Method for producing a lithium secondary battery containing perlithium manganese oxide

Abstract

The present invention relates to a method for producing a lithium secondary battery, comprising the steps of: preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, the battery cell including a perlithium manganese-based oxide in which the manganese content of all metals excluding lithium exceeds 50 mol % and the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium (Li / Me) exceeds 1; and activating the battery cell by charging and discharging under pressure, wherein in the activation step, charging is performed in a constant current mode up to a charge end voltage, and then charging is performed in a constant voltage mode, and the charge end voltage is greater than 4.35 V.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183684, filed December 23, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a lithium secondary battery containing a perlithium manganese-based oxide, and more specifically to a method for manufacturing a lithium secondary battery containing a perlithium manganese-based oxide that can suppress abnormal capacity increase and gas generation during battery operation. [Background technology]

[0003] Lithium secondary batteries are energy storage media that have been applied in various fields since their commercialization in 1991. As the market for products equipped with lithium secondary batteries expands, research into increasing the energy density of lithium secondary batteries is being actively conducted, and one of the most notable methods is the development of positive electrode active materials with a composition that allows for the use of more lithium than currently available.

[0004] As a positive electrode active material that can utilize more lithium, perlithium-based transition metal oxides with a layered structure and a lithium-to-transition metal molar ratio greater than 1 have been developed. These perlithium-based transition metal oxides achieve high capacity by simultaneously utilizing not only the cation redox reaction of the transition metal but also the anion redox reaction using oxygen within the positive electrode structure. A representative perlithium-based transition metal oxide currently being actively researched is perlithium manganese oxide, which has a lithium-to-transition metal molar ratio greater than 1 and a manganese content of 50 mol% or more of the total transition metals. Perlithium manganese oxides have a mixed structure of layered LiMO2 (where M is the transition metal) and rock-salt Li2MnO3. Li2MnO3 is activated by an activation process at a high voltage of 4.4 V or higher, achieving high capacity. However, this high-voltage activation process can cause oxygen desorption, excessive gas generation, and the leaching of transition metals such as manganese. If the activation voltage is lowered, the amount of gas generated during the activation process can be reduced, but in this case, the Li2MnO3 phase that remained in the crystal structure during the battery operation process is activated, which can cause abnormal behavior such as abnormal capacity increase and additional gas generation. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is intended to solve these problems, and aims to provide a method for manufacturing a lithium secondary battery that uses a perlithium manganese-based oxide, which can suppress abnormal capacity increase and gas generation during battery operation by activating the battery under specific conditions. [Means for solving the problem]

[0006] The present invention provides a method for manufacturing a lithium secondary battery, the method comprising the steps of: preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each containing a perlithium manganese-based oxide in which the manganese content of all metals excluding lithium exceeds 50 mol % and the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium (Li / Me) exceeds 1; and activating the battery cell by charging and discharging under pressure, wherein in the activation step, the charging is performed in a constant current mode up to a charge cut-off voltage and then in a constant voltage mode, and the charge cut-off voltage exceeds 4.35 V.

[0007] At this time, the constant current mode charging may be performed to include at least a part of the potential flattening section that appears during the constant current mode charging, and the cutoff current during the constant voltage mode charging may be 0.01C to 0.5C.

[0008] For example, in the activating step, the constant current mode charging can be performed from SOC60 to SOC100.

[0009] Alternatively, in the activation step, the charging may include a first charging step of performing constant current charging at a first current rate, and a second charging step of performing constant current charging at a second current rate different from the first current rate, followed by constant voltage charging, where the first current rate and the second current rate may be independently between 0.1 C and 1.0 C.

[0010] In this case, the first charging step can be performed until the SOC of the battery cell reaches 30 to 60, and the second charging step can be performed after the first charging step, that is, from SOC 30 to 60 until the SOC reaches 90 to 100.

[0011] On the other hand, the activation step is preferably performed while the battery cell is mounted in a jig and pressure is applied thereto.

[0012] Also, the step of activation can be performed while changing the pressurization pressure. For example, the step of activation can be carried out by charging under a relatively low pressurization pressure P1 until the SOC of the battery cell reaches 10 to 20, and then increasing the pressurization pressure to charge under a relatively high pressurization pressure P2. The pressurization pressure P1 and the pressurization pressure P2 can satisfy the following formula (1).

[0013] Formula (1): 5P1 ≤ P2 ≤ 15P1

[0014] On the other hand, in the present invention, in the dQ / dV graph obtained by differentiating the graph of the voltage V and the battery charge capacity Q measured while charging the battery cell to 4.6V, the charging curve area in the voltage range of 4.3V to 4.6V is A, and in the dQ / dV graph obtained by differentiating the graph of the voltage V and the battery charge capacity Q measured while charging the battery cell to the charging end voltage of the activation step, the charging curve area in the voltage range of 4.3V to the charging end voltage is B. It is preferable to satisfy the following formula (2).

[0015] Formula (2): 0.5A ≤ B ≤ A

[0016] In the present invention, the over-lithium manganese-based oxide may be represented by the following chemical formula 1.

[0017] [Chemical formula 1] Li [ Ni b Co c Mn d M e O2

[0018] In the chemical formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 < d < 1.0, 0 ≤ e ≤ 0.2, and M can include one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. Preferably, 1.1 ≤ a ≤ 1.5, 0.1 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.05, 0.5 < d ≤ 0.80, 0 ≤ e ≤ 0.1.

Brief Description of Drawings

[0019] [Figure 1] 1 is a graph showing the cycle characteristics of lithium secondary batteries activated by the methods of Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0020] The terms and words used in this specification and claims shall not be interpreted in a limited way to their ordinary or dictionary meanings, but shall be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0021] In the present invention, "primary particles" refers to particle units that do not appear to have grain boundaries when observed at a magnification of 5,000 to 20,000 using a scanning electron microscope. "Average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed in a scanning electron microscope image.

[0022] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of a plurality of primary particles.

[0023] In the present invention, the "average particle size D 50 " means the particle size at 50% of the volume cumulative particle size distribution of the particle powder to be measured (for example, positive electrode active material powder, negative electrode active material powder, etc.). 50 can be measured using the laser diffraction method. For example, a powder of the particles to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W. After obtaining a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the volume cumulative amount can be determined.

[0024] In the present invention, "SOC X" means a state where the percentage of the capacity charged to a battery cell relative to the discharge capacity that appears when the battery cell is discharged from 4.6 V to 2.0 V (i.e., (charged capacity / discharge capacity of battery cell in the voltage range of 4.6 to 2.0 V) × 100) is X.

[0025] The present inventors have conducted extensive research to improve the phenomenon of abnormally increasing capacity and increasing gas generation during operation of a lithium secondary battery using a perlithium manganese-based oxide, and have found that this can be improved by performing an activation process under specific conditions during the manufacture of the lithium secondary battery, thereby completing the present invention.

[0026] The present invention will be specifically described below.

[0027] The method for manufacturing a lithium secondary battery according to the present invention includes: (1) preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte; and (2) activating the battery cell by charging and discharging it under pressure, wherein the activation step is characterized in that the charging is performed in a constant current mode up to a cut-off voltage of charge, and then in a constant voltage mode, and the cut-off voltage of charge is greater than 4.35 V.

[0028] (1) Prepare the battery cells First, a battery cell including a positive electrode, a negative electrode, and an electrolyte is prepared.

[0029] The battery cell may be manufactured by, for example, forming an electrode assembly including a positive electrode and a negative electrode, housing the electrode assembly in a battery case, injecting an electrolyte, and sealing the battery case. In this case, the electrode assembly may include a separator between the positive electrode and the negative electrode.

[0030] The electrode assembly may be of various types well known in the art, such as a jelly roll type, a stack type, a stack and lamination type, or a stack and folding type, and the type is not particularly limited.

[0031] The jelly roll type electrode assembly can be manufactured by interposing a sheet-shaped separator between a sheet-shaped positive electrode and a sheet-shaped negative electrode, and then winding them in one direction.

[0032] The stacked electrode assembly can be manufactured by cutting the positive electrode, separator, and negative electrode into a desired shape, and then stacking the cut positive electrode / separator / negative electrode in this order.

[0033] The stack and lamination type electrode assembly may be manufactured by stacking a positive electrode, a separator, and a negative electrode to prepare a plurality of unit cells, stacking the plurality of unit cells with a separator interposed therebetween, and then laminating the stacked unit cells by a method such as heating.

[0034] The stack-and-fold type electrode assembly may be manufactured by stacking a positive electrode, a separator, and a negative electrode to manufacture a plurality of unit cells, arranging the plurality of unit cells on one or both sides of a long folding separator, and then winding up the folding separator.

[0035] Meanwhile, the electric case may be any of various battery cases known in the art, such as a cylindrical battery case, a square battery case, or a pouch-type battery case, and is not particularly limited in type.

[0036] Meanwhile, the positive electrode according to the present invention includes, as a positive electrode active material, a perlithium manganese-based oxide in which the manganese content of all metals excluding lithium exceeds 50 mol % and the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium (Li / Me) exceeds 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, and the positive electrode active material layer includes a perlithium manganese-based oxide in which the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium (Li / Me) exceeds 1.

[0037] In the case of a lithium-rich manganese-based oxide containing an excessive amount of lithium, it has a structure in which a layered structure phase (LiM’O2) and a rock-salt structure phase (Li2MnO3) coexist. During the initial activation process, while the rock-salt structure phase is being activated, excessive lithium ions are generated, enabling the realization of a high capacity.

[0038] Preferably, the lithium-rich manganese-based oxide can be represented by Chemical Formula 1.

[0039] [Chemical Formula 1] Li a Ni b Co c Mn d M e O2

[0040] In Chemical Formula 1, M can be one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0041] On the other hand, a is the molar ratio of Li in the lithium-rich manganese-based oxide, and it may be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3. When a is within the above range, it can sufficiently compensate for the irreversible capacity of the silicon-based negative electrode active material, enabling the realization of high-capacity characteristics.

[0042] The b is the molar ratio of Ni in the lithium-rich manganese-based oxide, and it can be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0043] The c is the molar ratio of Co in the lithium-rich manganese-based oxide, and it can be 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.08, or 0 ≤ c ≤ 0.05. When c exceeds 0.1, it is difficult to ensure a high capacity, gas generation and degradation of the positive electrode active material become severe, and the life characteristics may deteriorate.

[0044] Said d is the molar ratio of Mn in the over-lithiated manganese-based oxide, and can be 0.5 < d < 1.0, 0.50 < d ≤ 0.80, or 0.50 < d ≤ 0.70. When d is less than 0.5, the ratio of the rock-salt type structure phase is too small, and the negative electrode irreversible compensation and capacity improvement effects are small.

[0045] Said e is the molar ratio of the doping element M in the over-lithiated 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 active material capacity.

[0046] On the other hand, in the over-lithiated manganese-based oxide represented by Chemical Formula 1, the molar ratio of Li to the total number of moles of all metal elements excluding Li (Li / Me) may 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 characteristics and capacity characteristics are well manifested. If the Li / Me ratio is too high, the electrical conductivity may decrease, the rock-salt type structure phase (Li2MnO3) may increase, and the degradation rate may increase. If it is too low, the energy density improvement effect is negligible.

[0047] On the other hand, the composition of the over-lithiated manganese-based oxide can also be represented by the following Chemical Formula 2.

[0048] [Chemical Formula 2] XLi2MnO3·(1 - X)Li[Ni 1-y-z-w Mn y Co z M w O2

[0049] In Chemical Formula 2, M can be one or more selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0050] The X represents the ratio of the Li2MnO3 phase in the perlithium manganese-based oxide, and may 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 perlithium manganese-based oxide satisfies this range, the irreversible capacity of the silicon-based negative electrode active material can be sufficiently compensated for, and high capacity characteristics can be achieved.

[0051] The 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.

[0052] The value 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. If z exceeds 0.1, gas generation and degradation of the positive electrode active material become severe, which may result in a decrease in life characteristics.

[0053] The 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.

[0054] Meanwhile, the positive electrode active material according to the present invention may further include a coating layer on the surface of the perlithium manganese-based oxide, if necessary. When the positive electrode active material includes the coating layer, the coating layer inhibits contact between the perlithium manganese-based oxide and the electrolyte, thereby reducing electrolyte side reactions and improving life characteristics.

[0055] The coating layer is made of a coating element M 1 The coating element M 1 may be, for example, one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and may be preferably Al, Co, Nb, W, and combinations thereof, and more preferably Al, Co, and combinations thereof. 1may contain two or more kinds, for example, Al and Co.

[0056] The coating elements are in the oxide form in the coating layer, i.e., M 1 It can exist in Oz (1≦z≦4).

[0057] The coating layer can be formed by dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. Among these, atomic layer deposition is preferred because it allows the coating layer to be formed over a wide area.

[0058] The area where the coating layer is formed may be 10 to 100%, preferably 30 to 100%, and more preferably 50 to 100% of the total surface area of ​​the perlithium manganese-based oxide particles. When the area where the coating layer is formed satisfies the above range, the effect of improving the life characteristics is excellent.

[0059] Meanwhile, the cathode active material according to the present invention may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter D of the secondary particles may be 50 The D of the positive electrode active material may 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, the electrode density can be satisfactorily realized, and the deterioration of the capacity and rate characteristics can be minimized.

[0060] The positive electrode active material has a BET specific surface area of ​​1 m 2 / g~10m 2 / g, 3-8m 2 / g or 4~6m 2 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, whereas if the specific surface area is too high, moisture absorption is rapid, accelerating side reactions with the electrolyte and making it difficult to ensure long life characteristics.

[0061] Meanwhile, the perlithium manganese-based oxide can be prepared by mixing a transition metal precursor and a lithium source material and then calcining the mixture.

[0062] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). These may be used alone or in combination.

[0063] Meanwhile, the transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. When a precursor in the form of a carbonate is used, it is more preferable in that a cathode active material having a relatively high specific surface area can be prepared.

[0064] The transition metal precursor can be prepared through a co-precipitation process. For example, the transition metal precursor can be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, followed by a co-precipitation reaction. If necessary, an oxidizing agent or oxygen gas can be further added during the co-precipitation reaction.

[0065] In this case, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may 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, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt oxide, cobalt acetate, cobalt halide, etc.

[0066] The ammonium cation complexing agent can be one or more selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0067] The basic compound may be one or more selected from the group consisting of 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. Furthermore, when a basic compound is used together with an oxidizing agent, an oxide-form precursor can be obtained.

[0068] Meanwhile, the transition metal precursor and the lithium source material can be mixed in amounts such that the molar ratio of total transition metals (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.

[0069] The firing may be carried out at a temperature of 600 to 1000°C or 700 to 950°C for a period of 5 to 30 hours or 5 to 20 hours. The firing atmosphere may be air or oxygen, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0070] Meanwhile, the positive electrode active material layer may further include a conductive material and a binder in addition to the positive electrode active material.

[0071] Examples of the conductive material include spherical or flake graphite; carbonaceous 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.1 to 20 wt %, 1 to 20 wt %, or 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0072] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 20 wt %, 2 to 20 wt %, or 2 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0073] The negative electrode may include, for example, a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

[0074] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Examples of suitable materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the current collector surface may be provided with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0075] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β (0<β<2), metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these can be used.

[0076] A thin film of metallic lithium can also be used as the negative electrode active material. Carbon materials can be either low-crystalline or high-crystalline. Examples of low-crystalline carbon include soft carbon and hard carbon. Examples of high-crystalline carbon include amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbon such as petroleum or coal tar pitch-derived cokes.

[0077] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the battery and has electronic conductivity can be used without particular limitations. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material typically accounts for 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, of the total weight of the negative electrode active material layer.

[0078] The binder functions to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0079] For example, the negative electrode active material layer may be prepared by coating a negative electrode slurry containing a negative electrode active material, and optionally a binder and a conductive material, on a negative electrode current collector and drying the coating, or by casting the negative electrode slurry on a separate support, peeling the negative electrode slurry from the support, and laminating the resulting film on the negative electrode current collector.

[0080] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without limitation. A separator with low resistance to electrolyte ion movement and excellent electrolyte humidification is particularly preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or polymer material can also be used, and it can be used in either a single-layer or multi-layer structure.

[0081] Next, the electrolyte may be any of 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 the type is not particularly limited.

[0082] For example, the electrolyte can include an organic solvent and a lithium salt.

[0083] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate solvents such as ethylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes.

[0084] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the negative ions of the lithium salt include 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 - The lithium salt may be one or more selected from the group consisting of 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 used is preferably within the range of 0.1 to 5.0M.

[0085] In addition to the above components, the electrolyte may further contain additives for purposes such as improving the battery's lifespan, suppressing battery capacity degradation, and improving the battery's discharge capacity. Examples of additives include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, which may be used alone or in combination. The additives may be present in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %, based on the total weight of the electrolyte.

[0086] (2) Activation step Next, the battery cell is electrically activated by charging and discharging it at least once under pressure. The activation step is a process of charging and discharging the battery cell to impart electrical properties and forming a solid electrolyte interphase (SEI) film on the electrodes to stabilize the battery.

[0087] In the present invention, charging and discharging during the activation process are performed under pressure. The pressure can be applied by, for example, mounting the battery cell in a jig and then applying pressure to the battery cell through the jig. In the case of a battery cell using a perlithium manganese-based oxide, excessive gas is generated during the activation process. If the gas is not properly discharged, lithium deposition due to gas trapping or uneven activation may occur, resulting in reduced cell performance. Therefore, in the present invention, the activation process is performed under pressure to prevent gas trapping throughout the battery cell and ensure proper electrolyte impregnation, thereby enabling uniform activation of the Li2MnO3 phase at high voltages and preventing abnormal battery behavior during operation.

[0088] On the other hand, the pressure is 0.1 kgf / cm 2 ~10kgf / cm 2 , preferably 0.1 kgf / cm 2 ~8kgf / cm 2 , and more preferably 0.2 kgf / cm 2 ~7kgf / cm 2 When the pressure condition satisfies the above range, damage to the battery cell can be prevented, and the effects of improving gas discharge and electrolyte impregnation can be more excellent.

[0089] Meanwhile, in the present invention, the activation process can be performed while varying the pressurizing pressure as needed. For example, in the early stage of charging in the activation step (e.g., SOC 20 or less), pressurization can be performed at a relatively low pressure to allow a rich electrolyte to be present at the electrode interface and to stably form an SEI film. When the amount of gas generated by film formation increases (e.g., after SOC 20), the pressurizing pressure can be increased to remove gas from the electrode interface while charging. Charging can also be performed under a relatively high pressurizing pressure. Performing the activation process while varying the pressurizing pressure in this way minimizes deformation and damage to the battery cell due to pressurization, maximizes gas discharge, and enables charging at a relatively high current rate, thereby shortening the activation process time.

[0090] More specifically, in the activation step, charging can be performed under an increased pressure P1 until the SOC of the battery cell reaches 10 to 20, and then charging can be performed under an increased pressure P2. At this time, it is preferable that P1 and P2 satisfy the condition of the following formula 1.

[0091] Formula (1): 5P1≦P2≦15P1

[0092] When P1 and P2 satisfy the condition of the formula (1), the gas discharge effect can be maximized, charging can be performed at a relatively high current rate, and the activation process time can be shortened.

[0093] Meanwhile, the present invention is characterized in that during charging in the activation process, charging is performed in a constant current mode up to the end-of-charge voltage, and then in a constant voltage mode. By performing charging in a constant current / constant voltage mode as in the present invention, it is possible to minimize the non-activated Li2MnO3 phase, thereby preventing abnormal behavior during battery operation.

[0094] In one example of the activation step, the battery is charged in a constant current mode until the SOC reaches 60 to 100, and then charged in a constant voltage mode. The cut-off current during constant voltage mode charging can be 0.01C to 0.5C, or 0.06C to 0.5C.

[0095] Meanwhile, in another example of the activation step, the cut-off current during constant voltage mode charging can be 0.01 C to 0.15 C, preferably 0.03 C to 0.10 C, and more preferably 0.03 C to 0.06 C. If constant voltage mode charging is terminated too early, activation may not proceed sufficiently, whereas if it is terminated too late, the activation process time may become longer, potentially resulting in a problem of reduced production rate.

[0096] The charge cut-off voltage during charging may be greater than 4.35 V, for example, 4.4 V to 4.8 V, 4.4 V to 4.7 V, 4.4 V to 4.6 V, or 4.5 V to 4.6 V. If the charge cut-off voltage is 4.35 V or less, Li2MnO3 is not sufficiently activated, making it difficult to achieve a high capacity and possibly causing abnormal behavior in which the capacity increases during battery operation.

[0097] Meanwhile, the constant-current charging is preferably performed so as to include at least a portion of the plateau potential range (4.4 V to 4.6 V). In the case of a battery using a perlithium manganese-based oxide, a plateau potential range where the voltage remains relatively constant appears in the voltage range of 4.4 V to 4.6 V in the voltage profile depending on the charging rate. If the constant-current charging is performed so as to include at least a portion of this plateau potential range, the perlithium manganese-based oxide is activated, resulting in high capacity characteristics. If the plateau potential range is not included during activation charging, the Li2MnO3 phase is not sufficiently activated, resulting in a small capacity increase and the possibility of abnormal behavior during cycling.

[0098] More specifically, the end-of-charge voltage can be set to satisfy the following formula (2).

[0099] Formula (2): 0.5A≦B≦A

[0100] In the formula (2), A is the charge curve area in the voltage range of 4.3 V to 4.6 V on the dQ / dV graph obtained by differentiating the graph of the voltage V measured while charging the battery cell to 4.6 V and the battery charge capacity Q, and B is the charge curve area in the range of 4.3 V to the charge end voltage on the dQ / dV graph obtained by differentiating the graph of the voltage V measured while charging the battery cell to the charge end voltage in the activation step and the battery charge capacity Q.

[0101] When the end-of-charge voltage during activation charging is set to satisfy the above formula (2), high-voltage activation is sufficiently performed, the capacity is excellent, and the occurrence of abnormal behavior due to non-uniform activation of the Li2MnO3 phase can be more effectively suppressed.

[0102] Meanwhile, the charging may include two or more steps with different charging rates, as needed. For example, the charging may include a first charging step of performing constant current charging at a first current rate, and a second charging step of performing constant current charging at a second current rate different from the first current rate, followed by constant voltage charging.

[0103] In this case, the first current rate and the second current rate may be independently 0.1C to 1.0C, or 0.1C to 0.8C, or 0.2C to 0.8C, or 0.3C to 0.6C.

[0104] Preferably, the first current rate can be lower than the second current rate. That is, the first charging step can be performed at a relatively slow rate, and the second charging step can be performed at a relatively fast rate. If the current rate is fast in the first charging step, an SEI film may be formed unstably on the electrode surface. If the SEI film is formed unstably on the electrode surface, the SEI film may be easily decomposed during battery operation, causing rapid degradation of the electrode, which may significantly reduce the lifespan characteristics. However, if the charging rate is too slow, the total time for the activation process may increase and the production rate may decrease. However, as in the present invention, by performing charging at a slow rate in the first charging step, which is the initial stage of charging when the SEI film is formed, and charging at a high rate in the second charging step, which is after the SEI film has formed to a certain extent, the SEI film can be stably formed on the electrode surface while reducing the total time for the activation process.

[0105] Meanwhile, the first charging step can be performed until the SOC of the battery cell reaches 30 to 60. When the charge capacity in the first charging step satisfies the above range, a strong and dense SEI film is formed on the electrode surface, thereby achieving excellent life characteristics.

[0106] Meanwhile, the first charging step may be performed in two or more steps with different rate limits, as necessary. For example, the first charging step may include a 1-1 charging step in which the battery cell is charged at a C rate of 0.1 C to 0.3 C, and a 1-2 charging step in which the battery cell is charged at a C rate of 0.3 C to 1.0 C. In this case, the 1-1 charging step may be performed from SOC0 to SOC3-5, and the 1-2 charging step may be performed from SOC3-5 to SOC30-60. When the first charging step is performed in two steps as described above, the charging rate can be maintained lower in the initial stage of SEI film formation, forming a stronger and denser SEI film. Then, by increasing the charging rate, oxygen desorption and positive ion mixing can be suppressed, thereby shortening the time required for the activation process.

[0107] Meanwhile, the second charging step is preferably performed after the first charging step, i.e., from an SOC of 30-60 to an SOC of 90-100. When the charge capacity in the second charging step satisfies the above range, the SEI film can be prevented from being incompletely formed, Li2MnO3 can be sufficiently activated, and abnormal behavior during battery operation can be effectively prevented.

[0108] The second charging step is carried out in a constant current constant voltage mode, and the current rate (C rate) during the constant current charging can be 0.1C to 1.0C, more preferably 0.3C to 0.8C, and even more preferably 0.3C to 0.6C.

[0109] Next, the charged battery cell is discharged. At this time, the discharging can be performed at a C rate of 0.1 C to 1 C, preferably 0.3 C to 1 C. Meanwhile, the discharging can be performed in a constant current mode (CC mode), and the discharge end voltage can be 2.0 V to 3.0 V.

[0110] On the other hand, the activation step is preferably carried out at a temperature of 25° C. to 70° C., preferably 30° C. to 60° C., and more preferably 40° C. to 50° C. When the activation step is carried out within the above temperature range, Li2MnO3 is appropriately activated, and a high capacity can be achieved.

[0111] However, if necessary, the activation step may further include an aging step, which is intended to allow the electrolyte to uniformly penetrate the electrode assembly and stabilize the battery. The aging step may be performed one or more times before, during, and / or after charging.

[0112] The aging step can be carried out at a temperature of, for example, 20° C. to 60° C., 20° C. to 50° C., and preferably 30° C. to 50° C. When aging is carried out at the above temperatures, electrolyte impregnation and lithium mobility are improved, and activation can be carried out more smoothly.

[0113] The present invention will be described in more detail below through specific examples.

[0114] Example 1 The positive electrode active material, conductive material, and PVDF binder were mixed in a weight ratio of 97:1:2 in N-methylpyrrolidone to prepare a positive electrode slurry. 1.38 [Ni 0.363 Co 0.005 Mn 0.642 ]O2 was used as the cathode material, and CNT was used as the conductive material. The cathode slurry was applied to an aluminum current collector sheet, dried, and then rolled to prepare a cathode.

[0115] Anode active material, conductive material, and binder were mixed in water in a weight ratio of 96:1:3 to prepare anode slurry. Graphite was used as the anode active material, carbon black as the conductive material, and a mixture of SBR and CMC in a weight ratio of 2:1 was used as the binder. The anode slurry was applied to a copper current collector sheet, dried, and then rolled to prepare anodes.

[0116] A separator was interposed between the positive electrode and negative electrode to prepare an electrode assembly. The electrode assembly was then inserted into a battery case, and an electrolyte was then injected to prepare a battery cell.

[0117] The battery cell was attached to a jig and charged to 4.6 V in a 0.3 C constant current mode, then switched to a constant voltage mode and charging was continued, with charging terminating when the current reached 0.05 C. Next, the charged battery cell was discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during charging, the pressure was 0.5 kgf / cm from SOC 0 to 17. 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0118] Example 2 A battery cell was manufactured in the same manner as in Example 1. After mounting the manufactured battery cell on a jig, it was charged in a 1.0 C constant current mode to SOC 60 (first charging step). After that, it was charged in a 0.4 C constant current mode to 4.6 V, and then changed to a constant voltage mode for charging, and charging was terminated when the current reached 0.05 C (second charging step). After that, the charged battery cell was discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during the charging, a 0.5 kgf / cm 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0119] Example 3 A battery cell was manufactured in the same manner as in Example 1, and the manufactured battery cell was mounted on a jig and charged to 4.5 V in a 0.3 C constant current mode, and then switched to a constant voltage mode for charging, with charging terminating when the current reached 0.05 C. Next, the charged battery cell was discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during the charging, the pressure was 0.5 kgf / cm from SOC 0 to 17. 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0120] Comparative Example 1 A battery cell was manufactured in the same manner as in Example 1. The manufactured battery cell was charged to 4.6 V in a 0.3 C constant current mode without being mounted on a jig, and then the mode was changed to constant voltage mode for charging, and charging was terminated when the current reached 0.05 C. The charged battery cell was then discharged to 2.0 V at a constant current of 0.5 C.

[0121] Comparative Example 2 A battery cell was manufactured in the same manner as in Example 1, and the manufactured battery cell was mounted on a jig and charged to SOC 60 in a 1.0 C constant current mode. It was then charged to 4.6 V in a 0.4 C constant current mode. The charged battery cell was then discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during the charging, a 0.5 kgf / cm pressure was applied from SOC 0 to 17. 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0122] Comparative Example 3 A battery cell was manufactured in the same manner as in Example 1, and the manufactured battery cell was mounted on a jig and charged to 4.35 V in a 0.3 C constant current mode, and then switched to a constant voltage mode for charging. Charging was terminated when the current reached 0.05 C. The charged battery cell was then discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during charging, a 0.5 kgf / cm2 pressure was applied from SOC 0 to 17. 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0123] Comparative Example 4 A battery cell was manufactured in the same manner as in Example 1, and the manufactured battery cell was attached to a jig and charged to 3.9 V in a 0.3 C constant current mode, and then changed to a constant voltage mode for charging. Thereafter, the charged battery cell was discharged to 2.0 V at a constant current of 0.5 C, and then the battery cell was removed from the jig. Meanwhile, during the charging, the SOC was 0.5 kgf / cm 2 Charging was carried out while applying pressure of 5kgf / cm. Then, the jig was adjusted to apply pressure of 5kgf / cm. 2 Charging and discharging were carried out while pressurizing the battery at a pressure of 1000 kJ / cm.

[0124] Experimental Example 1 In the activation step of Examples 1 to 3 and Comparative Examples 1 to 4, the capacity was measured according to the voltage during the charging process to obtain a voltage-capacity graph, which was then differentiated to obtain a dQ / dV graph.

[0125] Thereafter, the percentages of the charge curve areas in the voltage range of 4.3 V to 4.6 V that appear on the dQ / dV graphs of Example 2 and Comparative Examples 1 to 4 were measured based on the charge curve areas in the voltage range of 4.3 V to 4.6 V that appear on the dQ / dV graphs of Example 1. The measurement results are shown in Table 1 below.

[0126] [Table 1]

[0127] Experimental Example 2: Initial Capacity The lithium secondary batteries activated according to the methods of Examples 1 to 3 and Comparative Examples 1 to 4 were charged to 4.35 V at 25°C in a constant current / constant voltage mode at 0.33 C, and then cut off when the current reached 0.05 C. Subsequently, they were discharged to 2.0 V at a constant current of 0.33 C, and the initial discharge capacity was measured. The relative ratios of the initial discharge capacities of the lithium secondary batteries of Example 2 and Comparative Examples 2 to 5 were measured, assuming that the initial discharge capacity of the lithium secondary battery of Example 1 was 100%. The measurement results are shown in Table 2 below. On the other hand, the lithium secondary battery activated according to the method of Comparative Example 1 exhibited Li plating, making it impossible to operate the battery.

[0128] [Table 2]

[0129] As shown in Table 2, the lithium secondary batteries of Examples 1 to 3, which were activated by charging to a voltage of 4.3 V or higher in a constant current / constant voltage mode while applying pressure using a jig, showed superior initial capacities compared to Comparative Examples 1 to 4. In contrast, the lithium secondary battery of Comparative Example 1, which was activated without applying pressure, was unable to operate due to the occurrence of lithium plating, and it was confirmed that the initial discharge capacity decreased when charging was performed only in a constant current mode, not in a constant current / constant voltage mode, even including the pressure step (Comparative Example 2), or when activation was performed at a charge cut-off voltage of 4.35 V or lower (Comparative Examples 3 and 4).

[0130] Experimental example 3: High temperature life characteristics The lithium secondary batteries activated by the methods of Examples 1 to 3 and Comparative Examples 1 to 4 were charged to 4.35 V at 45°C in a constant current / constant voltage mode (cutoff current 0.05 C) at 0.33 C, and then discharged to 2.0 V at a constant current of 0.33 C, counting as one cycle, and after 50 charge / discharge cycles, the capacity retention rate and the amount of voltage drop were measured. The measurement results are shown in Figure 1.

[0131] On the other hand, in the lithium secondary battery activated by the method of Comparative Example 1, Li plating occurred, and the battery could not be driven.

[0132] As shown in FIG. 1, the lithium secondary batteries activated by the methods of Examples 1 to 3 maintained a constant capacity and did not experience a significant increase in voltage drop during 50 charge-discharge cycles, whereas the lithium secondary batteries activated by the methods of Comparative Examples 2 to 4 exhibited abnormal operation in which the capacity increased with the increase in cycles and the voltage drop increased significantly. [Industrial Applicability]

[0133] The method for manufacturing a lithium secondary battery according to the present invention performs an activation process under pressure and charges the battery in a constant current / constant voltage mode, thereby facilitating gas discharge and minimizing the non-activated Li2MnO3 phase, thereby preventing lithium precipitation and abnormal behavior during battery operation.

Claims

1. providing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each of which includes a perlithium manganese-based oxide in which the manganese content of all metals other than lithium exceeds 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) exceeds 1; activating the battery cell by charging and discharging under pressure; In the activation step, the charging is performed in a constant current mode until the end-of-charge voltage exceeds 4.35 V, and then in a constant voltage mode,

2. The method for producing a lithium secondary battery according to claim 1 , wherein the charging in the constant current mode is carried out so as to include at least a part of a plateau potential section.

3. The perlithium manganese-based oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M ｅ O ２ 2. The method for manufacturing a lithium secondary battery according to claim 1, wherein in Chemical Formula 1, 1<a, 0≦b≦0.5, 0≦c≦0.1, 0.5<d<1.0, and 0≦e≦0.2, and M 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.

4. 4. The method for producing a lithium secondary battery according to claim 3, wherein in Chemical Formula 1, 1.1≦a≦1.5, 0.1≦b≦0.4, 0≦c≦0.05, 0.5<d≦0.80, and 0≦e≦0.

1.

5. 2. The method for producing a lithium secondary battery according to claim 1, wherein the cutoff current during charging in the constant voltage mode is 0.01 C to 0.5 C.

6. 6. The method for manufacturing a lithium secondary battery according to claim 5, wherein in the activation step, charging in the constant current mode is performed from SOC 60 to SOC 100.

7. 2. The method for manufacturing a lithium secondary battery according to claim 1, wherein in the activation step, the charging includes a first charging step of performing constant current charging at a first current rate, and a second charging step of performing constant current charging at a second current rate different from the first current rate, followed by constant voltage charging.

8. 8. The method for manufacturing a lithium secondary battery according to claim 7, wherein the first current rate and the second current rate are each independently 0.1 C to 1.0 C.

9. 8. The method for manufacturing a lithium secondary battery according to claim 7, wherein the first charging step is performed up to an SOC of 30 to 60, and the second charging step is performed from an SOC of 30 to 60 to an SOC of 90 to 100.

10. The method for manufacturing a lithium secondary battery according to claim 1 , wherein the activation step is performed while the battery cell is mounted in a jig and pressurized.

11. The method for producing a lithium secondary battery according to claim 1 , wherein the activation step is performed while changing the pressurizing pressure.

12. The activation step is performed by applying a pressurized pressure P １ Charging is performed under pressure P ２ The method for producing a lithium secondary battery according to claim 1 , wherein charging and discharging are carried out under the following conditions:

13. The pressurized pressure P １ and the pressurized pressure P ２ satisfies the following formula (1), Formula (1): 5P １ ≦P ２ ≦15P １ The method for producing a lithium secondary battery according to claim 12, wherein

14. In the dQ / dV graph obtained by differentiating the graph of the voltage V measured while charging the battery cell to 4.6 V and the battery charge capacity Q, the area of ​​the charge curve in the voltage range of 4.3 V to 4.6 V is defined as A, and in the dQ / dV graph obtained by differentiating the graph of the voltage V measured while charging the battery cell to the charge end voltage in the activation step and the battery charge capacity Q, the area of ​​the charge curve in the range of 4.3 V to the charge end voltage is defined as B. Formula (2): 0.5A≦B≦A The method for producing a lithium secondary battery according to claim 1, wherein

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