Method of activating a secondary battery

Abstract

A method for activating a secondary battery according to the present invention includes: a pre-aging step: aging the secondary battery at room temperature, wherein electrode components and electrolyte solution are contained in a battery casing; a formation step: initially charging the pre-aged secondary battery; a room temperature aging step: aging the initially charged secondary battery at room temperature; a step of fully charging the room temperature-aged secondary battery to a voltage of 4.4V or greater; and a degassing step: removing gas inside the secondary battery, wherein fully charging the secondary battery increases the amount of electrolyte solution remaining inside the electrodes.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2020-0061573, filed on May 22, 2020, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a method for activating a secondary battery, and more particularly, to a method for activating a secondary battery that can increase the amount of electrolyte solution remaining inside the electrodes. Background Technology

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

[0004] Lithium-ion secondary batteries primarily use lithium oxides and carbon materials as the positive and negative electrode active materials, respectively. A lithium-ion secondary battery includes: an electrode assembly in which positive and negative electrode plates, respectively coated with the positive and negative electrode active materials, are placed between the positive and negative electrode plates by a separator; and an external material that seals and stores the electrode assembly together with an electrolyte solution.

[0005] Meanwhile, depending on the shape of the battery casing, lithium secondary batteries can be classified into can-type secondary batteries in which the electrode components are embedded in a metal can and bag-type secondary batteries in which the electrode components are embedded in a bag of aluminum laminated sheets.

[0006] Secondary batteries are typically manufactured through a process in which liquid electrolyte is injected while electrode assemblies are stored in a battery casing, and the casing is then sealed. By performing a formation process involving repeated constant charge / discharge cycles, the battery structure becomes stable and usable.

[0007] However, recently, these secondary batteries have tended to be manufactured to operate at high voltages in order to ensure maximum capacity within a limited space. Thus, with the increase in battery capacity, it is necessary to ensure a greater amount of electrolyte solution remaining inside the electrodes in order to allow the battery to operate.

[0008] Figure 1 This is a schematic diagram illustrating the step-by-step process conditions of a traditional activation process. (Reference) Figure 1The traditional activation process includes: pre-aging the battery (S1); initial charging the pre-aged battery (S2); aging the initially charged battery (S3); repeated charging / discharging (S4); and performing a degassing process. However, in this traditional battery cell activation process, there is a problem that the electrolyte solution does not sufficiently penetrate into the interior of the electrode even during repeated charging / discharging. Therefore, a technology needs to be developed to ensure a sufficient amount of electrolyte solution remaining inside the electrode. Summary of the Invention

[0009] Technical issues

[0010] The present invention has been designed to solve the above-mentioned problems, and an object of the present invention is to provide an activation method for a secondary battery that sufficiently ensures the remaining amount of electrolyte solution while exhibiting sufficient capacity at high voltage. Furthermore, another object of the present invention is to provide an activation method for a secondary battery that minimizes the thickness of the electrode while ensuring sufficient remaining amount of electrolyte solution inside the electrode.

[0011] Technical solution

[0012] In one example, a method for activating a secondary battery according to the present invention includes: a pre-aging step: aging the secondary battery at room temperature, wherein electrode components and electrolyte solution are contained in a battery casing; a formation step: initially charging the pre-aged secondary battery; a room temperature aging step: aging the initially charged secondary battery at room temperature; a step of fully charging the room temperature aged secondary battery to a voltage of 4.4V or greater; and a degassing step: removing gas inside the secondary battery.

[0013] In a specific example, during the formation step, the secondary battery is charged to a voltage in the range corresponding to 55% to 90% of the full charge voltage.

[0014] In a specific example, the room temperature aging step includes measuring the open-circuit voltage (OCV) of the secondary battery and determining whether the secondary battery has a low-voltage defect.

[0015] In one example, the steps of fully charging a secondary battery include: charging the secondary battery with a constant current (CC) until it reaches the full charge voltage; charging the secondary battery with a constant voltage (CV) after it has reached the full charge voltage; and discharging the secondary battery with a constant current (CC) after it has been CV charged.

[0016] In a specific example, the process of CC charging a secondary battery includes charging the secondary battery at a C rate of 0.5C to 0.9C.

[0017] In a specific example, the process of CV charging a secondary battery includes charging the secondary battery at the full charging voltage until the CC charging current value or a smaller cutoff current is reached.

[0018] The process of CC discharge of a secondary battery includes discharging a fully charged secondary battery until it reaches a voltage corresponding to 80% of the full charge voltage or full discharge voltage.

[0019] In a specific example, the method for activating a secondary battery according to the present invention further includes a process of recharging a secondary battery that has been CC-discharged until a preset transport voltage is reached.

[0020] In another example, the steps of fully charging a secondary battery include: CC charging the secondary battery until it reaches the full charge voltage; and CC discharging the secondary battery after it has reached the full charge voltage, wherein the CC charging process and the CC discharging process are performed sequentially.

[0021] In a specific example, an additional charging step of recharging the secondary battery is performed between the room temperature aging step and the step of fully charging the secondary battery.

[0022] In a specific example, a step of transporting and charging the secondary battery is performed after the degassing step.

[0023] At this time, the steps for transporting and charging the secondary battery include the following process: after performing a full charge and a full discharge on the secondary battery with the internal gas removed, the secondary battery is charged to reach the preset transport voltage.

[0024] In one example, after the step of transporting and charging the secondary battery, a step of aging the secondary battery at room temperature is further performed.

[0025] In a specific example, the steps of fully charging the secondary battery and transport charging the secondary battery include checking the charging capacity of the secondary battery.

[0026] The present invention also provides a method for manufacturing a secondary battery including the method of activating the secondary battery.

[0027] Beneficial effects

[0028] According to the activation method of the secondary battery of the present invention, by fully charging the secondary battery at a voltage of 4.4V or greater, the remaining amount of electrolyte solution inside the electrode can be increased. Furthermore, in the present invention, by performing CC discharge immediately after CC charging during the full charging process without performing CV charging, excessive increase in electrode thickness can be prevented. Thus, a high-capacity secondary battery with good cycle characteristics can be manufactured. Attached Figure Description

[0029] Figure 1 It is a graph showing the process of performing an activation method according to conventional techniques.

[0030] Figure 2 This is a flowchart illustrating the activation method according to the present invention.

[0031] Figure 3 This is a graph illustrating the process of the activation method according to an embodiment of the present invention.

[0032] Figure 4 This is a graph illustrating the process of an activation method according to another embodiment of the present invention.

[0033] Figure 5 This is a graph showing the remaining amount of electrolyte solution according to examples and comparative examples of the present invention.

[0034] Figure 6 This is a graph showing the remaining amount of electrolyte solution according to Examples 2 to 6 of the present invention.

[0035] Figure 7 This is a graph showing the variation in the thickness of the electrode according to an embodiment of the present invention. Detailed Implementation

[0036] The invention will be described in detail below with reference to the accompanying drawings. The terms and words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concepts of the terms to best describe their invention. The terms and words should be understood to have meanings and concepts consistent with the technical concept of the invention.

[0037] In this application, it should be understood that terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and these terms do not preclude the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, plate, etc., is referred to as being "on" another part, this includes not only the case where the part is "directly" on the other part, but also the case where another part is located between them. On the other hand, when a part such as a layer, film, region, plate, etc., is referred to as being "under" another part, this includes not only the case where the part is "directly" under the other part, but also the case where another part is located between them. Additionally, in this application, "placed on" can include placement at the bottom and top.

[0038] The invention will now be described in detail with reference to the accompanying drawings.

[0039] Figure 2 This is a flowchart illustrating the activation method according to the present invention, and Figure 3 This is a graph illustrating the process of the activation method according to an embodiment of the present invention.

[0040] refer to Figure 2 and Figure 3 According to an embodiment of the present invention, a method for activating a secondary battery includes: a pre-aging step (S10) of aging the secondary battery at room temperature, wherein electrode components and electrolyte solution are contained in a battery casing; a formation step (S20) of initially charging the pre-aged secondary battery; a room temperature aging step (S30) of aging the initially charged secondary battery at room temperature; a step of fully charging the room temperature aged secondary battery to a voltage of 4.4V or greater (S40); and a degassing step (S50) of removing gas inside the secondary battery.

[0041] It has been found that if the secondary battery is charged at a high voltage of 4.4V or greater during the charging step after room temperature aging, the remaining amount of electrolyte solution inside the electrodes will increase, and the battery capacity will increase. The inventors of this invention have implemented the present invention based on this.

[0042] The present invention will be described in detail below.

[0043] Secondary batteries can be manufactured by housing an electrode assembly in which positive electrodes, negative electrodes, and separators are alternately stacked within a battery casing and then injecting an electrolyte solution. The steps for assembling such a battery are not particularly limited and can be performed according to known methods.

[0044] In addition, the electrode assembly is not particularly limited, as long as it is a structure that includes a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, and can be, for example, a jelly roll type, a stacked type or a stacked / folded type.

[0045] The battery casing is not particularly restricted, as long as it is used as an external material to encapsulate the battery, and it can be cylindrical, square, or pouch-shaped; specifically, a pouch-shaped battery casing can be used.

[0046] The electrolyte solution includes an organic solvent and a lithium salt, and may optionally further contain additives.

[0047] Organic solvents are not limited, as long as decomposition due to oxidation or other reactions during battery charging and discharging can be minimized, and can be, for example, cyclic carbonates, linear carbonates, esters, ethers, or ketones. These solvents can be used alone or in combination of two or more.

[0048] Among organic solvents, carbonate-based organic solvents are preferably used. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). 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).

[0049] There are no restrictions on the use of lithium salts commonly used in the electrolyte solution of lithium secondary batteries, such as LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4, and these lithium salts can be used alone or in combination of two or more.

[0050] Additionally, the electrolyte solution may optionally further include additives. As additives, mixtures of any one or more of the following selected from the group consisting of: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulfonyl lactone, unsaturated sulfonyl lactone, acyclic sulfone, lithium oxaloyl difluoroborate (LiODFB), and derivatives thereof, may be used to stably form an SEI film, but are not limited thereto.

[0051] Cyclic sulfites may include: vinyl sulfite, methyl vinyl sulfite, ethyl sulfite, 4,5-dimethyl sulfite, 4,5-diethyl sulfite, propylene sulfite, 4,5-dimethyl sulfite, 4,5-diethyl sulfite, 4,6-dimethyl propyl sulfite, 4,6-diethyl propyl sulfite, 1,3-butylene sulfite, etc. Saturated sulfonyl lactones may include: 1,3-propanesulfonyl lactone and 1,4-butanesulfonyl lactone, etc. Unsaturated sulfonyl lactones may include vinyl sulfonyl lactone, 1,3-propenesulfonyl lactone, 1,4-butenesulfonyl lactone, and 1-methyl-1,3-propenesulfonyl lactone. Acyclic sulfones may include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

[0052] These additives are added to the electrolyte solution to improve low-temperature output characteristics by forming a solid SEI film on the negative electrode and to suppress decomposition on the positive electrode surface, and to prevent oxidation of the electrolyte solution during high-temperature cycling.

[0053] Similarly, the battery, already injected with electrolyte solution, undergoes a pre-aging step (S10) at room temperature. The pre-aging step (S10) is a step to age the battery so that the electrolyte solution is fully immersed in the electrodes and separators after battery assembly.

[0054] More specifically, when a secondary battery is charged, if electrons move to the negative electrode and become charged, lithium ions are inserted into the negative electrode to achieve charge neutrality. At this time, lithium ions can be retained in the wetted areas (i.e., the areas that maintain the ion migration path) of the electrolyte solution, but retention in the non-wetting areas of the electrolyte solution is relatively difficult.

[0055] Therefore, through the pre-aging step, the battery can be aged for 0.5 to 72 hours at room temperature and atmospheric pressure, allowing the electrolyte solution to permeate into the positive and negative electrodes. For example, the pre-aging step (S10) can be performed at 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.

[0056] The pre-aged secondary battery undergoes a formation process (S20) by initially charging it within a predetermined range. As a result, a solid electrode interface (SEI) film is formed on the surface of the negative electrode. The formed SEI film reduces the irreversibility of the secondary battery to a specific level, even if it is subsequently charged to a high level during the battery's charge / discharge cycles.

[0057] In embodiments of the invention, charging in the formation step (S20) can be a process of charging the battery to a voltage corresponding to 55% to 95% of the full charge voltage. During the formation step, when the charging voltage is within this range, an SEI film can be stably formed on the surface of the negative electrode. Specifically, during the formation step, the charging termination voltage can be 3.5 to 4.2V, and charging can be performed at a C rate of 1.0C or less. If the charging voltage is too low, insufficient SEI film will not form, and the initial charging will take a long time, making it unsuitable for mass production, which is a problem. On the other hand, if the charging voltage is too high, an excessive load is applied to the battery, which may easily lead to overvoltage, preventing the formation of a uniform SEI film, and the battery shape may deform as the battery expands, which is also a problem.

[0058] Furthermore, when initially charging the secondary battery, charging can be performed under high temperature and pressure conditions. Since these pressure conditions can be appropriately set according to the battery specifications, a detailed description is omitted.

[0059] Subsequently, a room temperature aging step (S30) is performed to age the initially charged secondary battery at room temperature. During the room temperature aging step, as the SEI film generated in the formation step stabilizes, the SEI film is re-formed with a uniform thickness.

[0060] In the room temperature aging step (S30), the aging temperature can be between 20°C and 30°C, specifically between 22°C and 28°C, more specifically between 23°C and 27°C, and even more specifically between 25°C and 27°C. If the aging temperature is too high, the battery capacity may decrease, and the battery's cycle characteristics may be weakened due to the electrolyte solution reacting with heat. If the aging temperature is too low, the electrolyte solution will not react sufficiently on the electrode surface, thereby reducing the battery's cycle characteristics. In the room temperature aging step, the aging time can be appropriately set according to the battery's condition and can be between 1 and 7 days, specifically between 2 and 5 days.

[0061] The room temperature aging step (S30) includes measuring the open-circuit voltage (OCV) of the secondary battery and determining whether the secondary battery has a low-voltage defect. This can be configured to determine whether the secondary battery has a low-voltage defect by using the open-circuit voltage (OCV) measured at different time points. For example, a secondary battery that has been aged at high temperature is stored at room temperature, but the OCV is measured at at least two time points. And by comparing the difference between the corresponding OCVs with a reference value pre-stored in a storage unit or the like, it is possible to select whether the secondary battery has a low-voltage defect.

[0062] Specifically, the selection of whether a secondary battery has a low-voltage defect is performed by measuring the voltage value V1 at the starting point of aging at room temperature and the voltage value V2 at the ending point of aging at room temperature, and then determining whether the voltage drop (V1-V2), which is the difference between the starting and ending voltage values, meets the reference range condition. More specifically, when the measured voltage drop of the secondary battery to be inspected is 20mV and the reference value for the voltage drop of a good product is 10mV, the measured voltage drop is greater than the reference value, therefore this secondary battery can be judged to have a low-voltage defect.

[0063] The method for activating a secondary battery according to the present invention includes the step of fully charging the battery, which has been aged at room temperature, to a voltage of 4.4V or greater (S40).

[0064] This is to increase the amount of electrolyte solution remaining inside the electrode. When the secondary battery is fully charged, due to the high SOC, a large number of lithium ions can be inserted into the spaces between the crystal structures of the electrode active material. Thus, as the electrode expands, the internal pores become larger, and more electrolyte solution can permeate through the larger pores. Furthermore, a full charge should be performed at a voltage of 4.4V or higher, and this is to ensure sufficient charging of the interior of the negative electrode by charging the battery at a high voltage, even in the case of high-voltage cells. When the charging voltage is less than 4.4V, lithium ions are not charged to the central portion of the negative electrode in the high-voltage cell. Thus, the electrode lattice in the central portion of the negative electrode becomes smaller than the surface of the negative electrode, and in this portion, electrolyte solution becomes difficult to permeate. Furthermore, the upper limit of the voltage during full charge can be appropriately set by those skilled in the art. For example, the upper limit of the voltage during full charge can be 5.2V or less, 5.0V or less, 4.8V or less, or 4.6V or less.

[0065] As mentioned above, when the amount of electrolyte solution remaining inside the electrode increases, maximum capacity can be ensured for batteries with the same performance.

[0066] In one example, the step of fully charging the secondary battery (S40) includes: charging the secondary battery with a constant current (CC) until it reaches the full charge voltage; charging the secondary battery with a constant voltage (CV) after it has reached the full charge voltage; and discharging the secondary battery with a constant current (CC) after it has been CV charged.

[0067] That is, during the full charging step, a large number of lithium ions are inserted into the spaces between the crystal lattice in the active material, and afterwards, more lithium ions that were not inserted during the CC charging process can be inserted through CV charging. In other words, the CV charging process after CC charging allows the electrolyte solution to further penetrate into the interior of the electrode.

[0068] Specifically, a CC charging process is performed on the secondary battery to charge it at a C rate of 0.5C to 0.9C, and this is performed to stably charge the secondary battery to a predetermined voltage. During CC charging, the secondary battery can be charged at a C rate of 0.6C to 0.8C. When the magnitude of the constant current during the CC charging process is within the above range, the secondary battery can be stably charged without side reactions.

[0069] When a secondary battery is CC-charged, the current gradually decreases as it approaches the full charge voltage, and charging stops when the current reaches a predetermined termination voltage. The secondary battery is then CV-charged. The CV charging process involves charging the secondary battery at the full charge voltage until the CC charging current value or a smaller cutoff current is reached. During CV charging, the current value gradually decreases while maintaining the full charge voltage. The current value at which charging stops is called the cutoff current. The cutoff current is equal to or less than the CC charging current value, and can be a current value in the range of 0.025C to 1mA less than the CC charging current value, specifically 0.1C to 1mA less than the CC charging current value, and more specifically 0.2C to 1mA less than the CC charging current value. That is, the preferred cutoff current value is equal to or less than the CC charging current value, and can be 1mA less than the CC charging current value. Specifically, when the cutoff current value is greater than the CC charging current value, the CV charging process is not sufficiently performed. In this way, the electrolyte solution may have difficulty penetrating into the electrode. Conversely, when the cutoff current is excessively low, the amount of electrolyte solution remaining may increase due to over-CV charging, but the electrode thickness may also increase, which is problematic.

[0070] On the other hand, a fully charged secondary battery undergoes a CC discharge, in which the secondary battery is discharged at a constant current. In this case, the CC discharge process of the secondary battery includes discharging the fully charged secondary battery until it reaches a voltage corresponding to 80% of the full charge voltage or the full discharge voltage. That is, by performing a CC discharge, the secondary battery can be fully discharged, or the secondary battery can be discharged until it reaches a voltage corresponding to 80% of the full charge voltage. More specifically, a fully charged secondary battery can be discharged until it reaches the voltage at which it is fully discharged or a voltage corresponding to 55% of the full charge voltage. For example, the discharge termination voltage can be 3.0 to 3.5V.

[0071] Batteries that have reached a specific voltage after CC charging can undergo a recharging step until they reach a preset transport voltage. Similarly, during repeated charging / discharging processes, the secondary battery is activated and gas is generated due to reactions between the electrodes and the electrolyte solution.

[0072] In another example, the step of fully charging the secondary battery (S40) includes: CC charging the secondary battery until it reaches the full charge voltage; and CC discharging the secondary battery after it has reached the full charge voltage, wherein the CC charging process and the CC discharging process are performed sequentially. In this case, the details regarding the CC charging process and the CC discharging process are the same as those described above.

[0073] As mentioned above, CV charging is performed to maximize the remaining amount of electrolyte solution by additionally inserting lithium ions after CC charging. However, if a high SOC is maintained through CV charging, the battery thickness may become excessively large. In particular, pouch cells are sensitive to increases in thickness. Thus, by omitting the CV charging process and performing CC discharging immediately after completing CC charging, it is possible to ensure the remaining amount of electrolyte solution while simultaneously achieving an appropriate rate of thickness increase.

[0074] In another example, the method for activating a secondary battery according to the present invention may further include an additional charging step (S31).

[0075] Figure 4 This is a graph illustrating the process of an activation method according to another embodiment of the present invention.

[0076] refer to Figure 4The additional charging step (S31) is performed between the room temperature aging step (S30) and the full charging step (S40), and is a secondary charging process performed on the room temperature-aged secondary battery after the initial charging. In this invention, the secondary battery can be fully formed by performing the charging process twice. In the additional charging step, the charging end voltage is in the range of 3.5 to 4.2V, and can be set to be greater than the charging end voltage in the initial charging step. The additionally charged battery can be discharged so that the voltage becomes 3.0 to 4.0V.

[0077] Furthermore, according to the activation method of the present invention, side reaction gases generated inside the secondary battery due to charging and aging may cause battery bulging. Therefore, a degassing step (S50) for removing the side reaction gases can be performed after the full charging step (S40).

[0078] In this invention, various degassing techniques known at the time of filing of this application can be employed. For example, the degassing process can be performed by cutting off the extension portion in a pouch-type secondary battery having an extended side and sealing the cut portion. However, since such degassing techniques are well known to those skilled in the art, a more detailed description is omitted here.

[0079] In addition, refer to Figure 3 and Figure 4 After the degassing step (S50), a transport charging step (S60) can be performed separately. The transport charging step (S60) is performed to charge the secondary battery to an appropriate level before transport, provided that the secondary battery was not uniformly charged in the previous charge / discharge and aging steps.

[0080] In the activation method according to the invention, the step of transport charging the secondary battery may include the following process: after performing a full charge and a full discharge on the secondary battery with internal gas removed, the secondary battery is charged to reach a preset transport voltage. More specifically, after charging the secondary battery to a level corresponding to 95% (SOC 95%) or greater of the design capacity and then discharging the secondary battery to a level corresponding to 5% (SOC 5%) or less of the design capacity, the secondary battery may be recharged to a level corresponding to 40% to 60% (SOC 40% to 60%) of the design capacity. A room temperature aging step may be additionally performed on the transport-charged secondary battery. The time for performing the room temperature aging step can be appropriately set according to the process conditions. For example, the time for performing the room temperature aging step may be in the range of 1 to 4 days.

[0081] Furthermore, in the activation method according to the present invention, the step of detecting defects in the secondary battery can be performed multiple times, and as described above, secondary batteries with low voltage defects can be detected in the room temperature aging step. Additionally, the activation method according to the present invention may include the following process: checking the charging capacity of the secondary battery in the steps of fully charging the secondary battery and transport charging the secondary battery. Methods for measuring the charging capacity of the secondary battery are well known to those skilled in the art, and therefore a more detailed description thereof is omitted here.

[0082] Furthermore, as described above, the present invention provides a method for manufacturing a secondary battery including the activation method of the secondary battery as described above. The composition of this secondary battery is as described above.

[0083] The invention will be described in detail below with reference to examples. However, embodiments of the invention can be modified in various other forms, and the scope of the invention should not be construed as limited to the examples described below. Examples of the invention are provided to more fully describe the invention to those skilled in the art.

[0084] Preparation Example 1

[0085] By using 96.7 parts by weight of Li[Ni] as the positive electrode active material 0.6 Mn 0.2 Co 0.2 A positive electrode mixture was prepared by mixing O2, 1.3 parts by weight of graphite as a conductive material, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) as a binder. A positive electrode mixture slurry was prepared by dispersing the obtained positive electrode mixture in 1-methyl-2-pyrrolidone as a solvent. The positive electrode was prepared by coating, drying, and pressing the slurry onto both sides of an aluminum foil with a thickness of 20 μm.

[0086] A negative electrode mixture was prepared by mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) as the negative electrode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) as the binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC). A negative electrode mixture slurry was prepared by dispersing the negative electrode mixture in deionized water as a solvent. The negative electrode was prepared by coating, drying, and pressing the slurry onto both sides of a copper foil with a thickness of 20 μm.

[0087] A non-aqueous electrolyte solution was prepared by dissolving LiPF6 in an organic solvent in a 3:3:4 (volume ratio) mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC). Here, LiPF6 was dissolved in the organic solvent to a concentration of 1.0 M.

[0088] The lithium secondary battery is prepared by stacking porous polyethylene separators between the positive and negative electrodes prepared above, storing them in a bag, and then injecting an electrolyte solution.

[0089] Preparation Example 2

[0090] The secondary battery was manufactured in the same manner as in Preparation Example 1, except that LiCoO2 was used as the positive electrode active material and artificial graphite was used as the negative electrode active material.

[0091] Example 1

[0092] The secondary battery was pre-aged at room temperature (25°C) for 24 hours, and then initially charged at a C rate of 0.2C until a voltage of 3.9V was reached. The initially charged secondary battery was then aged at room temperature (25°C) for 3 days. Upon completion of room temperature aging, the secondary battery was CC-charged at a C rate of 0.7C until a voltage of 4.4V was reached. If the secondary battery voltage reached 4.4V, it was immediately CC-discharged without CV charging. Specifically, the secondary battery was CC-discharged at a C rate of 0.7C until a voltage of 3.5V was reached. Subsequently, the secondary battery was recharged until the transport voltage was reached.

[0093] Following this, a degassing process to remove internal gases from the battery is performed, followed by a transport charging process involving full charging, full discharging, and recharging until the State of Charge (SOC) reaches 55%. (As in...) Figure 3 The process of performing these series of steps is shown in the diagram.

[0094] Example 2

[0095] The secondary battery was pre-aged at room temperature (25°C) for 24 hours, and then initially charged at a C rate of 0.2C until a voltage of 3.9V was reached. The initially charged secondary battery was then aged at room temperature (25°C) for 3 days. Upon completion of room temperature aging, the secondary battery was recharged until a voltage of 4.2V was reached, and then discharged until a voltage of 3.5V was reached. Subsequently, the secondary battery was CC-charged at a C rate of 0.7C until a voltage of 4.4V was reached. If the secondary battery voltage reached 4.4V, it was immediately CC-discharged without CV-charging. Specifically, the secondary battery was CC-discharged at a C rate of 0.7C until a voltage of 3.0V was reached. Afterward, the secondary battery was recharged until the transport voltage was reached.

[0096] Following this, a degassing process to remove internal gases from the battery is performed, followed by a transport charging process involving full charging, full discharging, and recharging until the State of Charge (SOC) reaches 55%. (As in...) Figure 4 The process of performing these series of steps is shown in the diagram.

[0097] Comparison Example 1

[0098] The secondary battery was pre-aged at room temperature (25°C) for 24 hours, and then initially charged at a C rate of 0.2C until a voltage of 3.9V was reached. The initially charged secondary battery was then aged at room temperature (25°C) for 3 days. Upon completion of room temperature aging, the secondary battery was CC-charged at a C rate of 0.7C until a voltage of 4.2V was reached. When the secondary battery voltage reached 4.2V, it was CC-discharged at a C rate of 0.7C until a voltage of 3.5V was reached.

[0099] Following this, a degassing process to remove internal gases from the battery is performed, followed by a transport charging process involving full charging, full discharging, and recharging until the State of Charge (SOC) reaches 55%. (As in...) Figure 1 The process of performing these series of steps is shown in the diagram.

[0100] Experimental Example 1

[0101] After fabricating 150 batteries according to Preparation Example 1, the activation methods according to Example 1, Example 2, and Comparative Example 1 were performed, and the remaining amount of electrolyte solution was measured. Furthermore, when the remaining amount of electrolyte solution was less than 5.68 g, it was determined to be defective. Specifically, the remaining amount of electrolyte solution was determined by measuring the difference between the weight of the electrode assembly after the formation process and the weight of the dried electrode assembly. The remaining amount of electrolyte solution and the defect rate are shown in Table 1 and... Figure 5 As shown in the image.

[0102] [Table 1]

[0103] Example 1 Example 2 Comparison Example 1 Average electrolyte solution remaining (g) 5.77 5.91 5.71 Defect rate (%) 0.0 0.0 31.4

[0104] Refer to Table 1 and Figure 5 Compared to Comparative Example 1, the average remaining electrolyte solution was higher in Examples 1 and 2 when a full charge was performed at a voltage of 4.4V or greater. Furthermore, compared to Examples 1 and 2, the rate at which the remaining electrolyte solution failed to meet the predetermined standard was higher in Comparative Example 1. That is, as in Examples 1 and 2, the remaining electrolyte solution in the electrodes was further ensured by fully charging the secondary battery at a voltage of 4.4V, indicating excellent battery performance, such as capacity.

[0105] Example 3

[0106] The secondary battery was pre-aged at room temperature (25°C) for 24 hours, and then initially charged at a C rate of 0.2C until a voltage of 3.9V was reached. The initially charged secondary battery was then aged at room temperature (25°C) for 3 days. Upon completion of room temperature aging, the secondary battery was recharged until a voltage of 4.2V was reached, and then discharged until a voltage of 3.5V was reached. Subsequently, the secondary battery was CC-charged at a C rate of 0.7C until a voltage of 4.4V was reached. If the secondary battery voltage reached 4.4V, charging was continuously performed while maintaining the battery voltage until the secondary battery current reached the 0.5C cutoff current value. If the secondary battery current reached the cutoff current value, the secondary battery was CC-discharged at a C rate of 0.7C until a voltage of 3.5V was reached.

[0107] Following this, a degassing process to remove internal gases from the battery is performed, followed by a transport charging process involving full charging, full discharging, and recharging until the State of Charge (SOC) reaches 55%. (As in...) Figure 4 The process of performing these series of steps is shown in the diagram.

[0108] Example 4

[0109] Except that the cutoff current is set to 0.2C, the formation of the secondary battery is performed as shown in Example 3.

[0110] Example 5

[0111] Except that the cutoff current is set to 0.1C, the formation of the secondary battery is performed as shown in Example 3.

[0112] Example 6

[0113] Except that the cutoff current is set to 0.025C, the formation of the secondary battery is performed as shown in Example 3.

[0114] Experimental Example 2

[0115] After fabricating 500 batteries according to Preparation Example 2, the activation methods according to Examples 2 to 6 were performed, and the remaining amount of electrolyte solution was measured. At this point, if the remaining amount of electrolyte solution was less than 4.90 g, it was determined to be defective. The results were... Figure 6 As shown in the image.

[0116] In addition, the thickness of the negative electrode in Examples 2 to 6 was measured according to the number of cycles. The results are in... Figure 7 As shown in [the image]. Figure 7 In the graph, a point is shown with respect to the thickness distribution of the electrodes according to the cycle, and the thickness distribution of the electrodes according to Examples 2 to 6 is shown in order from left to right.

[0117] refer to Figure 6 In Example 2, where CC discharge is performed immediately after CC charging without CV charging, the remaining amount of electrolyte solution is not significantly different from that in Examples 3 to 6. Here, when a longer CV charge is performed (when the cutoff current is low), the remaining amount of electrolyte solution increases because the electrolyte solution has permeated into the pores that have been increased in the electrode as lithium ions have fully permeated into the central portion of the electrode.

[0118] refer to Figure 7 Compared to Examples 3 to 6, in Example 2 where the CV charging process is not performed, the average thickness of the electrode is smaller, indicating that the change in electrode thickness becomes smaller with the execution of cycles. That is, the method for activating a secondary battery according to the invention can further increase the remaining amount of electrolyte solution by performing CV charging after a full charging process, and can minimize the increase in electrode thickness by omitting the CV charging process.

[0119] The above description merely illustrates the technical concept of the present invention, and those skilled in the art can make various modifications and variations without departing from the essential characteristics of the invention. Therefore, the accompanying drawings disclosed herein are not intended to limit the technical concept of the invention, but rather to describe it, and the scope of the technical concept of the invention is not limited by these drawings. The scope of protection of the present invention should be interpreted through the appended claims, and all technical concepts within the scope equivalent to those claims should be understood to be included within the scope of the present invention.

[0120] On the other hand, the instruction manual uses terms such as up, down, left, right, front, and back to indicate direction, but it is obvious that these terms are only for convenience of description and can change depending on the position of the object or the position of the observer.

Claims

1. A method for activating a secondary battery, the method comprising: Pre-aging step: The secondary battery is aged at room temperature, in which the electrode assembly and electrolyte solution are contained in the battery casing; Formation step: Initial charge the pre-aged secondary battery; Room temperature aging step: The initially charged secondary battery is aged at room temperature; The step of fully charging the room-temperature aged secondary battery to 4.4V or greater after the formation step and the room-temperature aging step. as well as Degassing step: Remove the gas inside the secondary battery. The step of fully charging the secondary battery includes: charging the secondary battery with a constant current (CC) until it reaches the full charge voltage; and discharging the secondary battery with a constant current (CC) after it has reached the full charge voltage. The constant current (CC) charging process and the constant current (CC) discharging process are executed sequentially, and The process of charging the secondary battery with a constant current (CC) includes charging the secondary battery at a C rate of 0.5C to 0.9C.

2. The method according to claim 1, wherein, During the formation step, the secondary battery is charged to achieve a voltage in the range corresponding to 55% to 90% of the full charge voltage.

3. The method according to claim 1, wherein, The room temperature aging step includes measuring the open-circuit voltage (OCV) of the secondary battery and determining whether the secondary battery has a low voltage defect.

4. The method according to claim 1, wherein, The process of discharging the secondary battery with a constant current (CC) includes discharging the fully charged secondary battery until a voltage corresponding to 80% of the fully charged voltage or the fully discharged voltage is reached.

5. The method according to claim 1, further comprising a process of recharging the secondary battery, which has been discharged with a constant current (CC), until a preset transport voltage is reached.

6. The method according to claim 1, further comprising an additional charging step of recharging the secondary battery, the additional charging step being between the room temperature aging step and the step of fully charging the secondary battery.

7. The method according to claim 1, further comprising a step of transport charging the secondary battery after the degassing step.

8. The method according to claim 7, wherein, The step of charging the secondary battery during transport includes the following process: after fully charging and fully discharging the secondary battery after removing the internal gas, the secondary battery is charged to reach a preset transport voltage.

9. The method of claim 7, further comprising an aging step of the secondary battery at room temperature following the step of transport charging the secondary battery.

10. The method according to claim 7, wherein, The steps of fully charging the secondary battery and transport charging the secondary battery include checking the charging capacity of the secondary battery.

11. A method of manufacturing a secondary battery, comprising the method of activating the secondary battery according to any one of claims 1 to 10.

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