Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material having improved electrochemical properties and stability and a lithium secondary battery including the same.SOLUTION: A positive electrode active material is a bimodal type positive electrode active material including a first lithium composite oxide and a second lithium composite oxide having different particle sizes and compositions, where the first lithium composite oxide includes first bulk particles including at least nickel and cobalt, and the second lithium composite oxide includes cobalt-free second bulk particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically to a bimodal type positive electrode active material comprising a first lithium composite oxide and a second lithium composite oxide having different particle sizes and compositions, and a lithium secondary battery containing the same. [Background technology]

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

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

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

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

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages such as excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature characteristics. LiNiO2-based cathode active materials have the advantage of exhibiting high discharge capacity, but they are not only difficult to synthesize due to the active cation mixing of Li and Ni, but the synthesized cathode active materials also have the problem of very poor rate characteristics and lifetime characteristics.

[0007] As a result, in order to improve the low rate characteristics and lifetime characteristics of LiNiO2 while maintaining its high reversible capacity, ternary lithium 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 some of the nickel is replaced with cobalt, manganese, and / or aluminum. Since the reversible capacity decreases as the nickel content in such ternary or quaternary lithium composite oxides decreases, research has recently been actively conducted to increase the nickel content in lithium composite oxides.

[0008] Commercialized ternary or quaternary lithium composite oxides contain cobalt as an essential element to achieve a balance between mutually trade-off electrochemical properties and particle stability.

[0009] However, with the recent rapid growth in demand for lithium-ion batteries and the increasing cost of raw materials, the lithium-ion battery market has faced a strong demand for cost reduction. In particular, the cathode active material accounts for the largest cost share in lithium-ion batteries, and among these, cobalt, an essential element of ternary or quaternary lithium composite oxides, is not only the most expensive metal but also subject to supply and demand instability. Therefore, there is increasing market demand for cost-effective cathode active materials by adopting low-cobalt or cobalt-free compositions.

[0010] However, as explained above, cobalt is an essential element required to achieve both electrochemical properties and particle stability in commercially available ternary or quaternary lithium composite oxides.

[0011] For example, it has been reported that the lower the cobalt content in ternary or quaternary lithium composite oxides, the more likely it is that microcracks will form within the particles due to volume contraction / expansion (egstress-causing anisotropic change) of the lithium composite oxide during charging and discharging. The more microcracks that form within the particles, the more the electrolyte penetrates into the particles along these microcracks, accelerating particle decomposition. This phenomenon leads to a degradation in the performance of lithium secondary batteries.

[0012] Furthermore, as the cobalt content in ternary or quaternary lithium composite oxides decreases, the resistance of the positive electrode active material increases and the rate characteristics deteriorate. Therefore, even when adopting low-cobalt (generally cobalt content of 10 mol% or less) or cobalt-free compositions, it is necessary to develop positive electrode active materials that maintain the electrochemical properties of the positive electrode active material at a level similar to that of commercially available positive electrode active materials. [Overview of the project] [Problems that the invention aims to solve]

[0013] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is driving the market, and this is leading to a sustained increase in the demand for positive electrode active materials used in lithium-ion batteries.

[0014] For example, while lithium-ion batteries using lithium iron phosphate (LFP) have traditionally been the primary choice due to safety considerations, there has recently been a growing trend towards the use of nickel-based lithium composite oxides, which offer a higher energy capacity per unit weight compared to LFP. Of course, LFP, being relatively cheaper, is still sometimes used to reduce costs.

[0015] Furthermore, nickel-based lithium composite oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, generally have ternary compositions such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary compositions such as NCMA (Ni-Co-Mn-Al). However, because cobalt is not only unstable in supply and demand but also excessively expensive compared to other raw materials, there is a need to develop positive electrode active materials with low-cobalt or cobalt-free compositions.

[0016] Recently, low-cobalt or cobalt-free cathode active materials have been introduced through several manufacturers, but the prevailing assessment is that their electrochemical properties and stability are still insufficient to replace conventionally commercialized cathode active materials.

[0017] For example, as mentioned earlier, the lower the cobalt content in ternary or quaternary lithium composite oxides, the greater the resistance of the positive electrode active material, inevitably leading to a decrease in electrochemical properties such as the rate characteristics of lithium secondary batteries.

[0018] Furthermore, it has been pointed out that as the cobalt content of ternary or quaternary type lithium composite oxides decreases, the particle stability (such as crystal stability, thermal stability, or particle strength) declines sharply, which may lead to a premature deterioration of the lifespan of lithium secondary batteries using these lithium composite oxides as positive electrode active materials.

[0019] While it is true that conventional low-cobalt or cobalt-free lithium composite oxides have somewhat lower electrochemical properties and stability compared to commercially available ternary or quaternary lithium composite oxides, the inventors have confirmed that a bimodal type cathode active material designed to include a nickel-based lithium composite oxide containing cobalt and a cobalt-free lithium composite oxide can exhibit electrochemical properties and stability at a level suitable for commercialization.

[0020] Accordingly, the present invention aims to provide a bimodal type positive electrode active material comprising a first lithium composite oxide and a second lithium composite oxide having different particle sizes and compositions, wherein the nickel-based lithium composite oxide and cobalt-free lithium composite oxide exist in a bimodal form, thereby providing a positive electrode active material with improved electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0021] Another object of the present invention is to provide a positive electrode comprising a positive electrode active material as defined herein.

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

[0023] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and will be further made clear from the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations set forth in the claims. [Means for solving the problem]

[0024] According to one aspect of the present invention for solving the above-described technical problems, there is provided a bimodal-type cathode active material including a first lithium composite oxide and a second lithium composite oxide having an average particle size larger than that of the first lithium composite oxide.

[0025] In one embodiment, the first lithium composite oxide includes first bulk particles containing at least nickel and cobalt, and the second lithium composite oxide may include cobalt-free second bulk particles.

[0026] In one embodiment, the first bulk particles may be represented by the following Chemical Formula 1.

[0027] [Chemical Formula 1] Li , , b , , a ,

[0029] , 2-α , , c , , 1-(b+c) , z , ,<0000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Here, M3 is at least one selected from Mn and Al, M4 is at least one selected from Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, M3 and M4 are different elements from each other, X is at least one anionic element selected from F, P, S, Cl, and Br, and 0.5 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.50, 0 ≤ c ≤ 0.20, 0 ≤ α ≤ 0.20.

[0030] In some embodiments, in order to improve the electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxide compositions, a coating layer can be formed on the surface of the first bulk particles among the bimodal type cathode active materials.

[0031] Specifically, a coating layer is present on at least a part of the surface of the first bulk particles, and the coating layer may contain a metal oxide represented by the following Chemical Formula 3.

[0032] [Chemical Formula 3] Li d M5 e O f Here, M5 is at least one selected from Ni, Co, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, 0 ≤ d ≤ 8, 0 < e ≤ 8, 0 < f ≤ 13, and d, e, f represent numbers determined from the stoichiometric ratio according to the valence of M5.

[0033] Moreover, by ensuring that cobalt is present at an appropriate level based on the overall composition of the bimodal-type positive electrode active material, the electrochemical characteristics and stability can be improved compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0034] For this purpose, the coating layer present on the surface of the first bulk particles may contain a cobalt-containing oxide.

[0035] In another embodiment, in order to improve the electrochemical characteristics and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides, a coating layer can be formed on the surface of the second bulk particles among the bimodal-type positive electrode active material. At this time, coating layers may be present on the surfaces of both the first bulk particles and the second bulk particles among the positive electrode active material.

[0036] Specifically, a coating layer is present on at least a part of the surface of the second bulk particles, and the coating layer may contain a metal oxide represented by the following Chemical Formula 4.

[0037] [Chemical Formula 4] Li g M6 h [[ID=二十二]]O i Here, M6 is at least one selected from Ni, Co, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, 0 ≦ g ≦ 8, 0 < h ≦ 8, 0 < i ≦ 13, and g, h, and i represent numbers determined from the stoichiometric ratio according to the valence of M6.

[0038] In other embodiments, a coating layer may be present on at least a portion of the surface of the second bulk particle, and the coating layer may contain a compound represented by LiX' (where X' is an anionic element selected from F, Cl, and Br). For example, the compound represented by LiX' may contain LiF. In yet another embodiment, the coating layer may contain lithium sulfide, lithium sulfate, or lithium phosphate.

[0039] Furthermore, by ensuring that cobalt is present at an appropriate level based on the overall composition of the bimodal type positive electrode active material, the electrochemical properties and stability can be improved compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0040] For this reason, the coating layer present on the surface of the second bulk particle may contain a cobalt-containing oxide.

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

[0042] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided in which the positive electrode described above is used. [Effects of the Invention]

[0043] According to the present invention, by providing a bimodal type positive electrode active material containing a nickel-based lithium composite oxide (first lithium composite oxide) and a cobalt-free lithium composite oxide (second lithium composite oxide) that differ in particle size and composition from each other, it is possible to improve the electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0044] In particular, by forming a predetermined coating layer on the surface of the first bulk particles constituting the first lithium composite oxide and / or the second bulk particles constituting the second lithium composite oxide, it is possible to improve the electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0045] When a coating layer containing a cobalt-containing oxide is formed on the surface of the first bulk particles constituting the first lithium composite oxide and / or the second bulk particles constituting the second lithium composite oxide, the cobalt content within the first bulk particles can be further reduced. As a result, the cobalt content within the overall composition (bulk composition) of the bimodal type positive electrode active material can be reduced, achieving the objective of reducing the cost of the positive electrode active material.

[0046] Furthermore, according to the present invention, the electrochemical properties of the positive electrode active material can be further improved by designing appropriate metal compositions for the nickel-based lithium composite oxide (first lithium composite oxide) and the cobalt-free lithium composite oxide (second lithium composite oxide) among the bimodal type positive electrode active material. [Brief explanation of the drawing]

[0047] [Figure 1] Figure 1 shows the dQ / dV profile during the initial discharge of a lithium secondary battery, depending on the change in the mole fractions of nickel and manganese in the positive electrode active material (lithium composite oxide). [Figure 2] Figure 2 shows the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials according to Examples 1 to 3, respectively. [Figure 3] Figure 3 shows the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials of Comparative Examples 1 to 3, respectively. [Modes for carrying out the invention]

[0048] For the sake of easier understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0049] The positive electrode active material and the lithium secondary battery containing the positive electrode active material according to the present invention will be described in more detail below.

[0050] positive electrode active material According to one aspect of the present invention, a bimodal type positive electrode active material is provided, comprising a first lithium composite oxide and a second lithium composite oxide having different particle sizes and compositions.

[0051] In one embodiment, the bimodal type positive electrode active material may include a first lithium composite oxide and a second lithium composite oxide having a larger average particle size than the first lithium composite oxide. The first lithium composite oxide having a relatively small average particle size may be referred to as small particles, and the second lithium composite oxide having a relatively large average particle size may be referred to as large particles.

[0052] The particle size distribution and average particle size of the first lithium composite oxide and the second lithium composite oxide among the positive electrode active material can be measured using the laser diffraction method. For example, after dispersing the lithium composite oxide (small or large particles) in a dispersion medium, the material is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves at approximately 28 kHz are irradiated at an output of 60 W. After obtaining a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the volume cumulative amount is used to determine the average particle size (D 50) can be defined as follows. In other cases, the average particle size of the first lithium composite oxide and the second lithium composite oxide among the positive electrode active material can be calculated as the average value of the particle sizes of small and large particles confirmed from the SEM image.

[0053] In this application, the range of the average particle size (D50) of small and large particles is not particularly limited.

[0054] For example, small particles may refer to lithium composite oxides with an average particle size (D50) of 7 μm or less, 6.5 μm or less, 6 μm or less, 5.5 μm or less, 5 μm or less, 4.5 μm or less, 4 μm or less, 3.5 μm or less, or 3 μm or less. In order to prevent excessive aggregation of the small particles, the average particle size (D50) of the small particles is preferably 0.5 μm or more, 1 μm or more, 1.5 μm or more, or 2 μm or more. For example, large particles may refer to lithium composite oxides with an average particle size (D50) of more than 7 μm, 7.5 μm or more, 8 μm or more, 8.5 μm or more, 9 μm or more, 9.5 μm or more, 10 μm or more, 10.5 μm or more, 11 μm or more, 11.5 μm or more, or 12 μm or more. In order to ensure that the voids formed by the large particles are sufficiently filled with small particles having a relatively small average particle size, the average particle size (D50) of the large particles is preferably 30 μm or less, 27.5 μm or less, 25 μm or less, 22.5 μm or less, 20 μm or less, 17.5 μm or less, or 15 μm or less.

[0055] The bimodal type positive electrode active material according to various embodiments of the present invention may exist in a state in which the first lithium composite oxide and the second lithium composite oxide are mixed in a weight ratio of 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, or 80:20, or in a state in which the first lithium composite oxide and the second lithium composite oxide are mixed in any weight ratio between 5:95 and 80:20.

[0056] In this case, the first lithium composite oxide may exist in a form that fills the voids between the second lithium composite oxides, or it may exist in a form that is attached to the surface of the second lithium composite oxides, or the first lithium composite oxides may exist in an aggregated form. However, it is preferable that the voids formed by at least a plurality of the second lithium composite oxides are sufficiently filled with the first lithium composite oxide having a relatively small average particle size.

[0057] By having the gaps between large particles filled with relatively small particles with a smaller average particle size, the accumulation density of lithium composite oxide per unit volume is improved, and the energy density per unit volume can be increased. Furthermore, by having the gaps between large particles filled with relatively small particles with a smaller average particle size, volume changes during charging and discharging can be mitigated, stress generation due to volume changes can be minimized, and the occurrence of microcracks can be prevented.

[0058] If the ratio of the first lithium composite oxide to the second lithium composite oxide in the positive electrode active material is excessively low, the voids formed by the second lithium composite oxide may not be sufficiently filled with the first lithium composite oxide. On the other hand, if the ratio of the first lithium composite oxide to the second lithium composite oxide in the positive electrode active material is excessively high, the stability of the positive electrode active material may decrease, such as by a decrease in the press density of the positive electrode active material, as the proportion of aggregated first lithium composite oxides within the positive electrode active material increases.

[0059] In one embodiment, the first lithium composite oxide may include first bulk particles containing at least nickel and cobalt, and the second lithium composite oxide may include cobalt-free second bulk particles. Here, bulk particles refer to single particles or secondary particles. The cobalt-free nature of the second bulk particles means that the second bulk particles are substantially free of cobalt. However, in some embodiments, if a coating layer is present on at least a portion of the surface of the second bulk particles, the coating layer may contain cobalt. Therefore, even if a coating layer containing cobalt is present on at least a portion of the surface of the second bulk particles, if the second bulk particles do not contain cobalt, the second bulk particles can be defined as having a cobalt-free composition. Furthermore, the second lithium composite oxide may also include cobalt-free second bulk particles containing at least nickel and manganese.

[0060] For example, the particles having the average particle size and composition defined as the first lithium composite oxide and the second lithium composite oxide may be single particles in a non-aggregated state or secondary particles in the form of aggregated primary particles. In this case, both the single particles and the secondary particles can be referred to as bulk particles.

[0061] Therefore, the first bulk particles refer to single and secondary particles having the average particle size and composition defined as the first lithium composite oxide, and the second bulk particles refer to single and secondary particles having the average particle size and composition defined as the second lithium composite oxide.

[0062] As mentioned above, in the case of bimodal type positive electrode active materials, the presence of lithium composite oxides in a form in which the gaps between large particles are filled with small particles with a relatively small average particle size improves the accumulation density of lithium composite oxides per unit volume, increases the energy density per unit volume, reduces stress due to volume changes during charging and discharging, and prevents the occurrence of microcracks.

[0063] However, in bimodal type cathode active materials, smaller particles have a relatively larger specific surface area than larger particles, making them more susceptible to side reactions with the electrolyte (for example, initial irreversible reactions that form SEI (solid electrolyte interphase)). Such side reaction mechanisms can lead to a faster degradation rate of smaller particles than larger particles. Furthermore, in the case of lithium composite oxides that can leach manganese at high temperatures, a larger specific surface area allows for further activation of manganese leaching, thus accelerating life degradation due to repeated charging and discharging.

[0064] Therefore, having the first bulk particles, as small particles, have a composition containing at least nickel and cobalt, and the second bulk particles, as large particles, have a cobalt-free composition, improves electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides. Consequently, it is advantageous to reduce the cobalt content in the overall composition (bulk composition) of the bimodal type cathode active material, thereby achieving the objective of reducing the cost of the cathode active material.

[0065] Preferably, the mole fraction of nickel in the first bulk particles is greater than the mole fraction of nickel in the second bulk particles, and the mole fraction of manganese in the first bulk particles is smaller than the mole fraction of manganese in the second bulk particles.

[0066] To evaluate the electrochemical properties or behavior of the positive electrode active material, a dQ / dV graph obtained by differentiating the battery capacity with respect to voltage after charging and discharging is frequently used. For example, when a lithium secondary battery containing a positive electrode with an arbitrary lithium composite oxide containing nickel and manganese as the positive electrode active material and a negative electrode with lithium foil as the negative electrode is charged and discharged at 25°C, with a voltage range of 3.0V to 4.4V and a discharge rate of 0.1C, a graph showing the voltage (V) and battery capacity (Q) at the initial discharge, with the X axis representing the voltage (V) and the Y axis representing the battery capacity (Q), and plotted as the derivative of the battery capacity (Q) with respect to the voltage (V) (dQ / dV), shows a peak in the charging region of 4.1V to 4.3V voltage range indicating the presence of the H2 (hexagonal 2) → H3 (hexagonal 3) phase transformation. Generally, as the mole fraction of manganese in lithium composite oxide increases, the voltage range at which the H2→H3 peak is observed shifts to a relatively higher voltage. For example, when the mole fraction of manganese in lithium composite oxide is about 10%, the H2→H3 peak is observed at about 4.21V, but when the mole fraction of manganese increases to about 20%, the H2→H3 peak is observed at about 4.26V.

[0067] Thus, the further to the right the voltage range in which the H2→H3 peak is observed in the dQ / dV profile for any positive electrode active material shifts, the more it means that the positive electrode active material can exhibit its appropriate capacity at a relatively higher voltage. However, as the voltage range in which the positive electrode active material can exhibit its appropriate capacity increases, problems such as decreased stability or premature degradation of the positive electrode active material may occur, and problems such as accelerated gas generation due to side reactions may also occur.

[0068] Accordingly, according to embodiments of the present invention, by providing a bimodal type positive electrode active material in which the mole fraction of nickel in the first bulk particles is greater than the mole fraction of nickel in the second bulk particles, and the mole fraction of manganese in the first bulk particles is smaller than the mole fraction of manganese in the second bulk particles, it is possible to reduce the voltage range in which the positive electrode active material can exhibit its appropriate capacity.

[0069] The first bulk particle is represented by the following chemical formula 1 and is a lithium composite oxide having a layered crystalline structure.

[0070] [Chemical formula 1] Li w Ni 1-(x+y+z) Co x M1 y M2 z O2 Here, M1 is at least one selected from Mn and Al, and M2 is at least one selected from P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd and Cu, and M1 and M2 are different from each other, and 0.5 ≤ w ≤ 1.5, 0 <x≦0.40、0≦y≦0.30、0≦z≦0.20である。

[0071] The w, which represents the ratio of lithium to the total elements other than lithium in the first bulk particle, may be 0.5 or more and 1.5 or less, 0.75 or more and 1.25 or less, 0.90 or more and 1.1 or less, or 0.95 or more and 1.05 or less.

[0072] In one embodiment, the first bulk particle may be a lithium-nickel composite oxide in which the mole fraction of nickel relative to the total elements other than lithium in the first bulk particle is 60% or more. In this case, in the above chemical formula 1, x + y + z is 0.40 or less.

[0073] Furthermore, according to other embodiments, the mole fraction of nickel relative to the total elements other than lithium in the first bulk particle may be 65% or more (in this case, x+y+z is 0.35 or less), 70% or more (in this case, x+y+z is 0.30 or less), 75% or more (in this case, x+y+z is 0.25 or less), 80% or more (in this case, x+y+z is 0.20 or less), 85% or more (in this case, x+y+z is 0.15 or less), or 90% or more (in this case, x+y+z is 0.10 or less).

[0074] The mole fraction of cobalt relative to the total elements other than lithium in the first bulk particle may be 40% or less (in this case, x is 0.40 or less), 35% or less (in this case, x is 0.35 or less), 30% or less (in this case, x is 0.30 or less), 25% or less (in this case, x is 0.25 or less), 20% or less (in this case, x is 0.20 or less), 15% or less (in this case, x is 0.15 or less), or 10% or less (in this case, x is 0.10 or less).

[0075] If the first bulk particle contains manganese and / or aluminum, the mole fraction of manganese and / or aluminum relative to the total elements other than lithium in the first bulk particle may be 30% or less (in this case, y is 0.30 or less), 25% or less (in this case, y is 0.25 or less), 20% or less (in this case, y is 0.20 or less), 15% or less (in this case, y is 0.15 or less), 10% or less (in this case, y is 0.10 or less), or 5% or less (in this case, y is 0.05 or less).

[0076] Furthermore, the first bulk particle may contain an intra-bulk dopant (M2) for the purpose of improving the electrochemical properties of the first bulk particle.

[0077] If the first bulk particle selectively contains a dopant, the dopant may contain at least one selected from P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, or at least one selected from P, Sr, Ba, B, Ce, Cr, Mo, Na, K, Ti, Zr, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu. The type and combination of dopants can be appropriately selected within a range that does not negatively affect the electrochemical properties and stability of the bimodal type cathode active material comprising the first bulk particle and the second bulk particle, as well as the first bulk particle.

[0078] If the first bulk particle contains a dopant, the mole fraction of the dopant relative to the total elements other than lithium in the first bulk particle may be 20% or less (in this case, z is 0.20 or less), 10% or less (in this case, z is 0.10 or less), 5% or less (in this case, z is 0.05 or less), 4% or less (in this case, z is 0.04 or less), 3% or less (in this case, z is 0.03 or less), 2% or less (in this case, z is 0.02 or less), 1% or less (in this case, z is 0.01 or less), 0.5% or less (in this case, z is 0.005 or less), 0.4% or less (in this case, z is 0.004 or less), 0.3% or less (in this case, z is 0.003 or less), 0.2% or less (in this case, z is 0.002 or less), or 0.1% or less (in this case, z is 0.001 or less).

[0079] The upper and lower limits for the content of nickel, cobalt, M1, and M2 as defined in Chemical Formula 1 above can be appropriately selected within the range that satisfies the definition described above.

[0080] The second bulk particle is represented by the following chemical formula 2 and is a lithium composite oxide having a layered crystalline structure.

[0081] [Chemical formula 2] Li a Ni 1-(b+c) M3 b M4 c O 2-α X α Here, M3 is at least one selected from Mn and Al, M4 is at least one selected from Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, M3 and M4 are different elements from each other, and X is at least one anionic element selected from F, P, S, Cl, and Br, with 0.5 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.50, 0 ≤ c ≤ 0.20, and 0 ≤ α ≤ 0.20.

[0082] The value of 'a', which represents the ratio of lithium to the total elements other than lithium in the second bulk particle, may be 0.5 or more and 1.5 or less, 0.75 or more and 1.25 or less, 0.90 or more and 1.1 or less, or 0.95 or more and 1.05 or less.

[0083] As shown in Chemical Formula 2 above, at least a portion of the oxygen in the second bulk particle may be substituted with at least one anionic element selected from F, P, S, Cl, and Br, preferably F. In particular, F has a similar ionic radius to oxygen and is more stably present in the crystal structure of the second bulk particle than the other anionic elements. Furthermore, F can partially substitute for oxygen that forms M(metal)-O bonds, forming strong MF bonds and contributing to strengthening the reduced crystal structure of the second bulk particle by eliminating cobalt.

[0084] In one embodiment, the mole fraction of nickel in the metal elements excluding lithium in the second bulk particle (corresponding to "1-(b+c)" in chemical formula 2) may be 0.50-0.95, 0.60-0.90, or 0.70-0.80.

[0085] If M3 is manganese in the above chemical formula 2, the mole fraction of manganese in the metal elements excluding lithium in the second bulk particle (corresponding to "b" in chemical formula 2) may be 0.05 to 0.50, 0.10 to 0.40, or 0.10 to 0.30. In this case, b+c in chemical formula 2 may be 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, or 0.30 or less.

[0086] When the mole fraction of nickel in the second bulk particles is less than 0.50, the proportion of lithium composite oxide having a spinel crystal structure in the second bulk particles may increase. As the proportion of lithium composite oxide having a spinel crystal structure in the second bulk particles increases, a higher operating voltage is required, which may lead to a decrease in the capacity characteristics of a lithium secondary battery using the second bulk particles as the positive electrode active material. Furthermore, as the nickel content in the second bulk particles decreases, the manganese content increases, which can increase cation mixing throughout the lithium composite oxide.

[0087] Specifically, the charge of the overall transition metal constituting the lithium composite oxide is preferably in a trivalent state in order to exhibit a stable charge neutrality state. In this case, when synthesizing a lithium composite oxide with a low cobalt content and a high manganese content, Mn 4+ Since there is an excess of Ni, in order to exhibit a charge neutral state, 3+ Ni 2+ The content of increases. Ni present in excess during the synthesis reaction. 2+ (0.69 Å) is Li + Since it has a size similar to (0.76 Å), it can occupy the 3a site of Li in the crystal structure of the lithium composite oxide, and this occupancy phenomenon is called cation mixing.

[0088] On the other hand, if there is an excessive amount of nickel in the second bulk particles, the lithium composite oxide exhibits properties similar to LiNiO2. LiNiO2 not only has low thermal stability, but if an internal short circuit occurs due to external pressure or other factors while charged, the lithium composite oxide may decompose on its own, or side reactions between the electrolyte and the lithium composite oxide interface and surface may cause the lithium secondary battery to rupture and ignite.

[0089] Furthermore, if the mole fraction of manganese in the second bulk particle exceeds 0.50, the same problem may occur as when the mole fraction of nickel is less than 0.50.

[0090] Furthermore, the second bulk particles may contain an intra-bulk dopant (M4) for the purpose of improving the electrochemical properties of the second bulk particles having a cobalt-free composition.

[0091] If the second bulk particles selectively contain a dopant, the dopant may be at least one selected from Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, or may contain Sr, Ba, B, Ce, Cr, Mo, Na, K, Ti, Zr, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu. The type and combination of dopants can be appropriately selected within a range that does not negatively affect the electrochemical properties and stability of the bimodal type cathode active material comprising not only the second bulk particles but also the first bulk particles and the second bulk particles.

[0092] If the second bulk particle contains a dopant, the mole fraction of the dopant relative to the total elements other than lithium in the second bulk particle may be 20% or less (in this case, c is 0.20 or less), 10% or less (in this case, c is 0.10 or less), 5% or less (in this case, c is 0.05 or less), 4% or less (in this case, c is 0.04 or less), 3% or less (in this case, c is 0.03 or less), 2% or less (in this case, c is 0.02 or less), 1% or less (in this case, c is 0.01 or less), 0.5% or less (in this case, c is 0.005 or less), 0.4% or less (in this case, c is 0.004 or less), 0.3% or less (in this case, c is 0.003 or less), 0.2% or less (in this case, c is 0.002 or less), or 0.1% or less (in this case, c is 0.001 or less).

[0093] In some embodiments, in order to improve the electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxide compositions, a coating layer can be formed on the surface of the first bulk particles among the bimodal type cathode active materials. At this time, a coating layer may selectively exist on the surface of the second bulk particles.

[0094] Specifically, a coating layer exists on at least a part of the surface of the first bulk particles, and the coating layer may include a metal oxide represented by the following Chemical Formula 3. The metal oxide represented by the following Chemical Formula 3 is an oxide having a composition different from that of the first bulk particles.

[0095] [Chemical Formula 3] Li d M5 e O f Here, M5 is at least one selected from Ni, Co, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, preferably one or two elements. d, e, and f represent numbers determined from the stoichiometric ratio depending on the valence of M5. For example, d, e, and f can be appropriately selected within the ranges of 0 ≦ d ≦ 8, 0 < e ≦ 8, and 0 < f ≦ 13, respectively.

[0096] Also, by ensuring that cobalt is present at an appropriate level based on the overall composition of the bimodal type cathode active material, the electrochemical properties and stability can be improved compared to conventional low-cobalt or cobalt-free lithium composite oxide compositions.

[0097] For this purpose, the coating layer present on the surface of the first bulk particles may include a cobalt-containing oxide. The cobalt-containing oxide is Co <​​and / or Li d Co e O f may be represented by

[0098] When a coating layer containing a cobalt-containing oxide is formed on the surface of the first bulk particle, the molar fraction of cobalt in the metal elements excluding lithium based on the overall composition of the first bulk particle and the coating layer may be 0.15 or less, preferably 0.11 or less.

[0099] In other embodiments, in order to improve the electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides, a coating layer can be formed on the surface of the second bulk particle among the bimodal type cathode active materials. At this time, coating layers may be present on the surfaces of the first bulk particle and the second bulk particle among the cathode active materials.

[0100] Specifically, a coating layer may be present on at least a part of the surface of the second bulk particle, and the coating layer may include a metal oxide represented by the following Chemical Formula 4. The metal oxide represented by the following Chemical Formula 4 is an oxide having a composition different from that of the second bulk particle.

[0101] [Chemical Formula 4] Li g M6[[ID=u7]] h O i [[ID=u0]] Here, M6 is at least one selected from Ni, Co, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, preferably one or two elements. g, h, and i represent numbers determined from the stoichiometric ratio according to the valence of M6. For example, g, h, and i can be appropriately selected within the ranges of 0 ≦ g ≦ 8, 0 < h ≦ 8, and 0 < i ≦ 13, respectively.

[0102] Furthermore, by ensuring that cobalt is present at an appropriate level based on the overall composition of the bimodal type positive electrode active material, the electrochemical properties and stability can be improved compared to conventional low-cobalt or cobalt-free lithium composite oxides.

[0103] For this reason, the coating layer present on the surface of the second bulk particle may contain a cobalt-containing oxide. The cobalt-containing oxide is Co e O f and / or Li d Co e O f It may be displayed as follows.

[0104] As stated above, the cobalt-free nature of the second bulk particles means that they are substantially free of cobalt. However, as defined above, even if a coating layer containing cobalt is present on at least a portion of the surface of the second bulk particles, the second bulk particles are still cobalt-free, and therefore the second bulk particles may be cobalt-free lithium composite oxides.

[0105] When a coating layer containing a cobalt-containing oxide is formed on the surface of the second bulk particles, the mole fraction of cobalt in the metal elements excluding lithium, based on the overall composition including the second bulk particles and the coating layer, may be 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less.

[0106] In other embodiments, a coating layer may be present on at least a portion of the surface of the second bulk particle, and the coating layer may contain a compound represented by LiX' (where X' is an anion selected from F, Cl, and Br). For example, the compound represented by LiX' may contain LiF. LiF may be formed by the reaction of a fluorine-containing polymer with lithium impurities (e.g., LiOH and Li2CO3) present on the surface of the second bulk particle. In yet another embodiment, the coating layer may contain lithium sulfide, lithium sulfate, or lithium phosphate. In the case of lithium phosphate, it may selectively contain a metal element. The metal element may be at least one metal element selected from M3 and M4.

[0107] Based on the overall composition (bulk composition) of the positive electrode active material including the first lithium composite oxide and the second lithium composite oxide, the mole fraction of cobalt in the metal elements excluding lithium may be 0.005 or more and 0.05 or less, 0.005 or more and 0.045 or less, 0.005 or more and 0.040 or less, 0.005 or more and 0.035 or less, 0.01 or more and 0.045 or less, 0.01 or more and 0.040 or less, or 0.01 or more and 0.035 or less. In this application, the term "overall composition (bulk composition) of the positive electrode active material" means the average composition of the first lithium composite oxide and the second lithium composite oxide constituting the bimodal type positive electrode active material.

[0108] If the mole fraction of cobalt is less than 0.005 relative to the overall composition of the bimodal type positive electrode active material, the particle stability (crystal stability, thermal stability, or particle strength, etc.) of the first lithium composite oxide and the second lithium composite oxide may be insufficient, which can hinder the stable electrochemical properties of the lithium secondary battery. On the other hand, if the mole fraction of cobalt is greater than 0.05 relative to the overall composition of the bimodal type positive electrode active material, it does not align with the purpose of the present invention, which aims to improve electrochemical properties and stability compared to conventional low-cobalt or cobalt-free lithium composite oxides, and consequently reduce the cobalt content in the overall composition (bulk composition) of the bimodal type positive electrode active material, thereby achieving the goal of reducing the cost of the positive electrode active material.

[0109] Furthermore, the mole fraction of manganese in the metal elements excluding lithium, based on the overall composition (bulk composition) of the bimodal type positive electrode active material containing the first lithium composite oxide and the second lithium composite oxide, may be 0.10 or more and 0.40 or less, 0.10 or more and 0.35 or less, 0.10 or more and 0.30 or less, 0.10 or more and 0.25 or less, 0.15 or more and 0.35 or less, 0.15 or more and 0.35 or less, 0.15 or more and 0.25 or less, 0.17 or more and 0.40 or less, 0.17 or more and 0.35 or less, 0.17 or more and 0.30 or less, or 0.17 or more and 0.25 or less.

[0110] If the mole fraction of manganese is less than 0.10 relative to the overall composition of the bimodal type positive electrode active material, the capacitance characteristics (especially the discharge capacity) and rate characteristics of the bimodal type positive electrode active material are insufficient. On the other hand, if the mole fraction of manganese is greater than 0.40 relative to the overall composition of the bimodal type positive electrode active material, there is a risk that the voltage range in which the positive electrode active material can exhibit its appropriate capacitance will become excessively high.

[0111] When the manganese content is controlled within the aforementioned range based on the overall composition (bulk composition) of the bimodal type positive electrode active material containing the first lithium composite oxide and the second lithium composite oxide, the lithium secondary battery using the positive electrode active material exhibits the following dQ / dV behavior.

[0112] Specifically, when a lithium secondary battery, with the positive electrode active material as the positive electrode and lithium foil as the negative electrode, is charged and discharged at 25°C, a voltage range of 3.0V to 4.4V, and a discharge rate of 0.1C, a peak may exist within the charging region in the voltage range of 4.1V to 4.2V (more specifically, 4.2V or less).

[0113] Generally, the peak present in the charging region between 4.1V and 4.3V voltages indicates the presence of the H2 (hexagonal 2) → H3 (hexagonal 3) phase transformation. In this case, as the mole fraction of manganese in the lithium composite oxide increases, the voltage range in which the H2→H3 peak is observed shifts to a relatively higher voltage. For example, referring to Figure 1 (NM99-Ni:Mn=99:1; NM90-Ni:Mn=90:10; NM80-Ni:Mn=80:20; NM70-Ni:Mn=70:30; NM60-Ni:Mn=60:40), which shows the dQ / dV profile during the initial discharge of a lithium secondary battery due to changes in the mole fractions of nickel and manganese in the positive electrode active material (lithium composite oxide), when the mole fraction of manganese in the lithium composite oxide is about 10%, the H2→H3 peak is observed at about 4.21V. However, when the mole fraction of manganese increases to about 20%, the H2→H3 peak shifts to the higher voltage band and is observed at about 4.26V.

[0114] As mentioned above, reducing the cobalt content in commercially available ternary or quaternary lithium composite oxides increases the nickel or manganese content. In particular, an increase in the manganese content in the lithium composite oxide raises the voltage range in which the positive electrode active material can exert its proper capacity, leading to premature degradation of the positive electrode active material, which is vulnerable to high-voltage operating environments. Furthermore, in order to reduce the risks associated with such high-voltage operating environments, it may become necessary to change the commercially available electrolyte and / or negative electrode.

[0115] However, according to embodiments of the present invention, by providing a bimodal type positive electrode active material containing a nickel-based lithium composite oxide (first lithium composite oxide) and a cobalt-free lithium composite oxide (second lithium composite oxide), the voltage range in which the positive electrode active material can exhibit appropriate capacity can be shifted to a low voltage region (preferably 4.2V or less).

[0116] Lithium-ion battery According to another aspect of the present invention, a positive electrode can be provided comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include positive electrode active materials according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as described above, a detailed explanation will be omitted for convenience, and only the remaining undescribed components will be explained below.

[0117] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0118] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0119] In this case, the positive electrode active material may be present in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When present within this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0120] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the positive electrode active material layer.

[0121] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15 wt% relative to the total weight of the positive electrode active material layer.

[0122] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0123] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0124] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0125] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0126] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0127] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0128] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0129] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0130] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0131] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0132] The aforementioned negative electrode active material may be present in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0133] The binder may be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0134] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0135] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0136] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0137] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0138] Furthermore, the electrolytes used in this application include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0139] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0140] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0141] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0142] In the present invention, when the electrolyte used is a solid electrolyte, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, oxide-based solid electrolyte, nitride-based solid electrolyte, or halogen-based solid electrolyte may be used, and preferably a sulfide-based solid electrolyte may be used.

[0143] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the sulfide-based solid electrolyte 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, Li2S-P2S5-ZmSn (where m and n are integers and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li p MO q(Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In.)

[0144] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or a mixture of amorphous and crystalline materials.

[0145] As a material for oxide-based solid electrolytes, Li7La3Zr2O 12 Li 7-x La3Zr 1-x Nb x O 12 Li 7-3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0146] The aforementioned solid electrolyte may be arranged as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Furthermore, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0147] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 wt% relative to the total weight of the electrolyte.

[0148] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0149] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0150] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0151] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0152] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0153] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0154] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0155] In this case, the positive electrode active material may be present in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When present within this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0156] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the positive electrode active material layer.

[0157] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15 wt% relative to the total weight of the positive electrode active material layer.

[0158] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0159] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0160] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0161] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0162] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0163] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0164] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0165] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0166] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0167] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0168] The aforementioned negative electrode active material may be present in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0169] The binder may be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0170] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0171] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0172] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0173] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0174] Furthermore, the electrolytes used in this application include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0175] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0176] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0177] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0178] In the present invention, when the electrolyte used is a solid electrolyte, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, oxide-based solid electrolyte, nitride-based solid electrolyte, or halogen-based solid electrolyte may be used, and preferably a sulfide-based solid electrolyte may be used.

[0179] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the sulfide-based solid electrolyte 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, Li2S-P2S5-ZmSn (where m and n are integers and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li p MO q(Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In), etc.

[0180] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a state where amorphous and crystalline are mixed.

[0181] As materials for oxide-based solid electrolytes, there are Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al[[ID=2e1]] 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. <e000701> The above-mentioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Further, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer

[0183] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 wt% relative to the total weight of the electrolyte.

[0184] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0185] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0186] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0187] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0188] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0189] Manufacturing Example 1. Manufacturing of positive electrode active material Comparative Example 1 Using a known co-precipitation method, nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 3 μm is precipitated. 0.75 Mn 0.25 (OH)2 precursor (small particle precursor) and Ni with an average particle size of approximately 12 μm 0.75 Mn 0.25 (OH)2 precursors (large-grain precursors) were synthesized separately.

[0190] Next, a precursor mixture containing the small-grain precursor and the large-grain precursor in a weight ratio of 3:7 was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.05 ± 0.05). The mixture was then subjected to a first heat treatment at 830°C for 12 hours in an O2 atmosphere, followed by a second heat treatment at 700°C for 12 hours in an O2 atmosphere to obtain the final product (bimodal).

[0191] Comparative Example 2 Using a known co-precipitation method, nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 3 μm is precipitated. 0.75 Mn 0.25 (OH)2 precursor (small particle precursor) and Ni with an average particle size of approximately 12 μm 0.75 Mn0.25 (OH)2 precursors (large-grain precursors) were synthesized separately.

[0192] Next, a precursor mixture containing the small-grained precursor and the large-grained precursor in a weight ratio of 7:3 was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), and then subjected to a first heat treatment at 830°C for 12 hours in an O2 atmosphere to obtain an intermediate product.

[0193] Next, the intermediate product was mixed with Co3O4 (weighed so that the mole fraction of cobalt among the metal elements, excluding lithium, was 0.02 based on the overall composition of the final product (bimodal)), and then subjected to a second heat treatment in an O2 atmosphere at 700°C for 12 hours to obtain the final product (bimodal) with a cobalt-containing coating layer.

[0194] Comparative Example 3 Nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 12 μm is precipitated using a known co-precipitation method. 0.75 Mn 0.25 (OH)2 precursor (large-grain precursor) was synthesized.

[0195] Next, the large particle precursor was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), followed by a first heat treatment at 800°C for 12 hours in an O2 atmosphere, and a second heat treatment at 700°C for 12 hours in an O2 atmosphere to obtain the final product (large particles).

[0196] Comparative Example 4 Using a known co-precipitation method, nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 3 μm is precipitated. 0.75 Mn 0.25 (OH)2 precursor (small particle precursor) was synthesized.

[0197] Next, the small particle precursor was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), followed by a first heat treatment at 800°C for 12 hours in an O2 atmosphere, and then a second heat treatment at 700°C for 12 hours in an O2 atmosphere to obtain the final product (small particles).

[0198] Comparative Example 5 Using a known co-precipitation method, nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 3 μm is precipitated. 0.75 Mn 0.25 (OH)2 precursor (small particle precursor) was synthesized.

[0199] Next, the small particle precursor was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), and then subjected to a first heat treatment in an O2 atmosphere at 800°C for 12 hours to obtain an intermediate product.

[0200] Next, the intermediate product was mixed with Co3O4 (weighed so that the mole fraction of cobalt among the metal elements, excluding lithium, was 0.02 based on the overall composition of the final product (small particles)), and then subjected to a second heat treatment in an O2 atmosphere at 700°C for 12 hours to obtain the final product (small particles) with a cobalt-containing coating layer.

[0201] Example 1 Using a known co-precipitation method, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed in a 91:8:1 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 3 μm is used to precipitate nickel sulfate. 0.91 Co 0.08 Mn 0.01 (OH)2 precursor (small particle precursor) was synthesized.

[0202] Next, the small particle precursor was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), then subjected to a first heat treatment at 800°C for 12 hours in an O2 atmosphere, followed by vacuum drying at 120°C, washing with water, and obtaining the intermediate product.

[0203] Next, the intermediate product was mixed with Co3O4 (weighed so that the mole fraction of cobalt among the metal elements, excluding lithium, was 0.03, based on the overall composition of the final product (small particles)), and then subjected to a second heat treatment in an O2 atmosphere at 700°C for 12 hours to obtain the final product (small particles).

[0204] Subsequently, the final product (small particles) and the final product (large particles) produced in Comparative Example 3 were mixed in a weight ratio of 1:9 to obtain the final product (bimodal).

[0205] Example 2 The final product (bimodal) was prepared in the same manner as in Example 1, except that the final product (small particles) and the final product (large particles) produced in Comparative Example 3 were blended in a weight ratio of 2:8.

[0206] Example 3 The final product (bimodal) was prepared in the same manner as in Example 1, except that the final product (small particles) and the final product (large particles) produced in Comparative Example 3 were blended in a weight ratio of 3:7.

[0207] Example 4 Nickel sulfate and manganese sulfate are mixed in a 75:25 molar ratio in an aqueous metal salt solution, and nickel sulfate with an average particle size of approximately 12 μm is precipitated using a known co-precipitation method. 0.75 Mn 0.25 (OH)2 precursor (large-grain precursor) was synthesized.

[0208] Next, the coarse precursor was mixed with LiOH (Li / (Li-excluded metal)molar ratio = 1.05 ± 0.05), and then subjected to a first heat treatment in an O2 atmosphere at 800°C for 12 hours to obtain an intermediate product.

[0209] Next, the intermediate product was mixed with Co3O4 (weighed so that the mole fraction of cobalt among the metal elements, excluding lithium, was 0.01, based on the overall composition of the final product (large particles)), and then subjected to a second heat treatment in an O2 atmosphere at 700°C for 12 hours to obtain the final product (large particles) with a cobalt-containing coating layer.

[0210] Subsequently, the final product (small particles) produced in Example 1 and the final product (large particles) were blended in a weight ratio of 1:9 to obtain the final product (bimodal).

[0211] The composition of the positive electrode active material (final product) produced according to Production Example 1, as confirmed by ICP analysis, is shown in Table 1 below.

[0212] [Table 1]

[0213] Manufacturing Example 2: Manufacturing of Lithium-ion Secondary Batteries (Half-Cells) A cathode slurry was prepared by dispersing 94 wt% of each of the cathode active materials produced according to Production Example 1, 3 wt% of carbon black, and 3 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0214] A half-cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.15 M.

[0215] Experimental Example 1. Analysis of the crystal structure of the positive electrode active material. For lithium secondary batteries manufactured in Manufacturing Example 2 using the positive electrode active materials from Examples 1 to 3 and Comparative Examples 1 to 3, a two-cycle conversion process was completed using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.4V, and 0.1C / 0.1C. Following this, charging and discharging were performed at 25°C, a voltage range of 3.0V to 4.4V, and 0.1C / 0.1C.

[0216] In this case, the voltage (V) and battery capacity (Q) measured during initial discharge under the aforementioned charge and discharge conditions were used, with the X-axis representing the voltage (V) and the Y-axis representing the battery capacity (Q). The dQ / dV profile was obtained by differentiating the battery capacity (Q) with respect to the voltage (V).

[0217] Figure 2 shows the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials according to Examples 1 to 3, respectively. Figure 3 shows the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials according to Comparative Examples 1 to 3, respectively.

[0218] Referring to Figures 2 and 3, it can be confirmed that in the case of lithium secondary batteries using the positive electrode active material according to Examples 1 to 3, there is a peak in the charging region in the voltage range of approximately 4.1V to approximately 4.2V, whereas in the lithium secondary batteries using the positive electrode active material according to Comparative Examples 1 to 3, this peak does not exist in the voltage range of approximately 4.2V or less.

[0219] In other words, the results above confirm that lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 3 can exhibit appropriate capacity in the voltage range of approximately 4.3V, while lithium secondary batteries using the positive electrode active materials of Examples 1 to 3 can exhibit appropriate capacity in the voltage range of 4.2V or lower.

[0220] Experimental Example 2. Evaluation of the electrochemical properties of lithium secondary batteries (half-cells). The initial charge capacity, initial discharge capacity, and initial efficiency were measured for lithium secondary batteries (half-cells) manufactured in Manufacturing Example 2 through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and a discharge rate of 0.1C.

[0221] Furthermore, the same lithium secondary battery (half-cell) was subjected to 50 charge-discharge cycles using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and 1C / 1C. The ratio of the discharged capacity at the 50th cycle to the initial capacity (cycle capacity retention) was then measured.

[0222] The measurement results are shown in Table 2 below.

[0223] [Table 2]

[0224] Referring to the results in Table 2 above, it can be confirmed that the electrochemical properties of the bimodal type positive electrode active material containing a nickel-based lithium composite oxide containing cobalt and a cobalt-free lithium composite oxide are even better than those of Comparative Examples 1 and 2, which are bimodal type positive electrode active materials consisting only of small and large particles of a cobalt-free composition.

[0225] Furthermore, referring to the results of Comparative Examples 1 and 2, even when the positive electrode active material of Comparative Example 1 was coated with cobalt, and the cobalt was present at an appropriate level based on the overall composition of the bimodal type positive electrode active material, no significant change due to the cobalt coating was observed as long as the bulk particles themselves had a cobalt-free composition.

[0226] Experimental Example 3. Analysis of Residual Lithium in the Cathode Active Material The residual lithium (lithium impurity) content in the positive electrode active material produced according to Production Example 1 was analyzed by pH titration. In pH titration, the residual lithium (lithium impurity) content was measured by the amount of 0.1 M HCl used until the pH reached 4 during pH titration of the positive electrode active material. Specifically, 5 g of each positive electrode active material produced according to Production Example 1 was placed in 100 ml of DIW, stirred for 15 minutes, filtered, and 50 ml of the filtered solution was taken. 0.1 M HCl was then added to this solution, and the amount of HCl consumed due to the pH change was measured. The total content of LiOH and Li2CO3 was then calculated.

[0227] The measurement results are shown in Table 3 below.

[0228] [Table 3]

[0229] Referring to the results in Table 3 above, it can be confirmed that the residual lithium content in the positive electrode active material of the examples is generally lower than that of the positive electrode active material of the comparative examples. When coating bulk particles, the coating raw material reacts with the residual lithium present on the surface of the bulk particles to form a coating layer, which consequently reduces the residual lithium content. Nevertheless, considering that the residual lithium content measured from the positive electrode active materials of Comparative Examples 2 and 5, which underwent cobalt coating treatment, is higher than that of the examples, it can be confirmed that the generation of residual lithium is further suppressed in bimodal type positive electrode active materials using an appropriate blend of nickel-based lithium composite oxide containing cobalt and cobalt-free lithium composite oxide.

[0230] As a result, the content of residual lithium (total content of LiOH and Li2CO3) in the positive electrode active material according to the embodiment of the present invention can be controlled to 5,000 ppm, preferably 4,500 ppm or less.

[0231] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A bimodal type positive electrode active material comprising a first lithium composite oxide and a second lithium composite oxide having a larger average particle size than the first lithium composite oxide, The first lithium composite oxide comprises first bulk particles containing at least nickel and cobalt, A coating layer exists on at least a portion of the surface of the first bulk particle. The coating layer present on the surface of the first bulk particle contains a cobalt-containing oxide. The second lithium composite oxide contains cobalt-free second bulk particles. A positive electrode active material in which the mole fraction of cobalt in the metal elements excluding lithium, based on the overall composition of the positive electrode active material containing the first lithium composite oxide and the second lithium composite oxide, is 0.05 or less.

2. The positive electrode active material according to claim 1, wherein the mole fraction of nickel in the first bulk particle is greater than the mole fraction of nickel in the second bulk particle.

3. The positive electrode active material according to claim 1, wherein the mole fraction of manganese in the first bulk particle is smaller than the mole fraction of manganese in the second bulk particle.

4. The positive electrode active material according to claim 1, wherein the mole fraction of nickel in the metal elements excluding lithium in the first bulk particle is greater than 0.

75.

5. The positive electrode active material according to claim 1, wherein the mole fraction of cobalt in the metal elements excluding lithium in the first bulk particle is 0.15 or less.

6. The first bulk particle is represented by the following chemical formula 1, and is the positive electrode active material according to claim 1. [Chemical formula 1] Li ｗ Ni １－（ｘ＋ｙ＋ｚ） Co ｘ M1 ｙ M2 ｚ O ２ (Here, M1 is at least one selected from Mn and Al. M2 is at least one selected from P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu. M1 and M2 are different from each other. (0.5 ≤ w ≤ 1.5, 0 < x ≤ 0.40, 0 ≤ y ≤ 0.30, 0 ≤ z ≤ 0.20)

7. The second bulk particle is represented by the following chemical formula 2, and is the positive electrode active material according to claim 1. [Chemical formula 2] Li ａ ii １－（ｂ＋ｃ） 73 ｂ 74 ｃ 9 ２－α 8 α (Here, M3 is at least one selected from Mn and Al. M4 is at least one selected from Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu. M3 and M4 are different elements. X is at least one anionic element selected from F, P, S, Cl, and Br. (0.5 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.50, 0 ≤ c ≤ 0.20, 0 ≤ α ≤ 0.20)

8. The positive electrode active material according to claim 1, wherein the coating layer comprises a metal oxide represented by the following chemical formula 3. [Chemical formula 3] Li ｄ M5 ｅ O ｆ (Here, M5 is at least one selected from Ni, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, where 0 ≤ d ≤ 8, 0 < e ≤ 8, and 0 < f ≤ 13.

9. A coating layer exists on at least a portion of the surface of the second bulk particle. The positive electrode active material according to claim 1, wherein the coating layer comprises a metal oxide represented by the following chemical formula 4. [Chemical formula 4] Li ｇ M6 ｈ O ｉ (Here, M6 is at least one selected from Ni, Co, P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, Ca, Ga, Sb, Fe, Nd, and Cu, where 0 ≤ g ≤ 8, 0 < h ≤ 8, and 0 < i ≤ 13.

10. The positive electrode active material according to claim 9, wherein the coating layer present on the surface of the second bulk particle contains a cobalt-containing oxide.

11. The positive electrode active material according to claim 1, wherein the mole fraction of manganese in the metal elements excluding lithium, based on the overall composition of the bimodal type positive electrode active material comprising the first lithium composite oxide and the second lithium composite oxide, is 0.10 or more and 0.40 or less.

12. When a lithium secondary battery, with the aforementioned positive electrode active material as the positive electrode and lithium foil as the negative electrode, is charged and discharged at 25°C, with a voltage range of 3.0V to 4.4V and a discharge rate of 0.1C, In a graph where the voltage (V) and battery capacity (Q) are observed during initial discharge, with the X-axis representing the voltage (V) and the Y-axis representing the battery capacity (Q), and the battery capacity (Q) being shown as the derivative of the battery capacity (Q) with respect to the voltage (V) (dQ / dV), The positive electrode active material according to claim 1, wherein a peak exists within the charging region in the voltage range of 4.1V to 4.2V.

13. A coating layer exists on at least a portion of the surface of the second bulk particle. The positive electrode active material according to claim 1, wherein the coating layer comprises a compound represented by LiX' (where X' is an anionic element selected from F, Cl, and Br).

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

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

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