Lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a lithium secondary battery and a method of manufacturing a lithium secondary battery. In the lithium secondary battery, a cathode additive represented by Chemical Formula 1 is included as an irreversible additive in a cathode mixture layer, and a ratio (CC / DC) of an initial charge capacity (CC) to an initial discharge capacity (DC) is adjusted within a certain range, thereby reducing an amount of oxygen generated in a charge / discharge process of the lithium secondary battery, while suppressing self-discharge and improving an operating voltage by improving an open circuit voltage of the battery in initial activation and / or subsequent high-temperature storage. Accordingly, the lithium secondary battery including the same can be effectively used as a power source for a medium-large device such as an electric vehicle.

Description

Technical Field

[0001] This invention relates to a lithium secondary battery and a method for manufacturing the same, wherein the lithium secondary battery contains a positive electrode additive capable of replenishing lithium ions lost in irreversible reactions.

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2021-0071872, filed on June 3, 2021, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] With the technological advancements and increasing demands of mobile devices, the need for secondary batteries as energy sources is rapidly growing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high operating potential, long cycle life, and low self-discharge rate, have been extensively studied, commercialized, and applied in various fields.

[0004] Recently, with the increasing use of lithium-ion batteries as an energy source for medium to large-scale devices such as electric vehicles, there is a growing demand for high-capacity, high-energy-density, and low-cost lithium-ion batteries. Therefore, irreversible cathode additives that can improve capacity during subsequent charge / discharge periods by replenishing lithium ions lost due to the irreversible reaction occurring at the negative electrode during initial charging have been actively investigated, and irreversible additives such as Li₂NiO₂ and Li₆CoO₄ have been developed.

[0005] However, such conventional irreversible additives are typically prepared by reacting excess lithium oxide with precursors such as cobalt oxide or nickel oxide. Irreversible additives prepared as described above are structurally unstable and generate large amounts of oxygen (O2) as charging progresses. This oxygen generation can cause volume expansion of the electrode assembly, becoming one of the main causes of battery performance degradation.

[0006]

[0007] Furthermore, this irreversible additive may transform into a thermally unstable structure when stored at temperatures above 60°C after the initial charge / discharge, which may release additional oxygen and limit the battery's self-discharge.

[0008] Therefore, there is a need to develop a lithium secondary battery that uses an irreversible additive in the positive electrode to not only achieve a high operating voltage, but also improve battery safety and reduce self-discharge by reducing oxygen production during activation and subsequent high-temperature storage.

[0009] [Related Technical Documents]

[0010] [Patent Literature]

[0011] Korean Unexamined Patent Application Publication No. 10-2019-0078392 Summary of the Invention

[0012] Technical issues

[0013] Therefore, the present invention aims to provide a lithium secondary battery that uses an irreversible additive in the positive electrode, which not only achieves a high operating voltage, but also improves battery safety and reduces self-discharge by reducing oxygen production during activation and subsequent high-temperature storage.

[0014] Technical solution

[0015] To address the above problems, one aspect of the present invention provides a lithium secondary battery, the battery comprising:

[0016] The positive electrode includes a positive current collector and a positive electrode mixture layer disposed on the positive current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1; and

[0017] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector.

[0018] Among them, the ratio of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive during the initial charge / discharge period (CC / DC) is 50 to 100.

[0019] [Chemical Formula 1]

[0020] Li p Co (1-q) M 1 q O4

[0021] In chemical formula 1,

[0022] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0023] p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0024] Specifically, the ratio of initial charge capacity (CC) to initial discharge capacity (DC) during the initial charge / discharge period (CC / DC) can be 60 to 80.

[0025] Furthermore, the weight change rate of the cathode mixture layer before and after the initial charge / discharge can be from 0.01% to 2.00%.

[0026] Furthermore, the positive electrode additive contained in the positive electrode mixture layer may have a tetragonal structure with a space group of P42 / nmc, and relative to 100 parts by weight of the total positive electrode mixture layer, the content of the positive electrode additive may be 0.01 to 5 parts by weight.

[0027] Furthermore, the positive electrode active material contained in the positive electrode mixture layer may be a lithium metal composite oxide represented by the following Chemical Formula 2:

[0028] [Chemical Formula 2]

[0029] Li x [Ni y Co z Mn w M 2 v O u

[0030] In Chemical Formula 2,

[0031] M 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and

[0032] x, y, z, w, v and u respectively satisfy 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0≤w≤0.5, 0≤v≤0.2 and 1.5≤u≤4.5.

[0033] Furthermore, relative to the total weight of the positive electrode mixture layer, the positive electrode mixture layer may contain 0.1 to 5 parts by weight of a conductive material, and the usable conductive material may include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fiber.

[0034] Furthermore, the negative electrode mixture layer contains a carbon material and a silicon material, and relative to 100 parts by weight of the negative electrode mixture layer, the content of the silicon material may be 1 to 20 parts by weight.

[0035] Herein, the carbon material may include one or more selected from the group consisting of natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black, acetylene black, Ketjen black and carbon fiber.

[0036] Furthermore, the silicon material may include one or more of silicon (Si) particles and silicon oxide (SiOx, 1≤x≤2) particles.

[0037] Furthermore, another aspect of the present invention provides a method for manufacturing a lithium secondary battery, the method comprising the following steps:

[0038] A current below 1C is applied to the lithium secondary battery to initially charge it, the lithium secondary battery comprising:

[0039] The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1; and

[0040] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector.

[0041] During the initial charge / discharge period, the ratio of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive (CC / DC) is 50 to 100.

[0042] [Chemical Formula 1]

[0043] Li p Co (1-q) M 1 q O4

[0044] In chemical formula 1,

[0045] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0046] p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0047] The initial charging process can be performed as follows:

[0048] First activation step: Apply a current of 0.05C to 0.2C to charge the lithium secondary battery to below 30% SOC;

[0049] The second activation step involves applying a current of 0.3C to 0.5C to charge the lithium-ion battery, which has undergone the first activation step, to a state of charge (SOC) greater than 30% and less than 70%; and

[0050] The third activation step: Apply a current of 0.6C to 0.9C to charge the lithium secondary battery that has undergone the second activation step to a state of charge (SOC) of over 70%.

[0051] Furthermore, the initial charging step of lithium secondary batteries can be performed at temperatures ranging from 20°C to 70°C and at speeds ranging from 5 to 900 kgf / cm². 2 It is carried out under pressure conditions.

[0052] Beneficial effects

[0053] In the lithium secondary battery according to the present invention, a positive electrode additive represented by Chemical Formula 1 is included as an irreversible additive in the positive electrode mixture layer, and the ratio of initial charge capacity (CC) to initial discharge capacity (DC) (CC / DC) is adjusted within a specific range, thereby reducing the amount of oxygen generated during the charging / discharging of the lithium secondary battery. Simultaneously, self-discharge is prevented and the operating voltage is improved by suppressing the drop in the open-circuit voltage (OCV) of the battery during initial charging / discharging and / or subsequent high-temperature storage. Therefore, the lithium secondary battery containing the aforementioned irreversible additive can be effectively used as a power source for medium to large-sized devices such as electric vehicles. Attached Figure Description

[0054] Figure 1 It is a graph showing the change in the charging capacity of the positive electrode additive as a function of the ratio of charging capacity (CC) to discharging capacity (DC) during the initial charging / discharging period.

[0055] Figure 2 It is a graph showing the cumulative gas generation during the initial charge / discharge period at 45°C as a function of the ratio of the charge capacity (CC) to the discharge capacity (DC) of the positive electrode additive.

[0056] Figure 3 It is a graph showing the change in the cumulative gas generation during 4 weeks of storage at 60°C according to the ratio of the charge capacity (CC) to the discharge capacity (DC) of the positive electrode additive.

[0057] Figure 4 It is a graph showing the change of open circuit voltage (OCV) with the ratio of charging capacity (CC) to discharging capacity (DC) of the positive electrode additive during 4 weeks of storage at 60°C according to the charge / discharge cycle. Detailed Implementation

[0058] The present invention can have various variations and instances, and specific examples are shown in the accompanying drawings and described in detail in specific embodiments.

[0059] However, it should be understood that the present invention is not limited to the specific embodiments, but includes all variations, equivalents or alternatives within the spirit and scope of the present invention.

[0060] The terms “comprising,” “including,” and “having” as used herein indicate the presence of the features, quantities, steps, operations, components, or elements or combinations thereof described in the specification, but it should be understood that these terms do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, elements, or combinations thereof.

[0061] Furthermore, when a portion of a layer, film, region, or plate is disposed "on" another portion, this includes not only the case where one portion is disposed "directly" on the other portion, but also the case where another portion is inserted in between. Conversely, when a portion of a layer, film, region, or plate is disposed "below" another portion, this includes not only the case where one portion is disposed "directly" below the other portion, but also the case where another portion is inserted in between. Moreover, in this application, "on" includes not only the case where it is disposed on the upper part, but also the case where it is disposed on the lower part.

[0062] Furthermore, the term "major component" as used herein can refer to a component that has a content of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more relative to the total weight of the composition or a particular component, and in some cases, when the major component constitutes the entire composition or a particular component, its content can be 100% by weight.

[0063] Furthermore, the "Ah" used in this article refers to the capacity unit of lithium secondary batteries, also known as "ampere-hour," which refers to the current output per hour. For example, when the battery capacity is "3000mAh," it means that the battery can discharge at a current of 3000mA for 1 hour.

[0064] The invention will be described in more detail below.

[0065] Lithium secondary batteries

[0066] In one embodiment of the present invention, the lithium secondary battery comprises:

[0067] The positive electrode comprises: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1; and

[0068] The negative electrode comprises: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector, and

[0069] The ratio of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive (CC / DC) is between 50 and 100.

[0070] [Chemical Formula 1]

[0071] Li p Co (1-q) M 1 q O4

[0072] In chemical formula 1,

[0073] M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and

[0074] p and q are respectively 5≤p≤7 and 0≤q≤0.4.

[0075] The lithium secondary battery according to the present invention comprises a positive electrode and a negative electrode, and a separator may be interposed between the positive electrode and the negative electrode or no separator is included. In addition, the positive electrode and the negative electrode have a structure impregnated with an electrolyte for allowing lithium ions (Li + ) to migrate therebetween.

[0076] Here, the positive electrode may include a positive electrode mixture layer formed by coating a positive electrode slurry containing a positive electrode active material and a positive electrode additive on a positive electrode current collector, drying and pressing, and as needed, the positive electrode mixture layer may optionally further comprise a conductive material, a binder and other additives.

[0077] The positive electrode active material may include a lithium metal composite oxide containing three or more elements selected from nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al), and in some cases, the lithium metal composite oxide may be in a form doped with another transition metal (M1). For example, the positive electrode active material may be a lithium metal composite oxide represented by the following Chemical Formula 2, which is capable of reversibly intercalating / deintercalating lithium ions:

[0078] [Chemical Formula 2]

[0079] Li x [Ni y Co z Mn w M 2 v O u

[0080] In Chemical Formula 2,

[0081] M 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and

[0082] x, y, z, w, v and u are respectively 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0≤w≤0.5, 0≤v≤0.2 and 1.5≤u≤4.5.

[0083] The lithium metal composite oxide represented by Formula 2 can be a composite metal oxide comprising lithium and nickel, and may include one or more compounds selected from the following: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2.

[0084] In addition, relative to 100 parts by weight of the positive electrode mixture layer, the content of the positive electrode active material can be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight.

[0085] Furthermore, the cathode mixture layer may include a cathode additive that imparts irreversible capacity and a cathode active material that exhibits electroactivity, wherein the cathode additive may include a lithium metal oxide represented by the following chemical formula 1:

[0086] [Chemical Formula 1]

[0087] Li p Co (1-q) M 1 q O4

[0088] In chemical formula 1,

[0089] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0090] p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0091] The positive electrode additive can contain excess lithium to provide lithium for the lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during initial charging, thereby increasing charging capacity, reducing irreversible capacity, and improving lifetime characteristics.

[0092] In the cathode additive, the lithium-ion content of the cathode additive represented by Chemical Formula 1 can be higher than that of the lithium-ion content of nickel-containing oxides commonly used in the art. This can replenish the lithium-ions lost in irreversible reactions during the initial activation of the battery, thus significantly improving the battery's charge / discharge capacity. Furthermore, compared to iron- and / or manganese-containing oxides commonly used in the art, there are no side reactions caused by transition metal dissolution during battery charging / discharging, resulting in excellent battery stability.

[0093] Examples of lithium metal oxides represented by chemical formula 1 may include Li6CoO4, Li6Co 0.5 Zn 0.5 O4 and Li6Co 0.7 Zn 0.3 O4.

[0094] Furthermore, the lithium cobalt oxide represented by Formula 1 can have a tetragonal crystal structure, and within this tetragonal crystal structure, it can be included in the P42 / nmc space group having a twisted tetrahedral structure composed of cobalt and oxygen elements. Because the cathode additive has a twisted tetrahedral structure composed of cobalt and oxygen elements, this structure is unstable, potentially generating a large amount of oxygen during initial charging / discharging (i.e., activation) and / or subsequent charging / discharging, leading to reduced battery performance and safety due to volume expansion of the electrode assembly. Moreover, when stored at temperatures above 60°C after initial charging / discharging, the cathode additive transforms into a thermally unstable structure, further releasing oxygen and limiting the battery's self-discharge.

[0095] However, the lithium secondary battery according to the present invention contains a positive electrode additive represented by chemical formula 1, and adjusts the charge / discharge capacity ratio (CC / DC) of the positive electrode additive within a specific range during initial charge / discharge, thereby reducing the amount of oxygen generated during the charge / discharge of the lithium secondary battery, and also suppressing self-discharge and improving the operating voltage by improving the open circuit voltage of the battery during initial activation and subsequent high-temperature storage.

[0096] Specifically, the ratio of charge capacity (CC) to discharge capacity (DC) of the positive electrode additive in the initial charge / discharge phase (CC / DC) of the lithium secondary battery can be from 50 to 100. For example, the ratio of charge capacity (CC) to discharge capacity (DC) of the positive electrode additive in the initial charge / discharge phase (CC / DC) of the lithium secondary battery can be 50 to 90; 50 to 75; 50 to 70; 60 to 90; 60 to 80; 60 to 70; 75 to 100; 65 to 75; or 70 to 78. The ratio of charge capacity (CC) to discharge capacity (DC) of the positive electrode additive (CC / DC) can be adjusted according to the type or content of the positive electrode additive contained in the positive electrode mixture layer, and in some cases, it can be controlled by the initial charge / discharge conditions. In this invention, by adjusting the initial charge / discharge capacity ratio (CC / DC) of the positive electrode additive to meet the aforementioned range, the amount of oxygen generated during the charging / discharging of the lithium secondary battery can be reduced, and the open-circuit voltage of the battery during initial charging / discharging and subsequent high-temperature storage can be improved, thereby suppressing self-discharge and improving the operating voltage. Specifically, when the ratio (CC / DC) exceeds 100, a significant decrease in the open-circuit voltage of the battery during high-temperature storage can be prevented, and when the ratio (CC / DC) is very low, i.e., less than 50, the generation of a large amount of gas during charging / discharging after battery activation can be reduced.

[0097] Furthermore, the weight change rate of the positive electrode mixture layer of the lithium secondary battery before and after the initial charge / discharge is 0.01 to 2.00%, specifically 0.01 to 1.80%; 0.01 to 1.60%; 0.01 to 1.50%; 0.01 to 1.40%; 0.1 to 1.20%; 0.01 to 1.00%; 0.01 to 0.08%; 0.01 to 0.06%; 0. 0.01 to 0.05%; 0.01 to 0.04%; 0.04 to 0.4%; 0.04 to 0.5%; 0.04 to 1.0%; 0.04 to 1.5%; 0.05 to 1.0%; 0.08 to 0.5%; 1.0 to 2.0%; 1.5 to 2.0%; 0.05 to 0.9%; 0.2 to 1.7%; 1.0 to 1.7%; or 0.1 to 0.8%.

[0098] In this invention, by adjusting the weight change rate of the positive electrode mixture layer before and after the initial charging / discharging of the lithium secondary battery to within the above-mentioned range, the amount of oxygen generated during the charging / discharging of the lithium secondary battery can be reduced, and the open-circuit voltage of the battery during initial charging / discharging and subsequent high-temperature storage can also be improved, thereby suppressing self-discharge and improving the operating voltage.

[0099] Furthermore, the content of the positive electrode additive relative to 100 parts by weight of the positive electrode mixture layer can be from 0.01 to 5 parts by weight, specifically, from 0.01 to 4 parts by weight; from 0.01 to 3 parts by weight; from 0.01 to 2 parts by weight; from 0.01 to 1 part by weight; from 0.5 to 2 parts by weight; from 0.1 to 0.9 parts by weight; from 0.2 to 1.5 parts by weight; or from 1 to 2 parts by weight. In this invention, by adjusting the content of the positive electrode additive to the above range, it is possible to prevent the decrease in charge / discharge capacity caused by insufficient replenishment of lithium ions lost in irreversible reactions due to low positive electrode additive content, and it is also possible to prevent the generation of large amounts of oxygen during battery charging / discharging due to excessive positive electrode additive.

[0100] In addition to the positive electrode active material and positive electrode additives, the positive electrode mixture layer may further contain conductive materials, binders or additives.

[0101] Here, conductive materials can be used to improve the performance of the positive electrode, such as conductivity, and may include one or more selected from: natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black, acetylene black, Ketjen black, and carbon fiber. For example, conductive materials may include acetylene black.

[0102] Furthermore, the content of conductive material may be 0.1 to 5 parts by weight, specifically 0.5 to 4 parts by weight, 1 to 3.5 parts by weight, or 0.5 to 1.5 parts by weight, relative to 100 parts by weight of the positive electrode mixture layer.

[0103] In addition, the adhesive may include one or more resins selected from: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. In one example, the adhesive may include polyvinylidene fluoride.

[0104] In addition, the amount of binder may be 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, relative to a total of 100 parts by weight of the positive electrode mixture layer.

[0105] In addition, there is no particular limitation on the average thickness of the cathode mixture layer, but it can be 50 to 300 μm, more specifically 100 to 200 μm; 80 to 150 μm; 120 to 170 μm; 150 to 300 μm; 200 to 300 μm; or 150 to 190 μm.

[0106] Furthermore, in the positive electrode, materials with high conductivity that do not cause chemical changes in the battery can be used as the positive electrode current collector. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can be used as the positive electrode current collector, and in the case of aluminum or stainless steel, aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver can also be used. In addition, the positive electrode current collector can have fine irregularities formed on its surface to improve the adhesion of the positive electrode active material, and can be formed in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Furthermore, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied within the range of 3 to 500 μm.

[0107] On the other hand, the negative electrode may comprise a negative electrode mixture layer prepared by coating a negative electrode active material onto a negative electrode current collector, drying and pressing it, and if desired, as with the positive electrode, the negative electrode mixture layer may optionally further comprise conductive materials, binders and other additives.

[0108] Furthermore, the negative electrode active material may include, for example, carbon materials and silicon materials. Carbon materials refer to carbon materials containing carbon atoms as a major component, and examples of such carbon materials may include: graphite with a fully layered crystal structure, such as natural graphite; soft carbon with a low-crystallinity layered crystal structure (graphene structure; wherein hexagonal honeycomb planes of carbon are arranged in layers); and hard carbon wherein the above structures are mixed with amorphous portions; artificial graphite; expanded graphite; carbon nanofibers; non-graphitized carbon; carbon black; acetylene black; Ketjen black; carbon nanotubes; fullerenes; activated carbon; and graphene, preferably selected from one or more of natural graphite, artificial graphite, graphene, and carbon nanotubes. More preferably, the carbon material includes natural graphite and / or artificial graphite, and may also include any one or more of graphene and carbon nanotubes in addition to natural graphite and / or artificial graphite. In this case, the carbon material may contain 50 to 95 parts by weight, more specifically 60 to 90 parts by weight or 70 to 80 parts by weight of graphene and / or carbon nanotubes, relative to a total of 100 parts by weight of carbon material.

[0109] Furthermore, silicon materials are particles containing silicon (Si) as the main component, which is a metallic component, and may contain silicon (Si) particles and silicon oxide (SiO). X The silicon material may contain one or more of the following: (1 ≤ X ≤ 2) particles. In one instance, the silicon material may comprise silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or mixtures thereof.

[0110] Furthermore, the silicon material can be in the form of a mixture of crystalline and amorphous particles, and based on a total of 100 parts by weight of silicon material, the proportion of amorphous particles can be 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight. In this invention, by controlling the proportion of amorphous particles contained in the silicon material within the above range, thermal stability and flexibility can be improved without reducing the electrical performance of the electrode.

[0111] In addition, the negative electrode active material contains carbon material and silicon material, and based on 100 parts by weight of the negative electrode mixture layer, the content of silicon material can be 1 to 20 parts by weight, particularly 5 to 20 parts by weight; 3 to 10 parts by weight; 8 to 15 parts by weight; 13 to 18 parts by weight; or 2 to 7 parts by weight.

[0112] In this invention, by adjusting the content of carbon and silicon materials contained in the negative electrode active material to the above-mentioned range, lithium consumption and irreversible capacity loss during the initial charging / discharging of the battery can be reduced, and the charging capacity per unit mass can also be improved.

[0113] In one example, relative to 100 parts by weight of the negative electrode active material, the negative electrode active material may comprise: 95 ± 2 parts by weight of graphite; and 5 ± 2 parts by weight of a mixture wherein silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles are uniformly mixed. In this invention, by adjusting the content of carbon and silicon materials contained in the negative electrode active material to the above-mentioned range, lithium consumption and irreversible capacity loss during the initial charge / discharge process of the battery can be reduced, and the charge capacity per unit mass can also be improved.

[0114] In addition, the average thickness of the negative electrode mixture layer can be 100 to 200 μm, specifically 100 to 180 μm, 100 to 150 μm, 120 to 200 μm, 140 to 200 μm or 140 to 160 μm.

[0115] Furthermore, there are no particular limitations on the negative electrode current collector, as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, nickel, titanium, or calcined carbon can be used, and in the case of copper or stainless steel, copper or stainless steel with a surface treated with carbon, nickel, titanium, or silver can be used. In addition, like the positive electrode current collector, the negative electrode current collector has fine irregularities on its surface to enhance the adhesion of the positive electrode active material, and can be formed in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Furthermore, considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 500 μm.

[0116] Furthermore, in the lithium secondary battery according to the present invention, a separator can be inserted between the positive and negative electrodes. Here, an insulating film is used as the separator, which is inserted between the positive and negative electrodes and has high ion permeability and mechanical strength. There are no particular limitations on the separator, as long as it is commonly used in the art; specifically, sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene can be used. In some cases, composite separators can be used, wherein a porous polymer substrate such as a sheet or nonwoven fabric is coated with an organic binder polymer using inorganic / organic particles. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also act as a separator. Furthermore, the pore size of the separator can be from an average of 0.01 to 10 μm, and the thickness can be from an average of 5 to 300 μm.

[0117] On the other hand, the positive and negative electrodes can be wound and housed in a cylindrical, prismatic, or pouch-shaped battery in the shape of a roll, or they can be housed in a pouch-shaped battery in the form of folding or stacking and folding, but the present invention is not limited thereto.

[0118] Furthermore, the lithium-containing electrolyte according to the present invention can be composed of an electrolyte and a lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte can be used.

[0119] As non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0120] As organic solid electrolytes, polymers such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyalginate lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ion-dissociating groups can be used.

[0121] As an inorganic solid electrolyte, lithium nitrides, halides, or sulfates can be used, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, or Li3PO4-Li2S-SiS2.

[0122] Lithium salts are materials that are readily soluble in non-aqueous electrolytes, and can be, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate or lithium imide.

[0123] In addition, to improve charge / discharge characteristics and flame retardancy, substances such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds can be added to the electrolyte. The electrolyte may contain oxaliplatinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In some cases, to impart non-flammability, the electrolyte may further contain halogenated solvents such as carbon tetrachloride or trifluoroethylene, and to enhance high-temperature storage performance, it may further contain carbon dioxide gas, and may also contain fluoroethylene carbonate (FEC) or propylene sulfonate lactone (PRS).

[0124] Methods for manufacturing lithium secondary batteries

[0125] Furthermore, in one embodiment, the present invention provides a method for manufacturing a lithium secondary battery, the method comprising the following steps:

[0126] A current below 1C is applied to the lithium secondary battery to initially charge it, the lithium secondary battery comprising:

[0127] The positive electrode includes a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1, and

[0128] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector.

[0129] During the initial charge / discharge period, the ratio of the initial charge capacity (CC) to the initial discharge capacity (DC) of the additive (CC / DC) is between 50 and 100.

[0130] [Chemical Formula 1]

[0131] Li p Co (1-q) M 1 q O4

[0132] In chemical formula 1,

[0133] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0134] p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0135] The method of manufacturing a lithium secondary battery according to the present invention may include applying a current to the lithium secondary battery for initial charging, the lithium secondary battery comprising: a positive electrode comprising a positive current collector; and a positive electrode mixture layer disposed on the positive current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1; and a negative electrode comprising a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. Here, the current applied to the lithium secondary battery is less than 1C, thereby enabling the ratio of initial charge capacity (CC) to initial discharge capacity (DC) (CC / DC) during the initial charge / discharge period to be adjusted to a range of 50 to 100.

[0136] Specifically, the initial charging is achieved through a three-step charging process, namely one to three activation steps.

[0137] More specifically, the initial charging process can be performed as follows:

[0138] First activation step: Apply a current of 0.05C to 0.2C to charge the lithium secondary battery to below 30% SOC;

[0139] The second activation step involves applying a current of 0.3C to 0.5C to charge the lithium-ion battery, which has undergone the first activation step, to a state of charge (SOC) greater than 30% and less than 70%; and

[0140] The third activation step: Apply a current of 0.6C to 0.9C to charge the lithium secondary battery that has undergone the second activation step to a state of charge (SOC) of over 70%.

[0141] In one example, the initial charging step can be performed as follows:

[0142] First activation step: Apply a current of 0.08C to 0.15C to charge the lithium secondary battery to below 30% SOC;

[0143] The second activation step involves applying a current of 0.35C to 0.45C to charge the lithium-ion battery that has undergone the first activation step to a state of charge (SOC) greater than 30% and less than 70%; and

[0144] The third activation step: Apply a current of 0.65C to 0.8C to charge the lithium secondary battery that has undergone the second activation step to a state of charge (SOC) of over 70%.

[0145] In this invention, by controlling the current value so that the current applied to the lithium secondary battery during the initial charging period is below 1C, but gradually increases with the increase of SOC, the SEI film can be uniformly formed on the negative electrode mixture layer, and can prevent the dissociation of lithium ions in the positive electrode active material before the positive electrode additive at a relatively low current, or can prevent the degradation of electrical performance caused by the induction of over-lithiation of the positive electrode additive due to a current exceeding 1C.

[0146] Furthermore, the initial charging step can be performed at temperatures above room temperature to reduce electrode resistance. Specifically, the activation at each stage can be performed at temperatures of 20 to 70°C, more specifically 20 to 60°C; 20 to 40°C; 20 to 25°C; 40 to 60°C; 45 to 60°C; 50 to 65°C; 50 to 60°C; 52 to 58°C; 40 to 50°C; or 42 to 48°C. In this invention, when the initial charging is performed under the above temperature conditions, the secondary battery can be charged with lower positive electrode resistance, thereby improving charging efficiency and enhancing the uniformity of the SEI film formed on the negative electrode mixture layer.

[0147] On the other hand, during the initial charging, the outer surface of the lithium secondary battery can be pressurized simultaneously with charging, or sequentially after charging using a pressurizing device such as a clamp, and this pressure can range from 5 to 900 kgf / cm². 2 Continue for 4 to 6 seconds.

[0148] Furthermore, it may be further included to discharge the lithium secondary battery after the initial charge, in which case the discharge may be carried out at a current of 0.1 to 1C, specifically 0.1 to 0.9C; 0.1 to 0.8C; 0.1 to 0.6C; 0.1 to 0.5C; 0.5 to 1C; 0.2 to 0.8C; or 0.4 to 0.6C.

[0149] Furthermore, the method for manufacturing a lithium secondary battery according to the present invention may further include aging the charged lithium secondary battery after initial charging. This aging can make the SEI film more stable and reform it to a uniform thickness through thermal and electrochemical energy. For this purpose, the aging can be carried out at 20 to 80°C, specifically 30 to 70°C or 45 to 65°C for 0.5 to 30 hours.

[0150] According to the method for manufacturing a lithium secondary battery of the present invention, the initial charge / discharge capacity ratio (CC / DC) and / or the weight ratio of the positive electrode mixture layer before and after initial charge / discharge of the positive electrode additive represented by Chemical Formula 1 contained in the positive electrode mixture layer can be easily controlled within the range described above in the present invention. This not only reduces the amount of oxygen generated during charging / discharging of the manufactured lithium secondary battery, but also improves the open-circuit voltage of the battery during initial activation and / or subsequent high-temperature storage, thereby suppressing self-discharge and improving operating voltage. Therefore, the lithium secondary battery of the present invention can be effectively used as a power source for medium to large-sized devices such as electric vehicles.

[0151] [Example]

[0152] The invention will be described in further detail below with reference to embodiments and experimental examples.

[0153] However, the following embodiments and experimental examples are only used to illustrate the present invention, and the content of the present invention is not limited to the following embodiments and experimental examples.

[0154] Manufacturing of lithium secondary batteries in Examples 1 to 4 and Comparative Examples 1 to 4

[0155] The positive electrode slurry for lithium secondary batteries was prepared as follows: N-methylpyrrolidone was injected into a homogenizer, and 97.8 parts by weight of positive electrode active material LiNi were weighed and added relative to 100 parts by weight of the positive electrode slurry solids. 0.6 Co 0.2 Mn 0.2 O2 and positive electrode additives Li6CoO4 or Li6Co 0.7 Zn 0.3 O4; 0.7 parts by weight of a conductive material, said conductive material being a mixture of carbon nanotubes (average size: 60 ± 10 nm) and tandoor black (average size: 2 ± 0.5 μm) (75:25 wt / wt); and 1.5 parts by weight of a binder PVdF, and the resulting mixture was mixed at 2,000 rpm for 60 minutes. Here, the prepared positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 100°C, and the resulting mixture was rolled to produce the positive electrode. Here, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the manufactured positive electrode was approximately 200 μm.

[0156] Relative to 100 parts by weight of the negative electrode slurry solids, 84 parts by weight of natural graphite (a negative electrode active material) and 14 parts by weight of silicon oxide (SiOx, 1≤x≤2) particles were prepared; and 2 parts by weight of styrene-butadiene rubber (SBR) was used as the binder. The negative electrode slurry was prepared in the same manner as the positive electrode slurry. Here, the graphite used to form the negative electrode mixture layer was natural graphite (average particle size: 0.01 to 0.5 μm), and the average particle size of the silicon oxide (SiOx) particles was 0.9 to 1.1 μm. The negative electrode was manufactured by coating the prepared negative electrode slurry onto one surface of a copper current collector, drying the slurry at 100°C, and rolling the result. Here, the total thickness of the negative electrode mixture layer was 150 μm, and the total thickness of the manufactured negative electrode was approximately 250 μm.

[0157] A full-cell lithium secondary battery is prepared by stacking a separator (thickness: approximately 16 μm) made of porous polyethylene (PE) membrane to be inserted between the prepared positive and negative electrodes, and injecting E2DVC as the electrolyte.

[0158] Here, "E2DVC" refers to a carbonate electrolyte, which is a mixed solution in which lithium hexafluorophosphate (LiPF6, 1.0M) and ethylene carbonate (VC, 2% by weight) are added to a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0159] The initial charge capacity (CC) and initial discharge capacity (DC) of the positive electrode additive were measured by initially charging the manufactured full cells at 22±2°C under the conditions shown in Table 1 below, and their ratio (CC / DC) was calculated. Here, the battery potential ranged from 2.5 to 4.25 V. Furthermore, the positive electrode was removed from the full cell, the positive electrode mixture layer was peeled from the positive electrode current collector, and the weight of the positive electrode mixture layer was measured after the initial charge / discharge. The rate of weight change before and after the initial charge / discharge was derived from the weight measurements taken before and after the initial charge / discharge.

[0160] [Table 1]

[0161]

[0162] Experimental Example 1

[0163] To confirm the difference in effectiveness based on the ratio of initial charge capacity (CC) to initial discharge capacity (DC) of the positive electrode additive (CC / DC), the following experiment was conducted.

[0164] a) Manufacturing of lithium secondary batteries

[0165] To confirm the effect of the positive electrode additive contained in the lithium secondary battery on the change in the initial charge / discharge capacity ratio, in addition to not containing positive electrode active material, 97.8 parts by weight of positive electrode additive such as Li6CoO4 or Li6Co were used relative to 100 parts by weight of positive electrode slurry solids. 0.7 Zn 0.3 Apart from O4, the lithium secondary batteries of Examples 2a and 4a and Comparative Examples 1a to 4a were manufactured in the same manner as described in the corresponding Examples 2 and 4 and Comparative Examples 1 to 4.

[0166] The initial charge capacity (CC) and initial discharge capacity (DC) of the positive electrode additive were measured by initially charging the manufactured full cells at 22±2°C under the conditions shown in Table 2 below, and their ratio (CC / DC) was calculated. Here, the battery potential range is 2.5 to 4.25 V.

[0167] [Table 2]

[0168]

[0169] b) Evaluation of gas production

[0170] After initial charge / discharge of the lithium secondary batteries manufactured in Examples 2a and 4a and Comparative Examples 1a to 4a, for each secondary battery, the following were measured: ① the amount of gas generated during 50 cycles of repeated charge / discharge at 45°C and 0.3C / 0.3C; and ② the amount of gas generated during storage at 60°C for 4 weeks. The results are shown in Table 3 below. Figure 2 and Figure 3 middle.

[0171] c) Evaluation of high-temperature storage characteristics

[0172] The lithium secondary batteries manufactured in Examples 2a, 4a, and Comparative Examples 1a to 4a were stored at 60°C for 4 weeks, and the open-circuit voltage (OCV) was measured. The change in open-circuit voltage was calculated based on the open-circuit voltage before storage. The results are shown in Table 3 below. Figure 4 middle.

[0173] [Table 3]

[0174]

[0175] As shown in Table 3 and Figures 2 to 4 As shown, the lithium secondary battery according to the present invention not only generates less gas during charging / discharging, but also exhibits improved storage stability at high temperatures, thereby suppressing the decrease in open-circuit voltage (OCV). Therefore, the lithium secondary battery according to the present invention has the advantage of excellent electrical performance.

[0176] Specifically, in the lithium secondary batteries manufactured in Examples 2a and 4a, which contain a positive electrode additive represented by Chemical Formula 1, by adjusting the ratio (CC / DC) of the charge capacity (CC) to the discharge capacity (DC) during the initial charge / discharge period of the positive electrode additive within a specific range, and ensuring that the weight change rate of the positive electrode mixture layer meets a predetermined range, it was confirmed that the amount of accumulated gas generated after the initial charge / discharge, during charge / discharge, and after 4 weeks of high-temperature storage increases with the increase of the positive electrode additive content, but decreases compared to the same amount. Furthermore, the lithium secondary batteries of the examples showed a decrease in open-circuit voltage change (ΔOCV) after high-temperature storage.

[0177] As can be seen from the above results, in the lithium secondary battery according to the present invention, the positive electrode additive represented by chemical formula 1 is included in the positive electrode mixture layer as an irreversible additive, and the ratio (CC / DC) of the charging capacity (CC) and discharging capacity (DC) of the positive electrode additive during initial charging / discharging is adjusted to a specific range, thereby reducing the amount of oxygen generated by the lithium secondary battery during charging / discharging. At the same time, by improving the open circuit voltage of the battery during initial activation and / or subsequent high-temperature storage, self-discharge is suppressed and the operating voltage is improved.

[0178] In the foregoing, although the invention has been described with reference to exemplary embodiments, those skilled in the art or of ordinary skill in the art should understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as set forth in the appended claims.

[0179] Therefore, the technical scope of the present invention is not limited to the contents described in the specific embodiments of the specification, but should be defined by the claims.

Claims

1. A lithium secondary battery, the battery comprising: a positive electrode, the positive electrode comprising: a positive current collector, and a positive electrode mixture layer disposed on the positive current collector and containing a positive active material and a positive electrode additive represented by the following Chemical Formula 1; and a negative electrode, the negative electrode comprising: a negative current collector and a negative electrode mixture layer disposed on the negative current collector, in, wherein the lithium secondary battery has undergone initial charge / discharge, and the ratio (CC / DC) of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive during the initial charge / discharge is 50 to 100, wherein the initial charging step comprises: a first activation step: charging the lithium secondary battery to a SOC of 30% or less by applying a current of 0.05C to 0.2C; a second activation step: charging the lithium secondary battery that has undergone the first activation step to a SOC of more than 30% and less than 70% by applying a current of 0.3C to 0.5C; and a third activation step: charging the lithium secondary battery that has undergone the second activation step to a SOC of 70% or more by applying a current of 0.6C to 0.9C, wherein the initial discharging step is performed under a current condition of 0.1 to 1C, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In Chemical Formula 1, M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are respectively 5≤p≤7 and 0≤q≤0.

4.

2. The battery according to claim 1, wherein, The ratio (CC / DC) of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive is 60 to 80.

3. The battery according to claim 1, wherein, The weight change rate of the positive electrode mixture layer before and after initial charge / discharge is 0.01% to 2.00%.

4. The battery according to claim 1, wherein, The positive electrode additive has a tetragonal structure with a space group of P4₂ / nmc.

5. The battery according to claim 1, wherein, Relative to a total of 100 parts by weight of the positive electrode mixture layer, the content of the positive electrode additive is 0.01 parts by weight to 5 parts by weight.

6. The battery according to claim 1, wherein, The positive active material is a lithium metal composite oxide represented by the following Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mr w M 2 v ]O u In Chemical Formula 2, M 2 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, v and u are respectively 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0≤w≤0.5, 0≤v≤0.2 and 1.5≤u≤4.

5.

7. The battery according to claim 1, wherein, Relative to the total weight of the positive electrode mixture layer, the positive electrode mixture layer comprises 0.1 parts by weight to 5 parts by weight of a conductive material.

8. The battery according to claim 1, wherein, The positive electrode mixture layer comprises one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, carbon black and carbon fiber.

9. The battery according to claim 1, wherein, The negative electrode mixture layer comprises a carbon material and a silicon material, and Relative to 100 parts by weight of the negative electrode mixture layer, the content of the silicon material is 1 part by weight to 20 parts by weight.

10. The battery according to claim 9, wherein, The carbon material comprises one or more selected from the group consisting of natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black and carbon fiber.

11. The battery according to claim 9, wherein, The silicon material comprises one or more of silicon (Si) particles and silicon oxide SiOₓ particles, wherein 1≤x≤2.

12. A method of manufacturing a lithium secondary battery, the method comprising the steps of: applying a current of 1C or less to a lithium secondary battery to initially charge the lithium secondary battery, the lithium secondary battery comprising: The positive electrode comprises: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material and a positive electrode additive represented by the following chemical formula 1; and The negative electrode comprises: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector. in, During the initial charge / discharge period, the ratio of the initial charge capacity (CC) to the initial discharge capacity (DC) of the positive electrode additive (CC / DC) is 50 to 100. The initial charging steps include: First activation step: Apply a current of 0.05C to 0.2C to charge the lithium secondary battery to below 30% SOC; Second activation step: Applying a current of 0.3C to 0.5C to charge the lithium secondary battery that has undergone the first activation step to a SOC greater than 30% and less than 70%; and The third activation step: Applying a current of 0.6C to 0.9C to charge the lithium secondary battery that has undergone the second activation step to a SOC of over 70%. The initial discharge step is performed under a current condition of 0.1 to 1C. [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In chemical formula 1, M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

13. The method according to claim 12, wherein, The initial charging step is performed at a temperature of 20°C to 70°C.

14. The method according to claim 12, wherein, At 5 kgf / cm 2 Up to 900 kgf / cm 2 The initial charging step is performed on the lithium secondary battery under pressure conditions.

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