Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery having improved capacity and lifespan retention rate by controlling the voltage range during formation or operation of the lithium secondary battery. The present invention also relates to a lithium secondary battery in which deterioration of electrochemical characteristics, including rate characteristics, of the lithium secondary battery is mitigated and / or prevented by the presence of excess lithium and manganese in the lithium-manganese-based oxide used as a positive electrode active material, and in particular, deterioration of lifespan is prevented by suppressing or mitigating the elution of transition metals from the lithium-manganese-based oxide.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery having improved capacity and lifespan by controlling the voltage range during formation or operation of the lithium secondary battery. The present invention also relates to a lithium secondary battery in which deterioration of electrochemical characteristics, including rate characteristics, of the lithium secondary battery is prevented by excessive amounts of lithium and manganese in the lithium-manganese-based oxide used as a positive electrode active material, and in particular, deterioration of lifespan is prevented by suppressing or mitigating elution of transition metals from the lithium-manganese-based oxide. [Background technology]

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

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

[0004] Representative materials used as positive electrode active materials for lithium secondary batteries include lithium composite oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and oxides of Ni, Co, Mn, and Al as disclosed in Korean Patent Publication No. 10-2015-0069334 (published June 23, 2015).

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

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

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

[0008] Various candidate materials have been proposed to overcome the drawbacks of conventional positive electrode active materials. 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 transition metal content, as positive electrode active materials for lithium secondary batteries. Such overlithiated lithium manganese oxides are also called overlithiated layered oxides (OLO).

[0009] While OLO theoretically has the advantage of being able to exhibit high capacity under high-voltage operating conditions, it has the disadvantage of relatively low electrical conductivity due to the excessive Mn content in the oxide, resulting in poor rate performance of lithium secondary batteries using OLO. This poor rate performance can lead to problems such as reduced charge / discharge capacity and life efficiency (cycle capacity retention) during cycling of the lithium secondary battery.

[0010] Furthermore, since OLO has different formation and operating conditions from commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions, it is necessary to propose new OLOs and develop operating conditions that enable lithium secondary batteries using OLO to exhibit commercial-level electrochemical properties. Summary of the Invention [Problem to be solved by the invention]

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] For example, the present inventors have confirmed that lithium-manganese oxides are more likely to have transition metals eluted from the particle surface due to repeated charge and discharge than ternary lithium composite oxides, and in particular, Mn contained in an excess amount in lithium-manganese oxides is more likely to elute from the particle surface.

[0016] 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.

[0017] 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 move to the negative electrode using the electrolyte as a medium and deposit on the surface of the negative electrode.

[0018] For example, a side reaction occurs on the surface of the lithium manganese-based oxide with the electrolyte, or the lithium manganese-based oxide undergoes a structural change (such as a change in crystal structure) that causes excessive Mn contained in the lithium manganese-based oxide to be dissolved. 2+ The Mn dissolved in the electrolyte can be dissolved in the electrolyte. 2+ During formation or charging / discharging, Mn moves to the surface of the negative electrode 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.

[0019] 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.

[0020] 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.

[0021] However, there is currently no technology to solve the problems associated with the elution of transition metals from lithium-rich lithium manganese oxides.

[0022] 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 to prevent or mitigate the elution of transition metals.

[0023] In particular, the inventors have confirmed that the lithium manganese-based oxide can be formed as core-shell particles in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell, and the content of the transition metal that is relatively less likely to dissolve in the region corresponding to the shell is higher than that of other transition metals, thereby suppressing or mitigating the dissolution of the transition metal from the lithium manganese-based oxide.

[0024] 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 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.

[0025] Therefore, an object of the present invention is to provide a lithium secondary battery using a positive electrode active material that contains a lithium-excess lithium-manganese-based oxide, and that controls the bulk composition of the lithium-manganese-based oxide while forming a barrier layer on the surface of the lithium-manganese-based oxide, thereby making it possible to suppress or mitigate the elution of transition metals from the lithium-manganese-based oxide.

[0026] Another object of the present invention is to provide a lithium secondary battery using a cathode active material that can suppress or mitigate the leaching of transition metals from the lithium manganese-based oxide while improving the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium manganese-based oxide, by forming the lithium manganese-based oxide as core-shell particles in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell, and by increasing the content of the transition metal that is relatively less likely to leach out in the region corresponding to the shell compared to other transition metals.

[0027] Another object of the present invention is to provide a lithium secondary battery that uses the lithium manganese-based oxide defined herein as a positive electrode active material, thereby preventing a decrease in rate characteristics due to the excess lithium and manganese present in existing OLOs, and achieving high stability by reducing side reactions between the positive electrode active material and an electrolyte even during high-voltage operation.

[0028] In particular, the present invention aims to provide operating conditions under which a lithium secondary battery using the lithium manganese-based oxide defined herein as a positive electrode active material can exhibit commercial-level electrochemical properties. [Means for solving the problem]

[0029] According to one aspect of the present invention for solving the above-mentioned technical problems, there is provided a lithium secondary battery using a positive electrode active material including a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-solved or composite.

[0030] In order to activate the positive electrode active material containing a lithium-excess lithium manganese-based oxide, the lithium secondary battery is preferably formed for at least one cycle in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more based on the positive electrode potential.

[0031] In addition, in order to exhibit the high capacity characteristics of the lithium manganese-based oxide, it is preferable that the lithium secondary battery after chemical formation operates in an operating voltage range in which the upper limit voltage ov1 is greater than 4.3 V and less than 5.0 V, greater than 4.3 V and less than 4.8 V, or greater than 4.3 V and less than 4.6 V.

[0032] In order to increase the charge / discharge efficiency of the lithium secondary battery and improve the characteristics related to the capacity and life of the lithium secondary battery, it is preferable that the lithium secondary battery after formation operates in an operating voltage range in which the lower limit voltage ov2 is 2.0 V or more, preferably 2.0 V or more and less than 3.0 V.

[0033] Furthermore, it is preferable that the operating conditions be set so that the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is greater than 1.6V and less than 2.6V when the lithium secondary battery is operating.

[0034] When the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is 1.6 V or less, it means that the upper limit voltage ov1 of the operating voltage range is too low or the lower limit voltage ov2 is too high. If the upper limit voltage ov1 of the operating voltage range is too low or the lower limit voltage ov2 is too high, the discharge capacity of the lithium secondary battery may be excessively reduced.

[0035] Meanwhile, when the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is 2.6 V or more, it means that the upper limit voltage ov1 of the operating voltage range is too high or the lower limit voltage ov2 is too low. In this case, as the difference between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range increases, the charge / discharge efficiency of the lithium secondary battery may decrease.

[0036] If the upper limit voltage ov1 of the operating voltage range is too high, the capacity retention rate and the average discharge voltage retention rate of the lithium secondary battery may be rapidly reduced. If the lower limit voltage ov2 of the operating voltage range is too low, the average discharge voltage and the average discharge voltage retention rate of the lithium secondary battery may be reduced. The lower limit voltage ov2 of the operating voltage range may also affect the stability of the lithium secondary battery, which can be confirmed by gas generation-related indicators such as the volume change rate.

[0037] The positive electrode active material used in the present application contains a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are dissolved or combined.

[0038] Generally, commercially available ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition contain a single phase of the R-3m space group, whereas the lithium-rich lithium manganese oxide defined in this application is characterized by a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group.

[0039] Here, the lithium manganese-based oxide is provided as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell.

[0040] In this case, the lithium manganese-based oxide is formed as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell, and the content of the transition metal that is relatively less likely to be leached in the region corresponding to the shell is higher than that of other transition metals, thereby reducing the possibility of the transition metal being leached from the lithium manganese-based oxide.

[0041] In one embodiment, the lithium manganese-based oxide of the positive electrode active material may be present in at least one form selected from a single primary particle and a secondary particle formed by agglomeration of a plurality of primary particles.

[0042] For example, the positive electrode active material may include the lithium manganese-based oxide in the form of secondary particles formed by aggregation of a plurality of primary particles.

[0043] Here, the secondary particles may be core-shell particles in which the concentration of at least one transition metal exhibits a gradient from the center of the secondary particle to the surface of the secondary particle.

[0044] In this case, the barrier layer is present so as to cover at least a part of the surface of the secondary particles, thereby making it possible to suppress or mitigate the elution of the transition metal from the secondary particles.

[0045] In addition, a grain boundary is defined between adjacent primary particles within the secondary particle, and the barrier layer may be present along the grain boundary in a diffused state from the surface of the secondary particle toward the center of the secondary particle.

[0046] In another 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.

[0047] In this case, the barrier layer is present so as to cover at least a part of the surface of the primary particles, thereby making it possible to suppress or reduce the elution of the transition metal from the primary particles.

[0048] In yet another embodiment, the primary particle may comprise at least one crystallite, and the crystallite may exhibit a concentration gradient of at least one transition metal from a center of the crystallite to a surface of the crystallite.

[0049] In this case, the barrier layer may cover each crystallite present in the primary particle, and by covering the surface of the primary particle, the purpose of suppressing or reducing the leaching of the transition metal may be sufficiently achieved.

[0050] In one embodiment, the lithium manganese-based oxide may be represented by the following Chemical Formula 1: [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)

[0051] In another embodiment, the lithium manganese-based oxide may be represented by the following Formula 1-1: [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) [Effects 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 formed as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell, and the content of the transition metal that is relatively less likely to be eluted in the region corresponding to the shell is made higher than that of other transition metals, thereby making it possible to suppress or mitigate the elution of the transition metal from the lithium manganese-based oxide.

[0054] 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 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.

[0055] By suppressing or mitigating the elution of the transition metal from the lithium-manganese-based oxide, it is possible to prevent the transition metal eluted on the surface of the lithium-manganese-based oxide from reacting with the electrolyte to form impurities.

[0056] The transition metals dissolved from the lithium manganese-based oxide and / or impurities formed by the reaction of the dissolved transition metals with the electrolyte can migrate to the negative electrode through the electrolyte as a medium, and the impurities can deposit on the surface of the negative electrode, causing a rapid increase in negative electrode resistance. Therefore, as described in the present invention, it is necessary to limit the unintended migration of transition metals within a lithium secondary battery.

[0057] That is, according to the present invention, by preventing the elution of transition metals from the lithium-manganese-based oxide, it is possible to prevent the accelerated deterioration of the life of a lithium secondary battery caused by the elution of transition metals from the lithium-manganese-based oxide, which leads to the deposition of impurities on the positive electrode and / or negative electrode.

[0058] Furthermore, according to the present invention, by forming the lithium manganese-based oxide into core-shell particles in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient, it is possible to improve the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium manganese-based oxide.

[0059] When a cathode containing the cathode active material defined herein is used, it is possible to prevent a decrease in rate characteristics due to the excessive amounts of lithium and manganese present in existing OLOs, and to achieve high stability by reducing side reactions between the cathode active material and the electrolyte, especially during high-voltage operation.

[0060] Furthermore, according to the operating conditions of the lithium secondary battery disclosed in the present invention, a lithium secondary battery using a lithium-excess lithium manganese-based oxide as a positive electrode active material, which is known to be disadvantageous in terms of electrochemical properties and / or stability compared to commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, can exhibit electrochemical properties at a commercial level.

[0061] In particular, when a lithium secondary battery using the lithium manganese-based oxide defined in the present application is charged and discharged under predetermined operating conditions, it is possible to stably exhibit characteristics related to capacity and life.

[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, the positive electrode active material used in the lithium secondary battery and the lithium secondary battery according to some embodiments of the present invention will be described in more detail.

[0065] positive electrode active material A lithium secondary battery according to one embodiment of the present invention uses 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 R-3m space group are solid-solved or composite.

[0066] The lithium manganese-based oxide contains at least lithium, nickel, and manganese. Since 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), the lithium manganese-based oxide is also called an overlithiated layered oxide (OLO).

[0067] 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.

[0068] 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-based oxide has a relatively low ratio of nickel to all metal elements (e.g., less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0069] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined herein is larger than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese-based oxide defined herein is larger than 1, preferably 1.1 to 1.6.

[0070] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0071] The lithium manganese-based oxide contained in the positive electrode active material defined herein may exist as particles including at least one primary particle.

[0072] When the lithium manganese-based oxide exists as a single primary particle, the lithium manganese-based oxide can be referred to as a single particle, whereas when the lithium manganese-based oxide exists as an aggregate of a plurality of primary particles, the lithium manganese-based oxide can be referred to as a secondary particle.

[0073] The positive electrode active material may include at least one selected from a lithium manganese-based oxide that exists as a single particle and a lithium manganese-based oxide that exists as a secondary particle formed by aggregation of a plurality of primary particles.

[0074] The primary particles constituting the lithium manganese-based oxide may have a rod shape, an oval shape, and / or an irregular shape, and unless otherwise intended in the manufacturing process, primary particles of various shapes may exist within the same positive electrode active material.

[0075] The primary particles constituting the lithium manganese oxide defined herein may have an average particle size of 0.1 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).

[0076] When the lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, the secondary particles may have an average particle size of 0.5 μm to 15 μm, and the average particle size of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles.

[0077] 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 multiple primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0078] 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."

[0079] 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."

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The lithium manganese-based oxide defined herein may 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. [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。

[0085] 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.

[0086] 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.

[0087] In addition, a gradient may be formed in which the ratio of at least one selected from x and y in Chemical Formula 1 changes from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0088] 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 R-3m space group.

[0089] In another embodiment, the lithium manganese-based oxide may be represented by the following Formula 1-1: The composition represented by the following 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. [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, and 0 <r≦0.7、0<a′≦1、0≦b′≦0.1、0≦b″≦0.1、0<x′≦1、0≦y′<1および0<x′+y′≦1である。

[0090] 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.

[0091] In Chemical Formula 1 and Chemical Formula 1-1, when M1 is Ni, M2 may contain Mn, and when M1 is Mn, M2 may contain Ni. Also, when M1 is Ni and Mn, M2 may be absent, or, if present, may be an element other than Ni and Mn.

[0092] That is, when M1 is Ni, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd (preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably at least one selected from P, B, and Si), and Mn.

[0093] When M1 is Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd (preferably, at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably, at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably, at least one selected from P, B, and Si), and Ni.

[0094] When M1 is Ni and Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd, preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably at least one selected from P, B, and Si.

[0095] The lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may optionally contain cobalt. When the lithium manganese-based oxide contains cobalt, the mole fraction of cobalt relative to the total moles of metal elements in the lithium manganese-based oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese-based oxide represented by Chemical Formula 1 may have a cobalt-free composition.

[0096] The Li / Metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may be greater than 1, preferably 1.1 to 1.6. When the Li / Metal molar ratio measured from the lithium manganese-based oxide is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide. In addition, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.2 to 1.6 so that the lithium manganese-based oxide can appropriately form a solid solution or a composite of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group and can exhibit high capacity under high-voltage operating conditions.

[0097] In addition, in order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are dissolved or combined, 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.

[0098] To enable the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under high-voltage operating conditions, the manganese content of the total metal elements excluding lithium present in the lithium manganese-based oxide is preferably 50 mol% or more but less than 80 mol%, more preferably 55 mol% to 75 mol%. If the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the migration of transition metals (especially manganese) within the lithium manganese-based oxide during the formation and / or operation of the lithium secondary battery. This phase transition forms a spinel phase, and the spinel phase, acting as an impurity in the lithium manganese-based oxide, may cause a decrease in charge / discharge capacity or voltage decay during cycling of the lithium secondary battery.

[0099] In order to properly form a solid solution or a composite solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m 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%.

[0100] 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 R-3m 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.

[0101] In addition, as will be described later, in order to ensure that nickel is present sufficiently on the surface of the lithium manganese-based oxide provided as core-shell particles having a transition metal concentration gradient formed within the particles, the content of nickel in the lithium manganese-based oxide is preferably 25 mol% to 45 mol%.

[0102] 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 R-3m space group.

[0103] 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 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 R-3m phase form a solid solution or are combined with each other. For example, the lithium manganese-based oxide may exist in a state in which an oxide of the C2 / m phase and an oxide of the R-3m phase form a solid solution.

[0104] In this case, a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are simply physically and / or chemically bonded or attached does not fall under the category of a solid solution as defined in this application.

[0105] 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 R-3m space group and whose surface is coated with a metal oxide having a phase belonging to the R-3m space group, does not fall under the category of a solid solution as defined in the present application.

[0106] In the lithium manganese-based oxide represented by the chemical formula 1-1, when r exceeds 0.7, the lithium manganese-based oxide contains Li2MnO, which is an oxide of the C2 / m phase. 3-b″ X′ b″ The proportion of R-3m phase oxide is preferably present in a certain proportion or more, which ultimately results in an excessively high manganese content in the positive electrode active material and a decrease in discharge capacity. That is, in the lithium manganese-based oxide, in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance, and improve the surface kinetics, it is preferable that the R-3m phase oxide is present in a certain proportion or more.

[0107] The lithium manganese-based oxide defined herein exists as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell. In this case, the content of the transition metal that 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.

[0108] Furthermore, by forming the lithium manganese-based oxide into core-shell particles in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a 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.

[0109] When the concentration of transition metals in the shell (or surface portion) and the core (or center portion) of a given particle is different, the particle can 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 may be different between the core and the shell. Thus, the ratio of phases belonging to the C2 / m space group and the R-3m space group in the core may be different, and the ratio of phases belonging to the C2 / m space group and the R-3m space group in the shell may be different.

[0110] The shell can occupy at least a portion of the surface of the core, i.e., the shell can be partially present on the surface of the core or can occupy the entire surface of the core.

[0111] In the present application, the mole number of all metal elements in the lithium manganese-based oxide is M 1 is called, and 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 / M 1 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.

[0112] 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 of lower electrical conductivity as the Mn content increases.

[0113] Various reactions occur on the surface of the various types of cathode active materials mentioned 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, which can be referred to as a decrease in surface kinetics or intra-surface reaction kinetics.

[0114] As described above, the lithium manganese-based oxide defined herein can improve the surface kinetics of the lithium manganese-based oxide by forming a transition metal concentration gradient between the core and shell. This effect can be achieved through the transition metal concentration difference between the core and shell of primary particles, secondary particles, crystallites, and / or single particles, as described below, or the transition metal concentration gradient formed between the core and shell.

[0115] In one embodiment, the lithium manganese-based oxide in the positive electrode active material may exist in at least one form selected from a single primary particle and a secondary particle formed by aggregation of a plurality of primary particles, and the primary particle may be a core-shell particle having a gradient in concentration of at least one transition metal from the center of the primary particle to the surface of the primary particle. The lithium manganese-based oxide existing in the form of a secondary particle may be an aggregate of primary particles existing as a core-shell particle.

[0116] The surface kinetics of the primary particles and / or the secondary particles can be improved if 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.

[0117] 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.

[0118] Furthermore, when the concentration of the transition metal exhibits a gradient from the core to the shell of the primary particle, abrupt changes in the concentration of the metal element between the core and the shell of the primary particle can be reduced, and by preventing abrupt changes in the concentration of the metal element within the primary particle, instability of the crystal structure of the primary particle can be prevented.

[0119] The region of the primary particles present as the 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 may be 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 may be disadvantageous to exhibit high capacity under high-voltage operating conditions, which is one of the advantages of the lithium-manganese oxide.

[0120] In another embodiment, the primary particle may include at least one crystallite, and the crystallite may have the aforementioned core-shell morphology, and may exhibit a concentration gradient of at least one transition metal from the center of the crystallite to the surface of the crystallite.

[0121] For example, the crystallite may exhibit a concentration gradient of at least one element selected from nickel and manganese from the center to the surface. More specifically, the crystallite may exhibit a concentration gradient in which the nickel concentration increases while the manganese concentration decreases from the center to the surface.

[0122] When the primary particles include a plurality of crystallites, the plurality of crystallites constituting the primary particles may have the above-described core-shell morphology. The core-shell morphology may contribute to stabilizing the crystalline structure of the primary particles and improving the low electrical conductivity of the lithium manganese-based oxide.

[0123] The region of the crystallites present in the core-shell structure, where the transition metal concentration gradient exists, may be located adjacent to the surface of the crystallite, and the average thickness of the region of the crystallites where the transition metal concentration gradient exists may be 0.1 nm to 500 nm. If the thickness of the region of the crystallites where the transition metal concentration gradient exists is less than 0.1 nm, it may be difficult to sufficiently improve the surface kinetics of the crystallites and the primary particles formed by the crystallites. On the other hand, if the thickness of the region of the crystallites where the transition metal concentration gradient exists is greater than 500 nm, it may be disadvantageous to achieve high capacity under high-voltage operating conditions, which is one of the advantages of the lithium-manganese oxide.

[0124] In yet 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.

[0125] 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.

[0126] When the region of the secondary particles present as the 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 may be 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 may be disadvantageous to exhibit high capacity under high-voltage operating conditions, which is one of the advantages of the lithium-manganese oxide.

[0127] The concentration gradients present within the primary particles, secondary particles, and / or crystallites described above can suppress and / or mitigate phase transitions that occur due to unintended movement of transition metals within the particles.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] A part of the elements mainly contained in the barrier layer may be doped into the primary particles and / or the secondary particles.

[0135] The average thickness of the barrier layer covering the surfaces of the secondary particles is preferably 0.1 nm to 1 μm.

[0136] If the average thickness of the barrier layer covering the secondary particles is less than 0.1 nm, it may be 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 greater than 1 μm, the surface kinetics of the secondary particles may decrease or the electrical conductivity of the secondary particles may decrease.

[0137] 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.

[0138] The average thickness of the barrier layer covering the surfaces of the primary particles is preferably 0.1 nm to 1 μm.

[0139] If the average thickness of the barrier layer covering the primary particles is less than 0.1 nm, it may be 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 greater than 1 μm, the surface kinetics of the primary particles may decrease or the electrical conductivity of the secondary particles may decrease.

[0140] Furthermore, when a concentration gradient of the transition metal exists within the crystallites constituting the primary particles, the region where the concentration gradient of the transition metal exists may exist in a region adjacent to the surface of the crystallite. In this case, the barrier layer can cover at least a part of the surface of the primary particles, and the average thickness of the barrier layer is preferably 0.1 nm to 1 μm.

[0141] In one embodiment, the barrier layer may include a first oxide represented by the following Chemical Formula 2: [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。

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In another embodiment, the barrier layer may further include a second oxide represented by the following Chemical Formula 3: [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.

[0146] 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.

[0147] In this case, a gradient in which the concentration of M4 decreases from the barrier layer toward the core of the lithium manganese-based oxide may be formed due to diffusion and / or doping of the second oxide contained in the barrier layer.

[0148] In yet another embodiment, the barrier layer may include a third oxide represented by the following Chemical Formula 4: [Chemical formula 4] Li j M5k (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.

[0149] 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 and the like.

[0150] At this time, a gradient in which the concentration of at least one selected from M5 and P decreases from the barrier layer toward the core of the lithium manganese-based oxide may be formed due to diffusion and / or doping of the third oxide contained in the barrier layer.

[0151] It is known that the decrease in charge / discharge capacity or voltage decay during cycling 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 occur entirely and / or partially within the lithium manganese oxide.

[0152] 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 inducing crystal growth or particle growth of the primary particles constituting 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. The spinel phase present on the surface of the primary particles and / or the secondary particles can be represented by Chemical Formula 4.

[0153] Thus, by making the spinel phase compound present in the barrier layer, which exists to suppress the elution of transition metals from the primary particles and / or the secondary particles, 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.

[0154] 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.

[0155] Generally, ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition containing a relatively large amount of Ni undergo a rapid thermal weight loss starting at about 700°C, whereas lithium-excess lithium-manganese oxides do not experience a thermal weight loss until about 900°C. Therefore, when a lithium-manganese oxide that has not been surface-modified is analyzed by thermogravimetry, no thermal weight loss occurs in the range of 400°C to 700°C.

[0156] As defined herein, the lithium manganese-based oxide in which at least a portion of the surface of the primary particles and / or the secondary particles is covered with the barrier layer begins to experience thermal weight loss at approximately 500°C, and thermal weight loss can be observed for the lithium manganese-based oxide at 700°C.

[0157] Here, the thermal weight loss determined by thermogravimetric analysis of the lithium manganese-based oxide may be caused by components constituting the barrier layer, and thus, as the content of the barrier layer in the lithium manganese-based oxide increases, the thermal weight loss determined by thermogravimetric analysis of the lithium manganese-based oxide may increase.

[0158] When analyzing the thermal weight loss caused by heat-treating the lithium manganese-based oxide under an inert gas atmosphere, the difference yx between the weight loss rate x of the lithium manganese-based oxide at 400°C and the weight loss rate y of the lithium manganese-based oxide at 700°C is preferably 0.03 wt% or more, and more preferably 0.10 wt% or more from the viewpoint of effectively suppressing or mitigating the elution of transition metals from the lithium manganese-based oxide.

[0159] The difference yx in the weight loss rate being less than 0.03 wt % means that a barrier layer for suppressing or mitigating the elution of transition metals is not sufficiently formed on the surface of the lithium manganese-based oxide.

[0160] Furthermore, 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 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.

[0161] 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.

[0162] 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.

[0163] In addition, in order to effectively suppress or mitigate the elution of transition metals from the surface of the lithium-manganese-based oxide within a range that does not reduce the surface kinetics of the lithium-manganese-based oxide, it is more preferable that 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 1±0.1 mol% or more and 3±0.1 mol% or less (specifically, 0.9 mol% to 3.1 mol%, more specifically, 0.98 mol% to 3.04 mol%).

[0164] Lithium secondary battery According to one aspect of the present invention, there is provided an electrochemical device using a cathode active material comprising a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-solved or composite. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0165] The lithium secondary battery may specifically include a positive electrode, a negative electrode facing the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and 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.

[0166] The positive electrode used in the lithium secondary battery includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the lithium manganese-based oxide according to various embodiments of the present invention as a positive electrode active material.

[0167] 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.

[0168] 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 μm 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be fabricated by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0174] 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.

[0175] 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.

[0176] The negative electrode used in the lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] The sulfide-based solid electrolyte material may be 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. 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, and Li2S-P2S5-Z. m S n (where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MOq (where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0192] 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.

[0193] 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).

[0194] 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.

[0195] 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.

[0196] 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).

[0197] 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.

[0198] According to yet another aspect of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0199] 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.

[0200] In addition, the lithium secondary battery defined above is preferably formed for at least one cycle in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more based on the positive electrode potential in order to activate the positive electrode active material containing a lithium-excess lithium-manganese-based oxide.

[0201] Here, the term "formation" is also called activation, and refers to a process of activating a lithium secondary battery in an initially discharged state by repeatedly charging and discharging the battery.

[0202] If the upper limit voltage fv1 of the formation voltage range for the lithium secondary battery is less than 4.4 V, the positive electrode active material, particularly the phase of the positive electrode active material belonging to the C2 / m space group, may not be sufficiently activated, and the lithium secondary battery may not exhibit sufficient capacity characteristics. Therefore, by performing at least one formation cycle of the lithium secondary battery in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more relative to the positive electrode potential, activation of the positive electrode active material containing a lithium-excess lithium-manganese-based oxide can be induced.

[0203] In addition, by setting the upper limit voltage fv1 of the formation voltage range of the first cycle to 4.4 V or more during formation of the lithium secondary battery, the problem of insufficient activation of the positive electrode active material can be prevented in advance.

[0204] If the upper limit voltage fv1 of the formation voltage range is too high, a side reaction between the lithium manganese oxide contained in the positive electrode active material and the electrolyte may be accelerated, which may result in a rapid decrease in the capacity retention rate and average discharge voltage retention rate of the lithium secondary battery. Therefore, when the upper limit voltage fv1 of the formation voltage range is set to less than 5.0 V, preferably 4.75 V or less, and more preferably 4.6 V or less, the capacity and life-span related characteristics of the lithium secondary battery can be improved.

[0205] Furthermore, the lower limit voltage fv2 of the formation voltage range is preferably 2.0 V or more and less than 3.0 V. If the lower limit voltage fv2 of the formation voltage range is less than 2.0 V, unwanted structural changes in the positive electrode active material may occur, or a side reaction may occur between the lithium-manganese oxide contained in the positive electrode active material and the electrolyte. On the other hand, if the lower limit voltage fv2 of the formation voltage range is 3.0 V or more, the reduction reaction of the positive electrode active material may become insufficient, resulting in a reduced discharge capacity of the lithium secondary battery.

[0206] Optionally, when the lower limit voltage fv2 of the formation voltage range is increased, the lower limit voltage fv2 of the formation voltage range is set to 2.5 V or more, preferably 2.5 V, which can have a positive effect on improving the stability of the lithium secondary battery operating at high temperatures.

[0207] For example, the lithium secondary battery is formed at 25°C, in a formation voltage range of 2.5V to 4.6V, and at 0.2C / 0.2C for 6 cycles, and then charged and discharged at 45°C, in an operating voltage range of 2.5V to 4.6V, and at 1C / 1C for 500 cycles. The volume change rate of the full cell measured after this is at a level of 6% or less, which makes it possible to mitigate gas generation from the lithium secondary battery, particularly the positive electrode.

[0208] In addition, in order to exhibit the high capacity characteristics of the lithium manganese-based oxide, it is preferable that the lithium secondary battery after chemical formation operates in an operating voltage range in which the upper limit voltage ov1 is greater than 4.3 V and less than 5.0 V, greater than 4.3 V and less than 4.8 V, or greater than 4.3 V and less than 4.6 V.

[0209] In order to increase the charge / discharge efficiency of the lithium secondary battery and improve the characteristics related to the capacity and life of the lithium secondary battery, it is preferable that the lithium secondary battery after formation operates in an operating voltage range in which the lower limit voltage ov2 is 2.0 V or more, preferably 2.0 V or more and less than 3.0 V.

[0210] Furthermore, it is preferable that the operating conditions be set so that the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is greater than 1.6V and less than 2.6V when the lithium secondary battery is operating.

[0211] When the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is 1.6 V or less, it means that the upper limit voltage ov1 of the operating voltage range is too low or the lower limit voltage ov2 is too high. If the upper limit voltage ov1 of the operating voltage range is too low or the lower limit voltage ov2 is too high, the discharge capacity of the lithium secondary battery may be excessively reduced.

[0212] Meanwhile, when the difference ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range is 2.6 V or more, it means that the upper limit voltage ov1 of the operating voltage range is too high or the lower limit voltage ov2 is too low. In this case, as the difference between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range increases, the charge / discharge efficiency of the lithium secondary battery may decrease.

[0213] If the upper limit voltage ov1 of the operating voltage range is too high, the capacity retention rate and average discharge voltage retention rate of the lithium secondary battery may decrease rapidly. If the lower limit voltage ov2 of the operating voltage range is too low, the average discharge voltage and average discharge voltage retention rate of the lithium secondary battery may decrease. The lower limit voltage ov2 of the operating voltage range may also affect the stability of the lithium secondary battery, which can be confirmed by measuring an index related to gas generation within the lithium secondary battery, such as a volume change rate.

[0214] When setting the operating voltage range of the lithium secondary battery defined herein, the appropriate lower limit voltage ov2 may vary depending on the upper limit voltage ov1. Conversely, when setting the operating voltage range of the lithium secondary battery defined herein, the appropriate upper limit voltage ov1 may vary depending on the lower limit voltage ov2.

[0215] In one embodiment, when the upper limit voltage ov1 of the operating voltage range during operation of the lithium secondary battery is 4.6 V or more (e.g., 4.6 V or more and 5.0 V or less, or 4.6 V or more and 4.8 V or less), it is preferable that the lower limit voltage ov2 is set to be within a range of more than 2.0 V and less than 3.0 V (e.g., 2.5 V ± 0.25 V).

[0216] Specifically, when the upper limit voltage ov1 of the operating voltage range is 4.6 V or higher, the lower limit voltage ov2 is set to be greater than 2.0 V and less than 3.0 V, preferably within the range of 2.5 V ±0.25 V (e.g., approximately 2.5 V), thereby realizing stable capacity and life characteristics of the lithium secondary battery while also ensuring stability (low volume change rate).

[0217] If the lower limit voltage ov2 of the operating voltage range is 2.0 V or less, it may be difficult to ensure sufficient charge / discharge efficiency of the lithium secondary battery, and the stability of the lithium secondary battery may be reduced. On the other hand, if the lower limit voltage ov2 of the operating voltage range is 3.0 V or more, the discharge capacity and capacity retention rate of the lithium secondary battery may be reduced.

[0218] For example, when the lithium secondary battery prepared by the method defined herein (e.g., Preparation Example 2 or Preparation Example 3) is subjected to at least one cycle of formation in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more, and then charged and discharged within an operating voltage range in which the upper limit voltage ov1 is 4.6 V or more (e.g., 4.6 V to 5.0 V, or 4.6 V to 4.8 V) and the lower limit voltage ov2 is more than 2.0 V and less than 3.0 V, the ratio of the discharge capacity measured after 300 charge-discharge cycles to the initial discharge capacity of the lithium secondary battery (discharge capacity retention) may be at least 90% or more, preferably 91% or more.

[0219] Furthermore, when the lithium secondary battery is charged and discharged in the same manner as described above, the ratio of the average discharge voltage measured after 300 cycles of charge and discharge to the initial average discharge voltage of the lithium secondary battery (average discharge voltage retention rate) may be greater than 97.2%, preferably 98% or more.

[0220] In another embodiment, when the upper limit voltage ov1 of the operating voltage range is 4.5V or more and less than 4.6V during operation of the lithium secondary battery, it is preferable that the lower limit voltage ov2 is set to be within the range of 2.0V or more and less than 3.0V.

[0221] Specifically, when the upper limit voltage ov1 of the operating voltage range is 4.5 V or more and less than 4.6 V, the lower limit voltage ov2 is set to be within the range of 2.0 V or more and less than 3.0 V, preferably within the range of 2.0 V to 2.5 V, thereby realizing stable capacity and life characteristics of the lithium secondary battery while also ensuring stability (low volume change rate).

[0222] If the lower limit voltage ov2 of the operating voltage range is less than 2.0 V, it may be difficult to ensure sufficient charge / discharge efficiency of the lithium secondary battery, and the stability of the lithium secondary battery may be reduced. On the other hand, if the lower limit voltage ov2 of the operating voltage range is 3.0 V or more, the discharge capacity and capacity retention rate of the lithium secondary battery may be reduced.

[0223] For example, when the lithium secondary battery prepared by the method defined herein (e.g., Preparation Example 2 or Preparation Example 3) is subjected to at least one cycle of formation in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more, and then charged and discharged within an operating voltage range in which the upper limit voltage ov1 is 4.5 V or more and less than 4.6 V and the lower limit voltage ov2 is 2.0 V or more and less than 3.0 V, the ratio of the discharge capacity measured after 300 charge-discharge cycles to the initial discharge capacity of the lithium secondary battery (discharge capacity retention) may be at least 92.5% or more, preferably 95% or more.

[0224] Furthermore, when the lithium secondary battery is charged and discharged in the same manner as described above, the ratio of the average discharge voltage measured after 300 cycles of charge and discharge to the initial average discharge voltage of the lithium secondary battery (average discharge voltage retention rate) may be 98% or more.

[0225] In yet another embodiment, when the upper limit voltage ov1 of the operating voltage range during operation of the lithium secondary battery is less than 4.5 V (e.g., greater than 4.3 V and less than 4.5 V), it is preferable that the lower limit voltage ov2 is set to be within a range of 2.0 V or more and less than 3.0 V.

[0226] Specifically, when the upper limit voltage ov1 of the operating voltage range is less than 4.5 V, the lower limit voltage ov2 is set to be within the range of 2.0 V or more and less than 3.0 V, preferably within the range of 2.0 V to 2.5 V, thereby realizing stable capacity and life characteristics of the lithium secondary battery while also ensuring stability (low volume change rate).

[0227] If the lower limit voltage ov2 of the operating voltage range is less than 2.0 V, it may be difficult to ensure sufficient charge / discharge efficiency of the lithium secondary battery, and the stability of the lithium secondary battery may be reduced. On the other hand, if the lower limit voltage ov2 of the operating voltage range is 3.0 V or more, the discharge capacity and capacity retention rate of the lithium secondary battery may be reduced.

[0228] For example, when the lithium secondary battery prepared by the method defined herein (e.g., Preparation Example 2 or Preparation Example 3) is subjected to at least one cycle of formation in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more, and then charged and discharged within an operating voltage range in which the upper limit voltage ov1 is less than 4.5 V (e.g., greater than 4.3 V and less than 4.5 V) and the lower limit voltage ov2 is 2.0 V or more and less than 3.0 V, the ratio of the discharge capacity measured after 300 charge-discharge cycles to the initial discharge capacity of the lithium secondary battery (discharge capacity retention) may be at least 95.5% or more, preferably 96% or more.

[0229] Furthermore, when the lithium secondary battery is charged and discharged in the same manner as described above, the ratio of the average discharge voltage measured after 300 cycles of charge and discharge to the initial average discharge voltage of the lithium secondary battery (average discharge voltage retention rate) may be 98% or more.

[0230] 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.

[0231] Production Example 1. Production of positive electrode active material Example 1 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH, and NH4OH were added to the reactor and stirred. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was completed, the reactor was washed and dehydrated to produce Ni with an average particle size of 3.5 μm.0.4 Mn 0.6 (OH)2 precursor was obtained.

[0232] (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 give a concentration of 5 mol%. After the reaction was complete, the mixture was washed and dehydrated, then dried at 150°C for 14 hours to obtain the coated precursor.

[0233] (c) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550°C, followed by furnace cooling to obtain a precursor in an oxide state.

[0234] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / Metal molar ratio=1.25) as a lithium source material to prepare a mixture.

[0235] Next, the temperature of a calcination furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the furnace was cooled to obtain a lithium-excess lithium-manganese oxide.

[0236] TEM / EDS analysis of the lithium manganese-based oxide confirmed that the Ni precursor coating in step (b) formed a gradient in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0237] (e) Third heat treatment (barrier layer formation) The lithium manganese-based oxide obtained in step (d) was mixed with H3BO3, in which the boron content based on the metal elements excluding lithium of the lithium manganese-based oxide was weighed out to be 1.0 mol%, and then the mixture was heated to 400°C at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a firing furnace, and heat-treated for 8 hours. The mixture was then classified and crushed to obtain a final product (average particle size 3.5 μm) on which a barrier layer containing a B-containing compound was formed on the surface.

[0238] Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that 2.0 mol% of H3BO3 was used in step (e).

[0239] Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that H3BO3 weighed at 3.0 mol% was used in step (e).

[0240] Example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), 2.0 mol% of H3BO3 was used and the third heat treatment was performed at a final temperature of 300°C.

[0241] Example 5 (e) Wet pretreatment The lithium manganese-based oxide obtained in step (d) of Example 1 and SiO2 weighed out so that the Si content based on metal elements excluding lithium of the lithium manganese-based oxide was 1.0 mol% were added to distilled water under stirring, and the mixture was stirred at 40°C for 12 hours to obtain a lithium manganese-based oxide with SiO2 distributed on the surface.

[0242] (f) Third heat treatment (barrier layer formation) The lithium manganese oxide obtained in step (e) was heated in a firing furnace while maintaining an O atmosphere, and heated to 400°C at a rate of 4.4°C per minute for 8 hours. The oxide was then classified and crushed to obtain a final product (average particle size 3.5 μm) on the surface of which a barrier layer containing a Si-containing compound was formed.

[0243] Example 6 (e) Wet pretreatment The lithium manganese-based oxide obtained in step (d) of Example 1 and NH4H2PO4, which was weighed out so that the content of P based on metal elements excluding lithium in the lithium manganese-based oxide was 3.0 mol%, were added to distilled water while stirring, and the mixture was stirred at 40°C for 12 hours to obtain a lithium manganese-based oxide with NH4H2PO4 distributed on the surface.

[0244] (f) Third heat treatment (barrier layer formation) The lithium manganese oxide obtained in step (e) was heat-treated in a firing furnace for 8 hours while maintaining an O atmosphere, by increasing the temperature to 400°C at a rate of 4.4°C per minute, and then classified and crushed to obtain a final product (average particle size 3.5 μm) on the surface of which a barrier layer containing a P-containing compound was formed.

[0245] Comparative Example 1 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH, and NH4OH were added to the reactor and stirred. The temperature inside the reactor was maintained at 45°C, and N2 gas was introduced into the reactor to promote the precursor synthesis reaction. After the reaction was completed, the reactor was washed and dehydrated to obtain Ni particles with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0246] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C, followed by furnace cooling to obtain a precursor in an oxide state.

[0247] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / Metal molar ratio=1.25) as a lithium source material to prepare a mixture.

[0248] Next, the temperature of a firing furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the mixture was cooled in the furnace, classified, and crushed to obtain the final product, a lithium-excess lithium-manganese oxide (average particle size 3.5 μm).

[0249] Unlike the lithium manganese-based oxide according to Example 1, the lithium manganese-based oxide according to Comparative Example 1 does not involve a precursor coating using Ni, and therefore it was confirmed that no transition metal gradient was formed within the particles.

[0250] Comparative Example 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 and stirred. The temperature inside the reactor was maintained at 45°C, and N2 gas was introduced into the reactor to promote the precursor synthesis reaction. After the reaction was completed, the reactor was washed and dehydrated to obtain Ni particles with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0251] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C, followed by furnace cooling to obtain a precursor in an oxide state.

[0252] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / Metal molar ratio=1.25), which is a lithium source material, to prepare a mixture.

[0253] Next, the temperature of a calcination furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the furnace was cooled to obtain a lithium-excess lithium-manganese oxide.

[0254] (d) Third heat treatment (barrier layer formation) The lithium manganese-based oxide obtained in step (c) was mixed with H3BO3, in which the boron content based on the metal elements excluding lithium of the lithium manganese-based oxide was weighed out to be 2.0 mol%, and then the mixture was heated to 400°C at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a calcination furnace, and heat-treated for 8 hours. The mixture was then classified and crushed to obtain a final product (average particle size 3.5 μm).

[0255] Unlike the lithium manganese-based oxide according to Example 1, the lithium manganese-based oxide according to Comparative Example 2 does not involve a precursor coating using Ni, and therefore it was confirmed that no transition metal gradient was formed within the particles.

[0256] Comparative Example 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 and stirred. The temperature inside the reactor was maintained at 45°C, and N2 gas was introduced into the reactor to promote the precursor synthesis reaction. After the reaction was completed, the reactor was washed and dehydrated to obtain Ni particles with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0257] (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 give a concentration of 5 mol%. After the reaction was complete, the mixture was washed and dehydrated, then dried at 150°C for 14 hours to obtain the coated precursor.

[0258] (c) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550°C, followed by furnace cooling to obtain a precursor in an oxide state.

[0259] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / Metal molar ratio=1.25) as a lithium source material to prepare a mixture.

[0260] Next, the temperature of a calcination furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the mixture was cooled in the furnace, classified, and crushed to obtain the final product, a lithium-excess lithium manganese-based oxide (average particle size 3.5 μm).

[0261] TEM / EDS analysis of the lithium manganese-based oxide confirmed that the Ni precursor coating in step (b) formed a gradient in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0262] Comparative Example 4 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH, and NH4OH were added to the reactor and stirred. The temperature inside the reactor was maintained at 45°C, and N2 gas was introduced into the reactor to promote the precursor synthesis reaction. After the reaction was completed, the mixture was washed and dehydrated to obtain Ni particles with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0263] (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 give a concentration of 5 mol%. After the reaction was complete, the mixture was washed and dehydrated, then dried at 150°C for 14 hours to obtain a coated precursor.

[0264] (c) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550°C, followed by furnace cooling to obtain a precursor in an oxide state.

[0265] (d) Second heat treatment The oxide precursor obtained in step (c), a lithium source material LiOH (Li / Metal molar ratio = 1.25), and WO3, the content of W based on the metal elements excluding lithium in the precursor, was weighed out to be 1.0 mol%, to prepare a mixture.

[0266] Next, the temperature of a firing furnace in an O atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. After that, the mixture was cooled in the furnace, classified, and crushed to obtain the final product, a lithium-excess lithium-manganese oxide (average particle size 3.5 μm).

[0267] TEM / EDS analysis of the lithium manganese-based oxide confirmed that the Ni precursor coating in step (b) formed a gradient in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0268] Reference example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), H3BO3 weighed at 2.0 mol% was used and the third heat treatment was performed at a final temperature of 500°C.

[0269] Reference example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), 2.0 mol% of H3BO3 was used and the third heat treatment was performed at a final temperature of 600°C.

[0270] Reference example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), H3BO3 weighed at 2.0 mol% was used and the third heat treatment was performed at a final temperature of 700°C.

[0271] Reference example 4 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), 0.1 mol% of H3BO3 was used and the third heat treatment was performed at a final temperature of 300°C.

[0272] Reference example 5 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (e), H3BO3 weighed at 5.0 mol% was used and the third heat treatment was performed at a final temperature of 300°C.

[0273] Composition of lithium manganese oxide The composition (molar ratio of each element) of the lithium manganese-based oxide contained in the positive electrode active material prepared in Preparation Example 1 was measured by ICP, and the results are shown in Table 1 below.

[0274] [Table 1] *Li / Metal molar ratio indicates the molar ratio of lithium to all elements other than lithium in the lithium manganese-based oxide. *The element content (mol%) is calculated based on the total amount of elements other than lithium in the lithium manganese oxide.

[0275] Manufacturing example 2. 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 1, 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.

[0276] 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.

[0277] Manufacturing example 3. 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 1, 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.

[0278] 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.

[0279] Experimental Example 1: XPS analysis of positive electrode active material The lithium manganese-based oxides selected from the positive electrode active materials prepared in Preparation Example 1 were subjected to XPS analysis to measure the contents of the target elements contained in the lithium manganese-based oxides.

[0280] Specifically, the change in the content of the target element was measured from the surface of the lithium manganese-based oxide (secondary particles) to the center of the lithium manganese-based oxide (secondary particles) by increasing the etching time of the surface of the lithium manganese-based oxide using an XPS depth profile analysis method (ion energy 2000 eV, spot size 200 μm). The results of the XPS analysis are shown in Tables 2 and 3 below.

[0281] [Table 2] *The target element content (at%) is calculated based on all elements in the lithium manganese-based oxide except for lithium.

[0282] Referring to the results in Table 2, it can be seen that the content of the target element present on the surface of the lithium manganese-based oxide (secondary particles) according to Examples 1, 2, 5, and 6 is 20 at % or more. The fact that the content of the target element derived from the raw material used in the third heat treatment on the surface 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 of the lithium manganese-based oxide (secondary particles).

[0283] On the other hand, in the case of Comparative Example 4, the measured content of the target element decreases as the etching time increases, and it can be confirmed that the content of the target element present on the surface of the lithium manganese-based oxide (secondary particles) is too low compared to the lithium manganese-based oxides of Examples 1, 2, 5, and 6.

[0284] This result is because the target elements from the source material used in the second heat treatment step were mostly doped into the lithium manganese-based oxide (particularly the primary particles) instead of existing as a barrier layer on the surface of the lithium manganese-based oxide (secondary particles). The decrease in the content of the target elements as the etching time increased is also likely due to the doping and diffusion of the target elements from the surface to the center of the lithium manganese-based oxide.

[0285] Therefore, it can be confirmed that there is substantially no physical barrier that can function as a barrier layer on the surface of the lithium manganese-based oxide (secondary particles) according to Comparative Example 4.

[0286] [Table 3] *The target element content is calculated by setting the total content of Ni and Mn among all elements excluding lithium in the lithium manganese oxide as 100.

[0287] Referring to the results in Table 3, it can be seen that the Ni precursor coating was performed during the preparation of the lithium manganese-based oxide according to Example 1, resulting in the formation of a gradient in which the Ni concentration increased and the Mn concentration decreased from the center to the surface.

[0288] Experimental Example 2: Thermogravimetric Analysis (TGA) of Positive Electrode Active Material A thermal weight loss analysis was performed on the lithium manganese-based oxides selected from each of the cathode active materials prepared in Preparation Example 1 to determine whether a barrier layer was formed at an appropriate level on the surfaces of the primary particles and / or secondary particles constituting the lithium manganese-based oxides.

[0289] The TGA analysis was carried out under the following conditions, and the results are shown in Table 4 below. Sample: Lithium manganese oxide 65 mg Measurement atmosphere: Ar gas (gas flow rate: 60 ml / min) Measurement conditions: Temperature increased from 30°C to 900°C at a rate of 10°C / min

[0290] [Table 4]

[0291] Referring to the results in Table 4, it can be seen that the lithium manganese-based oxide according to Comparative Example 3 does not substantially experience thermal weight loss at 400°C and 700°C, taking into account the margin of error. That is, this is consistent with the trend of thermogravimetric analysis results for general lithium manganese-based oxides, which do not experience thermal weight loss up to about 900°C.

[0292] Meanwhile, it was confirmed that the lithium manganese-based oxides according to Examples 1, 2, and 6 experienced a thermal weight loss at temperatures between about 500° C. and 600° C. It was also confirmed that as the content of the barrier layer in the lithium manganese-based oxide increased, the thermal weight loss confirmed by thermogravimetric analysis of the lithium manganese-based oxide increased.

[0293] 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 2 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 charge capacity, initial discharge capacity, initial reversible efficiency, and rate capability (C-rate). The measurement results are shown in Table 5 below.

[0294] [Table 5]

[0295] Referring to the half-cell evaluation results in Table 5, it can be seen that in Comparative Examples 1 and 2, where the transition metal concentration does not show a gradient from the center to the surface of the particle, the discharge capacity ratio is lower than that of the lithium secondary battery using the lithium manganese-based oxide according to the Examples as a positive electrode active material, regardless of whether a barrier layer is present on the surface of the particle.

[0296] It was confirmed that electrochemical properties such as initial discharge capacity and discharge capacity ratio were deteriorated in Reference Examples 1 to 3, where the third heat treatment temperature for forming the barrier layer was high. This result is believed to be due to damage to the lithium manganese-based oxide, such as the loss of the concentration gradient of transition metals within the particles, caused by the excessively high third heat treatment temperature.

[0297] In addition, in the case of Reference Examples 4 and 5, the electrochemical properties are generally better than those of Comparative Examples 1 to 4, but it can be confirmed that the effect of improving the rate characteristics is somewhat insufficient compared to the examples because the amount of raw material forming the barrier layer is either too small or too large.

[0298] 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 3 using the cathode active materials of Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 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). Then, 500 charge-discharge experiments were carried out 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. The measurement results are shown in Table 6 below.

[0299] [Table 6]

[0300] Referring to the full cell evaluation results in Table 6, it can be seen that the transition metal concentration shows a gradient from the center to the surface of the particle, and that in Comparative Examples 3 and 4, where no barrier layer is present on the particle surface, the cycle capacity retention rate drops sharply. This result is thought to be due to the fact that as the transition metal elutes from the lithium manganese-based oxide, an abnormal resistance phenomenon occurs in the negative electrode, which accelerates the deterioration of the lifespan of the lithium secondary battery.

[0301] Although the transition metal concentration does not show a gradient from the center to the surface of the particle, in the case of Comparative Example 2 in which a barrier layer is formed on the surface of the particle, the resistance abnormality phenomenon that occurred in Comparative Example 3 is reduced, and it can be confirmed that the cycle capacity retention rate is improved compared to Comparative Example 3.

[0302] On the other hand, in Example 2, where the transition metal concentration shows a gradient from the center to the surface of the particle and a barrier layer is formed on the surface of the particle, it was confirmed that the elution of the transition metal from the lithium manganese-based oxide was prevented and the electrochemical properties, such as the surface kinetics of the particle, were improved, resulting in a better cycle capacity retention rate than Comparative Example 2.

[0303] Experimental Example 5: Experiment on transition metal elution The lithium secondary batteries (full cells) manufactured in Manufacturing Example 3 using the positive electrode active materials of Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 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, vacuum dried at 60°C, and then collected.

[0304] 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.

[0305] In addition, lithium secondary batteries (full cells) manufactured in Manufacturing Example 3 using the positive electrode active materials of Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 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.

[0306] 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. The measurement results are shown in Table 7 below.

[0307] [Table 7]

[0308] Referring to the results in Table 7, as expected from Experimental Example 4, it can be seen that the rapid deterioration in lifespan in Comparative Examples 3 and 4 is due to the increased content of transition metals deposited on the negative electrode active material after chemical formation or after 500 charge-discharge cycles.

[0309] It can be seen that in Comparative Example 2, in which the same barrier layer as in Example 2 was formed, the amount of transition metals eluted to the anode side was higher than in Example 2. This result is presumably because, in the lithium manganese-based oxide of Example 2, a concentration gradient was formed in which the content of transition metals that are relatively less likely to elute in the region corresponding to the particle surface (shell) was higher than that of other transition metals, whereas in the lithium manganese-based oxide of Comparative Example 2, no concentration gradient of transition metals was formed from the center of the particle to the surface.

[0310] Experimental Example 6: Evaluation of the characteristics of a lithium secondary battery (full cell) under different operating conditions The lithium secondary battery (full cell) prepared in Preparation Example 3 using the positive electrode active material of Example 1 was subjected to a formation process of 6 cycles at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then a charge-discharge experiment was carried out 300 times at 25°C and 1C / 1C.

[0311] Through the charge-discharge experiment, the discharge capacity after the 300th cycle charge-discharge, the ratio of the discharge capacity after the 300th cycle charge-discharge to the initial discharge capacity (capacity retention), the average discharge voltage after the 300th cycle charge-discharge, and the ratio of the average discharge voltage after the 300th cycle charge-discharge to the initial average discharge voltage (voltage retention) were measured. In addition, the volume change rate of the lithium secondary battery (full cell) was calculated as the ratio of the volume after the 300th cycle charge-discharge to the initial volume (before charge-discharge) in percentage.

[0312] The operating voltage range during charge and discharge of the lithium secondary battery (full cell) and the results of the charge and discharge experiment are shown in Table 8 below. In Table 8 below, full cells with different operating voltage ranges during charge and discharge are classified into L1 to L9.

[0313] [Table 8] *ov1: Upper limit voltage of the operating voltage range *ov2: Lower limit voltage of the operating voltage range

[0314] Referring to the full cell evaluation results in Table 8, it can be seen that even when the same lithium manganese-based oxide is used as a positive electrode active material, the characteristics related to capacity and lifespan vary significantly depending on the voltage range during operation of the lithium secondary battery (full cell).

[0315] Specifically, in the case of L1, the characteristics related to capacity and lifespan were measured to be good, but even after 300 charge-discharge cycles, a volume change rate of 0.7% was observed, confirming a rapid decline in the stability of the lithium secondary battery.

[0316] On the other hand, L2, which has the same upper limit voltage as L1 but a higher lower limit voltage than L1, exhibits capacity and life characteristics similar to L1, and the volume change rate is only 0.4%, confirming that the stability of the lithium secondary battery is improved compared to L1.

[0317] L3, which has the same upper limit voltage as L1 but a higher lower limit voltage than L2, shows similar levels of capacity retention and voltage retention to L1 and L2, but it can be seen that the discharge capacity (170.2 mAh / g) after the 300th charge-discharge cycle is slightly insufficient.

[0318] L4 and L5, which have a lower upper voltage limit than L1, showed better capacity retention and voltage retention than L1 and L2, confirming improved lithium secondary battery stability. Meanwhile, L6, which has the same upper voltage limit as L4 and L5 but a higher lower voltage limit, showed a slightly lower discharge capacity (168.1 mAh / g) after the 300th charge-discharge cycle as the lower voltage limit of the operating voltage range increased, and it was also confirmed that the capacity retention rate was lower than L4 and L5.

[0319] In the case of L7 and L8, which have a lower upper voltage limit than L4, the discharge capacity was slightly lower than L4, but the capacity retention and voltage retention were improved compared to L4 and L5. However, in the case of L9, which has the same upper voltage limit as L7 and L8 but a higher lower voltage limit, the discharge capacity (160.3 mAh / g) and capacity retention after the 300th charge-discharge cycle were found to have decreased.

[0320] Experimental Example 7: Evaluation of the characteristics of a lithium secondary battery (full cell) by changing the formation conditions The lithium secondary battery (full cell) prepared in Preparation Example 3 using the cathode active material of Example 1 was subjected to a formation process of 6 cycles at 25°C and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then a charge-discharge experiment was carried out 500 times at 25°C or 45°C and 1C / 1C.

[0321] Through the charge-discharge experiment, the discharge capacity after the 500th charge-discharge cycle, the ratio of the discharge capacity after the 500th charge-discharge cycle to the initial discharge capacity (capacity retention), the average discharge voltage after the 500th charge-discharge cycle, and the ratio of the average discharge voltage after the 500th charge-discharge cycle to the initial average discharge voltage (voltage retention) were measured. In addition, the volume change rate of the lithium secondary battery (full cell) was calculated as the ratio of the volume after the 500th charge-discharge cycle to the initial volume (before charge-discharge) in percentage.

[0322] The formation and operating voltage ranges during charge and discharge of the lithium secondary battery (full cell) and the results of the charge and discharge experiments are shown in Table 9 below. In Table 9 below, full cells with different formation and operating voltage ranges during charge and discharge are classified into L10 to L13.

[0323] [Table 9] *fv1: Upper limit voltage of the formation voltage range *fv2: Lower limit voltage of the formation voltage range *ov1: Upper limit voltage of the operating voltage range *ov2: Lower limit voltage of the operating voltage range

[0324] Referring to the full cell evaluation results in Table 9, it can be seen that even when the same lithium manganese-based oxide is used as a positive electrode active material, the volume change rate of the lithium secondary battery after its life (500 charge-discharge cycles) can vary depending on the voltage range during formation, operating temperature, and operating voltage range of the lithium secondary battery (full cell).

[0325] Specifically, when comparing L10 and L11, it can be seen that at an operating temperature of 25°C, there is no volume change in the lithium secondary battery after its lifespan (500 charge / discharge cycles), and the discharge capacity and capacity retention are similar, regardless of the formation voltage range and the lower limit voltage of the operating voltage range.On the other hand, at an operating temperature of 45°C, it can be seen that L13, whose formation voltage range and lower limit voltage of the operating voltage range are 2.5V, shows a more moderate volume change in the lithium secondary battery than L12, whose formation voltage range and lower limit voltage of the operating voltage range are 2.0V.

[0326] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. A lithium secondary battery using 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 R-3m space group are solid-solved or composite, The lithium secondary battery is operated in an operating voltage range in which an upper limit voltage ov1 is greater than 4.3 V after undergoing at least one cycle of formation in a formation voltage range in which an upper limit voltage fv1 is 4.4 V or greater based on a positive electrode potential; and The lithium secondary battery is configured such that a difference ov1-ov2 between an upper limit voltage ov1 and a lower limit voltage ov2 of an operating voltage range during operation of the lithium secondary battery is greater than 1.6V and less than 2.6V.

2. 2. The lithium secondary battery according to claim 1, wherein the first cycle of the formation of the lithium secondary battery is performed in a formation voltage range in which the upper limit voltage fv1 is 4.4 V or more.

3. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is formed within a formation voltage range in which a lower limit voltage fv2 is greater than 2.0 V and less than 3.0 V with respect to the positive electrode potential.

4. 2. The lithium secondary battery according to claim 1, wherein an upper limit voltage ov1 of an operating voltage range during operation of the lithium secondary battery is set to be in the range of more than 4.3 V and not more than 5.0 V.

5. 2. The lithium secondary battery according to claim 1, wherein a lower limit voltage ov2 of an operating voltage range is set to be within a range of 2.0 V or more and less than 3.0 V during operation of the lithium secondary battery.

6. 2. The lithium secondary battery according to claim 1, wherein when an upper limit voltage ov1 of an operating voltage range during operation of the lithium secondary battery is 4.6 V or more, the lower limit voltage ov2 is set to be in a range greater than 2.0 V and less than 3.0 V.

7. 2. The lithium secondary battery according to claim 1, wherein when an upper limit voltage ov1 of an operating voltage range during operation of the lithium secondary battery is 4.5 V or more and less than 4.6 V, the lower limit voltage ov2 is set to be within a range of 2.0 V or more and less than 3.0 V.

8. 2. The lithium secondary battery according to claim 1, wherein when an upper limit voltage ov1 of an operating voltage range during operation of the lithium secondary battery is less than 4.5 V, the lower limit voltage ov2 is set to be within a range of 2.0 V or more and less than 3.0 V.

9. 2. The lithium secondary battery according to claim 1, wherein the lithium manganese-based oxide is a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide exhibits a gradient from the core to the shell.

10. 10. The lithium secondary battery according to claim 9, wherein the lithium manganese-based oxide is a core-shell particle in which the concentration of at least one selected from nickel and manganese exhibits a gradient from the core to the shell.

11. 2. The lithium secondary battery of claim 1, wherein the lithium manganese-based oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 b (where, M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, 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)

12. 2. The lithium secondary battery of claim 1, wherein the lithium manganese-based oxide is represented by the following chemical formula 1-1: [Chemical formula 1-1] rLi ２ MnO ３－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)

13. 10. The lithium secondary battery according to claim 9, wherein a barrier layer is present that covers at least a portion of the surface of the core-shell particles.

14. The lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, The lithium secondary battery according to claim 13 , wherein the barrier layer covers at least a portion of the surfaces of the primary particles and the secondary particles.

15. Grain boundaries are defined between adjacent primary particles, 15. The lithium secondary battery according to claim 14, wherein the barrier layer exists in a state of being diffused from the surface portion of the secondary particle toward the center portion of the secondary particle along the crystal grain boundary.

16. The lithium secondary battery of claim 13 , wherein the barrier layer comprises a first oxide represented by the following Chemical Formula 2: [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)

17. The lithium secondary battery of claim 13 , wherein the barrier layer comprises a second oxide represented by the following Chemical Formula 3: [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)

18. The lithium secondary battery of claim 13 , wherein the barrier layer comprises a tertiary oxide represented by the following Chemical Formula 4: [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, excluding the case where j and k are both 0)

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