Lithium secondary battery driving method

Abstract

The present invention relates to a lithium secondary battery driving method capable of suppressing a voltage sag during driving while enhancing lifespan characteristics of a lithium secondary battery comprising an overlithiated manganese-rich-based oxide as a positive electrode active material, the method having the effect of enabling the effective manifestation of additional capacity resulting from a manganese redox reaction, by means of, while a charge-discharge cycle is progressing, progressing a charge-discharge cycle having a lower minimum discharge voltage applied for each predetermined interval of the cycle.

Description

Method of operating a lithium secondary battery

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0094403, filed July 17, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a method for operating a lithium secondary battery capable of improving the life characteristics of a lithium secondary battery including a lithium manganese-rich oxide as a cathode active material and suppressing voltage sagging during operation.

[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, since the lithium manganese-rich oxide has a structure in which a layered lithium metal oxide and a lithium manganese oxide (Li2MnO3) having a rock salt structure are mixed, the lithium manganese oxide is additionally activated during the activation process and / or charge / discharge process, and the manganese redox reaction thereby can contribute to capacity development. Accordingly, interest in and research on the lithium manganese-rich oxide are greatly increasing as a next-generation cathode active material with high capacity characteristics and low manufacturing cost.

[0008] However, the typical operating voltage of a lithium secondary battery including the above lithium manganese-rich oxide is known to be 3.0 to 4.3 V. However, additional capacity development by the manganese redox reaction is not properly achieved at the typical operating voltage. As a result, when the lithium secondary battery is continuously driven under the typical operating voltage, the additional capacity development is not properly achieved, and there is a disadvantage in that the capacity retention rate and lifespan characteristics of the lithium secondary battery are deteriorated.

[0009] Conversely, if the lithium secondary battery is continuously operated under a changed voltage to develop additional capacity by the manganese redox reaction, there is a disadvantage in that the voltage sagging occurs, which causes structural changes and deterioration of the positive electrode active material, lowering the average discharge voltage, and ultimately lowering the long-term life characteristics of the lithium secondary battery.

[0010] Due to these problems, there is a continuous demand for a driving method that can improve the life characteristics of a lithium secondary battery including the above lithium manganese-rich oxide and suppress voltage drop, etc.

[0011] Accordingly, the present invention provides a method for operating a lithium secondary battery capable of improving the life characteristics and capacity retention rate of a lithium secondary battery including a lithium manganese-rich oxide as a cathode active material, while suppressing voltage sagging during operation.

[0012] According to one embodiment of the invention, there is provided a method for driving 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 lithium secondary battery, a first driving step of performing a charge and discharge cycle between a first minimum discharge voltage and a first maximum charge voltage; and

[0014] For the lithium secondary battery, a second driving step is included for performing a charge and discharge cycle between a second minimum discharge voltage and a second maximum charge voltage,

[0015] The above 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,

[0016] The second minimum discharge voltage has a lower value than the first minimum discharge voltage, and a method for driving a lithium secondary battery is provided, wherein the second driving step is performed at regular intervals during repeated performance of the first driving step.

[0017] According to the driving method of the lithium secondary battery of the present invention, by performing charge and discharge cycles at regular intervals with a lower minimum discharge voltage applied, additional capacity can be effectively developed through the manganese redox reaction.

[0018] In addition, in the remaining charge and discharge cycles, by applying a relatively high minimum discharge voltage, it is possible to suppress the voltage drop that occurs during operation of the lithium secondary battery.

[0019] Therefore, according to the above driving method, the capacity retention rate and life characteristics of a lithium secondary battery can be further improved and voltage drop, etc. can be suppressed without changing the material of the positive electrode active material itself or the structure of the battery.

[0020] Figure 1 is a graph showing the results of capacity retention rate evaluation by cumulative energy for lithium secondary batteries of examples and comparative examples.

[0021] Figure 2 is a graph showing the results of evaluating the degree of voltage drop for lithium secondary batteries of examples and comparative examples.

[0022] A method for driving a lithium secondary battery according to one embodiment of the invention is a method for driving a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte including a positive electrode active material of lithium metal oxide,

[0023] For the lithium secondary battery, a first driving step of performing a charge and discharge cycle between a first minimum discharge voltage and a first maximum charge voltage; and

[0024] For the lithium secondary battery, a second driving step is included for performing a charge and discharge cycle between a second minimum discharge voltage and a second maximum charge voltage,

[0025] The above 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,

[0026] The second minimum discharge voltage may have a lower value than the first minimum discharge voltage, and the second driving step may be performed at regular intervals during repeated execution of the first driving step.

[0027] In the driving method of this embodiment, the lithium secondary battery including the lithium manganese rich oxide is driven in such a manner that a cycle with a lower minimum discharge voltage, i.e., a second driving stage, is performed at each predetermined cycle period of the first driving stage.

[0028] In this second driving stage, as charging / discharging is performed while the second minimum discharge voltage of the corresponding section is controlled to be lower, for example, 2.0 to 2.6 V or 2.1 to 2.5 V, additional capacity development by the manganese redox reaction is effectively achieved, and the capacity retention rate of the lithium secondary battery can be further improved.

[0029] However, if such a low minimum discharge voltage and second driving stage are continuously applied, irreversible structural changes or degradation of the lithium manganese-rich oxide may occur, resulting in a voltage drop that continuously lowers the average discharge voltage of the lithium secondary battery. Due to this voltage drop, the overall energy density, which considers both capacity and voltage, may continuously decrease, and consequently, the life characteristics of the lithium secondary battery may deteriorate.

[0030] In contrast, in the driving method of one embodiment, since the second driving step is performed at a certain interval for each cycle period, structural change or deterioration of the lithium manganese rich oxide can be relatively suppressed, and as a result, the voltage drop and deterioration of life characteristics can be suppressed.

[0031] Therefore, according to the driving method of one embodiment, the capacity retention rate and life characteristics of a lithium secondary battery including lithium manganese rich oxide can be further improved while suppressing voltage drop, etc.

[0032]

[0033] Hereinafter, a method for driving a lithium secondary battery according to an embodiment of the invention will be described in more detail.

[0034] In the driving method of the lithium secondary battery of the above embodiment, the lithium secondary battery includes, as a positive electrode active material, a lithium metal oxide having a manganese content of 50 mol% or more and less than 100 mol% among all metals excluding lithium, for example, a lithium manganese-rich oxide. More specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and an electrolyte including such a positive electrode active material.

[0035] In a specific embodiment, the lithium metal oxide that becomes the lithium manganese rich oxide may be represented by the following chemical formula 1.

[0036] [Chemical Formula 1]

[0037] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0038] In the above chemical formula 1,

[0039] 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,

[0040] 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.

[0041] 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 1.1≤a≤1.3일 수 있다. a가 상기 범위를 만족할 때, 고용량을 구현할 수 있다.

[0042] 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.

[0043] The above c is a molar ratio of the doping 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 doping element M may be, for example, Co, and if the content of the doping element is too high, it may not only have a negative effect on the capacity of the active material, but also increase the oxygen oxidation / reduction reaction, which may aggravate gas generation and deterioration of the positive electrode active material, and may deteriorate the life characteristics.

[0044] 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 phase is too small, so that the negative electrode irreversible compensation and capacity improvement effects are minimal.

[0045] In the case of such lithium manganese-rich oxide, it may have a structure in which a layered lithium metal oxide and a rock salt structured lithium manganese oxide (Li2MnO3) are mixed. Among these, the rock salt structured lithium manganese oxide is activated at a high voltage of, for example, 4.6 V or higher to generate an excess of ions, and can contribute to additional capacity development by causing a manganese redox reaction under the second minimum discharge voltage of the second driving stage.

[0046] Accordingly, the driving method of one embodiment may further include a step of activating the lithium secondary battery after preparing the lithium secondary battery and before the first driving step described below. This activation step may be performed under a voltage of 4.6 V or higher, or a voltage of 4.6 V to 4.9 V. By performing this activation step, the capacity retention rate and lifespan characteristics of the lithium secondary battery may be further improved. In a more specific example, the activation may be performed, for example, through a process of charging to a voltage of 4.6 V or higher at 0.1 C at 45° C. and then discharging to 2.0 V at 0.1 C, but is not limited thereto.

[0047] Meanwhile, in the lithium manganese-rich oxide represented by the above chemical formula 1, the molar ratio of Li to the molar ratio of all metal elements excluding Li (Li / Me) may be 1.2 to 1.5, or 1.25 to 1.5, or 1.30 to 1.45. When the Li / Me ratio satisfies the above range, the rate characteristics and capacity characteristics are excellent. If the Li / Me ratio is too high, the electrical conductivity may decrease and the rock salt phase (Li2MnO3) may increase, which may accelerate the degradation rate, and if it is too low, the effect of improving the energy density is minimal.

[0048] Meanwhile, the composition of the above lithium manganese rich oxide may be represented by the following chemical formula 2:

[0049] [Chemical Formula 2]

[0050] X Li2MnO3·(1-X)Li[Ni 1-y-z Mn y M z ]O2

[0051] In the above chemical formula 2,

[0052] 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,

[0053] 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.5.

[0054] The above X refers to the ratio of the Li2MnO3 phase (rock salt structure compound 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 in the lithium manganese rich oxide 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 structure compound phase, 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 ]; in the layered structure compound), the molar ratio of the doping element M may be 0≤z≤0.5, 0≤z≤0.3, or 0≤z≤0.1.

[0057] Meanwhile, the positive electrode active material may further include a coating layer on the surface of the lithium manganese-rich oxide, if necessary. When the positive electrode active material includes a coating layer, the contact between the lithium manganese-rich oxide and the electrolyte is suppressed by the coating layer, thereby reducing electrolyte side reactions, thereby improving the life characteristics.

[0058] The above coating layer comprises a coating element M 1 may include the coating element M 1 For example, the coating element M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, preferably Al, Co, Nb, W and combinations thereof, and more preferably Al, Co and combinations thereof. 1It may contain two or more kinds, for example, it may contain Al and Co.

[0059] The above coating element is in the form of oxide within the coating layer, i.e., M 1 It can exist as Oz(1≤z≤4).

[0060] The above coating layer can be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, formation through atomic layer deposition is preferable because it can form a large coating layer area.

[0061] In addition, the formation area of ​​the coating layer may be 10% to 100%, or 30% to 100%, or 50% to 100% based on the total surface area of ​​the lithium manganese-rich oxide particles. When the formation area of ​​the coating layer satisfies the above range, the effect of improving the life characteristics is excellent.

[0062] Meanwhile, the above-described positive electrode active material 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.

[0063] 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.

[0064] Meanwhile, the above lithium manganese-rich oxide can be manufactured by mixing a transition metal precursor and a lithium raw material and then calcining them. However, since this manufacturing method can follow the general manufacturing process and conditions for lithium manganese-rich oxide known in the past, further description thereof will be omitted.

[0065] In addition, a lithium secondary battery to which the driving method of one embodiment is applied may follow the configuration of a general lithium secondary battery, except that the above-described lithium manganese-rich oxide is used as a positive electrode active material. For example, the lithium secondary battery may be manufactured by sequentially laminating and drying a positive electrode including a positive electrode active material and a negative electrode including an negative electrode active material, and then inserting the electrode assembly into a case and sealing it by selectively injecting an electrolyte therein. The lithium secondary battery may be a cylindrical, square, coin-shaped, or pouch-shaped battery.

[0066] 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.

[0067] The composition for forming a positive electrode active material layer may optionally further include a binder, a conductive material, a filler, etc., in addition to the positive electrode active material including the lithium manganese rich oxide, as needed. The composition for forming a negative electrode active material layer may optionally further include a binder, a conductive material, a filler, etc., in addition to the negative electrode active material, as needed.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In a specific example, the electrolyte may be a liquid electrolyte comprising an organic solvent and a lithium salt.

[0085] 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.

[0086] 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.

[0087] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0088] Meanwhile, in the driving method of one embodiment, a first driving step is performed to perform a charge / discharge cycle between a first minimum discharge voltage and a first maximum charge voltage for the lithium secondary battery described above. In this first driving step, the first minimum discharge voltage may be 2.8 to 3.2 V, or 2.9 to 3.1 V, and the first maximum charge voltage may be 4.1 to 4.5 V, or 4.2 to 4.4 V.

[0089] In this first driving step, the metal cation redox reaction mainly included in the layered structure compound contributes to capacity development, and structural changes or degradation of the lithium manganese-rich oxide are suppressed, thereby allowing normal charge / discharge and driving of the lithium secondary battery. However, under the first minimum discharge voltage at which the first driving step is performed, the manganese redox reaction mainly by the rock salt structure compound and additional capacity development thereby are difficult, so if only the first driving step is continuously performed, the capacity retention rate of the lithium secondary battery may decrease. On the other hand, if the first minimum discharge voltage becomes excessively high, capacity development by the metal cation redox reaction of the layered structure compound may not be properly performed.

[0090] In this embodiment, in the driving method, during the repeated execution of the first driving step, a second driving step is performed at regular intervals, applying a lower second minimum discharge voltage. This second driving step may perform a charge / discharge cycle between, for example, a second minimum discharge voltage lower than the first minimum discharge voltage and a second maximum charge voltage.

[0091] In a more specific example, the second minimum discharge voltage may be 2.0 to 2.6 V, or 2.1 to 2.5 V, and the second maximum charge voltage may be 4.1 to 4.5 V, or 4.2 to 4.4 V. In this way, in the second driving stage, as a lower second minimum discharge voltage is applied, the manganese redox reaction by the rock salt structure compound and the additional capacity development thereby can be effectively performed.

[0092] However, in order to develop this additional capacity, if a lower second minimum discharge voltage is continuously applied or the minimum discharge voltage is continuously lowered, structural changes or deterioration of the lithium manganese-rich oxide may continue to occur, which may cause a voltage drop in the lithium secondary battery and ultimately significantly deteriorate the long-term life characteristics.

[0093] Accordingly, in the driving method of one embodiment, for example, by performing the first driving step 2 to 15 times, or 2 to 14 times, or 3 to 13 times, and then regularly performing the second driving step 1 to 2 times, the capacity development by the manganese redox reaction can be made more efficient while structural change or degradation of the lithium manganese-rich oxide can be suppressed. As a result, the capacity retention rate and life characteristics of a lithium secondary battery including the lithium manganese-rich oxide can be improved while voltage drop can be dramatically suppressed.

[0094] Meanwhile, in the driving method of the above embodiment, the charging of the first and second driving stages may be performed at a rate of 0.05 C to 2 C, or 0.1 C to 1.5 C, or 0.2 C to 1.2 C. In addition, the discharging of the first and second driving stages may be performed at a rate of 0.05 C to 3 C, or 0.1 C to 2 C, or 0.2 C to 1.2 C.

[0095] Additionally, in the above driving method, charging can be performed in a CC-CV (constant current-constant voltage) manner, and discharging can be performed in a CC (constant current) manner.

[0096]

[0097] 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.

[0098]

[0099] [Manufacturing example]

[0100] Li as a cathode active material 1.16 Ni 0.305 Co 0.004 Mn 0.531 A cathode slurry was prepared by adding lithium manganese-rich oxide having a composition of O2, carbon nanotubes as a conductive agent, polyvinylidene fluoride as a binder, and NBR as a dispersant to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.46:0.62:1.70:0.22. 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.

[0101] A negative electrode slurry was prepared by adding graphite and SiO (90:10 mixture) as negative active materials, carbon black as a conductive agent, SBR as a binder, and CMC as a thickener to water as a solvent at a weight ratio of 95.6:1.0:2.3:1.1. The negative electrode slurry was applied to a copper (Cu) thin film as a negative electrode current collector with a thickness of 8 μm, dried, and then roll pressed to prepare a negative electrode.

[0102] 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 1.0 M.

[0103] 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.

[0104]

[0105] [Example]

[0106] Example 1.

[0107] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger / discharger, and each was charged to SOC 100% (4.6 V) at 45°C at a rate of 0.1C for about 10 hours, then discharged to SOC 0% (2.0 V) at 45°C at a rate of 0.1C for about 10 hours to perform an activation (formation) process, and then aged at 60°C for 15 hours and then a degassing process was performed.

[0108] For the lithium secondary battery that had been degassed, the process of charging and discharging 9 times under the first charging and discharging conditions below and then charging and discharging once under the second charging and discharging conditions below was repeated 10 times, for a total of 100 charging and discharging cycles.

[0109] -First charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 3.0 V at a rate of 0.33 C under CC conditions.

[0110] -Second charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 2.5 V at a rate of 0.33 C under CC conditions.

[0111]

[0112] Example 2.

[0113] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger / discharger, and each was charged to SOC 100% (4.6 V) at 45°C at a rate of 0.1C for about 10 hours, then discharged to SOC 0% (2.0 V) at 45°C at a rate of 0.1C for about 10 hours to perform an activation (formation) process, and then aged at 60°C for 15 hours and then a degassing process was performed.

[0114] For the lithium secondary battery after degassing, the process of charging and discharging four times under the first charging and discharging condition below and then charging and discharging once under the second charging and discharging condition below was repeated 20 times, for a total of 100 charging and discharging cycles.

[0115] -First charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 3.0 V at a rate of 0.33 C under CC conditions.

[0116] -Second charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 2.5 V at a rate of 0.33 C under CC conditions.

[0117]

[0118] Example 3.

[0119] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger / discharger, and each was charged to SOC 100% (4.6 V) at 45°C at a rate of 0.1C for about 10 hours, then discharged to SOC 0% (2.0 V) at 45°C at a rate of 0.1C for about 10 hours to perform an activation (formation) process, and then aged at 60°C for 15 hours and then a degassing process was performed.

[0120] For the lithium secondary battery after degassing, the process of charging and discharging once under the first charging and discharging condition below and then charging and discharging once under the second charging and discharging condition below was repeated 50 times, for a total of 100 charging and discharging cycles.

[0121] -First charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 3.0 V at a rate of 0.33 C under CC conditions.

[0122] -Second charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 2.5 V at a rate of 0.33 C under CC conditions.

[0123]

[0124] Comparative Example 1.

[0125] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger / discharger, and each was charged to SOC 100% (4.6 V) at 45°C at a rate of 0.1C for about 10 hours, then discharged to SOC 0% (2.0 V) at 45°C at a rate of 0.1C for about 10 hours to perform an activation (formation) process, and then aged at 60°C for 15 hours and then a degassing process was performed.

[0126] For the lithium secondary battery after degassing, a total of 100 charge-discharge cycles were performed under the following first charge-discharge conditions.

[0127] -First charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 3.0 V at a rate of 0.33 C under CC conditions.

[0128]

[0129] Comparative Example 2.

[0130] The lithium secondary battery manufactured in the above manufacturing example was connected to a PNE charger / discharger, and each was charged to SOC 100% (4.6 V) at 45°C at a rate of 0.1C for about 10 hours, then discharged to SOC 0% (2.0 V) at 45°C at a rate of 0.1C for about 10 hours to perform an activation (formation) process, and then aged at 60°C for 15 hours and then a degassing process was performed.

[0131] For the lithium secondary battery after degassing, a total of 100 charge-discharge cycles were performed under the following second charge-discharge conditions.

[0132] -Second charge / discharge: Charged to 4.3 V at a rate of 0.33 C at 45°C under CC-CV (constant current-constant voltage) conditions, and discharged to 2.5 V at a rate of 0.33 C under CC conditions.

[0133]

[0134] [Experimental Example: Capacity Retention Rate and Voltage Drop Measurement]

[0135] As in the above examples and comparative examples, the capacity retention rate and voltage drop were measured through the process of measuring the capacity, discharge energy, and discharge average voltage corresponding to each cycle while performing charge and discharge. Fig. 1 shows the results of evaluating the capacity retention rate by cumulative energy for the lithium secondary batteries of the examples and comparative examples, and Fig. 2 shows the results of evaluating the degree of voltage drop for the lithium secondary batteries of the examples and comparative examples. For reference, in the driving methods of example 1 (mix (9+1)), example 2 (mix (4+1)), and example 3 (mix (1+1)), since the voltage ranges of the first and second charge and discharge conditions are different from each other, the energy range (retention rate) and discharge average voltage (degree of voltage drop) are derived differently for each charge and discharge condition. Accordingly, the data for each charge and discharge condition is displayed separately as upper and lower data.

[0136] Referring to Figures 1 and 2, it was confirmed that the lithium secondary battery to which the operating conditions of Examples 1 to 3 were applied exhibited a voltage drop similar to that of Comparative Example 1 (4.3-3.0 V), while exhibiting a capacity retention rate superior to that of Comparative Example 1. It was confirmed that the capacity retention rates of Examples 2 and 3 were superior.

[0137] Meanwhile, when the operating conditions of Comparative Example 2 (4.3-2.5 V) were applied, the capacity retention rate was relatively high (see Fig. 1), but as shown in Fig. 2, a large voltage drop occurred, which resulted in significant structural changes and degradation of the positive electrode active material, and as a result, it was confirmed that the life characteristics were very poor.

Claims

1. A method for driving 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 lithium secondary battery, a first driving step of performing a charge and discharge cycle between a first minimum discharge voltage and a first maximum charge voltage; and For the lithium secondary battery, a second driving step is included for performing a charge and discharge cycle between a second minimum discharge voltage and a second maximum charge voltage, The above 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, A driving method for a lithium secondary battery, wherein the second minimum discharge voltage has a lower value than the first minimum discharge voltage, and the second driving step is performed at regular intervals during repeated performance of the first driving step.

2. In the first paragraph, the lithium metal oxide is a driving method of a lithium secondary battery 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 driving method of 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 operating 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 driving a lithium secondary battery according to claim 1, wherein the first minimum discharge voltage is 2.8 to 3.2 V, and the second minimum discharge voltage is 2.0 to 2.6 V.

6. A method for driving a lithium secondary battery according to claim 1, wherein the first and second maximum charging voltages are 4.1 to 4.5 V.

7. A method for driving a lithium secondary battery, wherein, in the first paragraph, the step of performing the first driving step 1 to 15 times and then performing the second driving step 1 to 2 times is repeated.

8. In paragraph 1, A method for driving a lithium secondary battery, further comprising a step of activating (forming) the lithium secondary battery before the first driving step.

9. A method for driving a lithium secondary battery in accordance with claim 8, wherein the activation step is performed under a voltage of 4.6 V or higher.

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