Method for activating lithium secondary battery

Abstract

The present invention relates to a method for activating a lithium secondary battery comprising a manganese-rich positive electrode material, wherein the method can improve the capacity characteristics and lifespan characteristics of the lithium secondary battery and reduce the amount of gas generation of the lithium secondary battery. The activation method is a method for activating a lithium secondary battery comprising: a positive electrode comprising a positive electrode active material made of a lithium metal oxide; a negative electrode; and an electrolyte, and comprises the steps of: charging the lithium secondary battery at a first temperature; and discharging the lithium secondary battery at a second temperature that is at least 15°C higher than the first temperature, wherein the lithium metal oxide comprises at least 50 mol% and less than 100 mol% of manganese on the basis of the total content of metals excluding lithium.

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. 10-2024-0090143, filed July 9, 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 comprising a manganese-rich cathode material, which can improve capacity characteristics and lifespan characteristics and reduce gas generation.

[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 oxygen anion oxidation / reduction (redox) reaction. More specifically, the additional capacity development due to the oxygen oxidation / reduction reaction is additionally shown in the high-voltage charging section of, for example, 4.3 V or higher or 4.4 V or higher, and as a result, the lithium manganese-rich oxide can have a high theoretical reversible capacity and energy density of 250 mAh / g or higher.

[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 in the high voltage charging for a lithium secondary battery including the same.

[0009] However, during this initial activation process, problems such as excessive activation gas generation due to desorption of oxygen within the cathode crystal structure, large amounts of transition metals such as manganese within the cathode, and irreversible structural collapse of the cathode active material may occur. This may be a major factor in reducing the life and capacity characteristics of the lithium manganese-rich oxide or increasing gas generation.

[0010] Accordingly, for lithium secondary batteries containing the above lithium manganese-rich oxide, one of the major technical challenges is to conduct an appropriate activation process that effectively exhibits the high capacity characteristics unique to the above lithium manganese-rich oxide without causing the above problems.

[0011] Accordingly, the present invention provides a method for activating a lithium secondary battery that can improve capacity characteristics and life characteristics and reduce gas generation for a lithium secondary battery including a manganese-rich oxide as a positive electrode active material.

[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,

[0013] For the above lithium secondary battery, a step of performing charging at a first temperature and a step of performing discharging at a second temperature that is 15°C or higher than the first temperature are included.

[0014] A method for activating a lithium secondary battery is provided, wherein the lithium metal oxide contains manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium.

[0015] In the activation method of this embodiment, the lithium metal oxide may include a compound represented by the following chemical formula 1:

[0016] [Chemical Formula 1]

[0017] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0018] 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,

[0019] 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.

[0020] Additionally, in the activation method of the above embodiment, the charging and discharging steps may be performed in a single step, and the first temperature at which the charging step is performed may be 20 to 30°C, and the second temperature at which the discharging step is performed may be 40 to 50°C.

[0021] According to the activation method of the above embodiment, for example, when activating a lithium secondary battery including a manganese-rich oxide-based positive electrode active material by initial charging and discharging, the charging temperature can be controlled to a relatively low temperature, while the discharge temperature can be controlled to a relatively high temperature.

[0022] As a result of activation under these initial charge and discharge conditions, it was confirmed that not only was the amount of gas generated from the lithium secondary battery reduced, but the capacity characteristics and life characteristics of the lithium secondary battery were also improved.

[0023] This is because, by controlling the initial charge / discharge conditions, for example, by initial discharging at a relatively high temperature, oxygen dimers that generate gases such as oxygen can be effectively removed, and additional capacity development by the oxygen anion redox reaction is effectively achieved, as the oxygen anion redox reaction is reversibly and smoothly performed under high voltage. In addition, it appears that, as the initial charging is performed at a relatively low temperature, the amount of gas generation is suppressed, and the operation of the lithium secondary battery is stably achieved.

[0024] Therefore, according to the activation method of the above embodiment, the manganese-rich oxide-based cathode active material can be effectively activated, thereby exhibiting high capacity characteristics of the cathode active material, while reducing the amount of gas generated during operation of a lithium secondary battery including the same and improving the life characteristics.

[0025] Figure 1 is a graph showing the results of measuring the charge capacity and discharge capacity during the activation process of Reference Example 1 and Example 1, respectively.

[0026] Figures 2a and 2b are graphs showing the results of quantitative analysis of the amount of activated gas generated during the activation process of Reference Example 1 and Example 1.

[0027] Figure 3 is a graph showing the results of evaluating the capacity retention rate per cycle by conducting a charge / discharge test on the lithium secondary batteries of Reference Examples 1 to 3 and Example 1.

[0028] Hereinafter, a method for activating a lithium secondary battery according to an embodiment of the invention will be described in more detail.

[0029] A lithium manganese-rich oxide cathode active material containing an excess of lithium over the equivalent weight and having a manganese content of 50 mol% or more among all metals excluding lithium not only has a higher energy density than the currently commercialized lithium nickel cobalt manganese (NCM) active material, but also has the advantage of reducing the manufacturing cost because it can reduce the amount of expensive cobalt used.

[0030] These lithium manganese-rich oxide cathode active materials have 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 is activated by an activation process before operation of a lithium secondary battery, and additional capacity development is possible by an oxidation / reduction reaction of oxygen anions. In particular, for the additional capacity development, it is necessary to perform an initial activation process under a high voltage by utilizing a potential plateau section confirmed at a charge of 4.3 V or higher for a lithium secondary battery including the same.

[0031] For this reason, it is very important to optimize the activation process conditions, including the initial charge and discharge stages, for lithium secondary batteries containing the above-described lithium manganese-rich oxide cathode active material, to exhibit higher capacity characteristics. However, during the activation process, problems such as excessive gas generation due to desorption of oxygen within the cathode crystal structure, or large amounts of transition metals such as manganese within the cathode, which significantly reduces the lifespan characteristics of the battery, may occur.

[0032] An activation method of one embodiment solves this problem, in which, when activating the lithium secondary battery by initially charging and discharging, the initial charging step is performed at a first temperature near room temperature, for example, a relatively low first temperature of 20 to 30°C, or 21 to 29°C, or 23 to 27°C, and the initial discharging step is performed at a second temperature higher by 15°C or higher, or by 15 to 25°C, for example, a second temperature of 40 to 50°C, or 41 to 49°C, or 43 to 47°C.

[0033] According to the activation method of this embodiment, it was confirmed that the amount of gas generation from the lithium secondary battery is suppressed and the life characteristics of the battery are improved as the initial charging step is performed at a relatively low first temperature near room temperature. This is expected to be because the formation of oxygen vacancies is suppressed even in a high voltage range of 4.3 V or higher due to the initial charging at a relatively low temperature, thereby suppressing the amount of gas generation such as oxygen and enabling the battery to be operated stably.

[0034] Furthermore, in the activation method of the above embodiment, the initial discharge step is performed at a relatively high second temperature. By performing the initial discharge at such a high temperature, sufficient energy is applied to the oxygen dimers that have remained in an incomplete state within the crystal lattice structure of the positive electrode active material due to failure to overcome the thermodynamic energy barrier, thereby effectively removing them. Accordingly, the amount of gas generated, such as oxygen, during operation of the lithium secondary battery can be suppressed, and the lithium secondary battery can exhibit improved life characteristics.

[0035] In addition, since the oxygen anion oxidation / reduction (redox) under high voltage is smoothly and reversibly performed, additional capacity development is effectively achieved, and thus the capacity characteristics of the lithium secondary battery can also be further improved.

[0036] Therefore, according to the activation method of one embodiment, the capacity and life characteristics of a lithium secondary battery including a lithium manganese-rich oxide-based positive electrode active material can be improved, while the amount of gas generated during operation thereof can be significantly reduced.

[0037]

[0038] Hereinafter, the activation method of the above implementation example will be described in more detail.

[0039] 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:

[0040] [Chemical Formula 1]

[0041] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0042] 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,

[0043] 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.

[0044] 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, 당량보다 과량의 리튬에 의해 고용량을 구현할 수 있다.

[0045] 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.

[0046] 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 oxidation / reduction reaction of oxygen anions, which may aggravate gas generation and deterioration of the positive electrode active material.

[0047] 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.

[0048] 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, 4.3 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.

[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[Ni 1-y-z-w Mn y Co z M w ]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 This may be 2㎛ to 10㎛, or 2㎛ to 8㎛, or 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, but 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, an initial charging step at a first temperature and an initial discharging step at a second temperature are performed for the above-described lithium secondary battery. At this time, the first temperature and the second temperature are as described above.

[0083] First, the initial charging step under the first temperature can be performed in a CC-CV charging mode, in which constant current (CC) charging is performed up to a certain charging voltage and then constant voltage (CV) charging is performed. By performing the initial charging step in this CC-CV charging mode, additional capacity development is possible through activation of the rock salt structure or oxygen anion oxidation / reduction reaction during CV charging under high voltage.

[0084] In this CC-CV charging method, the lithium secondary battery is charged by constant current (CC) while maintaining a constant charging current until the charging voltage reaches a predetermined voltage, for example, 4.3 V or higher, or 4.3 V to 4.7 V, or 4.4 V to 4.65 V, and then constant voltage (CV) charging is performed from the predetermined charging voltage.

[0085] At this time, the constant current charging can be performed at a charging rate of, for example, 0.1 C to 1.2 C, or 0.1 C to 1.1 C, and can proceed until a voltage suitable for activating the rock salt phase included in the lithium manganese-rich oxide positive electrode active material, for example, a charging voltage of 4.3 V or higher, or 4.3 V to 4.7 V, or 4.4 V to 4.65 V, is reached.

[0086] Thereafter, while maintaining this constant charging voltage, constant voltage charging is performed, and during this process, the rock salt structure included in the positive electrode active material is activated, so that high capacity characteristics can be achieved. This constant voltage charging can be performed at a charging rate of, for example, 0.01 C or higher, or 0.05 C to 0.8 C, or 0.1 C to 0.6 C.

[0087] Meanwhile, after the initial charge under the first temperature, the lithium secondary battery can be initially discharged under a relatively high second temperature. In this initial discharge step, the constant voltage charge can proceed at a maximum charge 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, to a minimum discharge voltage of 2.0 V to 2.6 V.

[0088] Additionally, the initial discharge may be performed at a discharge rate of, for example, 0.1C to 1.2C, or 0.1C to 0.9C.

[0089] In addition, the initial charge and discharge steps for the above-described activation may be performed as a single charge / discharge step. When the initial charge and discharge steps are performed multiple times, it has been confirmed that the initial capacity characteristics of the lithium secondary battery are rather reduced. This is presumed to be because, during the activation process, the rock salt structure, etc. are excessively activated, and some of the excess lithium is lost during the excessive activation process. Therefore, in order to maximize the capacity characteristics of the lithium secondary battery, the initial charge and discharge steps for the activation are preferably performed as a single charge and discharge step, respectively.

[0090] Meanwhile, the activation method of the above-described embodiment may further include, if necessary, a step of aging the lithium secondary battery at a temperature of 40°C or higher after the initial charge / discharge step. This aging step may be 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.

[0091] 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 high capacity characteristics of the cathode active material, the amount of gas generated during operation of the lithium secondary battery can be reduced, and the life characteristics of the lithium secondary battery can be further improved.

[0092]

[0093] 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.

[0094]

[0095] [Manufacturing Example]: Manufacturing of Lithium Secondary Battery

[0096] Li as a cathode active material 1.12 Ni 0.31 Co 0.01 Mn 0.56 A cathode slurry was prepared by adding lithium manganese oxide having a composition of O2, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1.5:2.5. The cathode slurry was applied to a cathode current collector (Al thin film) having a thickness of 12 μm, and drying and roll pressing were performed to prepare a cathode.

[0097] A negative electrode slurry was prepared by adding graphite as a negative electrode active material, SBR-CMC as a binder, carbon black as a conductive material, and a thickener to water as a solvent at a weight ratio of 95.65:2.3:1.0:1.05. The negative electrode slurry was applied to an 8 μm thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll pressed to prepare a negative electrode.

[0098] The electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 and then dissolving LiPF6 to make 1M.

[0099] 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.

[0100]

[0101] Reference example 1.

[0102] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and constant current charging was performed at a rate of 0.1 C at room temperature (25°C) to activate up to 4.65 V.

[0103] After reaching the charging voltage of 4.65 V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at room temperature (25°C) until the current value reached 0.1 C to 0.05 C, and then terminated.

[0104] 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 0.1 C at the same room temperature (25°C).

[0105]

[0106] Reference example 2.

[0107] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and constant current charging was performed at a rate of 0.1 C at 45°C to activate up to 4.65 V.

[0108] After reaching the charging voltage of 4.65 V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at 45°C until the current value reached 0.1 C to 0.05 C, and then terminated.

[0109] Afterwards, the lithium secondary battery was activated by performing a constant current discharge up to 2.0 V at a discharge rate of 0.1 C while the battery was cooled to room temperature (25°C).

[0110]

[0111] Reference example 3.

[0112] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and constant current charging was performed at a rate of 0.1 C at 45°C to activate up to 4.65 V.

[0113] After reaching the charging voltage of 4.65 V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at 45°C until the current value reached 0.1 C to 0.05 C, and then terminated.

[0114] 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 0.1 C at the same temperature (45°C).

[0115]

[0116] Example 1: Activation charge / discharge in a single step

[0117] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and constant current charging was performed at a rate of 0.1 C at room temperature (25°C) to activate up to 4.65 V.

[0118] After reaching the charging voltage of 4.65 V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at room temperature (25°C) until the current value reached 0.1 C to 0.05 C, and then terminated.

[0119] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge up to 2.0 V at a discharge rate of 0.1 C while the temperature was raised to 45°C.

[0120]

[0121] Example 2: Activation charge / discharge is performed in multiple steps.

[0122] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger and discharger, and constant current charging was performed at a rate of 0.1 C at room temperature (25°C) to activate up to 4.35 V.

[0123] After reaching the charging voltage of 4.35 V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at room temperature (25°C) until the current value reached 0.1 C to 0.05 C, and then terminated.

[0124] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge up to 2.0 V at a discharge rate of 0.1 C while the temperature was raised to 45°C.

[0125] Constant current charging was then performed again at room temperature (25°C) at a rate of 0.1C to activate the battery up to 4.65V. After reaching the charging voltage of 4.65V, constant voltage charging was performed while maintaining this charging voltage. This constant voltage charging was performed at room temperature (25°C) until the current value reached 0.1C to 0.05C, and then terminated.

[0126] Afterwards, the activation process of the lithium secondary battery was performed by performing a constant current discharge up to 2.0 V at a discharge rate of 0.1 C while the temperature was raised to 45°C.

[0127]

[0128] Test example:

[0129] First, for Reference Example 1 and Example 1, the charge capacity and discharge capacity were measured during the activation process, respectively. The charge capacity was measured in the low voltage region up to 4.3 V (Q CR ) and charge capacity (Q) in the high voltage range from 4.3 V to 4.65 V. AR ) was divided and measured, and together with the discharge capacity (Q dichg ) was measured. The measurement data of Reference Example 1 and Example 1, which had different initial discharge temperatures, are compared and shown in Fig. 1.

[0130] Referring to Figure 1, when the activation method of Example 1 was used, it was confirmed that a higher discharge capacity was developed through initial discharge at high temperatures. This appears to be because additional capacity development through the oxidation / reduction reaction of oxygen anions was smoothly and reversibly achieved.

[0131] Additionally, for lithium secondary batteries manufactured through the activation process in Example 1 and Reference Example 1, the gas generated during additional charge and discharge cycles was captured and the amount of gas generated was quantitatively analyzed using GC-FID / TCD. The results of the analysis of the amount of activated gas generated are shown in comparison in Figures 2a and 2b.

[0132] Referring to FIGS. 2a and 2b, it was confirmed that the lithium secondary battery that underwent the activation process of Example 1 exhibited a significantly reduced amount of gas generation compared to Reference Example 1.

[0133] In addition, a charge and discharge test was conducted by charging the lithium secondary batteries of Reference Examples 1 to 3 and Example 1 to 4.35 V under 1 / 3C CC-CV (CV 5%) conditions and then discharging them to 2.0 V under 1 / 3C CC conditions. The capacity retention rate was evaluated while performing these charge and discharge cycles for 100 cycles, and the results are shown in Fig. 3.

[0134] Referring to FIG. 3, it was confirmed that the lithium secondary battery that went through the activation process of Example 1 exhibited superior capacity retention and lifespan characteristics compared to Reference Examples 1 to 3.

[0135] Additionally, the activation process of Examples 1 and 2 and the charge and discharge tests immediately after activation were conducted. During the initial charge and discharge steps for activation and the charge and discharge steps immediately after activation, the charge capacity, discharge capacity, and efficiency were measured, respectively, and are summarized and presented in Table 1 below:

[0136] First charge / discharge stage upon activation Second charge / discharge stage upon activation Charge / discharge stage immediately after activation Charge capacityDischarge capacity Efficiency Charge capacityDischarge capacity Efficiency Charge capacityDischarge capacity Efficiency mAh / gmAh / g% mAh / gmAh / g% mAh / gmAh / g% Example 1308.3276.889.8 Not in progress 215.1202.093.9 Example 2133.5131.098.1296.9270.691.2208.0194.593.5

[0137] Referring to Table 1 above, it was confirmed that relatively high initial capacity and efficiency were achieved by the activation methods of Examples 1 and 2. In particular, it was confirmed that higher initial capacity and initial efficiency were achieved in Example 1, in which the charge and discharge steps for activation were performed in a single step, compared to Example 2, in which the charge and discharge steps for activation were performed multiple times.

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, For the above lithium secondary battery, a step of performing charging at a first temperature and a step of performing discharging at a second temperature that is 15°C or higher than the first temperature are included. A method for activating a lithium secondary battery, wherein the lithium metal oxide contains manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium.

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[Ni 1-y-z-w Mr y Co z M w ]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. In the third paragraph, the lithium metal oxide is Li2MnO3 having a rock salt structure and Li[Ni having a layered structure. 1-y-z-w Mn y Co z M w ]A method for activating a lithium secondary battery containing O2 in a mixed state.

5. A method for activating a lithium secondary battery in accordance with claim 1, wherein the charging and discharging steps are performed in a single step.

6. A method for activating a lithium secondary battery in the first paragraph, wherein the first temperature is 20 to 30°C and the second temperature is 40 to 50°C.

7. A method for activating a lithium secondary battery in accordance with claim 1, wherein the charging and discharging steps are performed between a minimum discharge voltage of 2.0 to 2.6 V and a maximum charge voltage of 4.3 to 4.7 V.

8. A method for activating a lithium secondary battery in the first paragraph, wherein the charging step is performed in a CC-CV charging mode in which constant current (CC) charging is performed up to a certain charging voltage and then constant voltage (CV) charging is performed.

Images