Method for activating lithium secondary battery

Abstract

The present invention relates to a method for activating a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, in which the lithium secondary battery comprises a positive electrode active material made of a lithium metal oxide containing manganese in an amount of 50 mol% or more but less than 100 mol% based on the total metal content excluding lithium, the method includes activating the lithium secondary battery by a CC-CV charging method in which constant current (CC) charging is performed until a specified state of charge (% SOC) is reached, and then constant voltage (CV) charging is performed, in which the CC-CV charging of the activation step ends at a point in time at which an activation charging depth defined by the following mathematical formula 1 becomes 5.17% to 15.00%, [Mathematical formula 1] Depth of charge for activation (%) = (charge capacity for CV charge interval / total charge capacity for activation step) * 100.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0151843 filed on November 6, 2023, Korean Patent Application No. 10-2023-0162051 filed on November 21, 2023, and Korean Patent Application No. 10-2024-0142767 filed on October 18, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This invention relates to a method for activating a lithium secondary battery, which allows the lithium secondary battery containing a manganese-rich cathode material to fully exhibit the high capacity characteristics of the cathode material, reduces gas generation and the amount of transition metals dissolved from the lithium secondary battery, and can stably drive the battery. Background Technology

[0004] Recently, with the rapid expansion of the application fields of lithium secondary batteries, not only powering electronic devices such as power, electronics, communications and computers, but also storing and powering large devices such as automobiles and energy storage systems, the demand for secondary batteries with high capacity, high output and high stability is increasing.

[0005] Lithium-ion rechargeable batteries typically consist of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as the lithium-ion transport medium, and a separator. Currently, lithium transition metal oxides, such as lithium cobalt oxide, lithium nickel oxide, and lithium nickel cobalt manganese composite oxides, are mainly used as positive electrode active materials.

[0006] However, in order to reduce the unit price of cathode active materials and increase the energy density and capacity of lithium secondary batteries, lithium-rich manganese-rich oxides have recently attracted much attention as a next-generation cathode active material. Lithium-rich manganese-rich oxides can achieve relatively low manufacturing costs by increasing the content of relatively inexpensive and abundant manganese (Mn) and reducing the content of cobalt (Co).

[0007] Furthermore, lithium-rich and manganese-rich oxides can contribute to the performance of positive electrode active materials and secondary batteries not only through oxidation / reduction reactions of metal cations but also through oxidation / reduction (redox) reactions of oxygen anions. Therefore, lithium-rich and manganese-rich oxides can possess high theoretical reversible capacity and energy densities exceeding 250 mAh / g.

[0008] However, it is well known that in order to exhibit the high capacity characteristics of lithium-rich and manganese-rich oxides, an initial activation process is required for lithium secondary batteries containing them at high voltage, utilizing a potential plateau range established by charging above 4.3 V. In particular, if the initial activation process at high voltage is not performed properly, abnormal driving phenomena may occur, such as the inability to properly utilize the high capacity characteristics and energy density unique to lithium-rich and manganese-rich oxides, or the capacity retention rate of the lithium secondary battery containing them exceeding 100% during driving.

[0009] Furthermore, during the initial activation process at high voltage, problems may arise such as oxygen desorption from the cathode crystal structure, excessive generation of activation gas, or large amounts of transition metals like manganese dissolving from the cathode. Therefore, if the activation conditions are not optimized, battery performance may degrade, for example, the resistance of lithium-ion batteries may increase.

[0010] Therefore, performing appropriate activation processes for lithium secondary batteries containing lithium-rich and manganese-rich oxides has become one of the main technical challenges. Summary of the Invention

[0011] Technical issues

[0012] One object of the present invention is to provide a method for activating a lithium secondary battery, the method enabling the lithium secondary battery containing a manganese-rich cathode material to fully exhibit the high capacity characteristics of the cathode material, reducing gas generation and the amount of transition metal dissolved from the lithium secondary battery, and enabling stable battery operation.

[0013] Technical solution

[0014] According to one embodiment of the present invention, a method for activating a lithium secondary battery is provided, the lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the lithium secondary battery comprises a positive electrode active material made of lithium metal oxide, the lithium metal oxide containing manganese in a total metal content excluding lithium of 50 mol% or more but less than 100 mol%. The method includes: The lithium secondary battery is activated by a CC-CV charging method, in which constant current (CC) charging is performed until a specified state of charge (%SOC) is reached, followed by constant voltage (CV) charging. The CC-CV charging of the activation step ends at the time point when the activation charge depth, as defined by the following mathematical formula 1, becomes 5.17% to 15.00%.

[0015] [Mathematical Expression 1]

[0016] Activation depth of charge (%) = (Charging capacity of the CV charging range / Total charging capacity of the activation steps) × 100

[0017] In one embodiment of the activation method, the lithium metal oxide includes lithium-rich and manganese-rich oxides, for example, compounds represented by the following chemical formula 1: [Chemical Formula 1] Li a [Mn 1-b-c Ni b M c ] 2-a O2 In chemical formula 1, M is selected from at least one of the following elements: Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. a, b, and c are the atomic fractions of each independent element, where 1 <a,0≤b≤0.5,0≤c≤0.5,0<b+c≤0.5。

[0018] Beneficial effects

[0019] According to one embodiment of the activation method, for example, when initially charging and activating a lithium secondary battery containing a manganese oxide-rich cathode active material, a CC-CV charging method is applied, wherein the constant voltage (CV) charging following constant current (CC) charging ends at a time point where the activation charge depth, defined by a predetermined formula, satisfies a specific ratio. In another configuration, the constant voltage (CV) charging time following constant current (CC) charging can be adjusted to a specific ratio in the activation method.

[0020] According to the activation method of one embodiment of this initial charging, it has been confirmed that manganese oxide-based positive electrode active materials, such as lithium manganese oxide containing a rock salt structure, can be effectively activated, thereby exhibiting the high capacity characteristics of positive electrode active materials.

[0021] It has also been confirmed that lithium secondary batteries activated by one implementation scheme can be driven stably without abnormal drive cycles, thus exhibiting excellent cycle characteristics, such as capacity retention of over 100% during charge / discharge drive.

[0022] Furthermore, it has been confirmed that adjusting the constant voltage charging time to a specific ratio can reduce the amount of gas generated and transition metal leaching during the activation process. Attached Figure Description

[0023] Figure 1 This is a graph showing the comparison and evaluation results of the driving characteristics and capacity retention of lithium secondary batteries manufactured through the activation process of the examples and comparative examples for each cycle. Detailed Implementation

[0024] The method for activating a lithium secondary battery according to an embodiment of the present invention will be described in more detail below.

[0025] Manganese-rich oxide cathode active materials, which contain more than 50 mol% of manganese among all metals excluding lithium, such as lithium-rich manganese oxide cathode active materials, not only have higher energy density than currently commercialized lithium nickel cobalt manganese (NCM) cathode active materials, but also have the advantage of reducing the amount of expensive cobalt used, thereby saving unit manufacturing costs.

[0026] Incidentally, this lithium-rich and manganese-rich oxide-based positive electrode active material has the following structure: lithium manganese oxide (Li2MnO3) with a rock salt structure and lithium transition metal oxide (e.g., Li[Ni)) with a layered structure. 1-y-z- w Mn y Co z M w Compounds that are mixed with O2 and have a rock salt structure can be activated through an activation process before being driven by lithium secondary batteries, thus exhibiting higher capacity characteristics.

[0027] As a result, for lithium-ion secondary batteries containing lithium-rich and manganese-rich oxide-based cathode active materials, optimizing the activation process conditions and exhibiting higher capacity characteristics is crucial. If the activation process is not performed properly, and the rock-salt structured compounds are not properly activated, the rock-salt structured compounds may be abnormally activated during the charge / discharge process used to drive the lithium-ion secondary battery. This leads to abnormal driving phenomena, such as capacity retention exceeding 100% during the initial cycle drive.

[0028] One implementation of the activation method is designed to address this problem, wherein when a lithium secondary battery is initially charged by a CC-CV charging method and then activated, the main configuration is that the constant voltage (CV) charging following constant current (CC) charging ends at a time point where the activation charge depth (i.e., the ratio of the charging capacity of the constant voltage (CV) charging interval to the total charging capacity of the activation steps) is approximately 5.17% to 15.00%, or approximately 6.00% to 14.00%, or approximately 7.00% to 13.00%, as defined by the following mathematical formula 1.

[0029] [Mathematical Expression 1]

[0030] Activation depth of charge (%) = (Charging capacity of the CV charging range / Total charging capacity of the activation steps) × 100

[0031] As supported by examples and the like provided below, it has been confirmed that the progress ratio in the constant voltage (CV) charging range can be optimized to effectively activate a manganese-rich oxide-based positive electrode active material, such as a compound with a rock salt structure, thereby exhibiting higher capacity characteristics, and at the same time, abnormal driving phenomena, such as the capacity retention rate exceeding 100% during the driving of a lithium secondary battery containing the same, can be suppressed.

[0032] This is expected because, for example, as the progress ratio in the constant voltage (CV) charging range carried out at a high voltage of 4.4 V to 4.7 V or 4.5 V to 4.65 V is optimized, the compound with a rock salt structure is effectively activated in the corresponding high-voltage charging process. As a result, abnormal driving cycles due to abnormal activation do not occur during the driving of the lithium secondary battery.

[0033] Next, the activation method of one embodiment will be described in more detail.

[0034] The lithium secondary battery for carrying out the activation method of one embodiment includes a manganese-rich oxide-based positive electrode active material made of a lithium metal oxide, and the lithium metal oxide contains 50 mol% or more but less than 100 mol% of manganese based on the total metal content excluding lithium. Such a manganese-rich oxide-based positive electrode active material may be a lithium-rich and manganese-rich metal oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Li a [Mn 1-b-c Ni b M c 2-a O2 Wherein in Chemical Formula 1, M is at least one selected from the following elements: Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and a, b, and c are atomic fractions of each independent element, where 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and 0 < b + c ≤ 0.5.

[0035] Specifically, a is the molar ratio of Li in the lithium-rich and manganese-rich oxide, which may be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.2 ≤ a ≤ 1.4. When a satisfies the above range, high capacity can be achieved.

[0036] b is the molar ratio of Ni in the lithium-rich and manganese-rich oxide, which may be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0037] ​c is the molar ratio of the additional element M in the lithium-rich manganese-rich oxide, which can be 0≤c≤0.5, 0≤c≤0.3, or 0≤c≤0.1. M can be, for example, Co. If the content of the additional element is too high, it may not only adversely affect the capacity characteristics, but may also exacerbate gas generation and deterioration of the positive electrode active material due to the increased redox reaction of oxygen, which may lead to a decrease in lifetime characteristics.

[0038] 1-bc is the molar ratio of Mn in lithium-rich and manganese-rich oxides, which can be 0.50≤1-bc<1.0, 0.50≤1-bc≤0.80, or 0.50≤1-bc≤0.70. When 1-bc is less than 0.5, that is, when b+c exceeds 0.5, the proportion of rock salt structure decreases, so the irreversible compensation and capacity improvement effect of the negative electrode may be small.

[0039] On the other hand, lithium-rich manganese-rich oxides containing excessive lithium and more than 50 mol% manganese in the lithium-excluding metals can have a structure in which layered compounds (LiM'O2) are mixed with rock-salt compounds (Li2MnO3). Among these, the rock-salt compounds are activated, for example, at high voltages above 4.4 V to generate excess ions. Therefore, when lithium-rich manganese-rich oxides are used as positive electrode active materials, the excess lithium ions generated by the activation of the rock-salt phase in the high-voltage activation process are inserted into the negative electrode, thereby achieving a pre-lithiation effect, where the irreversible capacity of the negative electrode is compensated. However, depending on the activation conditions, some rock-salt phases can remain in an inactive state. If this inactive residual rock-salt phase is small, it can be further activated during the operation of the lithium secondary battery and helps improve the capacity retention of the lithium secondary battery.

[0040] However, if activation is not performed properly and a large amount of unactivated residual rock salt phase is present, abnormal cycling with a capacity retention exceeding 100% during lithium-ion battery operation may occur, potentially leading to abnormal operation of the lithium-ion battery. As described above, the activation method according to one embodiment can suppress problems such as abnormal operation because the rock salt phase is sufficiently activated.

[0041] In a more specific example, lithium metal oxides, such as lithium-rich and manganese-rich oxides, can include a mixture of Li₂MnO₃ with a rock-salt structure and Li[Ni] with a layered structure. 1-y-z-w Mn y Co z M w O2, and can be represented by the following chemical formula 2: [Chemical Formula 2] X Li2MnO3·(1-X) Li[Ni1-y-z-w Mn y Co z M w O2

[0042] In chemical formula 2, M is selected from at least one of the following elements: Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. Where 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, and 0≤w≤0.2.

[0043] In this chemical formula 2, X refers to the ratio of the Li2MnO3 phase (rock salt phase) in the lithium-rich and manganese-rich oxide, where 0.2≤X≤0.5, 0.25≤X≤0.5, or 0.25≤X≤0.4. When the ratio of the Li2MnO3 phase meets the above range, high capacity characteristics can be achieved.

[0044] y can be LiM'O2 (M'=[Ni 1-y-z Mn y M z The molar ratio of Mn in the layered structure, wherein 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0045] z can be LiM'O2 (M' = [Ni 1-y-z Mn y M z The molar ratio of additional element M in the layered structure, where 0≤z≤0.5, 0≤z≤0.3, or 0≤z≤0.1.

[0046] On the other hand, the aforementioned lithium-rich and manganese-rich oxide-based positive electrode active material can be in the form of secondary particles in which multiple primary particles are aggregated, wherein the average particle size D of the secondary particles is... 50 The diameter can be from 2 μm to 10 μm, preferably from 2 μm to 8 μm, and more preferably from 4 μm to 8 μm. When the D of the positive electrode active material... 50 When the above range is met, excellent electrode density can be achieved, and the reduction in capacity and rate performance can be minimized.

[0047] Furthermore, the BET specific surface area of ​​the aforementioned positive electrode active material can be 0.1 m². 2 / g to 10 m 2 / g, specifically 0.1m 2 / g to 5 m 2 / g, more specifically 0.1 m 2 / g to 1 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, it will absorb moisture quickly and accelerate the side reactions with the electrolyte, making it difficult to ensure lifetime characteristics.

[0048] Lithium-rich and manganese-rich oxides can be prepared by mixing transition metal precursors and lithium raw materials and then calcining them. The types of precursors and raw materials and the preparation conditions can be based on the preparation conditions of typical manganese-rich oxide cathode active materials, so further descriptions will be omitted.

[0049] On the other hand, lithium secondary batteries can have a typical lithium secondary battery structure, the difference being the use of lithium-rich and manganese-rich oxides as the positive electrode active material, and can be prepared by methods well known to those skilled in the art. For example, a lithium secondary battery can be manufactured by inserting a separator (or electrolyte membrane) between a positive electrode containing positive electrode active material and a negative electrode containing negative electrode active material, stacking them sequentially and drying them to prepare an electrode assembly, inserting the electrode assembly into a casing, selectively injecting electrolyte, and sealing the casing. Lithium secondary batteries can be cylindrical, prismatic, coin-shaped, or pouch-shaped batteries.

[0050] The positive and negative electrodes can be manufactured by coating an active material layer containing electrode active materials onto a current collector and then drying the coating.

[0051] Depending on the need, in addition to the positive electrode active material, the composition for forming the positive electrode active material layer may optionally further include a binder, a conductive material, a filler, etc. Depending on the need, in addition to lithium-rich and manganese-rich oxide-based positive electrode active materials, the composition for forming the positive electrode active material layer may optionally further include a binder, a conductive material, a filler, etc. Depending on the need, in addition to the negative electrode active material, the composition for forming the negative electrode active material layer may optionally further include a binder, a conductive agent, a filler, etc.

[0052] There are no particular restrictions on the current collector, as long as it has high conductivity and will not cause chemical changes in the battery. Materials used include, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Furthermore, the thickness of the current collector can typically range from 3 μm to 500 μm. Additionally, the current collector can have micro-textures formed on its surface to enhance the adhesion of the active material. For example, current collectors can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0053] In addition to the above-mentioned lithium-rich and manganese-rich oxides, the positive electrode active material may further include typical positive electrode active materials. For example, it may further include any one or more positive electrode active materials selected from the following substances: LCO (LiCoO2), LNO (LiNiO2), LFP (LiFePO4), and NCM (Li[Ni p Co q Mn r1 O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1). Preferably, based on the weight of all the positive electrode active materials, it may include at least 70 wt% or more of the lithium-rich and manganese-rich oxides, or may consist only of the lithium-rich and manganese-rich oxides.

[0054] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material may be 80 wt% to 99 wt%.

[0055] In a specific embodiment, the negative electrode may include at least one of the following substances as the negative electrode active material: carbon-based materials; silicone-based materials; metals or alloys of lithium and metals; metal composite oxides; materials that can be doped and undoped with lithium; lithium metal; and transition metal oxides. Preferably, it may include carbon-based materials, silicon-based materials, or mixtures thereof.

[0056] As the carbon-based materials, any carbon-based negative electrode active material commonly used in lithium secondary batteries can be used without particular limitation. As typical examples thereof, crystalline carbon, amorphous carbon, or both of them can be used. Examples of crystalline carbon may include graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0057] The silicon-based materials are at least one selected from the following substances: Si, SiO x (0 < x < 2), and Si-Y alloys (where Y is an element selected from the following substances: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Si), and preferably SiO. The capacity of the silicon-based negative electrode active material is nearly 10 times higher than that of graphite, so it is possible to reduce the mass loading (mg·cm -2 ) to improve the fast charging performance of the battery.

[0058] As the metal or alloy of lithium and metal, metals selected from the following substances can be used: Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or alloys of lithium and the metals.

[0059] As a metal composite oxide, at least one of the following substances can be used: PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1) and Sn x Me 1-x Me' y O z (Where Me represents Mn, Fe, Pb, and Ge; Me' represents Al, B, P, Si, elements of groups I, II, and III of the periodic table, and halogens; 0) <x≤1;1≤y≤3;1≤z≤8)。

[0060] Materials that can be doped and dedoped with lithium may include Sn, SnO2, Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements and combinations thereof, but not Sn), and at least one of these can be used in combination with SiO2.

[0061] In Si-Y and Sn-Y, element Y can be selected from the following substances: Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db(𬭊), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0062] Examples of transition metal oxides may include lithium-containing titanium oxide (LTO), vanadium oxides, lithium vanadium oxides, etc.

[0063] Based on the total weight of solids in the negative electrode slurry, the content of the negative electrode active material can be from 80% to 99% by weight.

[0064] Adhesives are components that facilitate bonding between conductive materials, active materials, and current collectors, and are added in amounts ranging from 0.1% to 10% by weight based on the total weight of the active material layer. Examples of adhesives may include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0065] Conductive materials are components used to further improve the conductivity of active materials, and the amount added can be less than 10% by weight, specifically less than 5% by weight, based on the total weight of the active material layer. There are no particular restrictions on such conductive materials, as long as they are conductive and do not cause chemical changes in the battery. For example, the following can be used: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; conductive materials, such as polyphenylene derivatives, etc.

[0066] On the other hand, lithium secondary batteries can be provided without a separate separator by forming an electrolyte layer (or a layer containing electrolyte) between the positive and negative electrodes, but can also include a separator inserted between the positive and negative electrodes. Such a separator is designed to separate the negative and positive electrodes and provide a path for lithium ions to move, and any separator can be used without particular limitation, as long as it is a separator commonly used in lithium secondary batteries. In particular, a separator with high electrolyte retention capacity and low resistance to ion movement in the electrolyte is preferred. Specifically, as a separator, porous polymer membranes can be used, such as porous polymer membranes prepared using polyolefin 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. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. In addition, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0067] In addition, electrolytes can include, but are not limited to, all of which can be used to manufacture lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0068] In one specific implementation, the electrolyte may comprise an organic solvent and a lithium salt.

[0069] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the battery electrochemical reaction can move. Specifically, organic solvents that can be used include: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; sulfolane, etc. Among these solvents, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity that can increase the charging / discharging performance of the battery is preferred.

[0070] Lithium salts can be used without particular restrictions, as long as they can provide lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the following anions: 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 -As lithium salts, the following can be used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Lithium salts can be used in concentrations ranging from 0.1 M to 2.0 M. When the concentration of the included lithium salt is within this range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent electrolyte performance, and lithium ions can move efficiently.

[0071] On the other hand, in one embodiment of the activation method described herein, the lithium secondary battery is initially charged for activation, and the initial charge is performed using a CC-CV charging method.

[0072] In this type of CC-CV charging method, the lithium secondary battery is charged with a constant current (CC) while maintaining a constant charging current until a predetermined state of charge (%SOC) is reached, and then charged with a constant voltage (CV) from the predetermined state of charge while maintaining a constant charging voltage.

[0073] First, constant current charging is performed, for example, until the state of charge is 50% to 95%. This constant current charging is used to reach a voltage suitable for activating the rock salt phase contained in lithium-rich manganese oxide-based cathode active materials, such as a charging voltage of 4.3 V or higher, or 4.4 V to 4.7 V, or 4.5 V to 4.65 V.

[0074] Subsequently, constant voltage charging is performed while maintaining this constant charging voltage, for example, above 4.3 V or between 4.4 V and 4.7 V. During this process, the rock salt phase can be activated to achieve high capacity characteristics. Specifically, this constant voltage charging can end at a time point where the activated charge depth, as defined by Formula 1, becomes approximately 5.17% to 15.00%, or approximately 6.00% to 14.00%, or approximately 7.00% to 13.00%. In a specific example, constant voltage charging can begin, for example, at a state of charge (SOC) of 50% to 95%, continue until a constant state of charge is reached, and end at a time point where the activated charge depth reaches a constant value.

[0075] In this context, the activation charge depth can be defined as the ratio of the charging capacity in the constant voltage charging region to the total charging capacity of the activation steps in the constant current charging region and the constant voltage charging region. This activation charge depth can refer to the ratio of an appropriate constant voltage charging region in the initial charging steps used for activation. When the activation charge depth meets a specific ratio, the progress ratio of the constant voltage charging region is optimized, allowing for optimized activation of the rock salt phase contained in lithium-rich manganese oxide-based cathode active materials. As a result, while exhibiting the high capacity characteristics of lithium secondary batteries, abnormal operation during battery operation can be suppressed.

[0076] On the other hand, in another embodiment of the invention, constant voltage charging can be performed such that the CV charging ratio, as defined by the following mathematical formula 2, is 27% to 40%, or 27% to 38%, or 27% to 35%, and preferably ends at the point where the CV charging ratio is satisfied: [Mathematical Expression 2] CV charge ratio (%) = (Charging time in the CV charging interval / Total charging time in the activation step) × 100 Furthermore, taking into account the appropriate time ratio of the constant voltage charging interval as defined by Equation 2, the constant current charging before constant voltage charging can be carried out at a time ratio of 60% to 73%, or 62% to 73%, or 65% to 73% based on the total charging time of the activation step (i.e., the total progress time of constant current charging and constant voltage charging).

[0077] For reference, due to the characteristics of lithium-rich and manganese-rich oxide positive electrode active materials, if the activation and charging process at high voltage becomes too long, excessive activation gas may be generated. At the same time, oxygen may desorb within the positive electrode crystal structure, or a large amount of transition metals such as manganese may dissolve within the positive electrode.

[0078] However, as can be seen from the examples provided below, it has been confirmed that by optimizing the time ratio of the constant voltage (CV) charging interval and the time ratio of the remaining constant current (CC) charging interval as defined by Formula 2, manganese oxide-rich cathode active materials, such as rock salt compounds, can be effectively activated, thereby exhibiting higher capacity characteristics while reducing gas generation and transition metal (such as manganese) dissolution during the activation process. It has also been confirmed that lithium-ion batteries undergoing this activation process exhibit excellent discharge capacity and voltage, as well as low resistance.

[0079] Conversely, if the constant voltage (CV) charging time ratio is very small, the amount of gas generated and transition metal dissolved during the activation process can increase significantly, which may lead to a significant increase in the resistance of the lithium secondary battery. In contrast, if the constant voltage (CV) charging time ratio is very large, the capacity characteristics of the lithium secondary battery may be insufficient due to overvoltage.

[0080] On the other hand, after initial charging using the CC-CV charging method, an initial discharge step can be performed on the lithium secondary battery. This initial discharge step can proceed from the maximum charging voltage at the point where constant voltage charging has been completed, such as a maximum charging voltage of 4.3 V or higher, or 4.4 V to 4.7 V, or 4.5 V to 4.65 V, down to a minimum charging voltage of 2.0 V to 3.5 V.

[0081] Furthermore, the activation steps, including the initial charging and initial discharging as described above, can be performed at temperatures ranging from 20°C to 55°C or from 25°C to 50°C.

[0082] Furthermore, in the activation step, the initial charging step can be performed at a charging rate of 0.2 C to 1.2 C, and the initial discharging step can be performed at a discharging rate of 0.4 C to 1.2 C or 0.5 C to 1.1 C. In a more specific example, the constant current charging of the initial charging step can be performed, for example, at a charging rate of 0.2 C to 1.2 C or 0.3 C to 1.1 C. Furthermore, the subsequent constant voltage charging can be performed, for example, at a charging rate of 0.2 C or higher, or 0.3 C to 0.8 C, or 0.3 C to 0.6 C. Additionally, constant voltage charging can be performed until the current value reaches 0.01 C to 0.15 C.

[0083] Therefore, lithium secondary batteries containing lithium-rich and manganese-rich oxide-based positive electrode active materials can be effectively activated, and the amount of gas generated and transition metal dissolved during the activation process can also be effectively reduced.

[0084] On the other hand, depending on the requirements, the activation method of one embodiment described herein may also include an aging step of the lithium secondary battery after or between the initial charge / discharge steps.

[0085] Furthermore, according to a specific embodiment of the present invention, the activation method of one embodiment described herein may optionally include a step of performing a second constant current charge on the lithium secondary battery after the initial charge / discharge step; and / or a step of aging the lithium secondary battery at a temperature above 40°C.

[0086] More specifically, the activation method may also include, for example, a step of performing a secondary constant current charge, such as until a state of charge of 70% or 60% is reached, and the secondary constant current charge step may be performed, for example, at a charge rate of 0.3 C or higher or 0.3 C to 1.0 C.

[0087] Furthermore, after the secondary constant current charging step, for example, the lithium secondary battery can be aged at a temperature above 40°C or between 40°C and 70°C for 10 to 30 hours or 12 to 20 hours. This further enhances the effectiveness of the activation method.

[0088] The activation method according to one embodiment described herein can effectively activate lithium secondary batteries containing lithium-rich and manganese-rich oxide-type positive electrode active materials, realize the capacity characteristics of the positive electrode active materials, reduce the amount of gas generated and transition metal dissolution in the activation process, and suppress abnormal driving cycles of lithium secondary batteries, thereby enabling stable driving.

[0089] In the following description, preferred embodiments are provided to aid in understanding the invention. However, the following embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the invention, and such changes and modifications also fall within the scope of the appended claims.

[0090] [Preparation Example]: Manufacturing of Lithium-ion Secondary Batteries

[0091] The composition of the positive electrode active material is Li 1.16 Ni 0.305 Co 0.004 Mn 0.531 Lithium- and manganese-rich oxides of O2, carbon black as a conductive material, and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96.6:2.1:1.3 to prepare a positive electrode slurry (solid content: 75.5% by weight). The positive electrode slurry was coated onto a positive current collector (Al film) with a thickness of 12 μm, dried, and rolled to manufacture the positive electrode.

[0092] Graphite as the negative electrode active material, SBR-CMC as the binder, and carbon black as the conductive material were added to water as the solvent in a weight ratio of 95.7:2.3:2.0 to prepare a negative electrode slurry (solid content: 60 wt%). The negative electrode slurry was coated onto an 8 μm thick copper (Cu) film serving as the negative electrode current collector, dried, and then rolled to manufacture the negative electrode.

[0093] The electrolyte was prepared by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 20:70:10 and then dissolving LiPF6 to a concentration of 1.2 M.

[0094] An electrode assembly is prepared by sequentially stacking a positive electrode, a polyolefin porous membrane coated with inorganic particles (Al2O3), and a negative electrode. The assembled electrode assembly is then placed in a pouch cell and injected with the prepared non-aqueous electrolyte to manufacture a lithium secondary battery.

[0095] Example 1.

[0096] The lithium-ion secondary battery manufactured in the preparation example was connected to a PNE charger and charged at 45°C at a rate of 1.0 C to 60% state of charge (SOC), followed by an initial charge at a rate of 0.4 C for activation. In this initial charge, the lithium-ion secondary battery was first charged with a constant current while maintaining a charging current of 0.4 C until a state of charge (SOC) of 91.53% and a charging voltage of 4.6 V were reached. This constant current charge was performed at a time ratio of 70.8% of the total charging time based on the activation step.

[0097] After reaching a charging voltage of 4.6 V, constant voltage charging is performed while maintaining this voltage. This constant voltage charging is carried out at a time ratio of 29.2% based on the total charging time of the activation step, which includes constant current charging and constant voltage charging, and at a temperature of 45°C until the current value reaches 0.05 C from 0.4 C, then ends after the stated time ratio. It was also confirmed that the charging capacity in the constant voltage charging range, based on the total charging capacity of constant current charging and constant voltage charging (100%), ends at a time point where the activation depth of charge according to Formula 1 is approximately 8.47%. The state of charge at the end of the time point is 100%.

[0098] Then, the lithium secondary battery is activated by constant current discharge at 45°C and a discharge rate of 0.4 C to 2.0 V.

[0099] Example 2.

[0100] The lithium-ion secondary battery manufactured in the preparation example was connected to a PNE charger and charged at 45°C at a rate of 1.0 C to 60% state of charge (SOC), followed by an initial charge at a rate of 0.4 C for activation. In this initial charge, the lithium-ion secondary battery was first charged with a constant current while maintaining a charging current of 0.4 C until a state of charge (SOC) of 91.53% and a charging voltage of 4.6 V were reached. This constant current charge was performed at a time ratio of 64.7% of the total charging time based on the activation step.

[0101] After reaching a charging voltage of 4.6 V, constant voltage charging is performed while maintaining this charging voltage. This constant voltage charging is carried out at a time ratio of 35.3% based on the total charging time including constant current charging and constant voltage charging activation steps, and at a temperature of 45°C until the current value reaches 0.05 C from 0.4 C, then ends after the stated time ratio. It was also confirmed that the charging capacity in the constant voltage charging range ended at a time point where the total charging capacity of constant current charging and constant voltage charging, based on 103.5%, was approximately 12.00% (in this case, the total charging capacity is calculated and shown as a ratio based on the total charging capacity of Example 1), and the activation charge depth according to Formula 1 was approximately 11.59% (=12.00 / 103.5×100). The state of charge at the end time point was 103.5%.

[0102] Then, the lithium secondary battery is activated by constant current discharge at 45°C and a discharge rate of 0.4 C to 2.0 V.

[0103] Comparative Example 1.

[0104] The lithium-ion secondary battery manufactured in the preparation example was connected to a PNE charger and charged at 45°C at a rate of 1.0 C to 60% state of charge (SOC), followed by an initial charge at a rate of 0.4 C for activation. In this initial charge, the lithium-ion secondary battery was first charged with a constant current while maintaining a charging current of 0.4 C until a state of charge (SOC) of 91.53% and a charging voltage of 4.6 V were reached. This constant current charge was performed at a time ratio of 73.7% of the total charging time based on the activation step.

[0105] After reaching a charging voltage of 4.6 V, constant voltage charging was performed while maintaining this voltage. This constant voltage charging was carried out at a time ratio of 26.3% based on the total charging time including the activation steps of constant current charging and constant voltage charging, and at a temperature of 45°C until the current value reached 0.05 C from 0.4 C, then ended after the stated time ratio. It was also confirmed that the charging capacity in the constant voltage charging interval ended at a time point where approximately 4.16% of the total charging capacity based on the combined constant current and constant voltage charging was reached (in this case, the total charging capacity was calculated and displayed as a ratio based on the total charging capacity of Example 1), and the activation depth of charge according to Formula 1 was approximately 4.35% (=4.16 / 95.69×100). The state of charge at the end time point was 95.69%.

[0106] Then, the lithium secondary battery is activated by constant current discharge at 45°C and a discharge rate of 0.4 C to 2.0 V.

[0107] Experimental Example 1: Evaluation of Drive Characteristics and Capacity Retention in Each Cycle

[0108] The lithium secondary batteries manufactured through the activation process in the examples and comparative examples were charged to 4.35 V at 45°C and discharged to 2.0 V under 1 / 3C CC-CV (CV 5%) conditions to perform charge and discharge tests. During these charge and discharge tests, the drive characteristics and capacity retention of each cycle were evaluated, and the evaluation results were compared and presented. Figure 1 middle.

[0109] refer to Figure 1 In Comparative Example 1, an abnormal operating phenomenon was confirmed, in which the capacity retention rate exceeded 100% during the initial cycle drive. This was expected because the rock salt phase in the positive electrode active material was not properly activated during the activation process and abnormal activation occurred during the cycle drive process.

[0110] In contrast, it was confirmed that Examples 1 and 2 exhibited high capacity retention rates of over 90% at up to 100 cycles, but were driven stably without causing abnormal driving phenomena.

[0111] Experimental Example 2: Evaluation of Gas Generation and Transition Metal Dissolution

[0112] For lithium secondary batteries manufactured through the activation process in the Examples and Comparative Examples, the gases generated during the activation process were collected, and the amount of generated gases was quantitatively analyzed using GC-FID / TCD. The analytical results of the amount of generated activation gases were converted to a ratio based on (100%) Example 1 and are shown in Table 1 below.

[0113] In addition, the amount of transition metals (nickel and manganese) dissolved during the activation process was analyzed by ICP and is shown in Table 1 below.

[0114] [Table 1]

[0115] Referring to Table 1, it was confirmed that Examples 1 and 2 were manufactured using an activation process optimized by the progress ratio of the constant voltage interval (time ratio of the CV charging interval) defined by Formula 2, thus showing lower gas generation and transition metal dissolution than Comparative Example 1.

Claims

1. A method of activating a lithium secondary battery, the lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the lithium secondary battery comprises a positive electrode active material made of a lithium metal oxide containing manganese in an amount of 50 mol% or more but less than 100 mol% based on the total metal content excluding lithium, the method comprising the steps of: activating the lithium secondary battery by a CC-CV charging method in which constant current (CC) charging is performed until a specified state of charge (%SOC) is reached, and then constant voltage (CV) charging is performed, wherein the CC-CV charging of the activation step ends at a point in time at which the activation depth of charge defined by the following mathematical formula 1 becomes 5.17% to 15.00%: [mathematical formula 1] Activation depth of charge (%) = (charge capacity of CV charging interval / total charge capacity of activation step) x 100.

2. The method of activating a lithium secondary battery according to claim 1, wherein the lithium metal oxide comprises a compound represented by the following chemical formula 1: [chemical formula 1] Li a [Mn 1-b-c Ni b M c ] 2-a O2 wherein in chemical formula 1, M is at least one selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and a, b, and c are atomic fractions of each individual element, wherein 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and 0 < b + c ≤ 0.

5.

3. The method of activating a lithium secondary battery according to claim 1, wherein the lithium metal oxide comprises a compound represented by the following chemical formula 2: [chemical formula 2] X Li2MnO3·(1-X) Li[Ni 1-y-z-w Mn y Co z M w ]O2 wherein in chemical formula 2, M is at least one selected from the group consisting of Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, wherein 0.2 ≤ X ≤ 0.5, 0.4 ≤ y < 1, 0 ≤ z ≤ 0.1, and 0 ≤ w ≤ 0.

2.

4. The method of activating a lithium secondary battery of claim 3, wherein the lithium metal oxide comprises Li2Mn03 having a rock-salt structure and Li[Ni 1-y-z-w Mn y Co z M w ]02 having a layered structure in a mixed state.

1. A method of activating a lithium secondary battery, the method comprising: preparing a lithium metal oxide having a layered structure; and mixing the lithium metal oxide with a lithium metal oxide having a rock-salt structure to form a mixed lithium metal oxide.

5. The method of activating a lithium secondary battery according to claim 1, wherein the constant current (CC) charging is performed until a state of charge (SOC) of 50% to 95% is reached.

6. The method of activating a lithium secondary battery according to claim 1, wherein the constant voltage (CV) charging is started and performed at a state of charge (SOC) of 50% to 95%, and the charging ends at a point in time at which the activation depth of charge defined by mathematical formula 1 becomes 5.17% to 15.00%.

7. The method of activating a lithium secondary battery according to claim 1, wherein the constant current (CC) charging is performed until a charging voltage of 4.3 V or more is reached.

8. The method of activating a lithium secondary battery according to claim 1, wherein the constant voltage (CV) charging is performed at a voltage of 4.4 V to 4.7 V.

9. The method of activating a lithium secondary battery according to claim 7, wherein the constant voltage charging ends at a point in time at which the CV charge ratio defined by the following mathematical formula 2 becomes 27% to 40%: [mathematical formula 2] CV charge ratio (%) = (charging time of CV charge interval / total charging time of activation step) x 100.

10. The method of activating a lithium secondary battery according to claim 9, wherein the constant current charging is performed for a time period reaching 60% to 73% of the total charging time of the activation step.

11. The method of activating a lithium secondary battery according to claim 1, wherein after the end of the CC-CV charging, the activation step further comprises the steps of: performing an initial discharge.

12. The method of activating a lithium secondary battery according to claim 11, wherein the activation step is performed between a minimum discharge voltage of 2.0 V to 3.5 V and a maximum charge voltage of 4.4 V to 4.7 V.

13. The method of activating a lithium secondary battery according to claim 11, wherein the constant current charging is performed at a charge rate of 0.2 C to 1.2 C, and the constant voltage charging is performed until the current value reaches 0.01 C to 0.15 C, and the initial discharge is performed at a discharge rate of 0.4 C to 1.2 C.

14. The method of activating a lithium secondary battery according to claim 1, wherein the activation step is performed at a temperature of 20 °C to 55 °C.

15. The method of activating a lithium secondary battery according to claim 11, wherein after the initial discharge step, the method further comprises the steps of: performing a secondary constant current charging of the lithium secondary battery; and performing an aging of the lithium secondary battery at a temperature above 40 °C.

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