Lithium-ion rechargeable 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 in which capacity and life retention rate are improved by controlling the voltage range during chemical formation or operation of the lithium secondary battery, and further relates to a lithium secondary battery in which life degradation is prevented by preventing the deterioration of the electrochemical properties of the lithium secondary battery, including rate characteristics, due to excess lithium and manganese present in the lithium manganese-based oxide used as the positive electrode active material, and in particular by suppressing or mitigating the elution of transition metals from the lithium manganese-based oxide. [Background technology]

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

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

[0004] Typical materials used as positive electrode active materials for lithium secondary batteries include lithium composite oxides. These lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides in which Ni, Co, Mn, or Al are combined, as disclosed in Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015).

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

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages such as excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature performance. On the other hand, LiNiO2-based cathode active materials exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to cation mixing problems between Li and transition metals, which results in significant problems with their rate characteristics.

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

[0008] Various candidate materials have been proposed to compensate for the shortcomings of these conventional cathode active materials. As an example, research is being conducted to use lithium-rich lithium-manganese oxides, which contain an excess amount of manganese (Mn) among the transition metals, and whose lithium content exceeds the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such lithium-rich lithium-manganese oxides are also called lithium-overlithiated layered oxides (OLOs).

[0009] While the aforementioned OLO has the advantage of theoretically exhibiting high capacity under high-voltage operating conditions, in reality, it has a disadvantage in that its electrical conductivity is relatively low due to the excess amount of Mn contained in the oxide, resulting in poor rate characteristics for lithium secondary batteries using OLO. When rate characteristics are low in this way, problems arise in which the charge / discharge capacity and life efficiency (cycle capacity retention) of lithium secondary batteries decrease during cycling.

[0010] Furthermore, since the aforementioned OLO has different formation and operation conditions from commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions, along with the proposal of a new OLO, it is necessary to develop operating conditions that enable lithium secondary batteries using the aforementioned OLO to exhibit commercially viable electrochemical properties. [Overview of the project] [Problems that the invention aims to solve]

[0011] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is driving the market, and this is leading to a sustained increase in the demand for positive electrode active materials used in lithium-ion batteries.

[0012] For example, conventionally, lithium-ion batteries using lithium iron phosphate (LFP) have been primarily used, mainly for safety reasons. However, recently, there has been a growing trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFP.

[0013] Furthermore, nickel-based lithium composite oxides, which are now primarily used as positive electrode active materials in high-capacity lithium secondary batteries, require the essential use of ternary metallic elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only subject to unstable supply and demand but is also excessively expensive compared to other raw materials, thus necessitating new compositions of positive electrode active materials that can reduce or eliminate cobalt content.

[0014] Considering these circumstances, lithium-rich lithium manganese oxides can meet the aforementioned market expectations, but they still have limitations in terms of electrochemical properties and stability, making them suitable as a substitute for commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0015] For example, the inventors have confirmed that lithium manganese oxides are more likely to leach transition metals from the particle surface due to repeated charging and discharging than ternary lithium composite oxides. In particular, there is a high possibility that excess Mn contained in lithium manganese oxides will leach from the particle surface.

[0016] When a transition metal is leached from the lithium manganese oxide, the leached transition metal can react with the electrolyte on the surface of the lithium manganese oxide to form impurities. These impurities not only increase the surface resistance of the lithium manganese oxide but also act as a cause of reduced intercalation / deintercalation efficiency of lithium ions via the lithium manganese oxide.

[0017] Furthermore, the transition metals dissolved from the lithium manganese oxide, or the impurities formed by the reaction of the dissolved transition metals with the electrolyte, can move to the negative electrode using the electrolyte as a medium and be deposited on the surface of the negative electrode.

[0018] For example, a side reaction may occur with the electrolyte on the surface of the lithium manganese oxide, or an excess amount of Mn may be present in the lithium manganese oxide due to a structural change in the lithium manganese oxide (such as a change in crystal structure). 2+ Mn can be dissolved into the electrolyte. 2+ During chemical conversion or charging / discharging, Mn can move to the surface of the negative electrode using the electrolyte as a medium and react with various substances present in the battery (electrons, electrolyte, electrodes, or by-products, etc.), resulting in Mn forming on the surface of the negative electrode. 2+ It will exist as an impurity containing Mn metal or Mn-containing compounds (e.g., MnCO3, MnO, MnF2, etc.).

[0019] The deposition of transition metals or impurities on the surface of the negative electrode can cause a sharp increase in negative electrode resistance, and this abnormal resistance phenomenon is a typical cause of accelerated degradation of the lifespan of lithium secondary batteries.

[0020] In particular, lithium secondary batteries using the aforementioned lithium manganese oxide as the positive electrode active material have a higher operating voltage than lithium secondary batteries using other commercially available ternary lithium composite oxides as the positive electrode active material, and are therefore more susceptible to the aforementioned problems.

[0021] However, currently there is no technology to resolve the issues caused by the leaching of transition metals from lithium-rich lithium-manganese oxides.

[0022] As mentioned above, conventional lithium-rich lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability when compared with other commercially available types of cathode active materials. However, the inventors have confirmed that lithium-rich lithium manganese oxides can exhibit electrochemical properties and stability at a level suitable for commercialization if the bulk composition of the lithium manganese oxide is controlled and a barrier layer is provided that can suppress or mitigate the elution of transition metals from the surface of the lithium manganese oxide.

[0023] In particular, the inventors have confirmed that by forming the lithium manganese-based oxide as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide shows a gradient from the core to the shell, and by making the content of the transition metal that is relatively less likely to dissolve higher in the region corresponding to the shell than that of other transition metals, the dissolution of transition metals from the lithium manganese-based oxide can be suppressed or mitigated.

[0024] Furthermore, the inventors have confirmed that when the surface of such core-shell particles, 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 particles, the elution of transition metals from the lithium manganese-based oxide can be further suppressed or mitigated.

[0025] Accordingly, the present invention aims to provide a lithium secondary battery that uses a positive electrode active material comprising a lithium-rich lithium manganese oxide, which controls the bulk composition of the lithium manganese oxide while simultaneously forming a barrier layer on the surface of the lithium manganese oxide, thereby suppressing or mitigating the elution of transition metals from the lithium manganese oxide.

[0026] Furthermore, the present invention aims to provide a lithium secondary battery that uses a positive electrode active material capable of suppressing or mitigating the elution of transition metals from the lithium manganese oxide while simultaneously improving the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium manganese oxide. This is achieved by forming the lithium manganese oxide as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese oxide exhibits a gradient from the core to the shell, and by making the content of the transition metal that is relatively less likely to elute in the region corresponding to the shell higher than that of other transition metals.

[0027] Furthermore, the present invention aims to provide a lithium secondary battery that can achieve high stability by using the lithium manganese oxide defined in this application as the positive electrode active material, preventing a decrease in rate characteristics due to excess lithium and manganese present in existing OLOs, and reducing side reactions between the positive electrode active material and the electrolyte even when driven at high voltage.

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

[0029] According to one aspect of the present invention for solving the aforementioned technical problems, a lithium secondary battery is provided that 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 in solid solution or composite form.

[0030] In order to activate the lithium-rich lithium manganese oxide in the lithium secondary battery, it is preferable to perform at least one formation cycle in a formation voltage range where the upper limit voltage fv1 is 4.4V or higher with respect to the positive electrode potential.

[0031] Furthermore, in order to exhibit the high capacity characteristics of the lithium manganese oxide, it is preferable that the lithium secondary battery operates within an operating voltage range where the upper limit voltage ov1 is greater than 4.3V and 5.0V or less, greater than 4.3V and 4.8V or less, or greater than 4.3V and 4.6V or less.

[0032] In order to improve the charge and discharge efficiency of the lithium secondary battery and enhance the characteristics related to the capacity and lifespan of the lithium secondary battery, it is preferable that after chemical formation, the lithium secondary battery operates within an operating voltage range of 2.0V or higher, preferably between 2.0V and 3.0V.

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

[0034] A difference of ov1-ov2 between the upper and lower limits of the operating voltage range means that the upper limit ov1 is too low or the lower limit ov2 is too high. If the upper limit ov1 is too low or the lower limit ov2 is too high, the discharge capacity of the lithium secondary battery may decrease excessively.

[0035] On the other hand, a difference of ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range of ov1 is 2.6V or more, which means that either 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 and discharge efficiency of the lithium secondary battery may decrease.

[0036] Furthermore, 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 sharply. Also, 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 can also affect the stability of the lithium secondary battery, and the stability of the lithium secondary battery can be confirmed by gas generation-related indicators such as the volume change rate.

[0037] Furthermore, the positive electrode active material used in this application includes 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 in solid solution or composite form.

[0038] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a single phase belonging to the R-3m space group, whereas the lithium-rich lithium manganese 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 oxide is formed as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese oxide shows 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 reducing the possibility of transition metals dissolving from the lithium manganese oxide.

[0041] In one embodiment, the lithium manganese-based oxide among the positive electrode active material may exist in at least one form selected from single primary particles and secondary particles formed by the aggregation of multiple primary particles.

[0042] For example, the positive electrode active material may include the lithium manganese-based oxide, which is a secondary particle formed by the aggregation of multiple 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 toward the surface of the secondary particle.

[0044] In this case, the barrier layer is present such that it covers at least a portion of the surface of the secondary particles, thereby suppressing or mitigating the elution of transition metals from the secondary particles.

[0045] Furthermore, grain boundaries are defined between adjacent primary particles within the secondary particles. The barrier layer may exist diffused along the grain boundaries, from the surface of the secondary particles toward the center of the secondary particles.

[0046] In other embodiments, the primary particles may be core-shell particles in which the concentration of at least one transition metal exhibits a gradient from the center of the primary particle toward the surface of the primary particle.

[0047] In this case, the barrier layer is present such that it covers at least a portion of the surface of the primary particles, thereby suppressing or mitigating the elution of transition metals from the primary particles.

[0048] In further embodiments, the primary particles may include at least one crystallite, and the crystallite may exhibit a gradient in the concentration of at least one transition metal from the center of the crystallite toward the surface of the crystallite.

[0049] In this case, the barrier layer can cover each crystallite present within the primary particles, but by covering the surface of the primary particles, the objective of suppressing or mitigating the elution of transition metals can be fully achieved.

[0050] In one embodiment, the lithium manganese oxide can be represented by the following chemical formula 1. [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from the group consisting of 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 part of the oxygen present in the lithium manganese-based oxide, 0<a≤0.7, 0≤b≤0.1, 0<x≤1, 0≤y<1, and 0<x+y≤1)

[0051] In another embodiment, the lithium manganese-based oxide may be represented by the following Chemical 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′ (wherein, M1 is at least one selected from Ni and Mn, M2 is at least one selected from the group consisting of 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 each a halogen capable of substituting at least part 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, and 0<x′+y′≤1) Effects of the Invention

[0052] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese oxides, which have various disadvantages in terms of electrochemical properties and / or stability when compared with commercially available ternary lithium composite oxides of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[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 shows 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 made higher than that of other transition metals, thereby suppressing or mitigating the dissolution of transition metals from the lithium manganese-based oxide.

[0054] Furthermore, if the surface of such core-shell particles, 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 particles, the elution of transition metals from the lithium manganese oxide can be further suppressed or mitigated.

[0055] By suppressing or mitigating the elution of transition metals from the lithium manganese oxide, it is possible to prevent the formation of impurities by the reaction of the eluted transition metals with the electrolyte on the surface of the lithium manganese oxide.

[0056] Transition metals leached from the lithium manganese oxide and / or impurities formed by the reaction of the leached transition metals with the electrolyte can move to the negative electrode using the electrolyte as a medium, and these impurities can deposit on the surface of the negative electrode, causing a rapid increase in the negative electrode resistance. As a result, it is necessary to restrict the unintended movement of transition metals within the lithium secondary battery, as described in the present invention.

[0057] In other words, according to the present invention, by preventing the elution of transition metals from the lithium manganese oxide, it is possible to prevent the acceleration of the life degradation of the lithium secondary battery as impurities are deposited on the positive and / or negative electrodes by the transition metals eluted from the lithium manganese oxide.

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

[0059] Thus, when using a positive electrode containing the positive electrode active material defined in this application, it is possible to prevent a decrease in rate characteristics due to excess lithium and manganese present in existing OLOs, and in particular, to reduce side reactions between the positive electrode active material and the electrolyte even when driven at high voltage, thereby achieving high stability.

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

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

[0062] Along with the effects described above, the specific effects of the present invention will be described below while explaining the specific matters for carrying out the invention. [Modes for carrying out the invention]

[0063] For the convenience of making the present invention easier to understand, certain terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in this invention have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0064] The following will provide a more detailed description of the positive electrode active material used in lithium secondary batteries and the lithium secondary batteries themselves, according to several embodiments of the present invention.

[0065] positive electrode active material A lithium secondary battery according to one aspect 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 in solid solution or composite form.

[0066] The lithium manganese oxide contains at least lithium, nickel, and manganese. In this case, the lithium manganese oxide is also called an overlithiated layered oxide (OLO) because the lithium content present in the lithium manganese oxide is greater than the total content of other transition metals (generally, the molar ratio of lithium to all metal elements other than lithium in the lithium manganese oxide (Li / Metal molar ratio) is greater than 1).

[0067] Generally, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a manganese content of 20 mol% or less in the total metal elements excluding lithium, the lithium manganese-based oxides have a relatively higher proportion of manganese in the total metal elements (for example, 50 mol% or more, preferably 55 mol% to 75 mol%) compared to commercially available ternary lithium composite oxides.

[0068] Furthermore, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a nickel content of 60 mol% or more (80 mol% or more in the case of high-Ni types) in the total metal elements excluding lithium, the lithium manganese-based oxide has a relatively lower proportion of nickel in the total metal elements (for example, less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0069] Another difference is that the Li / Metal molar ratio measured from lithium manganese oxides as defined in this application is greater than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of lithium manganese oxides as defined in this application is greater than 1, preferably between 1.1 and 1.6.

[0070] Despite the aforementioned compositional differences, the lithium manganese-based oxide can also function as a composite metal oxide capable of lithium ion intercalation / deintercalation.

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

[0072] When the lithium manganese oxide exists as a single primary particle, it can be referred to as a single particle. On the other hand, when the lithium manganese oxide exists as an aggregate formed by the aggregation of multiple primary particles, it can be referred to as a secondary particle.

[0073] The positive electrode active material may include at least one selected from lithium manganese oxides existing as single particles and lithium manganese oxides existing as secondary particles formed by the aggregation of multiple primary particles.

[0074] The primary particles constituting the lithium manganese oxide can have rod-like, elliptical, and / or amorphous shapes. Furthermore, unless specifically intended in the manufacturing process, primary particles of various shapes can be present within the same cathode active material.

[0075] The primary particles constituting the lithium manganese oxide as defined in this application may have an average particle size of 0.1 μm to 5 μm, preferably 0.1 μm to 1.0 μm, and more preferably 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated using the average value of the length in the long axis direction and the length in the short axis direction of the primary particles ([long axis length + short axis length] / 2).

[0076] When the lithium manganese oxide exists as secondary particles formed by the aggregation of multiple primary particles, the average particle size of the secondary particles may be 0.5 μm to 15 μm. The average particle size of the secondary particles can vary depending on the number of primary particles that constitute the secondary particles.

[0077] Unless otherwise defined, the term "surface of the primary particle" as used in this application means the outer surface of the primary particle that is exposed to the outside. Similarly, the term "surface of the secondary particle" as used in this application means the outer surface of the secondary particle that is exposed to the outside. In this case, the "surface of the secondary particle" formed by the aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present on the surface portion of the secondary particle.

[0078] Furthermore, unless otherwise defined, the terms "particle surface" as used in this application mean the region relatively close to the "surface" of the particle, and "particle center" means the region relatively closer to the "center" of the particle than the "surface." Thus, "primary particle surface" means the region relatively close to the "surface" of the primary particle, and "primary particle center" means the region relatively closer to the "center" of the primary particle than the "surface." Similarly, "secondary particle surface" means the region relatively close to the "surface" of the secondary particle, and "secondary particle center" means the region relatively closer to the "center" of the secondary particle than the "surface."

[0079] In this case, the region within any particle excluding the "particle surface" can be defined as the "particle's central region."

[0080] For example, if the radius of the primary particle is r, the region at a distance of 0 to 0.5r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle. If the radius of the primary particle is 0.5 μm, the surface portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the surface of the primary particle, and the center portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the center of the primary particle.

[0081] Furthermore, if necessary, when the radius of the primary particle is denoted as r, the region at which the distance from the surface of the primary particle is 0 to 0.1r or 0 to 0.2r can be defined as the surface portion of the primary particle, and the region at which the distance from the center of the primary particle is 0 to 0.2r or 0 to 0.5r can be defined as the center portion of the primary particle.

[0082] Similarly, when the radius of the secondary particle is denoted as r, the region at a distance of 0 to 0.5r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle. If the radius of the secondary particle is 2.0 μm, the surface portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the surface of the secondary particle, and the center portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the center of the secondary particle.

[0083] Furthermore, if necessary, when the radius of the secondary particle is denoted as r, the region at which the distance from the surface of the secondary particle is 0 to 0.1r or 0 to 0.2r can be defined as the surface portion of the secondary particle, and the region at which the distance from the center of the secondary particle is 0 to 0.2r or 0 to 0.5r can be defined as the center portion of the secondary particle.

[0084] The lithium manganese oxide as defined in this application may be a lithium-rich lithium manganese oxide represented by the following chemical formula 1. The composition represented by the following chemical formula 1 can represent an average composition that reflects the composition of the barrier layer present on at least a portion of the surface of the lithium manganese oxide. [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd, and M2 does not overlap with M1. X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, and 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である。

[0085] The types of halogens that can be used as X are determined by referring to the periodic table, and can be F, Cl, Br and / or I, and preferably F.

[0086] A gradient may be formed in which the ratio of at least one selected from x and y in the chemical formula 1 changes from the surface of the primary particle toward the center of the primary particle.

[0087] Furthermore, a gradient may be formed in which the ratio of at least one selected from x and y in the chemical formula 1 changes from the surface of the secondary particle toward the center of the secondary particle.

[0088] Furthermore, the lithium-rich lithium manganese oxide represented by chemical formula 1 may further contain 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 other embodiments, the lithium manganese oxide may be represented by the following chemical formula 1-1. The composition represented by the following chemical formula 1-1 can represent the average composition that reflects the composition of the barrier layer present on at least a portion of the surface of the lithium manganese oxide. [Chemical formula 1-1] rLi2MnO 3-b″ X' b″ ·(1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, 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 oxide, 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 types of halogens that can be used as X are determined by referring to the periodic table, and can be F, Cl, Br and / or I, and preferably F.

[0091] In the aforementioned chemical formulas 1 and 1-1, if M1 is Ni, M2 may also contain Mn, and if M1 is Mn, M2 may also contain Ni. Furthermore, if M1 is Ni and Mn, M2 may be absent, or if present, it may be an element other than Ni and Mn.

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

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

[0094] If M1 is Ni and Mn, then M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, 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 oxide represented by chemical formula 1 or chemical formula 1-1 may selectively contain cobalt. When the lithium manganese oxide contains cobalt, the mole fraction of cobalt relative to the total number of moles of metal elements in the lithium manganese oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese oxide represented by chemical formula 1 may have a cobalt-free composition.

[0096] The Li / Metal molar ratio measured from the lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 may be greater than 1, preferably 1.1 to 1.6. When the Li / Metal molar ratio measured from the lithium manganese oxide is greater than 1, it is possible to form a lithium-rich lithium manganese oxide. Furthermore, in order for the lithium manganese oxide to appropriately form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solidly dissolved or composited, and at the same time to exhibit high capacity under high voltage operating conditions, the Li / Metal molar ratio of the lithium manganese oxide is preferably 1.2 to 1.6.

[0097] Furthermore, in order to properly form a solid solution in which the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group are in solid solution or composite, it is preferable that the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 is 50 mol% or more.

[0098] In order for the lithium manganese oxide to exhibit OLO characteristics that allow it to exhibit high capacity under high-voltage operating conditions, the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide is preferably 50 mol% or more and less than 80 mol%, and more preferably 55 mol% to 75 mol%. When the manganese content in the lithium manganese oxide exceeds 80 mol%, a phase transition may occur due to the movement of transition metals (especially manganese) within the lithium manganese oxide during conversion and / or operation of the lithium secondary battery. Such a phase transition forms a spinel phase, and this spinel phase, acting as an impurity in the lithium manganese oxide, can induce a decrease in charge / discharge capacity or voltage decay during the cycling of the lithium secondary battery.

[0099] 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 in solid solution or composite, it is preferable that the nickel content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 1-1 is less than 50 mol%.

[0100] When the nickel content in the lithium manganese oxide is 50 mol% or more, the C2 / m phase may not form sufficiently, or the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group may not form a sufficient solid solution, which can cause phase separation during conversion and / or operation of the lithium secondary battery.

[0101] Furthermore, as will be described later, in order to ensure that sufficient nickel is present on the surface of the lithium manganese-based oxide provided as core-shell particles in which a transition metal concentration gradient is formed within the particles, the nickel content 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 have a single-phase phase belonging to the R-3m space group.

[0103] On the other hand, lithium-rich lithium manganese oxides represented by chemical formula 1 or chemical formula 1-1 are rLi2MnO 3-b″ X' b″ Oxides of phases belonging to the C2 / m space group represented by (hereinafter referred to as "C2 / m phase") and (1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ The oxides of the phases belonging to the R-3m space group (hereinafter referred to as "R-3m phase") shown by exist as a solid solution or composite oxide. For example, the lithium manganese-based oxide may exist in a state in which the oxide of the C2 / m phase and the oxide of the 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 definition 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, obtained by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R-3m space group, and having the surface coated with the metal oxide having a phase belonging to the R-3m space group, does not fall under the definition of a solid solution as defined in this application.

[0106] In the lithium manganese oxide represented by the chemical formula 1-1, if r exceeds 0.7, then the C2 / m phase oxide Li2MnO is present in the lithium manganese oxide. 3-b″ X' b″ If the proportion of R-3m becomes excessively high, this can result in an excessive manganese content in the positive electrode active material, potentially leading to a decrease in discharge capacity. In other words, in order to sufficiently activate the C2 / m phase oxide, which has relatively high resistance, in the lithium manganese-based oxide and improve surface kinetics, it is preferable that the R-3m phase oxide be present in a predetermined proportion or higher.

[0107] The lithium manganese-based oxide as defined in this application exists as a core-shell particle in which the concentration of at least one transition metal constituting the lithium manganese-based oxide shows a gradient from the core to the shell. In this case, the elution of transition metals from the lithium manganese-based oxide can be suppressed or mitigated by making the content of a transition metal that is relatively less likely to dissolve in the region corresponding to the shell higher than that of other transition metals.

[0108] Furthermore, by forming the lithium manganese-based oxide as core-shell particles in which the concentration of at least one transition metal 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] If the concentrations of transition metals present in the shell (or surface) and core (or center) of any given particle are different, then the particle can be called a core-shell particle. That is, as a core-shell particle, the lithium manganese oxide may have different average compositions of the total metal elements constituting the lithium manganese oxide in the core and the shell. As a result, the ratio of the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group in the core may be different from the ratio of the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group in the shell.

[0110] The shell can occupy at least a portion of the surface of the core. That is, the shell may be partially present on the surface of the core, or it may occupy the entire surface of the core.

[0111] In this application, the total number of moles of metallic elements in the lithium manganese oxide is M 1 And the number of moles of nickel is M 2 When defined as such, M is calculated from the average composition of all metal elements in the core of the lithium manganese oxide. 2 / M 1 and M calculated from the average composition of all metallic elements within the shell of the lithium manganese oxide 2 / M 1 They may be different from each other.

[0112] It is well known that lithium-rich lithium-manganese oxides containing an excess of manganese have lower electrical conductivity than lithium-cobalt oxides or ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition containing a relatively excess of Ni. Furthermore, ternary lithium composite oxides also suffer from the problem that their electrical conductivity decreases as the manganese content increases.

[0113] While various reactions occur on the surface of the diverse types of positive electrode active materials mentioned above, the higher the Mn content in the positive electrode active material, the more the charge transfer and / or diffusion of lithium ions on the surface is hindered. This phenomenon can be called surface kinetics or a decrease in in-surface reaction kinetics.

[0114] As described above, the lithium manganese oxides defined in this application can improve the surface kinetics of lithium manganese oxides by forming a transition metal concentration gradient between the core and the shell. Such effects can be achieved through the transition metal concentration difference in the core and shell of primary particles, secondary particles, crystallites, and / or single particles, or through the transition metal concentration gradient formed between the core and the shell, as described later.

[0115] In one embodiment, the lithium manganese oxide among the positive electrode active material exists in at least one form selected from single primary particles and secondary particles formed by the aggregation of multiple primary particles, wherein the primary particles may be core-shell particles in which the concentration of at least one transition metal is gradient from the center of the primary particle toward the surface of the primary particle. The lithium manganese oxide existing in the form of secondary particles may be an aggregate of primary particles existing as core-shell particles.

[0116] If the primary particles exist as core-shell particles exhibiting a gradient in the concentration of at least one transition metal from the core to the shell, the surface kinetics of the primary particles and / or the secondary particles can be improved.

[0117] For example, the primary particle may exhibit a concentration gradient from the core to the shell in which at least one concentration selected from nickel and manganese is increased. More specifically, the primary particle may exhibit a concentration gradient from the core to the shell in which the concentration of nickel increases while the concentration of manganese decreases.

[0118] Furthermore, if the concentration of the transition metal shows a gradient from the core to the shell of the primary particle, it is possible to reduce abrupt changes in the concentration of the metal element between the core and the shell of the primary particle. By preventing abrupt changes in the concentration of the metal element within the primary particle, it is possible to prevent instability in the crystal structure of the primary particle.

[0119] When the region in which a transition metal concentration gradient exists among the primary particles that exist as core-shell particles as described above is called 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 thickness of the shell of the primary particles is less than 0.1 nm, it may be difficult to sufficiently improve the surface kinetics of the primary particles. On the other hand, if the thickness of the shell of the primary particles is greater 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 other embodiments, the primary particles may contain at least one crystallite. In this case, the crystallite may exhibit a concentration gradient of at least one transition metal from the center of the crystallite toward the surface of the crystallite, in the core-shell configuration described above.

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

[0122] If the primary particle contains multiple crystallites, the multiple crystallites constituting the primary particle may have the core-shell configuration described above. The core-shell crystallites can stabilize the crystal structure of the primary particle and at the same time contribute to improving the low electrical conductivity of the lithium manganese oxide.

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

[0124] In further embodiments, 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 toward the surface of the secondary particle.

[0125] For example, the secondary particles may exhibit a concentration gradient from the core to the shell in which at least one concentration selected from nickel and manganese is present. More specifically, the secondary particles may exhibit a concentration gradient from the core to the shell in which the concentration of nickel increases while the concentration of manganese decreases.

[0126] When the region in which a transition metal concentration gradient exists among the secondary particles that exist as core-shell particles as described above is called 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 thickness of the shell of the secondary particles is less than 0.1 nm, it may be difficult to sufficiently improve the surface kinetics of the secondary particles. On the other hand, if the thickness of the shell of the secondary particles is greater 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 aforementioned concentration gradients present within primary particles, secondary particles, and / or crystallites can suppress and / or mitigate phase transitions that occur due to unintended migration 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 oxide can be suppressed or mitigated. By suppressing or mitigating the dissolution of the transition metal from the lithium manganese oxide, it is possible to prevent the formation of impurities by the reaction of the dissolved transition metal with the electrolyte on the surface.

[0129] When the surface of the core-shell particles as defined in this application, 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 particles, the elution of transition metals from the lithium manganese oxide can be further suppressed or mitigated.

[0130] When the secondary particles exist as core-shell particles, the barrier layer can suppress or mitigate the elution of transition metals from the secondary particles by covering at least a portion of the surface of the secondary particles. Furthermore, by covering the surface of the secondary particles, the barrier layer can prevent side reactions between the surface of the secondary particles and the electrolyte.

[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, the elution of transition metals through the region covered by the barrier layer can be suppressed or mitigated. Therefore, the presence of the barrier layer on the surface of the secondary particles must be distinguished from the mere presence of the lithium manganese oxide and other oxides dispersed on the surface of the secondary particles.

[0132] Furthermore, grain boundaries may be defined between adjacent primary particles within the secondary particles, and the barrier layer may exist diffused along the grain boundaries from the surface of the secondary particles toward the center of the secondary particles. As the barrier layer diffuses toward the center of the secondary particles, the elements mainly contained in the barrier layer may exhibit a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles.

[0133] The barrier layer forms a gradient from the surface of the secondary particles toward the center of the secondary particles, thereby effectively suppressing or mitigating the elution of transition metals, mainly on the surface of the secondary particles.

[0134] Some 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 surface 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 suppress the elution of transition metals from the secondary particles. On the other hand, 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 suppress or mitigate the elution of transition metals from the primary particles by covering at least a portion of the surface of the primary particles. Furthermore, the barrier layer can prevent side reactions between the surface of the primary particles and the electrolyte by covering the surface of the primary particles. In this case, the barrier layer can cover at least a portion of the surface of the secondary particles by covering the surface of the primary particles present on 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 surface 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 suppress the elution of transition metals from the primary particles. On the other hand, 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, if a concentration gradient of a transition metal exists within the crystallites constituting the primary particles, the region where the transition metal concentration gradient exists may be adjacent to the surface of the crystallite. In this case, the barrier layer can cover at least a portion 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 contain 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, where 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 compound or an LBO (lithium borate) compound, non-limiting examples of the first oxide include B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, and Li2B8O 13 These are some examples. Furthermore, the first oxide may have a composition in which the borate-based compound or lithium borate-based compound described above 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 lithium manganese-based oxide core due to the diffusion and / or doping of the first oxide contained in the barrier layer.

[0144] Such a concentration gradient acts as a pathway for lithium ions to move within and between primary particles, thereby improving the transport / diffusion efficiency of lithium ions mediated by the primary particles.

[0145] In other embodiments, the barrier layer may further contain 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, where 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, 2 ≤ i ≤ 13, except when g and h are both 0.

[0146] A non-limiting example of the second oxide represented by the chemical formula 3 is 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 These are some examples.

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

[0148] In further embodiments, the barrier layer may contain a third oxide represented by the following chemical formula 4. [Chemical formula 4] Li j M5k (P l O m ) n Wherein, M5 is at least one selected from the group consisting of 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 0 at the same time.

[0149] As non-limiting examples of the third oxide represented by Chemical Formula 4, 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, for example.

[0151] It is known that a decrease in charge / discharge capacity or voltage decay during the cycling of lithium secondary batteries using OLO is induced by a phase transition due to the migration of transition metals in lithium manganese oxides. For example, in layered crystalline lithium manganese oxides, if a phase transition is induced by the unintended migration of transition metals, a whole- and / or partial spinel or similar crystalline structure may be generated within the lithium manganese oxide.

[0152] However, unlike the spinel phase formed by a phase transition due to the migration of transition metals in the lithium manganese oxide, if the spinel phase induces crystal growth and particle growth of the primary particles constituting the lithium manganese oxide, and simultaneously forms on the surface of the primary and / or secondary particles, such a spinel phase not only contributes to the surface stabilization of the lithium manganese oxide, but can also act as a two-dimensional and / or three-dimensional pathway for the diffusion of lithium ions within the lithium manganese oxide. The spinel phase present on the surface of the primary and / or secondary particles can be represented by the chemical formula 4.

[0153] This allows the lithium manganese oxide to exhibit an appropriate level of electrical conductivity even when the surface of the primary particles and / or secondary particles is covered with the barrier layer, by ensuring that a spinel phase compound is present in the barrier layer, which is intended to suppress the elution of transition metals from the primary particles and / or secondary particles.

[0154] Furthermore, if necessary, the barrier layer may contain at least two oxides selected from the first to third oxides in order to effectively suppress or mitigate the elution of transition metals from the lithium manganese oxide while simultaneously improving the surface kinetics of the lithium manganese oxide.

[0155] Generally, ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition containing a relatively excess amount of Ni experience rapid thermal gravitational loss from around 700°C, while lithium-rich lithium-manganese oxides do not experience thermal gravitational loss up to around 900°C. As a result, no thermal gravitational loss occurs in the 400°C to 700°C range during thermogravimetric analysis of lithium-manganese oxides that have not undergone any surface modification.

[0156] Furthermore, as defined in this application, the lithium manganese 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 gravimetric loss at around 500°C, and thermal gravimetric loss to the lithium manganese oxide can be confirmed at 700°C.

[0157] In this case, the thermogravimetric loss confirmed by thermogravimetric analysis of the lithium manganese oxide may be caused by the components constituting the barrier layer. As a result, the more of the barrier layer present in the lithium manganese oxide increases, the more the thermogravimetric loss confirmed by thermogravimetric analysis of the lithium manganese oxide can increase.

[0158] When analyzing the thermal weight loss generated by heat-treating the lithium manganese oxide under an inert gas atmosphere, the difference yx between the weight loss rate x of the lithium manganese oxide at 400°C and the weight loss rate y of the lithium manganese 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 oxide.

[0159] The fact that the weight loss rate difference yx is less than 0.03 wt% means that a barrier layer for suppressing or mitigating the elution of transition metals was insufficiently formed on the surface of the lithium manganese oxide.

[0160] Furthermore, the content of the main constituent elements of the barrier layer, calculated based on the total metallic elements excluding lithium present in the lithium manganese oxide, is preferably greater than 0.1 mol% and less than 5 mol%. Here, if the first oxide is present in the barrier layer, the main constituent elements of the barrier layer are boron (B) and M3; if the second oxide is present in the barrier layer, the main constituent element of the barrier layer is M4; and if the third oxide is present in the barrier layer, the main constituent element of the barrier layer is M5. Also, if any combination of the first to third oxides 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 fact that the content of the main constituent elements of the barrier layer is less than 0.1 mol% means that a barrier layer is not adequately formed on the surface of the lithium manganese oxide to suppress or mitigate the elution of transition metals. As a result, it is difficult to effectively prevent the acceleration of the life degradation of the lithium secondary battery due to the deposition of impurities on the positive and / or negative electrodes by transition metals eluted from the lithium manganese oxide.

[0162] On the other hand, if the content of the main constituent elements of the barrier layer is 5 mol% or more, it can actually reduce the surface kinetics of the lithium manganese oxide, which may result in a decrease in electrochemical properties compared to when the main constituent elements of the barrier layer are present in appropriate amounts.

[0163] Furthermore, in order to effectively suppress or mitigate the elution of transition metals from the surface of the lithium manganese oxide within a range that does not reduce the surface kinetics of the lithium manganese oxide, it is more preferable that the content of the main constituent elements of the barrier layer, calculated based on the total metal elements excluding lithium present in the lithium manganese 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-ion rechargeable battery According to one aspect of the present invention, an electrochemical element is provided that uses a positive electrode active material containing a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-solved or composited. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0165] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. The lithium secondary battery may further selectively include a battery container housing the electrode assembly of the positive electrode, the negative electrode and the separator, and a sealing member for sealing 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. Here, the positive electrode active material layer may contain lithium manganese-based oxides according to the various embodiments of the present invention described above as the positive electrode active material.

[0167] Therefore, a detailed explanation of lithium manganese oxides will be omitted, and only the remaining components not mentioned above will be described below. Also, for convenience, the lithium manganese oxides mentioned above will be referred to as the positive electrode active material below.

[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, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric, etc.

[0169] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0170] In this case, the positive electrode active material may be present in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When present within this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0171] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the positive electrode active material layer.

[0172] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15 wt% relative to the total weight of the positive electrode active material layer.

[0173] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except for the use of the positive electrode active material. Specifically, it may be manufactured by coating a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0174] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0175] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[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, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0178] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and optionally a binder, to the negative electrode current collector.

[0179] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0180] The aforementioned negative electrode active material may be present in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0181] The binder may be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0182] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0183] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0184] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0185] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, and it is especially preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0186] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0188] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0189] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0190] In the present invention, when the electrolyte used is a solid electrolyte, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, oxide-based solid electrolyte, nitride-based solid electrolyte, or halogen-based solid electrolyte may be used, and preferably a sulfide-based solid electrolyte may be used.

[0191] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S may be used. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (where X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (Here, m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MOq (Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In.)

[0192] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous or crystalline, or a mixture of amorphous and crystalline materials.

[0193] As a material for oxide-based solid electrolytes, Li7La3Zr2O 12 Li 7-x La3Zr 1-x Nb x O 12 Li 7-3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0194] The aforementioned solid electrolyte may be arranged as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Furthermore, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0195] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 wt% relative to the total weight of the electrolyte.

[0196] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0197] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

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

[0199] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0200] Furthermore, for lithium secondary batteries as defined above, it is preferable to perform at least one formation cycle within a formation voltage range where the upper limit voltage fv1 is 4.4V or higher, relative to the positive electrode potential, in order to activate the positive electrode active material containing lithium-rich lithium manganese oxide.

[0201] Here, "formation" refers to what is also known as "activation," and it means the process of activating a lithium secondary battery in its initial discharged state by repeatedly charging and discharging it.

[0202] If the upper limit voltage fv1 of the formation voltage range for the lithium secondary battery is less than 4.4V, the positive electrode active material, particularly the phase 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 where the upper limit voltage fv1 is 4.4V or higher with respect to the positive electrode potential, it is possible to induce activation of the positive electrode active material containing lithium-rich lithium manganese oxide.

[0203] Furthermore, by applying an upper limit voltage fv1 of the initial cycle's chemical formation voltage range to 4.4V or higher during the chemical formation of the lithium secondary battery, the problem of insufficient activation of the positive electrode active material can be prevented in advance.

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

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

[0206] Furthermore, selectively increasing the lower limit voltage fv2 of the conversion voltage range, or setting the lower limit voltage fv2 of the conversion voltage range to 2.5V or higher, preferably 2.5V, can positively improve the stability of the lithium secondary battery operating at high temperatures.

[0207] For example, after the lithium secondary battery has undergone 6 cycles of chemical conversion at 25°C, a chemical conversion voltage range of 2.5V to 4.6V, and a current of 0.2C / 0.2C, and then 500 cycles of charge-discharge at 45°C, an operating voltage range of 2.5V to 4.6V, and a current of 1C / 1C, the volume change rate of the full cell measured is at a level of 6% or less, which demonstrates that it is possible to mitigate gas generation from the lithium secondary battery, particularly from the positive electrode.

[0208] Furthermore, in order to exhibit the high capacity characteristics of the lithium manganese oxide, it is preferable that the lithium secondary battery operates within an operating voltage range where the upper limit voltage ov1 is greater than 4.3V and 5.0V or less, greater than 4.3V and 4.8V or less, or greater than 4.3V and 4.6V or less.

[0209] In order to improve the charge and discharge efficiency of the lithium secondary battery and to enhance the characteristics related to the capacity and lifespan of the lithium secondary battery, it is preferable that after chemical formation, the lithium secondary battery operates within an operating voltage range of 2.0V or higher, preferably between 2.0V and less than 3.0V.

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

[0211] A difference of ov1-ov2 between the upper and lower limits of the operating voltage range means that the upper limit ov1 is too low or the lower limit ov2 is too high. If the upper limit ov1 is too low or the lower limit ov2 is too high, the discharge capacity of the lithium secondary battery may decrease excessively.

[0212] On the other hand, a difference of ov1-ov2 between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range of ov1 is 2.6V or more, which means that either 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 and discharge efficiency of the lithium secondary battery may decrease.

[0213] Furthermore, if the upper limit voltage ov1 of the operating voltage range is too high, the capacity retention rate and discharge average voltage retention rate of the lithium secondary battery may decrease sharply. Also, if the lower limit voltage ov2 of the operating voltage range is too low, the discharge average voltage and discharge average voltage retention rate of the lithium secondary battery may decrease. The lower limit voltage ov2 of the operating voltage range can also affect the stability of the lithium secondary battery, and the stability of the lithium secondary battery can be confirmed by indicators related to gas generation within the lithium secondary battery, such as the volume change rate.

[0214] When setting the operating voltage range of the lithium secondary battery as defined in this application, the appropriate lower voltage limit ov2 can be changed by the upper voltage limit ov1. Conversely, when setting the operating voltage range of the lithium secondary battery as defined in this application, the appropriate upper voltage limit ov1 can be changed by the lower voltage limit ov2.

[0215] In one embodiment, when the lithium secondary battery is in operation, if the upper limit voltage ov1 of the operating voltage range is 4.6V or higher (for example, 4.6V or higher and 5.0V or lower, or 4.6V or higher and 4.8V or lower), it is preferable to set the lower limit voltage ov2 to be within the range greater than 2.0V and less than 3.0V (for example, 2.5V ± 0.25V).

[0216] Specifically, when the upper limit voltage ov1 of the operating voltage range is 4.6V or higher, the lower limit voltage ov2 is set to be within a range greater than 2.0V and less than 3.0V, preferably within a range of 2.5V ± 0.25V (for example, about 2.5V). This ensures stable capacity and life characteristics of the lithium secondary battery while simultaneously guaranteeing stability (low volume change rate).

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

[0218] For example, if the lithium secondary battery prepared by the method defined in this application (e.g., Manufacturing Example 2 or Manufacturing Example 3) is subjected to at least one formation cycle in a formation voltage range where the upper limit voltage fv1 is 4.4V or higher, and then charged and discharged within an operating voltage range where the upper limit voltage ov1 is 4.6V or higher (e.g., 4.6V or higher and 5.0V or lower, or 4.6V or higher and 4.8V or lower) and the lower limit voltage ov2 is greater than 2.0V and less than 3.0V, 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 rate) may be at least 90%, preferably 91% or higher.

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

[0220] In other embodiments, when the lithium secondary battery is in operation, if the upper limit voltage ov1 of the operating voltage range is 4.5V or more and less than 4.6V, 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 4.5V or more and less than 4.6V, the lower limit voltage ov2 is set to be within the range of 2.0V or more and less than 3.0V, preferably within the range of 2.0V to 2.5V. This ensures stable capacity and life characteristics of the lithium secondary battery while simultaneously guaranteeing stability (low volume change rate).

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

[0223] For example, if the lithium secondary battery prepared by the method defined in this application (e.g., Manufacturing Example 2 or Manufacturing Example 3) is subjected to at least one formation cycle in a formation voltage range where the upper limit voltage fv1 is 4.4V or higher, and then charged and discharged within an operating voltage range where the upper limit voltage ov1 is 4.5V or higher and the lower limit voltage ov2 is 2.0V or higher and less than 3.0V, 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 rate) may be at least 92.5%, preferably 95% or higher.

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

[0225] In further embodiments, when the lithium secondary battery is in operation, if the upper limit voltage ov1 of the operating voltage range is less than 4.5V (for example, greater than 4.3V but less than 4.5V), 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.

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

[0227] When the lower limit voltage ov2 of said operating voltage range is less than 2.0 V, it is difficult to ensure sufficient charge-discharge efficiency of said lithium secondary battery, and there is a risk that the stability of said lithium secondary battery may decrease. On the other hand, when the lower limit voltage ov2 of said operating voltage range is 3.0 V or higher, the discharge capacity and capacity retention rate of said lithium secondary battery may decrease.

[0228] For example, after subjecting said lithium secondary battery prepared by the method defined in the present application (e.g., Production Example 2 or Production Example 3) to at least one cycle of formation in a formation voltage range where the upper limit voltage fv1 is 4.4 V or higher, when charging and discharging is performed 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 said 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 said lithium secondary battery (discharge capacity retention rate) may be at least 95.5% or more, preferably 96% or more.

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

[0230] Hereinafter, the present invention will be described in more detail by way of examples. However, these examples are intended to illustrate the present invention, and are not to be construed as limiting the scope of the present invention by these examples.

[0231] Manufacturing Example 1. Manufacturing of positive electrode active material Example 1 (a) Production of precursor Into a reactor, an aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60, NaOH and NH4OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while introducing N2 gas into the reactor. After completion of the reaction, washing and dehydration were performed to obtain Ni having an average particle diameter of 3.5 μm0.4 Mn 0.6 (OH)2 precursor was obtained.

[0232] (b) Precursor coating In step (a), an aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, the NiSO4·6H2O was weighed to a concentration of 5 mol% before being added. After the reaction was complete, the precursor was washed and dehydrated, and then dried at 150°C for 14 hours to obtain the coated precursor.

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

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

[0235] Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min for 8 hours while maintaining a temperature of 900°C, and then furnace-cooled to obtain a lithium-rich lithium manganese oxide.

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

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

[0238] Example 2 The cathode active material was prepared in the same manner as in Example 1, except that H3BO3 weighed at 2.0 mol% in step (e) was used.

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

[0240] Example 4 The cathode active material was manufactured in the same manner as in Example 1, except that the third heat treatment was performed using H3BO3 weighed at 2.0 mol% in step (e) above, and the final temperature reached was 300°C.

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

[0242] (f) Third heat treatment (barrier layer formation) The lithium manganese oxide obtained in step (e) was heat-treated in a calcination furnace at a rate of 4.4°C per minute up to 400°C while maintaining an O2 atmosphere for 8 hours, then classified and crushed to obtain a final product (average particle size 3.5 μm) on which a barrier layer containing a Si-containing compound was formed on the surface.

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

[0244] (f) Third heat treatment (barrier layer formation) The lithium manganese-based oxide obtained in step (e) was heated to 400°C at a rate of 4.4°C per minute in a firing furnace while maintaining an O2 atmosphere, heat-treated for 8 hours, classified and crushed, to obtain a final product (average particle diameter: 3.5 μm) having a barrier layer containing a P-containing compound formed on the surface.

[0245] Comparative Example 1 (a) Production of precursor An aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60, NaOH and NH4OH were charged into a reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was allowed to proceed while introducing N2 gas into the reactor. After completion of the reaction, the product was washed and dehydrated to obtain Ni with an average particle diameter of 3.5 μm 0.4 Mn 0.6 (OH)2 precursor.

[0246] (b) First heat treatment After heating a firing furnace in an O2 atmosphere at a rate of 2°C / min, 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 an oxide precursor.

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

[0248] Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min for 8 hours while maintaining a temperature of 900°C. After furnace cooling, classification, and crushing, the final product, lithium-rich lithium manganese oxide (average particle size 3.5 μm), was obtained.

[0249] Unlike the lithium manganese oxide in Example 1, it was confirmed that the lithium manganese oxide in Comparative Example 1, without a precursor coating using Ni, did not form a transition metal gradient within the particles.

[0250] Comparative Example 2 (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction proceeded while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated to obtain Ni with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

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

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

[0253] Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min for 8 hours while maintaining a temperature of 900°C, and then furnace-cooled to obtain a lithium-rich lithium manganese oxide.

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

[0255] Unlike the lithium manganese oxide in Example 1, the lithium manganese oxide in Comparative Example 2, without a precursor coating using Ni, did not result in the formation of a transition metal gradient within the particles.

[0256] Comparative Example 3 (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction proceeded while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated to obtain Ni with an average particle size of 3.5 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0257] (b) Precursor coating In step (a), an aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, the NiSO4·6H2O was weighed to a concentration of 5 mol% before being added. After the reaction was complete, the precursor was washed and dehydrated, and then dried at 150°C for 14 hours to obtain the coated precursor.

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

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

[0260] Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min for 8 hours while maintaining a temperature of 900°C. After furnace cooling, classification, and crushing, the final product, lithium-rich lithium manganese oxide (average particle size 3.5 μm), was obtained.

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

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

[0263] (b) Precursor coating In step (a), an aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, the NiSO4·6H2O was weighed to a concentration of 5 mol% before being added. After the reaction was complete, the precursor was washed and dehydrated, and then dried at 150°C for 14 hours to obtain the coated precursor.

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

[0265] (d) Second heat treatment The oxide precursor obtained in step (c), LiOH (Li / Metal molar ratio = 1.25), which is a lithium raw material, and WO3 weighed to have a metallic elemental W content of 1.0 mol% (excluding lithium from the precursor) were mixed to prepare the mixture.

[0266] Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min for 8 hours while maintaining a temperature of 900°C. After furnace cooling, classification, and crushing, the final product, lithium-rich lithium manganese oxide (average particle size 3.5 μm), was obtained.

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

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

[0269] Reference example 2 The cathode active material was manufactured in the same manner as in Example 1, except that the third heat treatment was performed using H3BO3 weighed at 2.0 mol% in step (e) above, and the final temperature reached was 600°C.

[0270] Reference example 3 The cathode active material was manufactured in the same manner as in Example 1, except that the third heat treatment was performed using H3BO3 weighed at 2.0 mol% in step (e) above, and the final temperature reached was 700°C.

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

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

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

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

[0275] Manufacturing Example 2: Manufacturing of Lithium-ion Secondary Batteries (Half-Cells) A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced by Production Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0276] A half-cell was manufactured using a lithium foil as the counter electrode to the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 2:4:4, with LiPF6 present at a concentration of 1.15 M.

[0277] Manufacturing Example 3: Manufacturing of Lithium-ion Rechargeable Batteries (Full Cells) A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced by Production Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0278] A full cell was manufactured using a graphite electrode as the counter electrode to the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 2:4:4, with LiPF6 present at a concentration of 1.15 M.

[0279] Experimental Example 1. XPS Analysis of Cathode Active Material XPS analysis was performed on lithium manganese-based oxides selected from each positive electrode active material produced according to Production Example 1, and the content of the target element contained in the lithium manganese-based oxide was measured.

[0280] Specifically, using an XPS depth profile analysis method (ion energy 2000 eV, spot size 200 μm), the change in the content of the target element was measured from the surface of the lithium manganese oxide (secondary particles) toward the center of the lithium manganese oxide (secondary particles) while increasing the etching time on the surface of the lithium manganese oxide (secondary particles). 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 the total elements excluding lithium in the aforementioned lithium manganese oxide.

[0282] Referring to the results in Table 2, it can be confirmed that the target element content on the surface of the lithium manganese oxide (secondary particles) produced in Examples 1, 2, 5, and 6 is 20 at% or more. The fact that the target element content on the surface of the lithium manganese oxide (secondary particles) is 20 at% or more, derived from the raw material used during the third heat treatment, is presumed to be due to the formation of a barrier layer on the surface of the lithium manganese oxide (secondary particles).

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

[0284] The above results are due to the fact that, instead of the target elements derived from the raw materials used in the second heat treatment step existing as a barrier layer on the surface of the lithium manganese oxide (secondary particles), most of them were doped into the lithium manganese oxide (particularly the primary particles). Furthermore, the decrease in the target element content as the etching time increases is also expected to be due to the doping and diffusion of the target elements from the surface to the center of the lithium manganese oxide.

[0285] Therefore, it can be confirmed that the surface of the lithium manganese oxide (secondary particles) according to Comparative Example 4 does not have a physical barrier that can substantially act as a barrier layer.

[0286] [Table 3] *The target element content is calculated by setting the sum of the Ni and Mn content in the lithium manganese oxide (excluding lithium) to 100.

[0287] Referring to the results in Table 3, it can be confirmed that when lithium manganese oxide is produced using the lithium manganese oxide method in Example 1, a gradient is formed in which the concentration of Ni increases from the center to the surface and the concentration of Mn decreases.

[0288] Experimental Example 2. Thermogravimetric Analysis (TGA) of Cathode Active Material Thermogravimetric analysis was performed on lithium manganese-based oxides selected from each positive electrode active material produced by Production Example 1 to confirm whether a barrier layer was formed at an appropriate level on the surface of the primary and / or secondary particles constituting the lithium manganese-based oxide.

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

[0290] [Table 4]

[0291] Referring to the results in Table 4 above, it can be confirmed that the lithium manganese oxide in Comparative Example 3 exhibits virtually no thermal gravimetric loss at 400°C and 700°C, taking into account the margin of error. In other words, it is consistent with the trend of thermogravimetric analysis results for typical lithium manganese oxides, where no thermal gravimetric loss occurs up to approximately 900°C.

[0292] On the other hand, it can be confirmed that the lithium manganese oxides from Examples 1, 2, and 6 exhibited thermal gravimetric loss from approximately 500°C to 600°C. Furthermore, it can be confirmed that the thermal gravimetric loss observed in the lithium manganese oxide increased as the content of the barrier layer present in the lithium manganese oxide increased.

[0293] Experimental Example 3. Evaluation of the electrochemical properties of lithium secondary batteries (half-cells). For lithium secondary batteries (half-cells) manufactured in Manufacturing Example 2, the initial charge capacity, initial discharge capacity, initial reversibility efficiency, and rate characteristics (discharge capacity ratio; rate capability (C-rate)) were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 2.0V to 4.6V and a discharge rate of 0.1C to 5.0C. The measurement results are shown in Table 5 below.

[0294] [Table 5]

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

[0296] In the cases of Reference Examples 1 to 3, where the third heat treatment temperature for forming the barrier layer is high, it can be confirmed that electrochemical properties such as initial discharge capacity and discharge capacity ratio actually decreased. This result is presumed to be because, as the third heat treatment temperature becomes excessively high, damage occurs to the lithium manganese oxide, such as the disruption of the transition metal concentration gradient within the particles.

[0297] In the case of Reference Examples 4 and 5, although they generally exhibit better electrochemical properties than Comparative Examples 1 to 4, it can be confirmed that the improvement in rate characteristics is somewhat less than in the Examples due to either too little or too much raw material forming the barrier layer.

[0298] Experimental Example 4. Evaluation of the electrochemical properties of a lithium secondary battery (full cell). Lithium secondary batteries (full cells) manufactured in Manufacturing Example 3 using the positive electrode active materials from Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. Following this, 500 charge-discharge experiments were conducted at 25°C, a voltage range of 2.0V to 4.6V, and 1C / 1C. Through these charge-discharge experiments, the initial (1st cycle) discharge capacity and the ratio of the discharge capacity 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 concentration of transition metals shows a gradient from the center to the surface of the particles. However, in Comparative Examples 3 and 4, where there is no barrier layer on the surface of the particles, it can be confirmed that the cycle capacity retention rate decreases sharply. This result is presumed to be because, as the transition metals leach out from the lithium manganese oxide, an abnormal resistance phenomenon occurs at the negative electrode, which accelerates the degradation of the lithium secondary battery's lifespan.

[0301] In Comparative Example 2, where the concentration of transition metals does not show a gradient from the center to the surface of the particles, but a barrier layer is formed on the surface of the particles, the abnormal resistance phenomenon that occurred in Comparative Example 3 is reduced, confirming that the cycle capacity retention rate is improved compared to Comparative Example 3.

[0302] On the other hand, in Example 2, where the concentration of the transition metal shows a gradient from the center to the surface of the particles, and a barrier layer is formed on the surface of the particles, it can be confirmed that a better cycle capacity retention rate is observed than in Comparative Example 2 by preventing the elution of the transition metal from the lithium manganese oxide and improving electrochemical properties such as the surface kinetics of the particles.

[0303] Experimental Example 5. Experiment on transition metal elution Using the positive electrode active materials from Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the lithium secondary battery (full cell) manufactured in Manufacturing Example 3 was subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. After that, the full cell was stabilized by 2 cycles of charge and discharge at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. Next, after disassembling the full cell, the negative electrode was washed with diethyl carbonate solvent, vacuum-dried at 60°C, and then recovered.

[0304] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the Ni and Mn content of the separated negative electrode active material was measured by ICP analysis.

[0305] Furthermore, lithium secondary batteries (full cells) manufactured in Manufacturing Example 3 using the positive electrode active materials from Example 2, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. Following this, 500 charge-discharge cycles were performed at 25°C, a voltage range of 2.0V to 4.6V, and 1C / 1C. Next, each full cell was stabilized by 2 charge-discharge cycles at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. After disassembling the full cells, the negative electrode was washed with diethyl carbonate solvent, vacuum-dried at 60°C, and then recovered.

[0306] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the Ni and Mn content of the separated negative electrode active material was measured by ICP analysis. The measurement results are shown in Table 7 below.

[0307] [Table 7]

[0308] Referring to the results in Table 7 above, it can be confirmed that, as predicted in Experimental Example 4, the rapid deterioration of lifespan in Comparative Examples 3 and 4 was due to an increase in the content of transition metals deposited in the negative electrode active material after chemical conversion or after 500 charge-discharge cycles.

[0309] Furthermore, in Comparative Example 2, in which the barrier layer was formed in the same manner as in Example 2, it can be confirmed that the content of transition metals eluted on the negative electrode side was higher than in Example 2. This result is presumed to be because, in the lithium manganese oxide of Example 2, a concentration gradient was formed in which the content of transition metals that are relatively less likely to elute was higher than that of other transition metals in the region corresponding to the surface (shell) of the particles, whereas in the lithium manganese oxide of Comparative Example 2, no concentration gradient of transition metals was formed from the center of the particles toward the surface.

[0310] Experimental Example 6. Evaluation of the characteristics of a lithium secondary battery (full cell) under changes in operating conditions. For lithium secondary batteries (full cells) manufactured in Manufacturing Example 3 using the positive electrode active material from Example 1, a conversion process was completed over 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). After that, 300 charge-discharge experiments were performed at 25°C and 1C / 1C.

[0311] Through the aforementioned charge-discharge experiments, the discharge capacity after 300 charge-discharge cycles, the ratio of the discharge capacity after 300 charge-discharge cycles to the initial discharge capacity (capacity retention), the average discharge voltage after 300 charge-discharge cycles, and the ratio of the average discharge voltage after 300 charge-discharge cycles 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 by converting the ratio of the volume after 300 charge-discharge cycles to the initial volume (before charge-discharge) into a percentage.

[0312] The operating voltage range during charging and discharging of the lithium secondary battery (full cell) and the results of the charging and discharging experiments are shown in Table 8 below. In Table 8 below, full cells with different operating voltage ranges during charging and discharging 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 confirmed that even when using the same lithium manganese oxide as the positive electrode active material, the characteristics related to capacity and lifespan change significantly depending on the operating voltage range of the lithium secondary battery (full cell).

[0315] Specifically, in the case of L1, although the characteristics related to capacity and lifespan were measured to be good, it showed a volume change rate of 0.7% despite 300 charge-discharge cycles, confirming that the stability of the lithium secondary battery deteriorated sharply.

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

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

[0318] In the case of L4 and L5, which have a lower upper voltage limit than L1, we were able to confirm that they showed better capacity retention and voltage retention than L1 and L2, and that the stability of the lithium secondary battery was also improved. On the other hand, in the case of L6, which has the same upper voltage limit as L4 and L5 but a higher lower voltage limit, we were able to confirm that the discharge capacity after 300 charge / discharge cycles (168.1 mAh / g) was somewhat insufficient as the lower voltage limit of the operating voltage range increased, and that the capacity retention rate was also reduced compared to L4 and L5.

[0319] In the case of L7 and L8, which have a lower upper voltage limit than L4, the discharge capacity decreased slightly compared to L4, but it was confirmed that they showed improved levels of capacity retention and voltage retention 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, it was confirmed that the discharge capacity (160.3 mAh / g) and capacity retention rate decreased after 300 charge-discharge cycles.

[0320] Experimental Example 7. Evaluation of the characteristics of lithium secondary batteries (full cells) under changes in chemical conversion conditions. A lithium secondary battery (full cell) manufactured in Manufacturing Example 3 using the positive electrode active material from Example 1 underwent a 6-cycle conversion process at 25°C and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100). After that, 500 charge-discharge experiments were performed at 25°C or 45°C and 1C / 1C.

[0321] Through the aforementioned charge-discharge experiments, the discharge capacity after 500 charge-discharge cycles, the ratio of the discharge capacity after 500 charge-discharge cycles to the initial discharge capacity (capacity retention), the average discharge voltage after 500 charge-discharge cycles, and the ratio of the average discharge voltage after 500 charge-discharge cycles 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 by converting the ratio of the volume after 500 charge-discharge cycles to the initial volume (before charge-discharge) into a percentage.

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

[0323] [Table 9] *fv1: Upper limit voltage of the chemical conversion voltage range *fv2: Lower limit voltage of the chemical conversion 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 above, it can be confirmed that even when using the same lithium manganese oxide as the positive electrode active material, the volume change rate of the lithium secondary battery after its lifespan (500 charge / discharge cycles) can change depending on the voltage range during chemical formation, the operating temperature, and the operating voltage range for the lithium secondary battery (full cell).

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

[0326] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A lithium secondary battery using a positive electrode active material containing a lithium manganese oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are in solid solution or composite form, The lithium secondary battery operates in an operating voltage range where the upper limit voltage fv1 is 4.4V or more and 4.75V or less with respect to the positive electrode potential, and after undergoing at least one cycle of formation in a formation voltage range where the lower limit voltage fv2 is greater than 2.0V and less than 3.0V, the upper limit voltage ov1 is greater than 4.3V, and A lithium secondary battery in which, when the lithium secondary battery is in operation, the difference between the upper limit voltage ov1 and the lower limit voltage ov2 of the operating voltage range ov1 - ov2 is set to be greater than 1.6V and less than 2.6V.

2. The lithium secondary battery according to claim 1, wherein the initial cycle during the formation of the lithium secondary battery is performed within a formation voltage range where the upper limit voltage fv1 is 4.4V or higher.

3. The lithium secondary battery according to claim 1, wherein when the lithium secondary battery is in operation, the upper limit voltage ov1 of the operating voltage range is set to be within a range greater than 4.3V and less than or equal to 5.0V.

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

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

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

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

8. 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 shows a gradient from the core to the shell.

9. The lithium secondary battery according to claim 8, wherein the lithium manganese 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.

10. The lithium manganese-based oxide is represented by the following chemical formula 1, the lithium secondary battery according to claim 1. [Chemical formula 1] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 b (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd, and M2 does not overlap with M1. X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, (0 < a ≤ 0.7, 0 ≤ b ≤ 0.1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < x + y ≤ 1)

11. The lithium manganese oxide is represented by the following chemical formula 1-1, as described in claim 1, for the lithium secondary battery. [Chemical formula 1-1] rLi ２ MnO ３－ｂ″ X′ ｂ″ ・(1-r)Li ａ′ M1 ｘ′ M2 ｙ′ O ２－ｂ′ X ｂ′ (Here, M1 is at least one selected from Ni and Mn. M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, 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 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)

12. The lithium secondary battery according to claim 8, wherein a barrier layer exists that covers at least a portion of the surface of the core-shell particles.

13. The aforementioned lithium manganese oxide exists as secondary particles formed by the aggregation of multiple primary particles. The lithium secondary battery according to claim 12, wherein the barrier layer covers at least a portion of the surfaces of the primary particles and the secondary particles.

14. A grain boundary is defined between adjacent primary particles. The lithium secondary battery according to claim 12, wherein the barrier layer exists in a diffused state along the grain boundary from the surface of the secondary particle toward the center of the secondary particle.

15. The lithium secondary battery according to claim 12, 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 (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. (0 ≤ c ≤ 8, 0 < d ≤ 8, 0 ≤ e ≤ 8, 2 ≤ f ≤ 13)

16. The lithium secondary battery according to claim 12, wherein the barrier layer comprises 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. (0 ≤ g ≤ 8, 0 ≤ h ≤ 8, 2 ≤ i ≤ 13, excluding the case where g and h are both 0.)

17. The lithium secondary battery according to claim 12, wherein the barrier layer comprises a third oxide represented by the following chemical formula 4. [Chemical formula 4] Li ｊ M5 ｋ (P ｌ O ｍ ) ｎ (Here, M5 is at least one selected from Ni, Mn, Co, Al, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd. (The conditions are 0 ≤ j ≤ 10, 0 ≤ k ≤ 8, 0 < l ≤ 4, 0 < m ≤ 10, and 0 < n ≤ 13, excluding the case where j and k are both 0.)

Images