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 activating the battery by charging and discharging the battery cells at least once, wherein the activating step includes: a first charging step of charging at SOC 5 or less in a constant current mode (CC mode); a second charging step in which charging is terminated at SOC 80 to SOC 98 from the point in time when charging is terminated in the first charging step; and performing primary discharge after the charging is completed.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority of Korean Patent Application No. 10-2022-0183692, filed with the Korean Intellectual Property Office on December 23, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present invention relates to a method of manufacturing a lithium secondary battery, and more particularly, to a manufacturing method capable of suppressing the generation of oxidizing gases caused by an 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 have been applied to various fields since their commercialization in 1991. As the market for products equipped with lithium secondary batteries has expanded, 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 capable of utilizing a larger amount of lithium, lithium-rich transition metal oxides having a layered structure and a molar ratio of lithium to transition metal greater than 1 have been developed. Such lithium-rich transition metal oxides can achieve high capacity by performing an activation step at a high voltage of 4.4 V or more.

[0006] However, in the initial activation stage of the high-voltage activation process, not only does the cathode structure change while lithium ions are desorbed from the lithium-rich transition metal oxide, and oxygen radicals are formed / desorbed through an oxygen redox reaction, but also a large amount of oxidizing gases such as CO, CO2, and O2 are generated due to side reactions between oxygen radicals and electrolytes and / or decomposition of the electrolyte under high-voltage conditions. When a large amount of oxidizing gases are generated in this way, the pressure inside the battery increases, leading to a short circuit, or it may be difficult to separate from the jig, and lithium plating may occur due to gas traps, which has limitations in reducing charge / discharge capacity and stability.

[0007] [Prior Art Documents]

[0008] [Patent Documents]

[0009] Korean Unexamined Patent Publication No. 2015-0015303

[0010] Korean Unexamined Patent Publication No. 2016-0035269 Summary of the Invention

[0011] Technical Problem

[0012] 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 containing a lithium-rich manganese-based oxide, which can suppress the generation of oxidizing gas caused by the activation step.

[0013] Technical solution

[0014] According to one aspect of the present invention, there is provided a method for manufacturing a lithium secondary battery, the method comprising the following steps:

[0015] 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

[0016] Charging and discharging the battery cell at least once to activate the battery,

[0017] wherein the activation step includes:

[0018] A first charging step of charging at a state of charge (SOC) of 5 or less in a constant current mode (CC mode);

[0019] A second charging step of terminating charging at an SOC of 80 to SOC 98 starting from the time point when charging is terminated in the first charging step; and

[0020] A step of discharging once after charging is completed.

[0021] On the other hand, the charging step can be performed at a C-rate of 0.3C to 1.0C, and the termination voltage of charging in the charging step can be 4.45 V to 4.55 V.

[0022] The activation step can include discharging at a C-rate of 0.3C to 1.0C until reaching 2.0 V.

[0023] Beneficial effects

[0024] According to the method for manufacturing a lithium secondary battery of the present invention, in certain intervals of the activation charging step, that is, terminating charging at an SOC of 80 to SOC 98, it is possible to significantly suppress the generation of oxidizing gas caused by the activation step. Description of the drawings

[0025] Figure 1 A graph showing the evaluation results of the amount of gas generated during the activation process according to Experimental Example 1. Detailed description of the invention

[0026] The terms or words used in this specification and the appended claims should not be construed as limited to their ordinary or dictionary meanings, and the present invention should be interpreted in accordance with the meaning and concept consistent with the technical gist of the present invention on the basis of the principle that the inventors can appropriately define the concept of the terms so as to appropriately describe their invention in the best way.

[0027] In the present invention, "primary particle" refers to a particle unit in which no grain boundary appears when observed with a scanning electron microscope at a magnification of 5000 to 20000 times. The "average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle size of the primary particles observed in the scanning electron microscope image.

[0028] In the present invention, "secondary particle" is a particle formed by agglomeration of a plurality of primary particles.

[0029] 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.) reaches 50% in the particle size distribution curve of the particles. D 50 can be measured by the laser diffraction method. It can be measured by the following method: The method includes 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.

[0030] Furthermore, in the present invention, "SOC X" refers to a state in which the percentage of the charge capacity in the battery cell with respect to the discharge capacity exhibited when the battery cell discharges from 4.6 V to 2.0 V is X.

[0031] In order to improve the voltage drop during the charging step for activation in a lithium secondary battery using a lithium-rich manganese-based oxide, the inventors conducted repeated studies and found that by performing the activation process under specific charging conditions when manufacturing the lithium secondary battery, the generation of oxidizing gases caused by the activation step can be suppressed, and the present invention was completed.

[0032] Now, the present invention will be described in detail.

[0033] The method for manufacturing a lithium secondary battery according to the present invention is characterized in that the method includes:

[0034] Steps of preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, where the positive electrode 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; and

[0035] Steps of charging and discharging the battery cell at least once to activate the battery,

[0036] where the activation step includes:

[0037] A first charging step of charging at SOC 5 or below in a constant current mode (CC mode);

[0038] A second charging step of terminating charging at SOC 80 - SOC 98 starting from the time point when charging is terminated in the first charging step; and

[0039] Steps of performing one discharge after charging is completed.

[0040] (1) Steps of preparing the battery cell

[0041] First, prepare a battery cell including a positive electrode, a negative electrode, and an electrolyte.

[0042] The battery cell can be prepared, for example, by the following steps: forming an electrode assembly including a positive electrode and a negative electrode, loading the electrode assembly into 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.

[0043] Each component of the battery cell according to the present invention will be described in more detail below.

[0044] Positive electrode

[0045] 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, where 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.

[0046] 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, while the rock salt phase is activated, an excessive amount of lithium ions are generated, thereby enabling high capacity.

[0047] Preferably, the lithium-rich manganese-based oxide can be represented by the following Chemical Formula 1.

[0048] [Chemical Formula 1]

[0049] Li a Ni b Co c Mn d M e O2

[0050] Wherein, in Chemical Formula 1, M can be at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0051] On the other hand, a is the molar ratio of Li in the lithium-rich manganese-based oxide, and can be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3.

[0052] b is the molar ratio of Ni in the lithium-rich manganese-based oxide, and can be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] On the other hand, in the lithium-rich manganese-based oxide represented by [Chemical Formula 1], the ratio of the number of moles of Li to the number of moles of all metal elements other than Li (Li / Me) 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.

[0057] On the other hand, the composition of the lithium-rich manganese-based oxide can be represented by the following [Chemical Formula 2].

[0058] [Chemical Formula 2]

[0059] XLi₂MnO₃·(1 - X)Li[Ni 1-y-z-w Mn y Co z M w O₂

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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, thereby enabling the effect of improving the life characteristics to be obtained.

[0066] The coating may include the coating element M 1 , the coating element M 1 can 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 1It may contain more than two kinds, such as Al and Co.

[0067] The coating element may exist in the coating in the form of an oxide, i.e., M 1 O z (1 ≤ z ≤ 4).

[0068] 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.

[0069] 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.

[0070] 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 agglomerated, and the average particle size D of the secondary particles 50 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, excellent electrode density can be achieved, and the deterioration of capacity and rate characteristics can be minimized.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] On the other hand, the transition metal precursor may 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.

[0075] The transition metal precursor can be prepared by a co-precipitation process. For example, the transition metal precursor can be prepared by dissolving raw materials each containing a transition metal in a solvent to prepare a metal solution, then mixing the metal solution, an ammonium cation complexing agent, and an alkaline compound, and performing a co-precipitation reaction. In addition, if necessary, an oxidizing agent or oxygen can also be added during the co-precipitation reaction.

[0076] At this time, the raw materials containing transition metals can be acetates, carbonates, nitrates, sulfates, halides, sulfides, etc. of the respective transition metals. 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, etc.

[0077] The ammonium cation complexing agent can be at least one selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3.

[0078] The alkaline compound can be at least one selected from NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor can vary depending on the type of alkaline compound used. For example, when using NaOH as the alkaline compound, a precursor in the form of a hydroxide can be obtained, and when using Na2CO3 as the alkaline compound, a precursor in the form of a carbonate can be obtained. In addition, when the alkaline compound is used together with an oxidizing agent, a precursor in the form of an oxide can be obtained.

[0079] On the other hand, the transition metal precursor and the lithium raw material can be mixed in the following amounts: such that the molar ratio of all 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.

[0080] On the other hand, the firing can be carried out at a temperature of 600 °C to 1000 °C or 700 °C to 950 °C, and the firing time can be 5 hours to 30 hours, or 5 hours to 20 hours. In addition, the firing atmosphere can be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100 volume% oxygen.

[0081] 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.

[0082] Examples of the conductive material include: spherical or flaky graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal 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. 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 can be 0.1 to 20% by weight, 1 to 20% by weight or 1 to 10% by weight.

[0083] In addition, the binder is a component that aids 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 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. Based on the total weight of the positive electrode active material layer, the content of the binder can be 1 to 20% by weight, 2 to 20% by weight or 2 to 10% by weight.

[0084] Negative electrode

[0085] 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 contain a negative electrode active material and optionally a binder and a conductive material.

[0086] 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. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel with its surface treated with carbon, nickel, titanium, silver, etc., aluminum cadmium alloy, etc. can be used. In addition, the negative electrode current collector usually has 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 can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams and non-woven fabric structures.

[0087] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium can be used. 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 alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; (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 either any one alone or a mixture of two or more thereof can be used.

[0088] In addition, a thin film of metallic lithium can be used as the negative electrode active material. Further, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon. Typical examples of high-crystalline carbon include irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microspheres, high-temperature sintered carbon such as mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0089] 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 chemical changes in the battery to be constructed. Specific examples thereof include: graphite such as natural graphite and artificial graphite; carbonaceous 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 oxides; or conductive polymers such as polyphenylene derivatives, and either any one alone or a mixture of two or more thereof 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.

[0090] 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 alone or a mixture of two or more thereof 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.

[0091] 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 onto the current collector.

[0092] Separator

[0093] The lithium secondary battery according to the present invention may further include a separator interposed 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 normal lithium secondary battery. In particular, a separator having a low resistance to ion migration of the electrolyte and excellent ability to impregnate the electrolyte is preferred. Specifically, the separator can be a porous polymer membrane, such as a porous polymer membrane 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. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used and can optionally be used as a single layer or a multi-layer structure.

[0094] Electrolyte

[0095] The electrolyte used herein can 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.

[0096] For example, the electrolyte may include an organic solvent and a lithium salt.

[0097] 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 and the like.

[0098] The lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in the lithium secondary battery. 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 in this text can 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.

[0099] In addition, in order to improve the life characteristics of the battery, suppress the decline of the battery capacity, improve the discharge capacity of the battery, etc., in addition to the above electrolyte components, the electrolyte can further contain additives. For example, the additive can be at least one selected from the following substances: vinylene carbonate, ethylene vinyl carbonate, fluoroethylene carbonate (FEC), ethylene sulfite (Esa), trimethylene sulfate (TMS), methyl trimethylene 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 can be 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0100] 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.

[0101] The jelly - roll 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 it in one direction.

[0102] The stacked type electrode assembly can be manufactured by cutting the positive electrode, the separator, and the negative electrode into desired shapes, and then sequentially stacking the cut positive electrode / separator / negative electrode.

[0103] The stacked and laminated type electrode assembly can be manufactured by the following method: stacking the positive electrode, the separator, and the 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.

[0104] The stacked and folded electrode assembly can be manufactured by the following method: stacking the positive electrode, the separator, and the negative electrode to manufacture a plurality of unit cells, arranging the plurality of unit cells on one surface or both surfaces of the long folded separator, and then winding the folded separator.

[0105] 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 its type.

[0106] (2) Activation step

[0107] Next, a step of charging and discharging the battery cell at least once to electrochemically activate the battery is performed. The activation step is a step of charging and discharging the battery cell to endow electrical performance and form a SEI (solid electrolyte interface) film on the electrode to stabilize the battery.

[0108] Specifically, as the charging voltage is higher, the charging time and the charging depth (capacity) are larger, and the reaction degree of Li2MnO3 during activation increases, thereby increasing the amount of activation gas (oxidizing gas). Therefore, in the present invention, the time point at the end of charging 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 gas.

[0109] On the other hand, the activation charging step may include a first charging step of charging at an SOC below 5.

[0110] Specifically, the first charging step can be carried out from SOC 0 to SOC 5 at a C rate of 0.1C to 0.3C.

[0111] When the charging rate in the first charging step satisfies the above range, a lower charging rate can be maintained at the initial stage of SEI film formation, 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 greater 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 easily decomposed during battery operation, resulting in rapid deterioration of the electrode, which may lead to a significant decrease in life characteristics.

[0112] On the other hand, the first charging step can be carried out in a constant current mode (CC mode).

[0113] Next, the activation charging step may further include a second charging step of terminating charging at an interval less than SOC 100.

[0114] Specifically, the second charging step may start from the time point when charging is terminated in the first charging step and charge at a C-rate of 0.3C to 1.0C until SOC 98.

[0115] By performing the second charging step at a C-rate of 0.3C to 1.0C, which is relatively faster than the first charging step, the manufacturing cost can be reduced by shortening the activation time, and the incomplete formation of the SEI film can be suppressed.

[0116] In particular, the second charging step terminates charging at SOC 80 to SOC 98, thereby controlling the activation degree of the Li2MnO3 (monoclinic) phase and effectively suppressing the generation of activation gases such as oxidizing gases.

[0117] At this time, the termination voltage of charging in the second charging step can be 4.45 V to 4.55 V, specifically 4.45 V to 4.5 V.

[0118] On the other hand, the second charging step can be performed in a constant current mode (CC mode) or a constant current-constant voltage mode (CCCV mode).

[0119] When the second charging step is performed in the constant current-constant voltage mode (CCCV mode), CC charging is performed while providing a C-rate of 0.3C to 1.0C until the termination voltage of charging is reached, and when the termination voltage of charging is reached, CV charging can be performed, where the charging C-rate is sequentially reduced to about 0.05C.

[0120] Next, the activation step discharges the battery cell charged by the first charging step and the second charging step. At this time, the discharging can be performed at a C-rate of 0.3C to 1.0C. 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.

[0121] On the other hand, the discharging can be performed in the constant current mode (CC mode).

[0122] On the other hand, the termination voltage of discharging can be 2.0 V to 3.0 V, specifically 2.0 V.

[0123] On the other hand, the activation step is preferably performed under temperature conditions of 25°C to 70°C, more preferably 40°C to 50°C. When the activation step is performed within the above temperature range, the effect of achieving high capacity can be obtained through the appropriate activation of Li2MnO3.

[0124] In addition, if necessary, the activation step can be carried out under pressurized conditions. Pressurization can be performed by mounting the battery cell onto a jig and then applying pressure to the battery cell via the jig. When the activation step is carried out under pressurized conditions, this has the advantage of being able to easily discharge the gas generated during the activation step.

[0125] On the other hand, although not necessary, if necessary, the activation step may further include an aging step. The aging step evenly impregnates the electrolyte 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.

[0126] 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 temperatures, the electrolyte impregnation property and lithium mobility are improved, enabling more smooth activation.

[0127] Hereinafter, the present invention will be described in more detail with reference to specific embodiments.

[0128] [Embodiment]

[0129] Example 1

[0130] (Manufacture of battery cell)

[0131] A 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 0.642 O2 was used as the positive electrode active material, and carbon nanotubes (CNT) were used as the conductive material. The positive electrode paste was coated on an aluminum current collector sheet, dried, and then calendered to manufacture a positive electrode.

[0132] A negative electrode active material: conductive material: binder were mixed at a weight ratio of 96:1:3 in water to prepare a negative electrode paste. At this time, graphite was used as the negative electrode active material, carbon black was used as the conductive material, and SBR and CMC were mixed at a weight ratio of 2:1 and used as the binder. The negative electrode paste was coated on a copper current collector sheet, dried, and then calendered to manufacture a negative electrode.

[0133] A separator was inserted between the positive electrode and the negative electrode manufactured as above to manufacture an electrode assembly, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected therein to manufacture a battery cell.

[0134] (Activation step)

[0135] After pre - aging the battery cells for 2 days, the following activation process is carried out to manufacture lithium secondary batteries:

[0136] Charge at a constant current mode at 45 °C until SOC 3 (0.2C) (the first charging step),

[0137] Charge in constant current - constant voltage mode (0.05C CV cut - off) until SOC 95 (0.3C) (the termination voltage of charging: 4.5 V) (the second charging step),

[0138] Then discharge at a constant current of 0.5C until 2.0 V.

[0139] Example 2

[0140] After pre - aging the battery cells manufactured in Example 1 for 2 days, the following activation steps are carried out to manufacture lithium secondary batteries:

[0141] Charge at a constant current mode at 45 °C until SOC 3 (0.2C) (the first charging step),

[0142] Charge in constant current - constant voltage mode (0.05C CV cut - off) until SOC 98 (0.3C) (the termination voltage of charging: 4.55 V) (the second charging step),

[0143] Then discharge at a constant current of 0.5C until 2.0 V.

[0144] Comparative Example 1

[0145] After pre - aging the battery cells manufactured in Example 1 for 2 days, the following activation steps are carried out to manufacture lithium secondary batteries:

[0146] Charge at a constant current mode at 45 °C until SOC 3 (0.2C) (the first charging step),

[0147] Charge in constant current - constant voltage mode (0.05C CV cut - off) until SOC 100 (0.3C) (the termination voltage of charging: 4.6 V) (the second charging step),

[0148] Then discharge at a constant current of 0.5C until 2.0 V.

[0149] [Experimental Example]

[0150] Experimental Example 1: Evaluation of gas generation amount

[0151] Measure the gas amounts generated during the activation steps of the lithium secondary batteries manufactured in Examples 1 and 2 and the secondary batteries manufactured in Comparative Example 1. The results are shown in Table 1 below and Figure 1 in.

[0152]

[0153] As shown in Table 1 and Figure 1 as shown therein, it can be seen that the total gas generation amount including oxygen is reduced in the case of the lithium secondary batteries of Examples 1 and 2 as compared with the lithium secondary battery of Comparative Example 1.

Claims

1. A method for manufacturing a lithium secondary battery, the method comprising the following steps: Preparing an electrode assembly including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode 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; And Charging and discharging the electrode assembly at least once to activate the battery, Wherein the activation step includes: A first charging step of charging at a constant current mode (CC mode) below SOC 5; A second charging step of terminating charging at SOC 80 to SOC 98 starting from the time point when charging is terminated in the first charging step; and A step of performing one discharge after the charging is completed.

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 second charging step is performed in a constant current mode (CC mode) or a constant current-constant voltage mode (CCCV mode).

5. The method for manufacturing a lithium secondary battery according to claim 1, wherein the second charging step is performed at a C rate of 0.3C to 1.0C.

6. The method for manufacturing a lithium secondary battery according to claim 1, wherein the termination voltage of charging in the second charging step is 4.45 V to 4.55 V.

7. The method for manufacturing a lithium secondary battery according to claim 1, wherein the first charging step includes charging from SOC 0 to SOC 5 at a C rate of 0.1C to 0.3C.

8. 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 1.0C until reaching 2.0 V.

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