Activation method of lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to an activation method of a lithium secondary battery and a lithium secondary battery manufactured by the activation method, wherein the activation method comprises: Step 1: preparing a secondary battery comprising a cathode having a sacrificial cathode material represented by Formula 1 and having an orthorhombic structure, an anode, a separator disposed between the cathode and the anode, and an electrolyte; and Step 2: charging the secondary battery and then maintaining the secondary battery at a voltage of 3.2 V or more for a predetermined period of time.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2020-0121825, filed on September 21, 2020, the disclosure of which is incorporated herein by reference.

[0002] The present application relates to an activation method of a lithium secondary battery and a lithium secondary battery. BACKGROUND

[0003] With the development of technology and the increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0004] Generally, a lithium secondary battery is manufactured in the following manner. A composition for forming an electrode active material layer containing an electrode active material is coated on an electrode current collector, and then dried to manufacture an electrode (a positive electrode and a negative electrode). A separator is inserted between the positive electrode and the negative electrode to form an electrode assembly, and the electrode assembly is inserted into a battery case and sealed. Thereafter, in order to determine whether the secondary battery has a defect and to ensure the stability of the performance of the secondary battery, particularly, the service life, an activation process must be performed before the product is shipped. The activation process is to repeat charging and discharging to activate the battery and remove gas therefrom. On the other hand, when the secondary battery is charged, lithium ions originating from lithium metal oxide used as a positive electrode move and are intercalated into a carbon electrode used as a negative electrode. At this time, compounds such as Li2CO3, LiO, LiOH, etc. are generated from the carbon (crystalline or amorphous) electrode due to the high reactivity of lithium. Then, the compounds such as Li2CO3, LiO, LiOH, etc. form a solid electrolyte interface (SEI) film on the surface of the negative electrode. On the other hand, irreversibility occurs between the positive electrode and the negative electrode due to the solid electrolyte interface film. Therefore, there is a problem that the energy density of the lithium secondary battery is reduced.

[0005] In order to prevent the problem, there is a method of using Li2NiO2 as a sacrificial positive electrode material. However, Li2NiO2 has an orthorhombic crystal structure with a space group of Immm in a lithium secondary battery in which the activation process is completed, thereby there is a problem that impurities or gas are generated because a three-step structural change (orthorhombic crystal structure with Immm space group → trigonal crystal structure with R-3m space group → monoclinic crystal structure with C2 / m space group) occurs within a usable voltage range after the activation process.

[0006] Therefore, there is a need for a method capable of solving the problem that impurities or gas are generated within a usable voltage range. SUMMARY

[0007] Technical problem

[0008] One aspect of the present application provides a method of activating a lithium secondary battery, which is capable of adjusting a crystal structure of a sacrificial cathode material, thereby minimizing side effects of the sacrificial cathode material occurring in a usable voltage range.

[0009] Technical solution

[0010] According to one aspect of the present application, there is provided a method of activating a lithium secondary battery, the method including:

[0011] Step 1: preparing a secondary battery including a cathode having a sacrificial cathode material represented by the following Formula 1 and having an orthorhombic structure, an anode, a separator disposed between the cathode and the anode, and an electrolyte; and

[0012] Step 2: charging the secondary battery, and then maintaining the secondary battery at a voltage of 3.2 V or more for a predetermined period of time.

[0013] [Formula 1]

[0014] Li2Ni 1-x M x O2

[0015] M is one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0016] 0≤x<0.9.

[0017] According to another aspect of the present application, there is provided a lithium secondary battery, which is a secondary battery including a cathode containing a sacrificial cathode material represented by the following Formula 2, an anode, a separator disposed between the cathode and the anode, and an electrolyte, wherein the sacrificial cathode material is a single phase having a trigonal structure in a discharged state.

[0018] [Formula 2]

[0019] LiNi 1-x M x O2

[0020] M is one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0021] 0≤x<0.9.

[0022] Beneficial effects

[0023] The method of activating a lithium secondary battery of the present application includes a process of converting a crystal structure of a sacrificial cathode material from an orthorhombic structure to a trigonal structure so that lithium ions can be easily supplemented during initial charging, and can provide a sacrificial cathode material having a crystal structure capable of minimizing side effects within a usable voltage range. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a view showing XRD patterns measured using in-situ XRD on a sacrificial cathode material during activation of a secondary battery of Example 1 and on the sacrificial cathode material during charging of the secondary battery after activation;

[0025] Figure 2 is a view showing XRD patterns measured using non-in-situ XRD on a sacrificial cathode material contained in a secondary battery of Comparative Example 1 after charging the secondary battery to SOC 30, 60, and 90 after a typical activation process;

[0026] Figure 3 is a view showing gas volumes generated during initial baseline performance tests of various secondary batteries manufactured in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0027] Hereinafter, the present application will be described in greater detail.

[0028] It is to be understood that the words or terms used in the specification and claims of this application should not be construed as limited to having the meanings defined in commonly used dictionaries. It will be further understood that the words or terms used in the specification and claims should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the present application.

[0029] Activation method of lithium secondary battery

[0030] The method of activating a lithium secondary battery according to the present application includes:

[0031] Step 1: preparing a secondary battery containing a cathode having a sacrificial cathode material represented by Formula 1 below and having an orthorhombic structure, an anode, a separator disposed between the cathode and the anode, and an electrolyte; and

[0032] Step 2: charging the secondary battery, and then maintaining the secondary battery at a voltage of 3.2 V or more for a predetermined period of time.

[0033] [Formula 1]

[0034] Li2Ni1-x M x O2

[0035] In the above Formula 1,

[0036] M is one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0037] 0≤x<0.9.

[0038] The activation method of the lithium secondary battery can further include a pre-aging step of preliminarily aging the secondary battery at room temperature before performing Step 2.

[0039] Further, the activation method of the lithium secondary battery can further include a room temperature aging step of aging the secondary battery after Step 2 at room temperature, a high temperature aging step of aging the secondary battery after the secondary aging at high temperature, and a degassing step of removing gas from the secondary battery after the tertiary aging.

[0040] Further, the activation method of the lithium secondary battery can further include a step of determining whether the secondary battery has a defect after performing the degassing step.

[0041] Hereinafter, the activation method of the lithium secondary battery according to the present application will be described in detail.

[0042] Step 1

[0043] Step 1 is a step of preparing a secondary battery including a positive electrode having a sacrificial positive electrode material represented by the following Formula 1 and having an orthorhombic structure, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0044] [Formula 1]

[0045] Li2Ni 1-x M x O2

[0046] M is one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0047] 0≤x<0.9.

[0048] The crystal structure of the sacrificial positive electrode material can be completely converted from the orthorhombic structure to the trigonal structure by Step 2.

[0049] The sacrificial positive electrode material is a material that compensates for lithium ions consumed in the formation of the SEI layer or in by-products. The sacrificial positive electrode material is a material that easily releases lithium, and because lithium is released through the following Step 2, the crystal structure of the sacrificial positive electrode material represented by the above Formula 1 and having an orthorhombic system is permanently transformed from an orthorhombic system structure to a thermodynamically stable trigonal system structure.

[0050] The secondary battery can specifically include one or more unit electrodes including a positive electrode and a negative electrode, and an electrode assembly in which a separator interposed between the unit electrodes is wound can be implanted in a battery case. The secondary battery can be a cylindrical, square, or pouch-type secondary battery.

[0051] The positive electrode and the negative electrode can be manufactured by applying a composition for forming an active material layer including an electrode active material to each current collector, followed by drying.

[0052] The composition for forming a positive electrode active material layer can selectively include a binder, a conductive material, a filler, and the like, as necessary, in addition to the sacrificial positive electrode material represented by the above Formula 1 and having an orthorhombic structure and the positive electrode active material. The composition for forming a negative electrode active material layer can selectively include a binder, a conductive material, a filler, and the like, as necessary, in addition to the negative electrode active material.

[0053] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon; aluminum or stainless steel treated with one of carbon, nickel, titanium, silver, and the like on the surface; an aluminum-cadmium alloy, and the like can be used. In addition, the current collector can generally have a thickness of 3 μm to 500 μm, and a fine concavo-convex can be formed on the surface of the current collector to improve the adhesion of the active material. For example, the current collector can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foamed body, and a nonwoven fabric body.

[0054] The positive electrode active material is a material capable of causing an electrochemical reaction, and is a lithium transition metal oxide including two or more transition metals, and for example, can be: a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; a lithium nickel-based oxide represented by the formula LiNi 1- y M y LiNi0.7-yMyO2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, or Ga and includes one or more of the above elements, 0.01 ≤ y ≤ 0.7) represents a lithium nickel-based oxide; Li 1+z Ni b Mn c Co 1-(b+c+d) Md O (2-e) A e (wherein -0.5 ≤ z ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.1 ≤ c ≤ 0.8, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2 and b + c + d < 1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl) such as Li 1+z Ni 1 / 3 CO 1 / 3 Mn 1 / 3 O2or Li 1+z Ni 0.4 Mn 0.4 CO 0.2 O2represents a lithium nickel cobalt manganese composite oxide; Li 1+x M 1-y M' y PO 4-z X z (wherein M = a transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, and -0.5 ≤ x ≤ +0.5, 0 ≤ y ≤ 0.5 and 0 ≤ z ≤ 0.1) represents an olivine-type lithium metal phosphate or the like, but is not limited thereto. The content of the positive electrode active material can be 80 to 99% by weight based on the total weight of the positive electrode active material layer.

[0055] As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples thereof can include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; (semi)metallic materials such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy which can form an alloy with lithium; (semi)metallic oxides such as SiO β (0 < β < 2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite material containing a (semi)metallic material and a carbonaceous material such as a Si-C composite material or a Sn-C composite material, and any one of these or a mixture of two or more of these can be used. In addition, as the negative electrode active material, a metal lithium thin film can be used. Furthermore, low-crystalline carbon, high-crystalline carbon or the like can be used as the carbon material. Representative examples of the low-crystalline carbon can be soft carbon and hard carbon, and representative examples of the high-crystalline carbon can include irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbead, mesophase pitch and high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke. The content of the negative electrode active material can be 80 to 99% by weight based on the total weight of the negative electrode active material layer.

[0056] The binder is a component that contributes to the binding between the conductive material, the active material, and the current collector, and the typical addition amount is 0.1 to 10% by weight, based on the total weight of the active material layer. Examples of the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber, nitrile butadiene rubber, fluororubber, various copolymers thereof, and the like.

[0057] The conductive material is a component for further improving the conductivity of the active material, and the addition amount can be 10% by weight or less, specifically 5% by weight or less, based on the total weight of the active material layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal crack black; conductive fibers such as carbon fibers and metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives, and the like can be used.

[0058] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used without particular limitation as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to the movement of electrolyte ions is preferable. Specifically, a porous polymer film, for example, a porous polymer film manufactured using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer; or a laminate structure having two or more layers thereof can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like, can be used. Furthermore, a coated separator containing a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and the coated separator can be selectively used in a single layer or a multi-layer structure.

[0059] In addition, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte, or the like, which can be used in the preparation of a lithium secondary battery, but is not limited thereto.

[0060] Specifically, the electrolyte can include an organic solvent and a lithium salt.

[0061] Any organic solvent can be used without particular limitation, as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol-based solvent such as ethanol and isopropanol; a nitrile such as R-CN (wherein R is a linear, branched, or cyclic C2-C20 hydrocarbon group and can include a double bond, an aromatic ring, or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or a sulfolane can be used. Among the above-mentioned solvents, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) having low viscosity is more preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution can be excellent.

[0062] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in the lithium secondary battery. Specifically, the anion of the lithium salt can be at least one selected from the group consisting of 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 -and as a lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. The lithium salt can be used in a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is in the above range, the electrolyte has a suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move efficiently.

[0063] In the electrolyte, in order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and increase the discharge capacity of the battery, one or more additives, such as a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylenediamine, a (condensed) glycol dimethyl ether, hexamethylphosphoramide, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. can be contained. At this time, the content of the additive can be 0.1 to 5% by weight, based on the total weight of the electrolyte.

[0064] Step 2

[0065] Step 2 is a step of charging the secondary battery and then maintaining the secondary battery at a voltage of 3.2 V or more for a predetermined period of time to transform the crystal structure of the sacrificial positive electrode material from an orthorhombic structure to a trigonal structure.

[0066] Specifically, Step 2 can be a step of charging the secondary battery at a C rate of 0.025 C to 0.2 C, preferably at a C rate of 0.05 C to 0.2 C, more preferably at a C rate of 0.05 C to 0.15 C, and then maintaining a predetermined voltage for a predetermined period of time to transform the crystal structure of the sacrificial positive electrode material from an orthorhombic structure to a trigonal structure. On the other hand, when the C rate is less than 0.020 C, the charging time increases, thereby there is a problem that the total time required for the activation process increases. When the C rate is greater than 0.2 C, charging is performed at a high rate, thereby the battery can be overloaded, resulting in overvoltage, and there is a problem that it is difficult to form a uniform SEI film.

[0067] When the secondary battery is charged to 3.2 V or more, preferably 3.5 V to 4.0 V, more preferably 3.6 V to 3.9 V, still more preferably 3.7 V to 3.9 V, and then maintained in the same voltage range for a predetermined period of time, the sacrificial positive electrode material of the orthorhombic structure is permanently transformed into the sacrificial positive electrode material of the trigonal structure.

[0068] In step 2, the time for maintaining the voltage can be 30 minutes or more, preferably 30 minutes to 6 hours, preferably 1 hour to 6 hours, and more preferably 2 hours to 5 hours. On the other hand, when the time for maintaining the voltage is less than 30 minutes, the crystal structure of the sacrificial cathode material can not be completely changed, and when the time is more than 6 hours, the productivity can be reduced due to an increase in the activation process time.

[0069] Step 2 can be, for example, a step of charging to 3.8 V at a C rate of 0.1C and then maintaining at a voltage of 3.8 V for 3 hours to convert the orthorhombic structure of the sacrificial cathode material having an Immm space group to a trigonal structure of the sacrificial cathode material having an R-3m space group.

[0070] The crystal structure of the sacrificial cathode material after step 2 is permanently converted to a trigonal structure.

[0071] The sacrificial cathode material after step 2 can be a single phase having a trigonal structure.

[0072] The sacrificial cathode material after step 2 can be converted only between a trigonal structure and a monoclinic structure in the usable voltage range (e.g., 2.5 V to 4.2 V) of an actual battery. Therefore, a three-step structure change (orthorhombic structure having an Immm space group → trigonal structure having an R-3m space group → monoclinic structure having a C2 / m space group) does not occur, and thus the amount of gas generated when a lithium secondary battery after the activation process according to the present application is stored for a long time at room temperature and at high temperature can be reduced.

[0073] The sacrificial cathode material having a trigonal structure can be represented by the following formula 2.

[0074] [Formula 2]

[0075] LiNi 1-x M x O2

[0076] In the above formula 2,

[0077] M is one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0078] 0 ≤ x < 0.9.

[0079] Pre-aging step

[0080] The pre-aging step is a step of preliminarily aging the secondary battery at room temperature before performing Step 2. Specifically, the pre-aging step is a step of leaving the secondary battery at room temperature for a certain amount of time so that the battery is impregnated with the injected electrolyte.

[0081] The pre-aging can be performed at room temperature and atmospheric pressure under conditions such that the electrolyte can be well infiltrated into the positive and negative electrodes, and can be performed for 24 to 72 hours, preferably 30 to 50 hours, more preferably 40 to 50 hours.

[0082] Room temperature aging step

[0083] The room temperature aging step is a step of secondarily aging the secondary battery after Step 2 at room temperature.

[0084] Through the room temperature aging step, the SEI film is more stable and is formed to have a uniform and uniform thickness without being partially uneven. That is, the SEI film is generally left at room temperature for a predetermined period of time to stabilize it. The room temperature aging improves the electrode impregnation performance of the battery electrolyte, thereby securing the capacity reliability of the battery.

[0085] The room temperature aging can be performed for 24 to 72 hours, preferably 30 to 50 hours, more preferably 40 to 50 hours.

[0086] High temperature aging step

[0087] The high temperature aging step is a step of thirdly aging the secondary battery after the secondary aging at a high temperature. The high temperature aging step is also a process of further stabilizing the SEI film and uniformly forming it by thermal energy and electrochemical energy.

[0088] The high temperature aging can be performed at 40 to 80°C, preferably 50 to 70°C, more preferably 55 to 65°C. When the temperature at which the high temperature aging is performed is less than 40°C, it is not good for further stabilization of the SEI film. When it is higher than 80°C, evaporation of the electrolyte can cause rupture of the outer material or cause the battery to catch fire, and there is a problem of degradation of the capacity and life of the battery.

[0089] The high temperature aging can be performed for 12 to 48 hours, preferably 20 to 40 hours, more preferably 20 to 30 hours.

[0090] Degassing step

[0091] The degassing step is a step of removing gas from the secondary battery after the third aging.

[0092] This is to remove the side reaction gas generated inside the battery due to the aging step, and the side reaction gas generated inside the battery can be removed through the degassing step. The gas generated in the aging step can cause the battery to swell, and thus the gas can be removed through the degassing process. The degassing process is performed by opening the seal of the battery case or having a separate gas removal device. When the battery case is opened to perform degassing, the opened portion can be resealed later.

[0093] Step of determining whether the secondary battery has a defect

[0094] The step of determining whether the secondary battery has a defect is to check abnormalities of the secondary battery, and can be performed using charge / discharge capacity data obtained by charging and discharging the secondary battery in a range of available voltage thereof.

[0095] Specifically, the step of determining whether the secondary battery has a defect can include:

[0096] a step of checking the battery capacity using charge / discharge capacity data obtained by charging and discharging in a range of 2.5 V to 4.2 V at a C rate of 0.1C; and

[0097] a step of checking the battery capacity using charge / discharge capacity data obtained by charging and discharging in a range of 2.5 V to 4.2 V at a C rate of C / 3, which is a charge / discharge rate used in an electronic product.

[0098] On the other hand, the lithium secondary battery manufactured according to the activation method according to the present application can be implemented such that the capacity thereof when charged and discharged at a C rate of C / 3 is 97% or more of the capacity thereof when charged and discharged at a C rate of 0.1C.

[0099] Lithium secondary battery

[0100] The lithium secondary battery according to the present application includes a positive electrode having a sacrificial positive electrode material represented by the following Formula 2, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0101] [Formula 2]

[0102] LiNi 1-x M x O2

[0103] In the above Formula 2,

[0104] M is one or more selected from Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W,

[0105] 0 < x < 0.9.

[0106] The sacrificial cathode material represented by the above Formula 2 and having a trigonal crystal structure can be a single phase having a trigonal crystal structure. The sacrificial cathode material of the trigonal crystal structure represented by Formula 2 can be prepared by adjusting the synthesis conditions at the time of synthesizing the sacrificial cathode material. However, when the trigonal crystal structure is formed by synthesis, the crystal structure is unstable, and appears in a state in which the trigonal crystal structure and the orthorhombic crystal structure coexist. However, when the crystal structure of the sacrificial cathode material is changed by a method such as maintaining charging at a voltage range of 3.2 V or more during the activation process for a predetermined period of time in the present invention, a single-phase trigonal crystal structure in which the orthorhombic crystal structure does not coexist can be formed. When the orthorhombic crystal structure is partially contained in the sacrificial cathode material, a three-step crystal structure change occurs among the orthorhombic crystal structure, the trigonal crystal structure, and the monoclinic crystal structure during the charging / discharging process of the battery, thereby reducing the effect of suppressing impurities and / or gas generation.

[0107] In contrast, the sacrificial cathode material contained in the secondary battery of the present invention is formed of a trigonal crystal single phase, so that only a crystal structure change between the trigonal crystal structure and the monoclinic crystal structure can occur within the usable voltage range (e.g., 2.5 V to 4.2 V) in which the battery is actually operated. Therefore, a three-step structure change (orthorhombic crystal structure having an Immm space group → trigonal crystal structure having an R-3m space group → monoclinic crystal structure having a C2 / m space group) does not occur, and thus the amount of gas generated when the lithium secondary battery after the activation process according to the present invention is stored for a long time at room temperature and at high temperature is reduced.

[0108] At this time, the trigonal crystal structure can have an R-3m space group, and the monoclinic crystal structure can have a C2 / m space group.

[0109] On the other hand, the sacrificial cathode material contained in the secondary battery of the present invention can be a material in which the lattice parameters a, c, and γ values of the unit cell are and γ = 120°. In this case, lithium ions can be easily deintercalated from the sacrificial cathode material during the initial charging process, and even when a crystal structure change between the trigonal crystal structure and the monoclinic crystal structure occurs within the usable voltage range (e.g., 2.5 V to 4.2 V) in which the battery is actually operated, the crystal structure is not significantly distorted, so that side effects can be minimized.

[0110] The lithium secondary battery can be a lithium secondary battery manufactured by the activation method according to the present invention.

[0111] Preferred Embodiments

[0112] Hereinafter, the present application will be described in detail with reference to the embodiments. However, the embodiments according to the present application can be modified in other various forms, and the scope of the present application should not be construed as being limited to the embodiments described below. The embodiments of the present application are provided to more fully describe the present application to those skilled in the art.

[0113] Preparation example

[0114] Li2NiO2 having an orthorhombic structure of Immm space group as a positive electrode material, LiNi 0.8 CO 0.1 Mn 0.1 , carbon nanotube as a conductive material, and PVdF as a binder were mixed in a weight ratio of 5.0:92.8:0.8:1.4 in an N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector, dried, and then calendered to manufacture a positive electrode.

[0115] Next, a negative electrode active material in which artificial graphite and natural graphite were mixed in a weight ratio of 9:1, Super C65 as a conductive material, SBR as a binder, and CMC as a thickening agent were mixed in a weight ratio of 95.6:1.5:2.3:1.1 in an N-methylpyrrolidone (NMP) solvent to prepare a negative electrode slurry. The negative electrode slurry was coated on one surface of a copper current collector, dried, and then calendered to manufacture a negative electrode.

[0116] A separator was interposed between the positive electrode and the negative electrode to manufacture an electrode assembly, and then the electrode assembly was placed in a battery case, and subsequently an electrolyte was injected thereto to manufacture a lithium secondary battery.

[0117] At this time, as the electrolyte, an electrolyte prepared by dissolving 1M of LiPF6 in an organic solvent in which ethylene carbonate:ethylmethyl carbonate:diethyl carbonate were mixed in a volume ratio of 3:4:3 was used.

[0118] Example

[0119] Example 1

[0120] The secondary battery manufactured in the preparation example was pre-aged at room temperature for 24 hours, and then charged to 3.8V at a C rate of 0.1C, and then maintained at a voltage of 3.8V for 3 hours to convert the crystal structure of the sacrificial positive electrode material from an orthorhombic structure to a trigonal structure. Then, the secondary battery containing the sacrificial positive electrode material whose crystal structure had been converted was aged at room temperature for 24 hours at room temperature, and then high-temperature aged at 60℃ for 24 hours. The case of the secondary battery after high-temperature aging was opened to degas, and then the opened portion was re-sealed.

[0121] The capacity of the battery was checked using charge / discharge capacity data obtained by charging and discharging in the range of 2.5 V to 4.2 V at a C rate of 0.1 C, and the capacity of the battery was checked using charge / discharge capacity data obtained by charging and discharging in the range of 2.5 V to 4.2 V at a C rate of C / 3, which is a charge / discharge rate used in electronic products, to manufacture a secondary battery of good quality.

[0122] Comparative example 1

[0123] The secondary battery manufactured in Preparation Example was pre-aged at room temperature for 24 hours, and then subjected to a process of charging at a C rate of 0.1 C until SOC 30 at room temperature, and then discharging 3 times. Then, the secondary battery containing the sacrificial positive electrode material whose crystal structure had been converted was aged at room temperature for 24 hours at room temperature, and then high-temperature aged at 60°C for 24 hours. The case of the secondary battery after high-temperature aging was opened to degas, and then the opened part was re-sealed.

[0124] The capacity of the battery was checked using charge / discharge capacity data obtained by charging and discharging in the range of 2.5 V to 4.2 V at a C rate of 0.1 C, and the capacity of the battery was checked using charge / discharge capacity data obtained by charging and discharging in the range of 2.5 V to 4.2 V at a C rate of C / 3, which is a charge / discharge rate used in electronic products, to manufacture a secondary battery of good quality.

[0125] Experimental example 1: Measurement of X-ray diffraction pattern

[0126] When the secondary battery was activated in Example 1, XRD data measurement was performed on the sacrificial positive electrode material (I) at the start of charging at a C rate of 0.1 C, the sacrificial positive electrode material (II) obtained after being charged to 3.8 V, and the sacrificial positive electrode material (III) after being held at a voltage of 3.8 V for three hours, using in-situ XRD (Empyrean, PANalytical Co., Ltd) (X-ray source: Mo sealed tube, 60 kV, 35 mA). In addition, when the secondary battery after activation in Example 1 was charged again at a C rate of 0.1 C, XRD data measurement was also performed on the sacrificial positive electrode material (IV) at 2.6 V and the sacrificial positive electrode material (V) at 3.8 V, using in-situ XRD (Empyrean, PANalytical Co., Ltd) (X-ray source: Mo sealed tube, 60 kV, 35 mA). The resulting data is shown in Figure 1

[0127] ​The good-quality secondary battery manufactured in Comparative Example 1 was charged to SOC 30, 60, and 90 at a C rate of 0.1C, and then XRD data measurement was performed on the sacrificial positive electrode material contained in the secondary battery using an ex situ XRD (D8 Endeavor, Bruker Co., Ltd.) (X-ray source: Cu sealed tube, 40 kV, 40 mA). The result data are shown in Figure 2 .

[0128] Referring to Figure 1 , while Step 2 according to the present application was performed in Example 1, it was confirmed that the (002) and (101) peaks as XRD peaks of the orthorhombic structure disappeared. Further, in the case of the secondary battery activated according to the present application, it was confirmed that the sacrificial positive electrode material did not transform into Li2NiO2 having the orthorhombic structure while the secondary battery was charged. That is, it was confirmed that there was no Li2NiO2 of the orthorhombic structure in the sacrificial positive electrode material contained in the secondary battery on which the activation according to the present application was performed.

[0129] In contrast, referring to Figure 2 , it was confirmed that Li2NiO2 of the orthorhombic structure still existed in the sacrificial positive electrode material contained in the secondary battery on which the typical activation process was performed, according to the appearance of the (101) peak as the XRD peak of the orthorhombic structure (the crystal structure of the sacrificial positive electrode material was sometimes the orthorhombic structure while the secondary battery was charged). For reference, Figure 2 , the reference data of Li2NiO2 of the orthorhombic structure having the Immm space group is the XRD data.

[0130] Experimental example 2

[0131] Initial reference performance tests (RPTs) were performed on various secondary batteries manufactured in Example 1 and Comparative Example 1, and the amount of gas generated when the initial reference performance tests were performed was measured using gas chromatography (gc Agilent 7890b). The results are shown in Table 1 below and Figure 3 .

[0132] [Table 1]

[0133] Gas generation amount (μL) Example 1 450 Comparative example 1 958

[0134] Referring to Table 1 and Figure 3The good-quality secondary battery of Example 1 manufactured by the secondary battery activation method according to the present application contains only the sacrifice positive electrode of the trigonal structure, and thus does not undergo the three-step structure change (orthorhombic structure having Immm space group → trigonal structure having R-3m space group → monoclinic structure having C2 / m space group). Therefore, it can be confirmed that the gas content generated when the initial reference performance test is performed is significantly lower than that of the good-quality secondary battery of Comparative Example 1.

[0135] Therefore, it can be seen that the secondary battery activation method according to the present application includes a process of changing the crystal structure of the sacrifice positive electrode material from the orthorhombic structure to the trigonal structure, and thus can provide a sacrifice positive electrode material having a crystal structure that can minimize side effects within a usable voltage range.

Claims

1. A method for activating a lithium secondary battery, the method comprising: Step 1: Prepare a secondary battery, which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, all of which are sacrificial positive electrode materials having an orthorhombic crystal structure as represented by Formula 1 below. as well as Step 2: Charge the secondary battery to 3.5V to 4.0V, and then maintain the secondary battery at 3.5V to 4.0V for 30 minutes to 6 hours. [Formula 1] Li2Ni 1-x M x O2 In equation 1 above, M is selected from one or more of the following: Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W. 0 ≤ x < 0.9。 2. The method according to claim 1, wherein, In step 2, charge to 3.5 V to 4.0 V at a C rate of 0.025 C to 0.2 C.

3. The method according to claim 1, wherein, through step 2, the crystal structure of the sacrificial cathode material is transformed from the orthorhombic crystal system to the trigonal crystal system.

4. The method according to claim 1, wherein the sacrificial cathode material after step 2 is a single phase with a trigonal crystal structure.

5. The method according to claim 3 or 4, wherein the trigonal sacrificial cathode material is represented by formula 2: [Equation 2] LiNi 1-x M x O2, In equation 2 above, M is selected from one or more of the following: Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W. 0 ≤ x < 0.9。 6. The method according to claim 1, further comprising, before performing step 2: A pre-aging step is performed to initially age the secondary battery at room temperature.

7. The method according to claim 1, further comprising: A room temperature aging step is performed on the secondary battery after step 2 at room temperature. The secondary battery after secondary aging is subjected to a three-stage high-temperature aging process at high temperature. as well as The degassing step involves removing gas from the secondary battery after the third aging process.

8. The method according to claim 7, further comprising, after performing the degassing step: The step of determining whether the secondary battery has defects.

9. The method of claim 8, wherein the step of determining whether the secondary battery has a defect is performed as follows: The charge / discharge capacity data is obtained by charging the secondary battery from 2.5 V to 4.2 V at a C rate of 0.1C to 0.5C, and then discharging the secondary battery from 4.2 V to 2.5 V.

10. A lithium secondary battery, the lithium secondary battery comprising: a positive electrode comprising a sacrificial positive electrode material represented by formula 2, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The sacrificial cathode material described therein is a single phase with a trigonal crystal structure in the discharge state, and The sacrificial cathode material described therein only transitions between a trigonal and a monoclinic crystal structure within the usable voltage range of the lithium secondary battery. [Equation 2] LiNi 1-x M x O2, In equation 2 above, M is selected from one or more of the following: Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, and W. 0 ≤ x < 0.9。 11. The lithium secondary battery according to claim 10, wherein the trigonal crystal structure has the space group R-3m.

12. The lithium secondary battery according to claim 10, wherein the monoclinic crystal structure has a C2 / m space group.

13. The lithium secondary battery according to claim 10, wherein the lattice parameters a, c, and γ values ​​of the unit cell in the sacrificial cathode material are respectively: 2.8000 Å ≤ a ≤ 3.3000 Å， 4.8000 Å ≤ c ≤ 5.2000 Å， γ = 120°.

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