Positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode and a lithium secondary battery comprising the same, the positive electrode containing, as a positive electrode active material, an over-lithiated manganese-based oxide in which the molar ratio of lithium to total metals other than lithium (Li / Me) is greater than 1.1, the content of manganese in all the metals other than lithium is 50% or more, and the formula (1) is satisfied, and a lithium secondary battery comprising the same. Equation (1): 0.05 lt; iTM / ILilt is selected; and 0.13. Wherein, in equation (1), ITM and ILi are the sum of peak areas appearing in the range of 1000 ppm to 2500 ppm and the sum of peak areas appearing in the range of 300 ppm to 900 ppm, respectively, when peak deconvolution is performed on a 1D NMR center band spectrum extracted from an NMR spectrum of 2D 7Li MATPASS (Magic angle steering phase adjustment rotating sideband) of the over-lithiated manganese-based oxide.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2022-0134434, filed on October 18, 2022, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a positive electrode and a lithium secondary battery, and more particularly to a positive electrode containing an overlithiated manganese-based oxide as a positive electrode active material and having excellent life characteristics, and a lithium secondary battery including the positive electrode. Background Art

[0003] In recent years, as interest in energy storage technology has grown, and its application has expanded to include energy sources for mobile phones, cameras, laptops, and even electric vehicles, research and development work on electrochemical devices has gradually become more specific. Among these electrochemical devices, people have become interested in the development of rechargeable secondary batteries, especially lithium secondary batteries developed in the early 1990s, which have attracted much attention due to their high operating voltage and significantly higher energy density.

[0004] Recently, with the increase in demand for high energy density secondary batteries (such as electric vehicle batteries), the demand for high capacity positive electrode active materials is also increasing. In order to increase the capacity of positive electrode active materials, high nickel positive electrode active materials are generally developed, that is, high nickel positive electrode active materials in which the nickel content in the ternary lithium composite transition metal oxide (hereinafter referred to as NCM) containing nickel, cobalt and manganese is increased. However, for high nickel positive electrode active materials, due to the high price of raw materials such as nickel and cobalt, there are restrictions on reducing the unit price, and due to the low structural stability, there are problems such as structural collapse of positive electrode active materials at high temperature and high voltage, transition metal dissolution and gas generation.

[0005] Therefore, in recent years, positive electrodes for lithium secondary batteries using over-lithiated manganese-based oxides have been actively developed, and the over-lithiated manganese-based oxides can achieve high capacity while containing a lower precious metal content than NCM. Over-lithiated manganese-based oxides are materials in which the molar ratio of lithium to transition metal is greater than 1 and the manganese content in the transition metal is more than 50 mol%, wherein it has a mixed structure of a Li2MnO3 phase with a rock salt structure and a LiMO2 phase with a layered structure (where M is nickel (Ni), cobalt (Co) and manganese (Mn)). Since the over-lithiated manganese-based oxide achieves capacity in a low voltage range through transition metal oxidation similar to conventional NCM, and achieves capacity in a high voltage range through oxygen redox, a higher capacity than conventional high-nickel NCM can be achieved. However, since excessive active oxygen is generated during the redox process of oxygen, there is a problem of lower battery life.

[0006] Therefore, there is a need to develop a lithium secondary battery having excellent life characteristics while containing an overlithiated manganese-based oxide. Summary of the invention

[0007] Technical issues

[0008] One aspect of the present invention provides a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode, wherein the positive electrode can achieve excellent life characteristics by using a superlithiated manganese-based oxide in which the ratio of lithium (Li) present in a transition metal layer to Li present in a lithium layer satisfies specific conditions.

[0009] Technical Solution

[0010] In one aspect, the present invention provides a positive electrode comprising an over-lithiated manganese-based oxide as a positive electrode active material, wherein the molar ratio of lithium to all metals other than lithium (Li / Me) of the over-lithiated manganese-based oxide is greater than 1.1, the content of manganese in all metals other than lithium is greater than 50%, and equation (1) is satisfied.

[0011] Equation (1): 0.05 TM / I Li <0.13

[0012] In equation (1), I TM and I Li The 2D 7 The sum of the peak areas appearing in the range of 1000ppm to 2500ppm and the sum of the peak areas appearing in the range of 300ppm to 900ppm when the 1D nuclear magnetic resonance (NMR) center band spectrum extracted from the Li MATPASS (magic angle steering phase adjustment spinning sideband) NMR spectrum is subjected to peak deconvolution.

[0013] Preferably, the overlithiated manganese-based oxide may satisfy equation (1-1).

[0014] Equation (1-1): 0.06≤I TM / I Li ≤0.12

[0015] In equation (1-1), I TM and I Li Same definition as in equation (1).

[0016] In another aspect, the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode is the positive electrode of the present invention described above.

[0017] Beneficial Effects

[0018] ​The positive electrode of the present invention is characterized in that it comprises an over-lithiated manganese-based oxide as a positive electrode active material, wherein the molar ratio of lithium to all metals other than lithium (Li / Me) of the over-lithiated manganese-based oxide is greater than 1.1, the content of manganese in all metals other than lithium is greater than 50%, and a 2D over-lithiated manganese-based oxide is used. 7 I obtained by peak deconvolution of the 1D NMR central band spectrum extracted from the Li MATPASS (Magic Angle Steering Phase Adjustment Spinning Sideband) NMR analysis TM / I Li In this case, I TM is the sum of the peak areas appearing in the range of 1000 ppm to 2500 ppm when the peak is deconvoluted, wherein it is a value indicating the proportion of lithium located in the transition metal layer, and I Li It is the sum of the peak areas appearing in the range of 300ppm to 900ppm when the peak is deconvoluted, wherein it is a value representing the proportion of lithium located in the lithium layer. If the proportion of lithium (Li) present in the transition metal layer increases, the capacity increases, but the life characteristics decrease due to the increase in oxygen redox. On the contrary, if the proportion of lithium in the transition metal layer decreases, the effect of capacity enhancement is not obvious. Therefore, in the present invention, since the ratio of Li present in the transition metal layer to Li present in the lithium layer satisfies a specific condition (i.e., I TM / I Li The overlithiated manganese-based oxide has a carbon content of greater than 0.05 and less than 0.13 as the positive electrode active material, and thus can achieve the effect of significantly improving the lifespan characteristics while achieving high capacity characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The NMR spectra of the lithiated manganese-based oxides were analyzed by 1D Hahn-echo MAS NMR analysis and by 2D 7 Comparison of NMR spectra obtained by analyzing lithiated manganese-based oxides using the Li MATPASS NMR analysis method.

[0020] Figure 2 2D images of the overlithiated manganese-based oxides A to F are shown. 7 1D NMR center band spectrum extracted from the Li MATPASS (Magic Angle Steering Phase Adjusted Spinning Sideband) NMR spectrum.

[0021] Figure 3 is a graph showing the results of evaluating the room temperature life characteristics of the lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2.

[0022] Figure 4: is a graph showing the results of measuring the discharge capacity of the lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2.

[0023] Figure 5 is a graph showing the results of evaluating the high temperature life characteristics of the lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0024] Hereinafter, the present invention will be described in detail.

[0025] As a result of extensive research on improving the life characteristics of lithium secondary batteries using overlithiated manganese-based oxides as positive electrode active materials, the present inventors have found that when an overlithiated manganese-based oxide in which the ratio of lithium (Li) present in the transition metal layer to Li present in the lithium layer satisfies a specific condition is used as a positive electrode active material, the life characteristics of the lithium secondary battery using the overlithiated manganese-based oxide can be significantly improved, thereby completing the present invention.

[0026] positive electrode

[0027] The positive electrode of the present invention is characterized in that it contains an overlithiated manganese-based oxide as a positive electrode active material, wherein the molar ratio of lithium to all metals other than lithium (Li / Me) of the overlithiated manganese-based oxide is greater than 1.1, and the content of manganese in all metals other than lithium is 50 mol% or more, wherein the overlithiated manganese-based oxide satisfies the following equation (1).

[0028] Equation (1): 0.05 TM / I Li <0.13

[0029] In equation (1), I TM and I Li The 2D 7 The sum of the peak areas appearing in the range of 1000ppm to 2500ppm and the sum of the peak areas appearing in the range of 300ppm to 900ppm when the 1D nuclear magnetic resonance (NMR) center band spectrum extracted from the Li MATPASS (magic angle steering phase adjustment spinning sideband) NMR spectrum is subjected to peak deconvolution.

[0030] The 2D in this invention 7 Li MATPASS NMR measurement conditions are as follows.

[0031] <Measurement conditions>

[0032] Solid-state 400MHz WB (wide bore) NMR system

[0033] MAS (Magic Angle Spin) rate: 55kHz​

[0034] Spectrum frequency (sfo1): 155.62MHz ( 7 Li)

[0035] Temperature: Ambient temperature

[0036] 7 Li chemical shift reference: secondary LiF(s) reference at -1ppm

[0037] Pulse program: 2D MATPASS

[0038] Spectral width (sw): 1250kHz

[0039] Measuring time: 5ms

[0040] Carrier frequency (o1p), 800ppm

[0041] Pulse length (p1): 1μs

[0042] Cycle delay (d1): 1s

[0043] TD(L1) in F1 dimension: 16

[0044] Scan times: 30000

[0045] After the measurement, the 9th slice was extracted from the 16 1D NMR spectra obtained after processing the 2D data with xfb to obtain the 1D NMR central band spectrum (after the measurement, the 2D data was processed with xfb, and then the central band slice was extracted ((L1 / 2+1)=(16 / 2+1)=9th slice).

[0046] DMFIT (64-bit, version #20190125) NMR software can be used to 7 The 1D NMR center band spectrum extracted from the Li MATPASS (Magic Angle Steering Phase Adjustment Spinning Sideband) NMR spectrum is subjected to peak deconvolution. 7 After the 1D NMR central band spectrum extracted from the LiMALPASS NMR spectrum is input into the DMFIT program, the following method can be used for peak deconvolution, that is, after selecting Gaussian / Lorentzian as the fitting model for peak deconvolution, and setting appropriate initial values ​​for peak amplitude, peak position, peak width and Gaussian / Lorentzian fraction (xG / (1-x)L), the fitting is repeated until a suitable convergence value is reached. In the present invention, during the peak deconvolution process, the Gaussian / Lorentzian fraction (xG / (1-x)L) is fixed to 0.5, and fitting is performed under the conditions of nParVar=15, step=1, and Thresh=0.001.

[0047] Conventionally, one-dimensional (1D) echo MAS NMR analysis methods are mainly used for structural analysis of positive electrode active materials. 7 When Li NMR analysis is used to measure over-lithiated manganese-based oxides, the main peak and the rotating side band ( Figure 1 In particular, since the characteristic peak of Li2MnO3 contained in the over-lithiated manganese-based oxide, the peak near 1500ppm, overlaps with the rotating sideband, it is difficult to analyze the structural characteristics of the positive electrode active material (see Figure 1 ).

[0048] However, if you use 2D 7 The Li MATPASS NMR analysis method can obtain high-resolution NMR spectra and distinguish the structural features of overlithiated manganese-based oxides by deconvolution of the extracted spectra. 7 The LiMATPASS NMR analysis method was used to analyze various over-lithiated manganese-based oxides. The inventors found that when I TM / I Li In the case where an overlithiated manganese-based oxide satisfying a specific condition (greater than 0.05 and less than 0.13) is used for a positive electrode, the life characteristics of a lithium secondary battery are significantly improved, thereby completing the present invention.

[0049] I TM / I Li is the ratio of lithium located in the transition metal layer to lithium located in the lithium layer in the crystal structure of the over-lithiated manganese-based oxide, wherein TM / I L When the ratio is greater than 0.05 and less than 0.13, since the degree of oxygen redox occurring during charge and discharge is appropriately controlled, high capacity and excellent life characteristics can be achieved.

[0050] Preferably, the overlithiated manganese-based oxide has TM / I Li Can be 0.06 to 0.12, preferably 1 TM / I Li is 0.08 to 0.12, more preferably 0.09 to 0.12, more preferably 0.097 to 0.11, and most preferably 0.10 to 0.11. TM / I Li When the above range is satisfied, high temperature life characteristics are further improved.

[0051] In the over-lithiated manganese-based oxide, the molar ratio of lithium to the molar number of all metal elements except lithium (Li / Me) can be 1.1 to 1.5, 1.2 to 1.5, 1.25 to 1.5, or 1.25 to 1.4. When the Li / Me ratio meets the above range, the rate performance and capacity characteristics are excellent. If the Li / Me ratio is too high, the conductivity may decrease and the rock salt phase (Li2MnO3) may increase, thereby accelerating the degradation rate; if the Li / Me ratio is too low, the effect of improving the energy density is not obvious.

[0052] In addition, the molar ratio of nickel to manganese contained in the over-lithiated manganese-based oxide may be 30:70 to 45:55, preferably 31:69 to 45:55. When the molar ratio of nickel to manganese in the over-lithiated manganese-based oxide satisfies the above range, the capacity characteristics and life characteristics are excellent. In the case where the nickel content is less than 30 mol%, the problem of accelerated battery degradation occurs due to the increase of the rock salt phase (Li2MnO3).

[0053] Preferably, the overlithiated manganese-based oxide may be represented by Formula 1.

[0054] [Formula 1]

[0055] Li a Ni b Co c Mn d M e O2

[0056] In Formula 1, M may be at least one selected from the group consisting of aluminum (Al), boron (B), cobalt (Co), tungsten (W), magnesium (Mg), vanadium (V), titanium (Ti), zinc (Zn), gallium (Ga), indium (In), ruthenium (Ru), niobium (Nb), tin (Sn), strontium (Sr), and zirconium (Zr).

[0057] a is the molar ratio of Li in the overlithiated manganese-based oxide, wherein a may satisfy 1<a, 1.1≤a≤1.5, or 1.1≤a≤1.3. When a satisfies the above range, the irreversible capacity of the silicon (Si)-based negative electrode active material can be fully compensated, and high capacity characteristics can be achieved.

[0058] b is a molar ratio of nickel (Ni) in the over-lithiated manganese-based oxide, wherein b may satisfy 0.1≤b<0.5, 0.2≤b<0.5, or 0.3≤b<0.5.

[0059] c is a molar ratio of Co in the overlithiated manganese-based oxide, wherein c may satisfy 0≤c<0.1, 0≤c≤0.08, or 0≤c≤0.05. In the case where c is greater than 0.1, it is difficult to ensure a high capacity, and gas generation and degradation of the positive electrode active material may be aggravated, so the life characteristics may be reduced.

[0060] d is the molar ratio of manganese (Mn) in the over-lithiated manganese-based oxide, wherein d may satisfy 0.5≤d≤0.9, 0.50≤d≤0.80, or 0.50≤d≤0.70. When d is less than 0.5, the effect of compensating the irreversible capacity of the negative electrode active material and improving the capacity is not obvious due to the small proportion of the rock salt phase.

[0061] e is the molar ratio of the doping element M in the over-lithiated manganese-based oxide, wherein e may satisfy 0≤e≤0.1 or 0≤e≤0.05. Excessive amounts of doping elements may adversely affect the capacity of the active material.

[0062] The over-lithiated manganese-based oxide has a mixed structure of a rock salt phase (Li2MnO3) and a layered phase (LiM'O2, wherein M' includes Ni and Mn), and its composition can also be expressed by the following [Formula 2].

[0063] [Formula 2]

[0064] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0065] In [Formula 2], M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0066] X represents the proportion of Li2MnO3 phase in the over-lithiated manganese-based oxide, wherein X may satisfy 0.2≤X≤0.5, 0.25≤X≤0.5, or 0.25≤X≤0.4. When the proportion of Li2MnO3 phase in the over-lithiated manganese-based oxide satisfies the above range, SiO x The irreversible capacity of the negative electrode active material can be fully compensated, and high capacity characteristics can be achieved.

[0067] y is a molar ratio of Mn in the LiM'O2 layered phase, wherein y may satisfy 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0068] z is a molar ratio of Co in the LiM'O2 layered phase, wherein z may satisfy 0≤z≤0.1, 0≤z≤0.08, or 0≤z≤0.05. In the case where z is greater than 0.1, since gas generation and degradation of the positive electrode active material may be aggravated, life characteristics may be reduced.

[0069] w is a molar ratio of the doping element M in the LiM'O2 layered phase, wherein w may satisfy 0≤w≤0.1 or 0≤w≤0.05.

[0070] If necessary, the positive electrode active material of the present invention may further include a coating on the surface of the over-lithiated manganese-based oxide. In the case where the positive electrode active material includes the coating, since the coating inhibits the contact between the over-lithiated manganese-based oxide and the electrolyte, the side reaction of the electrolyte is reduced, thereby achieving the effect of improving the life characteristics.

[0071] The coating may contain coating elements M 1 , where the coating element M 1 It may be, for example, at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, preferably Al, Co, Nb, W and a combination thereof, and more preferably Al, Co and a combination thereof. Two or more coating elements M may be included 1 , for example, may contain Al and Co.

[0072] The coating elements can be in the form of oxides, i.e., M 1 Oz (1≤z≤4) exists in the coating.

[0073] The coating can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. Among them, the coating formed by the atomic layer deposition method is more ideal in forming a coating area widely.

[0074] The area of ​​the formed coating layer may be 10% to 100%, preferably 30% to 100%, more preferably 50% to 100%, based on the total surface area of ​​the overlithiated manganese-based oxide particles. When the area of ​​the formed coating layer satisfies the above range, the effect of improving the life characteristics is excellent.

[0075] The positive electrode active material of the present invention may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle size D of the secondary particles is 50 It can be 2 μm to 10 μm, preferably 2 μm to 8 μm, and more preferably 4 μm to 8 μm. 50 When the above range is satisfied, excellent electrode density can be achieved, and reduction in capacity and rate performance can be minimized.

[0076] In addition, the Brunauer-Emmett-Teller (BET) specific surface area of ​​the positive electrode active material can be 1 m 2 / g to 10m 2 / g,3m 2 / g to 8m2 / g, or 4m 2 / g to 6m 2 If the BET specific surface area of ​​the positive electrode active material is too low, it is difficult to achieve sufficient capacity due to insufficient reaction area with the electrolyte; if the specific surface area is too high, the side reaction with the electrolyte is accelerated due to the rapid moisture absorption rate, making it difficult to ensure the life characteristics.

[0077] Overlithiated manganese-based oxides can be prepared by mixing a transition metal precursor and a lithium source and then sintering the mixture.

[0078] For example, the lithium raw material may include lithium-containing carbonates (such as lithium carbonate, etc.), hydrates (such as lithium hydroxide hydrate (LiOH·H2O), etc.), hydroxides (such as lithium hydroxide, etc.), nitrates (such as lithium nitrate (LiNO3)), etc.) or chlorides (such as lithium chloride (LiCl)), and any one of them or a mixture of two or more thereof can be used.

[0079] The transition metal precursor may be in the form of a hydroxide, an oxide or a carbonate. In the case of using a precursor in the form of a carbonate, a more preferred formula, a positive electrode active material having a relatively high specific surface area may be prepared.

[0080] The transition metal precursor can be prepared by a coprecipitation process. For example, after each transition metal-containing raw material is dissolved in a solvent to prepare a metal solution, the transition metal precursor can be prepared by mixing the metal solution, an ammonium cation complexing agent and an alkaline compound, and then performing a coprecipitation reaction. If necessary, an oxidant or oxygen can be further added during the coprecipitation reaction.

[0081] In this case, the raw material containing transition metals can be acetate, carbonate, nitrate, sulfate, halide or sulfide of each transition metal. Specifically, the raw material containing transition metals can be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, Co2O3, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt acetate or cobalt halide.

[0082] The ammonium cation complexing agent may be at least one selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4 and NH4CO3.

[0083] The basic compound can be at least one selected from the group consisting of NaOH, Na2CO3, KOH and Ca(OH)2. The form of the precursor can vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a precursor in the form of a hydroxide can be obtained, while when Na2CO3 is used as the basic compound, a precursor in the form of a carbonate can be obtained. In addition, when a basic compound and an oxidant are used simultaneously, a precursor in the form of an oxide can be obtained.

[0084] The transition metal precursor and the lithium raw material may be mixed in an amount such that the molar ratio of the total transition metal (Ni+Co+Mn):Li is 1:1.05 to 1:2, preferably 1:1.1 to 1:1.8, more preferably 1:1.25 to 1:1.8.

[0085] The sintering may be performed at a temperature of 600° C. to 1000° C., or 700° C. to 950° C., and the sintering time may be 5 hours to 30 hours, or 5 hours to 20 hours. In addition, the sintering atmosphere may be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 volume % to 100 volume % of oxygen.

[0086] If necessary, the positive electrode of the present invention may further include a conductive agent and a binder in addition to the positive electrode active material.

[0087] For example, the conductive agent may include: spherical or flaky 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 nanotubes, and multi-walled carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the content of the conductive agent may be 0.1% to 20% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight.

[0088] In addition, the binder can be, for example, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers, and any one thereof or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the binder can be 1% to 20% by weight, 2% to 20% by weight, or 2% to 10% by weight.

[0089] The positive electrode can be prepared by a method for preparing a positive electrode known in the art. For example, the positive electrode can be prepared by coating a positive electrode current collector with a positive electrode slurry prepared by dissolving or dispersing a positive electrode active material and an optional binder and / or conductive agent in a solvent, rolling and drying; or the positive electrode slurry can be cast on a separate support, and then a film separated from the support is laminated on the positive electrode current collector.

[0090] The positive electrode current collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector may be generally 3 μm to 500 μm, and microscopic irregularities may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various shapes such as a film, a sheet, a foil, a mesh, a porous body, a foam, a non-woven fabric, etc.

[0091] The solvent may be a commonly used solvent in the art, and may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water, and any one or a mixture of two or more thereof may be used. If the coating thickness, preparation yield or processability of the positive electrode slurry are taken into consideration, the positive electrode slurry may be adjusted to have an appropriate viscosity, and the amount of solvent may be sufficient without particular limitation.

[0092] As described above, since the positive electrode contains an overlithiated manganese-based oxide satisfying equation (1) as the positive electrode active material, it can operate stably even if the charge end voltage is set as high as 4.3 V to 4.5 V, thereby achieving high capacity characteristics and exhibiting excellent life characteristics under room temperature and high temperature conditions.

[0093] Lithium secondary battery

[0094] Next, the lithium secondary battery of the present invention will be described.

[0095] The lithium secondary battery of the present invention includes: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. In this case, the positive electrode is the positive electrode of the present invention described above. Since the positive electrode has been described above, its detailed description will be omitted.

[0096] negative electrode

[0097] The negative electrode of the present invention includes a negative electrode active material layer including a negative electrode active material, and if necessary, the negative electrode active material layer may further include a conductive agent and / or a binder.

[0098] Various negative electrode active materials used in the art, such as silicon-based negative electrode active materials, carbon-based negative electrode active materials, metal alloys, or combinations thereof, can be used as the negative electrode active material, and the negative electrode active material is not particularly limited.

[0099] Preferably, the negative electrode active material may include a silicon-based negative electrode active material.

[0100] For example, the silicon-based negative electrode active material may be selected from silicon (Si), SiO m (where 0 < m < 2), Si-C composites, Si-M a alloys (M a is at least one selected from Al, Sn, Mg, copper (Cu), iron (Fe), lead (Pb), Zn, Mn, chromium (Cr), Ti, and Ni), and combinations thereof.

[0101] In addition, the silicon-based negative electrode active material may be doped with M b metal. In this case, the M b metal may be a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element. For example, it may be Li or Mg. Specifically, the silicon-based negative electrode active material may be Si, SiO b (where 0 < m < 2), or Si-C composite doped with M m metal. For the silicon-based negative electrode active material doped with metal, although the capacity of the active material is reduced due to the doping element, the efficiency is high, so a high energy density can be achieved.

[0102] In addition, the silicon-based negative electrode active material may further include a carbon coating on the particle surface. In this case, based on the total weight of the silicon-based negative electrode active material, the amount of the carbon coating may be 20 wt% or less, preferably 0.1 wt% to 20 wt%. The carbon coating can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc.

[0103] In addition, regarding the particle size of the silicon-based negative electrode active material, D 50 may be 3 μm to 8 μm, preferably 4 μm to 7 μm, and the range of D min to D max may be 0.5 μm to 30 μm, preferably 0.5 μm to 20 μm, more preferably 1 μm to 15 μm.

[0104] Based on the total weight of the negative electrode active material contained in the negative electrode, the content of the silicon-based negative electrode active material may be 1 wt% to 100 wt%, 1 wt% to 50 wt%, 1 wt% to 30 wt%, 1 wt% to 15 wt%, 10 wt% to 70 wt%, or 10 wt% to 50 wt%.

[0105] In addition, the negative electrode may further include a carbon-based negative electrode active material, such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon or hard carbon, but is not limited thereto.

[0106] The content of the carbon-based negative electrode active material may be 1 to 100 weight %, 50 to 99 weight %, 70 to 99 weight %, 85 to 99 weight %, 30 to 90 weight %, or 50 to 90 weight %, based on the total weight of the negative electrode active material contained in the negative electrode.

[0107] According to one embodiment, the negative electrode active material may be a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material, wherein the mixing ratio (weight ratio) of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be 1:99 to 50:50, preferably 3:97 to 30:70. When the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material satisfies the above range, the volume expansion of the silicon-based negative electrode active material can be suppressed to ensure excellent cycle performance while improving capacity characteristics.

[0108] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer. When the amount of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical performance may be obtained.

[0109] For example, the conductive agent may include: spherical or flaky 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 nanotubes, and multi-walled carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more thereof may be used. Based on the total weight of the negative electrode active material layer, the content of the conductive agent may be 0.1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight.

[0110] Preferably, single-walled carbon nanotubes may be used as the conductive agent. In the case of using single-walled carbon nanotubes as the conductive agent, a conductive path may be uniformly formed on the surface of the negative electrode active material, thereby achieving an effect of improving cycle characteristics.

[0111] For example, the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers, and any one or a mixture of two or more thereof may be used. Based on the total weight of the negative electrode active material layer, the content of the binder may be 1% to 20% by weight, preferably 2% to 20% by weight, and more preferably 2% to 10% by weight.

[0112] In the negative electrode, the negative electrode active material layer may be a single layer or a multilayer structure consisting of two or more layers. In the case where the negative electrode active material layer has a multilayer structure consisting of two or more layers, each layer may have different types and / or contents of negative electrode active materials, binders and / or conductive agents. For example, in the negative electrode of the present invention, the lower layer may be formed so that the content of carbon-based negative electrode active material is higher than that of the upper layer, and the upper layer may be formed so that the content of silicon-based negative electrode active material is higher, in which case, compared with the case where the negative electrode active material layer forms a single layer, the effect of improving the fast charging performance may be obtained.

[0113] In the lithium secondary battery of the present invention, it is desirable to configure different N / P ratios (i.e., the ratio of the negative electrode capacity to the positive electrode capacity) according to the type of negative electrode active material used. For example, in the case where 100% Si is used as the negative electrode active material, it is desirable that the N / P ratio is about 150% to about 300%; in the case where SiO m In the case where a mixture of an aluminum alloy and a carbon-based negative electrode active material is used as the negative electrode active material, it is desirable that the N / P ratio is about 100% to about 150%.

[0114] The negative electrode may be prepared by a method for preparing a negative electrode known in the art. For example, the negative electrode may be prepared by coating a negative electrode current collector with a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material and an optional binder and / or conductive agent in a solvent, rolling and drying, or the negative electrode slurry may be cast on a separate support and then a film separated from the support is laminated on the negative electrode current collector.

[0115] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. In addition, the thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and similar to the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam body, a non-woven fabric body, etc.

[0116] The solvent may be a commonly used solvent in the art, and may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water, and any one or a mixture of two or more thereof may be used. If the coating thickness, manufacturing yield and processability of the negative electrode material mixture are taken into consideration, the negative electrode slurry may be adjusted to have an appropriate viscosity, and the amount of solvent may be sufficient without particular limitation.

[0117] Diaphragm

[0118] The separator in the lithium secondary battery of the present invention separates the negative electrode from the positive electrode and provides a migration channel for lithium ions, wherein any separator can be used as a separator without particular limitation, as long as it is generally used in a lithium secondary battery, in particular, a separator having high moisture retention capacity for electrolytes and low resistance to the migration of electrolyte ions can be used. Specifically, a porous polymer film, such as a porous polymer film prepared by a polyolefin polymer (such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer) or a laminated structure of more than two layers thereof can be used. In addition, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric formed by a high melting point glass fiber or a polyethylene terephthalate fiber. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator with a monolayer or multilayer structure can be optionally used.

[0119] Electrolytes

[0120] In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte or a molten inorganic electrolyte, etc., which can be used to manufacture a lithium secondary battery, but the present invention is not limited thereto.

[0121] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0122] As the organic solvent, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolanes; or sulfones.

[0123] The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions for use in a lithium secondary battery. Specifically, the anion of the lithium salt may be at least one selected from the group consisting of: - , 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 - , and LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2 can be used as the lithium salt. The lithium salt can be used in a concentration range of 0.1M to 5.0M.

[0124] In addition, in order to improve the life characteristics of the battery, inhibit the decrease in capacity, and inhibit gas generation, additives can also be added to the electrolyte. As additives, various additives used in the art can be used, for example, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalatophosphate) (LiDFBP), lithium tetrafluorooxalatophosphate (LiTFOP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propylene sultone (PRS), succinonitrile (SN), adiponitrile (AND), 1 ,3,6-hexanetrionitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyl di(propyl-2-yl-1-yl) phosphate (EDP), 5-methyl-5-propargyloxycarbonyl-1,3-dioxane-2-one (MPOD), a compound represented by the following formula A (e.g., cyanoethyl polyvinyl alcohol, PVA-CN), a compound represented by the following formula B (e.g., heptafluorobutylcyanoethyl polyvinyl alcohol, PF-PVA-CN), a compound represented by the following formula C (e.g., propargyl-1H-imidazole-1-carboxylate, PAC) and / or a compound represented by the following formula D (e.g., aryl imidazole, such as C6H8N2).

[0125] [Formula A]

[0126]

[0127] In Formula A, m and n are each independently an integer of 1 to 100.

[0128] [Formula B]

[0129]

[0130] [Formula C]

[0131]

[0132] In formula C, R 16 is a linear or non-linear alkylene group having 1 to 3 carbon atoms, R 17 To R 19 are each independently at least one selected from the group consisting of hydrogen, an alkyl group having 1 to 3 carbon atoms, and -CN, and D is CH or N.

[0133] [Formula D]

[0134]

[0135] In formula D,

[0136] R1, R2, R3 and R4 may each independently include hydrogen; or an alkyl group having 1 to 5 carbon atoms, a cyano group (CN), an allyl group, a propargyl group, an amine group, a phosphate group, an ether group, a phenyl group, a cyclohexyl group, a silyl group, an isocyanate group (-NCO) or a fluoro group (-F).

[0137] Preferably, a compound having an oxygen scavenger function can be used as an additive. The following substances can be used as compounds of oxygen scavengers: materials having a phosphite structure (see Formula E), such as tris(methylsilyl)phosphite (TMSPi), trimethylphosphite (TMPi) and tris(2,2,2-trifluoroethyl)phosphite (TTFP); tris(methylsilyl)phosphate (TMSPa); trimethylsilyl polyphosphate (PPSE); tris(pentafluorophenyl)borane (TPFPB); compounds containing a coumarin structure (see Formula F), such as coumarin; coumarin (TMSCM); 3-[(trimethylsilyl)oxy]-2H-1-benzopyran-2-one (TMSOCM), 3-(2-propyn-1-yloxy)-2H-1-benzopyran-2-one (POCM), or 2-propyn-1-yl-2-oxo-2H-1-benzopyran-3-carboxylate (OBCM).

[0138] [Formula E]

[0139]

[0140] [Formula F]

[0141]

[0142] In formulas E and F, R1 to R6 may each independently include an unsubstituted or substituted alkenyl group having 2 to 20 carbon atoms, an unsubstituted or substituted alkynyl group having 2 to 20 carbon atoms, a cyano group, a fluoro group (F), an ether group (COC), a carboxyl group (OC=O), a trimethylsilyl group (-TMS), an isocyanate group (-NCO) and / or an isothiocyanate group (-NCS).

[0143] As described above, the lithium secondary battery of the present invention can be suitably used in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0144] Therefore, according to another embodiment of the present invention, a battery pack including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the battery pack are provided.

[0145] The battery pack or battery package can be used as a power source for at least one of the following medium and large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0146] The shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical type using a can, a prismatic type, a pouch type, or a coin type may be used.

[0147] The lithium secondary battery of the present invention can be used not only as a battery cell used as a power source for small devices but also as a unit cell in a large or medium-sized battery pack including a plurality of battery cells.

[0148] Hereinafter, the present invention will be described in detail through specific examples.

[0149] Experimental Example 1: Ratio of metal composition, I TM / I Li Measurement

[0150] Six commercially available overlithiated manganese-based oxides A to F were prepared, and the metal component ratio of each overlithiated manganese-based oxide was measured by ICP analysis, and the measurement results are shown in the following Table 1. In this case, the mol% of Ni, Co and Mn refers to the percentage of the mole number of each metal element relative to the total mole number of the remaining metals except lithium.

[0151] Then, the 2D 7 After obtaining the Li MATPASS (magic angle steering phase adjustment spinning sideband) NMR spectrum, the 1D NMR central band spectrum was extracted. Figure 2 2D images of the overlithiated manganese-based oxides A to F are shown. 7 1D NMR center band spectrum extracted from the Li MATPASS (Magic Angle Steering Phase Adjusted Spinning Sideband) NMR spectrum.

[0152] Then, the I TM / I Li The measurement results are shown in Table 1 below.

[0153] In this case, I TM is the sum of the peak areas appearing in the range of 1000 ppm to 2500 ppm during the peak deconvolution process, I Li is the sum of the peak areas appearing in the range of 300 ppm to 900 ppm during the peak deconvolution process, 2D 7 The measurement of Li MATPASS NMR spectrum, extraction of 1D NMR central band spectrum and peak deconvolution were carried out under the same conditions as above.

[0154] [Table 1]

[0155]

[0156] Example 1

[0157] The overlithiated manganese-based oxide A, the conductive agent (Super C65) and the PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 96.5:1.5:2 to prepare a positive electrode slurry. One surface of the aluminum current collector was coated with the positive electrode slurry, dried, and then roll-pressed to prepare a positive electrode.

[0158] The lithium secondary battery was prepared by preparing an electrode assembly by placing a separator between a positive electrode and a lithium metal electrode, placing the electrode assembly in a battery shell, and then injecting an electrolyte into the shell. In this case, the electrolyte was prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 1:2:1, and then adding 2 wt% of vinylene carbonate (VC).

[0159] The lithium secondary battery prepared above was charged to 4.65 V at 0.1 C at 45° C. and then discharged to 2.0 V at 0.1 C to perform an activation process.

[0160] Example 2

[0161] A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the overlithiated manganese-based oxide B was used instead of the overlithiated manganese-based oxide A.

[0162] Example 3

[0163] A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the overlithiated manganese-based oxide C was used instead of the overlithiated manganese-based oxide A.

[0164] Example 4

[0165] A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the overlithiated manganese-based oxide D was used instead of the overlithiated manganese-based oxide A.

[0166] Comparative Example 1

[0167] A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the overlithiated manganese-based oxide E was used instead of the overlithiated manganese-based oxide A.

[0168] Comparative Example 2

[0169] A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the overlithiated manganese-based oxide F was used instead of the overlithiated manganese-based oxide A.

[0170] Experimental Example 2: Room Temperature Life Characteristics

[0171] The lithium secondary batteries prepared in the experimental examples and comparative examples were charged to 4.4 V at a constant current of 0.33 C at 25°C, and then discharged to 2.5 V at a constant current of 0.33 C as one cycle. After 50 charge and discharge cycles, the capacity retention rate was measured to evaluate the room temperature life characteristics. Figure 3 The measurement results are shown. Figure 3 As shown, it can be confirmed that the over-lithiated manganese-based oxides A to D (where I TM / I Li The room temperature life characteristics of the lithium secondary batteries of Examples 1 to 4 using the over-lithiated manganese-based oxide E (where I TM / I Li Greater than 0.12) as the positive electrode active material of the lithium secondary battery of Comparative Example 1 and the lithium secondary battery using the over-lithiated manganese-based oxide F (where I TM / I Li Less than 0.06) as the positive electrode active material of the lithium secondary battery of Comparative Example 2. In particular, for the lithium-ion manganese-based oxide E (where I TM / I Li It can be confirmed that the room temperature life characteristics of the lithium secondary battery of Comparative Example 1, which has a positive electrode active material of greater than 0.12, are significantly reduced.

[0172] Experimental Example 3: Evaluation of Initial Capacity

[0173] The lithium secondary batteries prepared in the examples and comparative examples were charged to 4.4 V at 25°C at a constant current of 0.1 C, and then discharged to 2.5 V at a constant current of 0.1 C to measure the discharge capacity. The measurement results are shown in FIG. Figure 4 and as shown in Table 2 below.

[0174] [Table 2]

[0175] 0.1C discharge capacity (mAh / g) Example 1 210.9 Example 2 216.7 Example 3 199.0 Example 4 225.3 Comparative Example 1 190.1 Comparative Example 2 208.1

[0176] according to Figure 4 From Table 2, it can be confirmed that compared with the lithium secondary batteries of Examples 1, 2 and 4, the use of I TM / I LiThe initial capacity characteristics of the lithium secondary batteries of Comparative Examples 1 and 2 using the overlithiated manganese-based oxides whose range is outside the scope of the present invention are reduced. Since the Li / Me ratio of the overlithiated manganese-based oxide in Example 3 is small, the initial capacity of the lithium secondary battery using the overlithiated manganese-based oxide is slightly low, but it can be confirmed that a higher initial capacity is achieved compared to the lithium secondary battery using the overlithiated manganese-based oxide of Comparative Example 1 having a higher Li / Me ratio.

[0177] Experimental Example 4: High temperature life characteristics

[0178] Each lithium secondary battery prepared in the experimental example and the comparative example was charged to 4.4V at a constant current of 0.33C at 45°C, and then each lithium secondary battery was discharged to 2.5V at a constant current of 0.33C as one cycle, and after 50 charge and discharge cycles, the capacity retention rate and the voltage drop were measured. In this case, the voltage drop is measured by measuring the difference between the average voltage after 25 cycles / 50 cycles (by measuring the average voltage after 25 cycles and 50 cycles) and the average voltage of 1 cycle.

[0179] The measurement results of capacity retention rate are as follows: Figure 5 As shown, the degree of voltage drop (ΔV) is shown in Table 3 below.

[0180] [Table 3]

[0181]

[0182] According to [Table 3], it can be confirmed that the voltage drop degree after high temperature cycle of the lithium secondary battery of Comparative Example 2 is greater than that of the lithium secondary batteries of Examples 1 to 4. Figure 5 For the lithium secondary battery of Comparative Example 1, it can be confirmed that the capacity retention rate after high temperature cycling is significantly lower than that of the lithium secondary batteries of Examples 1 to 4. As described above, since the lithium secondary batteries of Comparative Examples 1 and 2 have lower capacities or voltages after high temperature cycling, the energy density (capacity×voltage) after high temperature cycling is poor.

Claims

1. A positive electrode comprising an overlithiated manganese-based oxide as a positive electrode active material, wherein the molar ratio of lithium to all metals other than lithium in the overlithiated manganese-based oxide is greater than 1.1, the content of manganese in all metals other than lithium is greater than 50%, and the equation (1) is satisfied. Equation (1): 0.05 TM / I Li <0.13​ in, In equation (1), I TM and I Li The 2D 7 The sum of the peak areas appearing in the range of 1000ppm to 2500ppm and the sum of the peak areas appearing in the range of 300ppm to 900ppm when the 1D nuclear magnetic resonance (NMR) center band spectrum extracted from the Li MATPASS (magic angle steering phase adjustment spinning sideband) NMR spectrum is subjected to peak deconvolution.

2. The positive electrode according to claim 1, wherein The overlithiated manganese-based oxide A satisfies equation (1-1), Equation (1-1): 0.06≤I TM / I Li ≤0.12 In equation (1-1), I TM and I Li The 2D 7 The sum of the peak areas appearing in the range of 1000ppm to 2500ppm and the sum of the peak areas appearing in the range of 300ppm to 900ppm when the 1D NMR central band spectrum extracted from the Li MATPASS (Magic Angle Steering Phase Adjustment Spinning Sideband) NMR spectrum is subjected to peak deconvolution.

3. The positive electrode according to claim 1, wherein The overlithiated manganese-based oxide has a molar ratio of lithium to all metals other than lithium, Li / Me, of 1.2 to 1.

5.

4. The positive electrode according to claim 1, wherein The molar ratio of nickel to manganese in the over-lithiated manganese-based oxide is 30:70 to 45:

55.

5. The positive electrode according to claim 1, wherein The over-lithiated manganese-based oxide is represented by Formula 1, [Formula 1] Li a Ni b Co c Mr d M 1 e O2 Wherein, in Formula 1, 1.05≤a≤1.5, 0.1≤b<0.5, 0≤c<0.1, 0.5≤d≤0.9, 0≤e≤0.1, M 1 It is at least one selected from the group consisting of aluminum (Al), boron (B), cobalt (Co), tungsten (W), magnesium (Mg), vanadium (V), titanium (Ti), zinc (Zn), gallium (Ga), indium (In), ruthenium (Ru), niobium (Nb), tin (Sn), strontium (Sr) and zirconium (Zr).

6. The positive electrode according to claim 5, wherein In Formula 1, 1.1≤a≤1.3, 0.3≤b<0.5, 0≤c≤0.05, 0.5≤d<0.7, and 0≤e≤0.

1.

7. The positive electrode according to claim 1, wherein The over-lithiated manganese-based oxide has a structure in which a rock salt phase and a layered phase are mixed.

8. The positive electrode according to claim 1, wherein The over-lithiated manganese-based oxide is represented by Formula 2, [Formula 2] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mr y Co z M 2 w ]O2 Among them, in formula 2, M 2 It is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, and 0≤w≤0.

1.

9. A lithium secondary battery comprising: positive electrode; negative electrode; A separator disposed between the positive electrode and the negative electrode; as well as Electrolytes; The positive electrode is the positive electrode according to any one of claims 1 to 8.

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