Method for activating secondary batteries

Abstract

The activation method of the present invention includes a step of determining a reduction reaction voltage by an electrolyte additive, a pre-charging step of pre-charging a secondary battery into which an electrolyte containing the electrolyte additive is injected, and a pre-aging step of impregnating and aging an electrode assembly housed in the secondary battery in the injected electrolyte, wherein the cut-off voltage of the pre-charging step is lower than the reduction reaction voltage.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0121099 dated September 10, 2021, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for activating a secondary battery, and more particularly, to an activation method that can reduce only the negative electrode potential while suppressing the negative electrode reaction of some additives in an electrolyte when reducing the negative electrode potential through pre-charging before wetting. [Background technology]

[0003] Generally, a secondary battery is a battery that can be charged and discharged, unlike a primary battery that cannot be recharged, and is widely used in electronic devices such as mobile phones, laptops, computers, and video cameras, as well as electric vehicles, etc. In particular, lithium secondary batteries have a larger capacity than nickel-cadmium batteries or nickel-metal hydride batteries and a higher energy density per unit weight, so their use is rapidly increasing.

[0004] Such lithium secondary batteries mainly use lithium-based oxides and carbon materials as the positive and negative electrode active materials, respectively, and include an electrode assembly in which a positive electrode plate and a negative electrode plate coated with the positive and negative electrode active materials are arranged with a separator sandwiched therebetween, and an exterior material that seals and houses the electrode assembly together with an electrolyte.

[0005] Meanwhile, lithium secondary batteries can be classified into can-type secondary batteries, in which the electrode assembly is housed in a metal can, and pouch-type secondary batteries, in which the electrode assembly is housed in a pouch made of an aluminum laminate sheet, depending on the shape of the battery case.

[0006] Generally, a secondary battery is manufactured by injecting a liquid electrolyte into a battery case in which an electrode assembly is housed, and then sealing the battery case.

[0007] Such lithium secondary batteries may experience various types of defects due to various causes during the manufacturing process or during use. In particular, some manufactured secondary batteries may exhibit a phenomenon in which the voltage drops more than the self-discharge rate, which is called low voltage.

[0008] The low voltage defect of such secondary batteries is typically caused by metallic foreign matter present inside the battery. In particular, when metallic foreign matter such as iron or copper is present in the positive electrode plate of a secondary battery, such metallic foreign matter can grow into dendrites in the negative electrode. Furthermore, such dendrites can cause an internal short circuit in the secondary battery, resulting in failure or damage to the secondary battery, and in severe cases, fire.

[0009] Various attempts have been made to address this issue, with one typical example being pre-charging, a process in which charging is performed after electrolyte injection and before electrolyte wetting to reduce the negative electrode potential. The negative electrode potential before charging is 3 V or higher relative to the Li reduction potential, which is higher than the reduction potential of iron (2.59 V) and nickel (2.78 V) inside the cell. After the electrolyte is injected, it gradually wets into the electrode voids, which can oxidize and dissolve foreign materials or Cu. Therefore, by performing a pre-charging process between the injection of the electrolyte and the completion of electrolyte wetting, the negative electrode potential can be reduced to prevent the dissolution of foreign materials or metals such as Cu.

[0010] However, because pre-charging begins and proceeds before the electrolyte has fully penetrated the pores of the electrode, some additives contained in the electrolyte may undergo a reduction reaction on the surface of the negative electrode during pre-charging, causing an uneven coating to form on the surface of the negative electrode, which may result in a decrease in the battery life characteristics. Therefore, there is a need for development of a technology to suppress the reaction of electrolyte additives during pre-charging. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention is intended to solve the above-mentioned problems of the conventional art, and aims to reduce only the potential of the negative electrode current collector while suppressing the additive from reacting on the surface of the negative electrode and forming a coating when pre-charging is performed before wetting a secondary battery. [Means for solving the problem]

[0012] The method for activating a secondary battery according to the present invention includes a step of determining a reduction reaction voltage by an electrolyte additive, a pre-charging step of pre-charging a secondary battery into which an electrolyte containing the electrolyte additive is injected, and a pre-aging step of impregnating and aging an electrode assembly housed in the secondary battery in the injected electrolyte, wherein the cut-off voltage of the pre-charging step is lower than the reduction reaction voltage.

[0013] In an embodiment of the present invention, the reduction reaction voltage may be a voltage of an onset point at which the reduction reaction of the electrolyte begins in a dQ / dV graph obtained by differentiating a voltage-capacity profile during the first charge of a secondary battery including the electrolyte additive.

[0014] In one embodiment of the present invention, the charge cut-off voltage in the pre-charging stage may be set within a range of 70% to 99% of the reduction reaction voltage.

[0015] In one embodiment of the present invention, the pre-charging step can be initiated immediately after the injection of the electrolyte and within three hours.

[0016] In one embodiment of the present invention, the pre-charging step may be performed by a constant current charging method.

[0017] In one embodiment of the present invention, the pre-charging step may charge the secondary battery at a C-rate of 0.01 to 0.5.

[0018] In one embodiment of the present invention, after the pre-aging step, a primary charging step of charging the pre-aged secondary battery and an aging step of aging the primarily charged secondary battery may be further included.

[0019] In one embodiment of the present invention, the first charging step may charge the secondary battery while applying pressure to the secondary battery.

[0020] In an embodiment of the present invention, the method may further include fully discharging and fully charging the secondary battery.

[0021] In one embodiment of the present invention, the method may further include aging the secondary battery after the fully discharging and fully charging steps. [Effects of the Invention]

[0022] The activation method of the present invention has the effects of suppressing the negative electrode reaction of the electrolyte additive, reducing the potential of the negative electrode, preventing low voltage defects, and forming a uniform SEI coating. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a flowchart of an activation method according to one embodiment of the present invention. [Figure 2] 1 is a flowchart of an activation method according to one embodiment of the present invention. [Figure 3] 1 is a flowchart of an activation method according to one embodiment of the present invention. [Figure 4] 10 is a dQ / dV graph obtained by differentiating the voltage-capacity profile during the first charge of a secondary battery for each type of additive. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Before that, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to best describe his / her invention.

[0025] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0026] FIG. 1 is a diagram showing the sequence of a method for activating a secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the method for activating a secondary battery according to an embodiment of the present invention includes a step S100 of deriving a reduction reaction voltage by an electrolyte additive, a pre-charging step S200 of pre-charging a secondary battery into which an electrolyte containing an electrolyte additive is injected, and a pre-aging step S300 of impregnating and aging an electrode assembly housed in the secondary battery in the injected electrolyte.

[0027] Generally, after the assembly of a secondary battery is completed, the assembled battery undergoes an activation process, which includes processes such as charging, aging, and discharging, to stabilize the battery structure and prepare it for use. However, prior to the activation process, a pre-aging step is performed in which the secondary battery, into which the electrolyte has been injected, is left at room temperature for a certain period of time to stabilize the secondary battery so that the electrolyte injected into the secondary battery is sufficiently impregnated into the electrode assembly.

[0028] Referring to FIG. 1, after injecting an electrolyte into a secondary battery, a pre-aging step is performed in which the electrolyte is wetting into the electrode assembly. As mentioned above, in order to prevent low voltage defects due to the elution of foreign matter or metal, a technology has been introduced in which a pre-charging step S200 is performed in which the secondary battery is charged at a predetermined charging rate after the injection of the electrolyte and before completing the pre-aging step S300.

[0029] The introduction of a pre-charge step has the advantage of reducing the negative electrode potential while the electrolyte is impregnating the electrode, thereby preventing metal oxidation and elution and suppressing low voltage defects. However, the inventors of the present invention predicted that if the charge SOC is high during the pre-charge step, some additive components in the electrolyte will be reductively decomposed to form a non-uniform coating on the negative electrode, and that this non-uniformity may be exacerbated in the case of a high-loading electrode. Therefore, they arrived at the present invention to provide a pre-charge method that can reduce only the negative electrode potential while suppressing the negative electrode reaction of the electrolyte additive.

[0030] Electrolytes contain various types of additives to improve the ionic conductivity of the electrolyte, battery life, or safety. These additives can be classified according to their function into SEI formation / regulation agents on the negative electrode surface, overcharge prevention agents in secondary batteries, electrolyte ionic conductivity improvers, flame retardants, etc., and each additive has a different reduction potential at which it reacts on the negative electrode surface.

[0031] Therefore, the present invention determines the reduction reaction voltage according to the type of electrolyte additive, and then sets the end-of-charge voltage in the pre-charge step to be lower than the reduction reaction voltage. This induces the reduction decomposition reaction of the additive to proceed after impregnation with the electrolyte, thereby forming a uniform SEI film and reducing the potential of the negative electrode before impregnation with the electrolyte, thereby suppressing low-voltage defects.

[0032] <Step of determining reduction reaction voltage by additive> The step S100 of deriving a reduction reaction voltage according to the electrolyte additive is a step of deriving a reduction reaction voltage of a secondary battery according to an electrolyte additive, which serves as a reference for the end-of-charge voltage in order to set the end-of-charge voltage in the pre-charge step. Since the reductive decomposition reaction behavior and reductive decomposition voltage differ depending on the type of additive, an appropriate reference for the end-of-charge voltage in the pre-charge step can be derived through the step of deriving a reduction reaction voltage according to the present invention.

[0033] In one specific example, the reduction reaction voltage of the additive can be defined as the voltage at the onset point where the reduction reaction of the electrolyte begins in a dQ / dV graph obtained by differentiating the voltage-capacity profile during the first charge of a secondary battery containing the electrolyte additive.

[0034] FIG. 4 shows dQ / dV graphs obtained by differentiating voltage-capacity profiles during the first charge of secondary batteries for various additives according to an embodiment of the present invention (Ref. is a control group containing no additive). Referring to FIG. 4, the dQ / dV graph outline varies depending on the additive. The dQ / dV for Additive A shows no peak, while the dQ / dV for Additives B and C show peaks. Here, the "peak" refers to the transition point where the slope of dQ / dV suddenly increases and then suddenly decreases, and the "onset point" can be defined as the point where the slope of dQ / dV begins to increase. Specifically, as shown in FIG. 4, the onset point for Additive B is observed around 1.5 V, and the onset point for Additive C is observed around 1.9 V. Therefore, the pre-charge end-of-charge voltage for a battery containing Additive B can be set to 1.5 V, and the pre-charge end-of-charge voltage for a battery containing Additive C can be set to 1.9 V.

[0035] The charging method for obtaining the voltage-capacity profile can be performed by a known method. In one specific example, a secondary battery containing the electrolyte additive as an electrolyte is charged to an SOC (state of charge) of 40% at room temperature (23°C) within a driving voltage range of 1.0 to 2.7 V under a C-rate of 0.1, and the change in capacity depending on the voltage is observed to obtain the voltage-capacity profile, but the method is not limited thereto.

[0036] In one specific example, the secondary battery may be a full cell.

[0037] <Pre-charging stage> The pre-charging step S200 of the present invention is a step in which charging is performed after the injection of the electrolyte and before the impregnation of the electrolyte in order to reduce the potential of the negative electrode and prevent metal elution, and the present invention is characterized in that charging is performed by setting the end-of-charge voltage of the pre-charging step to be lower than the reduction reaction voltage of the electrolyte additive.

[0038] If charging is performed by setting the end-of-charge voltage in the pre-charge step to a voltage exceeding the additive's Hwang-Woong reaction voltage, some additives are reductively decomposed to form a non-uniform coating on the surface of the negative electrode. However, in the present invention, by setting the end-of-charge voltage in the pre-charge step to a voltage lower than the additive's reductive reaction voltage, the additive's reductive decomposition reaction proceeds after electrolyte impregnation, forming a uniform SEI coating, thereby improving life characteristics.

[0039] In one specific example, the end-of-charge voltage in the pre-charging step may be set within a range of 70 to 99% of the reduction reaction voltage of the electrolyte additive, and more preferably within a range of 75 to 95%. If the end-of-charge voltage is too high, the electrolyte additive may be reductively decomposed, which is undesirable, and if the end-of-charge voltage is too low, the negative electrode potential is not sufficiently reduced, which is undesirable, so the above-mentioned range is preferable.

[0040] The pre-charging step of the present invention is initiated after the injection of the electrolyte. Immediately after the electrolyte injection, the electrolyte gradually moves into the electrode assembly, and the reductive decomposition reaction of the electrolyte additive may proceed. Therefore, the shorter the time interval between the injection of the electrolyte and the start of the pre-charging step, the better. In one embodiment, the pre-charging step may be performed within 6 hours after the injection of the electrolyte, more preferably within 3 hours after the injection of the electrolyte, and most ideally immediately after the injection of the electrolyte.

[0041] The charging method in the pre-charging step of the present invention may be a CC (constant current) charging method or a CC-CV (constant voltage-constant current) charging method. Because the purpose of the pre-charging step of the present invention is to reduce the potential of the negative electrode, a CC charging method, which charges at a constant current, is basically suitable. However, in some cases, when an overcurrent flows through the battery, a CV (constant voltage) charging method may be supplementarily adopted to adjust the current.

[0042] The charge rate in the pre-charge step can be appropriately set in consideration of the desired time required for the pre-charge step, and specifically, it may be, but is not limited to, a C-rate of 0.01 to 0.5, preferably a C-rate of 0.02 to 0.4, and more preferably a C-rate of 0.03 to 0.3. A low charge rate can stably reduce the negative electrode potential, but the time required for pre-charge increases accordingly, which can lead to reductive decomposition of the additive before impregnation. Therefore, a charge rate that is too low is not preferable. Conversely, a charge rate that is too high can suddenly reduce the negative electrode potential, which can cause side effects.

[0043] <Pre-aging stage> The pre-aging step S300 is a step in which the battery is aged after assembly so that the electrolyte is sufficiently impregnated into the electrode assembly.

[0044] More specifically, when a secondary battery is charged, electrons travel along the conductor to the negative electrode, causing charge neutrality. Lithium ions are absorbed into the negative electrode to achieve charge neutrality. While lithium ions can be absorbed in areas impregnated with electrolyte (i.e., wetting areas where ion migration paths are maintained), it is relatively difficult to absorb them in non-wetting areas. Therefore, through the pre-aging process, the battery can be aged under certain temperature and humidity conditions to ensure that the electrolyte is properly impregnated into the positive and negative electrodes.

[0045] After the pre-aging step, a series of activation processes including a primary charging step in which the secondary battery is charged to a predetermined depth of charge and an aging step in which the charged battery is aged are fully carried out. In the present invention, the series of processes including the pre-aging step will be described as being included in the concept of the activation process.

[0046] In one embodiment, the time required for the pre-aging process may be 3 to 72 hours, 6 to 60 hours, or 12 to 48 hours, and this can be appropriately adjusted depending on the materials of the positive electrode, negative electrode, and electrolyte, the design capacity of the secondary battery, etc.

[0047] The pre-aging temperature may be set at room temperature, 20°C to 30°C, more specifically, 22°C to 28°C, more specifically, 23°C to 27°C, and even more specifically, 25°C to 27°C. However, the pre-aging temperature is not necessarily limited to this and may be appropriately changed depending on the characteristics of the battery to be designed.

[0048] The activation process of the present invention is performed on a lithium secondary battery, which is assembled through the following process and then undergoes the pre-aging step.

[0049] An electrode mixture containing an electrode active material and a binder is applied to an electrode current collector to prepare a positive electrode and a negative electrode, respectively, and then a separator is interposed between the positive electrode and the negative electrode to prepare an electrode assembly.

[0050] The electrode assembly thus prepared is housed in a battery case, after which an electrolyte is injected and the battery case is sealed to assemble the battery.

[0051] The step of assembling such a battery is not particularly limited, and can be carried out by a known method.

[0052] The electrode assembly is not particularly limited as long as it has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. Examples of the electrode assembly include a jelly roll type, a stack type, and a stack / folding type.

[0053] The battery case is not particularly limited as long as it is used as an exterior material for packaging a battery, and may be cylindrical, square, or pouch-shaped.

[0054] The electrolyte may include an organic solvent, a lithium salt, and an additive.

[0055] The organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charge and discharge process of the battery, and may be, for example, a cyclic carbonate, a linear carbonate, an ester, an ether, a ketone, etc. These may be used alone or in combination of two or more.

[0056] Of the above organic solvents, carbonate-based organic solvents may be particularly preferably used. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Typical examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0057] The lithium salt may be any lithium salt commonly used in electrolytes for lithium secondary batteries, such as LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4, and may be used alone or in combination of two or more thereof.

[0058] The electrolyte solution further contains an additive. For example, the additive may be any one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, unsaturated sultone, acyclic sulfone, lithium difluorooxalatoborate (LiODFB), and derivatives thereof, or a mixture of two or more of these, in order to stably form an SEI film, but is not limited thereto.

[0059] Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethylethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite. Examples of saturated sultones include 1,3-propane sultone and 1,4-butane sultone. Examples of unsaturated sultones include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-propene sultone. Examples of acyclic sulfones include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

[0060] These additives are added to the electrolyte to improve low-temperature output characteristics by forming a strong SEI film on the negative electrode, as well as to inhibit decomposition of the positive electrode surface and prevent oxidation of the electrolyte during high-temperature cycle operation.

[0061] When the battery case is a pouch type, an aluminum laminated pouch including an aluminum layer may be used. After the electrolyte is injected, the opened portion of the aluminum laminated pouch can be sealed by heat welding or heat sealing.

[0062] 2 is a flowchart of an activation method according to an embodiment of the present invention. Referring to FIG. 2, the activation method of a secondary battery according to the present invention further includes, after the pre-aging step S300, a primary charging step S400 of charging the pre-aged secondary battery, and an aging step S500 of aging the primarily charged secondary battery.

[0063] <First charging stage> The primary charging step S400 is a step of charging the pre-aged secondary battery to a predetermined charging depth. Through the primary charging step, the secondary battery can be activated.

[0064] The first charging step does not need to be a full charge, and the charge depth of the first charging step may be, specifically, 75% or less of the battery design capacity (SOC 100%), 15 to 70%, or 30 to 60%, but even within the above ranges, a sufficiently stable SEI coating can be formed and initial gas generation can be induced. The value of the charge depth is not limited to this and can be appropriately changed to suit the purpose of the activation process.

[0065] The charging conditions in the first charging stage may be those known in the art.

[0066] In one embodiment, the primary charging step may be performed at a charge cut-off voltage of 2.5 to 4.0 V and a C-rate of 1.0 C or less. However, such a charge cut-off voltage may vary depending on the characteristics of the battery, such as the capacity and material of the battery.

[0067] The temperature condition during the primary charge can be 20°C to 30°C, specifically 22°C to 28°C, and more specifically 23°C to 27°C.

[0068] In addition, the primary charging step may be performed while pressurizing the secondary battery. When the primary charging is performed while pressurizing the secondary battery, it is possible to prevent internal gas from escaping into the electrodes.

[0069] <Aging stage> In order to stabilize the battery that has been primarily charged according to the above method or to accelerate the stabilization of the SEI film formed through the primary charge, an aging step S500 is performed in which the secondary battery is aged under various conditions.

[0070] The aging step can be a room temperature aging process in which the secondary battery is aged for a predetermined period of time under room temperature and pressure conditions, or high temperature aging can be performed instead of room temperature aging, or both room temperature aging and high temperature aging can be performed depending on the purpose. High temperature aging is the aging of the battery in a high temperature environment, which can accelerate the stabilization of the SEI film, and the high temperature aging and room temperature aging processes can be performed sequentially on a primarily charged battery.

[0071] In one specific example, the high-temperature aging can be carried out at a temperature of 50° C. to 100° C., preferably 50° C. to 80° C. The high-temperature aging can be carried out for 1 to 30 hours, preferably 2 to 24 hours.

[0072] In one specific example, the room temperature aging can be carried out at a temperature of 20° C. to 30° C., specifically 22° C. to 28° C., more specifically 23° C. to 27° C., and even more specifically 25° C. to 27° C. The room temperature aging can be carried out for 12 to 120 hours, or 18 to 72 hours.

[0073] 3 is a flowchart of an activation method according to an embodiment of the present invention. Referring to FIG. 3, the secondary battery may be fully discharged to approximately 0% SOC and then fully charged to 95% or more of the discharged secondary battery's design capacity (SOC 95%). The fully discharged and fully charged steps may be performed once or repeated two or more times.

[0074] In one embodiment, the method for activating a secondary battery according to the present invention may further include an additional aging step after the fully discharged and fully charged steps. The additional aging step is a process for stabilizing the secondary battery and may be performed at room temperature or at a high temperature, specifically, for 1 to 21 days. The additional aging step may include a monitoring (OCV tracking) step, which includes measuring the open circuit voltage (OCV) of the battery at regular time intervals, in order to screen for low-voltage defective batteries in which a voltage drop occurs beyond the self-discharge of the battery.

[0075] The activation method of the present invention may further include a degassing step of discharging gas from the inside of the secondary battery to the outside, if necessary. Gas is generated inside the secondary battery due to a reaction between the electrolyte and the electrodes during the primary charging and aging steps. A degassing step may be performed to discharge the internal gas to the outside of the battery. The degassing step may be performed simultaneously with or after the aging step.

[0076] The present invention will be described in more detail below with reference to examples, etc. However, the configurations described in the examples in this specification are merely examples of the present invention and do not represent all of the technical ideas of the present invention, so it should be understood that there may be various equivalents and modifications that can replace them at the time of filing this application.

[0077] Manufacturing example NCM (Li[Ni 0.8 Co 0.1 Mn 0.1 100 parts by weight of ]O2), 1.5 parts by weight of carbon black (FX35, Denka) as a conductive material, and 2.3 parts by weight of polyvinylidene fluoride (KF9700, Kureha) as a binder polymer were added to NMP (N-methyl-2-pyrrolidone) as a solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was prepared at a concentration of 640 mg / 25 cm. 2The mixture was coated on both sides of an aluminum foil in a loading amount of 1000g, and then dried in a vacuum to obtain a positive electrode.

[0078] The negative electrode was prepared by adding 100 parts by weight of artificial graphite (GT, Zichen (China)) as a negative electrode active material, 1.1 parts by weight of carbon black (Super-P) as a conductive material, 2.2 parts by weight of styrene-butadiene rubber, and 0.7 parts by weight of carboxymethyl cellulose to water as a solvent to prepare a negative electrode active material slurry, which was then coated once on copper foil, dried, and pressed.

[0079] Meanwhile, a microporous polyethylene separator with an inorganic layer was fabricated and then interposed between the positive and negative electrodes to fabricate an electrode assembly. The electrode assembly was then placed in a pouch-type battery case, and an electrolyte solution containing 1M LiPF6 and 1 wt% of additive B as an electrolyte additive in an organic solvent mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 was injected to complete the battery.

[0080] Example The battery of the above preparation example was charged to 40% SOC (state of charge) at room temperature (23°C) within a driving voltage range of 1.0 to 2.7 V and a C-rate of 0.1. The capacity change as a function of voltage was observed, and the resulting voltage-capacity profile was differentiated and shown in Figure 4. Referring to Figure 4, it can be seen that the onset point of the reduction reaction for Additive B appears at a voltage of approximately 1.5 V.

[0081] Thirty minutes after the electrolyte was injected into the battery of the above manufacturing example, the battery of the manufacturing example was pre-charged at a constant current at a charge rate of 0.1 C-rate at a temperature of 23° C. with an end-of-charge voltage of 1.4 V. The pre-charged battery was then aged at a temperature of 23° C. under normal pressure for 48 hours to complete the pre-aging process.

[0082] The pre-aged battery was charged to 65% of the battery's design capacity (SOC 65%) at a C rate of 0.2C to complete the primary charge. The primary charged battery was subjected to high-temperature aging at 60°C for 24 hours, followed by room-temperature aging at 25°C for 4 days. The secondary battery was then fully discharged, fully charged, and further aged to complete the activation process.

[0083] Comparative Example 1 The activation process was performed in the same manner as in the above example, except that the step of determining the reduction reaction voltage of the additive and the pre-charging step were omitted.

[0084] Comparative Example 2 The activation process was carried out in the same manner as in the above example, except that the cut-off voltage of the pre-charging stage was set to 2.0V.

[0085] Experimental example 1: Voltage drop after high temperature storage Each of the secondary batteries prepared in the above Examples and Comparative Examples was fully charged (SOC 100%) to 4.2 V, 50 mA cut-off, under constant current / constant voltage conditions at room temperature (25°C) and a C-rate of 0.33. The initial voltage (V1) before storage was measured using a PNE-0506 charge / discharge device (manufacturer: PNE solution). Next, after storing the batteries for one month at a temperature of 60°C, the voltage (V2) after storage was measured using the same charge / discharge device, and the voltage drop is shown in Table 1.

[0086] Experimental example 2: Capacity retention after 100 cycles Each secondary battery prepared in the above Examples and Comparative Examples was charged under constant current and constant voltage conditions at a C-rate of 0.8 up to 4.35 V, followed by a 0.05 C cut-off charge, and then discharged at 0.5 C and 3.0 V. Next, one cycle was defined as charging under constant current and constant voltage conditions at a C-rate of 0.8 up to 4.35 V, followed by a 0.05 C cut-off charge, followed by discharge at 0.5 C and 3.0 V at room temperature. The cycle capacity retention after 100 cycles was shown as a percentage of the single-cycle capacity and is shown in Table 1 below.

[0087] [Table 1]

[0088] Referring to Table 1 above, the voltage drop after one month of storage in Comparative Example 1, which did not undergo a pre-charging step, is significantly larger than that of the batteries of the Examples. This is interpreted as an effect of the batteries of the Examples undergoing a pre-charging step, which prevents the elution of foreign matter and metals.

[0089] On the other hand, the battery of Comparative Example 2 underwent a pre-charge step. However, the cut-off voltage of charge was set to a voltage exceeding the voltage at which the reductive decomposition reaction of the electrolyte additive occurs during the pre-charge step. This is thought to have resulted in the reductive decomposition reaction of the additive occurring before the electrolyte was fully impregnated, resulting in the formation of a non-uniform SEI film, which resulted in the poor capacity retention compared to the batteries of the Examples.

[0090] As described above, the activation method of the present invention has the effect of suppressing the negative electrode reaction of the electrolyte additive, reducing the potential of the negative electrode, preventing low voltage defects, and forming a uniform SEI coating.

Claims

1. deriving a reduction reaction voltage by the electrolyte additive; a pre-charging step of pre-charging a secondary battery into which the electrolyte containing the electrolyte additive is injected; a pre-aging step of impregnating and aging the electrode assembly housed in the secondary battery in the injected electrolyte; a primary charging step of charging the pre-aged secondary battery after the pre-aging step; An aging stage in which the primary charged secondary battery is matured; Including, The end-of-charge voltage of the pre-charging stage is less than the reduction reaction voltage; The pre-charging step begins within 3 hours after the electrolyte is injected; The aging step includes high-temperature aging, in which the secondary battery is aged at a temperature of 50 to 100°C. A method for activating a secondary battery.

2. 2. The method of claim 1, wherein the reduction reaction voltage is a voltage at an onset point where a reduction reaction starts in a dQ / dV graph obtained by differentiating a voltage-capacity profile during a first charge of the secondary battery containing the electrolyte additive.

3. 3. The method of activating a secondary battery according to claim 2, wherein the end-of-charge voltage of the pre-charging stage is set within a range of 70% to 99% of the reduction reaction voltage.

4. The method of claim 1 , wherein the pre-charging step is performed by a constant current charging method.

5. 5. The method of claim 4, wherein the pre-charging step charges the secondary battery at a C rate of 0.01 to 0.

5.

6. The method of claim 1 , wherein the primary charging step charges the secondary battery while applying pressure to the secondary battery.

7. The method of activating a secondary battery according to claim 1 , further comprising the steps of fully discharging and fully charging the secondary battery.

8. The method of activating a secondary battery according to claim 7 , further comprising the step of aging the secondary battery after the steps of fully discharging and fully charging.

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