Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention provides a positive electrode active material and a lithium secondary battery containing the same that can mitigate the leaching of transition metals from lithium manganese oxides and suppress side reactions on the surface of lithium manganese oxides. [Solution] The present invention provides a positive electrode active material containing a lithium-rich lithium manganese oxide, and by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, the elution of transition metals from the lithium manganese oxide is mitigated.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery containing the same. More specifically, the present invention relates to a positive electrode active material comprising a lithium-rich lithium manganese oxide, wherein the elution of transition metals from the lithium manganese oxide and the suppression of side reactions on the surface of the lithium manganese oxide can be mitigated by forming a coating layer comprising a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, and to a lithium secondary battery containing the same. [Background technology]

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

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

[0004] Typical materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. These lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides formed by the combination of Ni, Co, Mn, or Al.

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

[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 performance. On the other hand, LiNiO2-based cathode active materials exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to cation mixing problems between Li and transition metals, which results in significant problems with their rate characteristics.

[0007] Furthermore, a large amount of Li by-products are generated depending on the degree of deepening of such cation mixing. These Li by-products mostly consist of LiOH and Li2CO3, which may cause gelation during the production of the positive electrode paste or generate gas due to repeated charging and discharging after electrode production. In addition, residual Li2CO3 among the Li by-products increases the swelling phenomenon of the cell, which reduces its lifespan characteristics.

[0008] Various candidate materials have been proposed to compensate for the shortcomings of these conventional cathode active materials.

[0009] As an example, research is being conducted to use lithium-rich lithium-manganese oxides, which contain an excess amount of manganese (Mn) among the transition metals, and whose lithium content exceeds the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such lithium-rich lithium-manganese oxides are also called lithium-overlithiated layered oxides (OLOs).

[0010] While the aforementioned OLO has the advantage of theoretically exhibiting high capacity under high-voltage operating conditions, in reality, it has a disadvantage in that its electrical conductivity is relatively low due to the excess amount of Mn contained in the oxide, resulting in poor rate characteristics for lithium secondary batteries using OLO. When rate characteristics are low in this way, problems arise in which the charge / discharge capacity and life efficiency (cycle capacity retention rate) of lithium secondary batteries decrease during cycling.

[0011] Research has been ongoing to modify the composition of OLO in order to solve the aforementioned problems, but so far, such attempts have not reached a commercial level. [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is playing a leading role in driving the market, and this is leading to a sustained increase in the demand for cathode active materials used in lithium-ion batteries.

[0013] 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 have a higher energy capacity per unit weight compared to LFP.

[0014] Furthermore, nickel-based lithium composite oxides, which are now primarily used as positive electrode active materials in high-capacity lithium secondary batteries, require the essential use of ternary metallic elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only subject to unstable supply and demand but is also excessively expensive compared to other raw materials, thus necessitating new compositions of positive electrode active materials that can reduce or eliminate cobalt content.

[0015] Considering these circumstances, lithium-rich lithium manganese oxides can meet the aforementioned market expectations, but they still have limitations in terms of electrochemical properties and stability, preventing them from replacing commercially available cathode active materials such as ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0016] For example, the inventors have confirmed that lithium manganese oxides are more likely to leach transition metals from the particle surface when repeatedly charged and discharged than ternary lithium composite oxides. In particular, there is a high possibility that excess Mn contained in lithium manganese oxides will leach from the particle surface.

[0017] When transition metals are leached from the lithium manganese oxide, the leached transition metals may react with the electrolyte on the surface of the lithium manganese oxide to form impurities. These impurities not only increase the surface resistance of the lithium manganese oxide but also act as a cause of reduced intercalation / deintercalation efficiency of lithium ions passing through the lithium manganese oxide.

[0018] Furthermore, transition metals leached from the lithium manganese oxide, or impurities formed by the reaction of the leached transition metals with the electrolyte, may migrate to the negative electrode using the electrolyte as a medium and may be deposited on the surface of the negative electrode.

[0019] For example, a side reaction may occur with the electrolyte on the surface of the lithium manganese oxide, or an excess of Mn may be present in the lithium manganese oxide due to structural changes in the lithium manganese oxide (such as changes in crystal structure). 2+ Mn can be dissolved into the electrolyte. 2+ During chemical conversion or charging / discharging, Mn can move to the surface of the negative electrode using the electrolyte as a medium and react with various substances present in the battery (electrons, electrolyte, electrodes, or by-products, etc.), resulting in Mn forming on the surface of the negative electrode.2+ It exists as an impurity containing Mn metal or Mn-containing compounds (e.g., MnCO3, MnO, MnF2, etc.).

[0020] The deposition of transition metals or impurities on the negative electrode surface can cause a sharp increase in negative electrode resistance, and such abnormal resistance phenomena are a typical cause of accelerated degradation of lithium secondary battery life.

[0021] In particular, lithium secondary batteries using the aforementioned lithium manganese oxide as the positive electrode active material have a higher operating voltage than other commercially available lithium secondary batteries using ternary lithium composite oxides as the positive electrode active material, making them vulnerable to the aforementioned problems.

[0022] However, currently there is absolutely no technology to resolve the issue of transition metal leaching from lithium-rich lithium-manganese oxides and the problems associated with it.

[0023] As mentioned above, conventional lithium-rich lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability compared to other commercially available types of cathode active materials. However, the inventors have confirmed that forming a barrier layer that can mitigate the leaching of transition metals from the surface of the lithium manganese oxide can suppress or mitigate the leaching of transition metals from the lithium manganese oxide.

[0024] Simultaneously, the inventors have confirmed that forming a barrier layer on the surface of the lithium manganese oxide prevents the elution of transition metals from the lithium manganese oxide, but increases the amount of gas generated inside the lithium secondary battery during long-term use. This gas stored inside the lithium secondary battery acts as a cause of reduced lifespan of the lithium secondary battery.

[0025] To solve the aforementioned problems, it may be considered to attach metal nanoparticles with the ability to capture or eliminate storage gases or HF, etc., to the surface of the lithium manganese oxide; however, such metal nanoparticles may alter the surface kinetic properties of the lithium manganese oxide.

[0026] Accordingly, the present invention aims to provide a positive electrode active material that includes a lithium-rich lithium manganese oxide, and which can mitigate the elution of transition metals from the lithium manganese oxide and suppress side reactions on the surface of the lithium manganese oxide by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide.

[0027] Furthermore, the present invention aims to provide a positive electrode active material that, unlike conventional barrier layers, prevents a rapid increase in the storage gas inside a lithium secondary battery using the lithium manganese oxide as the positive electrode active material by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide.

[0028] Furthermore, unlike conventional barrier layers, the present invention aims to provide a positive electrode active material that minimizes changes in the surface kinetic properties of the lithium manganese oxide by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, instead of attaching or embedding metal nanoparticles having the ability to capture or eliminate storage gases or HF on the surface of the lithium manganese oxide.

[0029] Furthermore, the present invention aims to provide a positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material defined in this application.

[0030] Furthermore, the present invention aims to provide a lithium secondary battery that can achieve high stability by using the positive electrode defined herein, thereby preventing the reduction in lifespan caused by excess lithium and manganese in conventional OLOs, and in particular by reducing side reactions between the positive electrode active material and the electrolyte under high-voltage storage or operating conditions through a coating formed on the surface of the lithium manganese oxide and metal nanoparticles. [Means for solving the problem]

[0031] According to one aspect of the present invention for solving the aforementioned technical problems, a positive electrode active material is provided which contains a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-dissolved.

[0032] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a single phase belonging to the R-3m space group, whereas the lithium-rich lithium manganese oxides defined in this application are characterized by being solid solutions in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group coexist.

[0033] A coating layer is located on the surface of the lithium manganese oxide, and the coating layer can suppress or mitigate the elution of transition metals from the lithium manganese oxide while minimizing changes in the surface kinetic properties of the lithium manganese oxide.

[0034] The lithium manganese-based oxide may be a composite oxide of lithium, nickel, and manganese. The content (mol%) of manganese in the lithium manganese-based oxide may be more than the content (mol%) of nickel. Further, the lithium manganese-based oxide may further contain one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0035] The lithium manganese-based oxide may be represented by the following Chemical Formula 1 or Chemical Formula 2. [Chemical Formula 1] Li(Li a Ni b Co c Mn d M1 e )O 2-f X f In Chemical Formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, X is a halogen capable of substituting a part of the oxygen present in the lithium manganese-based oxide, 0 < a ≤ 0.7, 0 ≤ b < 0.5, 0 ≤ c ≤ 0.2, 0.5 ≤ d < 0.8, 0 < e ≤ 0.1, 0 ≤ f ≤ 0.1.

[0036] The lithium manganese-based oxide exists as secondary particles in which a plurality of primary particles are aggregated, and the coating layer may be located on the surface of the secondary particles. Further, the coating layer may be present at the interface or gap between the primary particles located inside the secondary particles.

[0037] The coating layer contains at least one selected from oxides of Group 13 elements and composite oxides of lithium and Group 13 elements. Preferably, the coating layer contains boron and aluminum.

[0038] The coating layer may contain at least one oxide selected from aluminum oxide, lithium-aluminum oxide, lithium-boron oxide, and lithium-aluminum-boron oxide. Preferably, the coating layer contains lithium-aluminum-boron oxide, or at least one oxide selected from aluminum oxide, lithium-aluminum oxide, and lithium-boron oxide, and lithium-aluminum-boron oxide.

[0039] Furthermore, according to another aspect of the present invention, a positive electrode comprising a positive electrode active material as defined herein is provided. Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material is present within the positive electrode active material layer.

[0040] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided which includes a positive electrode as defined in this application. Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte as defined in this application. [Effects of the Invention]

[0041] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese oxides, which have various disadvantages in terms of electrochemical properties and / or stability compared to commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0042] Specifically, according to the present invention, by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, the elution of transition metals from the lithium manganese oxide can be suppressed or mitigated. By suppressing or mitigating the elution of transition metals from the lithium manganese oxide, it is possible to prevent the formation of impurities by the reaction of the eluted transition metals with the electrolyte on the surface of the lithium manganese oxide.

[0043] Transition metals dissolved from the lithium manganese oxide and / or impurities formed by the reaction of the dissolved transition metals with the electrolyte may migrate to the negative electrode using the electrolyte as a medium, and these impurities may deposit on the surface of the negative electrode, causing a rapid increase in the negative electrode resistance. In other words, according to the present invention, by preventing the dissolution of transition metals from the lithium manganese oxide, it is possible to prevent the acceleration of the life degradation of the lithium secondary battery caused by the deposition of impurities on the positive electrode and / or negative electrode by the transition metals dissolved from the lithium manganese oxide.

[0044] Furthermore, according to the present invention, unlike conventional barrier layers, by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, it is possible to prevent a rapid increase in the storage gas inside a lithium secondary battery using the lithium manganese oxide as the positive electrode active material.

[0045] Furthermore, unlike conventional barrier layers, the present invention minimizes changes in the surface kinetic properties of the lithium manganese oxide by forming a coating layer containing a crystalline phase and an amorphous phase on the surface of the lithium manganese oxide, instead of attaching or embedding metal nanoparticles with the ability to capture or eliminate storage gases or HF on the surface of the lithium manganese oxide. Through this, stable electrochemical properties can be achieved in a lithium secondary battery using the lithium manganese oxide as the positive electrode active material. Along with the effects described above, the specific effects of the present invention will be described below while explaining the specific matters for carrying out the invention. [Brief explanation of the drawing]

[0046] [Figure 1] Figure 1 shows the surface EDS analysis results (target element: Al) for lithium manganese oxide (secondary particles) according to Example 2. [Figure 2] Figure 2 shows the surface EDS analysis results (target element: Al) for lithium manganese oxide (secondary particles) according to Example 4. [Figure 3] Figure 3 shows the XRD analysis results for the cathode active material in Example 1, Example 2, Comparative Example 1, Comparative Example 3, and Comparative Example 4. [Modes for carrying out the invention]

[0047] For the sake of easier understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, the 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.

[0048] Below, several embodiments of the present invention will be described in more detail regarding positive electrode active materials containing lithium-rich lithium manganese oxides and lithium secondary batteries containing said positive electrode active materials.

[0049] (Cathode active material) According to one aspect of the present invention, a positive electrode active material is provided which contains a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-dissolved.

[0050] The phases belonging to the C2 / m space group and the phases belonging to the R-3m space group can be distinguished not only by the composition of each phase, but also by specific peaks for each phase during XRD analysis. For example, a specific peak for the phase belonging to the C2 / m space group may appear in the 2θ = 20.8 ± 1° region, and a specific peak for the phase belonging to the R-3m space group may appear in the 2θ = 18.6 ± 1° region.

[0051] The lithium manganese oxide is a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-solved, and the phases belonging to the C2 / m space group and the phases belonging to the R-3m space group coexist within the lithium manganese oxide. Furthermore, the lithium manganese oxide is different from composite oxides having a spinel crystal structure belonging to the Fd-3m space group (for example, LiMn2O4 or oxides having a similar composition).

[0052] The lithium manganese oxide may be a composite oxide of lithium, nickel, and manganese. Furthermore, the lithium manganese oxide may further contain one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0053] The aforementioned lithium manganese oxide is also called an overlithiated layered oxide (OLO) because the lithium content present in the lithium manganese oxide is greater than the total content of other transition metals (generally, when the molar ratio of lithium to all other metal elements in the lithium manganese oxide (Li / Metal molar ratio) is greater than 1).

[0054] Furthermore, because the lithium manganese oxide contains a higher amount of manganese than other transition metals, it is also referred to as a lithium and manganese-rich layered oxide.

[0055] Generally, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a manganese content of 20 mol% or less in the total metal elements excluding lithium, the aforementioned lithium manganese oxides have a relatively higher proportion of manganese in the total metal elements (e.g., 50 mol% or more, 52 mol% or more, 53 mol% or more, or 55 mol% or more) compared to commercially available ternary lithium composite oxides.

[0056] Furthermore, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a nickel content of 60 mol% or more (80 mol% or more in the case of high-Ni types) in the total metal elements excluding lithium, the lithium manganese-based oxides have a relatively lower proportion of nickel in the total metal elements (for example, less than 50 mol%, 48 mol% or less, 46 mol% or less, 45 mol% or less, 44 mol% or less, 42 mol% or less, or 40 mol% or less) compared to commercially available ternary lithium composite oxides.

[0057] There is also a difference in that the Li / Metal molar ratio measured from lithium manganese oxides as defined in this application is greater than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of lithium manganese oxides as defined in this application is greater than 1, preferably having a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0058] Therefore, in this application, lithium manganese oxide can be defined as a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol% or more, or as a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol% or more and the nickel content is less than 50 mol%.

[0059] Furthermore, in this application, lithium manganese oxides can be defined as composite oxides in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or has a value of 1.1-1.6, 1.1-1.5, 1.2-1.6, or 1.2-1.5, and the manganese content in all metal elements excluding lithium is 50 mol% or more; or as composite oxides in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or has a value of 1.1-1.6, 1.1-1.5, 1.2-1.6, or 1.2-1.5, the manganese content in all metal elements excluding lithium is 50 mol% or more, and the nickel content is less than 50 mol%.

[0060] Despite the aforementioned compositional differences, the lithium manganese-based oxide can also function as a composite metal oxide capable of lithium ion intercalation / deintercalation.

[0061] The lithium manganese-based oxide contained in the positive electrode active material as defined in this application may exist as aggregates formed by the aggregation of multiple primary particles. When the lithium manganese-based oxide exists as aggregates formed by the aggregation of multiple primary particles, the lithium manganese-based oxide can be called a secondary particle.

[0062] The aforementioned primary particles refer to particle units that, when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope, do not appear to have grain boundaries.

[0063] The primary particles constituting the lithium manganese oxide as defined in this application may have an average particle size of 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles may be the average value of the length in the long axis direction and the length in the short axis direction of the primary particle ([length in the long axis direction + length in the short axis direction] / 2). The average particle size of the primary particles can be calculated as the average value of the particle sizes of all primary particles observed from surface SEM images and / or cross-sectional SEM images of the lithium manganese oxide.

[0064] When the average particle size of the primary particles is smaller than 0.05 μm, the specific surface area of ​​the lithium manganese oxide (secondary particles) composed of the primary particles is relatively large. In this case, there is a higher possibility that the lithium manganese oxide and the electrolyte will undergo a side reaction during storage or operation of the lithium secondary battery.

[0065] On the other hand, if the average particle size of the primary particles is greater than 5 μm, the growth of the primary particles is excessively induced, which lengthens the diffusion pathway of lithium ions within the primary particles. When the diffusion pathway of lithium ions within the primary particles is excessively long, the mobility of lithium ions within the primary particles and the diffusivity of lithium ions mediated by the primary particles decrease, which increases the resistance of the lithium manganese oxide (secondary particles) composed of the primary particles.

[0066] To reduce the specific surface area of ​​the lithium manganese oxide while simultaneously preventing a decrease in the mobility of lithium ions within the primary particles and the diffusivity of lithium ions mediated by the primary particles, the average particle size of the primary particles may be 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm.

[0067] The average particle size (D) of the secondary particles 50 The average particle size (D) of the secondary particles can be 1.0 μm to 24.0 μm. 50 The particle size can vary depending on the number of primary particles that make up the secondary particles. The average particle size of the secondary particles can be measured using the laser diffraction method. For example, after dispersing the secondary particles in a dispersion medium, they can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and then measured by obtaining a volume cumulative particle size distribution graph and determining the particle size corresponding to 50% of the volume cumulative amount.

[0068] For example, the lithium manganese oxides defined herein can be used as positive electrode active materials exhibiting a bimodal or trimodal particle size distribution to improve the insufficient energy density per unit volume. Thus, the lithium manganese oxides defined herein can be used as small and / or large particles in a positive electrode active material exhibiting a bimodal particle size distribution, or as small, medium (particles with an average particle size between small and large particles) and / or large particles in a positive electrode active material exhibiting a trimodal particle size distribution.

[0069] When the lithium manganese oxide defined in this application is used as small particles of a positive electrode active material exhibiting a bimodal particle size distribution or a positive electrode active material exhibiting a trimodal particle size distribution, the average particle size (D 50 The size of the particles can be 1 μm to 8 μm, or 2 μm to 6 μm, or 2 μm to 5 μm.

[0070] When the lithium manganese oxide defined in this application is used as a large particle of a positive electrode active material exhibiting a bimodal particle size distribution or a positive electrode active material exhibiting a trimodal particle size distribution, the average particle size (D) of the secondary particles is... 50 The particle size can be 5.0 μm to 24.0 μm, 6.0 μm to 20.0 μm, 6.0 μm to 18.0 μm, 6.0 μm to 16.0 μm, or 6.0 μm to 15.0 μm.

[0071] When the lithium manganese oxide defined in this application is used as a middle particle in a positive electrode active material exhibiting a trimodal particle size distribution, the average particle size (D) of the secondary particles is 50 The particle size can be 5.0 μm to 15.0 μm, 5.0 μm to 10.0 μm, or 5.0 μm to 8.0 μm.

[0072] In this application, "particle size" is used interchangeably with "particle diameter" or "particle size," and unless otherwise defined, all "average particle size" refers to the intermediate volume-based particle size determined by laser diffraction.

[0073] Unless otherwise defined, the term "surface of the primary particle" as used in this application means the outer surface of the primary particle that is exposed to the outside. Similarly, the term "surface of the secondary particle" as used in this application means the outer surface of the secondary particle that is exposed to the outside. As described above, the "surface of the secondary particle" formed by the aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present on the surface portion of the secondary particle.

[0074] Furthermore, unless otherwise defined, the terms "particle surface" as used in this application mean the region relatively close to the "outermost surface" of the particle, and "particle center" means the region relatively closer to the "middle (center)" of the particle than the "surface." Thus, "primary particle surface" means the region relatively close to the "outermost surface" of the primary particle, and "primary particle center" means the region relatively closer to the "middle (center)" of the primary particle than the "surface." Similarly, "secondary particle surface" means the region relatively close to the "outermost surface" of the secondary particle, and "secondary particle center" means the region relatively closer to the "middle (center)" of the secondary particle than the "surface."

[0075] In this case, the region within any particle excluding the "particle surface" can be defined as the "particle's central region."

[0076] In the present application, when the radius of the lithium manganese oxide measured from the cross-sectional SEM image of the lithium manganese oxide is referred to as r, a region where the distance (d) from the center of the lithium manganese oxide satisfies (1 / 2)r < d is defined as the surface portion, and a region where the distance (d) from the center of the lithium manganese oxide satisfies 0 ≦ d ≦ (1 / 2)r is defined as the center portion. Here, it is assumed that the lithium manganese oxide is a secondary particle.

[0077] Since the secondary particle may not have a perfect spherical shape, the radius (r) of the secondary particle can be calculated from the average value of the length of the long axis and the length of the short axis of the lithium manganese oxide measured from the cross-sectional SEM image of the secondary particle. That is, the radius (r) of the secondary particle can be considered as half of the average value of the length of the long axis and the length of the short axis of the lithium manganese oxide measured from the cross-sectional SEM image of the secondary particle.

[0078] The lithium manganese oxide defined in the present application may be represented by the following Chemical Formula 1 or Chemical Formula 2. [Chemical Formula 1] Li(Li a Ni b Co c Mn d M1 e )O 2-f X f In Chemical Formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, X is a halogen that can substitute a part of the oxygen present in the lithium manganese oxide, 0 < a ≦ 0.7, 0 ≦ b < 0.5, 0 ≦ c ≦ 0.2, 0.5 ≦ d < 0.8, 0 < e ≦ 0.1, 0 ≦ f ≦ 0.1. [Chemical Formula 2] rLi2MnO3-p Xp·(1-r)Li u Ni w Co x Mn y M2 z O 2-p′ X' p′ In the aforementioned chemical formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X and X' are halogens capable of substituting some of the oxygen present in the lithium manganese oxide, 0.2 <r≦0.7、0<u≦1、0≦w≦1、0≦x≦0.2、0.3<y<1、0<z≦0.1、0≦p≦0.1、0≦p′≦0.1である。

[0079] In chemical formulas 1 and 2, X and X' are halogen elements that can independently substitute for some of the oxygen present in the lithium manganese oxide. The types of halogens that can be used for X and X' refer to the periodic table, but F, Cl, Br and / or I, etc., can be used, and preferably F can be used.

[0080] In the aforementioned chemical formulas 1 and 2, M1 and M2 are each independently at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and can be at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Ca, Mg, W, Ce, V, Ta, and Y, and at least one selected from Al, P, B, Si, Ti, Zr, and W.

[0081] The Li / Metal molar ratio measured from the lithium manganese oxide represented by the aforementioned chemical formula 1 or chemical formula 2 may be greater than 1, 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5. When the Li / Metal molar ratio measured from the lithium manganese oxide has a value greater than 1, it is possible to form a lithium-rich lithium manganese oxide. Furthermore, in order for the lithium manganese oxide to appropriately form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-dissolved, and at the same time to exhibit high capacity under high-voltage operating conditions, the Li / Metal molar ratio of the lithium manganese oxide is preferably 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0082] Furthermore, in order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are dissolved, it is preferable that the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 2 is 50 mol% or more.

[0083] In order for the lithium manganese oxide to have OLO characteristics that exhibit high capacity under high voltage operating conditions, the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide may be 50 mol% or more and less than 80 mol%, 51 mol% or more and less than 80 mol%, 52 mol% or more and less than 80 mol%, 53 mol% or more and less than 80 mol%, 54 mol% or more and less than 80 mol%, 55 mol% or more and less than 80 mol%, 50 mol% or more and 75 mol%, 51 mol% or more and 75 mol%, 52 mol% or more and 75 mol%, 53 mol% or more and 75 mol%, 54 mol% or more and 75 mol%, or 55 mol% to 75 mol%. If the manganese content in the lithium manganese oxide exceeds 80 mol%, a phase transition may occur due to the movement of transition metals (especially manganese) within the lithium manganese oxide during conversion to a lithium secondary battery and / or operation. Such a phase transition can form a spinel phase, and this spinel phase, acting as an impurity in the lithium manganese oxide, may induce a decrease in charge / discharge capacity or voltage decay during the cycling of the lithium secondary battery. Furthermore, if the manganese content in the lithium manganese oxide exceeds 80 mol%, it may be difficult to sufficiently form a phase belonging to the R-3m space group.

[0084] In order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are dissolved, the nickel content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 2 may be 0% or more and less than 50 mol%, 5 mol% or more and 48 mol%, 10 mol% or more and 46 mol%, 15 mol% or more and 45 mol%, 20 mol% or more and 44 molmol%, 20 mol% or more and 42 mol%, or 20 mol% or more and 40 mol%.

[0085] When the nickel content in the lithium manganese oxide is 50 mol% or more, the C2 / m phase may not form sufficiently, or the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group may not form a sufficient solid solution, which can cause phase separation during conversion and / or operation of the lithium secondary battery.

[0086] The lithium manganese oxide represented by chemical formula 1 or chemical formula 2 may selectively contain cobalt. When the lithium manganese oxide contains cobalt, the mole fraction of cobalt relative to the total number of moles of metal elements in the lithium manganese oxide may be 20% or less, 15% or less, or 10% or less. In other cases, the lithium manganese oxide represented by chemical formula 1 or chemical formula 2 may have a cobalt-free composition.

[0087] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a single-phase phase belonging to the R-3m space group.

[0088] On the other hand, lithium-rich lithium manganese oxides represented by chemical formula 1 or chemical formula 2 are oxides of a phase belonging to the C2 / m space group represented by Li2MnO3 (hereinafter referred to as the "C2 / m phase") and Li u Ni w Co x Mn y M2 z The lithium manganese oxide exists as a composite oxide in which an oxide of a phase belonging to the R-3m space group represented by O2 (hereinafter referred to as the "R-3m phase") is dissolved. For example, the lithium manganese oxide may exist in a state in which an oxide of the C2 / m phase and an oxide of the R-3m phase form a solid solution.

[0089] In this case, a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are simply physically and / or chemically bonded or attached does not fall under the definition of a solid solution as defined in this application.

[0090] For example, a composite oxide having a phase belonging to the C2 / m space group, obtained by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R-3m space group, and having the surface coated with the metal oxide having a phase belonging to the R-3m space group, does not fall under the definition of a solid solution as defined in this application.

[0091] In the lithium manganese oxide represented by the chemical formula 2, if r exceeds 0.7, the proportion of Li2MnO3, which is an oxide of the phase belonging to the space group in the lithium manganese oxide, becomes excessively large. This can lead to an increase in the irreversible capacity and resistance of the positive electrode active material, potentially reducing the discharge capacity. In other words, in order to sufficiently activate the oxide of the phase belonging to the C2 / m space group, which has relatively high resistance in the lithium manganese oxide, and improve surface kinetics, it is preferable that the oxide of the phase belonging to the R-3m space group be present in a predetermined proportion or higher. The ratio of the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group in the lithium manganese oxide can be calculated through the composition ratio of lithium and transition metal present in the lithium manganese oxide.

[0092] A coating layer is located on the surface of the lithium manganese oxide, and the coating layer can suppress or mitigate the elution of transition metals from the lithium manganese oxide while minimizing changes in the surface kinetic properties of the lithium manganese oxide. By suppressing or mitigating the elution of transition metals from the lithium manganese oxide, the coating layer can prevent the formation of impurities by reacting the electrolyte with the transition metals eluted on the surface of the lithium manganese oxide.

[0093] By preventing the leaching of transition metals from the lithium manganese oxide, it is possible to prevent the accelerating deterioration of the lifespan of the lithium secondary battery caused by the deposition of impurities on the positive and / or negative electrodes by the transition metals leached from the lithium manganese oxide.

[0094] The coating layer comprises a crystalline phase and an amorphous phase. The inclusion of a crystalline phase and an amorphous phase in the coating layer may mean that the coating layer contains compounds having a crystalline phase and compounds having an amorphous phase.

[0095] If the coating layer contains only an amorphous phase, it is possible to prevent the leaching of transition metals from the lithium manganese oxide in a short time. However, during long-term use, the amount of gas generated inside the lithium secondary battery increases, which ultimately contributes to reducing the lifespan of the lithium secondary battery. Furthermore, if the coating layer contains only a crystalline phase, it is not possible to form a uniform film on the surface of the lithium manganese oxide, which can make it difficult to effectively suppress or mitigate the leaching of transition metals from the lithium manganese oxide.

[0096] In other words, unlike conventional barrier layers, the coating layer, which includes a crystalline phase and an amorphous phase, can suppress or mitigate the increase in gas generation within the lithium secondary battery during long-term use. Furthermore, by including both a crystalline phase and an amorphous phase in the coating layer, it is possible to minimize changes in the surface kinetic properties of the lithium manganese-based oxide.

[0097] If the lithium manganese oxide is a secondary particle formed by the aggregation of multiple primary particles, the coating layer may be present on the surface of the primary particles and / or the secondary particles. The coating layer can diffuse along the grain boundaries between the primary particles from the surface of the secondary particles toward the center of the secondary particles.

[0098] The coating layer located inside the secondary particles may be present at the interface or gap between the primary particles. The interface between primary particles refers to the grain boundary formed when adjacent primary particles come into contact with each other. The gap between primary particles refers to the space between adjacent primary particles that do not come into direct contact with each other, and can also be called a pore.

[0099] The coating layer may include at least one selected from oxides of group 13 elements and composite oxides of lithium and group 13 elements.

[0100] Furthermore, the coating layer may also contain boron and aluminum. In this case, the molar ratio of boron to aluminum (B / Al) in the positive electrode active material is preferably 0.2 to 2.0, 0.25 to 2.0, 0.25 to 1.75, or 0.4 to 1.6. The molar ratio of boron to aluminum present in the positive electrode active material can be calculated from the boron and aluminum content (mol%) used in the manufacturing process of the positive electrode active material, or from the boron and aluminum content (mol%) measured through ICP analysis or EDS analysis of the positive electrode active material.

[0101] If the molar ratio of boron to aluminum (B / Al) in the positive electrode active material is 0.2 or less, an amorphous phase may not be properly formed in the coating layer, making it difficult to effectively suppress or mitigate the leaching of transition metals from the lithium manganese oxide. Furthermore, if an excessive amount of crystalline phase is formed in the coating layer, the electrochemical properties of the positive electrode active material may deteriorate due to changes in the surface resistance caused by the coating layer. On the other hand, if the molar ratio of boron to aluminum (B / Al) in the positive electrode active material is greater than 2.0, a crystalline phase may not be properly formed in the coating layer, potentially increasing the amount of gas generated inside the lithium secondary battery during long-term use.

[0102] The coating layer may contain at least one oxide selected from aluminum oxide, lithium-aluminum oxide, lithium-boron oxide, and lithium-aluminum-boron oxide. Preferably, the coating layer contains lithium-aluminum-boron oxide, or at least one oxide selected from aluminum oxide, lithium-aluminum oxide, and lithium-boron oxide, and lithium-aluminum-boron oxide. Furthermore, it is preferable that the coating layer does not contain boron oxide that is not compounded with lithium (for example, HBO2, which is a reaction intermediate phase of a boron-containing raw material).

[0103] The oxide present in the coating layer can be represented by the following chemical formula 3. [Chemical formula 3] Li g M3 h O i In the aforementioned chemical formula 3, M3 is at least one selected from Al and B, with 0 ≤ g ≤ 8, 0 ≤ h ≤ 15, and 2 ≤ i ≤ 20, except when h and i are both 0. In the above chemical formula 3, g, h, and i represent numbers determined from the stoichiometric ratio by the valence (oxidation number) of M3. For example, g, h, and i can be appropriately selected within the ranges of 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13, respectively.

[0104] More specifically, the oxide represented by the chemical formula 3 is Li g Al h O i Li g B h O i Li g (Al / B) h O i , or Al h O i This may also be the case, and non-restrictive examples include Al2O3, Li5AlO4, LiBO2, Li2B4O7, Li3BO3, Li2B5AlO 10 LiB4Al7O 17Examples include Li3AlB2O6.

[0105] Of the aforementioned oxides, aluminum oxide, lithium-aluminum oxide, and lithium-aluminum-boron oxide are in a crystalline phase, while lithium-boron oxide may be in an amorphous phase.

[0106] The coating layer may exist on the surface of the lithium manganese oxide as a film having an average film thickness of 1 nm to 300 nm, 10 nm to 200 nm, or 30 nm to 100 nm. The thickness of the coating layer can be measured by EDX analysis of the coating elements based on a cross-sectional SEM image of the lithium manganese oxide. The existence of the coating layer as a film should be distinguished from the oxide constituting the coating layer being dispersed and attached to the surface of the lithium manganese oxide in the form of individual particles.

[0107] If the average thickness of the coating layer is less than 1 nm, it may be difficult to mitigate the elution of transition metals from the lithium manganese oxide and suppress side reactions on the surface of the lithium manganese oxide. On the other hand, if the average thickness of the coating layer is thicker than 300 nm, there is a risk that the surface kinetics of the lithium manganese oxide will decrease or the electrical conductivity will be reduced.

[0108] (Lithium-ion secondary battery) According to another aspect of the present invention, a positive electrode can be provided that includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may contain a lithium manganese-based oxide according to the various embodiments of the present invention described above as the positive electrode active material. Therefore, a detailed explanation of lithium manganese oxides will be omitted, and only the remaining components not mentioned above will be described below. Also, for convenience, the lithium manganese oxides mentioned above will be referred to as the positive electrode active material below.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] In another 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 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.

[0129] 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.

[0130] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0131] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.)

[0136] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or a mixture of amorphous and crystalline materials.

[0137] 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).

[0138] The aforementioned solid electrolyte may be arranged as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Furthermore, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or a portion of the solid electrolyte may be included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0139] 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.

[0140] 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).

[0141] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but 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 preferably be used as a unit battery in a medium-to-large battery module containing multiple battery cells.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] (Manufacturing Example 1: Manufacturing of Cathode Active Material) (Comparative Example 1) (a) Production of precursors An aqueous solution of NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O mixed in a molar ratio of 40:2:58, along with NaOH(aq) and NH4OH(aq), was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 24 hours while N2 gas was introduced into the reactor. After the reaction was complete, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain an average particle size (D 50 ) is 12 μm Ni 0.4 Co 0.02 Mn 0.58 A (OH)2 precursor was obtained. The average particle size of the precursor (D 50 ) was measured by laser diffraction.

[0146] (b) First heat treatment Ni obtained in step (a) above 0.4 Co 0.02 Mn 0.58 The (OH)2 precursor was heat-treated in an O2 atmosphere furnace at 500°C for 6 hours, followed by furnace cooling to obtain the oxide-state precursor.

[0147] (c) Second heat treatment The oxide precursor obtained in step (b) above was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.22), which is a lithium raw material, to prepare a mixture.

[0148] Next, the mixture was heat-treated in an O2 atmosphere furnace at 850°C for 8 hours, followed by furnace cooling to obtain a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution.

[0149] (d) Third heat treatment After mixing the lithium manganese oxide obtained in step (c) and H3BO3 (weighed so that the boron content is 0.4 mol% based on the total metal elements excluding lithium in the lithium manganese oxide), the mixture was heat-treated in an O2 atmosphere furnace at 350°C for 8 hours, then classified and crushed to obtain a positive electrode active material containing lithium manganese oxide with a boron-containing coating layer formed on its surface.

[0150] (Comparative Example 2) The positive electrode active material was manufactured in the same manner as in Comparative Example 1, except that the third heat treatment temperature in step (d) was set to 450°C.

[0151] (Comparative Example 3) A positive electrode active material was produced in the same manner as in Comparative Example 1, except that in step (d) of Comparative Example 1, lithium manganese oxide, H3BO3 (weighed so that the boron content based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metal elements excluding lithium in the lithium manganese oxide is 0.5 mol%) were mixed and heat-treated at 350°C.

[0152] (Comparative Example 4) In step (d) of Comparative Example 1, a lithium manganese oxide, H3BO3 (weighed so that the content of boron based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the content of aluminum based on all metal elements excluding lithium in the lithium manganese oxide is 0.5 mol%) were mixed and heat-treated at 400 °C. An anode active material was produced in the same manner as in Comparative Example 1, except for this.

[0153] (Example 1) (a) Production of precursor An aqueous solution in which NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O were mixed at a molar ratio of 40:2:58, NaOH(aq), and NH4OH(aq) were charged into a reactor while stirring. The temperature inside the reactor was maintained at a temperature of 45 °C, and while introducing N2 gas into the reactor, the precursor synthesis reaction was advanced for 24 hours. After completion of the reaction, the precursor was separated, washed with deionized water, and dried at 120 °C for 10 hours to obtain a Ni 50 Co 0.4 Co 0.02 Mn 0.58 (OH)2 precursor having an average particle size (D 50 ) of 12 μm. The average particle size (D

[0154] (b) First heat treatment The Ni 0.4 Co 0.02 Mn 0.58 (OH)2 precursor obtained in step (a) was heat-treated at 500 °C for 6 hours in a firing furnace in an O2 atmosphere, and then furnace-cooled to obtain a precursor in an oxide state.

[0155] (c) Second heat treatment The precursor in an oxide state obtained in step (b) and LiOH (Li / (Li-excluding metal) molar ratio = 1.22), which is a lithium raw material substance, were mixed to prepare a mixture.

[0156] Next, the mixture was heat-treated in an O2 atmosphere furnace at 850°C for 8 hours, followed by furnace cooling to obtain a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution.

[0157] (d) Third heat treatment After mixing the lithium manganese oxide obtained in step (c) above, H3BO3 (weighed so that the boron content based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metal elements excluding lithium in the lithium manganese oxide is 0.5 mol%), the mixture was heat-treated at 450°C for 8 hours in a furnace under an O2 atmosphere, and then classified and crushed to obtain a positive electrode active material containing lithium manganese oxide with a boron-containing coating layer formed on its surface.

[0158] (Example 2) The positive electrode active material was manufactured in the same manner as in Example 1, except that the third heat treatment temperature in step (d) of Example 1 was set to 500°C.

[0159] (Example 3) A positive electrode active material was produced in the same manner as in Example 1, except that in step (d) of Example 1, lithium manganese oxide, H3BO3 (weighed so that the boron content based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metal elements excluding lithium in the lithium manganese oxide is 2.0 mol%) were mixed.

[0160] (Example 4) In step (d) of Example 1, a lithium manganese oxide, H3BO3 (weighed so that the content of boron based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the content of aluminum based on all metal elements excluding lithium in the lithium manganese oxide is 0.2 mol%) were mixed, and a positive electrode active material was produced in the same manner as in Example 1, except for this.

[0161] (Comparative Example 5) (a) Production of precursor An aqueous solution in which NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O were mixed at a molar ratio of 40:2:58, NaOH(aq), and NH4OH(aq) were charged into a reactor while stirring. The temperature inside the reactor was maintained at 45°C, and while introducing N2 gas into the reactor, the precursor synthesis reaction was advanced for 5 hours. After completion of the reaction, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain a Ni 50 Co 0.4 Mn 0.02 (OH)2 precursor with an average particle size (D 0.58 ) of 3 μm. The average particle size (D 50 ) of the precursor was measured through a laser diffraction method.

[0162] (b) First heat treatment The Ni 0.4 Co 0.02 Mn 0.58 (OH)2 precursor obtained in step (a) was heat-treated at 500°C for 6 hours in a firing furnace in an O2 atmosphere, and then furnace-cooled to obtain a precursor in an oxide state.

[0163] (c) Second heat treatment The precursor in an oxide state obtained in step (b) was mixed with LiOH, which is a lithium raw material substance (Li / (Li-excluding metal) molar ratio = 1.22), to prepare a mixture.

[0164] Next, the mixture was heat-treated in an O2 atmosphere furnace at 850°C for 8 hours, followed by furnace cooling to obtain a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution.

[0165] (d) Third heat treatment After mixing the lithium manganese oxide obtained in step (c) and H3BO3 (weighed so that the boron content based on all metallic elements excluding lithium in the lithium manganese oxide is 0.4 mol%), the mixture was heat-treated in an O2 atmosphere furnace at 350°C for 8 hours, then classified and crushed to obtain a positive electrode active material containing lithium manganese oxide with a boron-containing coating layer formed on its surface.

[0166] (Comparative Example 6) The positive electrode active material was manufactured in the same manner as in Comparative Example 5, except that the third heat treatment temperature was set to 450°C in step (d) of Comparative Example 5.

[0167] (Comparative Example 7) A positive electrode active material was produced in the same manner as in Comparative Example 5, except that in step (d) of Comparative Example 5, lithium manganese oxide, H3BO3 (weighed so that the boron content based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metal elements excluding lithium in the lithium manganese oxide is 0.5 mol%) were mixed and heat-treated at 350°C.

[0168] (Comparative Example 8) A positive electrode active material was produced in the same manner as in Comparative Example 5, except that in step (d) of Comparative Example 5, lithium manganese oxide, H3BO3 (weighed so that the boron content based on all metal elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metal elements excluding lithium in the lithium manganese oxide is 0.5 mol%) were mixed and heat-treated at 400°C.

[0169] (Example 5) (a) Production of precursors An aqueous solution of NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O mixed in a molar ratio of 40:2:58, along with NaOH(aq) and NH4OH(aq), was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was introduced into the reactor. After the reaction was complete, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain an average particle size (D 50 ) Ni 0.4 Co 0.02 Mn 0.58 A (OH)2 precursor was obtained. The average particle size of the precursor (D 50 ) was measured by laser diffraction.

[0170] (b) First heat treatment Ni obtained in step (a) above 0.4 Co 0.02 Mn 0.58 The (OH)2 precursor was heat-treated in an O2 atmosphere furnace at 500°C for 6 hours, followed by furnace cooling to obtain the oxide-state precursor.

[0171] (c) Second heat treatment The oxide precursor obtained in step (b) above was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.22), which is a lithium raw material, to prepare a mixture. Next, the mixture was heat-treated in an O2 atmosphere furnace at 850°C for 8 hours, followed by furnace cooling to obtain a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution.

[0172] (d) Third heat treatment After mixing the lithium manganese oxide obtained in step (c) above, H3BO3 (weighed so that the boron content based on all metallic elements excluding lithium in the lithium manganese oxide is 0.4 mol%), and Al2O3 (weighed so that the aluminum content based on all metallic elements excluding lithium in the lithium manganese oxide is 0.5 mol%), the mixture was heat-treated at 450°C for 8 hours in a furnace under an O2 atmosphere, and then classified and crushed to obtain a positive electrode active material containing lithium manganese oxide with a boron-containing coating layer formed on its surface.

[0173] (Example 6) The positive electrode active material was manufactured in the same manner as in Example 5, except that the third heat treatment temperature in step (d) of Example 5 was set to 500°C.

[0174] (Example 7) The cathode active material was produced in the same manner as in Example 5, except that in step (d) of Example 5, lithium manganese oxide, H3BO3 (weighed so that the boron content is 0.4 mol% based on all metal elements excluding lithium in the lithium manganese oxide), and Al2O3 (weighed so that the aluminum content is 2.0 mol% based on all metal elements excluding lithium in the lithium manganese oxide) were mixed.

[0175] (Example 8) The cathode active material was produced in the same manner as in Example 5, except that in step (d) of Example 5, lithium manganese oxide, H3BO3 (weighed so that the boron content is 0.4 mol% based on all metal elements excluding lithium in the lithium manganese oxide), and Al2O3 (weighed so that the aluminum content is 0.2 mol% based on all metal elements excluding lithium in the lithium manganese oxide) were mixed.

[0176] (Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries (Full Cells)) A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced according to Production Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP).

[0177] The aforementioned positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a positive electrode for a lithium secondary battery in which a positive electrode active material layer was formed.

[0178] A graphite electrode was used as the counter electrode for the positive electrode, and a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separation membrane. A full cell was manufactured using an electrolyte solution containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 2:4:4, with LiPF6 present at a concentration of 1.15 M.

[0179] (Experimental Example 1: Analysis of the coating layer of the positive electrode active material) Lithium manganese-based oxides, selected from the large particles of the positive electrode active material produced in Production Example 1, specifically from Comparative Examples 1 to 4 and Examples 1 to 4, were imaged with a scanning electron microscope to obtain surface SEM images of the secondary particles. Using Energy Dispersive X-ray Spectroscopy, EDS analysis for target elements (B and Al) was performed within the surface SEM images to confirm the presence or absence of a coating layer formation on the surface of the lithium manganese-based oxide (secondary particles).

[0180] Based on the surface SEM images and SEM-EDS analysis results, it was confirmed that a coating layer containing boron was present on the surface of the lithium manganese oxide (secondary particles) in Comparative Examples 1 and 2, and that a coating layer containing boron and aluminum was present on the surface of the lithium manganese oxide (secondary particles) in Comparative Examples 3, 4, and Examples 1 to 4. However, in Comparative Examples 3 and 4, it was confirmed that fine particles were present on the surface of the lithium manganese oxide (secondary particles). Considering that boron forms an amorphous film on the surface of the lithium manganese oxide (secondary particles), it could be inferred that the fine particles were aluminum-derived fine particles.

[0181] Next, X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials produced according to Production Example 1 to identify specific peaks for the coating material present in the coating layer. The XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å).

[0182] Referring to Figure 3, which shows the XRD analysis results, in Comparative Example 1, the intensity of the peak specific to lithium-boron oxide (Li3BO3) was low, and a peak specific to HBO2, the reaction intermediate phase of the boron-containing raw material, appeared. In Comparative Example 3, the intensity of the peak specific to lithium-boron oxide (Li3BO3) and the peak specific to lithium-aluminum oxide (Li5AlO4) were low, and a peak specific to HBO2, the reaction intermediate phase of the boron-containing raw material, appeared. In Comparative Example 4, peaks specific to lithium-boron oxide (Li3BO3) and lithium-aluminum oxide (Li5AlO4) were meaningfully detected, but a peak specific to HBO2, the reaction intermediate phase of the boron-containing raw material, still appeared. Furthermore, none of the positive electrode active materials from Comparative Examples 1, 3, and 4 showed a peak specific to lithium-aluminum-boron oxide (Li3AlB2O6). In other words, if the third heat treatment temperature is not sufficiently high, a coating layer with a proper balance of crystalline and amorphous phases will not be formed, and in particular, lithium-aluminum-boron oxide will not be formed.

[0183] On the other hand, in Examples 1 to 4, peaks specific to aluminum oxide (Al2O3), lithium-boron oxide (Li3BO3), lithium-aluminum oxide (Li5AlO4), and lithium-aluminum-boron oxide (Li3AlB2O6) were all significantly detected, while no peaks specific to HBO2, the reaction intermediate phase of the boron-containing raw material, were detected.

[0184] Furthermore, surface SEM images, SEM-EDS analysis, and XRD analysis results for the small-particle positive electrode active material (Comparative Examples 5-8 and Examples 5-8) produced in Manufacturing Example 1 confirmed that they yielded the same coating results as the large-particle version.

[0185] (Experimental Example 2: Experiment on Transition Metal Elution) For the lithium secondary batteries (full cells) manufactured in Manufacturing Example 2, a 6-cycle conversion process was completed using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. Following this, 500 charge-discharge cycles were performed at 25°C, a voltage range of 2.0V to 4.6V, and 1C / 1C. Next, each full cell was stabilized under 2-cycle charge-discharge conditions at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. After disassembling the full cells, the negative electrode was washed with diethyl carbonate solvent, vacuum-dried at 60°C, and then recovered.

[0186] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the Ni and Mn content of the separated negative electrode active material was measured by ICP analysis.

[0187] The measurement results are shown in Table 1 below. [Table 1]

[0188] Referring to the results in Table 1, it can be confirmed that the amount of B elution was reduced in the lithium secondary battery using the positive electrode active material according to Example 1, in which a coating layer containing a crystalline phase and an amorphous phase was formed. Thus, it can be inferred that B, an element derived from the positive electrode active material, eluted into the electrolyte and moved to the negative electrode using the electrolyte as a medium during charging and discharging. In this way, the impurity that moved to the negative electrode can act as a cause of increased gas generation inside the lithium secondary battery during prolonged use.

[0189] (Experimental Example 3: Experiment on volume change of lithium secondary battery (full cell)) For the lithium secondary battery (full cell) manufactured in Manufacturing Example 2, a 6-cycle conversion process was completed using an electrochemical analyzer (Toyo, Toscat-3100) at 45°C, a voltage range of 2.0V to 4.5V, and 0.2C / 0.2C. Following this, 500 charge-discharge cycles were performed at 45°C, a voltage range of 2.0V to 4.5V, and 1C / 1C. After completing the 500 charge-discharge cycles, the volume change was measured using an electronic hydrometer (SID-220W) compared to the initial full cell.

[0190] The measurement results are shown in Table 2 below. [Table 2]

[0191] Referring to the results in Table 2, in the case of Comparative Examples 5 to 8 and Examples 5 to 8, which are small particles of the positive electrode active material produced in Production Example 1, the difference in volume change was not significant. However, in the case of Comparative Examples 1 to 4 and Examples 1 to 4, which are large particles of the positive electrode active material produced in Production Example 1, it was confirmed that the volume change of Examples 1 to 4 was smaller than that of Comparative Examples 1 to 4. Furthermore, comparing the results of Examples 1 and 2 with those of Examples 3 and 4, it was confirmed that the volume change of Examples 1 and 2, in which amorphous and crystalline phases exist in an appropriate ratio within the coating layer, was smaller than that of Examples 3 and 4.

[0192] (Experimental Example 4. Evaluation of the electrochemical properties of lithium secondary batteries (full cells)) The lithium secondary battery (full cell) manufactured in Manufacturing Example 3 was subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 45°C, voltage range 2.0V~4.5V, and 0.2C / 0.2C. Following this, 500 charge-discharge cycles were performed at 45°C, voltage range 2.0V~4.5V, and 1C / 1C. After completing the 500 charge-discharge cycles, the initial (1 st Cycle) Discharge capacity, 500 relative to initial discharge capacity thThe cycle capacity retention rate (cycle capacity retention) was measured.

[0193] The measurement results are shown in Table 3 below. [Table 3]

[0194] Referring to the results in Table 3, in the case of Comparative Examples 1 to 4 and Examples 1 to 4, which are large particle sizes of the positive electrode active material produced in Production Example 1, there was no significant difference in initial discharge capacity and cycle capacity retention rate. However, in the case of Comparative Examples 5 to 8 and Examples 5 to 8, which are small particle sizes of the positive electrode active material produced in Production Example 1, it was confirmed that the initial discharge capacity and cycle capacity retention rate of Examples 5 to 8 were improved compared to those of Comparative Examples 5 to 8. Furthermore, comparing the results of Examples 5 and 6 with those of Examples 7 and 8, it was confirmed that the initial discharge capacity and cycle capacity retention rate of Examples 5 and 6, in which amorphous and crystalline phases exist in an appropriate ratio within the coating layer, were improved compared to those of Examples 7 and 8.

[0195] Although embodiments of the present invention have been described above, any person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. Lithium manganese oxides in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution, A coating layer located on the surface of the lithium manganese oxide, Includes, The coating layer is a positive electrode active material comprising a crystalline phase and an amorphous phase.

2. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide is a composite oxide of lithium, nickel, and manganese.

3. The positive electrode active material according to claim 2, wherein the manganese content (mol%) in the lithium manganese-based oxide is greater than the nickel content (mol%).

4. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide further comprises one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

5. The lithium manganese oxide is given by the following chemical formula 1 [Chemical formula 1] Li(Li ａ Ni ｂ Co ｃ Mn ｄ M1 ｅ )O ２－ｆ X ｆ [Here, in the chemical formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X is a halogen capable of substituting some of the oxygen present in the lithium manganese oxide, 0 < a ≤ 0.7, 0 ≤ b < 0.5, 0 ≤ c ≤ 0.2, 0.5 ≤ d < 0.8, 0 < e ≤ 0.1, 0 ≤ f ≤ 0.

1. The positive electrode active material according to claim 1, as shown in [the diagram].

6. The aforementioned lithium manganese oxide is given by the following chemical formula 2 [Chemical formula 2] rLi ２ MnO ３－ｐ X ｐ ・(1-r)- ｕ Ni ｗ Co ｘ Mn ｙ M2 ｚ O ２－ｐ′ X′ ｐ′ [Here, in the chemical formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X and X' are halogens capable of substituting some of the oxygen present in the lithium manganese oxide, 0.2 < r ≤ 0.7, 0 < u ≤ 1, 0 ≤ w ≤ 1, 0 ≤ x ≤ 0.2, 0.3 < y < 1, 0 < z ≤ 0.1, 0 ≤ p ≤ 0.1, 0 ≤ p' ≤ 0.

1. The positive electrode active material according to claim 1, as shown in [the diagram].

7. The aforementioned lithium manganese oxide exists as secondary particles formed by the aggregation of multiple primary particles. The coating layer is located on the surface of the secondary particles, as described in claim 1.

8. The aforementioned lithium manganese oxide exists as secondary particles formed by the aggregation of multiple primary particles. The positive electrode active material according to claim 1, wherein the coating layer is located at the interface or gap between the primary particles located inside the secondary particles.

9. The positive electrode active material according to claim 1, wherein the coating layer comprises at least one selected from oxides of group 13 elements and composite oxides of lithium and group 13 elements.

10. The positive electrode active material according to claim 1, wherein the coating layer comprises boron and aluminum.

11. The positive electrode active material according to claim 10, wherein the molar ratio (B / Al) of boron to aluminum in the positive electrode active material is 0.2 or more and 2.0 or less.

12. The coating layer comprises lithium-aluminum-boron oxide, as described in claim 1.

13. The positive electrode active material according to claim 1, wherein the coating layer comprises at least one oxide selected from aluminum oxide, lithium-aluminum oxide, and lithium-boron oxide, and lithium-aluminum-boron oxide.

14. The positive electrode active material according to claim 1, wherein the coating layer comprises aluminum oxide, lithium-aluminum oxide, lithium-boron oxide, and lithium-aluminum-boron oxide.

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

16. A lithium secondary battery comprising the positive electrode described in claim 15.

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