Positive active material and lithium secondary battery comprising the same

Abstract

The present invention relates to a positive electrode active material exhibiting improved capacity characteristics, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery. The positive electrode active material comprises a lithium transition metal oxide, wherein the lithium transition metal oxide has a molar ratio of lithium to the total number of moles of transition metals excluding lithium greater than 1, and comprises only divalent manganese ions (Mn2+), trivalent manganese ions (Mn3+), and tetravalent titanium ions (Ti4+) as the ions of the transition metals, and based on the total content of transition metals excluding lithium, the molar content of divalent manganese ions (Mn2+) is 10 to 40 mol% and the molar content of trivalent manganese ions (Mn2+) is 33 to 73 mol%.

Description

Technology Field

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0020149 filed February 17, 2025, and all contents disclosed in the literature of said Korean patent applications are incorporated herein as part of this specification.

[0003] The present invention relates to a positive electrode active material exhibiting improved capacity characteristics, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery. Background Technology

[0004] Recently, as the application areas of lithium-ion batteries have rapidly expanded to include not only power supply for electronic devices such as electrical, electronic, telecommunications, and computers, but also power storage for large-area devices such as automobiles and power storage systems, there is a growing demand for high-capacity, high-output, and high-stability secondary batteries.

[0005] The above-mentioned lithium secondary battery generally consists of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transporting lithium ions, and a separator. In this case, lithium transition metal oxides, such as lithium cobalt oxide, lithium nickel oxide, or lithium nickel-cobalt-manganese composite oxide, are mainly used as the positive active material.

[0006] These existing cathode active materials can be defined as cathode active materials (Cationic-Redox cathode active materials; CRCAMs) that generate capacity by inducing oxidation and reduction reactions of metal cations during the charging and discharging of lithium secondary batteries, and these CRCAM-based cathode active materials typically have a crystalline form with a layered structure.

[0007] To date, the development and advancement of cathode active materials have proceeded in the direction of increasing the nickel content to achieve higher capacity using the aforementioned CRCAM-based layered cathode active materials. However, as the maximum nickel content in currently commercialized cathode active materials reaches over 90 mol% of the total transition metals, attempts to achieve higher capacity with the aforementioned CRCAM-based cathode active materials are facing limitations. In particular, due to the high unit costs of nickel and cobalt, the manufacturing cost of high-capacity cathode active materials and lithium secondary batteries continues to rise, which also acts as an obstacle to the commercialization of high-capacity lithium secondary batteries.

[0008] Due to the development limitations of these existing CRCAM-based cathode active materials, anionic-redox cathode active materials (ARCAMs) that generate capacity through oxidation and reduction reactions of anions such as oxygen, as well as oxidation and reduction reactions of metal cations, are being considered as one of the candidates for next-generation high-capacity cathode active materials. As for these ARCAM-based cathode active materials, cathode active materials having a disordered rock-salt (DRX) structure are being considered, and active research is being conducted on them.

[0009] The above-mentioned cathode active material having a disordered rock salt structure can take the form of a lithium transition metal compound containing various transition metals, and since it has a disordered rock salt structure in its crystal structure, it can express capacity through oxidation / reduction reactions of anions as well as oxidation / reduction reactions of metal cations, and is known to be capable of expressing a larger capacity compared to conventional CRCAM-based cathode active materials having a layered structure.

[0010] Accordingly, many studies are being conducted on cathode active materials having the above-mentioned disordered rock salt structure (DRX) as next-generation cathode active materials. Among these, research is actively being conducted on DRX cathode active materials in the form of lithium transition metal oxides containing manganese and titanium as transition metals, for example, lithium manganese-titanium oxide (LMTO).

[0011] However, in the case of the above-mentioned DRX cathode active material, as it contains various types of transition metal ions, significant variations in discharge capacity characteristics at room temperature and high temperature may occur depending on the composition or molar ratio of each transition metal ion. Accordingly, there is a continuous demand for research on the composition of DRX cathode active materials capable of exhibiting improved discharge capacity characteristics, such as LMTO-type DRX cathode active materials. The problem to be solved

[0012] Accordingly, the present invention provides an anode active material having a disordered rock salt structure capable of exhibiting an improved discharge capacity at room temperature and high temperature.

[0013] The present invention also provides a positive electrode for a lithium secondary battery that includes the positive electrode active material and exhibits electrochemical characteristics such as an improved initial discharge capacity, and a lithium secondary battery including the same. means of solving the problem

[0014] According to one embodiment of the invention, as a positive electrode active material comprising a lithium transition metal oxide,

[0015] The above lithium transition metal oxide has a molar ratio of lithium to the total number of moles of transition metals excluding lithium greater than 1, and as the ion of the transition metal, divalent manganese ions (Mn 2+ ), trivalent manganese ions (Mn 3+ ) and tetravalent titanium ions (Ti 4+ Includes only ),

[0016] Based on the total content of transition metals excluding lithium, divalent manganese ions (Mn 2+The molar content of ) is 10 to 40 mol%, and trivalent manganese ions (Mn 3+ A positive electrode active material having a molar content of 33 to 73 mol% is provided.

[0017] In the positive electrode active material of this embodiment, the lithium transition metal oxide may have a disordered rock-salt (DRX) structure in its crystal structure.

[0018] In addition, in the above lithium transition metal oxide, based on the total content of transition metals excluding lithium, tetravalent titanium ions (Ti 4+ The molar content of ) can be 5 to 30 mol%.

[0019] In a more specific example, the lithium transition metal oxide can be represented by the following chemical formula 1:

[0020] [Chemical Formula 1]

[0021] Li a [M1 b M2 c M3 d ]O2F e

[0022] In the above chemical formula 1,

[0023] M1 is a divalent manganese ion (Mn 2+ ) and M2 is a trivalent manganese ion (Mn 3+ ) and M3 is a tetravalent titanium ion (Ti 4+ ) and,

[0024] a is greater than 1.0 and less than or equal to 1.6, b is 0.15 to 0.4, c is 0.2 to 0.8, d is 0.05 to 0.3, and e is 0 or greater and less than or equal to 0.6, wherein a to e are determined according to the oxidation number of each ion.

[0025] Meanwhile, according to another embodiment of the invention, a positive electrode for a lithium secondary battery comprising the positive electrode active material of the first embodiment is provided. Such a positive electrode may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material of the first embodiment.

[0026] According to a further embodiment of the invention, a lithium secondary battery is provided comprising a positive electrode of the other embodiment, a negative electrode facing the positive electrode, and a porous separator or electrolyte layer interposed between the positive electrode and the negative electrode. Effects of the invention

[0027] The positive active material of the above embodiment is a positive active material having a DRX structure that implements capacity using not only the oxidation and reduction reactions of metal cations but also the oxidation and reduction reactions of anions, and can exhibit excellent discharge capacity at room temperature and high temperature (e.g., 45°C).

[0028] In particular, as a result of the inventors' continued research, it was confirmed that the positive electrode active material of one embodiment exhibits an improved discharge capacity compared to the previously known LMTO-type DRX positive electrode active material. This is predicted to be because, as the composition and molar ratio of transition metal ions, such as manganese ions and titanium ions, contained in the positive electrode active material are optimized, not only the oxidation / reduction reaction of metal cations by the positive electrode active material of one embodiment but also the degree of oxidation / reduction reaction of anions and the degree of capacity development resulting from them are optimized.

[0029] Accordingly, the positive electrode active material according to one embodiment of the invention can be preferably used as a next-generation positive electrode active material that exhibits a higher capacity, and a lithium secondary battery containing the same can exhibit excellent electrochemical characteristics such as improved capacity characteristics. Specific details for implementing the invention

[0030] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0031] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0033] A positive electrode active material according to a specific embodiment of the invention, a positive electrode including the same, and a lithium secondary battery, etc., will be described below.

[0034] A positive electrode active material according to one embodiment of the invention is, for example, a positive electrode active material comprising a lithium transition metal oxide having a disordered rock-salt (DRX) structure in its crystal structure,

[0035] The above lithium transition metal oxide has a molar ratio of lithium to the total number of moles of transition metals excluding lithium greater than 1, and as the ion of the transition metal, divalent manganese ions (Mn 2+ ), trivalent manganese ions (Mn 3+ ) and tetravalent titanium ions (Ti 4+ Includes only ),

[0036] Based on the total content of transition metals excluding lithium, divalent manganese ions (Mn 2+ The molar content of ) is 10 to 40 mol%, and trivalent manganese ions (Mn 3+ The molar content of ) is 33 to 73 mol%.

[0037] The positive electrode active material of the above embodiment has a DRX crystal structure and is a positive electrode active material in the form of lithium manganese-titanium oxide (LMTO) containing manganese and titanium ions as transition metals, particularly comprising an excess amount of lithium relative to the total moles of transition metals, while containing divalent manganese ions (Mn 2+ ) and trivalent manganese ions (Mn 3+ The content ratio of ) is limited to a certain range.

[0038] The positive electrode active material of this embodiment contains an excess amount of lithium and has a DRX crystal structure, thereby enabling the realization of capacity using not only the oxidation and reduction reactions of metal cations but also the oxidation and reduction reactions of anions. Accordingly, the positive electrode active material of this embodiment can have excellent initial discharge capacity at room temperature (e.g., 25°C) and high temperature (e.g., 45°C).

[0039] Furthermore, it was confirmed that the positive electrode active material of the above embodiment can exhibit an improved initial discharge capacity compared to the previously known LMTO-type DRX positive electrode active material, as the content ratio of the divalent manganese ions and trivalent ions is optimized to a specific range. This is predicted to be because, as the composition and molar ratio of transition metal ions, such as multiple types of manganese ions, contained within the positive electrode active material are optimized, the degree of capacity development through the oxidation / reduction reaction of the metal cations and the oxidation / reduction reaction of the oxygen-containing anions is optimized, while the crystal structure of the lithium transition metal oxide can be stabilized.

[0040] Accordingly, the positive electrode active material of one embodiment can be preferably used as a next-generation positive electrode active material having a larger capacity.

[0041] Meanwhile, the positive electrode active material of the above-mentioned embodiment has excess lithium and a d orbital in which there are no electrons. 0It may include a lithium transition metal oxide having a disordered rock-salt (DRX) structure in its crystal structure, including a transition metal.

[0042] Such disordered rock salt structures can be identified, for example, by analyzing the lithium transition metal oxide by X-ray diffraction (XRD) analysis through the presence and intensity of characteristic peaks related to the disordered rock salt structure. In a more specific example, the disordered rock salt structure can be identified by confirming the presence and intensity of characteristic peaks defining the (200) crystal plane and / or (220) crystal plane from the XRD analysis results of the lithium transition metal oxide. Characteristic XRD peaks and patterns related to such disordered rock salt structures are also well known through Nature Communications volume 10, Article number: 592 (2019), “Hidden structural and chemical order controls lithium transport in cation-disordered oxides for rechargeable batteries”.

[0043] The lithium transition metal oxide included in the above-mentioned positive electrode active material may satisfy a molar ratio of lithium to the total number of moles of transition metals excluding lithium that is greater than 1, greater than 1 and less than or equal to 1.6, or 1.05 to 1.55, or 1.1 to 1.5, or 1.25 to 1.5. As excess lithium is present in such a ratio, the capacity characteristics of the above-mentioned positive electrode active material are further improved, while the lithium transition metal oxide may exhibit structural stability.

[0044] In addition, so that the degree of cation and anion oxidation / reduction reactions and the resulting capacity development can be optimized, the lithium transition metal oxide contains divalent manganese ions (Mn) based on the total content of transition metals excluding lithium. 2+The molar content of ) is 10 to 40 mol%, or 12 to 35 mol%, or 15 to 35 mol%, or 20 to 35 mol%, and trivalent manganese ions (Mn 3+ The molar content of ) is 33 to 73 mol%, or 40 to 72 mol%, or 42 to 71 mol%, or 45 to 65 mol%, and tetravalent titanium ions (Ti 4+ It can satisfy a transition metal composition in which the molar content of ) is 5 to 30 mol%, or 7 to 28 mol%, or 10 to 27 mol%, or 15 to 23 mol%.

[0045] As the lithium transition metal oxide contains divalent manganese ions, trivalent manganese ions, and tetravalent titanium ions in these molar ratios, the lithium transition metal oxide can maintain structural stability and exhibit improved capacity characteristics.

[0046] In addition, the lithium transition metal oxide may contain only the divalent manganese ions, trivalent manganese ions, and tetravalent titanium ions as transition metals, and may not contain additional transition metal ions, for example, additional transition metal ions having an oxidation state of 4 or higher. When such additional transition metal ions are included, as confirmed in the comparative examples below, the degree of capacity development by cation and anion oxidation / reduction reactions is insufficient, and the discharge capacity of the positive electrode active material may be reduced.

[0047] Meanwhile, the oxidation number of each transition metal ion contained in the lithium transition metal oxide, for example, the oxidation number of manganese ions and / or titanium ions, can be analyzed and confirmed through HXAS analysis (Hard X-ray Absorption Spectroscopy) or STXM analysis (Scanning transmission X-ray microscopy) on the lithium transition metal oxide. From the results of such analysis, the oxidation number of each transition metal contained in the lithium transition metal oxide can be confirmed, and furthermore, the molar ratio of the transition metal having each oxidation number can be confirmed from the oxidation number of the transition metal and the molar ratio of lithium, the transition metal, and oxygen and / or fluoride anions.

[0048] Meanwhile, the lithium transition metal oxide of the above embodiment is bonded to or doped with a halogen ion, for example, a monovalent fluoride ion (F - It may further include ). These halogen ions can contribute to the additional capacity development of the cathode active material through anion oxidation / reduction reactions together with the oxygen ions of the lithium transition metal oxide.

[0049] In a more specific example, the monovalent fluoride ions may be included in the lithium transition metal oxide such that the molar ratio of oxygen ions to fluoride ions included in the lithium transition metal oxide is 1:0.1 to 1:0.3, or 1:0.11 to 1:0.25. Due to this content ratio of monovalent fluoride ions, the degree of capacity development by anion oxidation / reduction reactions is optimized, so that the positive electrode active material of the above embodiment can exhibit an even improved discharge capacity.

[0050] In a more specific embodiment, the lithium transition metal oxide included in the above-described positive electrode active material can be defined by the compositional formula of Chemical Formula 1 below:

[0051] [Chemical Formula 1]

[0052] Li a [M1 b M2 c M3 d ]O2F e

[0053] In the above chemical formula 1,

[0054] M1 is a divalent manganese ion (Mn 2+ ) and M2 is a trivalent manganese ion (Mn 3+ ) and M3 is a tetravalent titanium ion (Ti 4+ ) and,

[0055] a is greater than 1.0 and less than or equal to 1.6, b is 0.15 to 0.4, c is 0.2 to 0.8, d is 0.05 to 0.3, and e is 0 or greater and less than or equal to 0.6, wherein a to e are determined according to the oxidation number of each ion.

[0056] In the above chemical formula 1, a defines the content ratio of lithium included in excess molar ratio in the lithium transition metal oxide, and may satisfy the range of greater than 1 and less than or equal to 1.6, or 1.05 to 1.55, or 1.1 to 1.5, or 1.25 to 1.5.

[0057] In addition, b to d each define the content ratio of divalent manganese ions, trivalent manganese ions, and tetravalent titanium ions contained in the lithium transition metal oxide, and b is 0.15 to 0.40, or 0.16 to 0.39, or 0.16 to 0.3, c is 0.2 to 0.8, or 0.4 to 0.75, or 0.42 to 0.7, or 0.44 to 0.6, and d is 0.05 to 0.3, or 0.07 to 0.28, or 0.14 to 0.27, satisfying the range.

[0058] And, the above e can define the content ratio of monovalent fluoride ions bonded to or doped in the anionic portion of the lithium transition metal oxide, and, for example, can be in the range of 0 or more and 0.6 or less, or 0.2 to 0.6, or 0.22 to 0.5.

[0059] Due to the content ratio of each ion or element described above, the chemical and crystallographic stability of the lithium transition metal oxide is maintained, while the degree of capacity development through oxidation / reduction reactions of cations and anions is maximized, so that the positive electrode active material of one embodiment can exhibit an improved discharge capacity at room temperature and high temperature.

[0060] The positive active material of the above-described embodiment may have a particle size of, for example, 3 μm to 7 μm, and thus can be appropriately used in a positive electrode for a lithium secondary battery while exhibiting high capacity characteristics.

[0061] Meanwhile, the positive electrode active material of the above-described embodiment can be manufactured by mixing, for example, a lithium raw material (e.g., lithium oxide, hydroxide, or carbonate, etc.), a raw material containing divalent manganese ions (e.g., manganese oxide such as MnO), a raw material containing trivalent manganese ions (e.g., manganese oxide such as Mn2O3), and a raw material containing tetravalent titanium ions (e.g., titanium oxide such as TiO2), ball milling the mixture under the application of shear force, and then sintering the mixture at a high temperature of 500°C or higher.

[0062] In this manufacturing method, the lithium raw materials may include, for example, lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O), etc.), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3), etc.), chlorides (e.g., lithium chloride (LiCl), etc.), oxides (Li2O), etc., and one of these alone or a mixture of two or more may be used.

[0063] In addition, as the raw material containing divalent manganese ions, raw material containing trivalent manganese ions, and / or raw material containing tetravalent titanium ions, hydroxides, oxides, or carbonates containing each transition metal may be used.

[0064] Each of these transition metal-containing raw materials and lithium raw materials may be mixed in an equivalent ratio according to the molar ratio of each element already described above, and the high-temperature calcination step may be carried out. This calcination step may be performed at a temperature of 500°C to 1000°C, or 600°C to 1000°C, or 700°C to 950°C, and the calcination time may be 3 hours to 30 hours or 5 hours to 20 hours. In addition, the calcination atmosphere may be an inert gas atmosphere such as an Ar atmosphere or a nitrogen atmosphere, an atmospheric atmosphere, or an oxygen atmosphere, and suitably, it may be an inert gas atmosphere.

[0065] However, in the above manufacturing method, each step can be carried out according to the general manufacturing process and conditions of the existing DRX cathode active material, so further explanation regarding this is omitted.

[0066] Meanwhile, according to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, comprising: a positive current collector; and a positive active material layer formed on the positive current collector and comprising the positive active material of the above-described embodiment. In addition, the positive active material layer may further comprise a polymer binder and a conductive material in addition to the positive active material.

[0067] In the positive electrode of the above other embodiment, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm and may have various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0068] In addition, in the positive electrode active material layer, the conductive material may be, for example, spherical or flake-like graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 to 25 weight%, or 0.5 to 20 weight%, or 1.0 to 15 weight% based on the total weight of the positive electrode active material layer.

[0069] In addition, the polymer binder may include, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The binder may be included in an amount of 0.1 to 25 weight%, or 0.5 to 20 weight%, or 1 to 10 weight% based on the total weight of the anode active material layer.

[0070] Additionally, the positive active material layer may contain the positive active material of one embodiment in an amount of 75% to 95% by weight relative to the total weight.

[0071] The anode of the other embodiment above may be manufactured according to a general anode manufacturing process, except that it includes the anode active material of one embodiment, for example, by mixing each of the above-described components in a solvent to prepare a slurry composition, and then applying, drying, and rolling it onto an anode current collector.

[0072] Meanwhile, according to an additional embodiment of the invention, a lithium secondary battery is provided comprising a positive electrode of the other embodiment, a negative electrode facing the positive electrode, and a porous separator or electrolyte layer interposed between the positive electrode and the negative electrode. By including the positive electrode active material of the above-described embodiment, such a lithium secondary battery can exhibit improved capacity characteristics.

[0073] In such a lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0074] At this time, the negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, the thickness and shape of the negative current collector may be the same as or corresponding to that of the positive current collector.

[0075] In addition, the cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0076] As the above-mentioned 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; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0077] Meanwhile, regarding the above-mentioned cathode active material layer, the types and content ranges of the binder and conductive material may be the same or substantially similar as those described for the above-mentioned anode active material layer; therefore, further explanation regarding this is omitted.

[0078] In addition, the above-described cathode active material layer and cathode may be manufactured by mixing each component of the above-described cathode active material, binder, and conductive material in a solvent to prepare a slurry composition, and then applying, drying, and rolling it onto a cathode current collector. In another example, the cathode composite material including the above-described cathode active material, binder, and conductive material may be manufactured by casting it onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0079] Meanwhile, the above lithium secondary battery may include an electrolyte, and the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a polymer-based solid electrolyte, a gel-type polymer electrolyte, an inorganic solid electrolyte, or a molten inorganic electrolyte that can be used when manufacturing a secondary battery. In this case, when a polymer-based solid electrolyte, a gel-type polymer electrolyte, or an inorganic solid electrolyte is used as the electrolyte, the electrolyte may be included in the form of an electrolyte layer that replaces the porous separator, or may be included in the form of an electrolyte layer that is integrated with or laminated with the porous separator. However, the form of such an electrolyte layer may follow the form of a general all-solid-state battery, a gel electrolyte battery, or a semi-solid-state battery.

[0080] Meanwhile, in a more specific example, the electrolyte may be an electrolyte containing an organic solvent and a lithium salt.

[0081] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used.

[0082] Among these, a carbonate-based solvent can be appropriately used, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferable.

[0083] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt may be at least one selected from the group consisting of F-, Cl-, Br-, I-, NO3-, N(CN)2-, BF4-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, and (CF3CF2SO2)2N-. More specifically, the lithium salts mentioned above may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2.

[0084] In addition, it is preferable to use a lithium salt concentration in the above liquid electrolyte within the range of 0.1 to 4.0 M. When the lithium salt concentration falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0085] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0086] Meanwhile, the lithium secondary battery described above may further include a porous separator that separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. As such a separator, a porous polymer film having low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used.

[0087] In addition, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0088] There are no specific restrictions on the external shape of the above lithium secondary battery, but it may be a cylindrical type using a can, a prismatic type, a pouch type, or a coin type.

[0089] The above-mentioned lithium secondary battery is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0090] Accordingly, the above-mentioned lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0091] Examples of the above-mentioned medium-to-large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but are not limited to these.

[0093] Hereinafter, embodiments of the invention are described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0095] Example 1: Preparation of cathode active material (Composition formula: Li 1.5 (Mn 2+ ) 0.167 (Mn 3+ ) 0.574 (Ti 4+ ) 0.221 O 2 F 0.440 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 17.36 mol%, molar content of trivalent manganese ions: approx. 59.67 mol%, molar content of tetravalent titanium ions: approx. 22.97 mol%)

[0096] Under an Ar atmosphere, each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in molar ratios corresponding to the stoichiometric ratio according to the composition of the cathode active material to be finally manufactured.

[0097] The above mixture was prepared by placing each of the above raw materials into a zirconia container, using bimodal zirconia balls (10 mm, 5 mm, large diameter / small diameter weight ratio = 0.1, 1.5 times the weight of the mixed powder), purging with Ar gas for 1 hour, milling at 350 rpm for 1 hour, and then performing 12 first ball milling cycles in the form of resting for 30 minutes.

[0098] Afterwards, the mixed powder, which was mixed as described above, was heat-treated in an Ar atmosphere using a tube furnace. The heat treatment was performed at 600°C for 3 hours at a heating rate of 5°C / min and at 900°C for 12 hours.

[0099] Through the process described above, Li 1.5 (Mn 2+ ) 0.167 (Mn 3+ ) 0.574 (Ti 4+ ) 0.221 O2F 0.440 The positive active material of Example 1, defined by the compositional formula, was prepared.

[0101] Example 2: Preparation of cathode active material (Composition formula: Li 1.2 (Mn 2+ ) 0.228 (Mn 3+ ) 0.749 (Ti 4+ ) 0.082 O 2 F 0.231 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 21.53 mol%, molar content of trivalent manganese ions: approx. 70.73 mol%, molar content of tetravalent titanium ions: approx. 7.74 mol%)

[0102] The cathode active material of Example 2 was prepared in the same manner as Example 1, except that each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in a changed molar ratio according to the composition of the cathode active material to be finally prepared.

[0103] Through the process described above, Li 1.2 (Mn 2+) 0.228 (Mn 3+ ) 0.749 (Ti 4+ ) 0.082 O2F 0.231 The positive active material of Example 2, defined by the compositional formula, was prepared.

[0105] Example 3: Preparation of cathode active material (Composition formula: Li 1.5 (Mn 2+ ) 0.284 (Mn 3+ ) 0.448 (Ti 4+ ) 0.264 O 2 F 0.468 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 28.51 mol%, molar content of trivalent manganese ions: approx. 44.98 mol%, molar content of tetravalent titanium ions: approx. 26.51 mol%)

[0106] The cathode active material of Example 3 was prepared in the same manner as Example 1, except that each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in a changed molar ratio according to the composition of the cathode active material to be finally prepared.

[0107] Through the process described above, Li 1.5 (Mn 2+ ) 0.284 (Mn 3+ ) 0.448 (Ti 4+ ) 0.264 O2F 0.468 The positive active material of Example 3, defined by the compositional formula, was prepared.

[0109] Example 4: Preparation of cathode active material (Composition formula: Li 1.2 (Mn 2+ ) 0.381 (Mn 3+ ) 0.617 (Ti 4+ ) 0.138 O 2 F 0.336 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 33.51 mol%, molar content of trivalent manganese ions: approx. 54.33 mol%, molar content of tetravalent titanium ions: approx. 12.16 mol%)

[0110] The cathode active material of Example 4 was prepared in the same manner as Example 1, except that each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in a changed molar ratio according to the composition of the cathode active material to be finally prepared.

[0111] Through the process described above, Li 1.2 (Mn 2+ ) 0.381 (Mn 3+ ) 0.617 (Ti 4+ ) 0.138 O2F 0.336 The positive active material of Example 4, defined by the compositional formula, was prepared.

[0113] Comparative Example 1: Preparation of cathode active material (Composition formula: Li 1.036 (Mn 2+ ) 1.081 (Mn 3+ ) 0.357 (Ti 4+ ) 0.061 O 2 F 0.513 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 72.11 mol%, molar content of trivalent manganese ions: approx. 23.82 mol%, molar content of tetravalent titanium ions: approx. 4.07 mol%)

[0114] The cathode active material of Comparative Example 1 was prepared in the same manner as Example 1, except that each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in a modified molar ratio according to the composition of the cathode active material to be finally prepared.

[0115] Through the process described above, Li 1.036 (Mn 2+ ) 1.081 (Mn 3+ ) 0.357 (Ti 4+ ) 0.061 O2F 0.513 A positive active material of Comparative Example 1, defined by the compositional formula, was prepared.

[0117] Comparative Example 2: Preparation of cathode active material (Composition formula: Li 1.077 (Mn 2+ ) 1.106 (Mn 3+ ) 0.271 (Ti 4+ ) 0.116 O 2 F 0.566 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 74.08 mol%, molar content of trivalent manganese ions: approx. 18.15 mol%, molar content of tetravalent titanium ions: approx. 7.77 mol%)

[0118] The cathode active material of Comparative Example 2 was prepared in the same manner as in Example 1, except that each raw material of Li2CO3, MnO2, Mn2O3, and TiO2 was mixed in a modified molar ratio according to the composition of the cathode active material to be finally prepared.

[0119] Through the process described above, Li 1.077 (Mn 2+ ) 1.106 (Mn 3+ ) 0.271 (Ti 4+ ) 0.116 O2F 0.566 A positive electrode active material of Comparative Example 2, defined by the compositional formula of, was prepared.

[0121] Comparative Example 3: Preparation of cathode active material (Composition formula: Li 1.2 (Mn 2+ ) 0.2 (Mn 3+ ) 0.4 (Ti 4+ ) 0.2 (Nb 5+ ) 0.1 O 2 F 0.1 ) - Molar content of divalent manganese ions relative to total transition metal content: approx. 22.22 mol%, molar content of trivalent manganese ions: approx. 44.44 mol%, molar content of tetravalent titanium ions: approx. 22.22 mol%, molar content of pentavalent niobium ions: approx. 11.11 mol%)

[0122] In addition to the raw materials of Li2CO3, MnO2, Mn2O3, and TiO2, pentavalent niobium ions (Nb5+ Nb2O5 was additionally used as a raw material containing ). The cathode active material of Comparative Example 3 was prepared in the same manner as in Example 1, except that each of these five raw materials was mixed in a modified molar ratio according to the composition of the cathode active material to be finally prepared.

[0123] Through the process described above, Li 1.2 (Mn 2+ ) 0.2 (Mn 3+ ) 0.4 (Ti 4+ ) 0.2 (Nb 5+ ) 0.1 O2F 0.1 The positive active material of Comparative Example 3, defined by the compositional formula, was prepared.

[0125] Manufacturing Example: Manufacturing of a lithium secondary battery

[0126] An anode slurry was prepared by mixing the anode active material of the example or comparative example, carbon black conductive material, and PVDF binder in N-methylpyrrolidone in a weight ratio of 76.5:13.5:10. The anode slurry was applied onto an aluminum current collector sheet, dried, and then rolled to produce an anode.

[0127] An electrode assembly was manufactured by interposing a polyethylene separator between the anode and the lithium metal cathode manufactured as described above, and after inserting the electrode assembly into a battery case, an electrolyte was injected, and an activation process was performed by charging at 45°C with a constant current of 0.1C until the voltage reached 4.65V, and then discharging at a constant current of 0.1C until the voltage reached 2.0V to manufacture a lithium secondary battery.

[0129] Experimental Example 1: Evaluation of Electrochemical Characteristics (High and Room Temperature Discharge Capacity)

[0130] For a lithium secondary battery manufactured with the positive active material of the above example or comparative example, a charge and discharge test was conducted at a high temperature (45°C). At this time, the test was conducted under conditions of a lower limit voltage of 2.0V, an upper limit voltage of 4.65V, and a C-rate of 0.1C, and the high-temperature discharge capacity of the first cycle was evaluated for comparison in this charge and discharge test.

[0131] In addition, a charge and discharge test was conducted at room temperature (25°C) on a lithium secondary battery manufactured with the positive active material of the above example or comparative example. At this time, the test was conducted under conditions of a lower limit voltage of 1.5 V, an upper limit voltage of 4.8 V, and a C-rate of 0.1 C, and the room temperature discharge capacity of the first cycle was evaluated for comparison during the charge and discharge test.

[0132] Table 1 below shows the results of a comparative evaluation of high-temperature discharge capacity for the positive electrode active materials of Examples 1, 2 and Comparative Example 3, and Table 2 below shows the results of a comparative evaluation of room-temperature discharge capacity for Examples 3 and 4 and Comparative Examples 1 to 3.

[0133] Initial high-temperature discharge capacity (mAh / g) Example 1 257.37 Example 2 250.18 Comparative Example 3 247.14

[0134] Initial room temperature discharge capacity (mAh / g) Example 3 260.42 Example 4 251.47 Comparative Example 1 239.03 Comparative Example 2 239.10 Comparative Example 3 246.90

[0135] Referring to Tables 1 and 2 above, it was confirmed that the positive electrode active materials of Examples 1 to 4 exhibit improved high-temperature and room-temperature discharge capacities compared to the positive electrode active material of the Comparative Example, as the content ratio of each transition metal ion and fluoride ion is optimized.

[0136] In contrast, it was confirmed that the positive active materials of Comparative Examples 1 and 2 exhibited poor discharge capacity compared to the examples as the content ratio of divalent manganese ions and / or trivalent manganese ions deviated from an appropriate ratio.

[0137] In addition, it was confirmed that the positive active material of Comparative Example 3 exhibited a poor discharge capacity compared to the example as it additionally contained pentavalent niobium ions.

Claims

Claim 1 A positive electrode active material comprising a lithium transition metal oxide, wherein the lithium transition metal oxide has a molar ratio of lithium to the total number of moles of transition metals excluding lithium greater than 1, and the ion of the transition metal is a divalent manganese ion (Mn 2+ ), trivalent manganese ions (Mn 3+ ) and tetravalent titanium ions (Ti 4+ It contains only ), and based on the total content of transition metals excluding lithium, divalent manganese ions (Mn 2+ The molar content of ) is 10 to 40 mol%, and trivalent manganese ions (Mn 3+ The molar content of ) is 33 to 73 mol%, and tetravalent titanium ions (Ti 4+ A positive active material having a molar content of ) 5 to 30 mol%. Claim 2 In claim 1, the lithium transition metal oxide is a positive active material having a disordered rock-salt (DRX) structure in its crystal structure. Claim 3 delete Claim 4 In claim 1, the lithium transition metal oxide is a positive active material further comprising a halogen ion bonded to or doped in an anionic portion. Claim 5 In claim 4, the halogen ion is a positive active material comprising a monovalent fluoride ion. Claim 6 In claim 5, the lithium transition metal oxide is a positive electrode active material containing monovalent fluoride ions such that the molar ratio of oxygen ions to fluoride ions is 1:0.1 to 1:0.

3. Claim 7 In claim 1, the lithium transition metal oxide is an anode active material represented by the following chemical formula 1: [Chemical Formula 1]Li a [M1 b M2 c M3 d ]O2F e In the above Chemical Formula 1, M1 is a divalent manganese ion (Mn 2+ ) and M2 is a trivalent manganese ion (Mn 3+ ) and M3 is a tetravalent titanium ion (Ti 4+ ) and a is greater than 1.0 and less than or equal to 1.6, b is 0.15 to 0.4, c is 0.2 to 0.8, d is 0.05 to 0.3, and e is 0 or greater and less than or equal to 0.6, wherein a to e are determined according to the oxidation number of each ion. Claim 8 A positive electrode for a lithium secondary battery comprising: a positive current collector; and a positive active material layer formed on the positive current collector and comprising a positive active material of any one of claims 1, 2 and 4 to 7. Claim 9 In claim 8, the positive electrode active material layer comprises 75 to 95 weight percent of a positive electrode active material based on the total weight, for a lithium secondary battery positive electrode. Claim 10 In claim 8, the positive electrode active material layer further comprises a polymer binder and a conductive material, for a lithium secondary battery positive electrode. Claim 11 A lithium secondary battery comprising a positive electrode of claim 8, a negative electrode facing the positive electrode, and a porous separator or electrolyte layer interposed between the positive electrode and the negative electrode. Claim 12 A lithium secondary battery according to claim 11, further comprising an electrolyte including a lithium salt and a non-aqueous organic solvent.