Method for manufacturing secondary battery

Abstract

Provided, according to exemplary embodiments, is a method for manufacturing a secondary battery. The method comprises the steps of: charging a battery cell at a first current rate during a first duration; charging the battery cell at a second current rate during a second duration subsequent to the first duration; and charging the battery cell at a third current rate during a third duration subsequent to the second duration, wherein the battery cell comprises an electrode assembly including a plurality of positive electrodes, a plurality of negative electrodes, and separators separating the plurality of positive electrodes from the plurality of negative electrodes, the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector, the positive electrode active material comprises lithium iron phosphate and lithium iron oxide, and the second current rate is greater than the first current rate.

Description

Method for manufacturing secondary batteries

[0001] The present invention relates to a method for manufacturing a secondary battery. The present application claims the benefit of Korean application No. 10-2024-0193011, filed on December 20, 2024, which is incorporated herein by reference in its entirety.

[0002] Unlike primary batteries, secondary batteries can be charged and discharged multiple times. Secondary batteries are widely used as energy sources for various wireless devices such as handsets, laptops, and cordless vacuum cleaners. Recently, as the manufacturing cost per unit capacity of secondary batteries has decreased dramatically due to improved energy density and economies of scale, and as the driving range of BEVs (battery electric vehicles) has increased to a level equivalent to that of fuel vehicles, the primary use of secondary batteries is shifting from mobile devices to mobility.

[0003] The manufacturing of a secondary battery includes an electrode process comprising mixing, coating, roll pressing, slitting, and notching processes; an assembly process for embedding the electrode assembly into a case; and an activation process for electrically activating and stabilizing the battery cells. After the activation process, the battery cells can be stacked to form a cell stack. The cell stack can be mounted in a housing together with a module frame, or directly mounted in a housing without a module frame.

[0004] The problem that the technical concept of the present invention aims to solve is to provide a method for manufacturing a secondary battery with improved reliability and throughput.

[0005] According to exemplary embodiments of the present invention for solving the above-described problem, a method for manufacturing a secondary battery is provided. The method comprises the steps of: charging a battery cell at a first current rate for a first duration; charging a battery cell at a second current rate for a second duration following the first duration; and charging a battery cell at a third current rate for a third duration following the second duration, wherein the battery cell comprises an electrode assembly comprising a plurality of positive electrodes, a plurality of negative electrodes, and separators separating the plurality of positive electrodes and the plurality of negative electrodes, wherein the positive electrode comprises a positive current collector and a positive active material coated on the positive current collector, wherein the positive active material comprises lithium iron phosphate and lithium iron oxide, and the second current rate is greater than the first current rate.

[0006] The second current speed is at least twice and no more than five times the first current speed.

[0007] The second current speed is at least twice the first current speed, and the second current speed is five times or less the first current speed.

[0008] The third current speed is at least 1 / 20 times the second current speed, and the third current speed is at least 1 / 5 times the second current speed.

[0009] The third current speed is at least 1 / 5 times the first current speed, and the third current speed is at least 1 / 2 times the first current speed.

[0010] During the first duration, the battery cell is charged to a State of Charge (SOC) range of 10% to 15%.

[0011] During the second duration mentioned above, the battery cell is charged to a range of SOC 60% to SOC 80%.

[0012] During the third duration mentioned above, the battery cell is charged to SOC 100%.

[0013] The above third current rate is in the range of 1 / 100 C to about 1 / 5 C.

[0014] The above second current rate is in the range of 1 / 3 C to about 1 C.

[0015] The sum of the first and second durations is shorter than the third duration.

[0016] The above third duration is more than twice the sum of the above first and second durations.

[0017] According to exemplary embodiments of the present invention, by charging a battery cell at a low current rate, the capacity of the lithium iron oxide, which is a sacrificial cathode material, can be fully realized. Furthermore, by charging the battery cell at a high current rate prior to the low current rate, the throughput of secondary battery manufacturing can be improved.

[0018] The effects obtainable from the exemplary embodiments of the present invention are not limited to those mentioned above, and other unmentioned effects can be clearly derived and understood by those skilled in the art to which the exemplary embodiments of the present disclosure belong from the following description. That is, unintended effects resulting from the implementation of the exemplary embodiments of the present disclosure can also be derived by those skilled in the art from the exemplary embodiments of the present disclosure.

[0019] FIGS. 1 and FIGS. 2 are flowcharts for explaining a method for manufacturing a secondary battery according to exemplary embodiments.

[0020] FIG. 3 is a drawing showing a secondary battery manufacturing facility according to exemplary embodiments.

[0021] FIG. 4 is a cross-sectional view of a plurality of battery cells according to exemplary embodiments.

[0022] FIG. 5 is a graph illustrating a method for manufacturing a secondary battery according to exemplary embodiments.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0024] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0025] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0026] Since embodiments of the present invention are provided to more fully explain the invention to those skilled in the art, the shapes and sizes of the components in the drawings may be exaggerated, omitted, or schematically depicted for clearer explanation. Accordingly, the size or proportion of each component does not entirely reflect the actual size or proportion.

[0027]

[0028] (1st and 2nd embodiments)

[0029] FIGS. 1 and FIGS. 2 are flowcharts for explaining a method for manufacturing a secondary battery according to exemplary embodiments.

[0030] FIG. 3 is a drawing showing a secondary battery manufacturing facility (100) according to exemplary embodiments.

[0031] FIG. 4 is a cross-sectional view of a plurality of battery cells (BC) according to exemplary embodiments.

[0032] FIG. 5 is a graph illustrating a method for manufacturing a secondary battery according to exemplary embodiments.

[0033] Referring to FIGS. 1, FIGS. 3 and FIGS. 4, a plurality of battery cells (BC) in P110 can be loaded into a secondary battery manufacturing facility (100).

[0034] A plurality of battery cells (BC) may include a cell case (CC) and an electrode assembly (EA). A plurality of battery cells (BC) may further include an electrolyte injected into the cell case (CC).

[0035] The technical concept of the present invention will be explained with reference to an example in which an electrode assembly (EA) comprises a plurality of positive electrodes (EP), a plurality of negative electrodes (EN), and a plurality of separators (SP). A person skilled in the art can easily arrive at an embodiment in which the electrode assembly comprises a positive electrode, a negative electrode, and a winding structure of a separator interposed between them, based on what is described herein.

[0036] Each of the plurality of positive electrodes (EP) may include a positive current collector and a positive active material. The thickness of the positive current collector may be in the range from about 3 μm to about 500 μm. The positive current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The positive current collector may include, for example, any one of stainless steel, nickel, titanium, calcined carbon, and aluminum. The positive current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the positive current collector may include a micro-irregular structure to increase the adhesion of the active material. The shape of the positive current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0037] The positive electrode active material is a material capable of causing an electrochemical reaction. The positive electrode active material may be a lithium transition metal oxide. The positive electrode active material is, for example, with the chemical formula Li 1+x M 1-y M' y PO 4-z X z It may include any one of the olivine-based lithium metal phosphates represented by (where M is a transition metal, more specifically one of Fe, Mn, Co, and Ni; M' is one of Al, Mg, and Ti; X is one of F, S, and N; -0.5≤x≤+0.5; 0≤y≤0.5; and 0≤z≤0.1). The positive electrode active material may include, for example, lithium iron phosphate. The positive electrode active material is Li 1+x M 1-y M'yO 2-z X zIt may further include a lithium metal oxide represented by (where M is a main metal one of Fe, Mn, Co, and Ni, M' is a substituent metal element different from M among Fe, Mn, Co, and Ni, and X is a substitutable non-metal element or defect). The positive electrode active material may include, for example, lithium iron oxide.

[0038] According to exemplary embodiments, when the positive electrode active material comprises a first active material comprising lithium iron phosphate (e.g., LiFePO4) and a second active material comprising lithium iron oxide (e.g., LiFeO2), the mass ratio of the first positive electrode active material in the positive electrode active material may be in the range of about 0.1 wt% to about 10 wt%, and the mass ratio of the second positive electrode active material in the positive electrode active material may be in the range of about 80 wt% to about 99 wt%.

[0039] Each of the plurality of negative electrodes (EN) may include a negative current collector and a negative active material. The thickness of the negative current collector may be in the range of about 3 μm to about 500 μm. The negative current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The negative current collector may include any one of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy. The negative current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the negative current collector may include a micro-irregular structure to increase the adhesion of the active material. The shape of the negative current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0040] The negative electrode active material may include carbon, for example, non-graphitizable carbon, graphite-based carbon, etc. The negative electrode active material is, for example, Li x Fe2O3(0≤x≤1), LixWO2(0≤x≤1), Sn x Me1-x Me y O z (wherein Me is any one of Mn, Fe, Pb, and Ge, and Me' is any one of Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, and halogens; 0 <x≤1이고; 1≤y≤3 이며; 1≤z≤8) 등의 금속 복합 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 리튬 금속; 리튬 합금; 규소계 합금; 및 주석계 합금 중 어느 하나를 포함할 수 있다. 음극 활물질은, 예컨대, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 포함할 수도 있다.

[0041] Each of the plurality of anodes (EP) may include an anode tab, and each of the plurality of cathodes (EN) may include a cathode tab. The anode tab of each of the plurality of anodes (EP) may be coupled to an anode lead (LP). The anode tab of each of the plurality of anodes (EP) may be welded to an anode lead (LP). The cathode tab of each of the plurality of cathodes (EN) may be coupled to a cathode lead (LN). The cathode tab of each of the plurality of cathodes (EN) may be welded to a cathode lead (LN).

[0042] The positive lead (LP) and the negative lead (LN) may protrude outside the cell case (CC). According to exemplary embodiments, the positive lead (LP) and the negative lead (LN) may be on opposite sides of the cell case (CC), and the positive lead (LP) and the negative lead (LN) may protrude in opposite directions. Unlike in FIG. 2, the positive lead (LP) and the negative lead (LN) may be on the same sides of the cell case (CC), and the positive lead (LP) and the negative lead (LN) may protrude in the same direction.

[0043] A plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may alternate with separators (SP). Accordingly, one of a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may be interposed between two adjacent separators (SP). Each of the separators (SP) may be in contact with at least one of a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN). Each of the separators (SP) can isolate a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) by preventing direct contact between the plurality of positive electrodes (EP) and a plurality of negative electrodes (EN), thereby preventing the formation of an unwanted closed loop due to a short circuit between the plurality of positive electrodes (EP) and a plurality of negative electrodes (EN). Each of the plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may have a flat film shape.

[0044] The cell case (CC) may include a cup-shaped receiving portion. The receiving portion may be formed by a pouch forming process. An electrode assembly (EA) may be received in the receiving portion. The cell case (CC) may be any one of a pouch case, a cylindrical can, and a rectangular can. An electrode assembly (EA) may be embedded within the cell case (CC). Hereinafter, the technical concept of the present invention is described based on an example in which the cell case (CC) is an aluminum laminate sheet; however, a person skilled in the art will be able to easily arrive at an example in which the cell case (CC) is one of a cylindrical can and a rectangular can based on what is described herein.

[0045] The cell case (CC) may include an inner resin layer, a metal layer, and an outer resin layer. An adhesive and an anti-corrosion layer may be further provided between the inner resin layer and the metal layer and between the outer resin layer and the metal layer.

[0046] The inner resin layer may have heat-sealability and may be referred to as a sealant layer. The inner resin layer enables sealing of the cell case (CC). The inner resin layer may include polyolefin-based resins such as polypropylene (PP) and polyethylene (PE), for example. The metal layer may include one of an alloy of iron, carbon, chromium, and manganese, an alloy of iron, chromium, and nickel, and aluminum. The metal layer may be a gas barrier. The metal layer may block the entry and exit of gas from the cell case (CC). The outer resin layer may be a surface protection layer. The outer resin layer may include a material having wear resistance and heat resistance, such as nylon resin.

[0047] The electrolyte may be any one of a non-aqueous electrolyte, an aqueous electrolyte, an ionic electrolyte, and a gel electrolyte. The electrolyte may also be a solid electrolyte. The non-aqueous electrolyte may include organic solvents such as ethylene carbonate and dimethyl carbonate, and lithium salts such as LiPF6 and LiBF4 dissolved in organic solvents. The non-aqueous electrolyte may also include ethylene carbonate dissolved in tetraethylammonium salts. The aqueous electrolyte may include sodium sulfate solution, sulfuric acid solution, hydrochloric acid solution, or sodium hydroxide solution. The ionic electrolyte is an ionic compound that is in a liquid state at room temperature, such as ethylmethylimidazolidium bis(trifluoromethylsulfonyl)amide, and has high thermal stability. The gel electrolyte may be provided by treating the liquid electrolyte using polyacrylonitrile and PVA, etc. The solid electrolyte may include a polymer material doped with a lithium salt (e.g., polyethylene oxide (PEO)) and a ceramic electrolyte composed of ceramic materials such as NASICON and LLZO.

[0048] The secondary battery manufacturing facility (100) may be configured to process a plurality of battery cells (BC). The secondary battery manufacturing facility (100) may be configured to perform a formation process on a plurality of battery cells (BC). The secondary battery manufacturing facility (100) may include a driving unit (110), a support unit (120), and a plurality of pressure plates (130).

[0049] The formation process is the initial charging process of multiple battery cells (BC). The formation process can induce a reaction between multiple positive electrodes (EP) and the electrolyte, and a reaction between multiple negative electrodes (EN) and the electrolyte. A CEI (Cathode Electrolyte Interphase) layer can be formed by the reaction between the multiple positive electrodes (EP) and the electrolyte. A SEI (Solid Electrolyte Interphase) layer can be formed by the reaction between the multiple negative electrodes (EN) and the electrolyte.

[0050] The CEI layer can improve the lifespan and performance of multiple battery cells (BC) by maintaining the stability of the anode surface, preventing oxidation of the electrolyte, and stabilizing the electrochemical reaction inside the multiple battery cells (BC). Furthermore, the CEI layer can prevent corrosion of multiple anodes (EP) by blocking electron conduction and allowing the movement of lithium ions.

[0051] The SEI layer can protect the electrode surface by preventing further decomposition of the electrolyte in the electrolyte, allow the movement of lithium ions, and block the movement of electrolyte molecules, thereby enhancing the stability of multiple battery cells (BC). In addition, the SEI layer can mitigate (or minimize) self-discharge and capacity loss.

[0052] The formation process can be performed by an energy source such as a current source. While the formation process is being performed, a plurality of battery cells (BC) can be pressed by pressure plates (130).

[0053] After the formation process, an aging process may be performed on multiple battery cells (BC) at high temperature and / or room temperature. The aging process can stabilize the electrochemical characteristics of the multiple battery cells (BC) after the formation process, monitor the performance of the battery cells to identify and remove defective products, and fully carry out chemical reactions within the cells to improve long-term performance and lifespan.

[0054] The aging process may include storing a plurality of battery cells (BC) in an environment having controlled temperature and humidity. Through the aging process, the electrolyte (EL, see FIG. 2) may be more evenly dispersed within the plurality of battery cells (BC). During the storage period of the plurality of battery cells (BC), the voltage, capacity, and internal resistance of the plurality of battery cells (BC) may be measured, and accordingly, the quality and defects of the plurality of battery cells (BC) may be determined.

[0055] After the aging process, additional charge / discharge processes may be performed on multiple battery cells (BC). The additional charge / discharge processes may be performed by a secondary battery manufacturing facility (100).

[0056] A plurality of battery cells (BC) loaded into a secondary battery manufacturing facility (100) may be located between pressure plates (130). While a formation process is performed on the plurality of battery cells (BC) or while the plurality of battery cells (BC) are being charged and / or discharged, the plurality of battery cells (BC) may be pressed by the pressure plates (130).

[0057] Gas trapping and lithium plating can be prevented by uniform pressurization of multiple battery cells (BC), and the uniformity of the SEI film can be enhanced. Multiple battery cells (BC) containing a uniform SEI film can have a relatively short charging time.

[0058] According to exemplary embodiments, the drive unit (110) may include a drive plate (111) and drive rods (116). The drive rods (116) may be configured to transmit an external driving force to the drive plate (111). The drive rods (116) may be connected, for example, to a hydraulic cylinder or a linear servo motor. The drive plate (111) may have a roughly flat shape.

[0059] The support member (120) may include a support plate (121) and elastic elements (126). The elastic elements (126) may be coupled to a second surface (121S2) of the support plate (121). Appropriate pressure may be applied to a plurality of battery cells (BC) by each of the elastic elements (126). The elastic elements (126) may be connected directly or indirectly to a sensor such as a load cell, and the pressure applied to the plurality of battery cells (BC) may be controlled based on the elastic force of the elastic elements (126).

[0060] According to exemplary embodiments, pressure plates (130) may be interposed between the driving plate (111) and the support plate (121). Each of the pressure plates (130) may be substantially parallel to the driving plate (111).

[0061] Each of the pressure plates (130) can be coupled to a shaft. Accordingly, the pressure plates (130) can be moved along the shaft by driving the driving plate (111). A plurality of battery cells (BC) can be inserted between the pressure plates (130), and the plurality of battery cells (BC) can be pressed by the pressure plates (130), the driving plate (111), and the support plate (121).

[0062] Each of the pressure plates (130) may have a flat plate shape. The pressure plates (130) may include a heat source such as a hot plate. Accordingly, the pressure plates (130) may be configured to heat the plurality of battery cells (BC) while a formation process is performed on the plurality of battery cells (BC) or while the plurality of battery cells (BC) are being charged and / or discharged. By heating the plurality of battery cells (BC) while the plurality of battery cells (BC) are being charged and / or discharged, the formation of the SEI layer and the CEI layer can be promoted.

[0063] According to exemplary embodiments, the surface temperature of each of the pressure plates (130) may be about 20°C or higher. According to exemplary embodiments, the surface temperature of each of the pressure plates (130) may be about 70°C or lower. According to exemplary embodiments, by heating a plurality of battery cells (BC) using pressure plates (130) having a surface temperature of about 70°C or lower, the performance of the plurality of battery cells (BC) can be prevented from deteriorating during the formation process.

[0064] The secondary battery manufacturing facility (100) may further include charging terminals configured to be electrically connected to the positive lead (LP) and negative lead (LN) of each of the plurality of battery cells (BC). The charging terminals may come into contact with the positive lead (LP) and negative lead (LN) of each of the plurality of battery cells (BC). The charging terminals may be configured to deliver external power to the plurality of battery cells (BC).

[0065]

[0066] Referring to FIGS. 1, 2 and 5, a formation process can be performed on a plurality of battery cells (BC) at P120. Performing the formation process at P120 may include charging a plurality of battery cells (BC) at a first current rate (C1) at P121, charging a plurality of battery cells (BC) at a second current rate (C2) at P123, and charging a plurality of battery cells (BC) at a third current rate (C3) at P125.

[0067] According to exemplary embodiments, the second current rate (C2) may differ from the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be greater than the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be at least about 1.5 times the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be at least about 2 times the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be at least about 5 times the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be at least about 4.5 times the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be at least about 4 times the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be about 3.5 times or less of the first current rate (C1). According to exemplary embodiments, the second current rate (C2) may be about 3 times or less of the first current rate (C1).

[0068] According to exemplary embodiments, the third current rate (C3) may differ from the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be smaller than the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be at least about 1 / 100 times the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be at least about 1 / 50 times the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be at least about 1 / 20 times the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be less than about 1 / 3 times the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be less than about 1 / 5 times the second current rate (C2). According to exemplary embodiments, the third current rate (C3) may be about 1 / 10 times or less of the second current rate (C2).

[0069] According to exemplary embodiments, the third current rate (C3) may differ from the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be smaller than the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be at least about 1 / 10 times the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be at least about 1 / 5 times the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be less than about 3 / 4 times the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be less than about 1 / 2 times the first current rate (C1). According to exemplary embodiments, the third current rate (C3) may be less than about 1 / 3 times the first current rate (C1).

[0070] According to exemplary embodiments, the first current rate (C1) may be about 1 / 3 C, but is not limited thereto. According to exemplary embodiments, the second current rate (C2) may be in the range of about 1 / 3 C to about 1 C, but is not limited thereto. According to exemplary embodiments, the third current rate (C2) may be in the range of about 1 / 100 C to about 1 / 5 C, but is not limited thereto.

[0071] According to exemplary embodiments, the first duration (D1) of the first current rate (C1) may differ from the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the first duration (D1) of the first current rate (C1) may be shorter than the second duration (D2) of the second current rate (C2). Here, the first duration (D1) of the first current rate (C1) is the duration during which a plurality of battery cells (BC) are charged at the first current rate (C1), and the second duration (D2) of the second current rate (C2) is the duration during which a plurality of battery cells (BC) are charged at the second current rate (C2). The second duration (D2) of the second current rate (C2) may follow the first duration (D1) of the first current rate (C1).

[0072] According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may differ from the first duration (D1) of the first current rate (C1). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be longer than the first duration (D1) of the first current rate (C1). Here, the third duration (D3) of the third current rate (C3) is the duration during which a plurality of battery cells (BC) are charged at the third current rate (C3). The third duration (D3) of the third current rate (C3) may continue until each of the plurality of battery cells (BC) is fully charged. The third duration (D3) of the third current rate (C3) may follow the second duration (D2) of the second current rate (C2).

[0073] According to exemplary embodiments, during a first duration (D1), a plurality of battery cells (BC) can be charged to a range of about 10% to about 15% State of Charge (SOC). According to exemplary embodiments, during a second duration (D2), a plurality of battery cells (BC) can be charged to a range of about 60% to about 80% SOC. According to exemplary embodiments, during a third duration (D3), a plurality of battery cells (BC) can be charged to about 100% SOC.

[0074] According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be different from the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be longer than the second duration (D2) of the second current rate (C2).

[0075] According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 10 times or less the first duration (D1) of the first current rate (C1). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 2 times or more the first duration (D1) of the first current rate (C1). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 3 times or more the first duration (D1) of the first current rate (C1). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 4 times or more the first duration (D1) of the first current rate (C1). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about five times or more the first duration (D1) of the first current rate (C1).

[0076] According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 10 times or less the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 2 times or more the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 3 times or more the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about 4 times or more the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about five times or more the second duration (D2) of the second current rate (C2).

[0077] According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about five times or less the sum of the second duration (D2) of the first current rate (C1) and the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about four times or less the sum of the second duration (D2) of the first current rate (C1) and the second duration (D2) of the second current rate (C2). According to exemplary embodiments, the third duration (D3) of the third current rate (C3) may be about two times or more the sum of the second duration (D2) of the first current rate (C1) and the second duration (D2) of the second current rate (C2).

[0078] According to exemplary embodiments, by charging a plurality of battery cells (BC) at a relatively low first current rate (C1) during a first duration (D1), which is an initial period of the formation process, the formation of a CEI film and an SEI film can be promoted.

[0079] In addition, by charging multiple battery cells (BC) at a sufficiently low third current rate (C3) during the third duration (D3), the capacity of the lithium iron oxide can be fully realized, and a large amount of gas generated from the lithium iron oxide at the beginning of the formation process can be captured. The third duration (D3) can be sustained up to SOC 100% to fully realize the capacity of the lithium iron oxide.

[0080] At this time, by charging a plurality of battery cells (BC) at a sufficiently high second current rate (C2) during the second duration (D2), the duration of the overall formation process (i.e., the sum of the first to third durations (D1, D2, D3)) can be prevented from becoming excessively long, and the throughput of secondary battery manufacturing can be improved.

[0081]

[0082] The present invention has been described in more detail above through drawings and embodiments. However, the configurations described in the drawings or embodiments described in this specification are merely one embodiment of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

Claims

1. A step of charging a battery cell at a first current rate during a first duration; A step of charging a battery cell at a second current rate during a second duration following a first duration; and The method includes the step of charging a battery cell at a third current rate during a third duration following a second duration, and The battery cell comprises an electrode assembly including a plurality of positive electrodes, a plurality of negative electrodes, and separators that isolate the plurality of positive electrodes and the plurality of negative electrodes. The above positive electrode comprises a positive current collector and a positive active material coated on the positive current collector, and The above positive active material comprises lithium iron phosphate and lithium iron oxide, and A method for manufacturing a secondary battery characterized in that the second current rate is greater than the first current rate.

2. In Paragraph 1, The second current speed is at least twice the first current speed, and A method for manufacturing a secondary battery characterized in that the second current rate is five times or less of the first current rate.

3. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the third current rate is smaller than the second current rate.

4. In Paragraph 1, The third current rate is at least 1 / 20 times the second current rate, and A method for manufacturing a secondary battery characterized in that the third current rate is 1 / 5 times or less of the second current rate.

5. In Paragraph 1, The third current rate is at least 1 / 5 times the first current rate, and A method for manufacturing a secondary battery characterized in that the third current rate is less than or equal to half the first current rate.

6. In Paragraph 1, A method for manufacturing a secondary battery characterized in that, during the first duration, the battery cell is charged to a State of Charge (SOC) range of 10% to 15%.

7. In Paragraph 1, A method for manufacturing a secondary battery characterized in that, during the second duration, the battery cell is charged to a range of SOC 60% to SOC 80%.

8. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the battery cell is charged to SOC 100% during the third duration.

9. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the third current rate is in the range of 1 / 100 C to about 1 / 5 C.

10. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the second current rate is in the range of 1 / 3 C to about 1 C.

11. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the sum of the first duration and the second duration is shorter than the third duration.

12. In Paragraph 1, A method for manufacturing a secondary battery characterized in that the third duration is at least twice the sum of the first and second durations.

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