0063] Figure 12 This is a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 3.

[0064] Figure 13 The image shows a surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Example 2.

[0065] Figure 14 The image shows a surface SEM / EDS image of the positive electrode active material (lithium transition metal oxide) based on Comparative Example 2.

[0066] Figure 15 The image shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) based on Comparative Example 3.

[0067] Figure 16 The image shows a cross-sectional SEM / EDS image of the positive electrode active material (lithium transition metal oxide) according to Comparative Example 4. Detailed Implementation

[0068] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific and technical terms used herein should have the meanings commonly understood by those skilled in the art. Furthermore, it should be understood that, as used herein, the singular form is intended to include the plural form, and vice versa, unless the context clearly indicates otherwise.

[0069] Positive electrode active material

[0070] According to one aspect of the invention, the positive electrode active material comprises a lithium transition metal oxide capable of lithium ion intercalation / deintercalation.

[0071] The aforementioned lithium transition metal oxides are composite metal oxides capable of intercalating / deintercalating lithium ions and possess a layered crystal structure belonging to the R-3m space group. The aforementioned lithium transition metal oxides with a layered crystal structure exhibit characteristic peaks in the region of 2θ ranging from 18° to 20° in the diffraction pattern obtained by XRD analysis.

[0072] In one embodiment, the lithium transition metal oxide comprises at least lithium and a transition metal. The transition metal may include at least one, at least two, at least three, or all of nickel, cobalt, and manganese.

[0073] Preferably, the lithium transition metal oxide can be a lithium nickel-based composite oxide containing nickel. Alternatively, the lithium transition metal oxide can be a lithium nickel-based composite oxide containing both nickel and cobalt.

[0074] In one embodiment, to improve low-rate and lifetime characteristics while maintaining high reversible capacity, the lithium nickel-based transition oxide (LiNiO2) can be a ternary type such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or a quaternary type such as NCMA (Ni-Co-Mn-Al), where a portion of the nickel is replaced by cobalt, manganese, and / or aluminum. The aforementioned ternary or quaternary lithium transition metal oxides may further include dopants other than nickel, cobalt, manganese, and aluminum.

[0075] In another embodiment, the aforementioned lithium transition metal oxide may be a cobalt-free lithium transition metal oxide, which does not contain cobalt in the bulk particles. The cobalt-free lithium transition metal oxide may also contain dopants other than nickel, cobalt, and manganese.

[0076] The lithium transition metal oxides defined in this paper are medium-nickel type lithium transition metal oxides with relatively low nickel content. In this paper, lithium transition metal oxides with a nickel content of less than 70 mol% are defined as medium-nickel type lithium transition metal oxides, and lithium transition metal oxides with a nickel content greater than 70 mol% are defined as high-nickel type lithium transition metal oxides.

[0077] In one embodiment, the nickel content in the transition metal (the nickel content in the total elements other than lithium in the lithium transition metal oxide) can be 40 mol% or more and 70 mol% or less, 45 mol% or more and 70 mol% or less, 50 mol% or more and 70 mol% or less, 55 mol% or more and 65 mol% or less, or 60 mol% or more and 65 mol% or less.

[0078] When the nickel content in the aforementioned lithium transition metal oxide exceeds 70 mol%, the mixing of cations in the crystal structure also increases, potentially leading to decreased stability or an increase in the content of unreacted lithium impurities such as LiOH and Li₂CO₃ on the surface. In particular, with the increase of nickel content in the aforementioned lithium transition metal oxide, stability may rapidly decrease under high-voltage operating conditions. On the other hand, when the nickel content in the aforementioned lithium transition metal oxide is less than 40 mol%, excess amounts of other transition metals besides nickel (e.g., manganese) may cause phase separation, thereby generating impurity phases belonging to space groups other than R-3m. These impurity phases can directly affect the deterioration of the electrochemical properties of the aforementioned positive electrode active material.

[0079] The cobalt content in the aforementioned transition metals can be less than 10 mol%, more than 2.5 mol% and less than 10 mol%, or more than 5 mol% and less than 10 mol%.

[0080] When the cobalt content in the aforementioned lithium transition metal oxide exceeds 10 mol%, the goal of reducing the cost of the aforementioned positive electrode active material cannot be achieved. Furthermore, when the cobalt content in the aforementioned lithium transition metal oxide is too high, the driving voltage of the lithium secondary battery using the aforementioned positive electrode active material may decrease, making it difficult to exhibit excellent high-output characteristics at relatively high voltages. Additionally, when the cobalt content in the aforementioned lithium transition metal oxide is too high, structural instability may occur at high charging rates, leading to decreased stability under high-voltage operating conditions.

[0081] The aforementioned lithium transition metal oxide can be a cobalt-free lithium transition metal oxide that does not contain cobalt in bulk particles, but in order to successfully form a layered crystal structure belonging to the R-3m space group, its cobalt content is preferably 2.5 mol% or more.

[0082] The manganese content in the aforementioned transition metals can be 20 mol% or more and 50 mol% or less, 20 mol% or more and 45 mol% or less, 20 mol% or more and 40 mol% or less, 25 mol% or more and 35 mol% or less, or 27 mol% or more and 33 mol% or less. The difference between the manganese and cobalt content in the aforementioned transition metals is preferably 10 mol% or more.

[0083] When the manganese content in the aforementioned lithium transition metal oxides exceeds 50 mol%, it may lead to a decrease in the charge / discharge capacity and energy density of the positive electrode active material. Furthermore, since manganese readily dissolves under high voltage, excessively high manganese content in the aforementioned lithium transition metal oxides may result in an increase in the amount of manganese dissolved from the positive electrode under high-voltage operating conditions, thereby causing a decline in the long-term characteristics or lifespan of the lithium secondary battery.

[0084] Furthermore, when the manganese content in the aforementioned lithium transition metal oxide exceeds 50 mol%, it may be difficult to form single-particle or pseudo-single-particle lithium transition metal oxides. Moreover, the excessive manganese in the lithium transition metal oxide may cause phase separation, leading to the formation of impurity phases belonging to space groups other than R-3m. These impurity phases can directly affect the deterioration of the electrochemical properties of the aforementioned positive electrode active material.

[0085] Conversely, when the manganese content in the aforementioned lithium transition metal oxide is less than 20 mol%, the stability of lithium transition metal oxides with relatively low nickel content (e.g., less than about 70 mol% or about 65 mol%) as defined herein may decrease, and the driving voltage of lithium secondary batteries using the aforementioned positive electrode active material may decrease, making it difficult to exhibit high output characteristics at relatively high voltages.

[0086] The aforementioned lithium transition metal oxides may have a composition represented by the following chemical formula 1.

[0087] [Chemical Formula 1]

[0088] Li a Ni 1-(b+c+d) Co b Mn c M1 d O2

[0089] 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, with 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.

[0090] The molar ratio 'a' of lithium to all other elements in the aforementioned lithium transition metal oxide 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.

[0091] When a in the above 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 above chemical formula 1 may decrease. On the other hand, when a in the above chemical formula 1 is greater than 1.15, due to the excess lithium and manganese in the above lithium transition metal oxide, phase separation may occur, resulting in the generation of impurity phases belonging to space groups other than R-3m.

[0092] In the above chemical formula 1, 1-(b+c+d), which represents the molar ratio of nickel to all elements other than lithium in the above lithium transition metal oxide, can 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.

[0093] In the above chemical formula 1, b, which represents the molar ratio of cobalt to all elements other than lithium in the above lithium transition metal oxide, can 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.

[0094] In the above chemical formula 1, c, which represents the molar ratio of manganese to all elements other than lithium in the above lithium transition metal oxide, can 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.

[0095] In the above chemical formula 1, M1 represents the dopant incorporated into the above lithium transition metal oxide. The above lithium transition metal oxide has a layered crystal structure, in which lithium layers and transition metal layers containing transition metals are arranged alternately, and the above dopant may exist in a doped state within the lattice of the above lithium transition metal oxide (at least one of the lithium layers and / or transition metal layers).

[0096] When the above-mentioned lithium transition metal oxide contains dopants, the molar ratio of the dopants to all elements other than lithium in the above-mentioned lithium transition metal oxide, as indicated in the above-mentioned chemical formula 1, is greater than 0.

[0097] When the above-mentioned lithium transition metal oxide contains a dopant, the molar fraction d in the above-mentioned chemical formula 1, which represents the dopant relative to all metal elements other than lithium in the above-mentioned lithium transition metal oxide, can be less than 0.10, less than 0.05, less than 0.04, less than 0.03, less than 0.02, or less than 0.01.

[0098] Furthermore, as described below, the surface of the aforementioned lithium transition metal oxide has a coating. This coating contains tungsten. If the tungsten contained in the coating formed on the surface of the aforementioned lithium transition metal oxide diffuses into and dops into the unit particles constituting the aforementioned lithium transition metal oxide, then d, which represents the molar ratio of the dopant to all elements other than lithium in the aforementioned lithium transition metal oxide in Chemical Formula 1, is greater than 0, and M1 contains tungsten.

[0099] When the aforementioned lithium transition metal oxide selectively includes a dopant, the dopant may include at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu. Preferably, it may include at least one selected from Mg, Ca, Al, Ti, Zr, Mo, W, and P. More preferably, it may include at least one selected from Ca, Al, Ti, W, and Zr. The type, combination, and content of the dopant may be appropriately selected within a range that does not negatively affect the electrochemical characteristics and stability of the aforementioned positive electrode active material.

[0100] The upper and lower limits of the content (molar ratio) of nickel, cobalt, manganese and dopants as defined in the above chemical formula 1 can be appropriately selected within the range that satisfies the above definitions.

[0101] As mentioned above, the aforementioned lithium transition metal oxide also includes cobalt and manganese as transition metals, and the manganese content in the aforementioned lithium transition metal oxide can be greater than the cobalt content. However, in conventional medium-nickel type lithium transition metal oxides, as the manganese content increases relative to the cobalt content, the kinetic properties of lithium ions, such as conductivity, may decrease, leading to a trend of deteriorating rate performance.

[0102] Therefore, in this paper, in order to improve the efficiency of reversible insertion / deintercalation of lithium ions through the above-mentioned lithium transition metal oxide and improve the rate capability, the number of unit particles constituting the above-mentioned lithium transition metal oxide is reduced.

[0103] Furthermore, the fewer the number of unit particles constituting the lithium transition metal oxide, the smaller the specific surface area of ​​the positive electrode active material including the lithium transition metal oxide, thereby reducing surface side reactions between the lithium transition metal oxide and the electrolyte during charging and discharging, and thus improving the lifespan characteristics of lithium secondary batteries made using positive electrode active materials containing the lithium transition metal oxide.

[0104] Specifically, the aforementioned lithium transition metal oxide has at least one of the following forms: a single-particle form consisting of a single unit particle and a pseudo-single-particle form composed of fewer than 30 unit particles. The aforementioned unit particle can be interpreted in the same sense as a primary particle.

[0105] The aforementioned unit particles can have spherical, rod-shaped, elliptical, and / or irregular shapes. Furthermore, unless specifically intended in the preparation process, unit particles of various shapes can coexist in the same positive electrode active material. Additionally, the aforementioned unit particles refer to particle units that do not exhibit grain boundaries when observed under a scanning electron microscope at magnification of 5000x to 20000x.

[0106] In other words, the single-particle morphology, consisting of a single unit particle, refers to the lithium transition metal oxide being composed of only one unit particle, rather than a secondary particle morphology formed by the aggregation of multiple unit particles. The average particle size (D) of the lithium transition metal oxide existing in the aforementioned single-particle morphology... 50 The micrometer 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.

[0107] The average particle size (D) of the above unit particles 50 The average length of the aforementioned unit particles along their major axis and minor axis can be calculated as ([major axis length + minor axis length] / 2). The average particle size of the aforementioned unit particles can be calculated as the average particle size of all unit particles observed from the surface SEM images and / or cross-sectional SEM images of the aforementioned lithium transition metal oxide.

[0108] When the average particle size of the aforementioned unit particles is less than 1.0 μm, the lithium transition metal oxide is more likely to exhibit a polycrystalline structure composed of 50 or more or 100 unit particles, rather than having a single-particle form and / or a pseudo-single-particle form. Furthermore, when the average particle size of the aforementioned unit particles is less than 1.0 μm, the specific surface area of ​​the positive electrode active material of lithium transition metal oxides, including those having at least one form selected from a single-particle form composed of one of the aforementioned unit particles and a pseudo-single-particle form composed of 30 or fewer unit particles, will increase, potentially leading to a decrease in stability due to side reactions with the electrolyte.

[0109] Conversely, when the average particle size of the aforementioned unit particles exceeds 8.0 μm, it may induce excessive growth of the unit particles, which in turn reduces the diffusion of lithium ions using these unit particles as a medium. Furthermore, due to the characteristics of medium-nickel type lithium transition metal oxides with relatively high contents of other transition metals besides nickel, the distribution of transition metals within the aforementioned unit particles may become uneven.

[0110] Typically, ternary or quaternary lithium transition metal oxides exhibit a secondary particle morphology consisting of hundreds or thousands of unit particles. The lithium transition metal oxides defined herein can exhibit a secondary particle morphology consisting of multiple unit particles, but they can also exhibit a pseudo-single particle morphology consisting of no more than 30, 20, or 10 unit particles. Hereinafter, to distinguish them from secondary particles consisting of hundreds or thousands of unit particles, secondary particles consisting of no more than 30, 20, or 10 unit particles will be referred to as "pseudo-single particles." Furthermore, the particle size of the primary particles constituting the ternary or quaternary lithium transition metal oxides, which are conventionally secondary particle morphologies, is smaller than the particle size of the unit particles defined herein.

[0111] The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned pseudo-single-particle morphology is... 50 The particle size can be 3.0 μm or larger and 12.0 μm or smaller, or 4.0 μm or larger and 12.0 μm or smaller. The average particle size (D) of the lithium transition metal oxide existing in the above-described pseudo-single-particle morphology is... 50 The number and size of the unit particles that make up the aforementioned pseudo-single particle may vary.

[0112] Furthermore, the unit particles constituting the aforementioned pseudo-single particles can have a size comparable to that of the lithium transition metal oxide existing in the aforementioned single-particle form. That is, the average particle size (D) of the unit particles constituting the aforementioned pseudo-single particles... 50 The micrometer 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.

[0113] The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned pseudo-single-particle morphology is... 50 The average particle size of the aforementioned pseudo-single particles can be calculated using SEM images.

[0114] In this paper, “particle size” has the same meaning as “particle diameter” or “particle size”. Unless otherwise defined, all “average particle size” refers to the particle size corresponding to a cumulative volume distribution of 50% as measured by the laser diffraction method described above.

[0115] The particle size distribution of the lithium transition metal oxide in the aforementioned positive electrode active material can be measured using laser diffraction. 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 irradiated with approximately 28 kHz ultrasound at a power of 60 W. After obtaining a volumetric cumulative particle size distribution chart, the particle sizes (D0) corresponding to 10%, 50%, and 90% of the volumetric cumulative amount can be calculated. 10 D 50 D 90 The minimum particle size (D) in the above-mentioned volumetric cumulative particle size distribution diagram min ) and the maximum particle size (D) of the above-mentioned volumetric cumulative particle size distribution map. max ).

[0116] The aforementioned positive electrode active material can simultaneously contain lithium transition metal oxides in single-particle form and lithium transition metal oxides in pseudo-single-particle form.

[0117] For the above-mentioned positive electrode active material comprising the above-mentioned single-particle lithium transition metal oxide and the above-mentioned pseudo-single-particle lithium transition metal oxide, the D measured by laser diffraction method 50 The nanometer size can 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 comprising a medium-nickel type lithium transition metal oxide with a nickel content of 40 mol% or more and 70 mol% or less in the transition metal is described above in D. 50 It exhibits the best energy density per unit volume within the range.

[0118] Typically, compared to cathode active materials containing high-nickel lithium transition metal oxides with a nickel content exceeding 70 mol%, cathode active materials containing medium-nickel lithium transition metal oxides with a relatively low nickel content (e.g., less than about 70 mol% or less than about 65 mol%) suffer from a decline in electrochemical characteristics related to lithium secondary battery output, such as capacity characteristics and rate characteristics. Therefore, they may not be suitable for exhibiting appropriate driving characteristics under high-voltage operating conditions.

[0119] Furthermore, in medium-nickel lithium transition metal oxides with relatively low nickel content, the higher the manganese content compared to the cobalt content, the lower the kinetic characteristics such as lithium-ion conductivity, leading to a downward trend in capacity and rate performance.

[0120] Therefore, according to the present invention, by surface-modifying a medium nickel-type lithium transition metal oxide having a relatively low nickel content (e.g., 70 mol% or less or 65 mol% or less) to form a tungsten-containing coating, the discharge capacity and rate characteristics can be improved.

[0121] In addition, according to the present invention, by modifying the surface of a medium nickel-type lithium transition metal oxide having a relatively low nickel content (e.g., 70 mol% or less or 65 mol% or less), the amount of residual lithium on the surface can be reduced, and the surface side reaction between the lithium transition metal oxide and the electrolyte during charge and discharge can be suppressed, thereby being able to suppress and / or alleviate the swelling phenomenon of the lithium secondary battery caused by gas generation.

[0122] The above-mentioned tungsten-containing coating may include a lithium tungsten oxide represented by the following Chemical Formula 2.

[0123] [Chemical Formula 2]

[0124] Li e W f O g

[0125] In the above Chemical Formula 2, 0 < e ≤ 8, 0 < f ≤ 15, 0 < g ≤ 20, and e, f, and g represent numbers determined according to the valence (oxidation number) and equivalent of tungsten in a stoichiometric ratio. Non-limiting examples of the above-mentioned lithium tungsten oxide include LiWO3, Li2WO4, Li3WO4, Li3WO6, Li4WO5, Li6WO6, Li8WO6, etc. <00​​​​​

[0128] The tungsten content, calculated based on all metal elements other than lithium present in the aforementioned positive electrode active material, can be greater than 0.1 mol% and less than 0.5 mol%, greater than 0.15 mol% and less than 0.45 mol%, greater than 0.2 mol% and less than 0.4 mol%, or greater than 0.2 mol% and less than 0.3 mol%. The tungsten content in the aforementioned tungsten-containing coating can be calculated by performing ICP analysis on the aforementioned positive electrode active material.

[0129] Specifically, the aforementioned ICP analysis method refers to the method of determining the element content in the above-mentioned positive electrode active material using an inductively coupled plasma spectrometer (ICP) according to known methods. Even considering the error range, the tungsten content measured by the above-mentioned ICP analysis method can reflect the tungsten content (design composition) used in the preparation process of the above-mentioned positive electrode active material.

[0130] When the tungsten content, calculated based on all metal elements other than lithium present in the above-mentioned positive electrode active material, is less than 0.1 mol%, not only is the effect of reducing residual lithium on the surface insufficient, but it may also be impossible to form a tungsten-containing coating on the surface. Therefore, it may result in insufficient improvement of the capacity and rate characteristics of medium-nickel lithium transition metal oxides with relatively low nickel content (e.g., less than about 70 mol% or less or less than about 65 mol%).

[0131] On the other hand, when the tungsten content, calculated based on all metal elements other than lithium present in the above-mentioned positive electrode active material, is 0.5 mol% or more, the surface dynamics of the medium-nickel 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, it may reduce the ionic conductivity or electrical conductivity of the above-mentioned lithium transition metal oxide, and may make it difficult to fully activate during the initial charging due to the suppression of the interaction between the above-mentioned lithium transition metal oxide and the electrolyte.

[0132] The coating can be formed on the surface of the lithium transition metal oxide in a continuous and / or discontinuous manner. For example, the coating can be formed in an island-like form that discontinuously occupies the surface of the lithium transition metal oxide.

[0133] When the aforementioned lithium transition metal oxide has a secondary particle morphology consisting of aggregates of at least two unit particles, the coating can 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 in the gaps between adjacent unit particles means that the oxides and / or lithium composite oxides constituting the coating exist in a form that fills the gaps between adjacent unit particles.

[0134] Furthermore, when the aforementioned lithium transition metal oxide has a secondary particle morphology consisting of aggregates of at least two unit particles, the coating can diffuse from the surface of the secondary particles toward the center of the secondary particles along the gaps between adjacent unit particles and / or the grain boundaries corresponding to the contact surfaces of adjacent unit particles. In this case, the tungsten contained in the coating can exhibit a concentration gradient that gradually decreases from the surface of the secondary particles toward the center of the secondary particles.

[0135] On the other hand, as defined herein, the more uneven the distribution of transition metals or the worse the crystal structure stability of medium-nickel lithium transition metal oxides with relatively low nickel content (e.g., less than about 70 mol% or less than about 65 mol%) and greater manganese content than cobalt content (especially when the difference between manganese and cobalt content in the aforementioned transition metals is more than 10 mol%), the greater the lattice strain may be.

[0136] As the crystal structure stability of the aforementioned lithium transition metal oxides decreases, the grain size or spacing between adjacent grains may become irregular. Lattice strain is one of the important indicators of grain regularity; the more irregular the grains, the greater the lattice strain.

[0137] For example, if the heat treatment temperature of the mixture of the nickel-containing medium-nickel lithium transition metal oxide with a relatively low nickel content (e.g., less than 70 mol% or less than 65 mol%) and the tungsten-containing raw material is too high (e.g., above 500°C), the tungsten contained in the tungsten-containing raw material may diffuse and dope into the lithium transition metal oxide, thereby causing the lattice strain to increase.

[0138] The aforementioned lattice strain (ε) can be calculated using various known methods from diffraction patterns obtained by Cu-Kα X-ray diffraction (XRD) analysis. For example, the lattice strain (ε) can be calculated using the Rietveld refinement method or the Williamson-Hall method from the diffraction patterns obtained by Cu-Kα XRD analysis of the aforementioned positive electrode active material. The lattice strain is expressed as Δd / d. A larger lattice strain (ε) may cause systematic atomic shifts and lead to broadening of the diffraction peaks. The Williamson-Hall method proposes a method to extract information about grain size and lattice strain from the integrated width of the diffraction peaks.

[0139] The lattice strain (ε) expressed in terms of Δd / d in the range of 2θ = 10° to 120° is represented by 1 / 4 of the slope of the straight line obtained by plotting the diffraction angle θ (radians) and half-width at half-maximum β (radians) on a coordinate plane with sinθ as the horizontal axis and βcosθ as the vertical axis (or it can be expressed as β / 4tanθ).

[0140] Furthermore, the aforementioned lattice strain (ε) can be calculated using the following formula.

[0141] βcosθ=4εsinθ+0.9λ / D

[0142] In the above formula, β is the full width at half maximum (FWHM), θ is the diffraction angle, and λ is the X-ray wavelength used for XRD analysis. D is the grain size of the aforementioned lithium transition metal oxide. The aforementioned lattice strain (ε) can be calculated by plotting the values ​​calculated according to the above formula and obtaining the intercept and slope of the straight line.

[0143] The lattice strain of medium-nickel lithium transition metal oxides, defined herein as having relatively low nickel content (e.g., less than about 70 mol% or about 65 mol%) and greater manganese content than cobalt content, can be reduced by surface modification treatments performed under predetermined conditions.

[0144] For the above-mentioned positive electrode active material, which includes a medium-nickel lithium transition metal oxide containing a relatively low nickel content (e.g., less than about 70 mol% or less or about 65 mol%) and a manganese content greater than the cobalt content as defined herein, the lattice strain obtained by X-ray diffraction (XRD) analysis using Cu-Kα rays is preferably less than 0.00025.

[0145] Furthermore, the average crystallite size of the lithium transition metal oxide calculated using the above method can be from 160 nm to 200 nm.

[0146] If the average grain size is less than 160 nm or greater than 200 nm, the improvement in electrochemical properties such as capacity and rate performance of lithium secondary batteries using the lithium transition metal oxide as the positive electrode active material may be minimal. When the growth of the unit particles constituting the lithium transition metal oxide is insufficient, the average grain size may be less than 160 nm. When the average grain size exceeds 200 nm, polarization may occur due to increased resistance, and cracks may form within the particles due to this polarization, ultimately leading to a reduction in the lifetime of the positive electrode active material.

[0147] For the diffraction patterns obtained by X-ray diffraction (XRD) analysis of the above-mentioned positive electrode active material using Cu-Kα lines, the average Ni occupancy within the Li 3a site calculated by Rietveld refinement can be less than 3.5%, or less than 3.4%, 3.35%, or 3.34%.

[0148] In this paper, the average Ni occupancy within the Li 3a site may vary due to the growth of the unit particles constituting the aforementioned lithium transition metal oxide or the results of surface modification of the aforementioned lithium transition metal oxide.

[0149] The average Ni occupancy within the Li 3a site is an indicator of the degree of cation mixing (lithium and nickel cation mixing) between the lithium layer and the transition metal layer. The higher the average Ni occupancy within the Li 3a site, the greater the lattice strain may be.

[0150] Lithium secondary batteries

[0151] According to another aspect of the present invention, a positive electrode can be provided comprising a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer may comprise the positive active material according to various embodiments of the present invention. Therefore, the positive active material is the same as described above, and for convenience, its specific description will be omitted hereafter; only the remaining undescribed components will be described.

[0152] There are no particular limitations on the aforementioned positive electrode current collector, as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the aforementioned positive electrode current collector typically has a thickness of 3μm to 500μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0153] The aforementioned positive electrode active material layer can be prepared by coating the aforementioned positive electrode current collector with a positive electrode slurry composition comprising the aforementioned positive electrode active material, a conductive material, and, if desired, a binder.

[0154] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight. When the positive electrode active material is included in the above content range, excellent capacity characteristics can be exhibited, but it is not limited thereto.

[0155] The aforementioned conductive materials are used to impart conductivity to the electrodes. In the constructed battery, they can be used without restriction as long as they do not cause chemical changes and possess electronic conductivity. Specific examples include graphite such as natural 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 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 or more mixtures of these materials may be used. The total weight of the positive electrode active material layer may range from 0.1% to 15% by weight of the aforementioned conductive materials.

[0156] The aforementioned binder enhances the adhesion between multiple positive electrode active material particles and the bonding force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), ethylene-vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof; one or more mixtures thereof may be used. The binder may comprise 0.1% to 15% by weight of the aforementioned binder relative to the total weight of the positive electrode active material layer.

[0157] In addition to utilizing the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition onto a positive electrode current collector and then drying and calendering it. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent.

[0158] The solvents mentioned above can be solvents commonly used in this technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more of them can be used. Considering the coating thickness and preparation yield of the slurry, the amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that exhibits excellent thickness uniformity when coated for the preparation of the positive electrode.

[0159] Furthermore, in another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating the thin film obtained by peeling off the support onto the positive electrode current collector.

[0160] Furthermore, according to another aspect of the present invention, an electrochemical device including the aforementioned positive electrode can be provided. Specifically, the aforementioned electrochemical device can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0161] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as described above; therefore, for convenience, a detailed description is omitted. The remaining components not previously described will be explained below.

[0162] The aforementioned lithium secondary battery may optionally include: a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separation membrane; and a sealing component for sealing the battery container.

[0163] The aforementioned negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the aforementioned negative electrode current collector.

[0164] There are no particular limitations on the aforementioned negative electrode current collector, as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the aforementioned negative electrode current collector typically has a thickness of 3μm to 500μm. Similar to the positive electrode current collector, the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0165] The aforementioned negative electrode active material layer can be prepared by coating the aforementioned negative electrode current collector with a negative electrode slurry composition comprising the aforementioned negative electrode active material and conductive material, and selectively including a binder as needed.

[0166] As the aforementioned negative electrode active material, compounds capable of reversible lithium-ion insertion and extraction can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal 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; such as SiO₂. βMetal oxides capable of being doped and dedoped with lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above-mentioned metal compounds and carbon materials, such as Si-C composites or Sn-C composites, may be used, and one or more mixtures thereof may be used. Furthermore, lithium metal films may also be used as the above-mentioned negative electrode active material. Moreover, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, while representative high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0167] Based on the total weight of the negative electrode active material layer, it may contain 80% to 99% of the aforementioned negative electrode active material.

[0168] The aforementioned binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, 0.1% to 10% by weight of the binder can be added based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0169] The aforementioned conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, up to 10% by weight of the aforementioned conductive material can be added, preferably up to 5% by weight. There are no particular limitations on this conductive material as long as it does not induce chemical changes in the corresponding battery and possesses conductivity. For example, graphite such as natural graphite or artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, 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.

[0170] The aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0171] On the other hand, in the aforementioned lithium secondary battery, the separator membrane is used to separate the negative electrode and the positive electrode and provide a channel for the movement of lithium ions. Any separator membrane commonly used in lithium secondary batteries can be used without limitation. In particular, it is preferable to have low impedance and excellent electrolyte moisture-holding capacity for electrolyte ion movement. Specifically, porous polymer films can be used, for example, porous polymer films prepared using polyolefin polymers 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. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separator membranes coated with ceramic components and polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0172] Furthermore, examples of electrolytes used in this invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, but they are not limited to these.

[0173] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0174] As the aforementioned organic solvents, organic solvents that can act as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the aforementioned organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (EPC) can be used. Carbonate solvents such as nate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where r is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxanes such as 1,3-dioxane; or sulfolane, etc. Among these, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge-discharge characteristics of the battery, are more preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte properties are observed.

[0175] The lithium salts described above can be any compound capable of providing lithium ions for use in lithium secondary batteries, without limitation. Specifically, the lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. Preferably, the concentration of the lithium salts is used in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte characteristics that allow for efficient lithium ion movement.

[0176] When the electrolyte used herein is a solid electrolyte, such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc., solid inorganic electrolytes can be used. Preferably, sulfide solid electrolytes can be used.

[0177] As materials for sulfide-based solid electrolytes, solid electrolytes containing Li, X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S can be used. Examples of the aforementioned sulfide-based solid electrolyte materials 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 (Where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.)

[0178] The solid electrolyte, preferably, is a sulfide-based solid electrolyte, which can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0179] Examples of oxide-based solid electrolytes include 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, Li3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0180] The aforementioned solid electrolyte can be arranged as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Furthermore, the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the positive electrode active material layer of the positive electrode, or the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the negative electrode active material layer of the negative electrode.

[0181] In addition to the electrolyte components described above, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity, the electrolyte may also contain one or more additives such as halogenated alkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the electrolyte may contain 0.1% to 5% by weight of the aforementioned additives relative to its total weight.

[0182] As described above, lithium secondary batteries containing the positive electrode active material of the present invention stably exhibit excellent discharge capacity, output characteristics, and lifespan characteristics. Therefore, they can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs).

[0183] The lithium secondary battery according to the present invention is not particularly limited in shape and can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc. Furthermore, preferably, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also as a unit battery in medium or large battery modules comprising multiple battery cells.

[0184] According to another aspect of the invention, a battery module comprising the aforementioned lithium secondary battery as a single unit and / or a battery pack comprising the same can be provided.

[0185] The aforementioned battery module or battery pack can be used as a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or a power source for one or more medium or large-sized devices in an energy storage system.

[0186] The invention will be described in more detail below by way of examples. However, these examples are merely illustrative and the scope of the invention should not be construed as being limited by these examples.

[0187] Preparation Example 1. Preparation of Positive Electrode Active Material

[0188] Example 1

[0189] Ni synthesized via coprecipitation reaction 0.62 Co 0.07 Mn 0.31 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and heat-treated in a furnace at 950°C for 10 hours in air atmosphere to obtain an intermediate product (lithium transition metal oxide).

[0190] Subsequently, the above intermediate product was mixed with WO3 (weighed such that the tungsten content in the above intermediate product relative to all transition metals is 0.3 mol%), and heat-treated in an air atmosphere in a calcining furnace at 350°C for 8 hours to form a tungsten-containing coating on the surface of the above lithium transition metal oxide, thereby obtaining the final product.

[0191] from Figure 1 Surface SEM images confirm that the positive electrode active material according to Example 1 includes single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product shows that the tungsten content is consistent with the designed composition.

[0192] Example 2

[0193] Except for changing the heat treatment temperature of the mixture of the above intermediate product and WO3 to 375°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0194] from Figure 2The surface SEM images confirm that the positive electrode active material according to Example 2 above includes lithium transition metal oxides in both single-particle and pseudo-single-particle forms. ICP analysis of the final product confirms that the tungsten content in the final product is consistent with the designed composition.

[0195] Example 3

[0196] Except for changing the heat treatment temperature of the mixture of the above intermediate product and WO3 to 400°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0197] from Figure 3 The surface SEM images confirm that the positive electrode active material according to Example 3 includes single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product confirms that the tungsten content in the final product is consistent with the designed composition.

[0198] Example 4

[0199] Except for mixing the above intermediate product with WO3 to make the tungsten content in the above intermediate product relative to the total transition metal 0.2 mol%, the positive electrode active material was prepared in the same manner as in Example 1.

[0200] Comparative Example 1

[0201] Ni synthesized via coprecipitation reaction 0.62 Co 0.07 Mn 0.31 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and then heat-treated at 950℃ for 10 hours in air atmosphere to obtain the final product.

[0202] from Figure 5 The surface SEM images confirm that the positive electrode active material of Comparative Example 1 includes single-particle and pseudo-single-particle lithium transition metal oxides.

[0203] Comparative Example 2

[0204] Ni synthesized via coprecipitation reaction 0.62 Co 0.07 Mn 0.31 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and then heat-treated at 850°C for 10 hours in air atmosphere to obtain an intermediate product (lithium transition metal oxide).

[0205] Subsequently, the above intermediate product was mixed with WO3 (weighed such that the tungsten content in the above intermediate product relative to all transition metals is 0.3 mol%), and heat-treated in an air atmosphere in a calcining furnace at 375°C for 8 hours to obtain a final product having a tungsten-containing coating formed on the surface of the above lithium transition metal oxide.

[0206] from Figure 6 The surface SEM images confirmed that the positive electrode active material according to Comparative Example 2 consisted of a multi-particle lithium transition metal oxide with more than 30 unit particles. ICP analysis of the final product showed that the tungsten content in the final product was consistent with the designed composition.

[0207] Comparative Example 3

[0208] Except for changing the heat treatment temperature of the mixture of the above intermediate product and WO3 to 250°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0209] from Figure 7 The surface SEM images confirmed that the positive electrode active material according to Comparative Example 3 included both single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product showed that the tungsten content was consistent with the designed composition.

[0210] Comparative Example 4

[0211] Except for changing the heat treatment temperature of the mixture of the above intermediate product and WO3 to 650°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0212] from Figure 8 The surface SEM images confirmed that the positive electrode active material according to Comparative Example 4 included both single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product showed that the tungsten content was consistent with the designed composition.

[0213] Comparative Example 5

[0214] Except for mixing the above intermediate product with WO3 to make the tungsten content in the above intermediate product relative to the total transition metal 0.1 mol%, the positive electrode active material was prepared in the same manner as in Example 1.

[0215] from Figure 9The surface SEM images confirmed that the positive electrode active material according to Comparative Example 5 included both single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product showed that the tungsten content was consistent with the designed composition.

[0216] Comparative Example 6

[0217] Except for mixing the above intermediate product with WO3 to make the tungsten content in the above intermediate product relative to the total transition metal 0.5 mol%, the positive electrode active material was prepared in the same manner as in Example 1.

[0218] from Figure 10 The surface SEM images confirmed that the positive electrode active material according to Comparative Example 6 included both single-particle and pseudo-single-particle lithium transition metal oxides. ICP analysis of the final product showed that the tungsten content was consistent with the designed composition.

[0219] Preparation Example 2. Manufacturing of a Lithium Secondary Battery (Half-Cell)

[0220] A positive electrode slurry was prepared by dispersing 94% by weight of each of the positive electrode active materials prepared according to Preparation Example 1, 3% by weight of carbon black, and 3% by weight of PVDF binder in 30g of N-methyl-2-pyrrolidone (NMP). The above positive electrode slurry was uniformly coated on an aluminum film with a thickness of 15μm and vacuum dried at 135°C to prepare a positive electrode for lithium secondary batteries.

[0221] In contrast to the above positive electrode, a lithium foil was used as the counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separation membrane, and a half-cell was prepared using an electrolyte containing 1.15 M of LiPF6 in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0222] Experimental Example 1. Analysis of Surface-Modified Positive Electrode Active Materials

[0223] Referring to the surface SEM images of the positive electrode active material (lithium transition metal oxide) prepared in Preparation Example 1 according to the Examples and Comparative Examples, Figures 1 to 10 It can be confirmed that an island-like coating exists on the surface of the surface-modified lithium transition metal oxide. On the other hand, referring to... Figure 6 It can be confirmed that the positive electrode active material according to Comparative Example 2 has a multi-particle morphology composed of more than 30 unit particles, unlike other examples and comparative examples.

[0224] SEM / EDS analysis was performed as follows. First, after selecting the lithium transition metal oxides contained in each positive electrode active material prepared according to Preparation Example 1, cross-sectional processing of the lithium transition metal oxides was performed using a FIB (Ga-ion source), and then cross-sectional FE-SEM images were captured using a scanning electron microscope. Subsequently, EDS mapping was performed on the cross-sectional FE-SEM images to map tungsten (W) as the target element, and the distribution of tungsten within the particles was analyzed.

[0225] Referring to the cross-sectional SEM / EDS images of the positive electrode active material (pseudo-single-particle lithium transition metal oxide) according to Examples 2 and 3, Figure 11 and Figure 12 This confirms that the tungsten-containing coating is uniformly formed at the interfaces or gaps between unit particles. Additionally, referring to the surface SEM / EDS image of the positive electrode active material (pseudo-single-particle morphology lithium transition metal oxide) according to Example 2... Figure 13 This confirms that tungsten is uniformly distributed on the surface of the unit particles, indicating that the tungsten-containing coating is uniformly formed on the surface of the unit particles.

[0226] On the other hand, referring to the surface SEM / EDS image of the positive electrode active material (pseudo-single-particle lithium transition metal oxide) according to Comparative Example 2, a reference is made. Figure 14 It can be confirmed that the coating material (tungsten) agglomerated on the surface of the unit particles. Furthermore, referring to the cross-sectional SEM / EDS image of the positive electrode active material (pseudo-single-particle lithium transition metal oxide) according to Comparative Example 3... Figure 15 It can be confirmed that the coating material agglomerates at the interfaces or gaps between unit particles. This is expected to be due to insufficient heat supplied during the formation of the tungsten-containing coating on the aforementioned lithium transition metal oxide surface, resulting in inadequate diffusion of the coating material and its failure to effectively transform into a coating.

[0227] Referring to the cross-sectional SEM / EDS image of the positive electrode active material (pseudo-single-particle lithium transition metal oxide) according to Comparative Example 4, Figure 16 Although no aggregation of the coating material was observed at the interfaces or gaps between the unit particles, it can be confirmed that most of the coating material has diffused into the interior of the unit particles. As described above, when tungsten, introduced as a coating material, diffuses into the interior of the unit particles constituting the aforementioned lithium transition metal oxide and undergoes doping, it alters the lattice strain of the aforementioned lithium transition metal oxide.

[0228] Experimental Example 2. XRD Analysis of Positive Electrode Active Material

[0229] X-ray diffraction (XRD) analysis was performed on each positive electrode active material prepared according to Preparation Example 1 to analyze the crystallographic properties of the lithium transition metal oxide and tungsten-containing coating contained in the above positive electrode active materials.

[0230] Specifically, by using Cu-Kα radiation The above XRD analysis was performed using a Bruker D8 EENDEAVOR diffractometer. XRD analysis of the above positive electrode active material using Cu-kα lines confirmed the presence of a phase corresponding to lithium tungsten oxide (Li₂WO₄) in the 2θ = 20.0°–22.0° region and a phase corresponding to tungsten oxide (WO₃) in the 2θ = 22.5°–25.0° region.

[0231] Furthermore, the lattice strain and average grain size were calculated from the obtained diffraction spectra by performing X-ray diffraction (XRD) analysis on the aforementioned positive electrode active material using Cu-kα lines. The lattice strain and average grain size were calculated by Rietveld refinement of the X-ray diffraction spectra of the aforementioned positive electrode active material, using a straight line obtained by plotting the diffraction angle θ (rad) and half-width at half-maximum β (rad) on a coordinate plane with sinθ as the horizontal axis and βcosθ as the vertical axis, within the range of 2θ = 10° to 120°. The lattice strain (ε), expressed as Δd / d, was calculated by dividing the slope of the aforementioned straight line by 1 / 4 (or can be expressed as β / 4tanθ).

[0232] Similarly, the average Ni occupancy at the Li 3a site was calculated by Rietveld refinement of the diffraction light obtained from X-ray diffraction (XRD) analysis of the above-mentioned positive electrode active material using Cu-kα rays.

[0233] The XRD analysis results are shown in Table 1 below.

[0234] Table 1

[0235]

[0236] “O” indicates that a distinct corresponding diffraction peak was detected; “△” indicates that a weaker corresponding diffraction peak was detected; “X” indicates that no corresponding diffraction peak was detected.

[0237] Referring to the results in Table 1 above, it can be seen that the positive electrode active materials according to Examples 1 to 4 do not contain a phase corresponding to WO3, but rather a phase corresponding to Li2WO4. In other words, it can be inferred that unreacted WO3 is not present in the positive electrode active materials according to Examples 1 to 4, but rather a coating containing Li2WO4 is formed on its surface. It can be confirmed that the lattice strain (ε) measured from the positive electrode active materials according to Examples 1 to 4 is less than 0.00025, the average grain size is 160 nm to 200 nm, and the Ni occupancy is less than 3.5%.

[0238] Considering that the lattice strain (ε) measured from the positive electrode active material of Comparative Example 1 without surface modification is less than 0.00041 and the Ni content is 4.86%, it can be confirmed that the surface modification proposed herein can reduce the lattice strain of the aforementioned lithium transition metal oxide and decrease the Ni content.

[0239] Unlike the positive electrode active materials according to Examples 1 to 4, the positive electrode active material according to Comparative Example 2, which has a multi-particle morphology, has a lattice strain (ε) of 0.00035, an average grain size of 147.51 nm, and a Ni content of 4.75%.

[0240] It can be confirmed that the positive electrode active material according to Comparative Example 3 does not contain the phase corresponding to Li2WO4, but rather the phase corresponding to WO3. The reason for this is presumably that insufficient heat was supplied during the formation of the tungsten-containing coating on the surface of the aforementioned lithium transition metal oxide, resulting in insufficient reaction between WO3 and lithium. The lattice strain (ε) measured from the positive electrode active material according to Comparative Example 3 is 0.00030, and the Ni content is 3.67%.

[0241] The positive electrode active material according to Comparative Example 4, similar to that according to Comparative Example 1, does not contain phases corresponding to WO3 and Li2WO4. This is likely because the tungsten introduced as a coating material failed to form a coating on the surface of the aforementioned lithium transition metal oxide, but instead diffused into the interior of the unit particles and was doped. As previously speculated, due to the diffusion of tungsten in the unit particles, the lattice strain (ε) measured from the positive electrode active material according to Comparative Example 4 is 0.00040, and the Ni content is 4.04%.

[0242] On the other hand, according to Comparative Example 5, the peak intensities corresponding to both the WO3 phase and the Li2WO4 phase in the positive electrode active material were detected to be extremely weak. This is presumably due to the low content of tungsten (WO3) introduced as a coating material, resulting in an inadequate formation of a Li2WO4-containing coating. According to Comparative Example 6, the high content of tungsten (WO3) introduced as a coating material in the positive electrode active material led to the coexistence of unreacted WO3.

[0243] The lattice strain (ε) measured according to the positive electrode active material of Comparative Example 5 was 0.00029, and the lattice strain (ε) measured according to the positive electrode active material of Comparative Example 6 was 0.00027. It can be confirmed that the tungsten content used to coat the surface of the above-mentioned lithium transition metal oxide will affect the lattice strain of the above-mentioned lithium transition metal oxide.

[0244] Example 3. Evaluation of the electrochemical characteristics of lithium secondary batteries (half-cells)

[0245] The lithium secondary battery (half-cell) prepared in Preparation Example 2 was subjected to charge / discharge experiments using an electrochemical analysis apparatus (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.4V, and a discharge rate of 2.0C / 0.1C to determine the initial charge capacity, initial discharge capacity, initial efficiency, and 2.0C / 0.1C rate characteristics.

[0246] The measurement results are shown in Table 2 below.

[0247] Table 2

[0248]

[0249] Referring to the results in Table 2 above, it can be seen that the discharge capacity and rate characteristics of the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 4 were significantly improved. Furthermore, compared to Comparative Example 2, which contains lithium transition metal oxides with multi-particle morphologies, the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 4 not only did not show a decrease in capacity characteristics, initial efficiency, and rate characteristics, but actually showed an improvement.

[0250] Experimental Example 4. Residual Lithium Analysis of Positive Electrode Active Material

[0251] The residual lithium content in each positive electrode active material prepared according to Preparation Example 1 was quantitatively analyzed using known methods. Specifically, 5g of each positive electrode active material prepared according to Preparation Example 1 and 100g of deionized water were added to a 300mL beaker, and then stirred at 300rpm for 15 minutes using a magnetic rod.

[0252] The solution was then filtered using a vacuum flask, and 50g of the filtrate was collected. The collected solution was poured into an automatic titrator container, and the contents of LiOH and Li2CO3 in the solution were determined by automatic titration with 0.1N hydrochloric acid (HCl) according to the Wader method.

[0253] The results of the residual lithium analysis are shown in Table 3 below.

[0254] Table 3

[0255]

[0256]

[0257] Compared with Comparative Example 1 without surface modification, it can be confirmed that the residual lithium content of the positive electrode active materials according to Examples 1 to 4 was reduced through surface modification. Furthermore, it can be confirmed that the residual lithium content of the positive electrode active materials according to Examples 1 to 4, which contain single-particle and pseudo-single-particle lithium transition metal oxides, was further reduced compared with that of Comparative Example 2, which contains multi-particle lithium transition metal oxides. Therefore, if the positive electrode active material according to Examples 1 to 4 is used instead of the positive electrode active material according to Comparative Example 2, it is expected to reduce gas generation and expansion phenomena in lithium secondary batteries, thereby improving their long-term lifespan characteristics.

[0258] While the embodiments of the present invention have been described above, those skilled in the art will understand that various modifications and alterations can be made to the present invention by adding, modifying, deleting, or supplementing the constituent elements without departing from the spirit of the present invention as described in the claims, and these modifications and alterations also fall within the scope of the present invention.

Claims

1. A positive electrode active material, characterized in that, include: Lithium transition metal oxides have a crystal structure belonging to the R-3m space group, and the nickel content in the transition metal is more than 40 mol% and less than 70 mol%. as well as A tungsten-containing coating is located on the surface of the aforementioned lithium transition metal oxide; The diffraction spectrum obtained by X-ray diffraction analysis of the above positive electrode active material using Cu-kα rays shows that the lattice strain calculated by Rietveld is below 0.00025.

2. The positive electrode active material according to claim 1, characterized in that, The cobalt content in the aforementioned transition metals is less than 10 mol%.

3. The positive electrode active material according to claim 1, characterized in that, The manganese content in the aforementioned transition metals is above 20 mol% and below 50 mol%.

4. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxides also include cobalt and manganese, with the manganese content being greater than the cobalt content among the aforementioned transition metals.

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

7.

6. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide has at least one of the following forms: a single-particle form consisting of a single unit particle and a pseudo-single-particle form consisting of an aggregate of 30 or fewer unit particles.

7. The positive electrode active material according to claim 1, characterized in that, The average particle size D of the lithium transition metal oxides existing in the above-mentioned single-particle form 50 It is between 1.0 μm and 8.0 μm.

8. The positive electrode active material according to claim 1, characterized in that, The average particle size D of the lithium transition metal oxides existing in the above-mentioned pseudo-single-particle morphology is... 50 It is above 3.0μm and below 12.0μm.

9. The positive electrode active material according to claim 1, characterized in that, The coating described above comprises lithium tungsten oxide represented by the following chemical formula 2: [Chemical Formula 2] Li e W f O g In the above chemical formula 2, 0 <e≤8,0<f≤15,0<g≤20。 10. The positive electrode active material according to claim 1, characterized in that, The diffraction spectrum obtained by X-ray diffraction analysis of the above positive electrode active material using Cu-kα rays shows that the average Ni occupancy at the Li 3a site is less than 3.5% as calculated by Rietveld refinement.

11. The positive electrode active material according to claim 1, characterized in that, The average grain size of the lithium transition metal oxide obtained by X-ray diffraction analysis of the above positive electrode active material using Cu-kα rays was calculated by Rietveld refinement to be 160 nm to 200 nm.

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

13. A positive electrode, characterized in that, It includes the positive electrode active material according to any one of claims 1 to 12.

14. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 13.

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