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, 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. [Background technology]

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

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

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and oxides of Ni, Co, Mn, and Al.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but suffer from low capacity and poor high-temperature characteristics. LiNiO2-based positive electrode active materials exhibit high discharge capacity, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, resulting in significant problems with rate characteristics.

[0007] Furthermore, depending on the depth of this cation mixing, a large amount of Li by-products are generated. These Li by-products, mostly consisting of LiOH and Li2CO3, can cause gelation during the preparation of the positive electrode paste or gas generation during repeated charge / discharge cycles after electrode fabrication. Furthermore, the residual Li2CO3 among these Li by-products increases cell swelling, thereby reducing the lifespan characteristics.

[0008] Various candidate materials have been proposed to overcome the drawbacks of conventional positive electrode active materials.

[0009] For example, research is being conducted to use overlithiated lithium manganese oxides, which contain an excess amount of Mn among transition metals and have a lithium content greater than the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such overlithiated lithium manganese oxides are also called overlithiated layered oxides (OLO).

[0010] While OLO theoretically has the advantage of being able to exhibit high capacity under high-voltage operating conditions, it has the disadvantage of relatively low electrical conductivity due to the excessive Mn content in the oxide, resulting in poor rate performance of lithium secondary batteries using OLO. This poor rate performance can lead to problems such as reduced charge / discharge capacity and life efficiency (cycle capacity retention) during cycling of the lithium secondary battery.

[0011] To solve the above problems, research has been conducted to change the composition of OLO, but these attempts have not yet reached a commercial level. Summary of the Invention [Problem to be solved by the invention]

[0012] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is playing a role as a market driver, and as a result, the demand for positive electrode active materials used in lithium secondary batteries is also continuously increasing.

[0013] For example, lithium secondary batteries using lithium iron phosphate (LFP) have traditionally been used primarily for safety reasons, but recently there has been a trend toward the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP.

[0014] In addition, nickel-based lithium composite oxides, which are currently mainly used as positive electrode active materials in high-capacity lithium secondary batteries, essentially contain ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only unstable in supply and demand but is also excessively expensive compared to other raw materials, so a new positive electrode active material with a reduced or eliminated cobalt content is needed.

[0015] Considering these various circumstances, lithium-excess lithium manganese-based oxides can meet the aforementioned market expectations, but they still have limitations in that their electrochemical properties and stability are insufficient as an alternative to commercially available ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA)-based ternary lithium composite oxides.

[0016] For example, the present inventors have confirmed that lithium-manganese oxides are more likely to leach transition metals from the particle surface due to repeated charge and discharge than ternary lithium composite oxides, and in particular, Mn contained in an excess amount in lithium-manganese oxides is more likely to leach from the particle surface.

[0017] When a transition metal is eluted from the lithium manganese-based oxide, the eluted transition metal may react with the electrolyte on the surface of the lithium manganese-based oxide to form impurities, which not only increase the surface resistance of the lithium manganese-based oxide but also act as a cause of reducing the intercalation / deintercalation efficiency of lithium ions through the lithium manganese-based oxide.

[0018] In addition, the transition metal dissolved from the lithium manganese-based oxide or impurities formed by the reaction of the dissolved transition metal with the electrolyte can migrate to the negative electrode using the electrolyte as a medium and deposit on the surface of the negative electrode.

[0019] For example, a side reaction occurs on the surface of the lithium manganese-based oxide with the electrolyte, or the lithium manganese-based oxide undergoes a structural change (such as a change in crystal structure) that causes excessive Mn contained in the lithium manganese-based oxide to be dissolved. 2+ The Mn dissolved in the electrolyte can be dissolved in the electrolyte. 2+ During formation or charging / discharging, Mn moves to the surface of the negative electrode through the electrolyte as a medium and reacts with various substances present in the battery (electrons, electrolyte, electrodes, by-products, etc.). As a result, Mn is deposited on the surface of the negative electrode. 2+ , Mn metal or Mn-containing compounds (e.g., MnCO3, MnO, MnF2, etc.) will be present as impurities.

[0020] Transition metals or impurities deposited on the surface of the negative electrode can rapidly increase the resistance of the negative electrode, and this abnormal resistance phenomenon is a major cause of accelerated deterioration of the lifespan of lithium secondary batteries.

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

[0022] However, there is currently no technology to solve the problems associated with the elution of transition metals from lithium-rich lithium manganese oxides.

[0023] As described above, when compared with other commercially available positive electrode active materials, conventional lithium-excess lithium manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability.

[0024] However, the present inventors have confirmed that when the lithium-manganese-based oxide is mixed with an additive capable of suppressing or reducing the elution of transition metals from the positive electrode active material containing the lithium-manganese-based oxide and / or a positive electrode manufactured using the positive electrode active material and used as a positive electrode active material, the lithium-excess lithium-manganese-based oxide can also exhibit electrochemical properties and stability at a level that allows it to be commercially used.

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

[0026] Therefore, the present invention uses a boron-containing compound as an additive capable of suppressing or mitigating the elution of transition metals from the cathode active material containing the lithium-manganese-based oxide and / or a cathode manufactured using the cathode active material, and aims to provide a cathode active material in which the lithium-manganese-based oxide and the boron-containing compound are provided in a physically mixed state, thereby suppressing or mitigating the elution of transition metals and / or the resistance abnormality phenomenon that acts as a cause of a shortened lifespan of the cathode active material.

[0027] Another object of the present invention is to provide a positive electrode including 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 contains a positive electrode active material defined in the present application, a boron-containing compound, and a conductive material, thereby capable of suppressing or mitigating elution of a transition metal from the positive electrode.

[0028] Furthermore, the present invention aims to provide a lithium secondary battery that can achieve high stability by using the cathode defined herein to prevent 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 cathode 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 above-mentioned technical problems, there is provided a positive electrode active material including 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 solid-solved or composite.

[0030] Generally, commercially available ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition contain a single phase of 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 include a boron-containing compound, wherein the boron-containing compound is physically mixed with the lithium manganese-based oxide.

[0032] The lithium manganese oxide, which is one of the components constituting the positive electrode active material, may exist as secondary particles formed by aggregation of a plurality of primary particles, and in this case, the boron-containing compound may exist independently of the secondary particles.

[0033] In addition, at least some of the lithium manganese-based oxides contained in the positive electrode active material may be in physical contact with the boron-containing compound.

[0034] The boron-containing compound may be present in the positive electrode active material in an amount of 0.1 wt % to 3.0 wt %.

[0035] 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′ (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 (where, 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-based oxide, 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である) In another embodiment, the lithium manganese-based oxide may be represented by the following 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′ (where, 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 independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based 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) According to another aspect of the present invention, there is provided a positive electrode including 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 includes a positive electrode active material as defined herein, a boron-containing compound, and a conductive material.

[0039] The lithium manganese-based 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, there is provided a lithium secondary battery comprising a positive electrode as defined herein, a negative electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. [Effects of the Invention]

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

[0042] Specifically, according to the present invention, by using the lithium manganese-based oxide and the boron-containing compound in a physically mixed state, it is possible to suppress or mitigate the elution of transition metals from the positive electrode active material containing the lithium manganese-based oxide and / or from a positive electrode manufactured using the positive electrode active material.

[0043] By suppressing or mitigating the elution of transition metals from the cathode active material containing the lithium manganese-based oxide and / or the cathode manufactured using the cathode active material, it is possible to prevent the eluted transition metals from reacting with the electrolyte and generating impurities that inhibit normal battery reactions in the lithium secondary battery.

[0044] The transition metals dissolved from the lithium manganese-based oxide and / or impurities formed by the reaction of the dissolved transition metals with the electrolyte can migrate to the negative electrode through the electrolyte as a medium, and the impurities can deposit on the surface of the negative electrode, causing a rapid increase in negative electrode resistance. Therefore, as described in the present invention, it is necessary to limit the unintended migration of transition metals within a lithium secondary battery.

[0045] That is, according to the present invention, by having the lithium manganese-based oxide and the boron-containing compound exist in a physically mixed state in the positive electrode active material, or by having the lithium manganese-based oxide and the boron-containing compound exist in a physically mixed state in 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-based oxide and / or a positive electrode manufactured using the positive electrode active material, thereby preventing the accelerated deterioration of the lifespan of a lithium secondary battery due to the deposition of impurities that inhibit normal battery reactions in the positive electrode and / or negative electrode.

[0046] In addition, as described above, the cathode active material in which the lithium manganese-based oxide and the boron-containing compound are simply physically mixed has an advantage over the cathode active material in which the lithium manganese-based oxide and the boron-containing compound form a composite in that it can mitigate gas generation in a lithium secondary battery under high-voltage storage or operating conditions.

[0047] Furthermore, by using the cathode defined herein, the present invention can prevent the rate characteristics and capacity degradation caused by excess lithium and manganese present in existing OLOs, and can achieve high stability by reducing side reactions between the cathode active material and the electrolyte, especially under high-voltage storage or operating conditions.

[0048] The above-mentioned effects and specific effects of the present invention will be described below together with specific matters for carrying out the invention. [Brief explanation of the drawings]

[0049] [Figure 1] FIG. 1 is an SEM image of the positive electrode active material prepared in Example 1. [Figure 2] FIG. 2 is a cross-sectional SEM image of a positive electrode active material layer prepared using the positive electrode active material prepared in Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0050] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0051] Hereinafter, a cathode active material including a lithium-excess lithium manganese-based oxide according to some embodiments of the present invention and a lithium secondary battery including the cathode active material will be described in more detail.

[0052] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material containing 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 dissolved or combined.

[0053] The lithium manganese-based oxide contains at least lithium, nickel, and manganese. In this case, the lithium manganese-based oxide is also called an overlithiated layered oxide (OLO) because the lithium content in the lithium manganese-based 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-based oxide (Li / Metal molar ratio) is greater than 1).

[0054] Generally, in commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, the manganese content of the total metal elements excluding lithium is 20 mol % or less. Considering this, the lithium-manganese-based oxide has a relatively high manganese content (e.g., 50 mol % or more, preferably 55 mol % to 75 mol %) of the total metal elements compared to commercially available ternary lithium composite oxides.

[0055] In addition, considering that commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a nickel content of 60 mol% or more (80 mol% or more in the case of a high-Ni type) of all metal elements excluding lithium, the lithium-manganese-based oxide has a relatively low ratio of nickel to all metal elements (e.g., less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0056] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined herein is larger 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 the lithium manganese-based oxide defined herein is larger than 1, preferably 1.1 to 1.6.

[0057] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

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

[0059] When the lithium manganese-based oxide exists as a single primary particle, the lithium manganese-based oxide may be referred to as a single particle, whereas when the lithium manganese-based oxide exists as an aggregate of a plurality of primary particles, the lithium manganese-based oxide may be referred to as a secondary particle.

[0060] The positive electrode active material may include at least one selected from a lithium manganese-based oxide that exists as a single particle and a lithium manganese-based oxide that exists as a secondary particle formed by aggregation of a plurality of primary particles.

[0061] The primary particles constituting the lithium manganese-based oxide may have a rod shape, an oval shape, and / or an irregular shape, and unless otherwise intended in the manufacturing process, primary particles of various shapes may exist within the same positive electrode active material.

[0062] The primary particles constituting the lithium manganese-based oxide defined herein 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 by the average value of the length of the major axis and the length of the minor axis of the primary particles ([major axis length + minor axis length] / 2).

[0063] When the lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, the secondary particles may have an average particle size of 0.5 μm to 15 μm, and the average particle size of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles.

[0064] Unless otherwise defined, the term "surface of the primary particle" used herein refers to the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" used herein refers to the outer surface of the secondary particle exposed to the outside. In this case, the "surface of the secondary particle" formed by aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0065] Unless otherwise defined, the term "surface portion of a particle" used herein refers to a region relatively closer to the "outermost surface" of a particle, and "center portion of a particle" refers to a region relatively closer to the "middle" of a particle than the "surface portion." Accordingly, "surface portion of a primary particle" refers to a region relatively closer to the "outermost surface" of a primary particle, and "center portion of a primary particle" refers to a region relatively closer to the "middle" of a primary particle than the "surface portion." Similarly, "surface portion of a secondary particle" refers to a region relatively closer to the "outermost surface" of a secondary particle, and "center portion of a secondary particle" refers to a region relatively closer to the "middle" of a secondary particle than the "surface portion."

[0066] In this case, the region of any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0067] For example, when the radius of the primary particle is r, the region that is 0 to 0.5r away from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region that is 0 to 0.5r away 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 that is 0 to 0.25 μm away from the surface of the primary particle, and the center portion of the primary particle can be defined as the region that is 0 to 0.25 μm away from the center of the primary particle.

[0068] Furthermore, if necessary, when the radius of the primary particle is referred to as r, the region that is 0 to 0.1r or 0 to 0.2r away from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region that is 0 to 0.2r or 0 to 0.5r away from the center of the primary particle can be defined as the center portion of the primary particle.

[0069] Similarly, when the radius of the secondary particle is referred to as r, the region that is 0 to 0.5r away from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region that is 0 to 0.5r away 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 that is 0 to 1.0 μm away from the surface of the secondary particle, and the center portion of the secondary particle can be defined as the region that is 0 to 1.0 μm away from the center of the secondary particle.

[0070] Furthermore, if necessary, when the radius of the secondary particle is referred to as r, the region that is 0 to 0.1r or 0 to 0.2r away from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region that is 0 to 0.2r or 0 to 0.5r away from the center of the secondary particle can be defined as the center portion of the secondary particle.

[0071] The lithium manganese-based oxide defined herein may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1:

[0072] [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b where 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 part of the oxygen present in the lithium manganese-based 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 type of halogen that can be used as X refers to the periodic table, and F, Cl, Br and / or I can be used, with F being preferred.

[0074] In another embodiment, the lithium manganese-based oxide may be represented by the following 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′ where: 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 independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, and <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 halogen usable as X and X' refer to the periodic table, and F, Cl, Br and / or I can be used, with F being preferred.

[0077] In Chemical Formula 1 and Chemical Formula 1-1, when M1 is Ni, M2 may contain Mn, and when M1 is Mn, M2 may contain Ni. Also, when M1 is Ni and Mn, M2 may be absent, or, if present, may be an element other than Ni and Mn.

[0078] That is, when M1 is Ni, 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), and Mn.

[0079] When M1 is Mn, 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), and Ni.

[0080] When M1 is Ni and Mn, 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-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may optionally contain cobalt. When the lithium manganese-based oxide contains cobalt, the mole fraction of cobalt relative to the total moles of metal elements in the lithium manganese-based oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese-based oxide represented by Chemical Formula 1 may have a cobalt-free composition.

[0082] The Li / Metal molar ratio measured from the lithium manganese-based 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-based oxide is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide. In addition, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.2 to 1.6 so that the lithium manganese-based oxide can appropriately form a solid solution or a composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group and can exhibit high capacity under high-voltage operating conditions.

[0083] In addition, in order to properly form 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, the content of manganese among all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 is preferably 50 mol% or more.

[0084] To enable the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under high-voltage operating conditions, the manganese content of the total metal elements excluding lithium present in the lithium manganese-based oxide is preferably 50 mol% or more but less than 80 mol%, and even more preferably 55 mol% to 75 mol%. If the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the migration of transition metals (especially manganese) within the lithium manganese-based oxide during formation and / or operation of the lithium secondary battery. This phase transition forms a spinel phase, and the spinel phase, acting as an impurity in the lithium manganese-based oxide, may cause a decrease in charge / discharge capacity or voltage decay during cycling of the lithium secondary battery.

[0085] In order to properly form a solid solution or a composite solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, the content of nickel in all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 is preferably less than 50 mol%.

[0086] When the nickel content in the lithium manganese-based oxide is 50 mol% or more, the C2 / m phase is not sufficiently formed, or the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group do not form a sufficient solid solution, which may cause phase separation during the formation 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 exist in a single phase belonging to the R3-m space group.

[0088] On the other hand, the lithium-excess lithium manganese oxide represented by the chemical formula 1 or the chemical formula 1-1 is an oxide of a phase belonging to the C2 / m space group represented by rLi2MnO3 (hereinafter referred to as "C2 / m phase") and (1-r)Li a M1 x M2 y O 2-b X b The lithium manganese-based oxide exists as a composite oxide in which an oxide of the C2 / m phase and an oxide of the R3-m phase form a solid solution or are combined with each other. For example, the lithium manganese-based oxide may exist in a state in which an oxide of the C2 / m phase and an 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 category 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, which is formed 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 whose surface is coated with a metal oxide having a phase belonging to the R3-m space group, does not fall under the category of a solid solution as defined in the present application.

[0091] In the lithium manganese-based oxide represented by Chemical Formula 1-1, if r exceeds 0.7, the proportion of the C2 / m phase oxide, Li2MnO3, in the lithium manganese-based oxide becomes excessively high, which ultimately increases the irreversible capacity and resistance of the positive electrode active material, and may result in a decrease in discharge capacity. That is, in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance in the lithium manganese-based oxide, and improve surface kinetics, it is preferable that the R3-m phase oxide be present in a certain proportion or more.

[0092] In one embodiment, the positive electrode active material may further include a boron-containing compound, wherein the boron-containing compound is physically mixed with the lithium manganese-based oxide.

[0093] The lithium manganese-based oxide and the boron-containing compound being present in a physically mixed state means that the lithium manganese-based oxide and the boron-containing compound are not composited, but are present as independent particles.

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

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

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

[0097] The boron-containing compound in the positive electrode active material 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 major axis length and the minor axis length ([major axis length + minor axis length] / 2), or D50 determined by particle size distribution analysis of the boron-containing compound.

[0098] If the average particle size of the boron-containing compound is less than 50 nm, the dispersibility of the boron-containing compound in the positive electrode slurry containing the positive electrode active material in which the lithium manganese-based oxide and the boron-containing compound are physically mixed may be low, making it difficult to uniformly control the particle size.

[0099] On the other hand, if the average particle size of the boron-containing compound is greater than 80 μm or 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 prepare a positive electrode active material layer using the positive electrode active material in which the lithium manganese-based 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 prevent or mitigate the leaching of transition metals from the positive electrode active material containing the lithium manganese-based oxide and / or a positive electrode manufactured using the positive electrode active material.

[0102] On the other hand, if the content of the boron-containing compound is more than 3.0 wt % based on the total weight of the positive electrode active material, the capacity of a lithium secondary battery using the positive electrode active material may be insufficient as the proportion of the lithium manganese-based oxide based on the total weight of the positive electrode active material decreases. Also, 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′ (0<α'<10, 0<β'<10, 0<γ'<20). The boron-containing compounds may be interchangeable within a lithium secondary battery using the positive electrode active material.

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

[0105] The positive electrode active material layer may include a positive electrode active material including a lithium manganese-based oxide as defined herein, a boron-containing compound, and a conductive material. When the positive electrode active material layer includes a boron-containing compound separately from the positive electrode active material, the positive electrode active material may not include the boron-containing compound.

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

[0107] The lithium manganese-based oxide and the boron-containing compound being present in a physically mixed state means that the lithium manganese-based oxide and the boron-containing compound are not composited, but are present as independent particles.

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

[0109] In this case, at least some of the lithium manganese-based oxides included in the positive electrode active material may be in physical contact with the boron-containing compound, but this physical contact state differs from the boron-containing compound being 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, 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 major axis length and the minor axis length ([major axis length + minor axis length] / 2), or D50 determined by particle size distribution analysis of the boron-containing compound.

[0111] If the average particle size of the boron-containing compound in the positive electrode active material layer is smaller than 50 nm, it is unlikely that the boron-containing compound will be uniformly dispersed in the positive electrode active material layer.

[0112] On the other hand, if the average particle size of the boron-containing compound in the positive electrode active material layer is larger than 60 μm or if the proportion of particles with a particle size of 60 μm or larger in the boron-containing compound exceeds 50 wt%, the boron-containing compound may be difficult to dissolve in the electrolyte. During storage and / or operation of the lithium secondary battery, the boron-containing compound present in the positive electrode active material or the positive electrode active material layer can dissolve in the electrolyte, and the boron-containing compound dissolved in the electrolyte forms 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] In addition, the boron-containing compound dissolved in the electrolyte may migrate to the negative electrode and form a physical barrier layer on the surface of the negative electrode. The physical barrier layer formed on the surface of the negative electrode may prevent the transition metal eluted from the lithium manganese-based oxide and / or impurities resulting from the eluted transition metal from being deposited on the surface of the negative electrode.

[0114] The physical barrier layer may include 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, and 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 Li2BO. 13In addition, the boron-containing oxide may have a composition in which the borate-based compound or the lithium borate-based compound is selectively doped with a different element M3.

[0117] The boron-containing compound may be present in the positive electrode active material layer in a content 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 the solids in the positive electrode active material layer, it may be difficult to sufficiently prevent or mitigate the leaching of transition metals from the positive electrode. Also, 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 more than 3.0 wt % based on the total weight of the positive electrode active material, the capacity of a lithium secondary battery using the positive electrode active material may be insufficient as the proportion of the lithium manganese-based oxide based on the total weight of the positive electrode active material decreases. Also, 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′ (0<α'<10, 0<β'<10, 0<γ'<20). The boron-containing compounds may be interchangeable 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, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0122] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0123] In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0124] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0125] The binder serves to improve adhesion between positive electrode active material particles and 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0126] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be fabricated by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0127] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0128] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0129] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0130] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0131] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals 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, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0134] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0135] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0136] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0137] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 for further improving 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. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, 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.

[0139] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0140] In another embodiment, the negative electrode active material layer may be fabricated by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0141] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

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

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

[0144] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based 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, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0145] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. 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. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0146] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-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, an X element (wherein 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 material include Li2S-P2S5, Li2S-P2S-LiX (wherein 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 (wherein m and n are integers and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0148] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0149] The oxide-based solid electrolyte material is 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 solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Alternatively, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0151] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0152] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0153] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

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

[0155] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized 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 the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0157] Production Example 1. Production of positive electrode active material Example 1 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH, and NH4OH were added to the reactor and stirred. The temperature inside the reactor 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 completed, the reactor was washed and dehydrated to produce 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 the reactor where the precursor obtained in step (a) was being stirred, NiSO4·6H2O aqueous solution, NaOH, and NH4OH were added. At this time, NiSO4·6H2O was weighed out to be 5 mol% and then added. After the reaction was completed, the precursor was washed and dehydrated, and then dried at 150°C for 14 hours to obtain the coated precursor.

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

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

[0161] Next, the temperature of a calcination furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the furnace was cooled to obtain a lithium-excess lithium-manganese-based oxide.

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

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

[0164] Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the boron-containing compound was mixed in an amount of 0.7 wt % based on the total weight of the final product.

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

[0166] Comparative Example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that step (e) was not performed.

[0167] Reference example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), B2O3 having an average particle size of 100 μm was mixed in an amount of 0.7 wt% based on the total weight of the final product.

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

[0169] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) Positive electrode slurries were prepared by dispersing 90 wt % of each of the positive electrode active materials prepared in Examples 1 to 3, Comparative Example 1, and Reference Examples 1 and 2 described in Preparation Example 1, 4.5 wt % of carbon black, and 5.5 wt % of PVDF binder in N-methyl-2-pyrrolidone (NMP).

[0170] The positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and dried at 135° C. in vacuum to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0171] A half-cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0172] In this case, when the positive electrode active material prepared in Reference Example 1 was used, scratches occurred on the surface of the positive electrode active material layer due to the excessively large average particle size of B2O3, and a normal positive electrode active material layer could not be formed.

[0173] Manufacturing Example 3: Manufacturing of lithium secondary battery (half cell) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared according to Comparative Example 1 described in Preparation Example 1, 4.5 wt% of carbon black, 5.5 wt% of PVDF binder, and B2O3 having an average particle size of 40 μm as a boron-containing compound in N-methyl-2-pyrrolidone (NMP). The boron-containing compound was mixed to a concentration of 0.6 wt% based on the total weight of solids in the positive electrode slurry.

[0174] The positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and dried at 135° C. in vacuum to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0175] A half-cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0176] Manufacturing Example 4: Manufacturing of lithium secondary batteries (full cells) Positive electrode slurries were prepared by dispersing 90 wt % of each of the positive electrode active materials prepared in Examples 1 to 3, Comparative Example 1, and Reference Examples 1 and 2 described in Preparation Example 1, 4.5 wt % of carbon black, and 5.5 wt % of PVDF binder in N-methyl-2-pyrrolidone (NMP).

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

[0178] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution containing 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0179] In this case, when the positive electrode active material prepared in Reference Example 1 was used, scratches occurred on the surface of the positive electrode active material layer due to the excessively large average particle size of B2O3, and a normal positive electrode active material layer could not be formed.

[0180] Manufacturing Example 5. Manufacturing of lithium secondary batteries (full cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared according to Comparative Example 1 described in Preparation Example 1, 4.5 wt% of carbon black, 5.5 wt% of PVDF binder, and B2O3 having an average particle size of 40 μm as a boron-containing compound in N-methyl-2-pyrrolidone (NMP). The boron-containing compound was mixed to a concentration of 0.6 wt% based on the total weight of solids in the positive electrode slurry.

[0181] The positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and dried at 135° C. in vacuum to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0182] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution containing 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0183] Experimental Example 1: SEM analysis of positive electrode active material FIG. 1 is a SEM image of the positive electrode active material prepared in Example 1.

[0184] 1, it can be seen that the lithium manganese-based oxide and the boron-containing compound in the form of secondary particles coexist within the positive electrode active material. That is, it can be seen that the lithium manganese-based oxide exists in the positive electrode active material as secondary particles formed by aggregation of a plurality of primary particles, and the boron-containing compound exists independently from the secondary particles.

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

[0186] Experimental Example 2: SEM analysis of the cross section of the positive electrode In Preparation Example 2, the distribution of the lithium manganese-based oxide and the boron-containing compound in the cathode active material layer was analyzed through cross-sectional SEM image analysis of the cathode active material layer prepared using the cathode active material prepared in Example 2. The cathode active material layer was analyzed in a state before being assembled into a half cell after the cathode was prepared by the method described in Preparation Example 2. The analysis results are shown in FIG.

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

[0188] This result is believed to be due to the boron-containing compound being partially dissolved by the solvent during the positive electrode preparation process. This allows the boron-containing compound to be present in a dispersed state throughout the positive electrode active material layer. Furthermore, the results of Figure 2 confirm that the boron-containing compound partially dissolved by the solvent during the positive electrode preparation process can be transformed into a physical barrier layer on the surface of the positive electrode active material layer.

[0189] Experimental Example 3: Dissolution analysis of boron-containing compounds The positive electrodes prepared using the positive electrode active material prepared in Example 2 in Preparation Example 2 and the positive electrodes prepared in Preparation Example 3 were stored in an electrolyte at 60°C for 3 days, and then recovered. The boron content in the positive electrodes 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 seen that when the positive electrodes prepared using the positive electrode active material prepared in Example 2 in Preparation Example 2 and the positive electrodes prepared in Preparation Example 3 were stored in a relatively high-temperature electrolyte, the boron-containing compound present in the positive electrodes was dissolved, and the content of the boron-containing compound in the positive electrodes decreased.

[0192] In this manner, the boron-containing compound in the positive electrode may be dissolved in the electrolyte, and the boron-containing compound dissolved in the electrolyte may 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 a lithium secondary battery (half cell) The lithium secondary batteries (half cells) prepared in Preparation Examples 2 and 3 were subjected to a charge-discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and discharge rates of 0.1 C, 1.0 C, and 2.0 C to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and rate capability (C-rate).

[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 seen that even when a boron-containing compound is physically mixed into the positive electrode active material or the positive electrode active material layer, the initial charge capacity, initial discharge capacity, initial reversible 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 characteristics of a lithium secondary battery (full cell) The lithium secondary batteries (full cells) manufactured in Manufacturing Examples 4 and 5 were subjected to a 6-cycle formation process at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then 500 charge-discharge cycles were carried out at 25°C, a voltage range of 2.0V to 4.6V, and 1C / 1C. st 500 cycles) discharge capacity, relative to initial discharge capacity th The percentage of discharge capacity after each cycle (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, unlike the evaluation results of the half cells in Table 2, it can be seen that the cycle capacity retention of the full cells using the cathode active materials of Examples 1 to 3 is significantly higher than that of the full cell using the cathode active material of Comparative Example 1. This result is presumably due to the fact that in the case of the full cell using the cathode active material of Comparative Example 1, an abnormal resistance phenomenon occurs in the anode as transition metals are eluted from the lithium manganese-based oxide, thereby accelerating the deterioration of the battery life.

[0201] In addition, although Reference Example 2 exhibits a higher cycle capacity retention rate than the full cell using the cathode active material of Comparative Example 1, it is expected that the content of the boron-containing compound physically mixed with the lithium manganese-based oxide is somewhat lower, resulting in a further deterioration in lifespan compared to the full cells using the cathode active materials of Examples 1 to 3.

[0202] It was also confirmed that the full cell of Production Example 5, which uses the positive electrode active material of Comparative Example 1 but physically mixes a boron-containing compound during the positive electrode production process, also exhibits a cycle capacity retention rate at a level similar to that of Example 1.

[0203] Experimental Example 6: Analysis of transition metal elution In Preparation Example 4, the lithium secondary batteries (full cells) prepared using the positive electrode active materials prepared in Example 2 and Comparative Example 1 and the lithium secondary batteries (full cells) prepared in Preparation Example 5 were subjected to a six-cycle formation process at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100). The full cells were then stabilized by two cycles of charge / discharge at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. The full cells were then disassembled, and the negative electrodes were washed with diethyl carbonate solvent, dried in a vacuum at 60°C, and then collected.

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

[0205] In addition, lithium secondary batteries (full cells) manufactured using the positive electrode active materials manufactured in Example 2 and Comparative Example 1 in Manufacturing Example 4 and lithium secondary batteries (full cells) manufactured in Manufacturing Example 5 were subjected to a six-cycle formation process at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100). Then, 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 two charge-discharge cycles at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. The full cells were then disassembled, and the negative electrodes were washed with diethyl carbonate solvent, vacuum dried at 60°C, and then collected.

[0206] The negative electrode active material was separated from the recovered Cu foil (current collector) of the negative electrode, and the separated negative electrode active material was subjected to ICP analysis to measure the contents 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, as predicted in Experimental Example 5, it can be seen that the rapid deterioration in lifespan of the full cell using the cathode active material according to Comparative Example 1 is due to the relatively increased content of transition metals deposited on the anode active material as charge-discharge cycles are repeated.

[0210] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. 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 dissolved or combined; a boron-containing compound physically mixed with the lithium manganese-based oxide.

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

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

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

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

6. 2. The positive electrode active material of 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 boron-containing compound is B ２ O ３ , H α B β O γ (0<α<10, 0<β<10, 0<γ<20) and Li α′ B β′ O γ′ 2. The positive electrode active material according to claim 1, comprising at least one selected from (0<α'<10, 0<β'<10, 0<γ'<20).

8. The positive electrode active material of claim 1 , wherein the lithium manganese-based oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 ｂ (where, 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-based oxide, 0<a≦0.7, 0≦b≦0.1, 0<x≦1, 0≦y<1, 0<x+y≦1)

9. 2. The positive electrode active material of claim 1, wherein the lithium manganese-based oxide is represented by the following chemical formula 1-1: [Chemical formula 1-1] rLi ２ MnO ３－ｃ X′ ｃ ・(1-r)Li ａ′ M1 ｘ′ M2 ｙ′ O ２－ｂ′ X ｂ′ (where, 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 independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based 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)

10. A positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, The positive electrode active material layer includes a positive electrode active material, a boron-containing compound, and a conductive material.

11. The positive electrode of claim 10 , wherein the lithium manganese-based oxide and the boron-containing compound are present in the positive electrode active material layer in a physically mixed state.

12. 11. The positive electrode according to claim 10, wherein the positive electrode active material is 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 solid-solved or composite.

13. The positive electrode according to claim 10, wherein the average particle size of the boron-containing compound is 50 nm to 60 μm.

14. The positive electrode according to claim 10, wherein the boron-containing compound is present in an amount of 0.09 wt % to 3.0 wt % based on the total weight of the solid content in the positive electrode active material layer.

15. The boron-containing compound is B ２ O ３ , H α B β O γ (0<α<10, 0<β<10, 0<γ<20) and Li α′ B β′ O γ′ 11. The positive electrode of claim 10, comprising at least one selected from (0<α'<10, 0<β'<10, 0<γ'<20).

16. A lithium secondary battery comprising: the positive electrode according to claim 10; a negative electrode; and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

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