Method for manufacturing lithium secondary battery

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery, the method comprising the steps of: preparing a battery cell comprising a positive electrode, a negative electrode, and an electrolyte, in which the positive electrode comprises a lithium-rich manganese-based oxide in which the content of manganese in all metals other than lithium is greater than 50 mol%; and the ratio of the number of moles of lithium to the number of moles of all metals other than lithium (Li / Me) is greater than 1; and charging and discharging the battery cell at least once to activate the battery, wherein the activating step includes: a ratio (Y / X) of a charge capacity (mAh / g) (Y) of the secondary battery to an estimated capacity (mAh / g) (X) of the positive electrode active material at a point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure corresponds to 1.10 lt; and when Y / X is less than or equal to 1.13, stopping charging.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority benefits of Korean Patent Application No. 10-2023-0024513, filed with the Korean Intellectual Property Office on February 23, 2023, and Korean Patent Application No. 10-2024-0026192, filed with the Korean Intellectual Property Office on February 23, 2024. The disclosures of the said patent applications are incorporated herein by reference in their entireties.

[0003] The present invention relates to a method for manufacturing a lithium secondary battery, and more particularly, to a method for manufacturing a lithium secondary battery that can suppress the generation of oxidizing gases caused during the activation step of a lithium secondary battery containing a lithium-rich manganese-based oxide. Background Art

[0004] Lithium secondary batteries are energy storage media, and since their commercialization in 1991, they have been applied in various fields. With the expansion of the market for products equipped with lithium secondary batteries, research has been actively conducted to increase the energy density of lithium secondary batteries. One of the most concerned methods is to develop a cathode active material having a composition that can utilize a larger amount of lithium than before.

[0005] As a cathode active material that can utilize a larger amount of lithium, a lithium-rich transition metal oxide having a layered structure and a molar ratio of lithium to transition metal greater than 1 has been developed. Such a lithium-rich transition metal oxide can achieve a high capacity by performing an activation step at a high voltage of 4.4 V or more.

[0006] However, during such a high-voltage activation step, oxygen detachment and cation mixing occur in the crystal structure of the lithium-rich transition metal oxide, which causes a problem of a significant increase in the cathode resistance. Specifically, during the high-voltage activation step, the cathode structure changes as lithium ions detach, and the formation / detachment of oxygen radicals occurs through the redox reaction of oxygen. Due to the side reaction between the oxygen radicals and the electrolyte, a large amount of oxidizing gases such as CO, CO2, and O2 may be generated. In addition, under high-voltage activation conditions, the electrolyte may decompose, and a large amount of oxidizing gases may be generated.

[0007] When a large amount of oxidizing gases are generated in this way, the pressure inside the battery increases, resulting in a short circuit, making it difficult to separate from the fixture, and lithium precipitation is caused by gas traps, which limits the stability and charge / discharge capacity.

[0008] Therefore, there is a need to develop a method that can suppress the generation of oxidizing gases during the high-voltage activation step.

[0009] [Prior Art Documents]

[0010] [Patent Documents]

[0011] Korean Unexamined Patent Publication No. 2022-0068016 Summary of the Invention

[0012] Technical Problem

[0013] The present invention aims to solve the above problems. Therefore, an object of the present invention is to provide a method for manufacturing a lithium secondary battery, which can suppress the generation of oxidizing gases caused during the high-voltage activation step.

[0014] Technical Solution

[0015] According to an aspect of the present invention, there is provided a method for manufacturing a lithium secondary battery, the method comprising the steps of:

[0016] Preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a lithium-rich manganese-based oxide, wherein the content of manganese among all metals other than lithium is greater than 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1; and

[0017] Charging and discharging the battery cell at least once to activate the battery,

[0018] wherein the activation step includes: terminating charging when the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 < Y / X ≤ 1.13 at the point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure.

[0019] On the other hand, the estimated capacity (C) (mAh / g) of the positive electrode active material can be calculated using the following Mathematical Formula 1.

[0020] [Mathematical Formula 1]

[0021] C (mAh / g) = Q × (i / 100)

[0022] In Mathematical Formula 1,

[0023] Q is the theoretical capacity (mAh / g) of the lithium-rich manganese-based oxide, and

[0024] i is the percentage (%) of the molar ratio of lithium ions that have moved until only lithium ions forming a Li / Li dumbbell structure remain to the total molar ratio of lithium ions contained in the lithium-rich manganese-based oxide, and can be defined by the following Mathematical Formula 2:

[0025] [Mathematical Formula 2]

[0026]

[0027] In Mathematical Formula 2, the Li molar ratio is the total molar ratio of lithium ions contained in the lithium-rich manganese-based oxide.

[0028] In addition, the activation step may include a step of charging from 4.5 V to 4.6 V at 0.3C to 1.0C.

[0029] The charging step may be performed in a constant current mode (CC mode) or a constant current-constant voltage mode (CCCV mode), and the cut-off current in the constant voltage charging mode may be 0.05C to 0.15C. Description of the Drawings

[0030] Figure 1 is a graph showing the results of evaluating the amount of gas generation during the activation step according to Experimental Example 1.

[0031] Figure 2 is a graph showing the initial resistance evaluation results according to Experimental Example 2.

[0032] Figure 3 is a graph showing the results of the capacity retention rate in the high-temperature cycle evaluation according to Experimental Example 3.

[0033] Figure 4 is a graph for explaining the structural change of the lithium-rich manganese-based oxide and whether oxidative gas is generated during the activation step as charging progresses.

[0034] Figure 5 is a graph showing based on Li x (Ni 0.5 Mn 0.5 )O2 compound, the change rate of the lithium concentration (Li site concentration) at the lithium site. Detailed Description of the Invention

[0035] The terms or words used in this specification and the appended claims should not be construed as limited to the ordinary meaning or dictionary meaning, and the present invention should be interpreted as having a meaning and concept consistent with the technical gist of the present invention based on the principle that the inventor can appropriately define the concept of the terms so as to appropriately describe their invention in the best way.

[0036] In the present invention, a "primary particle" refers to a particle unit in which no grain boundary is seen when observed with a scanning electron microscope at a magnification of 5000 to 20000 times. The "average particle size of the primary particles" refers to the arithmetic mean calculated by measuring the particle size of the primary particles observed in the scanning electron microscope image.

[0037] In the present invention, a "secondary particle" is a particle formed by aggregation of a plurality of primary particles.

[0038] In the present invention, "average particle size D 50 " refers to the particle size at which the cumulative volume of powder particles (e.g., positive electrode active material, negative electrode active material, etc.) in the particle size distribution curve of the particles reaches 50%. D 50 can be measured by the laser diffraction method. It can be measured through a process including the following steps: dispersing the powder of the particles to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves at an output power of 60 W at about 28 kHz, thereby obtaining a volume cumulative particle size distribution, and determining the particle size corresponding to 50% cumulative volume.

[0039] In addition, in the present invention, "SOC X" refers to a state in which the percentage of the charging capacity in the battery cell based on the discharge capacity exhibited when the battery cell is discharged from 4.6 V to 2.0 V is X.

[0040] In order to suppress the generation of oxidizing gas during the activation process of a lithium secondary battery using a lithium-rich manganese-based oxide, the present inventors conducted repeated studies and found that by adjusting the charging end point, the generation of oxidizing gas during the high-voltage activation process can be suppressed, and the present invention was completed.

[0041] Now, the present invention will be described in detail.

[0042] <Method for manufacturing a lithium secondary battery>

[0043] The method for manufacturing a lithium secondary battery according to the present invention includes:

[0044] a step of preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a lithium-rich manganese-based oxide, the content of manganese among all metals other than lithium is greater than 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1; and

[0045] a step of charging and discharging the battery cell at least once to activate the battery,

[0046] wherein the activation step includes: a step of terminating charging when the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 < Y / X ≤ 1.13 at the point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure.

[0047] (1) Step of preparing the battery cell

[0048] First, prepare a battery cell including a positive electrode, a negative electrode, and an electrolyte.

[0049] The battery cell can be manufactured, for example, by the following steps: forming an electrode assembly including a positive electrode and a negative electrode, placing the electrode assembly in a battery case, and then injecting an electrolyte to seal the battery case. At this time, the electrode assembly may include a separator between the positive electrode and the negative electrode.

[0050] Each component of the battery cell according to the present invention will be described in more detail below.

[0051] Positive Electrode

[0052] The positive electrode according to the present invention includes a lithium-rich manganese-based oxide, in which the content of manganese among all metals other than lithium is greater than 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1. Specifically, the positive electrode according to the present invention includes a positive electrode current collector, and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a lithium-rich manganese-based oxide, in which the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1.

[0053] When the lithium-rich manganese-based oxide contains an excessive amount of lithium, it has a structure in which a layered phase (LiM'O2) and a rock salt phase (Li2MnO3) are mixed. During the initial activation process, the rock salt phase is activated and generates an excessive amount of lithium ions, thereby achieving a high capacity.

[0054] Preferably, the lithium-rich manganese-based oxide can be represented by the following Chemical Formula 1.

[0055] [Chemical Formula 1]

[0056] Li a Ni b Co c Mn d M e O2

[0057] Wherein, in Chemical Formula 1, M may be at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0058] On the other hand, a is the molar ratio of Li in the lithium-rich manganese-based oxide, and may be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3.

[0059] b is the molar ratio of Ni in the lithium-rich manganese-based oxide, and may be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0060] c is the molar ratio of Co in the lithium-rich manganese-based oxide, and can be 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.08, or 0 ≤ c ≤ 0.05. If c is greater than 0.1, it is difficult to ensure a high capacity, and the generation of gas and the deterioration of the positive electrode active material become aggravated, and the life characteristics may deteriorate.

[0061] d is the molar ratio of Mn in the lithium-rich manganese-based oxide, and can be 0.5 ≤ d < 1.0, 0.50 ≤ d ≤ 0.80, or 0.50 ≤ d ≤ 0.70. If d is less than 0.5, the proportion of the rock salt phase becomes too small, so the effects of negative electrode irreversible compensation and capacity improvement are slight.

[0062] e is the molar ratio of the doping element M in the lithium-rich manganese-based oxide, and can be 0 ≤ e ≤ 0.2, 0 ≤ e ≤ 0.1, or 0 ≤ e ≤ 0.05. If the content of the doping element is too high, it may have an adverse effect on the capacity of the active material.

[0063] On the other hand, in the lithium-rich manganese-based oxide represented by [Chemical Formula 1], the ratio (Li / Me) of the number of moles of Li to the number of moles of all metal elements other than Li can be 1.2 to 1.5, 1.25 to 1.5, or 1.25 to 1.4. When the Li / Me ratio satisfies the above range, the rate performance and capacity characteristics can be excellently exhibited. When the Li / Me ratio is too high, the conductivity may decrease, and the rock salt phase (Li2MnO3) may increase, which may increase the degradation rate. When the Li / Me ratio is too low, the effect of improving the energy density is slight.

[0064] On the other hand, the composition of the lithium-rich manganese-based oxide can be represented by the following [Chemical Formula 2].

[0065] [Chemical Formula 2]

[0066] XLi2MnO3·(1 - X)Li[Ni 1-y-z-w Mn y Co z M w O2

[0067] Among them, in [Chemical Formula 2], M can be at least one metal ion selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0068] X refers to the ratio of the Li2MnO3 phase in the lithium-rich manganese-based oxide, and can be 0.2 ≤ X ≤ 0.5, 0.25 ≤ X ≤ 0.5, or 0.25 ≤ X ≤ 0.4. When the ratio of the Li2MnO3 phase in the lithium-rich manganese-based oxide satisfies the above range, high capacity characteristics can be achieved.

[0069] y is the molar ratio of Mn in the LiM'O2 layer and can be 0.4 ≤ y < 1, 0.4 ≤ y ≤ 0.8 or 0.4 ≤ y ≤ 0.7.

[0070] z is the molar ratio of Co in the LiM'O2 layer and can be 0 ≤ z ≤ 0.1, 0 ≤ z ≤ 0.08 or 0 ≤ z ≤ 0.05. When z is greater than 0.1, the generation of gas and the deterioration of the positive electrode active material may become aggravated, and the life characteristics may deteriorate.

[0071] w is the molar ratio of the doping element M in the LiM'O2 layer and can be 0 ≤ w ≤ 0.2, 0 ≤ w ≤ 0.1 or 0 ≤ w ≤ 0.05.

[0072] On the other hand, the positive electrode active material according to the present invention may further include a coating on the surface of the lithium-rich manganese-based oxide as needed. When the positive electrode active material includes a coating, the contact between the lithium-rich manganese-based oxide and the electrolyte is inhibited by the coating, and the side reaction of the electrolyte is reduced, so that the effect of improving the life characteristics can be obtained.

[0073] The coating may include the coating element M 1 , and the coating element M 1 may be, for example, at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, preferably Al, Co, Nb, W, and combinations thereof, more preferably Al, Co, and combinations thereof. The coating element M 1 may include two or more kinds, such as Al and Co.

[0074] The coating element may exist in the coating in the form of an oxide, that is, M 1 Oz (1 ≤ z ≤ 4).

[0075] The coating can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among them, it is preferably formed by atomic layer deposition in which a coating with a larger area can be formed.

[0076] Based on the total surface area of the lithium-rich manganese-based oxide particles, the formation area of the coating can be 10% to 100%, preferably 30% to 100%, more preferably 50% to 100%. When the formation area of the coating satisfies the above range, the effect of improving the life characteristics is excellent.

[0077] On the other hand, the positive electrode active material according to the present invention may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle size D of the secondary particles 50It can be 2 μm to 10 μm, preferably 2 μm to 8 μm, more preferably 4 μm to 8 μm. When the D of the positive electrode active material 50 satisfies the above range, the electrode density can be excellently achieved, and the degradation of the capacity and rate characteristics can be minimized.

[0078] In addition, the BET specific surface area of the positive electrode active material can be 1 m 2 / g to 10 m 2 / g, 3 to 8 m 2 / g or 4 to 6 m 2 / g. If the BET specific surface area of the positive electrode active material is too low, the reaction area with the electrolyte is insufficient, making it difficult to achieve sufficient capacity. If the specific surface area is too high, water adsorption is rapid, and the side reaction with the electrolyte is accelerated, making it difficult to ensure the life characteristics.

[0079] On the other hand, the lithium-rich manganese-based oxide can be manufactured by mixing a transition metal precursor and a lithium raw material and then firing the mixture.

[0080] As the lithium raw material, for example, 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.), chlorides (such as lithium chloride (LiCl), etc.) can be used, and among them, a single kind or a mixture of two or more kinds can be used.

[0081] On the other hand, the transition metal precursor can be in the form of a hydroxide, an oxide or a carbonate. When using a precursor in the form of a carbonate, it is more preferable to be able to manufacture a positive electrode active material having a relatively high specific surface area.

[0082] The transition metal precursor can be prepared by a coprecipitation process. For example, the transition metal precursor can be prepared by dissolving raw materials containing each transition metal in a solvent to prepare a metal solution, then mixing the metal solution, an ammonium cation complex former and a basic compound, and performing a coprecipitation reaction. In addition, an oxidant or oxygen can be added during the coprecipitation reaction as needed.

[0083] At this time, the raw materials containing transition metals can be acetates, carbonates, nitrates, sulfates, halides, sulfides, etc. of each transition metal. Specifically, the raw materials 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, etc.

[0084] The ammonium cation complexing agent may be at least one selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3.

[0085] The basic compound may be at least one selected from NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. In addition, when the basic compound is used together with an oxidizing agent, an oxide-form precursor can be obtained.

[0086] On the other hand, the transition metal precursor and the lithium raw material may be mixed in the following amounts: 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, and more preferably 1:1.25 to 1:1.8.

[0087] On the other hand, the firing may be carried out at a temperature of 600°C to 1000°C or 700°C to 950°C, and the firing time may be 5 hours to 30 hours or 5 hours to 20 hours. In addition, the firing atmosphere may be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0088] On the other hand, in addition to the positive electrode active material, the positive electrode active material layer may further contain a conductive material and a binder.

[0089] Examples of the conductive material include spherical or flaky graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, single-walled carbon nanotube, and multi-walled carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc. Among them, a single kind or a mixture of two or more kinds can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material may be 0.1 to 20% by weight, 1 to 20% by weight, or 1 to 10% by weight.

[0090] In addition, the binder is a component that aids in the adhesion between the positive electrode active materials and the adhesion force between the positive electrode active material and the current collector, and examples thereof include: fluororesin binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-like binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol-based binders, including polyvinyl alcohol; polyolefin-based binders, including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; silane-based binders, etc. Based on the total weight of the positive electrode active material layer, the content of the binder may be 1 to 20% by weight, 2 to 20% by weight, or 2 to 10% by weight.

[0091] Negative Electrode

[0092] The negative electrode may include, for example, a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material and optionally a binder and a conductive material.

[0093] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause chemical changes in the battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., aluminum cadmium alloy, etc. may be used. In addition, the negative electrode current collector usually may have a thickness of 3 µm to 500 µm. In addition, similar to the positive electrode current collector, the negative electrode current collector may have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric structure.

[0094] Compounds capable of reversibly inserting and extracting lithium can be used as the negative electrode active material. Specific examples of the negative electrode active material may include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; (semi) metallic materials capable of forming an alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; (semi) metal oxides capable of doping and undoping lithium, such as SiO β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; composites containing (semi) metallic materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one of them may be used alone or a mixture of two or more thereof may be used.

[0095] In addition, a thin film of metallic lithium can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of the low-crystalline carbon include soft carbon and hard carbon. Typical examples of the high-crystalline carbon include natural graphite or artificial graphite which is irregular, planar, flaky, spherical or fibrous, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, high-temperature sintered carbon such as mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0096] A conductive material is used to impart conductivity to the electrode, and the conductive material can be used without particular limitation as long as it has electron conductivity and does not cause a chemical change in the battery to be formed. Specific examples thereof include graphite such as natural graphite and artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, and carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of them can be used alone or a mixture of two or more of them can be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material is usually 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0097] The binder serves to improve the adhesion between the negative electrode active material particles and the adhesion force between the negative electrode active material and the negative electrode current collector. Specific examples thereof include: fluororesin binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol binders including polyvinyl alcohol; polyolefin binders including polyethylene and polypropylene; polyimide binders; polyester binders; silane binders, etc., and any one of them can be used alone or a mixture of two or more of them can be used. Based on the total weight of the negative electrode active material layer, the content of the binder can be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0098] The negative electrode active material layer can be prepared, for example, by coating a negative electrode slurry containing the negative electrode active material and optionally a binder and a conductive material onto the negative electrode current collector and drying the coated slurry, or by casting the negative electrode slurry onto a separate support and then laminating the film peeled from the support on the current collector.

[0099] Separator

[0100] The lithium secondary battery according to the present invention may further include a separator disposed between the positive electrode and the negative electrode. The separator separates the negative electrode and the positive electrode from each other and provides a migration path for lithium ions. The separator can be used without particular limitation as long as it is used as a separator in a conventional lithium secondary battery. In particular, a separator having a low resistance to ion migration of the electrolyte and an excellent ability to impregnate the electrolyte is preferred. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, typical porous non-woven fabrics, such as non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., can be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and it can be optionally used as a single layer or a multi-layer structure.

[0101] Electrolyte

[0102] The electrolyte used herein may include various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or combinations thereof, and there is no particular limitation on their types.

[0103] For example, the electrolyte may include an organic solvent and a lithium salt.

[0104] The organic solvent can be used without any particular limitation as long as it serves as a medium through which ions participating in the electrochemical reaction of the battery can migrate. Specific examples of the organic solvent may include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolane, etc.

[0105] The lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt may be at least one selected from the following substances: 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 - , and the lithium salts that can be used herein may be LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt can preferably be used in the range of 0.1 to 5.0 M.

[0106] In addition, in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, improve the discharge capacity of the battery, etc., in addition to the above electrolyte components, the electrolyte may further contain additives. For example, the additives may be at least one selected from the following substances: vinylene carbonate, ethylene vinyl carbonate, fluoroethylene carbonate (FEC), ethylene sulfite (Esa), trimethylene sulfate (TMS), methyltrimethylene sulfate (MTMS), 1,3 - propane sultone (1,3 - PS), 1,3 - propene sultone, 1,4 - butane sultone, lithium oxydifluoroborate (LiODFB), lithium bis(oxalato)borate (LiBOB), fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, lithium difluorophosphate (LiPO2F2, LiDFP), and LiBF4, but not limited thereto. Based on the total weight of the electrolyte, the content of the additive may be 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0107] On the other hand, the electrode assembly can be various forms of electrode assemblies known in the art. For example, it can be a jelly - roll type, a stacked type, a stacked and laminated type, or a stacked and folded type electrode assembly, and there is no particular limitation on its form.

[0108] The wound type electrode assembly can be manufactured by inserting a sheet-like separator between a sheet-like positive electrode and a sheet-like negative electrode and then winding them in one direction.

[0109] The stacked type electrode assembly can be manufactured by cutting the positive electrode, separator, and negative electrode into desired shapes and then successively stacking the cut positive electrode / separator / negative electrode.

[0110] The stacked and laminated type electrode assembly can be manufactured by the following method: stacking the positive electrode, separator, and negative electrode to manufacture a plurality of unit cells, stacking the plurality of unit cells with the separator interposed therebetween, and then laminating them by a method such as heating.

[0111] The stacked and folded type electrode assembly can be manufactured by the following method: stacking the positive electrode, separator, and negative electrode to manufacture a plurality of unit cells, arranging the plurality of unit cells on one surface or both surfaces of a long folded separator, and then winding the folded separator.

[0112] On the other hand, as the battery case, various battery cases known in the art can be used, such as a cylindrical battery case, a prismatic battery case, or a pouch battery case, etc., and there is no particular limitation on their types.

[0113] (2) Activation step

[0114] Next, a step of charging and discharging the battery cell at least once to electroactivate the battery is performed. The activation step is a step of charging and discharging the battery cell to endow electrical properties and form a SEI (solid electrolyte interface) film on the electrode to stabilize the battery.

[0115] Specifically, as the charging voltage is higher, the charging time and charging depth (capacity) are larger, and the reaction degree of Li2MnO3 during activation increases, so that the amount of activation gas (oxidizing gas) increases. Therefore, in the present invention, the charging end point is adjusted in the activation charging step to adjust the activation degree of the Li2MnO3 (monoclinic) phase, thereby suppressing the generation of gases such as oxidizing gases.

[0116] On the other hand, the activation charging step may include a first charging step of charging at an SOC of 5 or less.

[0117] Specifically, the first charging step can be performed at a C rate of 0.1C to 0.3C from SOC 0 to SOC 5.

[0118] When the charging rate during the first charging satisfies the above range, the charging rate at the initial stage of SEI film formation can be maintained lower, so that a stronger and denser SEI film can be formed, and a strong and dense SEI film is formed on the electrode surface, thereby achieving excellent life characteristics. When the current rate in the first charging step is faster than 0.3C, the SEI film may be formed unstably on the electrode surface. When the SEI film is formed unstably on the electrode surface, the SEI film is likely to decompose during battery operation, leading to rapid deterioration of the electrode, which can cause a significant decrease in life characteristics.

[0119] On the other hand, the first charging step can be carried out in a constant current mode (CC mode).

[0120] In addition, the method of the present invention may include the following second charging step: when the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure during the activation charging corresponds to 1.10 < Y / X ≤ 1.13, specifically, when the ratio corresponds to 1.11 ≤ Y / X ≤ 1.12, the charging is terminated.

[0121] Figure 4 It is a diagram for explaining the structural change of the lithium-rich manganese-based oxide as the charging progresses in the activation step. Refer to Figure 4 , in the case of the lithium-rich manganese-based oxide represented by Chemical Formula 1, nickel first starts to be oxidized in the initial second charging step, and then the lithium ions contained in the lattice formed by the oxygen elements of the first MO layer (metal oxide layer), the second MO layer, and the third MO layer adjacent to each other move from the octahedral position to the tetrahedral positions between the first MO layer and the second MO layer and between the second MO layer and the third MO layer, so that some lithium ions start to form a dumbbell Li / Li structure within the Mn honeycomb pattern. At this time, the first flattening interval (plateau) may appear near 3.X V. In addition, from the 4.4 V point where all nickel is oxidized during charging ( Figure 4 the point (1) in Figure 5 to the point where all lithium ions exist only in this Li / Li dumbbell structure, that is, as shown in Figure 2(b)), a second flattening region appears ( Figure 4 point (2) in). On the other hand, during high-voltage charging above 4.4 V, the in-plane migration of transition metal ions occurs rapidly, and due to the side reaction between the electrolyte and the lattice oxygen element, oxidizing gases containing oxygen such as CO / CO2 gradually begin to form. That is, if the activation charging continues even after all lithium ions are present in the Li / Li dumbbell structure, the lithium ions detach and are removed from the Li / Li dumbbell structure, and the change in the transition metal structure in the positive electrode becomes rapidly aggravated. In addition, due to the influence of the aggregation of vacancies in the transition metal layer from which lithium has detached, a large amount of O2 is formed, and the generation of oxidizing gases containing oxygen such as CO / CO2 becomes aggravated ( Figure 4 point (3) in).

[0122] The method of the present invention includes the following second charging step: when the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 < Y / X ≤ 1.13 at the point where all lithium ions contained in the lithium-rich manganese-based oxide form the Li / Li dumbbell structure, the charging is terminated, thereby providing a method for suppressing and reducing the generation of oxidizing gases.

[0123] By terminating the second charging step within the range where the ratio (Y / X) of the charging capacity (Y) of the secondary battery to the estimated capacity (X) of the positive electrode active material is greater than 1.10, the amount of lithium that can be utilized through the O / Mn redox reaction can be increased, and a sufficient charging capacity can be ensured. In addition, by terminating the second charging step within the range where the ratio (Y / X) of the charging capacity (Y) of the secondary battery to the estimated capacity (X) of the positive electrode active material is 1.13 or less, overcharging can be prevented, thereby reducing the generation of oxidizing gases, minimizing the rapid phase change in the positive electrode, and obtaining the effect of improving the initial resistance of the battery. In particular, by terminating the second charging step when the ratio (Y / X) of the charging capacity (Y) of the secondary battery to the estimated capacity (X) of the positive electrode active material is 1.13, a sufficient activation process can be carried out until near only the Li / Li dumbbell point, which prevents another activation process from occurring again during the subsequent charge / discharge process of the battery and can prevent the generation of gas during the subsequent charge / discharge process.

[0124] On the other hand, the estimated capacity (C) (mAh / g) of the positive electrode active material can be estimated and calculated by the calculation formula shown in the following mathematical formula 1.

[0125] [Mathematical formula 1]

[0126] C (mAh / g)=Q×(i / 100)

[0127] In Mathematical Formula 1,

[0128] Q is the theoretical capacity (mAh / g) of the lithium-rich manganese-based oxide, and

[0129] i is the percentage (%) of the molar ratio of the lithium ions that move until only the lithium ions forming the Li / Li dumbbell structure remain to the total molar ratio of the lithium ions contained in the lithium-rich manganese-based oxide.

[0130] Specifically, the theoretical capacity of the lithium-rich manganese-based oxide can be defined by the following conventional mathematical formula shown in Mathematical Formula 3.

[0131] [Mathematical Formula 3]

[0132]

[0133] In Mathematical Formula 3,

[0134] F is the Faraday constant, which is 96485.3321 (C / mol·e - ), and

[0135] MW is the weight-average molecular weight (g / mol) of the lithium-rich manganese-based oxide.

[0136] In the above mathematical formula, 3600 C (coulomb) is a constant, which defines the amount of electric charge (Ah) that moves when a current of 1 ampere (A) flows for 1 hour (h).

[0137] On the other hand, i can be defined by the following Mathematical Formula 2.

[0138] [Mathematical Formula 2]

[0139]

[0140] In Mathematical Formula 2,

[0141] The Li molar ratio is the total molar ratio of the lithium contained in the lithium-rich manganese-based oxide.

[0142] Specifically, the Li molar ratio means "a" in the lithium-rich manganese-based oxide represented by Chemical Formula 1 (Li a Ni b Co c Mn d M e O2). For example, in the lithium-rich manganese-based oxide Li 1.16 Ni 0.305 Co 0.004 Mn 0.531 O2, the Li molar ratio can be defined as 1.16. In this case, i is 72.5%, and the ratio of the number of moles of lithium to the number of moles of all metals other than lithium (Li / Me) can be 1.38.

[0143] On the other hand, the charging capacity (Y) of the secondary battery may be the measured capacity obtained through visual real-time monitoring of the display of the detector during the charging of the battery cell.

[0144] On the other hand, the second charging step may be performed at a C-rate of 0.3C to 1.0C. If necessary, it may be performed in more than two steps at different C-rates. For example, the second charging step may include a 2-1 charging step of charging the battery cell at a C-rate of 0.5C to 1.0C, and a 2-2 charging step of charging the battery cell at a C-rate lower than that of the 2-1 charging step. At this time, the 2-1 charging step may be performed until the SOC reaches 60, and the 2-2 charging step may be started from the SOC of 60 until the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 < Y / X ≤ 1.13 at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form the Li / Li dumbbell structure. When the second charging step is performed in two steps as described above, the activation charging time can be effectively shortened.

[0145] On the other hand, the termination voltage of the charging in the second charging stage may be 4.5 V to 4.6 V, specifically 4.55 V to 4.6 V.

[0146] The second charging step may be performed in a constant current mode (CC mode) or a constant current-constant voltage mode (CCCV mode).

[0147] When the second charging step is performed in the constant current-constant voltage mode (CCCV mode), CC charging is performed until the termination voltage of the charging is reached, and when the termination voltage of the charging is reached, CV charging may be performed, in which the charging C-rate is sequentially reduced to about 0.05C to 0.15C.

[0148] Next, in the activation step, the battery cell charged through the first charging step and the second charging step is discharged. At this time, the discharging may be performed at a C-rate of 0.3C to 0.7C. When the discharging rate satisfies the above range, the activation time can be appropriately controlled, and the discharging capacity characteristics within the desired range can be achieved.

[0149] On the other hand, the discharging may be performed in the constant current mode (CC mode).

[0150] On the other hand, the termination voltage of the discharging may be 2.0 V to 3.0 V, specifically 2.0 V.

[0151] On the other hand, the activation step is preferably carried out under temperature conditions of 25°C to 70°C, more preferably 40°C to 50°C. When the activation step is carried out within the above temperature range, the effect of achieving high capacity can be obtained through appropriate activation of Li2MnO3.

[0152] In addition, if necessary, the activation step can be carried out under pressure conditions. Pressurization can be carried out by mounting the battery cell on a jig and then applying pressure to the battery cell via the jig. When the activation step is carried out under pressure conditions, this has the advantage of being able to easily discharge the gas generated during the activation step.

[0153] On the other hand, although this is not essential, if necessary, the activation step may further include an aging step. The aging step impregnates the electrolyte uniformly into the electrode assembly and stabilizes the battery, and can be carried out before charging, during charging, and / or after discharging, and can be carried out more than once.

[0154] The aging step can be carried out at a temperature of, for example, 20°C to 60°C, 20°C to 50°C, preferably 30°C to 50°C. When aging is carried out at the above temperature, the electrolyte impregnation property and lithium mobility are improved, enabling the activation to proceed more smoothly.

[0155] <Lithium secondary battery>

[0156] In addition, the present invention includes a lithium secondary battery manufactured according to the method for manufacturing a lithium secondary battery.

[0157] The lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte,

[0158] wherein the positive electrode contains a lithium-rich manganese-based oxide, in which the content of manganese among all metals other than lithium is greater than 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1.

[0159] Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0160] [Examples]

[0161] Example 1.

[0162] (Manufacture of battery cell)

[0163] The positive electrode active material: conductive material: PVDF binder were mixed at a weight ratio of 97:1:2 in N-methylpyrrolidone to prepare a positive electrode paste. At this time, Li 1.38 [Ni 0.363 Co 0.005 Mn 0.632O2(Li / Me = 1.38) is used as the positive electrode active material, and carbon nanotubes (CNT) are used as the conductive material. The positive electrode paste is coated on an aluminum current collector sheet, dried, and then calendered to fabricate the positive electrode.

[0164] The negative electrode active material: conductive material: binder are mixed in water at a weight ratio of 96:1:3 to prepare the negative electrode paste. At this time, graphite is used as the negative electrode active material, carbon black is used as the conductive material, and SBR and CMC are mixed at a weight ratio of 2:1 and used as the binder. The negative electrode paste is coated on a copper current collector sheet, dried, and then calendered to fabricate the negative electrode.

[0165] A separator is inserted between the positive electrode and the negative electrode fabricated as above to fabricate an electrode assembly, and the electrode assembly is inserted into a battery case, and then an electrolyte is injected therein to fabricate a battery cell.

[0166] (Activation step)

[0167] The battery cell is pre-aged for 2 days, and then first charged in a constant current mode of 0.2C until SOC3 at a temperature of 45 °C, second charged in a constant current-constant voltage mode of 0.33C (0.05C CV cut-off) until the charging capacity (Y) of the secondary battery reaches 287 mAh / g (the termination voltage of charging: 4.5 V), and then discharged at a constant current of 0.5C until 2.0 V. The activation step is performed in this way to fabricate a lithium secondary battery.

[0168] The charging step can be performed by connecting the fabricated battery to a charger / discharger and visually checking the charging capacity value that continuously changes during charging through the display of the detector. When the desired charging capacity of the secondary battery is obtained, the charging is terminated. On the other hand, the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is shown in Table 1 below.

[0169] Example 2.

[0170] The battery cell fabricated in Example 1 is pre-aged for 2 days, and then first charged in a constant current mode of 0.2C until SOC 3 at a temperature of 45 °C, charged in a constant current of 1.0C until SOC 60, second charged in a constant current-constant voltage mode of 0.4C (0.15C CV cut-off) until the charging capacity (Y) of the secondary battery reaches 290 mAh / g (the termination voltage of charging: 4.6 V), and then discharged at a constant current of 0.5C until 2.0 V. The activation step is performed in this way to fabricate a lithium secondary battery.

[0171] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is as shown in Table 1 below.

[0172] Comparative Example 1.

[0173] The battery cell manufactured in Example 1 was pre-aged for 2 days, then first charged in a constant current mode of 0.2C until SOC 3 at a temperature of 45°C, second charged in a constant current-constant voltage mode of 0.33C (0.05C CV cut-off) until the charge capacity (Y) of the secondary battery reached 297 mAh / g (charge termination voltage: 4.6 V), and then discharged at a constant current of 0.5C until 2.0 V. The activation step was carried out in this way to manufacture a lithium secondary battery.

[0174] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is as shown in Table 1 below.

[0175] Comparative Example 2.

[0176] The battery cell manufactured in Example 1 was pre-aged for 2 days, then first charged in a constant current mode of 0.2C until SOC 3 at a temperature of 45°C, charged in a constant current of 0.33C until SOC 60, second charged in a constant current-constant voltage mode of 0.1C (0.05C CV cut-off) until the charge capacity (Y) of the secondary battery reached 293 mAh / g (charge termination voltage: 4.6 V), and then discharged at a constant current of 0.5C until 2.0 V. The activation step was carried out in this way to manufacture a lithium secondary battery.

[0177] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is as shown in Table 1 below.

[0178] Comparative Example 3.

[0179] The battery cells manufactured in Example 1 were pre-aged for 2 days, and then first charged at a constant current of 0.2C until the SOC reached 3 at a temperature of 45°C, charged at a constant current of 1.0C until the SOC reached 60, second charged at a constant current of 0.4C until the charge capacity (Y) of the secondary battery reached 278 mAh / g (the termination voltage of charging: 4.6 V), and then discharged at a constant current of 0.5C until 2.0V. The activation step was carried out in this way to manufacture a lithium secondary battery.

[0180] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form the Li / Li dumbbell structure is shown in Table 1 below.

[0181] Comparative Example 4.

[0182] The battery cells manufactured in Example 1 were pre-aged for 2 days, and then first charged at a constant current of 0.2C until the SOC reached 3 at a temperature of 45°C, second charged at a constant current of 0.1C until the charge capacity (Y) of the secondary battery reached 244 mAh / g (the termination voltage of charging: 4.6 V), and then discharged at a constant current of 0.5C until 2.0V. The activation step was carried out in this way to manufacture a lithium secondary battery.

[0183] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form the Li / Li dumbbell structure is shown in Table 1 below.

[0184] Comparative Example 5.

[0185] The battery cells manufactured in Example 1 were pre-aged for 2 days, and then first charged at a constant current of 0.2C until the SOC reached 3 at a temperature of 45°C, charged at a constant current of 1.0C until the SOC reached 60, second charged in a constant current-constant voltage mode of 0.1C (0.05C CV cut-off) until the charge capacity (Y) of the secondary battery reached 305 mAh / g (the termination voltage of charging: 4.6 V), and then discharged at a constant current of 0.5C until 2.0V. The activation step was carried out in this way to manufacture a lithium secondary battery.

[0186] Example 3.

[0187] The battery cells were manufactured in the same manner as in Example 1, except that Li 1.34 [Ni 0.354 Mn 0.646 O2 (Li / Me = 1.34) was used as the positive electrode active material.

[0188] The fabricated battery cells were pre-aged for 2 days, and then first charged in a constant current mode of 0.2C until SOC 3 at a temperature of 45°C, and second charged in a constant current-constant voltage mode of 0.33C (0.05C CV cut-off) until the charge capacity (Y) of the secondary battery reached 286 mAh / g (the termination voltage of charging: 4.6 V), and then discharged at a constant current of 0.5C until 2.0 V. The activation step was carried out in this way to fabricate a lithium secondary battery.

[0189] On the other hand, the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is shown in Table 1 below.

[0190]

[0191] [Experimental Example]

[0192] Experimental Example 1.

[0193] The amount of gas generated during the activation step of the lithium secondary batteries fabricated in Examples 1 to 3 and the secondary batteries fabricated in Comparative Examples 1 to 5 was measured, and the results are shown in Table 2 below and Figure 1 in.

[0194]

[0195] Referring to Table 2 and Figure 1 , it can be seen that, compared with the lithium secondary batteries of Comparative Examples 1, 2, and 5, in the cases of the lithium secondary batteries of Examples 1 and 2 and Example 3, the total amount of oxidizing gas (including oxygen, etc.) generated decreased. That is, in the cases of the lithium secondary batteries of Comparative Examples 1, 2, and 5 where the ratio (Y / X) of the charge capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure is greater than 1.13, it can be confirmed that the total amount of gas generated increases with the intensification of lithium detachment and transition metal structure change in the positive electrode.

[0196] On the other hand, compared with the lithium secondary batteries of Examples 1, 2, and 3, in the cases of the lithium secondary batteries of Comparative Examples 3 and 4, the total amount of gas (including oxygen) generated seems to have decreased, but this is considered to be a phenomenon caused by insufficient activation process. The specific reason can be explained by the capacity retention rate evaluation results in Experimental Example 3 below.

[0197] Experimental Example 2. Evaluation of initial resistance

[0198] The lithium secondary batteries fabricated in Examples 1, 2, and 3 and the secondary batteries fabricated in Comparative Examples 1 to 5 were charged at a rate of 0.33C under CC-CV (constant current-constant voltage) conditions up to 4.35 V at 45°C and discharged at a rate of 0.33C under CC conditions down to 2.0 V. With one charge and discharge cycle being one cycle, the initial charge and discharge were carried out for 2 cycles.

[0199] The SOC (state of charge) was adjusted to 50% of the discharge capacity based on the second charge and discharge. The DC internal resistance was calculated from the voltage drop that occurred when a discharge pulse was applied at 2.5C for 10 seconds at SOC 50%, and the resistance at this time was set as the initial resistance, as shown Figure 2 below.

[0200] Reference Figure 2 , it can be seen that the initial resistance of the lithium secondary batteries of Examples 1, 2, and 3 was improved compared to the lithium secondary batteries of Comparative Examples 1, 2, and 5.

[0201] On the other hand, in the case of the lithium secondary batteries of Comparative Examples 3 and 4, it was confirmed that the initial resistance was lower than or similar to the initial resistance of the lithium secondary batteries of Examples 1, 2, and 3, but it was considered that this was a phenomenon caused by insufficient activation process. The specific reason can be explained by the capacity retention rate evaluation results in the following Experimental Example 3.

[0202] Experimental Example 3. Evaluation of capacity retention rate

[0203] The lithium secondary batteries fabricated in Examples 1, 2, and 3 and the secondary batteries fabricated in Comparative Examples 3 and 4 were charged at a rate of 0.33C under CC-CV (constant current-constant voltage) conditions up to 4.35 V at 25°C and discharged at a rate of 0.33C under CC conditions down to 2.0 V. With one charge and discharge cycle being one cycle, the initial charge and discharge were carried out for 2 cycles. At this time, the discharge capacity of the second cycle was set as the initial discharge capacity.

[0204] Then, at a high temperature (45°C), each lithium secondary battery was charged at a rate of 0.33C under CC-CV conditions up to 4.35 V and discharged at a rate of 0.33C under CC conditions down to 2.0 V. With one charge and discharge cycle being one cycle, 50 cycles were carried out.

[0205] The capacity retention rate was calculated by substituting the capacity after the first cycle and the capacity after the 50th cycle into the following Mathematical Formula A, and the results are shown Figure 3 below.

[0206] [Formula A]

[0207] Retention ratio of capacity (%) = (Discharge capacity after 50 cycles at high temperature / Discharge capacity after 1 cycle at high temperature) × 100

[0208] Reference Figure 3 , it can be confirmed that in the case of the lithium secondary batteries of Examples 1 to 3, due to the sufficient activation process, a stable retention ratio of capacity can be achieved during high-temperature cycling.

[0209] On the other hand, it can be confirmed that in the case of the lithium secondary batteries of Comparative Examples 3 and 4, the retention ratio of capacity continuously increases during high-temperature cycling. That is, in the case of the lithium secondary batteries of Comparative Examples 3 and 4, since the activation process was not sufficiently carried out in the previous activation process step, another activation process was triggered during the subsequent cycling process, and an abnormal phenomenon occurred in which the capacity increased as the number of cycles increased.

[0210] Industrial applicability

[0211] The method for manufacturing a lithium secondary battery according to the present invention can control the charging end point in the activation step so that the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 at the point where all the lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure.

Claims

1. A method for manufacturing a lithium secondary battery, the method comprising the following steps: Preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a lithium-rich manganese-based oxide, wherein the content of manganese among all metals other than lithium is greater than 50 mol%, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium is greater than 1; And Charging and discharging the battery cell at least once to activate the battery, wherein the activation step includes: terminating charging when the ratio (Y / X) of the charging capacity (mAh / g) (Y) of the secondary battery to the estimated capacity (mAh / g) (X) of the positive electrode active material corresponds to 1.10 < Y / X ≤ 1.13 at the point where all lithium ions contained in the lithium-rich manganese-based oxide form a Li / Li dumbbell structure.

2. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The lithium-rich manganese-based oxide is represented by the following Chemical Formula 1: [Chemical Formula 1] Li a Ni b Co c Mn d M e O2 Wherein, in Chemical Formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, 0 ≤ e ≤ 0.2, and M is at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

3. The method for manufacturing a lithium secondary battery according to claim 2, wherein: In Chemical Formula 1, 1.1 ≤ a ≤ 1.5, 0.1 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.05, 0.5 ≤ d ≤ 0.80, 0 ≤ e ≤ 0.

1.

4. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The estimated capacity (C) (mAh / g) of the positive electrode active material is calculated using the following Mathematical Formula 1: [Mathematical Formula 1] C (mAh / g) = Q × (i / 100) In Mathematical Formula 1, Q is the theoretical capacity (mAh / g) of the lithium-rich manganese-based oxide, and i is the percentage (%) of the molar ratio of lithium ions that have moved until only lithium ions forming a Li / Li dumbbell structure remain to the total molar ratio of lithium ions contained in the lithium-rich manganese-based oxide.

5. The method for manufacturing a lithium secondary battery according to claim 4, wherein: i is defined by the following Mathematical Formula 2: [Mathematical Formula 2] In Mathematical Formula 2, The Li molar ratio is the total molar ratio of lithium ions contained in the lithium-rich manganese-based oxide.

6. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The charging capacity (Y) of the secondary battery is the capacity measured by real-time monitoring via the display of a detector during the charging of the battery cell.

7. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The activation step includes charging from 4.5 V to 4.6 V at 0.3C to 1.0C.

8. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The charging step is performed in a constant current mode (CC mode) or a constant current - constant voltage mode (CCCV mode).

9. The method for manufacturing a lithium secondary battery according to claim 8, wherein: The cut-off current in the constant voltage charging mode is 0.05C to 0.15C.

10. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The activation step further includes charging from SOC 0 to SOC 5 at a C-rate of 0.1C to 0.3C.

11. The method for manufacturing a lithium secondary battery according to claim 10, wherein: The charging step is performed in a constant current mode (CC mode).

12. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The activation step includes discharging at a C-rate of 0.3C to 0.7C until reaching 2.0 V.

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