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 particularly, to a positive electrode active material comprising a medium nickel (Mid-Ni) type lithium transition metal oxide having a relatively low nickel content, and a lithium secondary battery comprising the same, the positive electrode active material increases the reversible insertion / extraction efficiency of lithium ions by increasing the c-axis length of the unit particles constituting the lithium transition metal oxide, thereby improving the electrochemical performance that is comparatively inferior to that of a high-nickel (High-Ni) type lithium transition metal oxide having a relatively high nickel content.

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 comprising a mid-Ni type lithium transition metal oxide with a relatively low nickel content. By increasing the c-axis length of the unit particles constituting the aforementioned lithium transition metal oxide, the reversible insertion / extraction efficiency of lithium ions is improved, thereby improving the relatively insufficient electrochemical performance compared to high-Ni type lithium transition metal oxides with a relatively high 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 lifespan performance 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 problem of very low rate performance and lifespan performance of the synthesized cathode active materials.

[0007] Accordingly, in order to improve low-rate performance and lifetime performance 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 as described 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 mid-Ni 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 performance 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 dominant role, the demand for positive electrode active materials used in lithium secondary batteries is also constantly changing.

[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 transition metal oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, are usually composed of ternary types such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary types such as NCMA (Ni-Co-Mn-Al) with a nickel content of about 70 mol% to 80 mol% or more.

[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 positive electrode active materials, reducing the nickel content in lithium transition metal oxides may lead to a decrease in electrochemical performance, such as capacity or rate characteristics (discharge capacity ratio).

[0020] Therefore, the object of the present invention is to provide a positive electrode active material comprising a mid-Ni type 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%), which improves the reversible insertion / extraction efficiency of lithium ions by increasing the c-axis length of the unit particles constituting the lithium transition metal oxide, thereby improving the insufficient electrochemical performance compared with high-Ni type lithium transition metal oxides with a relatively high nickel content.

[0021] Furthermore, the present invention also aims 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 than about 65 mol%), wherein the positive electrode active material particularly improves rate performance by doping the lithium transition metal oxide with calcium to achieve a predetermined range of grain size.

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

[0023] 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.

[0024] Solution to the problem

[0025] According to one aspect of the present invention, a positive electrode active material is provided, which is a positive electrode active material comprising a lithium transition metal oxide capable of lithium insertion / extraction, wherein the lithium transition metal oxide has at least one of a single-particle form composed of a single unit particle and a pseudo-single-particle form composed of 30 or fewer unit particles.

[0026] 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.

[0027] 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%.

[0028] 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.

[0029] As defined in this paper, in medium-nickel lithium transition metal oxides with relatively low nickel content, the kinetic properties of lithium ions, such as conductivity, tend to decrease as the manganese content increases relative to the cobalt content, leading to a deterioration in rate performance.

[0030] Therefore, in this paper, in order to improve the reversible insertion / extraction efficiency of lithium ions to improve the relatively insufficient electrochemical performance compared with high-Ni lithium transition metal oxides with relatively high nickel content, the aforementioned lithium transition metal oxides have 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 30 or fewer unit particles.

[0031] 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. 50 The 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.

[0032] Furthermore, in this paper, in order to increase the c-axis length of the unit particles constituting the lithium transition metal oxide by improving the reversible insertion / extraction efficiency of lithium ions through the aforementioned lithium transition metal oxide, the average crystallite size of the aforementioned lithium transition metal oxide is 160 nm to 195 nm, 165 nm to 190 nm, 170 nm to 185 nm, or 175 nm to 182 nm.

[0033] The c-axis length obtained from Rietveld analysis of X-ray diffraction of the aforementioned lithium transition metal oxides can be: above, The above and Below, or The above and The following or The above and the following.

[0034] The c-axis length and grain size of the lithium transition metal oxides defined in this paper can be represented by calcium doping in the lithium transition metal oxides.

[0035] The aforementioned lithium transition metal oxide may have a layered crystal structure in which lithium layers containing lithium and transition metal layers containing transition metal are alternately arranged, and at least one of the lithium layers and the transition metal layers may be doped with calcium.

[0036] The calcium content in all elements other than lithium in the above-mentioned lithium transition metal oxides can be 0.01 mol% or more and 1.0 mol% or less, 0.05 mol% or more and 0.75 mol% or less, 0.1 mol% or more and 0.7 mol% or less, or 0.1 mol% or more and 0.5 mol% or less.

[0037] The aforementioned lithium transition metal oxide can be represented by the following chemical formula 1. Similarly, the aforementioned lithium transition metal oxide existing in the form of a single particle, the aforementioned lithium transition metal oxide existing in the form of a pseudo-single particle, and the unit particles constituting the pseudo-single particle can have a composition represented by the following chemical formula 1.

[0038] [Chemical Formula 1]

[0039] Li a Ni 1-(b+c+d+e) Co b Mn c Ca d M1 e O2

[0040] In the above chemical formula 1, M1 is at least one selected from Na, K, 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, 0.0001≤d≤0.01, 0≤e≤0.10, and 0.4≤1-(b+c+d+e)≤0.7.

[0041] Furthermore, according to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material is provided.

[0042] Furthermore, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

[0043] The effects of the invention

[0044] According to the present invention, by increasing the c-axis length of the unit particles constituting lithium transition metal oxides, the reversible insertion / extraction efficiency of lithium ions is improved, thereby improving the relatively insufficient electrochemical performance, especially the capacity or rate characteristics (discharge capacity ratio), compared with high-nickel (High-Ni) type lithium transition metal oxides with relatively high nickel content.

[0045] Furthermore, according to the present invention, by doping calcium into lithium transition metal oxide, the grain size is made to have a predetermined range, thereby particularly improving the rate characteristics of the positive electrode active material.

[0046] 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

[0047] Figure 1 The image shows a surface SEM image of the positive electrode active material according to Example 1.

[0048] Figure 2 The surface SEM image of the positive electrode active material according to Example 3, Figure 3 This is a cross-sectional SEM / EDS image of the positive electrode active material according to Example 3.

[0049] Figure 4 The image shows a surface SEM image of the positive electrode active material according to Example 5.

[0050] Figure 5 The image shows a surface SEM image of the positive electrode active material according to Comparative Example 1.

[0051] Figure 6 The image shows a surface SEM image of the positive electrode active material according to Comparative Example 2.

[0052] Figure 7 The image shows a surface SEM image of the positive electrode active material according to Comparative Example 9. Detailed Implementation

[0053] 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.

[0054] Positive electrode active material

[0055] According to one aspect of the invention, the positive electrode active material comprises a lithium transition metal oxide capable of lithium ion intercalation / deintercalation.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] In one embodiment, to improve low-rate performance and lifetime performance while maintaining high reversible capacity, the aforementioned lithium nickel-based transition oxide 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), in which 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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. Conversely, when the nickel content in the aforementioned lithium transition metal oxide is below 40 mol%, excess amounts of other transition metals (e.g., manganese) may cause phase separation, resulting in 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.

[0064] 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%.

[0065] 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, the stability of the lithium secondary battery using the aforementioned positive electrode active material may decrease as the amount of gas generated increases.

[0066] 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.

[0067] When the manganese content in the aforementioned lithium transition metal oxides exceeds 50 mol%, it may be difficult to form single-particle and pseudo-single-particle lithium transition metal oxides. Furthermore, the excessive manganese in the lithium transition metal oxides 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.

[0068] 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.

[0069] The aforementioned lithium transition metal oxides may further include cobalt and manganese as transition metals, with the manganese content being 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.

[0070] 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.

[0071] 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 term "unit particle" can be interpreted as having the same meaning as "primary particle."

[0072] The aforementioned primary particles can have 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 with a scanning electron microscope at magnification of 5000x to 20000x.

[0073] In other words, the single-particle form consisting of a single unit particle refers to the lithium transition metal oxide being composed of only one unit particle, rather than the secondary particle form formed by the aggregation of multiple unit particles (see reference). Figure 1 , Figure 2 (High-magnification SEM image). The average particle size (D) of the lithium transition metal oxides existing in the above-mentioned single-particle morphology. 50 The range can be greater than 0.5 μm and less than 10.0 μm, 0.5 μm to 8 μm, 0.5 μm to 6 μm, 0.5 μm to 5 μm, 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 6 μm, 1 μm to 5 μm, 2 μm to 10 μm, 2 μm to 8 μm, 2 μm to 6 μm, or less than 2 μm to 5 μm.

[0074] 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.

[0075] When the average particle size of the aforementioned unit particles is less than 0.5 μm, the specific surface area of ​​the positive electrode active material, including lithium transition metal oxides having at least one of the forms 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, which may lead to a decrease in stability due to side reactions with the electrolyte.

[0076] Conversely, when the average particle size of the aforementioned unit particles exceeds 10.0 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.

[0077] Typically, ternary or quaternary lithium transition metal oxides exist as secondary particles composed of hundreds or thousands of unit particles. The lithium transition metal oxides defined herein can exist as secondary particles composed of multiple unit particles, but they can also have a pseudo-single particle form composed of no more than 30, 20, or 10 unit particles. Hereinafter, to distinguish them from secondary particles composed of hundreds or thousands of unit particles, secondary particles composed of no more than 30, 20, or 10 unit particles will be referred to as "pseudo-single particles." Furthermore, the particle size of the particles constituting the conventional secondary particle form of ternary or quaternary lithium transition metal oxides is smaller than the particle size of the unit particles defined herein.

[0078] The average particle size (D) of the lithium transition metal oxides exhibiting the aforementioned pseudo-single-particle morphology 50 The particle size can be 3.0 μm or larger and 15.0 μm or smaller, 4.0 μm or larger and 12.0 μm or smaller, or 5.0 μm or larger and 10.0 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.

[0079] 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 range can be greater than 0.5 μm and less than 10.0 μm, 0.5 μm to 8 μm, 0.5 μm to 6 μm, 0.5 μm to 5 μm, 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 6 μm, 1 μm to 5 μm, 2 μm to 10 μm, 2 μm to 8 μm, 2 μm to 6 μm or less than 2 μm to 5 μm.

[0080] 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, as confirmed by SEM images, can be used for calculation.

[0081] Furthermore, 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, a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000) is used to irradiate the particles with ultrasound at approximately 28 kHz at an output power of 60 W. The cumulative volume distribution curve is then obtained, and the particle size corresponding to 50% of the cumulative volume distribution is defined as the average particle size (D). 50 ).

[0082] 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.

[0083] Furthermore, in order to improve the efficiency of reversible insertion / extraction of lithium ions in the aforementioned lithium transition metal oxide, the present invention is characterized by increasing the c-axis length of the unit particles constituting the aforementioned lithium transition metal oxide. Therefore, the average grain size of the aforementioned lithium transition metal oxide can be 160nm to 195nm, 165nm to 190nm, 170nm to 185nm, or 175nm to 182nm.

[0084] The aforementioned average grain size can be quantitatively analyzed using Cu-Kα X-ray diffraction (XRD) analysis of the aforementioned lithium transition metal oxide. Specifically, the aforementioned average grain size can be calculated by performing XRD analysis on the positive electrode active material containing the aforementioned lithium transition metal oxide, obtaining an X-ray diffraction pattern in the range of 2θ = 10° to 120°, and then performing Rietveld refinement.

[0085] The average crystallite size of the aforementioned lithium transition metal oxide is preferably between 160 nm and 195 nm. When the average crystallite size is less than 160 nm or greater than 195 nm, the improvement in electrochemical characteristics, such as rate performance, of lithium secondary batteries using the aforementioned lithium transition metal oxide as the positive electrode active material may be minimal. When the average crystallite size exceeds 195 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 aforementioned positive electrode active material.

[0086] Furthermore, the c-axis length obtained from Rietveld analysis of X-ray diffraction of the aforementioned lithium transition metal oxides can be... above, The above and Below, or The above and The following or The above and the following.

[0087] The c-axis length and grain size of the lithium transition metal oxides defined in this paper can be represented by calcium doping in the lithium transition metal oxides. The c-axis length and / or grain size of the lithium transition metal oxides defined in this paper can be represented by doping with cations other than calcium, but this may lead to problems such as increased resistance of the positive electrode active material.

[0088] Furthermore, when doping with cations other than calcium, the c-axis length and grain size may not increase simultaneously; only one may increase, or one may increase while the other decreases. For example, magnesium doping has no significant effect on both c-axis length and grain size, while strontium or barium doping may decrease the c-axis length while excessively increasing the grain size. Additionally, when doping with sodium or potassium, the grain size increases, but the c-axis length may decrease.

[0089] The effect of calcium doping may vary depending on the morphology of the aforementioned lithium transition metal oxides. For example, when the aforementioned lithium transition metal oxides do not have a single-particle morphology and / or a pseudo-single-particle morphology, but rather a secondary particle morphology composed of hundreds or thousands of unit particles, the grain size may not change or may even decrease when calcium is doped; on the contrary, the c-axis length may increase.

[0090] The aforementioned lithium transition metal oxide can have a layered crystal structure with alternating lithium layers containing lithium and transition metal layers containing transition metal, and at least one of the lithium layers and the transition metal layers can be doped with calcium. With the doping of calcium into the crystal structure of a medium-nickel type lithium transition metal oxide with a nickel content of 40 mol% or more and 70 mol% or less as defined herein, the aforementioned average grain size and c-axis length can satisfy the ranges defined herein.

[0091] On the other hand, even if the range of average grain size and c-axis length defined in this paper is met, if the transition metal does not have a medium-nickel composition with a nickel content of 40 mol% or more and 70 mol% or less, or if the crystal structure of the aforementioned lithium transition metal oxide is not doped with calcium, the improvement in capacity or rate characteristics (discharge capacity ratio) may be insufficient.

[0092] In the aforementioned lithium transition metal oxides, the calcium content in all elements other than lithium can be 0.01 mol% or more and 1.0 mol% or less, 0.05 mol% or more and 1.0 mol% or less, 0.1 mol% or more and 1.0 mol% or less, 0.05 mol% or more and 0.75 mol% or more, 0.1 mol% or more and 0.7 mol% or less, or 0.1 mol% or more and 0.5 mol% or less.

[0093] When the calcium content in all elements other than lithium in the above-mentioned lithium transition metal oxide is less than 0.01 mol%, the changes in the c-axis length and grain size of the above-mentioned lithium transition metal oxide due to calcium doping may be negligible.

[0094] On the other hand, when the calcium content in all elements other than lithium in the aforementioned lithium transition metal oxide exceeds 1.0 mol%, the changes in the c-axis length and grain size of the lithium transition metal oxide become excessive, leading to increased resistance and potentially causing polarization. Due to this polarization, cracks may appear inside the particles, ultimately reducing the lifetime of the positive electrode active material. Furthermore, when the calcium content in all elements other than lithium in the aforementioned lithium transition metal oxide exceeds 1.0 mol%, the calcium content that fails to penetrate into the lithium layer and / or transition metal layer... 2+ Ions may exist on the surface of the aforementioned lithium transition metal oxide in the form of an impedance layer, which may lead to a decrease in the electrochemical performance of the positive electrode active material due to changes in the surface kinetic properties (decreased conductivity) of the aforementioned lithium transition metal oxide.

[0095] In one embodiment, the lithium transition metal oxide described above can be represented by the following chemical formula 1. Similarly, the lithium transition metal oxide existing in the above-described single-particle form, the lithium transition metal oxide existing in the above-described pseudo-single-particle form, and the unit particles constituting the above-described pseudo-single particles can have a composition represented by the following chemical formula 1.

[0096] [Chemical Formula 1]

[0097] Li a Ni 1-(b+c+d+e) Co b Mn c Ca d M1 e O2

[0098] In the above chemical formula 1, M1 is at least one selected from Na, K, 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, 0.0001≤d≤0.01, 0≤e≤0.10, and 0.4≤1-(b+c+d+e)≤0.7.

[0099] The term 'a', which indicates the ratio of lithium to all elements other than lithium 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 1.03 or more and 1.07 or less.

[0100] 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, phase separation may occur due to the presence of excess lithium and manganese in the lithium transition metal oxide, resulting in the formation of impurity phases belonging to space groups other than R-3m.

[0101] In the above chemical formula 1, 1-(b+c+d+e), which represents the 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.

[0102] In the above chemical formula 1, b, which represents the 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.

[0103] In the above chemical formula 1, c, representing the 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. When the molar fraction of manganese in the above lithium transition metal oxide meets the above range, a stable crystal structure can be formed.

[0104] In the above chemical formula 1, d, which represents the ratio of calcium to all elements other than lithium in the above lithium composite oxide, can be 0.0001 or more and 0.01 or less, 0.0005 or more and 0.0075 or less, 0.001 or more and 0.007 or less, or 0.001 or more and 0.005 or less.

[0105] In the above chemical formula 1, M1 represents a dopant other than calcium 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).

[0106] When the lithium transition metal oxide includes dopants other than calcium, e in the above chemical formula 1 is greater than 0; when the lithium transition metal oxide does not include dopants other than calcium, e in the above chemical formula 1 is 0.

[0107] In the above chemical formula 1, e, which represents the ratio of dopant M1 to all elements other than lithium in the above 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, less than 0.01, less than 0.005, less than 0.004, less than 0.003, less than 0.002, or less than 0.001.

[0108] When the aforementioned lithium transition metal oxide selectively includes a dopant, the dopant may include at least one selected from Na, K, 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 B, Al, Ti, Zr, Mo, W, and P. The type, combination, and content of the dopant may be appropriately selected within a range that does not negatively affect the electrochemical performance and stability of the aforementioned positive electrode active material.

[0109] The upper and lower limits of the contents of nickel, cobalt, manganese, calcium and dopant element M1 as defined in the above chemical formula 1 can be appropriately selected within the range that meets the aforementioned definitions.

[0110] Lithium secondary batteries

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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 performance can be shown, but it is not limited thereto.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separation membrane and an 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 following description will only cover the remaining components not previously mentioned.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] In one embodiment, 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.

[0131] 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.

[0132] 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.

[0133] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0134] 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. Among these, carbonate solvents are preferred, and more preferably, 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 performance of the battery, are more suitable. 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 performance is observed.

[0135] 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 performance and enabling efficient movement of lithium ions.

[0136] 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.

[0137] 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.)

[0138] The solid electrolyte, preferably, is a sulfide-based solid electrolyte, which can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0139] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 Li 7-x La3Zr1-x Nb x O 12 Li 7- 3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0140] 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.

[0141] 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.

[0142] 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, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0143] The lithium secondary battery according to the present invention has no particular limitation on its 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] Preparation Example 1. Preparation of Positive Electrode Active Material

[0148] Example 1

[0149] Ni was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a known co-precipitation method. 0.62 Co 0.07 Mn 0.31 (OH)2 hydroxide precursor (Ni:Co:Mn=62:7:31 (atomic%)).

[0150] Next, the above hydroxide precursor, Ca(OH)2 (Ca / (Ni+Co+Mn+Ca) molar ratio = 0.001) and LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) were mixed and calcined at 945°C for 10 hours under an O2 atmosphere to obtain a positive electrode active material including a calcium-doped lithium transition metal oxide.

[0151] from Figure 1 The surface SEM images confirm that the positive electrode active material according to Example 1 above includes lithium transition metal oxides in single-particle and pseudo-single-particle forms.

[0152] Example 2

[0153] Except for the calcination temperature of 935°C, the positive electrode active material comprising calcium-doped lithium transition metal oxide was obtained in the same manner as in Example 1. Based on the surface SEM image of the positive electrode active material according to Example 2 above, it can be confirmed that the positive electrode active material according to Example 2 contains both single-particle and pseudo-single-particle lithium transition metal oxides.

[0154] Example 3

[0155] Except for the use of 0.3 mol% calcium (Ca / (Ni+Co+Mn+Ca) molar ratio = 0.003), the positive electrode active material comprising calcium-doped lithium transition metal oxide was obtained in the same manner as in Example 1.

[0156] from Figure 2 The surface SEM images confirm that the positive electrode active material according to Example 3 above comprises lithium transition metal oxides in both single-particle and pseudo-single-particle forms. Furthermore, through... Figure 3 The cross-sectional SEM / EDS images confirmed that the particles were doped with calcium.

[0157] Example 4

[0158] Except for the calcination temperature of 935°C, the positive electrode active material comprising calcium-doped lithium transition metal oxide was obtained in the same manner as in Example 3. Surface SEM images of the positive electrode active material according to Example 4 confirmed that the positive electrode active material according to Example 4 contained both single-particle and pseudo-single-particle forms of lithium transition metal oxide.

[0159] Example 5

[0160] Except for the use of 0.5 mol% calcium (Ca / (Ni+Co+Mn+Ca) molar ratio = 0.005), the positive electrode active material comprising calcium-doped lithium transition metal oxide was obtained in the same manner as in Example 1.

[0161] from Figure 4 The surface SEM images confirm that the positive electrode active material according to Example 5 above contains lithium transition metal oxides in single-particle and pseudo-single-particle forms.

[0162] Comparative Example 1

[0163] Ni was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a known coprecipitation method. 0.62 Co 0.07 Mn 0.31 (OH)2 hydroxide precursor (Ni:Co:Mn=62:7:31 (atomic%)).

[0164] Then, the above hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) and calcined at 945°C for 10 hours under an O2 atmosphere to obtain a positive electrode active material including lithium transition metal oxide.

[0165] from Figure 5 The surface SEM images confirm that the positive electrode active material of Comparative Example 1 includes lithium transition metal oxides in single-particle and pseudo-single-particle forms.

[0166] Comparative Example 2

[0167] Except for the calcination temperature of 850°C, the positive electrode active material, including calcium-doped lithium transition metal oxide, was obtained in the same manner as in Example 3.

[0168] from Figure 6 The surface SEM images confirm that the positive electrode active material of Comparative Example 2 described above comprises a multi-particle lithium transition metal oxide with more than 30 unit particles.

[0169] Comparative Example 3

[0170] Except for using NaOH (Na / (Ni+Co+Mn+Na) molar ratio = 0.001) instead of Ca(OH)2, the positive electrode active material was obtained in the same manner as in Example 1. Based on the surface SEM image of the positive electrode active material of Comparative Example 3, it can be confirmed that the positive electrode active material of Comparative Example 3 contains lithium transition metal oxides in both single-particle and pseudo-single-particle forms.

[0171] Comparative Example 4

[0172] Except for using NaOH (Na / (Ni+Co+Mn+Na) molar ratio = 0.003) instead of Ca(OH)2, the positive electrode active material was obtained in the same manner as in Example 3. Based on the surface SEM image of the positive electrode active material of Comparative Example 4, it can be confirmed that the positive electrode active material of Comparative Example 4 contains both single-particle and pseudo-single-particle lithium transition metal oxides.

[0173] Comparative Example 5

[0174] Except for using NaOH (Na / (Ni+Co+Mn+Na) molar ratio = 0.005) instead of Ca(OH)2, the positive electrode active material was obtained using the same method as in Example 5. Based on the surface SEM image of the positive electrode active material of Comparative Example 5, it can be confirmed that the positive electrode active material of Comparative Example 5 contains lithium transition metal oxides in both single-particle and pseudo-single-particle forms.

[0175] Comparative Example 6

[0176] Except for using Na2CO3 (Na / (Ni+Co+Mn+Na) molar ratio = 0.005) instead of Ca(OH)2, the positive electrode active material was obtained using the same method as in Example 5. Based on the surface SEM image of the positive electrode active material of Comparative Example 6, it can be confirmed that the positive electrode active material of Comparative Example 6 contains both single-particle and pseudo-single-particle lithium transition metal oxides.

[0177] Comparative Example 7

[0178] Except for using KOH (K / (Ni+Co+Mn+K) molar ratio = 0.003) instead of Ca(OH)2, the positive electrode active material was obtained using the same method as in Example 3. Based on the surface SEM image of the positive electrode active material of Comparative Example 7, it can be confirmed that the positive electrode active material of Comparative Example 7 contains lithium transition metal oxides in both single-particle and pseudo-single-particle forms.

[0179] Comparative Example 8

[0180] Except for using KOH (K / (Ni+Co+Mn+K) molar ratio = 0.005) instead of Ca(OH)2, the same method as in Example 5 was used to obtain the positive electrode active material containing lithium transition metal oxide. Based on the surface SEM image of the positive electrode active material of Comparative Example 8, it can be confirmed that the positive electrode active material of Comparative Example 8 contains both single-particle and pseudo-single-particle lithium transition metal oxides.

[0181] Comparative Example 9

[0182] Except for using Mg(OH)2 (Mg / (Ni+Co+Mn+Mg) molar ratio = 0.003) instead of Ca(OH)2, the positive electrode active material was obtained in the same manner as in Example 3.

[0183] from Figure 7 The surface SEM images confirm that the positive electrode active material of Comparative Example 9 includes single-particle and pseudo-single-particle lithium transition metal oxides.

[0184] Comparative Example 10

[0185] Except that the calcination temperature was set to 920°C, the positive electrode active material comprising lithium transition metal oxide was obtained using the same method as in Comparative Example 1. Observation of the surface SEM image of the positive electrode active material of Comparative Example 10 confirmed that the positive electrode active material of Comparative Example 10 comprises a multi-particle lithium transition metal oxide with more than 30 unit particles.

[0186] Comparative Example 11

[0187] Except that the calcination temperature was set to 920°C, the positive electrode active material, including a calcium-doped lithium transition metal oxide, was obtained in the same manner as in Example 3. Observation of the surface SEM image of the positive electrode active material of Comparative Example 11 confirmed that the positive electrode active material of Comparative Example 11 included a multi-particle lithium transition metal oxide with more than 30 unit particles.

[0188] Comparative Example 12

[0189] Except for using Sr(OH)2 (Sr / (Ni+Co+Mn+Sr) molar ratio = 0.003) instead of Ca(OH)2, the positive electrode active material was obtained in the same manner as in Example 3. Based on the surface SEM image of the positive electrode active material of Comparative Example 12, it can be confirmed that the positive electrode active material of Comparative Example 12 contains lithium transition metal oxides in both single-particle and pseudo-single-particle forms.

[0190] Comparative Example 13

[0191] Except for using Ba(OH)2 (Ba / (Ni+Co+Mn+Ba) molar ratio = 0.003) instead of Ca(OH)2, the positive electrode active material was obtained in the same manner as in Example 3. Based on the surface SEM image of the positive electrode active material of Comparative Example 13, it can be confirmed that the positive electrode active material of Comparative Example 13 contains lithium transition metal oxides in both single-particle and pseudo-single-particle forms.

[0192] Preparation Example 2. Manufacturing of a Lithium Secondary Battery (Half-Cell)

[0193] 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.

[0194] 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.

[0195] Experimental Example 1. XRD Analysis of Positive Electrode Active Material

[0196] X-ray diffraction (XRD) analysis was performed on each positive electrode active material prepared according to Preparation Example 1 to calculate the average grain size and c-axis length of the lithium transition metal oxide contained in the positive electrode active material.

[0197] By using Cu-Kα radiation XRD analysis was performed using a Bruker D8 Advance diffractometer. The average grain size and c-axis length mentioned above were obtained by XRD analysis of the above positive electrode active material using Cu-Kα lines. Using Rietveld Refinement, within the range of 2θ = 10° to 120°, the diffraction angle θ (rad) and half-width at half-maximum β (radians) were plotted on a coordinate plane with sinθ as the horizontal axis and βcosθ as the vertical axis, respectively. The results were calculated by fitting the obtained straight line.

[0198] The XRD analysis results are shown in Table 1 below. In Table 1, the change in the c-axis is expressed as a percentage (%) of the increase or decrease in the c-axis length, based on the c-axis length measured from the positive electrode active material of Comparative Example 1.

[0199] Table 1

[0200]

[0201]

[0202] Referring to the results in Table 1 above, it can be confirmed that compared with Comparative Example 1 used as a reference, the change in c-axis length measured for the positive electrode active materials according to Examples 1 to 5 increased by 0.01% to 0.05%. On the other hand, the c-axis lengths of Comparative Examples 3 to 8, 12, and 13 decreased compared with Comparative Example 1 used as a reference, and the change in c-axis length of Comparative Example 9 was relatively small. On the other hand, since the lithium transition metal oxide contained in the positive electrode active materials of Comparative Examples 2, 10, and 11 is in a multi-particle form, it is not possible to directly compare them with Examples 1 to 5 or Comparative Example 1 used as a reference in terms of grain-related characteristics.

[0203] Example 2. Evaluation of the electrochemical characteristics of lithium secondary batteries (half-cells)

[0204] The lithium secondary battery (half-cell) prepared according to Preparation Example 2 was subjected to charge / discharge experiments using an electrochemical analysis apparatus (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and a discharge rate of 0.1C to 2.0C to determine the charge capacity, discharge capacity, and rate capability (discharge capacity ratio; rate capability, C-rate).

[0205] The results of the above measurements are shown in Tables 2 and 3 below.

[0206] Table 2

[0207]

[0208]

[0209] Compared with positive electrode active materials containing single-particle and pseudo-single-particle lithium transition metal oxides (Comparative Examples 1, 3 to 9, 12 and 13), it can be confirmed that when using the positive electrode active materials of Examples 1 to 5, their capacity or rate characteristics (discharge capacity ratio) are improved.

[0210] On the other hand, referring to Table 3 below, compared with the positive electrode active materials containing lithium transition metal oxides in the form of multiple particles (Comparative Example 2, Comparative Example 10 and Comparative Example 11), it can be confirmed that when using the positive electrode active materials of Examples 1 to 5, the rate performance is significantly improved.

[0211] Table 3

[0212]

[0213] 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 adding 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 comprising a lithium transition metal oxide capable of lithium intercalation / deintercalation, characterized in that, The aforementioned lithium transition metal oxides have 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 aggregation of 30 or fewer unit particles. The aforementioned lithium transition metal oxides contain at least lithium and a transition metal. The nickel content in the aforementioned transition metals is 40 mol% or more and 70 mol% or less. The average grain size of the aforementioned lithium transition metal oxides ranges from 160 nm to 195 nm.

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. The manganese content in the aforementioned transition metals is greater than that in cobalt.

5. 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 The size ranges from 0.5μm to 10.0μm.

6. 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 The size is above 3.0 μm and below 15.0 μm.

7. The positive electrode active material according to claim 1, characterized in that, The c-axis length obtained from Rietveld analysis of X-ray diffraction of the aforementioned lithium transition metal oxides is: above.

8. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide has a layered crystal structure in which lithium layers containing lithium and transition metal layers containing transition metal are arranged alternately. At least one of the lithium layer and the transition metal layer is doped with calcium.

9. The positive electrode active material according to claim 1, characterized in that, In the aforementioned lithium transition metal oxides, the calcium content of all elements except lithium is 0.01 mol% or more and 1.0 mol% or less.

10. 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+e) Co b Mr c Approx d M1 e O2 In the above chemical formula 1, M1 is selected from at least one of Na, K, 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, 0.0001≤d≤0.01, 0≤e≤0.10, 0.4≤1-(b+c+d+e)≤0.

7.

11. A positive electrode, characterized in that, It includes the positive electrode active material according to any one of claims 1 to 10.

12. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 11.

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