Method for activating lithium secondary battery

Abstract

The present invention relates to a method for activating a lithium secondary battery, which comprises: a cathode comprising a cathode active material of a lithium metal oxide that comprises manganese in an amount greater than or equal to 50 mol% and less than 100 mol% on the basis of the total amount of metals excluding lithium; an anode; and an electrolyte, the method comprising a step of activating a lithium secondary battery through CC-CV charging in which constant current (CC) charging is performed until a determined state of charge (SOC) (%) is reached, and then constant voltage (CV) charging is performed, and terminating, when the depth of activation charge defined by the following relation 1 becomes 5.17-15.00%, CC-CV charging of the activation step. [Relation 1] Depth of activation charge (%) = (charge capacity of CV charging section / total charge capacity of activation step) * 100

Description

Activation method of lithium secondary batteries

[0001] Cross-citation with related application(s)

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

[0003] The present invention relates to a method for activating a lithium secondary battery including a manganese-rich cathode material, which allows the lithium secondary battery to sufficiently exhibit the high-capacity characteristics of the cathode material while reducing the amount of gas generated and the amount of transition metal released from the lithium secondary battery and enabling stable operation of the battery.

[0004] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for high-capacity, high-output, and high-stability secondary batteries is increasing.

[0005] The above lithium secondary battery generally consists of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte that serves as a medium for transferring lithium ions, and a separator. At this time, lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, or lithium nickel-cobalt-manganese composite oxide are mainly used as the positive electrode active material.

[0006] However, to lower the unit cost of cathode active materials and increase the energy density and capacity of lithium secondary batteries, lithium manganese-rich oxides have recently been attracting attention as next-generation cathode active materials. Lithium manganese-rich oxides can have relatively low manufacturing costs by increasing the content of manganese (Mn), which is relatively inexpensive and abundant, and decreasing the content of cobalt (Co).

[0007] In addition, the lithium manganese-rich oxide can contribute to the capacity development of the cathode active material and the secondary battery not only through the oxidation / reduction reaction of the metal cation but also through the anion oxidation / reduction (redox) reaction of oxygen. Therefore, the lithium manganese-rich oxide can have a high theoretical reversible capacity and energy density of 250 mAh / g or more.

[0008] However, in order to realize the high capacity characteristics of such lithium manganese-rich oxide, it is known that it is necessary to perform an initial activation process under high voltage by utilizing the potential plateau section confirmed at a charge of 4.3 V or higher for a lithium secondary battery including the same. In particular, if this initial activation process under high voltage is not properly performed, the high capacity characteristics and energy density unique to the lithium manganese-rich oxide may not be properly utilized, or an abnormal operation phenomenon may occur, such as a capacity retention rate exceeding 100% during operation of the lithium secondary battery including the same.

[0009] In addition, during the initial activation process under the high voltage, problems such as excessive activation gas generation or large amounts of transition metals such as manganese being eluted from the anode due to desorption of oxygen within the anode crystal structure may occur. Accordingly, if the conditions for the activation process are not optimized, the cell performance of the lithium secondary battery may deteriorate, such as an increase in resistance.

[0010] Accordingly, for lithium secondary batteries containing the above lithium manganese-rich oxide, performing an appropriate activation process is emerging as one of the major technical challenges.

[0011] Accordingly, the present invention provides a method for activating a lithium secondary battery, which sufficiently exhibits the high-capacity characteristics of a lithium secondary battery containing a manganese-rich oxide as a cathode active material, while reducing the amount of gas generated and the amount of transition metal elution from the lithium secondary battery and enabling stable operation of the battery.

[0012] According to one embodiment of the invention, there is provided a method for activating a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, including a positive electrode active material of lithium metal oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium,

[0013] For the lithium secondary battery, a step of activating the CC-CV charging method by performing constant current (CC) charging until a specified state of charge (State of Charge %; SOC) is reached, and then performing constant voltage (CV) charging is performed,

[0014] A method for activating a lithium secondary battery is provided, which terminates the CC-CV charging of the activation step at a point where the activation depth of charge defined by the following equation 1 becomes 5.17% to 15.00%:

[0015] [Formula 1]

[0016] Activation charge depth (%) = (charge capacity of the above CV charge section / total charge capacity of the above activation stage) * 100

[0017] In the activation method of this embodiment, the lithium metal oxide may be a lithium manganese-rich oxide, for example, a compound represented by the following chemical formula 1:

[0018] [Chemical Formula 1]

[0019] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0020] In the above 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,

[0021] a, b and c are the atomic fractions of independent elements, respectively, 1 <a, 0≤b≤0.5, 0≤c≤0.5, 0<b+c≤0.5이다.

[0022] According to the activation method of the above embodiment, for example, when activating a lithium secondary battery including a manganese-rich oxide positive electrode active material by initial charging, a CC-CV charging method is applied, and among these, constant voltage (CV) charging after constant current (CC) charging is terminated at a point in time when an activation charge depth defined by a predetermined relational expression satisfies a certain ratio. In an additional configuration, in the activation method, the constant voltage (CV) charging time after the constant current (CC) charging can be adjusted at a certain ratio.

[0023] According to an embodiment of the activation method applying such initial charging, it was confirmed that the manganese-rich oxide-based positive electrode active material, for example, lithium manganese oxide having a rock salt structure included therein, can be effectively activated, thereby exhibiting high capacity characteristics of the positive electrode active material.

[0024] In addition, it was confirmed that a lithium secondary battery that has undergone the activation method of the above-described embodiment can exhibit excellent cycle characteristics by being operated stably without occurrence of abnormal operation cycles, such as a capacity retention rate exceeding 100% during charge / discharge operation.

[0025] In addition, it was confirmed that the amount of gas generated and the amount of transition metal elution during the activation process can be reduced as the constant voltage charging time is adjusted at a certain rate.

[0026] Figure 1 is a graph showing the results of a comparative evaluation of cycle-by-cycle driving characteristics and capacity retention rates for lithium secondary batteries manufactured through the activation processes of examples and comparative examples.

[0027] Hereinafter, a method for activating a lithium secondary battery according to an embodiment of the invention will be described in more detail.

[0028] A manganese-rich oxide-based cathode active material having a manganese content of 50 mol% or more among all metals excluding lithium, for example, a perlithium manganese-rich oxide-based cathode active material, not only has a higher energy density than the currently commercialized lithium nickel cobalt manganese (NCM)-based active material, but also has the advantage of reducing the manufacturing cost because it can reduce the amount of expensive cobalt used.

[0029] However, this lithium manganese-rich oxide cathode active material has a mixed structure of lithium manganese oxide (Li2MnO3) having a rock salt structure and lithium transition metal oxide having a layered structure (e.g., Li[Ni1-yz-wMnyCozMw]O2), and the compound having the rock salt structure can be activated by an activation process prior to operation of a lithium secondary battery, thereby exhibiting higher capacity characteristics.

[0030] For this reason, it is very important to optimize the activation process conditions for lithium secondary batteries including the lithium manganese-rich oxide cathode active material to exhibit higher capacity characteristics. If the activation process does not proceed properly and the rock salt structure compound is not properly activated, the rock salt structure compound may be abnormally activated during the charge / discharge process for driving the lithium secondary battery, resulting in abnormal operation phenomena such as a capacity retention rate exceeding 100% during the initial cycle operation.

[0031] An activation method of one embodiment is to solve this problem, and the main configuration is to terminate the constant voltage (CV) charging after the constant current (CC) charging when the ratio of the charge capacity of the constant voltage (CV) charging section to the total charge capacity of the activation step is about 5.17% to 15.00%, or about 6.00% to 14.00%, or about 7.00% to 13.00%, at the point where the activation charge depth defined by the following equation 1, i.e., the charge capacity of the CV charging section, is about 5.17% to 15.00%, or about 6.00% to 14.00%, or about 7.00% to 13.00%, in activating the lithium secondary battery by initially charging it with the CC-CV charging method:

[0032] [Formula 1]

[0033] Activation charge depth (%) = (charge capacity of the above CV charge section / total charge capacity of the above activation stage) * 100

[0034] As supported by the examples described below, it was confirmed that by optimizing the progress rate of the constant voltage (CV) charging section, the manganese-rich oxide-based positive electrode active material, for example, the rock salt structure compound, can be effectively activated to exhibit higher capacity characteristics, while suppressing abnormal operation phenomena such as a capacity retention rate exceeding 100% during operation of a lithium secondary battery including the same.

[0035] This is because, as the rate of progress in the constant voltage (CV) charging section that is performed under a high voltage of, for example, 4.4 V to 4.7 V or 4.5 V to 4.65 V is optimized, the compound of the rock salt structure is effectively activated during the high voltage charging process, and as a result, an abnormal driving cycle due to abnormal activation does not occur during the operation of the lithium secondary battery.

[0036]

[0037] Hereinafter, the activation method of the above implementation example will be described in more detail.

[0038] The lithium secondary battery in which the activation method of the above embodiment is performed includes a manganese-rich oxide-based cathode active material made of a lithium metal oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium. Such a manganese-rich oxide-based cathode active material may be, for example, a lithium manganese-rich metal oxide represented by the following chemical formula 1:

[0039] [Chemical Formula 1]

[0040] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0041] In the above 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,

[0042] a, b and c are the atomic fractions of independent elements, respectively, 1 <a, 0≤b≤0.5, 0≤c≤0.5, 0<b+c≤0.5이다.

[0043] Specifically, the above a is the molar ratio of Li in the lithium manganese-rich oxide of 1 <a, 1.1≤a≤1.5, 또는 1.2≤a≤1.4일 수 있다. a가 상기 범위를 만족할 때, 고용량을 구현할 수 있다.

[0044] The above b is the molar ratio of Ni in the lithium manganese-rich oxide, and may be 0≤b≤0.5, 0.1≤b≤0.4, or 0.2≤b≤0.4.

[0045] The above c is a molar ratio of an additional element M in the lithium manganese-rich oxide, and may be 0≤c≤0.5, 0≤c≤0.3, or 0≤c≤0.1. The above M may be, for example, Co, and if the content of the additional element is too high, not only may it have a negative effect on the capacity characteristics, but there is also a concern that the life characteristics may be deteriorated due to the increased oxygen-redox reaction, which may aggravate gas generation and deterioration of the positive electrode active material.

[0046] The above 1-bc is the molar ratio of Mn in the lithium manganese-rich oxide, and may 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 the rock salt structure may be small, so that the negative electrode irreversible compensation and capacity improvement effects may be minimal.

[0047] Meanwhile, in the case of a perlithium manganese-rich oxide containing an excess of lithium together with manganese of 50 mol% or more among the metals excluding lithium, it may have a structure in which a layered structure compound (LiM'O2) and a rock salt structure compound (Li2MnO3) are mixed. Among these, the rock salt structure compound is activated at a high voltage of, for example, 4.4 V or higher to generate an excess of ions. Therefore, when a perlithium manganese-rich oxide is used as a positive electrode active material, the excess lithium ions generated when the rock salt phase is activated during the high-voltage activation process are inserted into the negative electrode, thereby obtaining a prelithiation effect in which the irreversible capacity of the negative electrode is compensated. However, depending on the activation conditions, some of the rock salt phase may remain in an unactivated state. If this unactivated residual rock salt phase is not large, it can be further activated during the operation of the lithium secondary battery, thereby contributing to improving the capacity retention rate of the lithium secondary battery.

[0048] However, if the activation is not performed properly and a large amount of the unactivated residual rock salt phase is included, an abnormal cycle in which the capacity retention rate exceeds 100% during operation of the lithium secondary battery may occur, which may result in an abnormal operation phenomenon of the lithium secondary battery. As described above, in the case of the activation method of one embodiment, since the rock salt phase is sufficiently activated, problems such as the abnormal operation phenomenon can be suppressed.

[0049] In a more specific example, the lithium metal oxide, for example, the lithium manganese-rich oxide, may include Li2MnO3 having a rock salt structure and Li[Ni1-yz-wMnyCozMw]O2 having a layered structure in a mixed state, and may be represented by the following chemical formula 2:

[0050] [Chemical Formula 2]

[0051] X*Li2MnO3·(1-X)*Li[Ni1-yz-wMnyCozMw]O2

[0052] In the above chemical formula 2,

[0053] 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, and 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.2.

[0054] In this chemical formula 2, X represents the ratio of the Li2MnO3 phase (rock salt phase) in the lithium manganese-rich 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 satisfies the above range, high-capacity characteristics can be realized.

[0055] The above y is LiM'O2(M'= [Ni 1-y-z Mn y M z ]; in the layered form, the molar ratio of Mn may be 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0056] The above z is LiM'O2(M'= [Ni 1-y-z Mn y M z ]; the molar ratio of the additional element M in the layered structure may be 0≤z≤0.5, 0≤z≤0.3, or 0≤z≤0.1.

[0057] Meanwhile, the lithium manganese-rich oxide cathode active material described above may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle diameter of the secondary particles is D 50 It may be 2㎛ to 10㎛, preferably 2㎛ to 8㎛, more preferably 4㎛ to 8㎛. D of the positive electrode active material 50 When this above range is satisfied, the electrode density can be implemented excellently, and the deterioration of capacity and rate characteristics can be minimized.

[0058] In addition, the above-mentioned positive electrode active material has a BET specific surface area of ​​0.1 m 2 / g to 10m 2 / g, specifically 0.1m 2 / g to 5m 2 / g, more specifically 0.1m 2 / g to 1m 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 realize sufficient capacity. If the specific surface area is too high, moisture absorption is rapid, and side reactions with the electrolyte are accelerated, making it difficult to secure life characteristics.

[0059] The above lithium manganese-rich oxide can be manufactured by mixing a transition metal precursor and a lithium raw material and then calcining them. The types of each precursor and raw material and the manufacturing conditions can be based on the manufacturing conditions of a general manganese-rich oxide-based positive electrode active material, and therefore, further description thereof will be omitted.

[0060] Meanwhile, the lithium secondary battery may have a configuration of a general lithium secondary battery, except that the lithium manganese-rich oxide is used as a cathode active material, and may be manufactured by a method well known to those skilled in the art. For example, the method may be performed by sequentially stacking and drying an electrode assembly by interposing a separator (or electrolyte membrane) between a cathode including a cathode active material and an anode including an anode active material, and then inserting the electrode assembly into a case and sealing it by selectively injecting an electrolyte. The lithium secondary battery may be a cylindrical, square, coin-shaped, or pouch-shaped battery.

[0061] The above positive and negative electrodes can be manufactured by applying a composition for forming an active material layer including an electrode active material on a current collector and then drying the composition.

[0062] The composition for forming a positive electrode active material layer may optionally further include a binder, a conductive agent, a filler, etc., in addition to the lithium manganese-rich oxide positive electrode active material, as needed. The composition for forming a negative electrode active material layer may optionally further include a binder, a conductive agent, a filler, etc., in addition to the negative electrode active material, as needed.

[0063] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0064] The above cathode active material may further include a conventional cathode active material in addition to the above-described lithium manganese-rich oxide, for example, LCO (LiCoO2), LNO (LiNiO2), LFP (LiFePO4) and NCM (Li[Ni p Co q Mn r1 ]O2, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) may further include one or more positive electrode active materials selected from the group consisting of, but preferably, at least 70 wt% or more of the lithium manganese-rich oxide based on the weight of the entire positive electrode active material may be included, and may be composed only of the lithium manganese-rich oxide.

[0065] The above positive electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the positive electrode active material layer.

[0066] In a specific embodiment, the negative electrode may include at least one selected from the group consisting of a carbon-based material, a silicon-based material, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, lithium metal, and a transition metal oxide as a negative electrode active material, and preferably may include a carbon-based material, a silicon-based material, or a mixture thereof.

[0067] As the above carbon-based material, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the above crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the above amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc.

[0068] The above silicon-based material is Si, SiO x (0 <x<2) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합 중 선택되는 원소이며, Si는 될 수 없음.) 중 선택된 1종 이상이고, 바람직하게는 SiO이다. 실리콘계 음극 활물질은 용량이 그라파이트 대비 약 10배 가까이 높아 질량 로딩(mg·cm -2 ) can be lowered to improve the rapid charging performance of the battery.

[0069] As the above metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals with lithium may be used.

[0070] The above metal composite oxides include 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 (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8)로 이루어진 군에서 선택된 1종 이상이 사용될 수 있다.

[0071] Materials capable of doping and dedoping the lithium include Sn, SnO2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use.

[0072] In the above Si-Y and Sn-Y, the element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db(dubnium), 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.

[0073] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0074] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the negative electrode slurry.

[0075] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0076] The conductive agent is a component for further improving the conductivity of the active material, and may be added in an amount of 10 wt% or less, specifically 5 wt% or less, based on the total weight of the active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0077] Meanwhile, the lithium secondary battery may be provided by forming an electrolyte layer (or electrolyte-containing layer) between the positive and negative electrodes without a separate separator, but may further include a separator interposed between the positive and negative electrodes. Such a separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries may be used without particular limitation, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. Additionally, a coated separator containing ceramic components or polymeric materials may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0078] In addition, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0079] In a specific example, the electrolyte may be a liquid electrolyte comprising an organic solvent and a lithium salt.

[0080] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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 dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0081] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is 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 - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0082] Meanwhile, in the activation method of the above-described embodiment, initial charging for activation is performed on the above-described lithium secondary battery, and this initial charging is performed using a CC-CV charging method.

[0083] In this CC-CV charging method, the lithium secondary battery is subjected to constant current (CC) charging while maintaining a constant charging current until a predetermined state of charge (State of Charge %; SOC), and then subjected to constant voltage (CV) charging while maintaining a constant charging voltage from the predetermined state of charge.

[0084] First, the constant current charging is performed to, for example, a state of charge of 50% to 95%, and by this constant current charging, a voltage suitable for activating the rock salt phase included in the lithium manganese-rich oxide cathode active material is reached, for example, 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.

[0085] Thereafter, while maintaining a constant charge voltage, for example, 4.3 V or higher, or 4.4 V to 4.7 V, constant voltage charging is performed, and during this process, the salt phase is activated to achieve high capacity characteristics. In particular, the constant voltage charging may be terminated when the activation charge depth defined by the above equation 1 becomes about 5.17% to 15.00%, or about 6.00% to 14.00%, or about 7.00% to 13.00%. In a specific example, the constant voltage charging may be initiated at a state of charge (SOC) of, for example, 50% to 95% and performed until a constant charge state is reached, and may be terminated when the activation charge depth reaches a constant value.

[0086] At this time, the activation charge depth may be defined as the ratio of the charge capacity charged in the constant voltage charge section based on the total charge capacity of the activation step charged in the constant current charge section and the constant voltage charge section. This activation charge depth may mean the ratio of an appropriate constant voltage charge section in the initial charge step for the activation. When the activation charge depth satisfies a certain ratio, the progress ratio of the constant voltage charge section is optimized, so that the activation of the rock salt phase included in the lithium manganese-rich oxide cathode active material can be achieved to an optimized degree. As a result, the high capacity characteristics of the lithium secondary battery can be expressed, while abnormal operation during operation of the battery can be suppressed.

[0087] Meanwhile, in another embodiment of the invention, the constant voltage charging may be performed so that the CV charging ratio defined by the following Equation 2 is 27% to 40%, or 27% to 38%, or 27% to 35%, and it is preferable to terminate at the point in time when the CV charging ratio is satisfied:

[0088] [Formula 2]

[0089] CV charging ratio (%) = (charging time of the above CV charging section / total charging time of the above activation stage) * 100

[0090] In addition, the constant current charging before the constant voltage charging may be performed at a time ratio of 60% to 73%, or 62% to 73%, or 65% to 73%, of the total charging time of the activation step, which is the total progress time of the constant current charging and constant voltage charging, considering an appropriate time ratio of the constant voltage charging section defined by the above equation 2.

[0091] For reference, due to the characteristics of the lithium manganese-rich oxide cathode active material, if the activation charging process time ratio under high voltage is excessively long, oxygen within the cathode crystal structure may be desorbed, resulting in the generation of excessive activation gas or the elution of a large amount of transition metals such as manganese within the cathode.

[0092] However, as confirmed through the examples described below, by optimizing the time ratio of the constant voltage (CV) charging section defined by the above equation 2 and the time ratio of the remaining constant current (CC) charging section, it was confirmed that the manganese-rich oxide-based positive electrode active material, for example, the rock salt structure compound, can be effectively activated to exhibit higher capacity characteristics, while reducing the amount of gas generated and the amount of transition metals such as manganese eluted during the activation process. In addition, it was confirmed that a lithium secondary battery that went through such an activation process can exhibit excellent discharge capacity and voltage along with low resistance.

[0093] Conversely, if the time ratio of the above constant voltage (CV) charging is excessively short, the amount of gas generated and the amount of transition metal released during the activation process may significantly increase, and the resistance of the lithium secondary battery may also significantly increase. Conversely, if the time ratio of the constant voltage (CV) charging is excessively long, the capacity characteristics of the lithium secondary battery may not be sufficient due to overvoltage.

[0094] Meanwhile, after the initial charging performed using the CC-CV charging method, a step of initially discharging the lithium secondary battery may be further performed. In this initial discharging step, the constant voltage charging may be performed at a maximum charging voltage of, for example, 4.3 V or higher, or 4.4 V to 4.7 V, or 4.5 V to 4.65 V, and may be performed to a minimum discharging voltage of 2.0 V to 3.5 V.

[0095] Additionally, the activation step including the initial charge and initial discharge described above may be performed at a temperature of 20°C to 55°C, or 25°C to 50°C.

[0096] In addition, in the activation step, the initial charge step may be performed at a charge rate of 0.2C to 1.2C, and the initial discharge step may be performed at a discharge rate of 0.4C to 1.2C, or 0.5C to 1.1C. In a more specific example, the constant current charge of the initial charge step may be performed at a charge rate of, for example, 0.2C to 1.2C, or 0.3C to 1.1C. In addition, the constant voltage charge thereafter may be performed at a charge rate of, for example, 0.2C or higher, or 0.3C to 0.8C, or 0.3C to 0.6C. In addition, such constant voltage charge may be performed until the current value reaches 0.01C to 0.15C.

[0097] Through this, a lithium secondary battery including a lithium manganese-rich oxide-based cathode active material can be effectively activated while effectively reducing the amount of gas generated and the amount of transition metal elution during the activation process.

[0098] Meanwhile, the activation method of the above-described embodiment may further include, if necessary, performing a step of aging the lithium secondary battery after or between the initial charge / discharge steps.

[0099] In addition, according to a specific embodiment of the invention, the activation method of the above-described embodiment may further include, if necessary, a step of secondary constant current charging of the lithium secondary battery after the initial charge / discharge step; and / or a step of aging the lithium secondary battery at a temperature of 40°C or higher.

[0100] More specifically, the activation method may further include a step of performing a secondary constant current charging to, for example, a state of charge of 70% or 60%, and this secondary constant current charging step may be performed at a charging rate of, for example, 0.3 C or more, or 0.3 C to 1.0 C.

[0101] In addition, after the secondary constant current charging step, a step of aging the lithium secondary battery may be further performed, for example, at a temperature of 40°C or higher, or 40 to 70°C, for 10 to 30 hours, or 12 to 20 hours. This can further enhance the effectiveness of the activation method.

[0102]

[0103] Through the activation method of the above-described embodiment, a lithium secondary battery including a lithium manganese-rich oxide-based cathode active material can be effectively activated, and while implementing the capacity characteristics of the cathode active material, the amount of gas generated and the amount of transition metal elution during the activation process can be reduced, and abnormal operation cycles of the lithium secondary battery can be suppressed, thereby enabling stable operation thereof.

[0104]

[0105] In order to help understand the invention below, preferred embodiments are presented; however, the following embodiments are merely illustrative of the invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the invention and technical idea, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0106]

[0107] [Manufacturing Example]: Manufacturing of Lithium Secondary Battery

[0108] Li as a cathode active material 1.16 Ni 0.305 Co 0.004 Mn 0.531A lithium manganese oxide having a composition 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 wt%). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 12 μm, and dried and roll pressed to prepare a positive electrode.

[0109] Graphite as an anode active material, SBR-CMC as a binder, and carbon black as a conductive material were added to water as a solvent in a weight ratio of 95.7:2.3:2.0 to prepare a cathode slurry (solid content: 60 wt%). The cathode slurry was applied to a copper (Cu) thin film as an anode current collector with a thickness of 8 μm, dried, and then roll pressed to prepare a cathode.

[0110] 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 make 1.2 M.

[0111] An electrode assembly was manufactured by sequentially stacking the positive electrode, a polyolefin porous separator coated with inorganic particles (Al2O3), and a negative electrode. The assembled electrode assembly was stored in a pouch-type battery case, and the manufactured non-aqueous electrolyte was injected therein to manufacture a lithium secondary battery.

[0112]

[0113] Example 1.

[0114] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and an initial charge for activation was performed at a rate of 1.0 C at 45°C until a state of charge (SOC) of 60%, followed by an initial charge at a rate of 0.4 C. In this initial charge, a constant current charge was first performed on the lithium secondary battery while maintaining a charge current of 0.4 C until a state of charge (SOC) of 91.53% and a charge voltage of 4.6 V. This constant current charge was performed for a time ratio of 70.8% of the total charging time of the activation step.

[0115] After reaching the above 4.6 V charging voltage, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed for a time ratio of 29.2% of the total charging time of the activation stage including the constant current charging and constant voltage charging, and was performed at a temperature of 45°C until the current value reached 0.05C from 0.4C, and then terminated after the above time ratio elapsed. In addition, it was confirmed that the charging capacity of the constant voltage charging section was approximately 8.47% based on the total charging capacity of 100% by the constant current charging and constant voltage charging, and thus the charging depth was terminated when it was approximately 8.47% according to Equation 1. The state of charge at the termination point was 100%.

[0116] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge to 2.0 V at a discharge rate of 0.4 C at 45°C.

[0117]

[0118] Example 2.

[0119] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and an initial charge for activation was performed at a rate of 1.0 C at 45°C until a state of charge (SOC) of 60%, followed by an initial charge at a rate of 0.4 C. In this initial charge, a constant current charge was first performed on the lithium secondary battery while maintaining a charge current of 0.4 C until a state of charge (SOC) of 91.53% and a charge voltage of 4.6 V. This constant current charge was performed for a time ratio of 64.7% of the total charging time of the activation step.

[0120] After reaching the above 4.6 V charging voltage, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed for a time ratio of 35.3% of the total charging time of the activation stage including the constant current charging and constant voltage charging, and was performed at a temperature of 45°C until the current value reached 0.05C from 0.4C, and then terminated after the above time ratio elapsed. In addition, based on the total charging capacity of 103.5% by the constant current charging and constant voltage charging (at this time, the total charging capacity was calculated and expressed as a ratio based on the total charging capacity of Example 1), it was confirmed that the charging capacity of the constant voltage charging section was approximately 12.00%, and the activation charging depth according to Equation 1 was approximately 11.59% (= 12.00 / 103.5*100), and the termination was completed. The state of charge at the termination time was 103.5%.

[0121] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge to 2.0 V at a discharge rate of 0.4 C at 45°C.

[0122]

[0123] Comparative Example 1.

[0124] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and was charged at a rate of 1.0 C at 45°C to 60% state of charge (SOC), followed by an initial charge for activation at a rate of 0.4 C. In this initial charge, first, constant current charging was performed on the lithium secondary battery while maintaining a charge current of 0.4 C until a state of charge (SOC) of 91.53% and a charge voltage of 4.6 V. This constant current charging was performed for a time ratio of 73.7% of the total charging time of the activation step.

[0125]

[0126] After reaching the above 4.6 V charging voltage, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed for a time ratio of 26.3% of the total charging time of the activation stage including the constant current charging and constant voltage charging, and was performed at a temperature of 45°C until the current value reached 0.05C from 0.4C, and then terminated after the above time ratio elapsed. In addition, based on the total charging capacity of 95.69% by the above constant current charging and constant voltage charging (at this time, the total charging capacity was calculated and expressed as a ratio based on the total charging capacity of Example 1), it was confirmed that the charging capacity of the constant voltage charging section was approximately 4.16%, and the activation charging depth according to Equation 1 was approximately 4.35% (=4.16 / 95.69*100), and the termination was completed. The state of charge at the termination point was 95.69%.

[0127] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge to 2.0 V at a discharge rate of 0.4 C at 45°C.

[0128]

[0129] Test Example 1: Cycle-by-cycle driving characteristics and capacity retention rate evaluation

[0130] In the examples and comparative examples, the lithium secondary batteries manufactured through the activation process were charged to 4.35 V under 1 / 3C CC-CV (CV 5%) conditions at a temperature of 45°C, and then discharged to 2.0 V under 1 / 3C CC conditions, thereby conducting a charge and discharge test. During the charge and discharge test, the driving characteristics and capacity retention rate for each cycle were evaluated, and the results of the evaluations were compared and shown in Fig. 1.

[0131] Referring to Figure 1, in Comparative Example 1, an abnormal operation phenomenon was observed in which the capacity retention rate exceeded 100% during the initial cycle operation. This is presumed to be because the rock salt phase of the positive electrode active material was not properly activated during the activation process, resulting in abnormal activation during the cycle operation.

[0132] In comparison, in Examples 1 and 2, it was confirmed that the device exhibited a high capacity retention rate of 90% or more up to 100 cycles, while operating stably without the above-mentioned abnormal operation phenomenon occurring.

[0133]

[0134] Test Example 2: Evaluation of gas generation and transition metal release

[0135] For lithium secondary batteries manufactured through the activation process in Examples and Comparative Examples, the gas generated during the activation process was captured and the amount of gas generated was quantitatively analyzed using GC-FID / TCD. The analysis results of the amount of activated gas generated were converted into a ratio based on Example 1 (100%) and are shown in Table 1 below.

[0136] In addition, the amount of transition metals (nickel and manganese) eluted (mg / kg) during the above activation process was analyzed by ICP and is shown in Table 1 below.

[0137] Activation gas (%) Transition metal elution amount (Ni+Mn) mg / kg Comparative example 1151.4360 Example 1100.0 (standard) 75 Example 289.460

[0138] Referring to Table 1 above, it was confirmed that Examples 1 and 2 exhibited lower gas generation and transition metal elution amounts compared to Comparative Example 1, as they were manufactured through an activation process in which the progression rate of the constant voltage section (time ratio of the CV charging section) defined by Equation 2 was optimized.

Claims

1. A method for activating a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte including a positive electrode active material of lithium metal oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium, For the lithium secondary battery, a step of activating the CC-CV charging method by performing constant current (CC) charging until a specified state of charge (State of Charge %; SOC) is reached, and then performing constant voltage (CV) charging is performed, A method for activating a lithium secondary battery, wherein the CC-CV charging of the activation step is terminated at a point where the activation charge depth defined by the following equation 1 becomes 5.17% to 15.00%. [Formula 1] Activation charge depth (%) = (charge capacity of the above CV charge section / total charge capacity of the above activation stage) * 100 2. In the first paragraph, a method for activating a lithium secondary battery, wherein the lithium metal oxide comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] Li a [Mr 1-b-c Ni b M c ] 2-a O2 In the above 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, a, b and c are the atomic fractions of independent elements, respectively, 1 <a, 0≤b≤0.5, 0≤c≤0.5, 0<b+c≤0.5이다.

3. In the first paragraph, the lithium metal oxide is a method for activating a lithium secondary battery represented by the following chemical formula 2: [Chemical Formula 2] X*Li2MnO3·(1-X)*Li[Ni1-yz-wMnyCozMw]O2 In the above 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, and 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.

2.

4. A method for activating a lithium secondary battery in the third paragraph, wherein the lithium metal oxide contains Li2MnO3 having a rock salt structure and Li[Ni1-yz-wMnyCozMw]O2 having a layered structure in a mixed state.

5. A method for activating a lithium secondary battery, wherein the constant current (CC) charging is performed until the state of charge (SOC) reaches 50% to 95% in the first paragraph.

6. In the first paragraph, the constant voltage (CV) charging is initiated and performed at a state of charge (SOC) of 50% to 95%, A method for activating a lithium secondary battery, wherein the activation depth of charge defined by the above formula 1 is terminated at a point in time when the activation depth of charge is 5.17% to 15.00%.

7. A method for activating a lithium secondary battery in accordance with claim 1, wherein the constant current (CC) charging is performed until the charging voltage reaches 4.3 V or higher.

8. A method for activating a lithium secondary battery in the first paragraph, wherein the constant voltage (CV) charging is performed under a voltage of 4.4 V to 4.7 V.

9. In the 7th paragraph, a method for activating a lithium secondary battery, wherein the constant voltage charging is terminated when the CV charging ratio defined by the following Equation 2 becomes 27% to 40%: [Formula 2] CV charging ratio (%) = (charging time of the above CV charging section / total charging time of the above activation stage) * 100 10. A method for activating a lithium secondary battery in accordance with claim 9, wherein the constant current charging is performed for a time ranging from 60% to 73% of the total charging time of the activation step.

11. A method for activating a lithium secondary battery in accordance with claim 1, wherein the activation step further comprises an initial discharging step after the end of the CC-CV charging.

12. A method for activating a lithium secondary battery in accordance with 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. In the 11th paragraph, the constant current charging is performed at a charging rate of 0.2C to 1.2C, and the constant voltage charging is performed until the current value reaches 0.01C to 0.15C. A method for activating a lithium secondary battery, wherein the above initial discharge is performed at a discharge rate of 0.4C to 1.2C.

14. A method for activating a lithium secondary battery, wherein the activation step is performed at a temperature of 20°C to 55°C in the first paragraph.

15. A method for activating a lithium secondary battery, further comprising, in claim 11, a step of secondary constant current charging of the lithium secondary battery after the initial discharge step; and a step of aging the lithium secondary battery at a temperature of 40°C or higher.

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