Positive electrode active material and lithium secondary battery

Abstract

To provide a bimodal type positive electrode active material containing a lithium-rich lithium manganese-based oxide, capable of preventing rapid deterioration of battery performance due to a side reaction during an initial battery reaction under a high voltage condition, and capable of preventing life deterioration of a lithium secondary battery.SOLUTION: Wherein the first lithium manganese oxide and the second lithium manganese oxide are oxides in which a phase belonging to C2 / m space groups and a phase belonging to R3 / m space groups are solid-dissolved or combined, each of the first lithium manganese oxide and the second lithium manganese oxide is independently a lithium manganese oxide including nickel and manganese, and a content (mol%) of manganese with respect to total transition metals present in a surface portion of the first lithium manganese oxide is smaller than a content (mol%) of manganese with respect to total transition metals present in a surface portion of the second lithium manganese oxide.SELECTED DRAWING: None

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 bimodal type positive electrode active material that can improve the low energy density per unit volume of lithium-excess lithium-manganese-based oxides, prevent deterioration in the electrochemical characteristics of lithium secondary batteries, including rate characteristics, due to the presence of excess lithium and manganese in the lithium-manganese-based oxides, and in particular, prevent or mitigate elution of transition metals from the lithium-manganese-based oxides, thereby preventing deterioration in the lifespan of lithium secondary batteries, and a lithium secondary battery including the same. [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 active material and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte 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 can generate gas during repeated charge / discharge cycles after electrode fabrication. Furthermore, the residual Li2CO3 among these Li by-products can increase 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 (capacity retention) during charge / discharge cycling of the lithium secondary battery.

[0011] In addition, due to the characteristics of the material, OLO has a high porosity within the particles, which means that it has a disadvantage of low energy density per unit volume.

[0012] To solve the above problems, research has been conducted to change the composition of OLO, but so far, these attempts have not reached a commercial level. Summary of the Invention [Problem to be solved by the invention]

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] For example, OLO has the aforementioned drawback of low energy density per unit volume due to the material's composition (containing excess lithium) and structural characteristics (high intra-particle porosity).

[0018] However, the present inventors have confirmed that the low energy density per unit volume of lithium-excess lithium-manganese-based oxide can be improved by preparing the lithium-manganese-based oxide into small particles and large particles, and then providing a bimodal type cathode active material as a mixture of the small particles and the large particles.

[0019] Therefore, an object of the present invention is to provide a bimodal type positive electrode active material for improving the low energy density per unit volume of lithium-excess lithium manganese-based oxides.

[0020] Furthermore, 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. In particular, there is a high possibility that Mn contained in an excess amount in lithium-manganese oxides will leach from the particle surface.

[0021] 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.

[0022] 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.

[0023] 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+ Mn may be dissolved into the electrolyte. 2+ During formation or charging / discharging, Mn moves to the surface of the negative electrode using 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.

[0024] 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.

[0025] 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.

[0026] However, there is currently no technology to solve the problems associated with the elution of transition metals from lithium-rich lithium manganese oxides.

[0027] As described above, conventional lithium-excess lithium-manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability when compared with other commercially available positive electrode active materials. However, the present inventors have confirmed that lithium-excess lithium-manganese-based oxides can also exhibit commercially viable electrochemical properties and stability when the bulk composition of the lithium-manganese-based oxide is controlled and a barrier layer is provided on the surface of the lithium-manganese-based oxide that can prevent or mitigate the elution of transition metals.

[0028] In particular, the inventors have confirmed that the lithium manganese-based oxide can be formed as core-shell particles that exhibit a concentration gradient of at least one transition metal constituting the lithium manganese-based oxide from the center to the surface, and that the content of the transition metal that is relatively less likely to be eluted in the shell region is higher than that of other transition metals, thereby suppressing or mitigating the elution of the transition metal from the lithium manganese-based oxide.

[0029] Furthermore, the present inventors have confirmed that when the surface of such a core-shell particle, i.e., the surface of the shell, is covered with a barrier layer capable of suppressing the elution of transition metals from the core-shell particle, the elution of transition metals from the lithium manganese-based oxide can be further suppressed or alleviated.

[0030] Therefore, the present invention provides a bimodal cathode active material comprising small and large particles to improve the low energy density per unit volume of lithium-excess lithium-manganese-based oxides, wherein at least one of the small and large particles is a core-shell particle exhibiting a transition metal concentration gradient, and the content of the transition metal, which is relatively less likely to dissolve, in the shell region is higher than that of other transition metals, thereby suppressing or mitigating the dissolution of the transition metal from the lithium-manganese-based oxide and simultaneously improving the charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium-manganese-based oxide.

[0031] Another object of the present invention is to provide a bimodal type positive electrode active material containing small particles and large particles in order to improve the low energy density per unit volume of lithium-excess lithium-manganese-based oxides, and to provide a positive electrode active material in which a barrier layer is formed on the surface of at least one of the small particles and the large particles, thereby suppressing or mitigating the elution of transition metals from the lithium-manganese-based oxide.

[0032] Another object of the present invention is to provide a lithium secondary battery that can achieve high stability by using a positive electrode including a bimodal type positive electrode active material defined herein, thereby preventing deterioration in electrochemical characteristics of the lithium secondary battery, including rate characteristics, due to the excessive lithium and manganese present in conventional OLOs, and reducing side reactions between the positive electrode active material and the electrolyte during high voltage operation. [Means for solving the problem]

[0033] According to one aspect of the present invention for solving the above-mentioned technical problems, there is provided a bimodal type positive electrode active material including a first lithium-manganese-based oxide and a second lithium-manganese-based oxide having different average particle sizes.

[0034] In the present application, the first lithium-manganese-based oxide may also be referred to as small particles, and the second lithium-manganese-based oxide may also be referred to as large particles. The first lithium-manganese-based oxide and the second lithium-manganese-based oxide constituting the bimodal-type positive electrode active material are oxides 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.

[0035] Generally, commercially available ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a single phase belonging to the R3-m space group, whereas the lithium-excess 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.

[0036] In one embodiment, the first lithium manganese-based oxide and the second lithium manganese-based oxide may each independently contain at least one selected from nickel, cobalt, and manganese.

[0037] The first lithium manganese-based oxide and the second lithium manganese-based oxide may each independently be represented by the following Chemical Formula 1:

[0038] [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, 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。)

[0039] In another embodiment, the first lithium manganese-based oxide and the second lithium manganese-based oxide may each independently be represented by the following Chemical Formula 1-1:

[0040] [Chemical formula 1-1] rLi2MnO 3-b″ X′ b″ (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, and Nd, and M2 does not overlap with M1; X and X' are halogens 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。)

[0041] In addition, at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide may be provided in the form of core-shell particles that exhibit a concentration gradient of at least one selected from nickel and manganese from the center toward the surface.

[0042] In this case, the content of the transition metal, which is relatively less likely to be dissolved, in the region corresponding to the shell is higher than that of other transition metals, thereby reducing the possibility of the transition metal being dissolved from the core-shell particles.

[0043] In addition, by providing at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of core-shell particles, the charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the core-shell particles can be improved.

[0044] In one embodiment, a barrier layer may be present on at least a portion of the surface of at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide. The barrier layer covering at least a portion of the surface of the first lithium manganese-based oxide and / or the second lithium manganese-based oxide can prevent or mitigate the elution of transition metals from the first lithium manganese-based oxide and / or the second lithium manganese-based oxide.

[0045] The barrier layer may include an oxide containing at least one selected from a metal element, a metalloid element, and phosphorus (P).

[0046] Specifically, the barrier layer may include at least one selected from a first oxide represented by the following chemical formula 2, a second oxide represented by the following chemical formula 3, and a third oxide represented by the following chemical formula 4:

[0047] [Chemical formula 2] Li c B d M3 e O f (where, 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, and Nd, 0 ≦ c ≦ 8, 0 < d ≦ 8, 0 ≦ e ≦ 8, 2 ≦ f ≦ 13.

[0048] [Chemical Formula 3] Li g M4 h O i (Here, M4 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, and Nd, 0 ≦ g ≦ 8, 0 ≦ h ≦ 8, 2 ≦ i ≦ 13, excluding the case where g and h are both 0.

[0049] [Chemical Formula 4] Li j M5 k (P l O m ) n (Here, M5 is at least one selected from Ni, Mn, Co, Al, 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, and Nd, 0 ≦ j ≦ 10, 0 ≦ k ≦ 8, 0 < l ≦ 4, 0 < m ≦ 10, 0 < n ≦ 13, excluding the case where j and k are both 0.

[0050] Moreover, according to another aspect of the present invention, a positive electrode including the above-described positive electrode active material is provided.

[0051] Furthermore, according to still another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

Advantages of the Invention

[0052] 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.

[0053] Specifically, according to the present invention, the lithium manganese-based oxide is prepared into small particles and large particles, and then a bimodal type cathode active material is provided as a mixture of the small particles and the large particles, thereby improving the low energy density per unit volume of lithium-excess lithium manganese-based oxide.

[0054] In addition, according to the present invention, the small particles and / or large particles are formed as core-shell particles exhibiting a transition metal concentration gradient, and the content of the transition metal that is relatively less likely to be eluted in the shell region is higher than that of other transition metals, thereby suppressing or mitigating the elution of the transition metal from the lithium manganese-based oxide.

[0055] By forming the small particles and / or large particles as core-shell particles that exhibit a transition metal concentration gradient, the charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium manganese-based oxide can be improved.

[0056] Furthermore, when the surface of such a core-shell particle, i.e., the surface of the shell, is covered with a barrier layer capable of suppressing or mitigating the leaching of transition metals from the core-shell particle, the leaching of transition metals from the small particles and / or large particles can be further suppressed or mitigated.

[0057] By suppressing or mitigating the elution of transition metals from small particles and / or large particles, it is possible to prevent the transition metals eluted on the surface of the lithium manganese-based oxide from reacting with the electrolyte to form impurities.

[0058] 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 the lithium secondary battery.

[0059] That is, according to the present invention, by forming a barrier layer on at least a portion of the surface of the small particles and / or large particles, it is possible to prevent the accelerated deterioration of the life of the lithium secondary battery caused by the transition metal eluted from the lithium manganese-based oxide depositing impurities on the positive electrode and / or negative electrode.

[0060] In addition, the barrier layer can act as a physical barrier between the small particles and / or large particles and the electrolyte. In particular, OLO, such as the lithium manganese-based oxide, has the advantage of exhibiting high capacity under high-voltage operating conditions. However, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte increases as the operating voltage increases. Therefore, it is important to reduce side reactions between the lithium manganese-based oxide and the electrolyte.

[0061] Therefore, by forming a barrier layer on at least a portion of the surface of the small particles and / or large particles, side reactions between the lithium manganese-based oxide and the electrolyte are reduced, thereby improving the stability and lifespan of a lithium secondary battery using the bimodal type cathode active material defined herein. In particular, a cathode active material with reduced side reactions with the electrolyte can operate a lithium secondary battery at a higher voltage.

[0062] The above-mentioned effects and specific effects of the present invention will be described below together with specific matters for carrying out the invention. DETAILED DESCRIPTION OF THE INVENTION

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Here, the lithium manganese-based oxide may be classified into a first lithium manganese-based oxide as small particles and a second lithium manganese-based oxide as large particles based on the average particle size, and the positive electrode active material defined herein is a bimodal type positive electrode active material including the first lithium manganese-based oxide as small particles and the second lithium manganese-based oxide as large particles.

[0067] Hereinafter, unless otherwise defined, the lithium manganese-based oxide can be understood to refer to the first lithium manganese-based oxide and the second lithium manganese-based oxide.

[0068] The lithium manganese-based oxide is also called an overlithiated layered oxide (OLO) when 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).

[0069] The lithium-manganese-based oxide contains at least one selected from nickel, cobalt, and manganese, i.e., the first lithium-manganese-based oxide and the second lithium-manganese-based oxide each independently contain at least one selected from nickel, cobalt, and manganese.

[0070] 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 ratio of manganese (e.g., 50 mol % or more, preferably 55 mol % to 75 mol %) in the total metal elements compared to commercially available ternary lithium composite oxides.

[0071] 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) in all metal elements excluding lithium, the lithium-manganese oxide has a relatively low ratio of nickel to all metal elements (for example, less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0072] 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 1.7.

[0073] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0074] In one embodiment, the first lithium manganese-based oxide and the second lithium manganese-based oxide include secondary particles formed by agglomeration of a plurality of primary particles.

[0075] The primary particles 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.

[0076] The primary particles may have an average particle size of 0.05 μm to 5 μm, preferably 0.1 μm to 1.0 μm, 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).

[0077] If the average particle size of the primary particles is less than 0.05 μm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles is relatively large, which increases the possibility of side reactions occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0078] On the other hand, when the average particle size of the primary particles is larger than 5 μm, excessive growth of the primary particles is induced, and the diffusion path of lithium ions within the primary particles becomes longer. When the diffusion path of lithium ions within the primary particles is too long, the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles decrease, which causes an increase in the resistance of the lithium manganese-based oxide (secondary particles) composed of the primary particles.

[0079] By making the difference in average particle size between the second lithium-manganese-based oxide and the first lithium-manganese-based oxide 3 μm or more, preferably 4 μm or more, the energy density per unit volume of the bimodal positive electrode active material can be increased.

[0080] The main peak of a volumetric particle size distribution graph (x-axis: particle size (μm), y-axis: volume %) for the first lithium-manganese oxide may preferably be between 1 μm and 8 μm, and more preferably between 2 μm and 7 μm. The average particle size calculated as the average value of the length in the major axis direction and the length in the minor axis direction of the first lithium-manganese oxide ([major axis length + minor axis length] / 2) may be between 2 μm and 6 μm.

[0081] The main peak of a volumetric particle size distribution graph (x-axis: particle size (μm), y-axis: volume %) for the second lithium-manganese oxide may preferably be between 6 μm and 24 μm, more preferably between 8 μm and 22 μm. The average particle size calculated as the average value of the major axis length and minor axis length of the second lithium-manganese oxide ([major axis length + minor axis length] / 2) may be between 7 μm and 14 μm.

[0082] In addition, in order to optimize the energy density per unit volume of the bimodal positive electrode active material, the first lithium manganese-based oxide and the second lithium manganese-based oxide in the positive electrode active material are preferably contained in a weight ratio of 10:90 to 80:20.

[0083] The first lithium-manganese-based oxide may be present in a form in which it fills gaps between the second lithium-manganese-based oxide, or may be attached to the surface of the second lithium-manganese-based oxide, or may be present in a form in which the first lithium-manganese-based oxide aggregates together.

[0084] If the ratio of the first lithium-manganese-based oxide to the second lithium-manganese-based oxide in the positive electrode active material is too low, the first lithium-manganese-based oxide may not be sufficiently filled into voids formed by the second lithium-manganese-based oxide.

[0085] Meanwhile, if the ratio of the first lithium manganese-based oxide to the second lithium manganese-based oxide in the positive electrode active material is excessively high, the energy density per unit volume of the positive electrode active material may decrease.

[0086] 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.

[0087] Unless otherwise defined, the term "surface portion of a particle" used herein refers to a region relatively closer to the "surface" of a particle, and the term "core portion of a particle" refers to a region relatively closer to the "center" of a particle than the "surface portion." Accordingly, the term "surface portion of a primary particle" refers to a region relatively closer to the "surface" of a primary particle, and the term "core portion of a primary particle" refers to a region relatively closer to the "center" of a primary particle than the "surface portion." Similarly, the term "surface portion of a secondary particle" refers to a region relatively closer to the "surface" of a secondary particle, and the term "core portion of a secondary particle" refers to a region relatively closer to the "center" of a secondary particle than the "surface portion."

[0088] 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."

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In one embodiment, the first lithium manganese-based oxide and the second lithium manganese-based oxide defined herein may each independently be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1. The composition represented by the following Chemical Formula 1 may represent an average composition reflecting the composition of a barrier layer present on at least a portion of the surface of the lithium manganese-based oxide.

[0094] [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, 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。

[0095] 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.

[0096] A gradient may be formed in which the ratio of at least one selected from x and y in Formula 1 changes from the surface portion of the primary particle toward the center portion of the primary particle.

[0097] In addition, a gradient may be formed in which the ratio of at least one selected from x and y in Formula 1 changes from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0098] In addition, the lithium-excess lithium manganese-based oxide represented by Chemical Formula 1 may further include a spinel phase in addition to the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group.

[0099] In another embodiment, the first lithium manganese-based oxide and the second lithium manganese-based oxide defined herein may each independently be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1-1: The composition represented by the following Chemical Formula 1-1 may represent an average composition reflecting the composition of a barrier layer present on at least a portion of the surface of the lithium manganese-based oxide.

[0100] [Chemical formula 1-1] rLi2MnO 3-b″ X′ b″ (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, and Nd, and M2 does not overlap with M1. X and X′ are halogens capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, where 0 < r ≦ 0.7, 0 < a′ ≦ 1, 0 ≦ b′ ≦ 0.1, 0 ≦ b″ ≦ 0.1, 0 < x′ ≦ 1, 0 ≦ y′ < 1, and 0 < x′ + y′ ≦ 1. The types of halogens that can be used as X and X′ can be referred to the periodic table, and F, Cl, Br, and / or I, etc. can be used, and preferably, F can be used.

[0101] In the case where M1 is Ni in the chemical formula 1 and the chemical formula 1-1, M2 may contain Mn, and in the case where M1 is Mn, M2 may contain Ni. Also, in the case where M1 is Ni and Mn, M2 may not exist, or if it exists, it may be other elements excluding Ni and Mn.

[0102] That is, when M1 is Ni, M2 may contain at least one (preferably at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd; 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) selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd and Mn.

[0103] When M1 is Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, 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, Ti, Zr, Si, and W, and even more preferably, at least one selected from P, B, and Si), and Ni.

[0104] When M1 is Ni and Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd, preferably at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, and W, more preferably at least one selected from Co, P, B, Ti, Zr, Si, and W, and even more preferably at least one selected from P, B, and Si.

[0105] 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 moles of all 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.

[0106] 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 1.7. 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.

[0107] In addition, in order for the lithium manganese-based oxide to 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 to exhibit high capacity under a high voltage operating environment, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.1 to 1.6.

[0108] 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 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 50 mol% or more.

[0109] In order for the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under a high-voltage operating environment, the manganese content of all metal elements excluding lithium present in the lithium manganese-based oxide is more preferably 50 mol % or more and less than 80 mol %, and even more preferably 55 mol % to 75 mol %.

[0110] When 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 the formation and / or operation of the lithium secondary battery. This phase transition forms a spinel phase, which acts as an impurity in the lithium manganese-based oxide and may cause a decrease in charge / discharge capacity or voltage decay during the charge / discharge cycles of the lithium secondary battery.

[0111] 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 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%.

[0112] 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.

[0113] If the first lithium-manganese-based oxide or the second lithium-manganese-based oxide is a core-shell particle that exhibits a concentration gradient of at least one selected from nickel and manganese from the center (core) to the surface (shell), the content of nickel in the core-shell particle is preferably 25 mol % to 45 mol % so that nickel is sufficiently present on the surface of the core-shell particle.

[0114] 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.

[0115] Meanwhile, the lithium-excess lithium manganese oxide represented by the formula 1 or the formula 1-1 is rLi2MnO 3-b″ X′ b″ The oxides of the phase belonging to the C2 / m space group (hereinafter also 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.

[0116] 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.

[0117] 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.

[0118] In the lithium manganese-based oxide represented by the chemical formula 1-1, when r exceeds 0.7, the lithium manganese-based oxide is a C2 / m phase oxide, Li2MnO 3-b″ X′ b″ The proportion of R3-m phase oxide is preferably present in a certain proportion or more in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance, and improve the surface kinetics of the lithium manganese-based oxide.

[0119] As described above, at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide may be a core-shell particle exhibiting a concentration gradient of at least one selected from nickel and manganese from the center (core) to the surface (shell). In this case, by making the content of a transition metal that is relatively less likely to be leached in the shell region higher than that of other transition metals, leaching of the transition metal from the core-shell particle can be suppressed or alleviated.

[0120] In addition, by providing at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of core-shell particles, the charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the core-shell particles can be improved.

[0121] When the concentration of transition metals in the shell (or surface portion) and core (or center portion) of a particle is different, the particle may be referred to as a core-shell particle. That is, the lithium manganese-based oxide may be a core-shell particle, and the average composition of all metal elements constituting the lithium manganese-based oxide in the core and the shell may be different. Therefore, the ratio of phases belonging to the C2 / m space group and phases belonging to the R3-m space group in the core may be different from the ratio of phases belonging to the C2 / m space group and phases belonging to the R3-m space group in the shell.

[0122] The shell may occupy at least a portion of the surface of the core, i.e., the shell may be partially present on the surface of the core or may occupy the entire surface of the core.

[0123] In the present application, the mole number of all metal elements in the lithium manganese-based oxide is M 1 The number of moles of nickel is M 2 When the above definition is used, M calculated from the average composition of all metal elements in the core of the lithium manganese-based oxide is 2 / M1 and M calculated from the average composition of all metal elements in the shell of the lithium manganese-based oxide. 2 / M 1 may be different from each other.

[0124] It is well known that lithium-excess lithium manganese oxides containing an excess amount of Mn have lower electrical conductivity than lithium-cobalt oxides or ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions containing a relatively large amount of Ni. Furthermore, ternary lithium composite oxides also have the problem that their electrical conductivity decreases as the Mn content increases.

[0125] Various reactions occur on the surface of the various types of cathode active materials described above. As the Mn content in the cathode active material increases, the charge-transfer and / or diffusion of lithium ions on the surface is hindered, and this phenomenon can be referred to as a decrease in the surface kinetic or intra-surface reaction kinetic.

[0126] As described above, the bimodal type positive electrode active material defined herein can improve surface kinetics by providing at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of core-shell particles having a transition metal concentration gradient between the core and the shell.

[0127] In one embodiment, the first lithium manganese-based oxide may be a core-shell particle that exhibits a concentration gradient of at least one selected from nickel and manganese from the center (also referred to as the core) to the surface (also referred to as the shell).

[0128] In this case, the second lithium-manganese-based oxide may be a particle (also referred to as a bulk or bulk particle) in which the nickel and manganese concentrations are constant (i.e., the nickel and manganese concentrations are constant from the center to the surface) or may be a particle that exhibits a concentration gradient with a smaller slope than the concentration gradient exhibited in the first lithium-manganese-based oxide. Here, "the nickel and manganese concentrations are constant within the particle" means that the nickel or manganese concentrations may increase or decrease partially in any region within the particle, but do not tend to increase or decrease from the center (core) to the surface (shell) of the particle.

[0129] In the bimodal type positive electrode active material, the first lithium manganese-based oxide is present in a relatively uniformly dispersed state, and the specific surface area of ​​the first lithium manganese-based oxide is larger than that of the second lithium manganese-based oxide. Therefore, the first lithium manganese-based oxide is selectively provided as core-shell particles, which can contribute to improving the overall surface kinetics of the bimodal type positive electrode active material.

[0130] In addition, since the second lithium manganese-based oxide is larger than the first lithium manganese-based oxide, it is difficult to realize an overall concentration gradient within the particle. Therefore, it is difficult to expect the kinetic improvement effect that can be obtained by applying a concentration gradient to the first lithium manganese-based oxide from the second lithium manganese-based oxide.

[0131] Therefore, by selectively providing the first lithium manganese-based oxide in the bimodal type positive electrode active material as core-shell particles exhibiting a concentration gradient, the manganese content (mol%) relative to the total transition metals in the first lithium manganese-based oxide becomes smaller than the manganese content (mol%) relative to the total transition metals in the second lithium manganese-based oxide.

[0132] In addition, the manganese content (mol%) relative to the total transition metals in the first lithium manganese-based oxide may be adjusted so that the manganese content (mol%) relative to the total transition metals present at least in the surface region of the first lithium manganese-based oxide is smaller than the manganese content (mol%) relative to the total transition metals present in the surface region of the second lithium manganese-based oxide.

[0133] The core-shell particles can be provided as primary particles and / or secondary particles.

[0134] In one embodiment, the primary particles may be core-shell particles that exhibit a concentration gradient of at least one transition metal from the center of the primary particle to the surface of the primary particle. Thus, the first lithium manganese-based oxide and / or the second lithium manganese-based oxide that exist in the form of secondary particles may be an aggregate of primary particles that exist as the core-shell particles defined above.

[0135] When the primary particles are present as core-shell particles that exhibit a concentration gradient of at least one transition metal from the core to the shell, the surface kinetics of the primary particles and the secondary particles formed by aggregation of the primary particles can be improved.

[0136] For example, the primary particles may exhibit a concentration gradient of at least one element selected from nickel and manganese from the core to the shell. More specifically, the primary particles may exhibit a concentration gradient in which the nickel concentration increases while the manganese concentration decreases from the core to the shell.

[0137] Furthermore, when the primary particles are provided as core-shell particles as defined above, it is possible to reduce abrupt changes in the concentration of metal elements between the core and shell of the primary particles, and by preventing abrupt changes in the concentration of metal elements within the primary particles, it is possible to prevent instability in the crystal structure of the primary particles.

[0138] The region of the primary particles present as core-shell particles where a transition metal concentration gradient exists is referred to as the shell of the primary particles. The average thickness of the shell may be 0.1 nm to 2 μm, preferably 50 nm to 1 μm. If the shell thickness of the primary particles is thinner than 0.1 nm, it is difficult to sufficiently improve the surface kinetics of the primary particles. On the other hand, if the shell thickness of the primary particles is thicker than 2 μm, it is disadvantageous to exhibit high capacity under high-voltage operating conditions, which is one of the advantages of the lithium manganese-based oxide. The shell thickness of the primary particles may vary depending on the average particle size of the primary particles.

[0139] In another embodiment, the secondary particles may be core-shell particles that exhibit a concentration gradient of at least one transition metal from the center of the secondary particle to the surface of the secondary particle.

[0140] For example, the secondary particles may exhibit a concentration gradient of at least one element selected from nickel and manganese from the core to the shell. More specifically, the secondary particles may exhibit a concentration gradient in which the nickel concentration increases while the manganese concentration decreases from the core to the shell.

[0141] The region of the secondary particles present as core-shell particles where a transition metal concentration gradient exists is referred to as the shell of the secondary particles. The average thickness of the shell may be 0.1 nm to 5 μm, preferably 100 nm to 2 μm. If the shell thickness of the secondary particles is thinner than 0.1 nm, it is difficult to sufficiently improve the surface kinetics of the secondary particles. On the other hand, if the shell thickness of the secondary particles is thicker than 5 μm, it is disadvantageous to exhibit high capacity under high-voltage operating conditions, which is one of the advantages of the lithium manganese-based oxide. The shell thickness of the secondary particles may vary depending on whether the secondary particles are small or large.

[0142] The concentration gradient present within the primary particles and / or secondary particles described above can suppress and / or mitigate phase transitions that occur due to unintended migration of transition metals within the particles.

[0143] Furthermore, if the content of a transition metal that is relatively less likely to dissolve in the region corresponding to the shell is higher than that of other transition metals, the dissolution of the transition metal from the lithium manganese-based oxide can be suppressed or alleviated. By suppressing or alleviating the dissolution of the transition metal from the lithium manganese-based oxide, it is possible to prevent the transition metal dissolved on the surface from reacting with the electrolyte to form impurities.

[0144] When the surface of the core-shell particle defined herein, i.e., the surface of the shell, is covered with a barrier layer capable of suppressing or mitigating the elution of transition metals from the core-shell particle, the elution of transition metals from the lithium manganese-based oxide can be further suppressed or mitigated.

[0145] When the secondary particles are present as core-shell particles, the barrier layer can cover at least a portion of the surface of the secondary particles to suppress or mitigate the elution of the transition metal from the secondary particles to the outside, and can prevent side reactions between the surface of the secondary particles and the electrolyte by covering the surface of the secondary particles.

[0146] When the barrier layer covers a portion of the surface of the secondary particles, the barrier layer may exist in an island form. That is, even if the barrier layer covers at least a portion of the surface of the secondary particles in an island form, it is possible to suppress or mitigate the elution of the transition metal through the region covered by the barrier layer. Therefore, the presence of the barrier layer on the surface of the secondary particles should be distinguished from the case where the lithium-manganese-based oxide and a different oxide are simply dispersed on the surface of the secondary particles.

[0147] In addition, a grain boundary may be defined between adjacent primary particles within the secondary particle, and the barrier layer may exist along the grain boundary, diffusing from the surface of the secondary particle toward the center of the secondary particle. As the barrier layer diffuses toward the center of the secondary particle, the elements primarily contained in the barrier layer may exhibit a decreasing concentration gradient from the surface of the secondary particle toward the center of the secondary particle.

[0148] The barrier layer forms a gradient from the surface portion of the secondary particle toward the center portion of the secondary particle, thereby effectively suppressing or mitigating the elution of transition metals mainly at the surface portion of the secondary particle.

[0149] A part of the elements mainly contained in the barrier layer may be doped into the primary particles and / or the secondary particles.

[0150] The average thickness of the barrier layer covering the surfaces of the secondary particles is preferably 0.1 nm to 1 μm, and may vary depending on whether the secondary particles are small or large.

[0151] If the average thickness of the barrier layer covering the secondary particles is less than 0.1 nm, it is difficult to sufficiently prevent the transition metal from leaching out from the secondary particles, whereas if the average thickness of the barrier layer covering the secondary particles is more than 1 μm, the surface kinetics of the secondary particles may be reduced or the electrical conductivity of the secondary particles may be reduced.

[0152] When the primary particles exist as core-shell particles, the barrier layer can cover at least a portion of the surface of the primary particles, thereby suppressing or reducing the elution of transition metals from the primary particles to the outside. Furthermore, by covering the surface of the primary particles, the barrier layer can prevent side reactions between the surface of the primary particles and the electrolyte. In this case, the barrier layer can cover the surface of the primary particles present on the surface portion of the secondary particles, thereby covering at least a portion of the surface of the secondary particles. When the barrier layer covers a portion of the surface of the primary particles and / or the secondary particles, the barrier layer may exist in an island form.

[0153] The average thickness of the barrier layer covering the surfaces of the primary particles is preferably 0.1 nm to 1 μm.

[0154] If the average thickness of the barrier layer covering the primary particles is less than 0.1 nm, it is difficult to sufficiently prevent the transition metal from leaching from the primary particles, whereas if the average thickness of the barrier layer covering the primary particles is more than 1 μm, the surface kinetics of the primary particles may be reduced or the electrical conductivity of the secondary particles may be reduced.

[0155] In one embodiment, a barrier layer may be present on at least a portion of the surface of at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide. Accordingly, the barrier layer may prevent or mitigate the leaching of transition metals from the first lithium manganese-based oxide and / or the second lithium manganese-based oxide. To prevent or mitigate the leaching of transition metals from the first lithium manganese-based oxide and the second lithium manganese-based oxide, the barrier layer may be present on the entire first lithium manganese-based oxide and the second lithium manganese-based oxide.

[0156] The barrier layer may include an oxide containing at least one selected from a metal element, a metalloid element, and phosphorus (P).

[0157] In one embodiment, the barrier layer may include a first oxide represented by the following Chemical Formula 2:

[0158] [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, and Nd, and 0≦c≦8, 0 <d≦8、0≦e≦8、2≦f≦13である。

[0159] When the first oxide represented by Chemical Formula 2 is a borate-based compound or an LBO (lithium borate)-based compound, non-limiting examples of the first oxide include B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, and Li2BO. 13 The first 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.

[0160] In this case, a gradient may be formed in which the concentration of at least one selected from B and M3 decreases from the barrier layer toward the core of the lithium manganese-based oxide due to diffusion and / or doping of the first oxide contained in the barrier layer.

[0161] Such a concentration gradient serves as a path for lithium ions to move within and between the primary particles, thereby improving the transport / diffusion efficiency of lithium ions via the primary particles.

[0162] In another embodiment, the barrier layer may further include a second oxide represented by the following Chemical Formula 3:

[0163] [Chemical formula 3] Li g M4 h O i Here, M4 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, and Nd, and 0≦g≦8, 0≦h≦8, 2≦i≦13, except when g and h are simultaneously 0.

[0164] Non-limiting examples of the second oxide represented by Formula 3 include Li g Zr h O i , Li g Ti h O i , Li g Ni h O i , Li g Nb h O i , Li g Co h O i , Li g Si h O i , Li g Al h O i , Co h O i , Mn h O i , Al h O i , Si h O i , Zr h O i , Ti h O i etc.

[0165] At this time, a gradient in which the concentration of M4 decreases from the barrier layer toward the core of the lithium manganese oxide may be formed due to diffusion and / or doping of the second oxide contained in the barrier layer.

[0166] In still another embodiment, the barrier layer may include a third oxide represented by the following Chemical Formula 4.

[0167] [Chemical Formula 4] Li j M5 k (P l O m ) n Here, M5 is at least one selected from Ni, Mn, Co, Al, 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, and Nd, 0 ≦ j ≦ 10, 0 ≦ k ≦ 8, 0 < l ≦ 4, 0 < m ≦ 10, 0 < n ≦ 13, and the case where j and k are simultaneously 0 is excluded.

[0168] Non-limiting examples of the third oxide represented by Chemical Formula 4 include Li j (P l O m ) n , Li j Al k (P l O m ) n , Al k (P l O m ) n , (P l O m ) n , Li j Mn k (P l O m ) n , Mn k (P l O m ) n , Li j Ni k (P l O m )n , Ni k (P l O m ) n etc.

[0169] In this case, a gradient may be formed in which the concentration of at least one element selected from M5 and P decreases from the barrier layer toward the core of the lithium manganese-based oxide due to diffusion and / or doping of the third oxide contained in the barrier layer.

[0170] It is known that the decrease in charge / discharge capacity or voltage decay during charge / discharge cycles of lithium secondary batteries using OLO is caused by a phase transition due to the movement of transition metals in lithium manganese oxide. For example, if a phase transition is induced by the unintended movement of transition metals in a layered crystalline lithium manganese oxide, a spinel or similar crystalline structure may be formed entirely and / or partially within the lithium manganese oxide.

[0171] However, unlike the spinel phase formed by a phase transition due to the migration of a transition metal in the lithium manganese-based oxide, when a spinel phase is formed on the surface of the primary particles and / or the secondary particles while forming a barrier layer on the surface of the lithium manganese-based oxide, such a spinel phase not only contributes to surface stabilization of the lithium manganese-based oxide but also serves as a two-dimensional and / or three-dimensional path for lithium ions to diffuse within the lithium manganese-based oxide.

[0172] Thus, by forming the barrier layer that exists to suppress the elution of transition metals from the primary particles and / or the secondary particles, a spinel phase compound is present on the surface of the lithium manganese-based oxide, and thus the lithium manganese-based oxide can exhibit an appropriate level of electrical conductivity even when the surfaces of the primary particles and / or the secondary particles are covered with the barrier layer.

[0173] Furthermore, if necessary, the barrier layer may contain at least two or more oxides selected from the first oxide to the third oxide in order to effectively suppress or mitigate the elution of the transition metal from the lithium-manganese-based oxide and at the same time improve the surface kinetics of the lithium-manganese-based oxide.

[0174] The content of the main constituent elements of the barrier layer, calculated based on all metal elements excluding lithium present in the lithium manganese oxide, is preferably greater than 0.1 mol% and less than 5 mol%. Here, when the first oxide is present in the barrier layer, the main constituent elements of the barrier layer are boron (B) and M3; when the second oxide is present in the barrier layer, the main constituent element of the barrier layer is M4; and when the third oxide is present in the barrier layer, the main constituent element of the barrier layer is M5. Furthermore, when any combination of the first oxide to the third oxide is present in the barrier layer, the main constituent elements of the barrier layer are selected from boron (B), M3, M4, and M5.

[0175] The content of the main constituent elements of the barrier layer being less than 0.1 mol% means that the barrier layer for suppressing or mitigating the elution of transition metals is insufficiently formed on the surface of the lithium manganese-based oxide, which makes it difficult to effectively prevent the accelerated deterioration of the lifespan of the lithium secondary battery caused by the elution of transition metals from the lithium manganese-based oxide and the deposition of impurities on the positive and / or negative electrodes.

[0176] On the other hand, if the content of the main constituent element of the barrier layer is 5 mol% or more, the surface kinetics of the lithium manganese-based oxide may be decreased, and as a result, the electrochemical properties may be lower than when the main constituent element of the barrier layer is present in an appropriate content.

[0177] In addition, in order to effectively suppress or mitigate the elution of transition metals from the surface of the lithium manganese-based oxide without decreasing the surface kinetics of the lithium manganese-based oxide, the content of the main constituent elements of the barrier layer, calculated based on all metal elements excluding lithium present in the lithium manganese-based oxide, is more preferably 1±0.1 mol% or more and 3±0.1 mol% or less.

[0178] 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 layer of the above-described positive electrode active material formed on the positive electrode current collector, wherein the positive electrode active material layer may include the lithium manganese-based oxide according to the various embodiments of the present invention as the positive electrode active material.

[0179] Therefore, a detailed description of the lithium-manganese-based oxide will be omitted, and only the remaining components not described above will be described below. For convenience, the lithium-manganese-based oxide will be referred to as the positive electrode active material below.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured 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, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0190] 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.

[0191] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0192] 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.

[0193] 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.

[0194] 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. βExamples 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] 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 of the electrolyte 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.

[0201] 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.

[0202] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0203] 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 high dielectric constants, 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 chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0204] 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.

[0205] 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.

[0206] 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).

[0207] 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.

[0208] 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).

[0209] 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 partially contained in the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or partially contained in the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0210] 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 reduction, improving battery discharge capacity, etc. 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.

[0211] 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).

[0212] 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.

[0213] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0214] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0215] 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.

[0216] Production Example 1: Production of positive electrode active material Production Example 1-1. Production of First Lithium Manganese Oxide (A-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 while stirring. The temperature inside the reactor was kept 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, and the Ni 0.4 Mn 0.6 A hydroxide precursor with an (OH)2 composition (average particle size 3.0 μm, particle size can be adjusted by a known method) was obtained.

[0217] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0218] (c) Second heat treatment The oxide precursor obtained in the step (b) and LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, were mixed to prepare a mixture. Next, the temperature of the firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was maintained at 900°C. The mixture was heat-treated for 8 hours, and then cooled in the furnace to obtain a first lithium manganese-based oxide (A-1).

[0219] Preparation Example 1-2. Preparation of first lithium manganese oxide (A-2) (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 while stirring. The temperature inside the reactor was kept 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, and the Ni 0.4 Mn 0.6 A hydroxide precursor with an (OH)2 composition (average particle size 3.0 μm, particle size can be adjusted by a known method) was obtained.

[0220] (b) Precursor coating An aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to the reactor in which the precursor obtained in step (a) was stirred. NiSO4·6H2O was weighed out to a concentration of 5 mol% and then added. After the reaction was complete, the mixture was washed and dehydrated, and then dried at 150°C for 14 hours to obtain a coated precursor.

[0221] (c) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (b) was subjected to a heat treatment for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0222] (d) Second heat treatment The oxide precursor obtained in the step (c) and LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, were mixed to prepare a mixture. Next, the temperature of the firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was maintained at 900°C. The mixture was heat-treated for 8 hours, and then cooled in the furnace to obtain a first lithium manganese-based oxide (A-2). As a result of TEM / EDS analysis of the first lithium manganese-based oxide (A-2), it was confirmed that as the precursor coating using Ni was performed in step (b), a gradient was formed in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0223] Preparation Example 1-3. Preparation of first lithium manganese oxide (A-3) (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 while stirring. The temperature inside the reactor was kept 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, and the Ni 0.4 Mn 0.6 A hydroxide precursor with an (OH)2 composition (average particle size 3.0 μm, particle size can be adjusted by a known method) was obtained.

[0224] (b) Precursor coating An aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to the reactor in which the precursor obtained in step (a) was stirred. NiSO4·6H2O was weighed out to a concentration of 5 mol% and then added. After the reaction was complete, the mixture was washed and dehydrated, and then dried at 150°C for 14 hours to obtain a coated precursor.

[0225] (c) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (b) was subjected to a heat treatment for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0226] (d) Second heat treatment The oxide precursor obtained in the step (c) and LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, were mixed to prepare a mixture. Next, the temperature of a calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated at 900°C for 8 hours, followed by furnace cooling to obtain a lithium-excess lithium-manganese oxide. TEM / EDS analysis of the lithium manganese-based oxide confirmed that as the precursor coating using Ni was performed in step (b), a gradient was formed in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0227] (e) Third heat treatment (barrier layer formation) The lithium manganese-based oxide obtained in step (d) was mixed with H3BO3 weighed so that the boron content of the lithium manganese-based oxide was 2.0 mol% based on metal elements excluding lithium. The mixture was then heated in a firing furnace in an O2 atmosphere at a rate of 4.4°C per minute up to 400°C for 8 hours, and then classified and crushed to obtain a first lithium manganese-based oxide (A-3) having a barrier layer containing a B-containing compound formed on the surface.

[0228] Preparation Example 1-4. Preparation of second lithium manganese oxide (B-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 while stirring. The temperature inside the reactor was kept 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, and the Ni 0.4 Mn 0.6 A hydroxide precursor with an (OH)2 composition (average particle size 12.0 μm, particle size can be adjusted by a known method) was obtained.

[0229] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0230] (c) Second heat treatment The oxide precursor obtained in the step (b) and LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, were mixed to prepare a mixture. Next, the temperature of the firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was maintained at 900°C. The mixture was heat-treated for 8 hours, and then cooled in the furnace to obtain a second lithium manganese-based oxide (B-1).

[0231] Preparation Example 1-5. Preparation of second lithium manganese oxide (B-2) (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 while stirring. The temperature inside the reactor was kept 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, and the Ni 0.4 Mn 0.6 A hydroxide precursor with an (OH)2 composition (average particle size 12.0 μm, particle size can be adjusted by a known method) was obtained.

[0232] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0233] (c) Second heat treatment The oxide precursor obtained in the step (b) and LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, were mixed to prepare a mixture. Next, the temperature of a firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was kept at 900°C and heat-treated for 8 hours. After that, the furnace was cooled to obtain a lithium manganese oxide.

[0234] (d) Third heat treatment (barrier layer formation) The lithium manganese-based oxide obtained in step (c) was mixed with H3BO3 weighed so that the boron content of the lithium manganese-based oxide was 2.0 mol% based on metal elements excluding lithium. The mixture was then heated in a firing furnace in an O2 atmosphere at a rate of 4.4°C per minute up to 400°C for 8 hours, and then classified and crushed to obtain a second lithium manganese-based oxide (B-2) having a barrier layer containing a B-containing compound formed on the surface.

[0235] Production Example 2: Production of positive electrode active material The first lithium manganese-based oxide and the second lithium manganese-based oxide prepared in Preparation Example 1 were mixed in the weight ratio shown in Table 1 below to prepare a positive electrode active material.

[0236] [Table 1]

[0237] 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 in Preparation Example 2, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0238] A half cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (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.

[0239] Manufacturing Example 4: Manufacturing of lithium secondary batteries (full cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 2, 4.5 wt% of carbon black, and 5.5 wt% of a PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0240] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene film (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.

[0241] Experimental Example 1: XPS analysis of lithium manganese oxide The lithium manganese-based oxides prepared in Preparation Examples 1-1 to 1-5 were subjected to XPS analysis to measure the contents of the target elements contained in the lithium manganese-based oxides.

[0242] Specifically, the change in the content of the target element from the surface of the lithium manganese-based oxide (secondary particles) to the lithium manganese-based oxide (secondary particles) was measured by increasing the etching time for the surface of the lithium manganese-based oxide using an XPS depth profile analysis method (ion energy 2000 eV, spot size 200 μm).

[0243] The results of the XPS analysis are shown in Tables 2 and 3 below.

[0244] [Table 2] *The target element content (at%) is calculated based on all elements except lithium in the lithium manganese oxide.

[0245] Referring to the results in Table 2, in the case of A-2 and A-3, it can be seen that, as the precursor coating using Ni is performed during the preparation of the lithium manganese-based oxide, a gradient is formed in which the Ni concentration increases and the Mn concentration decreases from the center to the surface.

[0246] It can also be seen that the nickel content relative to the total transition metals present in the surface regions of A-2 and A-3 is greater than the nickel content relative to the total transition metals present in the surface regions of B-1 and B-2.

[0247] [Table 3] *The target element content (at%) is calculated based on all elements except lithium in the lithium manganese oxide.

[0248] Referring to the results in Table 3, it can be seen that in the cases of A-3 and B-2, the content of the target element present in the surface region is 20 at% or more as the third heat treatment (barrier layer formation) is carried out during the preparation of the lithium manganese-based oxide. The fact that the content of the target element derived from the raw material used in the third heat treatment in the surface region of the lithium manganese-based oxide (secondary particles) is 20 at% or more is presumably due to the formation of a barrier layer on the surface region of the lithium manganese-based oxide (secondary particles).

[0249] Experimental Example 2: Measurement of compressed density of positive electrode active material 3 g of each of the positive electrode active materials prepared in Preparation Example 2 was pressed at 4.5 tons for 5 seconds using a pelletizer, and then the compressed density was measured.

[0250] The measurement results are shown in Table 4 below.

[0251] [Table 4]

[0252] Referring to the results in Table 4, it can be seen that the 4.5-ton compaction densities of Examples 1 to 6, which are bimodal cathode active materials in which the first lithium manganese-based oxide and the second lithium manganese-based oxide are mixed, are greater than those of Comparative Examples 1 and 2, which are unimodal cathode active materials.

[0253] Experimental Example 3: Evaluation of the electrochemical properties of a lithium secondary battery (half cell) The lithium secondary battery (half cell) prepared in Preparation Example 3 was 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 a discharge rate of 0.1 C to 5.0 C to measure the initial discharge capacity, capacity per volume, and rate capability (C-rate).

[0254] The capacity per volume was calculated by multiplying the initial discharge capacity by the compaction density (4.5 ton compaction density in Table 4).

[0255] The measurement results are shown in Table 5 below.

[0256] [Table 5]

[0257] Referring to the half-cell evaluation results in Table 5, it can be seen that the initial discharge capacity and rate characteristics of Examples 1 to 6, which are bimodal cathode active materials in which the first lithium manganese-based oxide and the second lithium manganese-based oxide are mixed, are improved compared to Comparative Examples 1 and 2, which are unimodal cathode active materials.

[0258] In particular, it can be seen that the capacities per unit volume of Examples 1 to 6, which are bimodal cathode active materials in which the first lithium manganese-based oxide and the second lithium manganese-based oxide are mixed, are significantly higher than those of Comparative Examples 1 and 2, which are unimodal cathode active materials. Furthermore, when comparing the results of Examples 1 to 6, it can be seen that, despite the similar compressed densities of the cathode active materials, Examples 2 to 6, especially Examples 3 to 6, have higher capacities per unit volume than Example 1.

[0259] Experimental Example 4: Evaluation of the electrochemical characteristics of a lithium secondary battery (full cell) The lithium secondary batteries (full cells) prepared in Preparation Example 4 using the positive electrode active materials of Examples 1 and 6 were subjected to a six-cycle formation process at 25°C, a voltage range of 2.0V to 4.6V, and a rate of 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100). They were then subjected to 500 charge-discharge cycles at 25°C, a voltage range of 2.0V to 4.6V, and a rate of 1C / 1C. The initial (first cycle) discharge capacity and the ratios of the discharge capacities at the 100th, 300th, and 500th cycles to the initial discharge capacity (cycle capacity retention) were measured.

[0260] The measurement results are shown in Table 6 below.

[0261] [Table 6]

[0262] Referring to the full cell evaluation results in Table 6, it can be seen that the cycle capacity retention rate of Example 1 is lower than that of Example 6. This result is presumably due to the fact that the transition metal elution from the lithium manganese-based oxide causes an abnormal resistance phenomenon in the negative electrode, which accelerates the deterioration of the lifespan of the lithium secondary battery.

[0263] This confirms that the positive electrode active material according to Example 6 is suitable for lithium secondary batteries that require a longer life.

[0264] Experimental Example 5: Experiment on transition metal elution The lithium secondary batteries (full cells) prepared in Preparation Example 4 using the positive electrode active materials of Examples 1 and 6 were subjected to six cycles of formation 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.

[0265] 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 and Mn contained in the negative electrode active material.

[0266] In addition, lithium secondary batteries (full cells) prepared in Preparation Example 4 using the positive electrode active materials of Examples 1 and 6 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. Each full cell was then subjected to two charge-discharge cycles at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C for stabilization. The full cells were then disassembled, and the negative electrodes were washed with diethyl carbonate solvent, vacuum dried at 60°C, and then collected.

[0267] 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 and Mn contained in the negative electrode active material.

[0268] The measurement results are shown in Table 7 below.

[0269] [Table 7]

[0270] Referring to the results in Table 7, as expected from Experimental Example 4, it can be seen that the lower cycle capacity retention rate of Example 1 compared to Example 6 is due to the increased content of transition metals deposited on the negative electrode active material after chemical formation and / or after 500 charge / discharge cycles.

[0271] 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 bimodal type positive electrode active material including a first lithium-manganese-based oxide and a second lithium-manganese-based oxide having different average particle sizes, the difference in average particle size between the first lithium-manganese-based oxide and the second lithium-manganese-based oxide is 3 μm or more; the first lithium-manganese-based oxide and the second lithium-manganese-based oxide are oxides in which a phase belonging to a C2 / m space group and a phase belonging to an R3-m space group are solid-solved or composite, the first lithium-manganese-based oxide and the second lithium-manganese-based oxide are each independently a lithium-manganese-based oxide containing nickel and manganese, the content (mol %) of manganese relative to the total transition metals present in the surface portion of the first lithium-manganese-based oxide is lower than the content (mol %) of manganese relative to the total transition metals present in the surface portion of the second lithium-manganese-based oxide; Cathode active material.

2. 2. The positive electrode active material according to claim 1, wherein the first lithium manganese-based oxide has an average particle size of 2 μm to 6 μm.

3. 2. The positive electrode active material according to claim 1, wherein the second lithium manganese-based oxide has an average particle size of 7 μm to 14 μm.

4. 2. The positive electrode active material of claim 1, wherein the first lithium manganese-based oxide and the second lithium manganese-based oxide are contained in a weight ratio of 10:90 to 80:20 in the positive electrode active material.

5. 2. The positive electrode active material according to claim 1, wherein a manganese content (mol %) relative to the total transition metals in the first lithium-manganese-based oxide is lower than a manganese content (mol %) relative to the total transition metals in the second lithium-manganese-based oxide.

6. 2. The positive electrode active material according to claim 1, wherein at least one of the first lithium-manganese-based oxide and the second lithium-manganese-based oxide is a core-shell particle that exhibits a concentration gradient of at least one selected from nickel and manganese from the center toward the surface.

7. 7. The positive electrode active material according to claim 6, wherein the core-shell particles exhibit a gradient in which the concentration of nickel increases and the concentration of manganese decreases from the center to the surface.

8. the first lithium manganese-based oxide is a core-shell particle exhibiting a concentration gradient of at least one selected from nickel and manganese from the center toward the surface, 2. The positive electrode active material according to claim 1, wherein the second lithium-manganese-based oxide is a particle in which the nickel and manganese concentrations are constant from the center to the surface or exhibit a concentration gradient having a smaller slope than the concentration gradient exhibited in the first lithium-manganese-based oxide.

9. 2. The positive electrode active material according to claim 1, wherein the first lithium-manganese-based oxide and the second lithium-manganese-based oxide are each independently represented by the following chemical formula 1-1: [Chemical formula 1-1] rLi ２ MnO ３－ｂ″ X′ ｂ″ ・(1-r)Li ａ′ M1 ｘ′ M2 ｙ′ O ２－ｂ′ X ｂ′ (where, M1 is Ni; M2 is at least one selected from 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, and Nd, and M2 does not overlap with M1; X and X' are halogens 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)

10. 2. The positive electrode active material according to claim 1, wherein a barrier layer is present on at least a portion of the surface of at least one of the first lithium-manganese-based oxide and the second lithium-manganese-based oxide.

11. the first lithium manganese-based oxide is a core-shell particle exhibiting a concentration gradient of at least one selected from nickel and manganese from the core to the shell, The positive electrode active material according to claim 10 , wherein a barrier layer is present on at least a portion of the surface of the shell.

12. The second lithium-manganese-based oxide is a particle in which the concentrations of nickel and manganese are constant from the center to the surface or exhibit a concentration gradient that is smaller than the concentration gradient exhibited in the first lithium-manganese-based oxide, The positive electrode active material according to claim 10 , wherein a barrier layer is present on at least a portion of the surface of the second lithium manganese-based oxide.

13. The positive electrode active material according to claim 10 , wherein the barrier layer contains an oxide containing at least one selected from a metal element, a metalloid element, and phosphorus (P).

14. 11. The positive electrode active material of claim 10, wherein the barrier layer comprises at least one selected from a first oxide represented by the following Chemical Formula 2, a second oxide represented by the following Chemical Formula 3, and a third oxide represented by the following Chemical Formula 4: [Chemical formula 2] Li ｃ B ｄ M3 ｅ O ｆ (where, 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, and Nd; 0≦c≦8, 0<d≦8, 0≦e≦8, 2≦f≦13) [Chemical formula 3] Li ｇ M4 ｈ O ｉ (where, M4 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, and Nd; 0≦g≦8, 0≦h≦8, 2≦i≦13, excluding the case where g and h are both 0) [Chemical formula 4] Li ｊ M5 ｋ (P ｌ O ｍ ) ｎ (where, M5 is at least one selected from Ni, Mn, Co, Al, 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, and Nd; 0≦j≦10, 0≦k≦8, ​​0<l≦4, 0<m≦10, 0<n≦13, except when j and k are both 0)

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