Positive electrode active material, positive electrode and lithium secondary battery

Abstract

To provide a positive electrode active material that can prevent abrupt degradation in battery performance due to side reactions in an initial battery reaction under a high-voltage condition by reducing a specific surface area of a lithium manganese-based oxide.SOLUTION: A positive electrode active material comprises a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved or complexed. The lithium manganese-based oxide comprises a secondary particle formed by aggregating a plurality of primary particles. The lithium manganese-based oxide comprises at least one selected from tungsten, molybdenum and niobium as a dopant. At least some of oxygen present in the lithium manganese-based oxide is substituted with halogen. An interparticle porosity between the primary particles, measured from a cross-sectional SEM image of the secondary particle, is 10% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cathode active material, a cathode, and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material including a lithium-excess lithium-manganese-based oxide, which can prevent a decrease in the electrochemical characteristics of a lithium secondary battery, including rate characteristics, due to the excess lithium and manganese present in the lithium-manganese-based oxide, by inducing growth of primary particles constituting the lithium-manganese-based oxide, and can reduce side reactions between the lithium-manganese-based oxide and an electrolyte during high-voltage operation. The present invention also relates to a cathode active material, a cathode, and a lithium secondary battery including the same.

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

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

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

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

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

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

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

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

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

[0011] Furthermore, the decrease in charge / discharge capacity or voltage decay during charge / discharge cycles of a lithium secondary battery using OLO can be caused by a phase transition due to the migration of transition metals in the lithium manganese-based oxide. For example, if a phase transition is induced by the unintended migration of transition metals in a layered crystalline lithium manganese-based oxide, a spinel or similar crystalline structure may be formed entirely and / or partially within the lithium manganese-based oxide.

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

[0013] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is playing a role as a market driver, and as a result, the demand for positive electrode active materials used in lithium secondary batteries is also continuously increasing.

[0014] For example, lithium secondary batteries using lithium iron phosphate (LFP) have traditionally been used primarily for safety reasons, but recently there has been a trend toward the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP.

[0015] In addition, nickel-based lithium composite oxides, which are currently mainly used as positive electrode active materials in high-capacity lithium secondary batteries, essentially contain ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only unstable in supply and demand but is also excessively expensive compared to other raw materials, so a new positive electrode active material with a reduced or eliminated cobalt content is needed.

[0016] Considering these various circumstances, lithium-excess lithium manganese-based oxides can meet the aforementioned market expectations, but they still have limitations in that their electrochemical properties and stability are insufficient as an alternative to commercially available ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA)-based ternary lithium composite oxides.

[0017] For example, as mentioned above, if a transition metal in a lithium manganese-based oxide moves in an unintended direction, and a spinel or similar crystalline structure is formed entirely and / or partially in the lithium manganese-based oxide, a decrease in charge / discharge capacity or voltage decay may occur during charge / discharge cycling of a lithium secondary battery using OLO.

[0018] However, compared to other types of commercially available positive electrode active materials, conventional lithium-excess lithium-manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability. However, the present inventors have confirmed that by inducing the growth of primary particles constituting the lithium-manganese-based oxide so that the primary particles have a different shape than conventional ones, the lithium-excess lithium-manganese-based oxide can also exhibit electrochemical properties and stability at a level that allows it to be commercially available.

[0019] Therefore, the present invention aims to provide a cathode active material including a lithium-excess lithium-manganese-based oxide, in which the growth of primary particles constituting the lithium-manganese-based oxide is induced so that the primary particles constituting the lithium-manganese-based oxide have a different shape from that of previously known lithium-manganese-based oxides.

[0020] In particular, the present invention aims to provide a cathode active material that can reduce the specific surface area of ​​the lithium manganese-based oxide by inducing the growth of primary particles constituting the lithium manganese-based oxide, thereby preventing a rapid decrease in battery performance due to side reactions during the initial battery reaction under high voltage conditions.

[0021] Another object of the present invention is to provide a cathode active material capable of improving the electrochemical properties of the lithium manganese-based oxide composed of the primary particles by inducing the growth of the primary particles constituting the lithium manganese-based oxide while co-doping different elements.

[0022] Another object of the present invention is to provide a lithium secondary battery that can achieve high stability by using a cathode containing the cathode active material defined herein, thereby preventing deterioration in electrochemical characteristics of the lithium secondary battery, including rate characteristics, caused by excessive amounts of lithium and manganese present in conventional OLO, and reducing side reactions between the cathode active material and an electrolyte during high-voltage operation. [Means for solving the problem]

[0023] According to one aspect of the present invention for solving the above-described technical problems, there is provided a positive electrode active material including a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved or composite.

[0024] Generally, commercially available ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition contain a single phase of the R3-m space group, whereas the lithium-rich lithium manganese oxide defined in this application is characterized by a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0025] In one embodiment, the lithium manganese-based oxide includes secondary particles formed by agglomeration of a plurality of primary particles.

[0026] In this case, when the oxide precursor of the lithium manganese-based oxide is calcined, the growth of the primary particles is induced and the oxide precursor is simultaneously doped with a different element, thereby forming a specific shape of the primary particles constituting the lithium manganese-based oxide.

[0027] Here, the lithium manganese-based oxide may contain at least one dopant selected from tungsten, molybdenum, and niobium, and at least a portion of oxygen present in the lithium manganese-based oxide may be substituted with a halogen.

[0028] The average minor axis length of the primary particles constituting the lithium manganese oxide may be 160 nm or more, preferably 160 nm or more and 500 nm or less, and more preferably more than 210 nm and 400 nm or less.

[0029] The average minor axis length of the primary particles can be measured for the primary particles exposed on the surface of the secondary particles from the SEM image of the secondary particles (for example, calculated from 20 primary particles selected in descending order of minor axis length from the primary particles exposed on the surface of the secondary particles from the SEM image of the secondary particles).

[0030] Furthermore, the interparticle porosity between the primary particles measured from a cross-sectional SEM image of the secondary particles formed by aggregation of the primary particles may be 10% or less, preferably 5% or less.

[0031] The lithium manganese-based oxide may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1:

[0032] [Chemical formula 1] rLi2MnO 3-b′ X′ b′ (1-r)Lia M1 x M2 y M3 z 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, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, M3 is at least one selected from W, Mo, and Nb, M1 to M3 do not overlap with each other, X and X′ are halogens capable of substituting at least a 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, 0 < z ≤ 0.1, and 0 < x + y + z ≤ 1, provided that b and b′ are not simultaneously 0.)

[0033] At least a part of the oxygen present in the lithium manganese-based oxide may be substituted with a halogen, preferably fluorine. Specifically, the primary particles may be doped with fluorine.

[0034] It is preferable that M3 and a halogen (e.g., fluorine) are doped into the primary particles while inducing the growth of the primary particles during the firing of the oxide precursor of the lithium manganese-based oxide.

[0035] Also, according to another aspect of the present invention, a positive electrode containing the above-described positive electrode active material is provided.

[0036] Also, according to still another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

Effects of the Invention

[0037] According to the present invention, it is possible to improve upon the limitations of conventional lithium-excess lithium manganese-based oxides, which have various disadvantages in terms of electrochemical properties and / or stability, when compared with commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[0038] Specifically, by inducing the growth of the primary particles constituting the lithium manganese-based oxide according to the present invention, the primary particles can have a shape different from that of the primary particles constituting the lithium manganese-based oxides known so far. As such, according to the present invention, by making the primary particles have a shape different from that of the conventional primary particles, even lithium-excess lithium manganese-based oxides can exhibit electrochemical properties and stability at a level that allows them to be commercially used.

[0039] First, when inducing the growth of primary particles constituting the lithium manganese-based oxide, the specific surface area of ​​the lithium manganese-based oxide can be reduced, thereby preventing a rapid decrease in battery performance due to side reactions during the initial battery reaction under high voltage conditions.

[0040] When the specific surface area of ​​the lithium manganese-based oxide is reduced, it is possible to reduce side reactions between the lithium manganese-based oxide and the electrolyte. In particular, OLO, such as the lithium manganese-based oxide, has the advantage of exhibiting high capacity under high-voltage operating conditions. However, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte increases as the operating voltage increases. Therefore, it is important to reduce side reactions between the lithium manganese-based oxide and the electrolyte.

[0041] Therefore, the side reaction between the lithium manganese-based oxide and the electrolyte is reduced, thereby improving the stability and lifespan of a lithium secondary battery using the lithium manganese-based oxide as a cathode active material. In particular, the cathode active material with reduced side reaction with the electrolyte can operate the lithium secondary battery at a higher voltage.

[0042] Furthermore, as described above, when inducing the growth of the primary particles, co-doping with different elements can reduce the interparticle porosity between the primary particles that form the secondary particles. In this way, reducing the porosity within the lithium manganese-based oxide can increase the capacity per unit volume and compensate for the insufficient electrochemical properties of the positive electrode active material including the lithium manganese-based oxide.

[0043] In particular, when inducing the growth of the primary particles, the capacity and rate characteristics of the lithium manganese-based oxide can be improved depending on the doping element.

[0044] As described above, when a cathode including the cathode active material defined herein is used, it is possible to prevent deterioration in the electrochemical characteristics of a lithium secondary battery, including rate characteristics, due to the excessive amounts of lithium and manganese present in conventional OLO, and to achieve high stability by reducing side reactions between the cathode active material and the electrolyte during high-voltage operation.

[0045] The specific effects of the present invention, together with the above-mentioned effects, will be described below while explaining specific matters for carrying out the invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0047] Hereinafter, a cathode active material including a lithium-excess lithium manganese-based oxide and a lithium secondary battery including the cathode active material according to some embodiments of the present invention will be described in more detail.

[0048] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material containing a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved or combined.

[0049] The lithium manganese-based oxide contains at least lithium, nickel, and manganese. In this case, the lithium manganese-based oxide is also called an overlithiated layered oxide (OLO) when the lithium content in the lithium manganese-based oxide is greater than the total content of other transition metals (generally, when the molar ratio of lithium to all metal elements other than lithium in the lithium manganese-based oxide (Li / Metal molar ratio) is greater than 1).

[0050] Generally, in commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, the manganese content of all metal elements excluding lithium is 20 mol % or less. Considering this, the lithium-manganese-based oxide has a relatively high manganese content (e.g., 50 mol % or more, preferably 55 mol % to 75 mol %) among all metal elements compared to commercially available ternary lithium composite oxides.

[0051] In addition, considering that commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a nickel content of 60 mol% or more (80 mol% or more in the case of a high-Ni type) of all metal elements excluding lithium, the lithium-manganese-based oxide has a relatively low ratio of nickel to all metal elements (e.g., less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0052] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined herein is larger than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese-based oxide defined herein is larger than 1, preferably 1.1 to 1.7, and more preferably 1.2 to 1.6.

[0053] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0054] The lithium manganese-based oxide included in the positive electrode active material defined herein includes secondary particles formed by aggregation of a plurality of primary particles, and the lithium manganese-based oxide may partially exist as a single primary particle.

[0055] The primary particles constituting the lithium manganese-based oxide may have various shapes within the range defined herein.

[0056] Conventional lithium-excess lithium manganese oxides have a secondary particle form in which a plurality of primary particles are aggregated, and generally have a form in which primary particles having an average particle size of several to several tens of nanometers are aggregated.

[0057] On the other hand, according to the present invention, the growth of the primary particles is induced, so that the primary particles constituting the lithium manganese-based oxide 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.

[0058] The major axis length of the primary particles, the minor axis length of the primary particles, the ratio of the major axis length to the minor axis length of the primary particles (major axis length / minor axis length), and the average particle size of the primary particles ([major axis length+minor axis length] / 2) can be calculated as the average value after measuring the major axis length and minor axis length of the primary particles exposed on the surface of the secondary particles.

[0059] For example, the average value of the results measured from all primary particles exposed on the surface of the secondary particles or the average value of the results measured from a plurality of primary particles selected from the primary particles exposed on the surface of the secondary particles (for example, calculated from a plurality of primary particles (e.g., 10 primary particles, 20 primary particles, etc.) selected in descending order of minor axis length from the primary particles exposed on the surface of the secondary particles from an SEM image of the secondary particles) can be used.

[0060] If the average particle size of the primary particles is less than 0.1 μm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles is relatively large, which increases the possibility of side reactions occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0061] On the other hand, when the average particle size of the primary particles is larger than 5 μm, excessive growth of the primary particles is induced, and the diffusion path of lithium ions within the primary particles becomes longer. When the diffusion path of lithium ions within the primary particles is too long, the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles decrease, which causes an increase in the resistance of the lithium manganese-based oxide (secondary particles) composed of the primary particles.

[0062] In order to reduce the specific surface area of ​​the lithium manganese oxide and prevent a decrease in the mobility of lithium ions within the primary particles and the diffusibility of lithium ions through the primary particles, the average particle size of the primary particles is preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 1.0 μm, even more preferably 0.25 μm to 0.75 μm, and particularly preferably 0.40 μm to 0.65 μm.

[0063] According to the present application, when the primary particles constituting the lithium manganese-based oxide satisfy the definition of the minor axis length described below on the premise that the primary particles satisfy the above-mentioned range of average particle diameter (more preferably, when the definitions of the minor axis length and the major axis length described below are simultaneously satisfied on the premise that the above-mentioned range of average particle diameter is satisfied), the specific surface area of ​​the primary particles can be effectively reduced within a range that alleviates a decrease in the diffusibility of lithium ions mediated by the primary particles.

[0064] The average minor axis length of the primary particles constituting the lithium manganese-based oxide may be 160 nm or more, preferably 160 nm to 500 nm, more preferably 210 nm to 400 nm. As described above, the average minor axis length of the primary particles may be the average minor axis length measured from all primary particles exposed on the surface of the secondary particles or a plurality of primary particles (e.g., 10 primary particles, 20 primary particles, etc.) selected in descending order of minor axis length from among the primary particles exposed on the surface of the secondary particles.

[0065] If the average minor axis length of the primary particles is less than 160 nm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles becomes relatively large, increasing the possibility of a side reaction occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0066] In addition, from the viewpoint of reducing the deviation in the minor axis length of the primary particles exposed on the surface of the secondary particles, the minimum value of the minor axis length measured for the primary particles exposed on the surface of the secondary particles may be 80 nm or more, preferably 100 nm to 300 nm, more preferably 160 nm to 250 nm, and the maximum value of the minor axis length measured for the primary particles exposed on the surface of the secondary particles may be 1 μm or less, preferably 230 nm to 1 μm, more preferably 250 nm to 800 nm. The smaller the deviation in the minor axis length of the primary particles exposed on the surface of the secondary particles, the more uniform the surface kinetics of the secondary particles can be maintained.

[0067] The average minor axis length of the primary particles being greater than 500 nm means that the growth of the primary particles constituting the secondary particles is generally excessively induced, and the unnecessary promotion of the growth of the primary particles may reduce the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles.

[0068] The average major axis length of the primary particles constituting the lithium manganese-based oxide may be 570 nm or more, preferably 570 nm to 1 μm, more preferably 600 nm to 820 nm. As described above, the average major axis length of the primary particles may be the average major axis length measured from all primary particles exposed on the surface of the secondary particles or a plurality of primary particles (e.g., 10 primary particles, 20 primary particles, etc.) selected in descending order of minor axis length from among the primary particles exposed on the surface of the secondary particles.

[0069] If the average major axis length of the primary particles is less than 570 nm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles becomes relatively large, increasing the possibility of a side reaction occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0070] In addition, from the viewpoint of reducing the deviation in the major axis length of the primary particles exposed on the surface of the secondary particles, the minimum value of the major axis length measured for the primary particles exposed on the surface of the secondary particles may be 245 nm or more, preferably 245 nm to 450 nm, and the maximum value of the major axis length measured for the primary particles exposed on the surface of the secondary particles may be 1.5 μm or less, preferably 880 nm to 1.5 μm, more preferably 920 nm to 1.3 μm. The smaller the deviation in the major axis length of the primary particles exposed on the surface of the secondary particles, the more uniform the surface kinetics of the secondary particles can be maintained.

[0071] The average major axis length of the primary particles being greater than 1 μm means that the growth of the primary particles constituting the secondary particles is generally excessively induced, and the unnecessary promotion of the growth of the primary particles may reduce the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles.

[0072] Furthermore, if the major axis length within the primary particles is excessively long, the diffusion path of lithium ions within the primary particles becomes excessively long, reducing the diffusibility of lithium ions through the primary particles and increasing the resistance of the primary particles. Furthermore, the possibility of polarization occurring within the primary particles increases. If the polarization phenomenon within the primary particles intensifies, the possibility of cracks occurring within the primary particles may increase.

[0073] When the lithium manganese-based oxide exists as secondary particles formed by agglomeration of a plurality of primary particles, the secondary particles may have an average particle size ([major axis length + minor axis length] / 2) of 0.5 μm to 15 μm. The average particle size of the secondary particles may vary depending on the number of primary particles constituting the secondary particles. Furthermore, as the growth of the primary particles is induced and the average particle size of the primary particles increases, the number of primary particles constituting the secondary particles may decrease.

[0074] As a result, the lithium manganese-based oxide as defined herein exhibits an overall reduced specific surface area due to the induced growth of primary particles constituting the lithium manganese-based oxide. This allows the lithium manganese-based oxide to achieve sufficient surface kinetics and improve surface stability, thereby reducing side reactions between the lithium manganese-based oxide and the electrolyte. As a result, this can prevent premature degradation of the cathode active material containing the lithium manganese-based oxide as defined herein and further contribute to extending the life of lithium secondary batteries using the cathode active material.

[0075] There are various methods for inducing the growth of the primary particles in the lithium manganese-based oxide, but differences in the method for inducing the growth of the primary particles may prevent the intended effect of the present application from being achieved. According to the present invention, a method is used in which the growth of the primary particles is induced during the calcination of the oxide precursor of the lithium manganese-based oxide, while the oxide precursor is doped with a different element. However, even if doping is induced during the calcination of the hydroxide precursor of the lithium manganese-based oxide or the oxide precursor of the lithium manganese-based oxide, the intended effect of crystal growth may not be achieved. Therefore, for a detailed explanation of this, please refer to the experimental examples described below.

[0076] The lithium manganese-based oxide defined herein may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1:

[0077] [Chemical formula 1] rLi2MnO 3-b′ X′ b′ (1-r)Li a M1 x M2 y M3 z O 2-b X b where: M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd and Nd, M3 is at least one selected from W, Mo and Nb, M1 to M3 do not overlap with each other, X and X′ are halogens capable of substituting at least a part of the oxygen present in the lithium manganese oxide, where 0 < r ≦ 0.7, 0 < a ≦ 1, 0 ≦ b ≦ 0.1, 0 ≦ b′ ≦ 0.1, 0 < x ≦ 1, 0 ≦ y < 1, 0 < z ≦ 0.1 and 0 < x + y + z ≦ 1, provided that b and b′ are not both 0 at the same time.

[0078] In the case where M1 is Ni in the chemical formula 1, M2 may contain Mn, and in the case where M1 is Mn, M2 may contain Ni. Also, in the case where M1 is Ni and Mn, M2 may not exist, or if it exists, it may be an element other than Ni and Mn.

[0079] Among the lithium manganese oxides represented by the chemical formula 1, different dopants are represented as M3 and X. M3 is at least one selected from W, Mo and Nb, and may contain a plurality of elements selected from W, Mo and Nb as required.

[0080] The types of halogens that can be used as X and X′ can be referred to the periodic table, and F, Cl, Br and / or I can be used, and preferably F can be used.

[0081] As described above, when inducing the growth of the primary particles constituting the lithium manganese oxide and doping with a halogen, preferably, at least a part of the oxygen present in the lithium manganese oxide may be substituted with a halogen.

[0082] When an over-firing method is used in which a heat treatment is performed at a relatively high temperature without doping with a halogen to induce the growth of the primary particles constituting the lithium manganese-based oxide, the primary particles can grow, but the crystal structure of the primary particles may be damaged, resulting in early deterioration of the positive electrode active material.

[0083] When fluorine is used as an anion dopant during the growth of the primary particles, the growth of the primary particles can be induced within a range that alleviates a decrease in the diffusibility of lithium ions through the primary particles.

[0084] For fluorine doping of the primary particles, at least one anion dopant selected from LiF, MgF2, HF, F2, XeF2, TbF4, CeF4, CoF3, AgF2, MoF3, AgF, CuF2, FeF3, CuF, VF3, CrF3, ZrF4, BaF2, CaF2, AlF3, NHF, CeF3 and CsF, preferably at least one anion dopant selected from LiF and MgF2, can be used.

[0085] The content of fluorine doped in the primary particles can be predicted from the content of fluorine in the lithium manganese-based oxide represented by Formula 1 (i.e., the values ​​of b and b' in Formula 1). In addition, when neither b nor b' in Formula 1 is 0, b + b' may be 0.2 or less, preferably 0.1 or less.

[0086] When the oxide precursor is calcined, if a M3-containing dopant is further used in addition to the anion dopant to induce co-doping, the primary particles may grow to a nearly spherical shape instead of a plate-like shape.

[0087] The M3-containing dopant can be at least one selected from the group consisting of hydroxides, oxides, carbonates, nitrides, sulfides, and phosphates containing at least one element selected from tungsten, molybdenum, and niobium.

[0088] As described above, when the anion dopant and the M3-containing dopant are used in combination to simultaneously dope the primary particles and induce the growth of the primary particles during calcination of the oxide precursor, the shape of the primary particles becomes closer to a sphere, and the porosity of the secondary particles formed by aggregation of the primary particles can be reduced.

[0089] When the porosity in the lithium manganese-based oxide is reduced, the capacity per unit volume can be increased, thereby compensating for the insufficient electrochemical properties of the positive electrode active material including the lithium manganese-based oxide.

[0090] Specifically, the interparticle porosity between the primary particles, which can be measured from a cross-sectional SEM image of the secondary particles, may be 10% or less, preferably 5% or less. By reducing the interparticle porosity within the secondary particles, the energy density per unit volume of the lithium manganese-based oxide can be improved.

[0091] In addition, when the anion dopant and the M3-containing dopant are used in combination during calcination of the oxide precursor to simultaneously dope the primary particles and induce growth of the primary particles, this is particularly effective in reducing the porosity at the surface of the secondary particles.

[0092] For example, when the distance from the center of the secondary particle determined from a cross-sectional SEM image of the secondary particle to the surface of the secondary particle is referred to as r, the surface portion of the secondary particle can be defined as a region that is a distance of 0.5r to 1.0r from the center of the secondary particle as an outer bulk region. In this case, the porosity in the outer bulk region that can be measured from the cross-sectional SEM image of the secondary particle may be 1% or less, preferably 0.72% or less.

[0093] The improvement in the porosity within the lithium manganese-based oxide may also have a positive effect on the improvement of the BET specific surface area and the compressed density of the positive electrode active material including the lithium manganese-based oxide.

[0094] The lithium manganese oxide defined in this application is 2.0m 2 More specifically, the lithium manganese-based oxide can have a specific surface area of ​​2.0 m / g or less by simultaneously doping the primary particles and inducing the growth of the primary particles using the anion dopant and the M3-containing dopant in combination during the calcination of the oxide precursor. 2 / g or less, preferably 0.3m 2 / g or more 2.0m 2 / g or less, more preferably 0.3m 2 / g or more 1.1m 2 / g or less.

[0095] Furthermore, when the positive electrode active material containing the lithium manganese oxide is compressed under a pressure of 4.5 tons, the pressed density is greater than 2.53 g / cc, and preferably, can exhibit a pressed density of 2.58 g / cc or more.

[0096] The lithium manganese-based oxide represented by Chemical Formula 1 may optionally contain cobalt. When the lithium manganese-based oxide contains cobalt, the molar fraction of cobalt relative to the total moles of metal elements in the lithium manganese-based oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese-based oxide represented by Chemical Formula 1 may have a cobalt-free composition.

[0097] The Li / Metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 may be greater than 1, preferably 1.1 to 1.7, and more preferably 1.2 to 1.6. When the Li / Metal molar ratio measured from the lithium manganese-based oxide is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide. In addition, in order for the lithium manganese-based oxide to properly form a solid solution or a composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and to simultaneously exhibit high capacity under high-voltage operating conditions, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.2 to 1.6.

[0098] In addition, in order to properly form a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, the manganese content of all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 is preferably 50 mol% or more. In order to enable the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under high-voltage operating conditions, the manganese content of all metal elements excluding lithium present in the lithium manganese-based oxide is more preferably 50 mol% or more but less than 80 mol%, and even more preferably 55 mol% to 75 mol%.

[0099] When the manganese content of the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the migration of transition metals (especially manganese) within the lithium manganese-based oxide during the formation and / or operation of the lithium secondary battery. This phase transition forms a spinel phase, and the spinel phase, acting as an impurity in the lithium manganese-based oxide, may cause a decrease in charge / discharge capacity or voltage decay during the charge / discharge cycles of the lithium secondary battery.

[0100] In order to properly form a solid solution or a composite solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, the content of nickel among all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 is preferably less than 50 mol%.

[0101] When the nickel content in the lithium manganese-based oxide is 50 mol% or more, the C2 / m phase may not be sufficiently formed, or the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group may not form a sufficient solid solution, which may cause phase separation during formation and / or operation of the lithium secondary battery.

[0102] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions exist in a single phase belonging to the R3-m space group.

[0103] Meanwhile, the lithium-excess lithium manganese oxide represented by the formula 1 is rLi2MnO 3-b′ X′ b′ The oxides of the phase belonging to the C2 / m space group (hereinafter referred to as "C2 / m phase") and (1-r)Li a M1 x M2 y M3 z O 2-b X b The lithium manganese-based oxide exists as a composite oxide in which an oxide of the C2 / m phase and an oxide of the R3-m phase form a solid solution.

[0104] In this case, a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are simply physically and / or chemically bonded or attached does not fall under the category of a solid solution as defined in this application.

[0105] For example, a composite oxide having a phase belonging to the C2 / m space group, which is formed by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R3-m space group and whose surface is coated with a metal oxide having a phase belonging to the R3-m space group, does not fall under the category of a solid solution as defined in the present application.

[0106] In the lithium manganese-based oxide represented by Chemical Formula 1, when r exceeds 0.7, the lithium manganese-based oxide is a C2 / m phase oxide, Li2MnO 3-b′ X′ b′ In other words, in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance among the lithium-manganese-based oxides, and improve the surface kinetics, it is preferable that the R3-m phase oxide be present in a certain proportion or more.

[0107] Lithium secondary battery According to another aspect of the present invention, there is provided a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include a lithium manganese-based oxide according to any of the various embodiments of the present invention described above as a positive electrode active material.

[0108] Therefore, a detailed description of the lithium manganese-based oxide will be omitted, and only the remaining components not described above will be described below. For convenience, the lithium manganese-based oxide will be referred to as the positive electrode active material hereinafter.

[0109] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0110] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0111] In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0112] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0113] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0114] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0115] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0116] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0117] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0118] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0119] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0121] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

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

[0123] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0124] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0125] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0126] The conductive material may be added as a component for further improving the conductivity of the negative electrode active material in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives.

[0127] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0128] In another embodiment, the negative electrode active material layer may be fabricated by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0129] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration of the electrolyte and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0130] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0131] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0132] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0133] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0134] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-based solid electrolyte may be used, and preferably, a sulfide-based solid electrolyte may be used.

[0135] The sulfide-based solid electrolyte material may be a solid electrolyte containing Li, an X element (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(wherein p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0136] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0137] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0138] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Alternatively, the solid electrolyte may be partially contained in the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or partially contained in the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0139] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0140] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0141] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0142] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0143] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0144] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0145] Production Example 1: Production of positive electrode active material Example 1 (a) Preparation of precursor The reactor was filled with an aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, and NaOH and NH4OH were added while stirring. The temperature inside the reactor was kept at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was completed, the reactor was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor with the composition (OH)2 was obtained.

[0146] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated at 550°C for 5 hours, followed by furnace cooling to obtain an oxide precursor.

[0147] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b), LiOH (Li / Metal molar ratio = 1.25) as a lithium source material, LiF weighed out so that the fluorine (F) content based on metal elements excluding lithium in the precursor was 1.0 mol%, and WO3 weighed out so that the tungsten (W) content based on metal elements excluding lithium in the precursor was 0.75 mol%.

[0148] Next, the temperature of a firing furnace in an O atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated for 8 hours at 850°C. After that, the mixture was cooled in the furnace, classified, and crushed to obtain the final product, a cathode active material containing lithium manganese-based oxide (average particle size 4.0 μm).

[0149] Example 2 A positive electrode active material (average particle size: 4.0 μm) was prepared in the same manner as in Example 1, except that the heat treatment temperature in step (c) was 900° C. instead of 850° C.

[0150] Example 3 A positive electrode active material (average particle size: 4.0 μm) was prepared in the same manner as in Example 1, except that the heat treatment temperature in step (c) was 950° C. instead of 850° C.

[0151] Example 4 A positive electrode active material (average particle size 4.0 μm) was prepared in the same manner as in Example 1, except that MoO 3 was used instead of WO 3 in step (c) and the heat treatment temperature was 900° C. instead of 850° C.

[0152] Example 5 A positive electrode active material (average particle size 4.0 μm) was prepared in the same manner as in Example 1, except that Nb 2 O 5 was used instead of WO 3 in step (c) and the heat treatment temperature was 900° C. instead of 850° C.

[0153] Comparative Example 1 A positive electrode active material (average particle size 4.0 μm) was produced in the same manner as in Example 1, except that LiF and WO 3 were not mixed in the step (c).

[0154] Comparative Example 2 A positive electrode active material (average particle size: 4.0 μm) was produced in the same manner as in Example 1, except that LiF was not mixed in the step (c).

[0155] Comparative Example 3 A positive electrode active material (average particle size: 4.0 μm) was prepared in the same manner as in Example 1, except that WO 3 was not mixed in the step (c).

[0156] Comparative Example 4 A positive electrode active material (average particle size 4.0 μm) was prepared in the same manner as in Example 1, except that LiF and WO were not mixed in step (c) and the heat treatment temperature was 1,000°C instead of 850°C.

[0157] Comparative Example 5 A positive electrode active material (average particle size 4.0 μm) was produced in the same manner as in Example 1, except that LiF weighed out to be 0.1 mol % and WO3 weighed out to be 0.1 mol % were mixed in the step (c).

[0158] Composition of lithium manganese oxide The composition (molar ratio of each element) of the lithium manganese-based oxide contained in each positive electrode active material prepared in Preparation Example 1 was measured through ICP analysis.

[0159] The measurement results are shown in Table 1 below.

[0160] [Table 1] *Li / Metal Molar ratio indicates the molar ratio of lithium to all elements other than lithium in the lithium manganese-based oxide. *The element content (mol%) is calculated based on the total amount of elements other than lithium in the lithium manganese-based oxide.

[0161] Manufacturing Example 2: Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0162] A half cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0163] Experimental Example 1: Structural analysis of positive electrode active material (1) Secondary particle-type lithium manganese-based oxide was separated from each of the cathode active materials prepared in Preparation Example 1, and then photographed using a scanning electron microscope to obtain SEM images.

[0164] Next, using the Image Analyzer program, one secondary particle was selected from the SEM image, and 20 primary particles exposed on the surface of that secondary particle were selected in descending order of minor axis length, and the major and minor axis lengths of each were measured. From the measurement results, the average major axis length A of the primary particles, the minimum major axis length B of the primary particles, the maximum major axis length C of the primary particles, the average minor axis length D of the primary particles, the minimum minor axis length E of the primary particles, the maximum minor axis length F of the primary particles, and the average particle size G of the primary particles ([major axis length + minor axis length] / 2) were calculated.

[0165] (2) In addition, each of the lithium manganese-based oxides (secondary particles) was processed to prepare a cross section using a cross-section polisher (accelerating voltage 5.0 kV, milling for 4 hours), and then photographed using a scanning electron microscope to obtain a cross-sectional SEM image.

[0166] Next, the number of pores H was counted from the cross section of the secondary particle in the cross section SEM image using the Image analyzer program, and the cross section porosity I was calculated.

[0167] The cross-sectional porosity I was calculated by binarizing the cross-sectional SEM image and then calculating the ratio of the sum of the areas of all voids present in the secondary particles to the total area of ​​the cross section of the secondary particles ([sum of the areas of all voids present in the secondary particles / total area of ​​the cross section of the secondary particles] / 100).

[0168] In addition, the center of the secondary particle was set from the binarized cross-sectional SEM image, and the distance from the center of the secondary particle to the surface of the secondary particle was defined as r. The region at a distance of 0.5r to 1.0r from the center of the secondary particle was defined as an outer bulk region.

[0169] The external bulk porosity J ([sum of all void areas present in the external bulk region / total area of ​​the external bulk region] × 100) was calculated by dividing the sum of all void areas present in the external bulk region by the total area of ​​the cross section of the external bulk region.

[0170] (3) The BET specific surface area K was calculated from the amount of nitrogen gas adsorbed by the lithium manganese oxide at liquid nitrogen temperature (77 K) using a specific surface area measuring device by gas adsorption method (MicrotaracBEL BELSORP-mini II).

[0171] (4) 3 g of each of the positive electrode active materials produced in Production Example 1 was weighed into a pelletizer, and then pressed at 4.5 tons for 5 seconds, and the compressed density L was measured.

[0172] The measurement results are shown in Tables 2 and 3 below.

[0173] [Table 2]

[0174] [Table 3]

[0175] Comparing the lithium manganese-based oxides contained in the cathode active materials according to Example 1 (an example in which co-doping of tungsten and fluorine was induced during the calcination of the oxide precursor) and Comparative Example 1 (an example prepared under the same conditions as Example 1 except that co-doping of tungsten and fluorine was not induced during the calcination of the oxide precursor), it was found that co-doping of tungsten and fluorine during the calcination of the oxide precursor induced growth of the major and minor axes of the primary particles.

[0176] It was also confirmed that the cross-sectional porosity I and external bulk porosity J of the lithium manganese-based oxide according to Example 1 were smaller than those of the lithium manganese-based oxide according to Comparative Example 1. It was also confirmed that this difference affected the BET specific surface area K and the compacted density L of the cathode active material containing the lithium manganese-based oxide according to Example 1 and the cathode active material according to Comparative Example 1.

[0177] Comparing the lithium manganese-based oxides contained in the cathode active materials according to Example 2 (an example in which co-doping of tungsten and fluorine was induced during the calcination of the oxide precursor) and Comparative Example 2 (an example prepared under the same conditions as Example 2 except that only tungsten doping was induced during the calcination of the oxide precursor), it was found that co-doping of tungsten and fluorine during the calcination of the oxide precursor had a more significant effect on the growth of the major and minor axis lengths of the primary particles than doping with tungsten alone.

[0178] Similarly, in Examples 4 and 5, which used different co-doping sources from Examples 1 to 3, it was confirmed that the co-doping of molybdenum and fluorine or the co-doping of niobium and fluorine induced growth in the major axis length and minor axis length of the primary particles while simultaneously reducing the cross-sectional porosity and external bulk porosity.

[0179] In addition, referring to the results of Comparative Example 4 in which the calcination temperature of the oxide precursor was increased to 1,000°C, it was confirmed that the growth of primary particles was generally induced, but the effect of reducing the external bulk porosity was insufficient compared to the Examples.

[0180] Furthermore, even though raw materials for co-doping with tungsten and fluorine were used during calcination of the oxide precursor, the results of Comparative Example 5, in which the content of the raw materials was too low, confirmed that the growth of the primary particles was hardly induced.

[0181] Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries The lithium secondary battery (half cell) prepared in Preparation Example 2 was subjected to a charge-discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and a discharge rate of 0.1 C to 5.0 C. The initial charge capacity, initial discharge capacity, capacity per volume, initial reversible efficiency, and rate capability (C-rate) were measured. The capacity per volume was calculated by multiplying the initial discharge capacity by the packing density (L in Table 3).

[0182] In addition, the same lithium secondary battery was charged and discharged 50 times at 25°C and 1C / 1C within a driving voltage range of 2.0V to 4.6V, and then the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity (cycle capacity retention rate; capacity retention) was measured.

[0183] The measurement results are shown in Table 4 below.

[0184] [Table 4]

[0185] Referring to the results in Table 4, it can be seen that the lithium secondary battery using the cathode active material including the lithium manganese-based oxide according to Example 1 (which induces simultaneous doping of tungsten and fluorine when the oxide precursor is calcined) has higher initial charge capacity, initial discharge capacity, discharge capacity ratio, and cycle capacity retention rate than the lithium secondary battery using the cathode active material including the lithium manganese-based oxide according to Comparative Example 1 (which does not induce simultaneous doping of tungsten and fluorine when the oxide precursor is calcined). In particular, it can be seen that Example 1 has a significantly improved capacity per unit volume compared to Comparative Example 1.

[0186] Furthermore, when looking at the results of Comparative Example 2, in which tungsten was selectively doped during calcination of the oxide precursor, it can be seen that although the initial charge capacity and initial discharge capacity were at similar levels to those of the Examples, the capacity per unit volume and cycle capacity retention rate were lower than those of the Examples.

[0187] Similarly, when looking at the results of Comparative Example 3 in which fluorine was selectively doped during calcination of the oxide precursor, it can be seen that the capacity per unit volume and rate characteristics were lower than those of the Examples.

[0188] In Comparative Example 4, where the calcination temperature of the oxide precursor was increased to 1,000°C, primary particle growth was generally similar to that of the Examples, but the initial charge capacity, initial discharge capacity, capacity per unit volume, and discharge capacity ratio were lower than those of the Examples. These results suggest that deterioration occurred due to thermal damage to the lithium manganese-based oxide caused by the excessively high calcination temperature during the second heat treatment. In particular, the initial discharge capacity was significantly lower than that of the Examples, indicating a significant difference in capacity per unit volume.

[0189] Furthermore, in Comparative Example 5, in which raw materials for co-doping with tungsten and fluorine were used during calcination of the oxide precursor but the amount of the raw materials was too low, the initial charge capacity, initial discharge capacity, capacity per volume, discharge capacity ratio, and cycle capacity retention rate were lower than those of Example 1.

[0190] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. A positive electrode active material comprising a lithium manganese-based oxide in which a phase belonging to a C2 / m space group and a phase belonging to an R3-m space group are solid-solved or composite, The lithium manganese-based oxide includes secondary particles formed by agglomeration of a plurality of primary particles, The lithium manganese-based oxide contains at least one dopant selected from tungsten, molybdenum, and niobium, and at least a portion of oxygen present in the lithium manganese-based oxide is substituted with a halogen; When the distance from the center of the secondary particle determined from the cross-sectional SEM image of the secondary particle to the surface of the secondary particle is referred to as r, and a region at a distance of 0.5r to 1.0r from the center of the secondary particle is referred to as an outer bulk region, The positive electrode active material, wherein the porosity in the external bulk region is 1% or less.

2. 2 . The positive electrode active material according to claim 1 , wherein the average minor axis length of the primary particles exposed on the surfaces of the secondary particles is 160 nm or more and 500 nm or less.

3. 2 . The positive electrode active material according to claim 1 , wherein the average major axis length of the primary particles exposed on the surfaces of the secondary particles is 570 nm or more and 1 μm or less.

4. 2. The positive electrode active material according to claim 1, wherein the average value of the major axis length and the minor axis length of the primary particles exposed on the surfaces of the secondary particles ([major axis length + minor axis length] / 2) is 0.1 μm to 5 μm.

5. The positive electrode active material of claim 1 , wherein the lithium manganese-based oxide is represented by the following chemical formula 1: [Chemical formula 1] rLi ２ MnO ３－ｂ′ X′ ｂ′ ・(1-r)Li ａ M1 ｘ M2 ｙ M3 ｚ O ２－ｂ X ｂ (where, M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; M3 is at least one selected from W, Mo, and Nb; M1 to M3 do not overlap with each other, X and X' are halogens capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, 0<r≦0.7, 0<a≦1, 0≦b≦0.1, 0≦b'≦0.1, 0<x≦1, 0≦y<1, 0<z≦0.1, and 0<x+y+z≦1, with the proviso that b and b' are not simultaneously 0.

6. The cathode active material of claim 5 , wherein the primary particles are doped with fluorine.

7. The BET specific surface area of ​​the secondary particles is 0.3 m ２ / g or more 2.0m ２ The positive electrode active material according to claim 1 , wherein the SiO 2 content is 1 / g or less.

8. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a press density of greater than 2.53 g / cc when compressed under a pressure of 4.5 tons.

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