Lithium secondary battery manufacturing method

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery, comprising the steps of: preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each containing a lithium-excess 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 it at least once, the activation step including a first charging step of charging in a constant current mode (CC mode) at an SOC of 5 or less, a second charging step of finishing charging at an SOC of 80 to 98 from the end of charging in the first charging step, and a step of discharging it once after charging is completed.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183692 dated December 23, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a lithium secondary battery, and more particularly to a method for manufacturing a lithium secondary battery containing a lithium-excess manganese-based oxide, which can suppress the generation of oxidizing gases caused during the activation step. [Background technology]

[0003] Lithium secondary batteries are energy storage media that have been used in a variety of 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 actively underway, and one of the methods that is attracting attention is the development of positive electrode active materials with a composition that allows for the use of a larger amount of lithium than currently available.

[0004] As a positive electrode active material that can use a larger amount of lithium, lithium-rich transition metal oxides have been developed, which have a layered structure and a lithium to transition metal molar ratio of more than 1. Lithium secondary batteries that use such lithium-rich transition metal oxides can achieve high capacity by performing an activation process at a high voltage of generally 4.4 V or higher.

[0005] However, in the initial activation step of this high-voltage activation process, lithium ions are released from the lithium-excess transition metal oxide, changing the cathode structure and causing the generation / release of oxygen radicals due to an oxygen redox reaction. Furthermore, side reactions between the oxygen radicals and the electrolyte and / or decomposition of the electrolyte under high voltage conditions can result in the generation of large amounts of oxidizing gases such as CO, CO2, and O2. The generation of large amounts of oxidizing gases can increase the internal pressure of the cell, leading to short circuits, making separation from the jig difficult, or inducing lithium plating due to the gas trap, resulting in limitations such as reduced stability and reduced charge / discharge capacity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2015-0015303 [Patent Document 2] Korean Patent Publication No. 10-2016-0035269 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to solve these problems and to provide a method for manufacturing a lithium secondary battery including a lithium-excess manganese-based oxide that can suppress the generation of oxidizing gas induced during the activation step. [Means for solving the problem]

[0008] In one aspect, the present invention provides a method for manufacturing a lithium secondary battery, comprising the steps of: preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each containing a lithium-overcharged 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 it at least once, wherein the activation step includes a first charging step of charging in constant current mode (CC mode) at an SOC of 5 or less, a second charging step of finishing charging at an SOC of 80 to 98 from the end of charging in the first charging step, and performing the discharging once after charging is completed.

[0009] Meanwhile, the charging step may be performed at a C-rate of 0.3C to 1.0C, and the end-of-charge voltage of the charging step may be 4.45V to 4.55V.

[0010] The activation step may include discharging at a C-rate of 0.3C to 1.0C until 2.0V is reached. [Effects of the Invention]

[0011] The method for manufacturing a lithium secondary battery according to the present invention can significantly reduce the rate of gas generation induced in the activation step by terminating the charge in a portion of the activation charge step, i.e., at SOC 80 to SOC 98. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the evaluation results of the amount of gas generated during the activation step in Experimental Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The terms and words used in this specification and claims should not be interpreted in a limited manner based on their ordinary or dictionary meanings, but should be interpreted in a meaning and concept 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.

[0014] In the present invention, "primary particles" refers to particle units that do not appear to have grain boundaries when observed under a scanning electron microscope at a magnification of 5,000 to 20,000 times. "Average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed under a scanning electron microscope image.

[0015] In the present invention, the "secondary particles" are particles formed by agglomeration of a plurality of primary particles.

[0016] In the present invention, "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 (e.g., positive electrode active material powder, negative electrode active material powder, etc.). 50 may be measured using a laser diffraction method. For example, a powder of particles to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), where ultrasonic waves of about 28 kHz are irradiated at an output of 60 W to obtain a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount is determined.

[0017] In addition, in the present invention, "SOC X" means a state in which the percentage of the capacity charged in a battery cell is X based on the discharge capacity that appears when the battery cell is discharged from 4.6V to 2.0V.

[0018] The present inventors have conducted extensive research into improving the voltage drop during the charging step for activation of lithium secondary batteries using lithium-excess manganese-based oxides, and as a result have found that the generation of oxidizing gas during the activation step can be suppressed by performing the activation step under specific charging conditions during the manufacture of lithium secondary batteries, thereby completing the present invention.

[0019] The method for producing a lithium secondary battery according to the present invention will be described below.

[0020] A method for producing a lithium secondary battery according to the present invention includes the steps of: preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each of which includes a lithium-excess manganese-based oxide in which the manganese content exceeds 50 mol % of all metals excluding lithium 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 it at least once; The method for manufacturing a lithium secondary battery is characterized in that the activation step includes a step of terminating charging at SOC 80 to SOC 98.

[0021] (1) Prepare the battery cells First, a battery cell including a positive electrode, a negative electrode, and an electrolyte is prepared.

[0022] 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, and the electrode assembly may include a separator between the positive electrode and the negative electrode.

[0023] Each component of the battery cell of the present invention will be described in more detail below.

[0024] positive electrode The positive electrode according to the present invention comprises, as a positive electrode active material, a lithium-excess manganese 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 comprises 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 comprises a lithium-excess manganese 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.

[0025] In the case of lithium-excess manganese oxides that contain excess lithium, they have a structure in which the layered phase (LiM'O2) and the rock salt phase (Li2MnO3) are mixed. During the initial activation process, the rock salt phase is activated and generates excess lithium ions, enabling high capacity to be achieved.

[0026] Preferably, the lithium-excess manganese oxide may be represented by Chemical Formula 1.

[0027] [Chemical formula 1] Li a Ni b Co c Mn d M e O2

[0028] In the above Chemical Formula 1, M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0029] On the other hand, a is the molar ratio of Li in the lithium-excess manganese oxide, and 1 <a、1.1≦a≦1.5、または1.1≦a≦1.3であってもよい。

[0030] The b is the molar ratio of Ni in the lithium-excess manganese oxide, and may be 0≦b≦0.5, 0.1≦b≦0.4, or 0.2≦b≦0.4.

[0031] The c is the molar ratio of Co in the lithium-excess manganese oxide and may be 0≦c≦0.1, 0≦c≦0.08, or 0≦c≦0.05. If c exceeds 0.1, it may be difficult to ensure high capacity, and gas generation and deterioration of the positive electrode active material may become severe, which may result in reduced life characteristics.

[0032] The d is the molar ratio of Mn in the lithium-excess manganese oxide, and may 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 ratio of the rock salt phase becomes too small, resulting in a small effect of compensating for irreversibility and improving capacity of the negative electrode.

[0033] The e is the molar ratio of the doping element M in the lithium-excess manganese oxide, and may 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 adversely affect the capacity of the active material.

[0034] Meanwhile, in the lithium-excess manganese oxide represented by [Chemical Formula 1], the molar ratio of Li to the total molar number of 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, excellent rate characteristics and capacity characteristics can be exhibited. If the Li / Me ratio is too high, electrical conductivity may decrease and the rock salt phase (Li2MnO3) may increase, which may accelerate the rate of degradation. If the Li / Me ratio is too low, the effect of improving energy density is small.

[0035] Meanwhile, the composition of the lithium-excess manganese oxide may be represented by the following [Chemical Formula 2].

[0036] [Chemical formula 2] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0037] In the above [Chemical Formula 2], M may be at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0038] The X represents the ratio of the Li2MnO3 phase in the lithium-excess 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 lithium-excess manganese-based oxide satisfies this range, high capacity characteristics can be achieved.

[0039] The y is the molar ratio of Mn in the LiM′O 2 layer, and may be 0.4≦y<1, 0.4≦y≦0.8, or 0.4≦y≦0.7.

[0040] The z is the molar ratio of Co in the LiM'O2 layer and may be 0≦z≦0.1, 0≦z≦0.08, or 0≦z≦0.05. If z exceeds 0.1, gas generation and deterioration of the positive electrode active material may become severe, possibly resulting in reduced life characteristics.

[0041] The w is the molar ratio of the doping element M in the LiM'O2 layer, and may be 0≦w≦0.2, 0≦w≦0.1, or 0≦w≦0.05.

[0042] Meanwhile, the positive electrode active material according to the present invention may further include a coating layer on the surface of the lithium-excess manganese-based oxide, if necessary. When the positive electrode active material includes the coating layer, the coating layer inhibits contact between the lithium-excess manganese-based oxide and the electrolyte, thereby reducing side reactions of the electrolyte and thereby improving the life characteristics.

[0043] The coating layer is made of a coating element M 1 The coating element M 1may be, for example, at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, preferably Al, Co, Nb, W and combinations thereof, more preferably Al, Co and combinations thereof. 1 may contain two or more kinds of elements, for example, Al and Co.

[0044] The coating elements are in the oxide form in the coating layer, i.e., M 1 Oz (1≦z≦4) are possible.

[0045] 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 large area.

[0046] The area on which the coating layer is formed may be 10 to 100%, preferably 30 to 100%, more preferably 50 to 100% of the total surface area of ​​the lithium-excess manganese oxide particles. When the area on which the coating layer is formed satisfies the above range, the effect of improving the life characteristics is excellent.

[0047] 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 50 The thickness 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 satisfies the above range, excellent electrode density can be achieved and the decrease in capacity and rate characteristics can be minimized.

[0048] The positive electrode active material has a BET specific surface area of ​​1 m 2 / g~10m 2 / g, 3m 2 / g~8m 2 / g or 4m 2 / g~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.

[0049] Meanwhile, the lithium-excess manganese-based oxide may be prepared by mixing a transition metal precursor and a lithium source material and then calcining the mixture.

[0050] 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)). One of these may be used alone, or two or more may be used in combination.

[0051] 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 large specific surface area can be produced.

[0052] The transition metal precursor may be prepared by a co-precipitation process. For example, the transition metal precursor may 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 to perform a co-precipitation reaction. If necessary, an oxidizing agent or oxygen gas may be further added during the co-precipitation reaction.

[0053] 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, etc.

[0054] The ammonium cation complexing agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0055] The basic compound may be at least one 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.

[0056] On the other hand, 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.

[0057] The firing may be performed at a temperature of 600°C to 1000°C or 700°C to 950°C for a time 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.

[0058] Meanwhile, the positive electrode active material layer may further include a conductive material and a binder in addition to the positive electrode active material.

[0059] Examples of the conductive material include spherical or flake-shaped 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 wt % to 20 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt %, based on the total weight of the positive electrode active material layer.

[0060] The binder is a component that improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Examples include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders. The binder may be included in an amount of 1 wt % to 20 wt %, 2 wt % to 20 wt %, or 2 wt % to 10 wt % based on the total weight of the positive electrode active material layer.

[0061] negative electrode 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.

[0062] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. 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 μm to 500 μm. As with the positive electrode current collector, the current collector may have a finely textured surface 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.

[0063] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, 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.

[0064] The negative electrode active material may be a thin film of metallic lithium. The carbon material may be either low-crystalline or high-crystalline carbon. Typical examples of low-crystalline carbon include soft carbon and hard carbon. Typical 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-calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0065] The conductive material is used to impart conductivity to the electrode and can be any material that exhibits electronic conductivity without causing chemical changes in the resulting battery. 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 powder or fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically present in an amount of 1 wt % to 30 wt %, preferably 1 wt % to 20 wt %, and more preferably 1 wt % to 10 wt %, based on the total weight of the negative electrode active material layer.

[0066] The binder serves to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples of binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders, which may be used alone or in combination. The binder may be included 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.

[0067] For example, the negative electrode active material layer may be manufactured 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.

[0068] separation membrane The lithium secondary battery according to the present invention may further include a separator interposed between the positive and negative electrodes. The separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used, with low resistance to ion migration and excellent electrolyte impregnation capability being 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, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may also be used, and may be selectively used in a single-layer or multi-layer structure.

[0069] electrolyte 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 is not particularly limited.

[0070] For example, the electrolyte can include an organic solvent and a lithium salt.

[0071] The organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, 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), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate solvents such as propylene 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.

[0072] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitation. Specifically, the anion of the lithium salt can be 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 at least one selected from the group consisting of LiPF6, LiN(FSO2), LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2), LiN(CF3SO2) 2. LiCl, LiI, LiB(C2O4)2, etc. can be used. The concentration of the lithium salt is preferably in the range of 0.1M to 5.0M.

[0073] In addition to the above components, the electrolyte may further include an additive for the purpose of improving the battery's life characteristics, suppressing a decrease in battery capacity, improving the battery's discharge capacity, etc. For example, the additive may include at least one selected from the group consisting of halogen-substituted or unsubstituted carbonate-based compounds, sulfate-based compounds, sultone-based compounds, borate-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds. Specifically, the additive may be at least one selected from, but not limited to, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate (FEC), ethylene sulfate (ESA), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), 1,3-propane sultone (1,3-PS), 1,3-propane sultone, 1,4-butane sultone, lithium oxalyl difluoroborate (LiODFB), lithium bis(oxalato)borate (LiBOB), fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, lithium difluorophosphate (LiPOF, LiDFP), and LiBF. The additive may be included in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 5 wt %, based on the total weight of the electrolyte.

[0074] Meanwhile, the electrode assembly may be an electrode assembly of various types well known in the art, for example, 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.

[0075] The jelly roll electrode assembly may be manufactured by interposing a sheet-shaped separator between a sheet-shaped positive electrode and a sheet-shaped negative electrode, and then winding the electrodes in one direction.

[0076] The stacked electrode assembly may be manufactured by cutting out a positive electrode, a separator, and a negative electrode into a desired shape, and then stacking the cut-out positive electrode / separator / negative electrode in order.

[0077] The stack-and-lamination type electrode assembly may be manufactured by stacking a positive electrode, a separator, and a negative electrode to manufacture 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.

[0078] The stack-and-folding 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.

[0079] Meanwhile, the type of battery case is not particularly limited, and various battery cases known in the art, such as a cylindrical battery case, a prismatic battery case, or a pouch-type battery case, may be used.

[0080] (2) Activation step Next, an activation step is performed in which the battery cell is charged and discharged at least once to electrically activate the battery. The activation step is a process in which the battery cell is charged and discharged to impart electrical characteristics and form a solid electrolyte interphase (SEI) film on the electrodes to stabilize the battery.

[0081] Specifically, the higher the charging voltage, the longer the charging time and depth of charge (capacity), and the greater the degree of reaction of Li2MnO3 during activation, resulting in an increased amount of activated gas (oxidizing gas). Therefore, in the present invention, the generation of gases such as oxidizing gas can be suppressed by adjusting the end point of charge in the activation charging step and adjusting the degree of activation of the Li2MnO3 (monoclinic) phase.

[0082] Meanwhile, the activation charging step may include a first charging step of charging at SOC 5 or less.

[0083] Specifically, the first charging step may be performed at a C rate of 0.1C to 0.3C at SOC 0 to SOC 5.

[0084] When the charging rate in the first charging satisfies the above range, the current rate at the beginning of SEI film formation can be maintained lower, and a harder and denser SEI film can be formed on the surface of the electrode, resulting in excellent life characteristics. If the current C rate in the first charging step is fast, such as 0.3 C or higher, the SEI film may be formed unstably on the surface of the electrode. If the SEI film is formed unstably on the surface of the electrode, the SEI film may be easily decomposed during battery operation, causing rapid deterioration of the electrode and resulting in a significant decrease in life characteristics.

[0085] Meanwhile, the first charging step may be performed in a constant current mode (CC mode).

[0086] Next, the activation charging step may further include a second charging step of terminating charging in a section below SOC 100.

[0087] Specifically, the second charging step may be performed from the end of the first charging step to an SOC of 98 at a C rate of 0.3C to 1.0C.

[0088] By performing the second charging step at a C rate of 0.3 C to 1.0 C, which is relatively faster than the first charging step, the activation time can be shortened, thereby reducing manufacturing costs, and the incomplete formation of the SEI film can be suppressed.

[0089] In particular, the second charging step can adjust the activation level of the Li2MnO3 (monoclinic) phase by terminating charging at SOC 80 to SOC 98, thereby effectively suppressing the generation of activation gases such as oxidizing gases.

[0090] At this time, the charge end voltage of the second charging step may be 4.45V to 4.55V, specifically, 4.45V to 4.5V.

[0091] Meanwhile, the second charging step may be performed in a constant current mode (CC mode) or a constant current-constant voltage mode (CCCV mode).

[0092] If the second charging step is performed in a constant current-constant voltage mode (CC-CV mode), CC charging may be performed by supplying a C rate of 0.3 C to 1.0 C until the end-of-charge voltage is reached, and then CV charging may be performed by gradually decreasing the charge C rate to about 0.05 C once the end-of-charge voltage is reached.

[0093] Next, the activation step involves discharging the battery cell charged through the first and second charging steps. At this time, the discharge may be performed at a C rate of 0.3 C to 1.0 C. When the discharge C rate satisfies this range, the activation time can be appropriately controlled, and a desired range of discharge capacity characteristics can be achieved.

[0094] Alternatively, the discharge may be performed in a constant current mode (CC mode).

[0095] On the other hand, the discharge cut-off voltage may be 2.0V to 3.0V, specifically 2.0V.

[0096] Meanwhile, the activation process is preferably carried out at a temperature of 25° C. to 70° C., preferably 40° C. to 50° C. When the activation process is carried out within this temperature range, a high capacity can be achieved by proper activation of Li2MnO3.

[0097] The activation process may be performed under pressurized conditions, if necessary. The pressurization may be performed by mounting the battery cell on a jig and applying pressure to the battery cell using the jig. Performing the activation process under pressurized conditions has the advantages of improving electrolyte impregnation and facilitating the release of gas generated during the activation process.

[0098] Meanwhile, if necessary, but not necessarily, the activation step may further include an aging step, which is intended to allow the electrolyte to uniformly impregnate the electrode assembly and stabilize the battery, and may be performed before charging, during charging, and / or after discharging, and may be performed one or more times.

[0099] The aging step may 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, electrolyte impregnation and lithium mobility are improved, and activation can be carried out more smoothly.

[0100] The present invention will be described in more detail below through specific examples.

[0101] [Example] Example 1 (battery cell manufacturing) 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 carbon nanotubes (CNTs) were used as the conductive material. The cathode slurry was applied to an aluminum current collector sheet, dried, and then rolled to produce a cathode.

[0102] 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 was used as the conductive material, and SBR and CMC were mixed in a weight ratio of 2:1 to prepare a binder. The anode slurry was applied to a copper current collector sheet, dried, and then rolled to prepare anodes.

[0103] A separator was interposed between the positive electrode and the negative electrode to prepare an electrode assembly. The electrode assembly was then inserted into a battery case, and an electrolyte was injected to prepare a battery cell.

[0104] (Activation step) The battery cell was pre-aged for 2 days, and then activated by charging it at 45°C in a constant current mode at 0.2C to an SOC of 3 (first charging step), charging it at a constant current-constant voltage mode at 0.3C (0.05C CV cut-off) to an SOC of 95 (end-of-charge voltage: 4.5V) (second charging step), and discharging it at a constant current of 0.5C to 2.0V to prepare a lithium secondary battery.

[0105] Example 2. The battery cell prepared in Example 1 was pre-aged for two days, and then activated by charging it at 45°C in a constant current mode at 0.2C to an SOC of 3 (first charging step), charging it at a constant current-constant voltage mode at 0.3C (0.05C CV cut-off) to an SOC of 98 (charge end voltage: 4.55V) (second charging step), and discharging it at a constant current of 0.5C to 2.0V to prepare a lithium secondary battery.

[0106] Comparative Example 1 The battery cell prepared in Example 1 was pre-aged for two days, and then activated by charging it at 45°C in a constant current mode at 0.2C to an SOC of 3% (first charging step), charging it at a constant current-constant voltage mode at 0.3C (0.05C CV cut-off) to an SOC of 100 (cut-off voltage of charge: 4.6V) (second charging step), and discharging it at a constant current of 0.5C to 2.0V to prepare a lithium secondary battery.

[0107] [Experimental Example] Experimental example 1. Evaluation of gas generation amount The amounts of gas generated during the activation step of the lithium secondary batteries prepared in Examples 1 and 2 and the secondary battery prepared in Comparative Example 1 were measured, and the results are shown in Table 1 below and FIG. 1.

[0108] [Table 1]

[0109] As shown in Table 1 and FIG. 1, in the lithium secondary batteries of Examples 1 and 2, the total amount of gas generated, including oxygen (O) gas, was reduced compared to the lithium secondary battery of Comparative Example 1.

Claims

1. Preparing a battery cell including a positive electrode, a negative electrode, and an electrolyte, each containing a lithium-excess manganese-based oxide in which the manganese content exceeds 50 mol % of all metals excluding lithium 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 it at least once; The activation step includes a first charging step of charging in a constant current mode at an SOC of 5 or less, a second charging step of terminating charging at an SOC of 80 to 98 from the end of charging in the first charging step, and a step of discharging once after charging is completed.

2. 2. The method for manufacturing a lithium secondary battery according to claim 1, wherein the lithium-excess 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 In the above 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 the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

3. 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, and 0≦e≦0.

1.

4. 4. The method for producing a lithium secondary battery according to claim 1, wherein the second charging step is performed in a constant current mode or a constant current-constant voltage mode.

5. 4. The method of claim 1, wherein the second charging step is performed at a C rate of 0.3 C to 1.0 C.

6. 4. The method for manufacturing a lithium secondary battery according to claim 1, wherein an end-of-charge voltage of the second charging step is 4.45V to 4.55V.

7. 4. The method of claim 1, wherein the first charging step includes charging at a C rate of 0.1 C to 0.3 C at an SOC of 0 to SOC of 5.

8. 4. The method for manufacturing a lithium secondary battery according to claim 1, wherein the activation step includes discharging at a C rate of 0.3 C to 1.0 C until the voltage reaches 2.0 V.

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