Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material including a lithium-excess lithium-manganese-based oxide, which prevents the electrochemical characteristics of the lithium secondary battery, including rate characteristics, from being reduced due to the excess lithium and manganese present in the lithium-manganese-based oxide, and in particular, to a positive electrode active material and a lithium secondary battery including the same, which can prevent deterioration in the lifespan of the lithium secondary battery by suppressing or mitigating the elution of transition metals from the lithium-manganese-based oxide.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material including a lithium-excess lithium manganese-based oxide, wherein the electrochemical properties of a lithium secondary battery including rate characteristics and the like are prevented from deteriorating due to lithium and manganese present in excess in the lithium manganese-based oxide, and particularly, the present invention relates to a positive electrode active material capable of preventing the life degradation of a lithium secondary battery by suppressing or alleviating the elution of transition metals from the lithium manganese-based oxide, and a lithium secondary battery including the same.

Background Art

[0002] A battery stores electric power by using substances capable of electrochemical reactions for a positive electrode and a negative electrode. As a typical example of the battery, there is a lithium secondary battery that stores electric energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive electrode and the negative electrode.

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

[0004] A typical substance used as a positive electrode active material of a lithium secondary battery is a lithium composite oxide. The lithium composite oxide includes LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or an oxide in which Ni, Co, Mn, or Al is compounded.

[0005] Among the positive electrode active materials, LiCoO2 is excellent in life characteristics and charge / discharge efficiency and is most widely used. However, due to the resource limitation of cobalt used as a raw material, it is expensive, and thus has a disadvantage of limited 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 the electrode is manufactured. 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) of lithium secondary batteries decrease during cycling.

[0011] Research has been ongoing to modify the composition of OLO to address the aforementioned problems, but such attempts have not yet reached a commercialization level. [Overview of the project] [Problems that the invention aims to solve]

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

[0013] For example, conventionally, lithium-ion batteries using lithium iron phosphate (LFP) have been primarily used, mainly for safety reasons. However, recently, there has 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, making them suitable as a substitute for commercially available 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 due to repeated charging and discharging 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 a transition metal is leached from the lithium manganese oxide, the leached transition metal can 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 via the lithium manganese oxide.

[0018] Furthermore, the transition metals dissolved from the lithium manganese oxide, or the impurities formed by the reaction of the dissolved transition metals with the electrolyte, can move to the negative electrode using the electrolyte as a medium and 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 amount of Mn may be present in the lithium manganese oxide due to a structural change in the lithium manganese oxide (such as a change 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 will exist 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 surface of the negative electrode can cause a sharp increase in negative electrode resistance, and this abnormal resistance phenomenon is a typical cause of accelerated degradation of the lifespan of lithium secondary batteries.

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

[0022] However, currently there is no technology to resolve the issues caused by the leaching of transition metals from lithium-rich lithium-manganese oxides.

[0023] As mentioned above, when compared to other commercially available types of cathode active materials, conventional lithium-rich lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability.

[0024] However, the inventors have confirmed that when the lithium manganese oxide is mixed with an additive that can suppress or mitigate the elution of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from a positive electrode manufactured using the positive electrode active material, and used as a positive electrode active material, lithium-rich lithium manganese oxide can also exhibit electrochemical properties and stability at a level suitable for commercialization.

[0025] Furthermore, as mentioned above, the inventors have confirmed that when the additive and the lithium manganese oxide are mixed and used as a positive electrode active material, gas generation inside the lithium secondary battery under high-voltage storage or operating conditions can be mitigated more effectively than when the additive is used as a coating on the surface of the lithium manganese oxide.

[0026] Accordingly, the present invention aims to provide a positive electrode active material that can suppress or mitigate the leaching of transition metals and / or abnormal resistance phenomena that act as causes of reduced lifespan of the positive electrode active material, by using a boron-containing compound as an additive that can suppress or mitigate the leaching of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from a positive electrode manufactured using the positive electrode active material, while providing the lithium manganese oxide and the boron-containing compound in a physically mixed state.

[0027] 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 a positive electrode active material, a boron-containing compound, and a conductive material as defined in this application, thereby suppressing or mitigating the elution of transition metals from the positive electrode.

[0028] Furthermore, the present invention aims to provide a lithium secondary battery that can achieve high stability by using the positive electrode defined in this application, thereby preventing a decrease in rate characteristics and capacity due to excess lithium and manganese present in existing OLOs, and in particular by reducing side reactions between the positive electrode active material and the electrolyte under high-voltage storage or operating conditions. [Means for solving the problem]

[0029] 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-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are in solid solution or composite.

[0030] 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 R3-m space group, whereas the lithium-rich lithium manganese oxide defined in this application is characterized by a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0031] In one embodiment, the positive electrode active material may further contain a boron-containing compound. At this time, the boron-containing compound exists in a state physically mixed with the lithium manganese-based oxide.

[0032] The lithium manganese-based oxide, which is one of the components constituting the positive electrode active material, may exist as secondary particles in which a plurality of primary particles are aggregated. At this time, the boron-containing compound may exist independently of the secondary particles.

[0033] Further, at least a part of the plurality of lithium manganese-based oxides contained in the positive electrode active material may exist in a state physically contacting the boron-containing compound.

[0034] In the positive electrode active material, the boron-containing compound may exist in a content of 0.1 wt% to 3.0 wt%.

[0035] The boron-containing compound may contain at least one selected from B2O3, H α B β O γ (0 < α < 10, 0 < β < 10, 0 < γ < 20) and Li α′ B β′ O γ′ (0 < α' < 10, 0 < β' < 10, 0 < γ' < 20).

[0036] In one embodiment, the lithium manganese-based oxide may be represented by the following Chemical Formula 1.

[0037] [Chemical Formula 1] Li(Li a M1 x M2 y )O 2-b X b (Here, M1 is at least one selected from Ni and Mn, M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である) In other embodiments, the lithium manganese oxide may be represented by the following chemical formula 1-1.

[0038] [Chemical formula 1-1] rLi2MnO 3-c X' c ·(1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X and X' are each a halogen capable of independently substituting at least a portion of the oxygen present in the lithium manganese oxide. 0 <r≦0.7、0<a′≦1、0≦b′≦0.1、0≦b″≦0.1、0<x′≦1、0≦y′<1、0<x′+y′≦1である) Furthermore, according to another aspect of the present invention, a positive electrode is provided comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Herein, the positive electrode active material layer comprises a positive electrode active material as defined in this application, a boron-containing compound, and a conductive material.

[0039] The lithium manganese oxide and the boron-containing compound may be present in the positive electrode active material layer in a physically mixed state.

[0040] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided comprising a positive electrode as defined in this application, a negative electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte. [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 when compared with commercially available ternary lithium composite oxides of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[0042] Specifically, according to the present invention, by using the lithium manganese oxide and the boron-containing compound in a physically mixed state, the elution of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from the positive electrode manufactured using the positive electrode active material can be suppressed or mitigated.

[0043] By suppressing or mitigating the leaching of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from the positive electrode manufactured using the positive electrode active material, it is possible to prevent the generation of impurities that hinder normal battery reactions in the lithium secondary battery by reacting the leached transition metals with the electrolyte.

[0044] Transition metals leached from the lithium manganese oxide and / or impurities formed by the reaction of the leached transition metals with the electrolyte can move to the negative electrode using the electrolyte as a medium, and these impurities can deposit on the surface of the negative electrode, causing a rapid increase in the negative electrode resistance. As a result, it is necessary to restrict the unintended movement of transition metals within the lithium secondary battery, as described in the present invention.

[0045] In other words, according to the present invention, by ensuring that the lithium manganese oxide and the boron-containing compound are physically mixed within the positive electrode active material, or by ensuring that the lithium manganese oxide and the boron-containing compound are physically mixed within the positive electrode, it is possible to suppress or mitigate the leaching of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from the positive electrode manufactured using the positive electrode active material. This prevents the deposition of impurities that inhibit normal battery reactions in the positive electrode and / or negative electrode, which would accelerate the deterioration of the lifespan of the lithium secondary battery.

[0046] Furthermore, as mentioned above, a positive electrode active material in which the lithium manganese oxide and the boron-containing compound are simply physically mixed has the advantage of being able to mitigate gas generation within the lithium secondary battery under high-voltage storage or operating conditions compared to a positive electrode active material in which the lithium manganese oxide and the boron-containing compound form a complex.

[0047] Furthermore, by using the positive electrode defined in this application, the present invention can prevent a decrease in rate characteristics and capacity due to excess lithium and manganese present in existing OLOs, and in particular, it can achieve high stability by reducing side reactions between the positive electrode active material and the electrolyte under high-voltage storage or operating environments.

[0048] 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]

[0049] [Figure 1] Figure 1 is an SEM image of the cathode active material produced by Example 1. [Figure 2] Figure 2 shows a cross-sectional SEM image of a cathode active material layer manufactured using the cathode active material produced in Example 2. [Modes for carrying out the invention]

[0050] For the convenience of making the present invention easier to understand, certain terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in this invention 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.

[0051] The following describes in more detail some embodiments of the present invention, specifically positive electrode active materials containing lithium-rich lithium manganese oxides and lithium secondary batteries containing such positive electrode active materials.

[0052] positive electrode 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 R3-m space group are in solid solution or composite.

[0053] The lithium manganese oxide contains at least lithium, nickel, and manganese. In this case, the 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 metal elements other than lithium in the lithium manganese oxide (Li / Metal molar ratio) is greater than 1).

[0054] 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 lithium manganese-based oxides have a relatively higher proportion of manganese in the total metal elements (for example, 50 mol% or more, preferably 55 mol% to 75 mol%) compared to commercially available ternary lithium composite oxides.

[0055] 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 oxide has a relatively lower proportion of nickel in the total metal elements (for example, less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0056] Another difference is 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 between 1.1 and 1.6.

[0057] Despite the aforementioned compositional differences, the lithium manganese-based oxide can also function as a composite metal oxide capable of lithium ion intercalation / deintercalation.

[0058] The lithium manganese-based oxide contained in the positive electrode active material as defined in this application may exist as particles containing at least one primary particle.

[0059] When the lithium manganese oxide exists as a single primary particle, it can be referred to as a single particle. On the other hand, when the lithium manganese oxide exists as an aggregate formed by the aggregation of multiple primary particles, it can be referred to as a secondary particle.

[0060] The positive electrode active material may include at least one selected from lithium manganese oxides existing as single particles and lithium manganese oxides existing as secondary particles formed by the aggregation of multiple primary particles.

[0061] The primary particles constituting the lithium manganese oxide can have rod-like, elliptical, and / or amorphous shapes. Furthermore, unless specifically intended in the manufacturing process, primary particles of various shapes can exist within the same positive electrode active material.

[0062] 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, preferably 0.05 μm to 1.0 μm, and more preferably 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated using the average value of the length in the long axis direction and the length in the short axis direction of the primary particles ([long axis length + short axis length] / 2).

[0063] When the lithium manganese oxide exists as secondary particles formed by the aggregation of multiple primary particles, the average particle size of the secondary particles may be 0.5 μm to 15 μm. The average particle size of the secondary particles can vary depending on the number of primary particles that constitute the secondary particles.

[0064] 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. In this case, the "surface of the secondary particle" formed by the aggregation of multiple primary particles corresponds to the exposed surface of the primary particle present on the surface portion of the secondary particle.

[0065] 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" 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" 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" of the secondary particle than the "surface."

[0066] In this case, the region within any particle excluding the "particle surface" can be defined as the "particle's central region."

[0067] For example, if the radius of the primary particle is r, the region at a distance of 0 to 0.5r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle. If the radius of the primary particle is 0.5 μm, the surface portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the surface of the primary particle, and the center portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the center of the primary particle.

[0068] Furthermore, if necessary, when the radius of the primary particle is denoted as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the primary particle can be defined as the central part of the primary particle.

[0069] Similarly, when the radius of the secondary particle is denoted as r, the region at a distance of 0 to 0.5r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle. If the radius of the secondary particle is 2.0 μm, the surface portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the surface of the secondary particle, and the center portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the center of the secondary particle.

[0070] Furthermore, if necessary, when the radius of the secondary particle is denoted as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the secondary particle can be defined as the central part of the secondary particle.

[0071] The lithium manganese oxide as defined in this application may be a lithium-rich lithium manganese oxide represented by the following chemical formula 1.

[0072] [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, and 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である。

[0073] The types of halogens that can be used as X are determined by referring to the periodic table, and can be F, Cl, Br and / or I, and preferably F.

[0074] In other embodiments, the lithium manganese oxide may be represented by the following chemical formula 1-1.

[0075] [Chemical formula 1-1] rLi2MnO 3-c X' c ·(1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X and X' are each a halogen capable of independently substituting at least a portion of the oxygen present in the lithium manganese oxide, and 0 <r≦0.7、0≦c≦0.1、0<a′≦1、0≦b′≦0.1、0<x′≦1、0≦y′<1および0<x′+y′≦1である。

[0076] The types of halogens that can be used for X and X' are determined by referring to the periodic table, and can be F, Cl, Br and / or I, and preferably F.

[0077] In the aforementioned chemical formulas 1 and 1-1, if M1 is Ni, M2 may also contain Mn, and if M1 is Mn, M2 may also contain Ni. Furthermore, if M1 is Ni and Mn, M2 may be absent, or if present, it may be an element other than Ni and Mn.

[0078] That is, if M1 is Ni, then M2 may include at least one selected from Co, 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 (preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W; more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W; even more preferably at least one selected from P, B, and Si) and Mn.

[0079] If M1 is Mn, then M2 may include at least one selected from Co, 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 (preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W; more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W; even more preferably at least one selected from P, B, and Si) and Ni.

[0080] If M1 is Ni and Mn, then M2 may include at least one selected from Co, 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, preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably at least one selected from P, B, and Si.

[0081] The lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 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, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese oxide represented by chemical formula 1 may have a cobalt-free composition.

[0082] The Li / Metal molar ratio measured from the lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 may be greater than 1, preferably 1.1 to 1.6. 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 R3-m space group are solidly dissolved or composited, and at the same time to exhibit high capacity under a high-voltage operating environment, the Li / Metal molar ratio of the lithium manganese oxide is preferably 1.2 to 1.6.

[0083] Furthermore, in order to properly form a solid solution in which the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are in solid solution or composite, 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 1-1 is 50 mol% or more.

[0084] To enable the lithium manganese oxide to exhibit OLO (Optical Load Oxide) characteristics that allow it to exhibit high capacity under high-voltage operating conditions, the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide is more preferably 50 mol% or more and less than 80 mol%, and even more preferably 55 mol% to 75 mol%. When 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 and / or operation of the lithium secondary battery. Such a phase transition forms a spinel phase, and this spinel phase, acting as an impurity in the lithium manganese oxide, can induce a decrease in charge / discharge capacity or voltage decay during the cycling of the lithium secondary battery.

[0085] 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 R3-m space group are in solid solution or composite, it is preferable that the nickel content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 is less than 50 mol%.

[0086] 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 R3-m space group may not form a sufficient solid solution, which can cause phase separation during conversion and / or operation of the lithium secondary battery.

[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 R3-m space group.

[0088] On the other hand, lithium-rich lithium manganese oxides represented by chemical formula 1 or chemical formula 1-1 consist of an oxide of a phase belonging to the C2 / m space group represented by rLi2MnO3 (hereinafter referred to as the "C2 / m phase") and (1-r)Li a M1 x M2 y O 2-b X b The oxides of the phases belonging to the R3-m space group (hereinafter referred to as "R3-m phase") shown by exist as a solid solution or composite oxide. For example, the lithium manganese-based oxide may exist in a state in which the oxide of the C2 / m phase and the oxide of the R3-m 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 R3-m 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 R3-m space group, and having the surface coated with the metal oxide having a phase belonging to the R3-m 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 1-1, if r exceeds 0.7, the proportion of Li2MnO3, which is the C2 / m phase oxide, in the lithium manganese oxide becomes excessively high. As a result, the irreversible capacity and resistance of the positive electrode active material increase, which may lead to a decrease in discharge capacity. In other words, in order to sufficiently activate the C2 / m phase oxide, which has relatively high resistance, in the lithium manganese oxide and improve surface kinetics, it is preferable that the R3-m phase oxide be present in a predetermined proportion or higher.

[0092] In one embodiment, the positive electrode active material may further contain a boron-containing compound. In this case, the boron-containing compound exists in a state where it is physically mixed with the lithium manganese-based oxide.

[0093] The statement that the lithium manganese oxide and the boron-containing compound exist in a physically mixed state means that the lithium manganese oxide and the boron-containing compound do not exist as a composite, but rather as independent particles.

[0094] Here, the existence of the lithium manganese oxide and the boron-containing compound in a physically mixed state must be distinguished from the existence of the lithium manganese oxide with the boron-containing compound in oxide form coated on its surface.

[0095] In other words, the existence of the lithium manganese oxide and the boron-containing compound in a physically mixed state means that, if the lithium manganese oxide, which is one of the components constituting the positive electrode active material, exists as secondary particles formed by the aggregation of multiple primary particles, then the boron-containing compound exists independently of the primary particles and / or the secondary particles.

[0096] In this case, at least some of the multiple lithium manganese-based oxides contained in the positive electrode active material may be in physical contact with the boron-containing compound, but this physical contact state is different from a state in which the boron-containing compound is inseparably coated on the surface of the lithium manganese-based oxide.

[0097] In the positive electrode active material, the boron-containing compound may have an average particle size of 50 nm to 80 μm, preferably 50 nm to 60 μm, and more preferably 50 nm to 30 μm. In this case, the average particle size of the boron-containing compound may be the average value of the length in the long axis direction and the length in the short axis direction ([long axis length + short axis length] / 2), or the D50 obtained by particle size distribution analysis of the boron-containing compound may be used.

[0098] If the average particle size of the boron-containing compound is smaller than 50 nm, the dispersibility of the boron-containing compound in the cathode slurry containing the cathode active material, in which the lithium manganese oxide and the boron-containing compound are physically mixed, may be low, making uniform control difficult.

[0099] On the other hand, if the average particle size of the boron-containing compound is greater than 80 μm, or if the proportion of particles with a particle size of 80 μm or more in the boron-containing compound exceeds 50 wt%, it may be difficult to manufacture a positive electrode active material layer using the positive electrode active material in which the lithium manganese oxide and the boron-containing compound are physically mixed.

[0100] The boron-containing compound may be present in the positive electrode active material in an amount of 0.1 wt% to 3.0 wt%, preferably 0.1 wt% to 2.0 wt%, and more preferably 0.3 wt% to 1.5 wt%.

[0101] If the content of the boron-containing compound is less than 0.1 wt% based on the total weight of the positive electrode active material, it may be difficult to sufficiently suppress or mitigate the leaching of transition metals from the positive electrode active material containing the lithium manganese oxide and / or from a positive electrode manufactured using the positive electrode active material.

[0102] On the other hand, if the content of the boron-containing compound is greater than 3.0 wt% relative to the total weight of the positive electrode active material, the capacity of the lithium secondary battery using the positive electrode active material may become insufficient as the proportion of the lithium manganese oxide decreases relative to the total weight of the positive electrode active material. Furthermore, as the content of the boron-containing compound in the positive electrode active material increases relatively, the resistance of the positive electrode active material may become unnecessarily high.

[0103] The boron-containing compound is B2O3, H α B β O γ (0<α<10, 0<β<10, 0<γ<20) and Li α′ B β′ O γ′ The boron-containing compound may also contain at least one selected from (0 < α' < 10, 0 < β' < 10, 0 < γ' < 20). Furthermore, the boron-containing compound can be converted between itself and other components within a lithium secondary battery using the positive electrode active material.

[0104] Lithium-ion rechargeable battery According to another aspect of the present invention, a positive electrode is provided, comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0105] Here, the positive electrode active material layer may include a positive electrode active material containing a lithium manganese-based oxide as defined in this application, a boron-containing compound, and a conductive material. If the positive electrode active material layer contains a boron-containing compound separately from the positive electrode active material, the positive electrode active material does not need to contain the boron-containing compound.

[0106] In one embodiment, the boron-containing compound in the positive electrode active material layer exists in a state where it is physically mixed with the lithium manganese-based oxide.

[0107] The statement that the lithium manganese oxide and the boron-containing compound exist in a physically mixed state means that the lithium manganese oxide and the boron-containing compound do not exist as a composite, but rather as independent particles.

[0108] Here, the existence of the lithium manganese oxide and the boron-containing compound in a physically mixed state must be distinguished from the existence of the lithium manganese oxide with the boron-containing compound in oxide form coated on its surface.

[0109] In this case, at least some of the multiple lithium manganese-based oxides contained in the positive electrode active material may be in physical contact with the boron-containing compound, but this physical contact state is different from a state in which the boron-containing compound is inseparably coated on the surface of the lithium manganese-based oxide.

[0110] In the positive electrode active material layer, the boron-containing compound may have an average particle size of 50 nm to 60 μm, preferably 50 nm to 30 μm, and more preferably 50 nm to 15 μm. In this case, the average particle size of the boron-containing compound may be the average value of the length in the long axis direction and the length in the short axis direction ([long axis length + short axis length] / 2), or the D50 obtained by particle size distribution analysis of the boron-containing compound may be used.

[0111] If the average particle size of the boron-containing compound within the positive electrode active material layer is less than 50 nm, the likelihood of the boron-containing compound being uniformly dispersed within the positive electrode active material layer is low.

[0112] On the other hand, if the average particle size of the boron-containing compound in the positive electrode active material layer is greater than 60 μm, or if the proportion of particles with a particle size of 60 μm or more in the boron-containing compound exceeds 50 wt%, the boron-containing compound may be difficult to dissolve in the electrolyte. The boron-containing compound present in the positive electrode active material or the positive electrode active material layer during storage and / or operation of the lithium secondary battery can dissolve in the electrolyte, and the boron-containing compound dissolved in the electrolyte can form a physical barrier layer on the surface of the positive electrode, thereby suppressing or mitigating the elution of transition metals from the positive electrode.

[0113] Furthermore, the boron-containing compound dissolved in the electrolyte can migrate to the negative electrode and form a physical barrier layer on the surface of the negative electrode. In this way, the physical barrier layer formed on the surface of the negative electrode can prevent the deposition of transition metals leached from the lithium manganese oxide and / or impurities caused by the leached transition metals on the surface of the negative electrode.

[0114] The aforementioned physical barrier layer may contain a boron-containing oxide represented by the following chemical formula 2.

[0115] [Chemical formula 2] Li c B d M3 e O f Here, M3 is at least one selected from Ni, Mn, Co, Al, Nb, 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, where 0 ≤ c ≤ 8, 0 <d≦8、0≦e≦8、2≦f≦13である。

[0116] When the boron-containing oxide represented by chemical formula 2 is a borate-based compound or an LBO (lithium borate)-based compound, non-limiting examples of the boron-containing oxide include B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, and Li2B8O 13These are some examples. Furthermore, the boron-containing oxide may have a composition in which the aforementioned borate-based compound or lithium borate-based compound is selectively doped with a different element, M3.

[0117] In the positive electrode active material layer, the boron-containing compound may be present in an amount of 0.09 wt% to 3.0 wt%, preferably 0.09 wt% to 2.0 wt%.

[0118] If the content of the boron-containing compound is less than 0.09 wt% based on the total weight of solids in the positive electrode active material layer, it may be difficult to sufficiently suppress or mitigate the elution of transition metals from the positive electrode. Furthermore, as the amount of the boron-containing compound dissolved in the electrolyte decreases, it may be difficult to sufficiently form a physical barrier layer on the surface of the positive electrode and / or the negative electrode during storage and / or operation of the lithium secondary battery.

[0119] On the other hand, if the content of the boron-containing compound is greater than 3.0 wt% relative to the total weight of the positive electrode active material, the capacity of the lithium secondary battery using the positive electrode active material may become insufficient as the proportion of the lithium manganese oxide decreases relative to the total weight of the positive electrode active material. Furthermore, as the content of the boron-containing compound in the positive electrode active material increases relatively, the resistance of the positive electrode active material may become unnecessarily high.

[0120] The boron-containing compound is B2O3, H α B β O γ (0<α<10, 0<β<10, 0<γ<20) and Li α′ B β′ O γ′ The boron-containing compound may also contain at least one selected from (0 < α' < 10, 0 < β' < 10, 0 < γ' < 20). Furthermore, the boron-containing compound can be converted between itself and other components within a lithium secondary battery using the positive electrode active material.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except for the use of the positive electrode active material. Specifically, it may be manufactured by coating a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0127] 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.

[0128] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0141] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0142] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0144] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent electrolyte performance.

[0145] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

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

[0147] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the sulfide-based solid electrolyte 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.)

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

[0149] As a material for oxide-based solid electrolytes, Li7La3Zr2O 12 Li 7-x La3Zr 1-x Nb x O 12 Li 7-3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0150] The aforementioned solid electrolyte may be arranged as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Furthermore, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0151] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds 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.

[0152] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0153] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0154] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0155] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0156] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0157] Manufacturing Example 1. Manufacturing of positive electrode active material Example 1 (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated to obtain Ni with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0158] (b) Precursor coating In step (a), an aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, the NiSO4·6H2O was weighed to a concentration of 5 mol% before being added. After the reaction was complete, the precursor was washed and dehydrated, then dried at 150°C for 14 hours to obtain the coated precursor.

[0159] (c) First heat treatment After heating an air-filled furnace at a rate of 2°C / min, the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550°C, and then furnace-cooled to obtain the oxide-state precursor.

[0160] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with the lithium raw material LiOH (Li / (Li-excluded metal) mol ratio = 1.22) to prepare the mixture.

[0161] Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 900°C. After furnace cooling, lithium-rich lithium manganese oxide was obtained.

[0162] TEM / EDS analysis of the lithium manganese oxide confirmed that the precursor coating using Ni in step (b) created a gradient in which the concentration of Ni increased from the center to the surface and the concentration of Mn decreased.

[0163] (e) Mixed with boron-containing compounds The lithium manganese oxide obtained in step (d) was mixed with B2O3, a boron-containing compound with an average particle size of 40 μm, to obtain a final product in which the lithium manganese oxide and the boron-containing compound were physically mixed. At this time, the boron-containing compound was mixed to a concentration of 0.3 wt% based on the total weight of the final product.

[0164] Example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing compound was mixed to a concentration of 0.7 wt% based on the total weight of the final product.

[0165] Example 3 The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing compound was mixed to a concentration of 1.5 wt% based on the total weight of the final product.

[0166] Comparative Example 1 The positive electrode active material was manufactured in the same manner as in Example 1, except that step (e) was omitted.

[0167] Reference example 1 The positive electrode active material was manufactured in the same manner as in Example 1, except that in step (e) above, B2O3 with an average particle size of 100 μm was mixed in such a manner that it constituted 0.7 wt% of the total weight of the final product.

[0168] Reference example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing compound was mixed to a concentration of 0.05 wt% based on the total weight of the final product.

[0169] Manufacturing Example 2: Manufacturing of Lithium-ion Secondary Batteries (Half-Cells) A cathode slurry was prepared by dispersing 90 wt% of the cathode active material produced by Examples 1 to 3, Comparative Example 1, and Reference Examples 1 to 2 described in Production Example 1, along with 4.5 wt% of carbon black and 5.5 wt% of PVDF binder, in N-methyl-2-pyrrolidone (NMP).

[0170] 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.

[0171] A half-cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate, 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.

[0172] In this case, when using the positive electrode active material manufactured according to Reference Example 1, the average particle size of B2O3 was excessively large, causing scratches to occur on the surface of the positive electrode active material layer, making it impossible to form a normal positive electrode active material layer.

[0173] Manufacturing Example 3: Manufacturing of Lithium-ion Secondary Batteries (Half-Cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material produced by Comparative Example 1 described in Production Example 1, 4.5 wt% of carbon black, 5.5 wt% of PVDF binder, and B2O3 with an average particle size of 40 μm as a boron-containing compound in N-methyl-2-pyrrolidone (NMP). Here, the boron-containing compound was mixed into the positive electrode slurry to a concentration of 0.6 wt% of the total weight of solids.

[0174] 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.

[0175] A half-cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate, 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.

[0176] Manufacturing Example 4: Manufacturing of Lithium-ion Rechargeable Batteries (Full Cells) A cathode slurry was prepared by dispersing 90 wt% of the cathode active material produced by Examples 1 to 3, Comparative Example 1, and Reference Examples 1 to 2 described in Production Example 1, along with 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] In this case, when using the positive electrode active material manufactured according to Reference Example 1, the average particle size of B2O3 was excessively large, causing scratches to occur on the surface of the positive electrode active material layer, making it impossible to form a normal positive electrode active material layer.

[0180] Manufacturing Example 5: Manufacturing of Lithium-ion Rechargeable Batteries (Full Cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material produced by Comparative Example 1 described in Production Example 1, 4.5 wt% of carbon black, 5.5 wt% of PVDF binder, and B2O3 with an average particle size of 40 μm as a boron-containing compound in N-methyl-2-pyrrolidone (NMP). Here, the boron-containing compound was mixed into the positive electrode slurry to a concentration of 0.6 wt% of the total weight of solids.

[0181] 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.

[0182] 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.

[0183] Experimental Example 1. SEM Analysis of Cathode Active Material Figure 1 is an SEM image of the cathode active material produced by Example 1.

[0184] Referring to Figure 1, it can be confirmed that the lithium manganese oxide and the boron-containing compound in secondary particle form within the positive electrode active material coexist with each other. That is, it can be confirmed that the lithium manganese oxide within the positive electrode active material exists as secondary particles formed by the aggregation of multiple primary particles, and that the boron-containing compound exists independently of the secondary particles.

[0185] Furthermore, it can be confirmed that at least some of the multiple lithium manganese-based oxides contained in the positive electrode active material are present in physical contact with the boron-containing compound.

[0186] Experimental Example 2. SEM Analysis of the Cathode Cross Section In Manufacturing Example 2, the distribution of lithium manganese oxides and boron-containing compounds within the positive electrode active material layer was analyzed by cross-sectional SEM image analysis of the positive electrode active material layer manufactured using the positive electrode active material manufactured in Example 2. In this analysis, the positive electrode active material layer was analyzed after the positive electrode was manufactured using the method described in Manufacturing Example 2, but before it was assembled into a half-cell. The analysis results are shown in Figure 2.

[0187] Referring to Figure 2, it can be confirmed that boron is distributed throughout the positive electrode active material layer, and that the particle size of the boron-containing compound has decreased by tens to hundreds of nanometers compared to the boron-containing compound confirmed in Figure 1.

[0188] The above results are presumed to be due to the partial dissolution of the boron-containing compound by the solvent during the cathode manufacturing process. This allows the boron-containing compound to exist in a generally dispersed state within the cathode active material layer. Furthermore, the results in Figure 2 confirm that the boron-containing compound, which was partially dissolved by the solvent during the cathode manufacturing process, can be converted into a physical barrier layer on the surface of the cathode active material layer.

[0189] Experimental Example 3. Dissolution Analysis of Boron-Containing Compounds In Production Example 2, the positive electrode produced using the positive electrode active material produced in Example 2, and the positive electrode produced in Production Example 3, were stored in an electrolyte at 60°C for 3 days, then recovered, and the boron content in the positive electrode was measured by ICP analysis. The measurement results are shown in Table 1 below.

[0190] [Table 1]

[0191] Referring to the results in Table 1, it can be confirmed that when the positive electrode manufactured using the positive electrode active material manufactured in Example 2 and the positive electrode manufactured in Manufacturing Example 3 were stored in an electrolyte at a relatively high temperature, the amount of boron-containing compound in the positive electrode decreased as the boron-containing compound present in the positive electrode dissolved.

[0192] Thus, the boron-containing compound in the positive electrode can be dissolved in the electrolyte, and the boron-containing compound dissolved in the electrolyte can be converted into a physical barrier layer on the surface of the positive electrode active material layer and / or the negative electrode active material layer.

[0193] Experimental Example 4. Evaluation of the electrochemical properties of lithium secondary batteries (half-cells). For lithium secondary batteries (half-cells) manufactured in Manufacturing Example 2 and Manufacturing Example 3, the initial charge capacity, initial discharge capacity, initial reversibility efficiency, and rate characteristics (discharge capacity ratio; rate capability (C-rate)) were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, voltage range 2.0V~4.6V, and discharge rates of 0.1C, 1.0C, and 2.0C.

[0194] The measurement results are shown in Table 2 below.

[0195] [Table 2]

[0196] Referring to the evaluation results of the half-cells in Table 2, it can be confirmed that even when a boron-containing compound is physically mixed into the positive electrode active material or positive electrode active material layer, the initial charge capacity, initial discharge capacity, initial reversibility efficiency, and rate characteristics do not decrease, and in particular, some indicators (e.g., initial efficiency and discharge capacity) are partially improved.

[0197] Experimental Example 5. Evaluation of the electrochemical properties of a lithium secondary battery (full cell). The lithium secondary batteries (full cells) manufactured in Manufacturing Example 4 and Manufacturing Example 5 were subjected to a 6-cycle conversion process 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. Initial (1 st Cycle) Discharge capacity, 500 relative to initial discharge capacity th The cycle capacity retention rate (cycle capacity retention) was measured.

[0198] The measurement results are shown in Table 3 below.

[0199] [Table 3]

[0200] Referring to the evaluation results of the full cells in Table 3, it can be confirmed that, unlike the evaluation results of the half cells in Table 2, the cycle capacity retention rate of the full cells using the positive electrode active materials in Examples 1 to 3 is exceptionally high compared to the full cell using the positive electrode active material in Comparative Example 1. This result is presumed to be because, in the case of the full cell using the positive electrode active material in Comparative Example 1, an abnormal resistance phenomenon occurred in the negative electrode as the transition metal leached out from the lithium manganese oxide, thereby accelerating the degradation of the lifespan.

[0201] In the case of Reference Example 2, although it shows a higher cycle capacity retention rate than the full cell using the positive electrode active material of Comparative Example 1, it is expected that the lifespan degradation occurred further than that of the full cell using the positive electrode active material of Examples 1 to 3 because the content of the boron-containing compound physically mixed with lithium manganese oxide was somewhat lower.

[0202] Furthermore, it can be confirmed that a full cell produced in Production Example 5, which uses the positive electrode active material from Comparative Example 1 but incorporates a boron-containing compound physically during the positive electrode manufacturing process, exhibits a cycle capacity retention rate similar to that of Example 1.

[0203] Experimental Example 6. Analysis of Transition Metal Elution In Manufacturing Example 4, lithium secondary batteries (full cells) manufactured using the positive electrode active materials produced in Example 2 and Comparative Example 1, and lithium secondary batteries (full cells) manufactured in Manufacturing Example 5, under the conditions of 25°C, voltage range 2.0V~4.6V, and 0.2C / 0.2C, were subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100). After that, the full cells were stabilized by 2 cycles of charge and discharge under the conditions of 25°C, voltage range 2.0V~4.6V, and 0.05C / 0.05C. Next, after disassembling the full cells, the negative electrodes were washed with diethyl carbonate solvent, vacuum dried at 60°C, and then recovered.

[0204] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the separated negative electrode active material was subjected to ICP analysis to measure the content of Ni, Mn, and B contained in the negative electrode active material.

[0205] Furthermore, in Manufacturing Example 4, lithium secondary batteries (full cells) manufactured using the positive electrode active materials produced in Example 2 and Comparative Example 1, and lithium secondary batteries (full cells) manufactured in Manufacturing Example 5, were subjected to a 6-cycle conversion process 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 by 2-cycle charge-discharge at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. After disassembling the full cells, the negative electrodes were washed with diethyl carbonate solvent, vacuum-dried at 60°C, and then recovered.

[0206] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the separated negative electrode active material was subjected to ICP analysis to measure the content of Ni, Mn, and B contained in the negative electrode active material.

[0207] The measurement results are shown in Table 4 below.

[0208] [Table 4]

[0209] Referring to the results in Table 4 above, as predicted in Experimental Example 5, it can be confirmed that the rapid deterioration of the lifespan of the full cell using the positive electrode active material in Comparative Example 1 was due to the relatively increased content of transition metals deposited in the negative electrode active material as charging and discharging cycles were repeated.

[0210] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are in solid solution or composite form; The lithium manganese oxide and a boron-containing compound physically mixed together; The boron-containing compound is a positive electrode active material comprising at least one selected from B₂O₃, HαBβOγ (0<α<10, 0<β<10, 0<γ<20) and Liα′Bβ′Oγ′ (0<α′<10, 0<β′<10, 0<γ′<20).

2. The positive electrode active material according to claim 1, wherein the lithium manganese oxide exists as secondary particles formed by the aggregation of a plurality of primary particles, and the boron-containing compound exists independently of the secondary particles.

3. The positive electrode active material according to claim 1, wherein the average particle size of the lithium manganese-based oxide is 0.5 μm to 15 μm.

4. The positive electrode active material according to claim 1, wherein the average particle size of the boron-containing compound is 50 nm to 80 μm.

5. The positive electrode active material according to claim 1, wherein at least a portion of the plurality of lithium manganese-based oxides contained in the positive electrode active material are in physical contact with the boron-containing compound.

6. The positive electrode active material according to claim 1, wherein the boron-containing compound is present in an amount of 0.1 wt% to 3.0 wt% based on the total weight of the positive electrode active material.

7. The lithium manganese oxide is represented by the following chemical formula 1, and is the positive electrode active material according to claim 1. [Chemical formula 1] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 ｂ (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, (0 < a ≤ 0.7, 0 ≤ b ≤ 0.1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < x + y ≤ 1)

8. The lithium manganese oxide is represented by the following chemical formula 1-1, and is the positive electrode active material according to claim 1. [Chemical formula 1-1] rLi ２ MnO ３－ｃ X′ ｃ ・(1-r)Li ａ′ M1 ｘ′ M2 ｙ′ O ２－ｂ′ X ｂ′ (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, 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 M2 does not overlap with M1. X and X' are halogens that can independently substitute at least a portion of the oxygen present in the lithium manganese oxide. (0 < r ≤ 0.7, 0 ≤ c ≤ 0.1, 0 < a' ≤ 1, 0 ≤ b' ≤ 0.1, 0 < x' ≤ 1, 0 ≤ y' < 1, 0 < x' + y' ≤ 1)

9. 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 a positive electrode active material, a boron-containing compound, and a conductive material. The positive electrode active material is a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are in solid solution or composite form. The boron-containing compound comprises at least one selected from B₂O₃, HαBβOγ (0<α<10, 0<β<10, 0<γ<20) and Liα′Bβ′Oγ′ (0<α′<10, 0<β′<10, 0<γ′<20), and is a positive electrode.

10. The positive electrode according to claim 9, wherein the lithium manganese oxide and the boron-containing compound are physically mixed and present in the positive electrode active material layer.

11. The positive electrode according to claim 9, wherein the average particle size of the boron-containing compound is 50 nm to 60 μm.

12. The positive electrode according to claim 9, wherein the boron-containing compound is present in an amount of 0.09 wt% to 3.0 wt% based on the total weight of solids in the positive electrode active material layer.

13. A lithium secondary battery comprising a positive electrode according to any one of claims 9 to 12, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte.

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