Secondary battery activation method

Abstract

The present invention relates to a secondary battery activation method in which a proper initial charging rate (SOC) and a high-temperature aging time are calculated according to the size of a secondary battery during an activation process, and the secondary battery activation method is applied to the activation process, efficiently removing gas generated inside an electrode assembly during charging, thereby having the effect of improving the charging uniformity of electrodes in a subsequent charging step and increasing the available capacity of the battery.

Description

Technical Field

[0001] This application is based on the interest claimed in Korean Patent Application No. 10-2021-0144212, filed on October 27, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for activating a secondary battery, and more particularly to a method for discharging gases inside the secondary battery during the activation process of the secondary battery. 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, computers, cameras, and electric vehicles. In particular, the use of lithium secondary batteries is rapidly increasing because they have higher capacity and higher energy density per unit weight than nickel-cadmium or nickel-metal hydride batteries.

[0004] These lithium-ion secondary batteries primarily use lithium-based oxides and carbon materials as the cathode and anode active materials, respectively. A lithium-ion secondary battery comprises: an electrode assembly in which cathode and anode plates, respectively coated with the cathode and anode active materials, are placed with a separator between them; and an external material for sealing and containing the electrode assembly together with the electrolyte.

[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 the following process: when the electrode assembly is housed in the battery casing, an electrolyte in a liquid state, i.e., an electrolyte solution, is injected, and then the battery casing is sealed.

[0007] These secondary batteries undergo a charging and discharging activation process before shipment. Traditional activation processes typically proceed in the order of pre-aging, initial charging, main aging, and defect inspection. After the initial charging, a gas trap phenomenon occurs due to gas retained within the electrode assembly, leading to reduced electrode uniformity and high internal pressure within the battery. Consequently, non-uniform charging occurs, ultimately resulting in degraded battery performance. These problems can be particularly severe in cylindrical or prismatic batteries where processes for removing residual gas are difficult to implement. Therefore, it is necessary to develop a secondary battery activation technology that improves battery efficiency by modifying the charging method during the activation phase of the conventional secondary battery manufacturing process to expel the internal gases of the secondary battery. Summary of the Invention

[0008] Technical issues

[0009] This invention relates to a method for activating a secondary battery, and aims to provide a novel method for activating a secondary battery that, by efficiently removing the gas retained inside the secondary battery, can perform initial charging within an appropriate SOC range and ensure the maximum capacity of the secondary battery.

[0010] Technical solution

[0011] This invention provides a method for activating a secondary battery. In an example, the method includes: an initial charging phase of charging the manufactured secondary battery; and a degassing phase of emitting gases from the charged secondary battery, wherein the degassing phase further includes a high-temperature aging process performed at a temperature of 50°C to 80°C, and regarding the state of charge (SOC) during the initial charging phase,

[0012] a) For one or more types of secondary batteries with different initial charge SOCs, degassing is performed by carrying out a high-temperature aging process at 50°C to 80°C for 3 to 5 hours, and

[0013] b) The discharge capacity is evaluated based on the results of a), wherein the SOC charged during the initial charging phase is the SOC at which the discharge capacity is at its highest.

[0014] In a specific example, in the secondary battery activation method according to the present invention, the execution time of the high-temperature aging process in the degassing stage is the sum of the following times: the heating time during which the secondary battery reaches 98% of its maximum temperature when it is charged with a current of 0.15C to 0.25C; and the holding time for maintaining the maximum temperature of the secondary battery at 98% to 100%.

[0015] In another specific example, in the secondary battery activation method according to the present invention, one or more types of secondary batteries with different initial charge SOCs have an initial charge SOC range from 1% to 15%.

[0016] In another specific example, in the secondary battery activation method according to the present invention, the discharge capacity evaluation is a method of discharging to 20% or lower SOC after full charging.

[0017] In another example, in the secondary battery activation method according to the present invention, the degassing stage further includes a room temperature aging process following the high-temperature aging process, and the room temperature aging process is allowed to wait for 0.5 to 72 hours.

[0018] In another example, in the secondary battery activation method according to the present invention, after the high-temperature aging process, the degassing stage further includes a process of charging to 60% to 70% SOC.

[0019] In a specific example, the secondary battery activation method according to the present invention further includes a process of charging the secondary battery to 70% or higher SOC after the degassing stage.

[0020] In another specific example, in the secondary battery activation method according to the present invention, after the stage of charging the secondary battery to 70% or higher SOC, it further includes a stage of discharging the secondary battery to a SOC level of 20% or lower.

[0021] In another specific example, in the secondary battery activation method according to the invention, prior to the initial charging phase of charging the assembled secondary battery, the secondary battery is maintained at a state of charge (SOC) of 0% or higher and lower than 1%.

[0022] In one example, in the secondary battery activation method according to the present invention, prior to the degassing stage, a process is included in forming a solid electrode interface (SEI) film on all or part of the anode surface of the electrode assembly.

[0023] In another example, in the secondary battery activation method according to the present invention, the secondary battery has a structure in which an electrode assembly and an electrolyte are stored in a battery casing, the electrode assembly having a structure including a positive electrode, a negative electrode and a separator between the positive electrode and the negative electrode, and the electrolyte comprising a lithium salt.

[0024] In another example, in the secondary battery activation method according to the present invention, the secondary battery is any one of prismatic, cylindrical, or pouch-shaped.

[0025] Beneficial effects

[0026] According to the present invention, a method is provided for selecting an optimal SOC range during the initial charging of a secondary battery, and when this method is applied, a channel for discharging gases generated inside the electrode assembly due to the initial charging is adequately ensured.

[0027] Furthermore, in the degassing stage for removing gas generated inside the electrode assembly of the secondary battery during initial charging, a method for calculating the optimal high-temperature aging time is provided. The secondary battery using this method prevents gas traps in the electrode assembly, thereby improving charging uniformity. As a result, the usable capacity increases and the battery failure rate can be reduced. Attached Figure Description

[0028] Figure 1 The figure shows the results of evaluating the discharge capacity of secondary batteries with a diameter of 21 mm and different SOCs after initial charging.

[0029] Figure 2 The figure shows the results evaluating the discharge capacity of a secondary battery with a diameter of 21 mm and initially charged at 7% SOC, after the initial charge, depending on the high-temperature aging time.

[0030] Figure 3 Temperature changes over time are depicted during the charging process of secondary batteries with a diameter of 21 mm and 46 mm, respectively.

[0031] Figure 4 The results show the evaluation of the discharge capacity of a secondary battery with a diameter of 46 mm and different SOCs after initial charging.

[0032] Figure 5 The figure shows the results of evaluating the discharge capacity of a secondary battery with a diameter of 46 mm and initially charged at 9% SOC, after the initial charge, depending on the high-temperature aging time.

[0033] Figure 6 The figure shows the results of evaluating the discharge capacity of a secondary battery with a diameter of 46 mm, depending on the initial charge state of charge (SOC) and the high-temperature aging time. Detailed Implementation

[0034] The invention will be described in detail below. First, the terms and words used in this specification and claims should not be construed as limited to their common or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the scope of the invention, based on the principle that the inventors have appropriately defined the concepts of the terms in order to best describe the invention.

[0035] This invention relates to a method for activating a secondary battery. This method involves performing a degassing stage, including a high-temperature aging process, after charging at a low SOC level, selecting an appropriate SOC range, and calculating the execution time of the high-temperature aging process. In this disclosure, SOC 0% means that the secondary battery capacity is completely consumed, and SOC 100% means that the secondary battery capacity is maximally filled. This can be measured by selecting any one or more known measurement methods, such as SOC chemical measurement methods, voltammetric methods, current integration methods, pressure measurement methods, etc.

[0036] This invention provides a method for activating a secondary battery. In an example, the method for activating a secondary battery according to the present invention may include: an initial charging stage for charging the manufactured secondary battery; and a degassing stage for emitting gases from the charged secondary battery.

[0037] Here, the degassing stage can further include a high-temperature aging process performed at a temperature of 50°C to 80°C.

[0038] In addition, regarding the SOC during the initial charging phase, for one or more types of secondary batteries with different initial charging SOCs, degassing is performed by carrying out a high-temperature aging process at 50°C to 80°C for 3 to 5 hours, and the discharge capacity of the degassed product is evaluated to obtain the SOC at which the discharge capacity is highest.

[0039] Simultaneously, due to the nature of secondary batteries, it is necessary to perform an activation process during the first cycle to activate the positive electrode active material and create a solid electrode interface (SEI) film on the negative electrode. During the activation process, a large amount of gas is generated inside the secondary battery. If the gas generated inside the secondary battery is not efficiently removed, it remains in specific spaces within the battery, causing a gas trap phenomenon and resulting in high internal pressure. This internal pressure causes structural deformation of the secondary battery, which adversely affects battery performance and lifespan, such as usable capacity and output.

[0040] When the initial charge is performed at a predetermined SOC level, gas is generated inside the electrode assembly of the secondary battery, and gas trapping can be prevented by properly discharging the generated gas to the outside of the electrode assembly by aging it at a predetermined time at a high temperature.

[0041] Therefore, selecting an appropriate SOC level during the initial charging phase is crucial. If the aforementioned appropriate SOC range is not reached, gas generation may be insufficient, leading to gas regeneration during subsequent charging stages. On the other hand, if the appropriate SOC range is exceeded, the thickness of the positive and negative electrodes expands even more due to battery charging, making it difficult to ensure adequate channels for gas removal.

[0042] Furthermore, the amount of gas formed inside the secondary battery changes when the size of the secondary battery increases or decreases, so the appropriate state of charge (SOC) should be selected in consideration of the size of the secondary battery.

[0043] Meanwhile, when degassing a secondary battery initially charged at its optimal SOC is performed by high-temperature aging, the amount of gas formed inside varies depending on the size of the secondary battery, making it necessary to properly calculate the time required for the high-temperature aging process.

[0044] Accordingly, the inventors of the present invention have confirmed that a secondary battery that utilizes the appropriate initial charge state of charge required by the activation process of the secondary battery and is aged under appropriate conditions necessary for performing high-temperature aging as a stage of degassing effectively dissipates gases and exhibits maximum discharge capacity confirms the effect of improving the electrochemical activity of the battery, thus leading to the present invention.

[0045] First, the initial charging phase of charging the manufactured secondary battery will be described. The initial charging phase of charging the manufactured secondary battery is the phase of initial charging at a predetermined SOC.

[0046] Specifically, in the selection of SOC during the initial charging phase, a high-temperature aging process performed at a temperature of 50°C to 80°C is carried out for 3 to 5 hours to degas one or more types of secondary batteries with different initial charging SOCs, and the discharge capacity is evaluated based on the results to select the SOC with the highest discharge capacity as the initial charging SOC.

[0047] More specifically, in one or more types of secondary batteries with different initial charge SOCs, the initial charge SOC can range from 1% to 15%. Specifically, the initial charge SOC ranges from 3% to 12%, or from 5% to 10%. If the initial charge SOC range is too small, as mentioned above, gas generation is insufficient, and gas may be generated again in subsequent charging stages. Conversely, if the initial charge SOC range is too high, the electrode thickness expands excessively, leading to problems in ensuring adequate gas emission channels within the secondary battery.

[0048] Alternatively, the initial charging phase can be performed in constant current (CC) mode. Considering the time required for the manufacturing process and to ensure charging uniformity, the intensity of the charging current during the initial charging period can be appropriately controlled within the range of 0.05C to 1C.

[0049] In addition, it is possible to degas one or more types of secondary batteries with different initial charge SOCs by performing a high-temperature aging process at 50°C to 80°C for 3 to 5 hours.

[0050] The high-temperature aging process promotes the release of gases generated during the initial charging phase to the outside of the electrode assembly. Here, when the electrolyte viscosity decreases and its fluidity increases, it facilitates the formation of channels for gas emission within the electrode assembly.

[0051] Here, the high-temperature aging process can be performed at a temperature of 50°C to 80°C. Preferably, the temperature can be 55°C to 70°C. If the temperature is below 50°C, it is not easy to reduce the viscosity of the electrolyte, making it difficult to form gas channels. If the temperature exceeds 80°C, electrochemical elements such as electrolytes or electrode active materials may deteriorate, and this may lead to side reactions such as oxidation and reduction of the electrolyte.

[0052] Furthermore, the high-temperature aging process can be performed for 3 to 5 hours. The high-temperature aging time can be appropriately increased or decreased depending on the temperature. If performed at elevated temperatures, a shorter duration is desirable to prevent excessive exposure of the electrochemical device to high temperatures. However, sufficient aging time must be ensured because if the aging time is too short, all the gases generated inside the electrode assembly may remain without being released. Therefore, the aging time can be appropriately set taking into account the temperature and the release rate of the generated gases.

[0053] By aging one or more types of secondary batteries with different initial charge SOCs at high temperatures, the discharge capacity of degassed products can be evaluated, and the SOC at which the discharge capacity is highest can be selected as the initial charge SOC.

[0054] Specifically, discharge capacity evaluation can be achieved by discharging to a level of 20% or lower after a full charge (SOC 100%). As an example, discharge can be performed to 0% SOC. Here, the secondary battery can be shown with a voltage ranging from 2V to 46V. Through this charging and discharging phase, the maximum discharge capacity of the secondary battery can be measured, and the initial charge SOC of the secondary battery with the maximum discharge capacity can be selected as the SOC charged in the initial charging phase of this invention.

[0055] In one example of the invention, after selecting the optimal initial charge state of charge (SOC) through discharge capacity evaluation, a degassing stage may be included to discharge gases generated inside the electrode assembly of the secondary battery that has already undergone the initial charging stage at the optimal initial charge state of charge.

[0056] The degassing stage may further include a high-temperature aging process performed at temperatures ranging from 50°C to 80°C. Here, as mentioned above, the execution temperature for the high-temperature aging process can be determined by considering the viscosity and flowability of the electrolyte within the range of 50°C to 80°C.

[0057] Furthermore, when the size of a secondary battery that has already completed its initial charge increases or decreases, the required high-temperature aging time for the gases generated inside the secondary battery may differ. Accordingly, it is necessary to calculate the appropriate execution time for the high-temperature aging process.

[0058] Accordingly, in an example of the present invention, when the secondary battery is charged with a current of 0.15C to 0.25C, the execution time of the high-temperature aging process in the degassing stage can be the sum of the heating time for the secondary battery to reach 98% of its maximum temperature and the holding time for maintaining the secondary battery at 98% to 100% of its maximum temperature.

[0059] As described below, based on the evaluation results of the discharge capacity of a secondary battery aged at high temperature for a time equal to the sum of the heating time and the holding time, and a secondary battery aged at high temperature for an arbitrary time, it can be confirmed that the former has a larger discharge capacity than the latter. Therefore, when conditions including the size of the secondary battery change, by measuring the heating time and holding time during the charging process of the secondary battery, it is beneficial to predict the appropriate high-temperature aging execution time while taking into account the battery's discharge capacity.

[0060] In another example of the invention, the degassing stage may further include a room temperature process following the high-temperature aging process, and the room temperature aging process may be a process of waiting from 0.5 hours to 72 hours. Specifically, the room temperature may be implemented in the form of storing the secondary battery at a temperature of 20°C to 30°C, or in the form of storing the secondary battery in a chamber configured to maintain room temperature.

[0061] In another example of the invention, the degassing stage may further include a process of charging to 60% to 70% of the state of charge (SOC) after a high-temperature aging process. Because the degassing process can release gases that might be generated during additional charging, this can further improve battery safety.

[0062] Simultaneously, for the secondary battery that has completed the degassing process, a further stage of charging to 70% or higher may be included. In this stage, the secondary battery can be charged to a State of Charge (SOC) of 70% or higher. Preferably, the secondary battery is charged to a SOC range of 70% to 100%, and the battery is activated so that it can be normally driven by this charging.

[0063] Furthermore, after charging the secondary battery to a SOC of 70% or higher, a further stage of discharging the secondary battery to a SOC of 20% or lower can be included. Discharging can be performed down to a SOC of 0%. Here, the secondary battery can exhibit a voltage from 2V to 46V. This discharge stage allows for selection of the battery capacity and prevents non-uniformity of current density caused by non-uniform distribution of electrode active materials.

[0064] Meanwhile, in one example of the present invention, the secondary battery that has applied the initial charging phase does not perform the charging process after electrolyte injection, and this is the first charging applied after the electrolyte injection in the above-mentioned phase.

[0065] In one example of the invention, the secondary battery can be maintained at 0% or higher and below 1% SOC before the initial charging phase of charging the assembled secondary battery. When pre-charging is performed as described above, the dissolution of copper, which serves as the negative electrode current collector, can be suppressed by reducing the potential of the negative electrode, and as a result, this is effective in suppressing low voltage in the battery.

[0066] In another example of the invention, prior to the degassing stage, a process may be included to form a solid electrode interface (SEI) film on all or part of the negative electrode surface of the electrode assembly. The formed SEI film serves to reduce the irreversibility of the secondary battery to a certain level, even when charged at a high level during the degassing stage. This SEI film is formed on the surface of the negative electrode during the initial charging stage, for example, when the electrolyte contains ethylene carbonate (EC) as a cyclic carbonate compound, requiring sufficient reduction of the ethylene carbonate during the initial charging stage. Furthermore, the stabilization of the SEI film can be accelerated through a high-temperature aging process.

[0067] Meanwhile, "activation" in this specification refers to the process of supplying a consistent electrical current to an electrode assembly or battery cell that does not possess electrical characteristics, thereby enabling the positive and negative electrodes to acquire electrical characteristics, and this can be understood to include all reactions accompanying the initial charging. Non-limiting examples of reactions accompanying the initial charging include the activation of the negative electrode, such as the formation of the SEI film, partial charging of the battery capacity, and lithiation of carbon-based negative electrode active materials.

[0068] In one example of the invention, the secondary battery used in the activation method may be composed of one or more of those described below. The secondary battery has a structure comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator between the positive and negative electrodes; an electrolyte for impregnating the electrode assembly; and a battery casing containing the electrode assembly and a non-aqueous electrolyte. The non-aqueous electrolyte is, for example, an electrolyte containing a lithium salt.

[0069] The positive electrode has a structure in which a layer of positive electrode active material is stacked on one or both surfaces of the positive electrode current collector. In one example, the layer of positive electrode active material includes a positive electrode active material, a conductive material, a binder polymer, etc. And, if necessary, may further include cathode additives commonly used in this art.

[0070] The positive electrode active material may be a lithium-containing oxide, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used.

[0071] For example, the lithium-containing transition metal oxide may be any one selected from the group consisting of the following materials: Li x CoO2 (0.5<x<1.3), Li x NiO2 (0.5<x<1.3), Li x MnO2 (0.5<x<1.3), Li x Mn2O4 (0.5<x<1.3), Li x (Ni a Co b Mn c )O2 (0.5<x<1.3, 0<a<1, 0<b<1, 0<c<1, a+b+c=1), Li x Ni 1-y Co y O2 (0.5<x<1.3, 0<y<1), Li x Co 1-y Mn y O2 (0.5<x<1.3, 0≤y<1), Li x Ni 1-y Mn y O2 (0.5<x<1.3, 0≤y<1), Li x (Ni a Co b Mn c )O4 (0.5<x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li x Mn 2-z Ni z O4 (0.5<x<1.3, 0<z<2), Li x Mn 2- z Co z O4 (0.5<x<1.3, 0<z<2), Li x CoPO4 (0.5<x<1.3) and Li x FePO4 (0.5<x<1.3), or a mixture of two or more of the above materials. In addition, the lithium-containing transition metal oxide may be coated with a metal or metal oxide, such as aluminum (Al). Besides the lithium-containing transition metal oxide, one or more of sulfides, selenides and halides may be used.

[0072] The positive electrode active material layer may include positive electrode active material in the range of 94.0 to 98.5% by weight. When the content of positive electrode active material meets the above range, it becomes advantageous for manufacturing high-capacity batteries and for providing positive electrode conductivity or adhesion between electrode materials.

[0073] The current collector used in the positive electrode is a highly conductive metal that can be easily bonded to the positive electrode active material slurry, and any metal that does not react within the voltage range of the electrochemical device can be used. Specifically, non-limiting examples of the current collector for the positive electrode include foils made of aluminum, nickel, or combinations thereof. The positive electrode active material layer further includes a conductive material.

[0074] Carbon-based conductive materials are widely used as conductive materials, including spherical or needle-shaped carbon-based conductive materials. In a mixture with a binder, the spherical carbon-based conductive material fills the pores (the empty spaces between the active material particles) to improve the physical contact between the active materials, thereby reducing the interfacial resistance and improving the adhesion between the lower positive electrode active material and the current collector.

[0075] Examples of spherical carbon-based conductive materials include carbon black, including Denka Black, and examples include FX35 (Denka), SB50L (Denka), and Super-P, but are not limited thereto. Here, "spherical" means having a spherical particle shape and an average diameter (D50) of 10 to 500 nm, particularly 15 to 100 nm or 15 to 40 nm.

[0076] Corresponding to the meaning of spherical carbon-based conductive materials, there are needle-shaped carbon-based conductive materials. Needle-shaped carbon-based conductive materials can be carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), carbon nanofibers (CNFs), or mixtures of two or more of the above. Here, "needle-shaped" means having a needle-like particle shape, for example, having an aspect ratio (length / diameter value) in the range of 50 to 650, particularly 60 to 300, or 100 to 300.

[0077] Compared to needle-shaped conductive materials, spherical carbon-based conductive materials have advantages in terms of dispersibility and improve the insulating properties of the layer by having lower conductivity compared to needle-shaped carbon-based conductive materials.

[0078] The positive electrode active material layer may include conductive material in the range of 0.5 to 5% by weight. When the content of conductive material meets the above range, it has the effect of providing sufficient cathode conductivity and reducing the interfacial resistance between the current collector and the active material.

[0079] As with adhesive polymers, adhesives commonly used in this art can be used without limitation. For example, the adhesive can be a water-insoluble polymer that is soluble in organic solvents but insoluble in water, or a water-soluble polymer that is insoluble in organic solvents but soluble in water. The water-insoluble polymer can be one or more selected from the group consisting of: polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), ethylene oxide-polypropylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene-butadiene rubber (SBR), polyacrylates, and derivatives of the above materials.

[0080] The water-soluble polymer can be one or more of the following materials: various cellulose derivatives, such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methyl cellulose (HPMC), etc.

[0081] The content of the binder polymer is proportional to the content of conductive material included in higher and lower positive electrode active material layers. This is to impart adhesion to the conductive material, which has a relatively small particle size compared to the active material, because more binder polymer is required when the conductive material content increases, and less binder polymer can be used when the conductive material content decreases.

[0082] The negative electrode has a structure in which a layer of negative electrode active material is stacked on one or both surfaces of the negative electrode current collector. In one example, the negative electrode active material layer includes a negative electrode active material, a conductive material, a binder polymer, etc. And, if necessary, may further include an anolyte additive commonly used in this art.

[0083] Negative electrode active materials can include carbon materials, lithium metal, silicon, or tin. When carbon materials are used as negative electrode active materials, both low-crystallinity carbon and high-crystallinity carbon can be used. Soft carbon and hard carbon are representative examples of low-crystallinity carbon, and high-temperature calcined carbon is a representative example of high-crystallinity carbon, such as natural graphite, condensed graphite, pyrolytic carbon, carbon fibers based on mesophase pitch, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0084] Non-limiting examples of current collectors for the negative electrode include foils made of copper, gold, nickel, or copper alloys, or combinations thereof. The positive electrode active material layer further includes a conductive material. Alternatively, the current collector can be used by stacking substrates made of the above materials.

[0085] Additionally, the negative electrode may include conductive materials and adhesives commonly used in related technologies.

[0086] Any porous substrate used in lithium secondary batteries can be used as the separator, and for example, polyolefin-based porous membranes or nonwoven fabrics can be used, but are not particularly limited thereto.

[0087] Examples of polyolefin-based porous membranes include polyethylene-based polymers, such as high-density polyethylene alone, needle-type low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, or membranes formed from polymers mixed with these materials.

[0088] Besides polyolefin-based nonwoven fabrics, nonwoven fabrics also include, for example, nonwoven fabrics made from polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether oxide, polyphenylene sulfide, and polyvinyl naphthalene, or polymers formed from blends of these materials. The structure of nonwoven fabrics can be spunbond nonwoven fabrics or meltblown nonwoven fabrics composed of long fibers.

[0089] The thickness of the porous substrate is not particularly limited, but can be 5 to 50 μm, and the pore size and porosity present in the porous substrate are also not particularly limited, but can be 0.01 to 50 μm and 10 to 95%, respectively.

[0090] Meanwhile, at least one surface of the porous substrate may further include a porous coating comprising inorganic particles and a binder polymer to improve the mechanical strength of the diaphragm formed by the porous substrate and suppress short circuits between the positive and negative electrodes.

[0091] The electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. As the lithium salt, those lithium salts commonly used as non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt contains Li... + As a cation and as an anion, lithium salts may contain at least one selected from the group consisting of: F - Cl - ,Br - I - NO 3- N(CN) 2- BF 4- ,ClO 4- AlO 4- AlCl 4- PF 6- 、SbF 6- AsF 6- BF2C2O 4- BC4O 8- (CF3)2PF4- (CF3)3PF 3- (CF3)4PF 2- (CF3)5PF - (CF3)6P - CF3SO 3- C4F9SO 3- CF3CF2SO 3- (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO 3- CF3CO 2- CH3CO 2- SCN - and (CF3CF2SO2)2N - .

[0092] As the organic solvent contained in the above-mentioned electrolyte, those organic solvents commonly used as electrolytes for secondary batteries can be used without limitation. For example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc., can be used alone or in combination of two or more. Typically, cyclic carbonates, linear carbonates, or mixtures thereof can be included as carbonate compounds.

[0093] Specific examples of cyclic carbonate compounds are any one selected from the group consisting of: ethylene carbonate (EC), propylene carbonate (PC), 1,2-butenyl carbonate, 2,3-butenyl carbonate, 1,2-pentenyl carbonate, 2,3-pentenyl carbonate, vinylene carbonate, vinyl ethylene carbonate, and halides of the above, or mixtures of two or more of the above. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited to this group.

[0094] In addition, specific examples of linear carbonate compounds include any one selected from the group consisting of: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, or mixtures of two or more of the above materials may be used, but are not limited thereto.

[0095] In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents with high dielectric constants, allowing for better dissociation of lithium salts in the electrolyte. When these cyclic carbonates are mixed in appropriate ratios with low-viscosity, low-dielectric-constant linear carbonates (such as dimethyl carbonate and diethyl carbonate), this can produce electrolytes with higher conductivity.

[0096] In addition, the ether used as an organic solvent may be any one selected from the group consisting of: dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or a mixture of two or more of the above materials, but is not limited thereto.

[0097] Furthermore, as an organic solvent, the ester may be any one selected from the group consisting of: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone and β-caprolactone, or a mixture of two or more of the above materials, but is not limited thereto.

[0098] The injection of non-aqueous electrolytes can be performed at an appropriate stage during the manufacturing process of the electrochemical device, depending on the manufacturing process of the final product and its required physical properties. That is, the injection of non-aqueous electrolytes can be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

[0099] In this case, the secondary battery includes a lithium secondary battery, which may be a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery. Depending on its shape, the secondary battery may include a cylindrical, prismatic, or pouch-shaped secondary battery.

[0100] Best mode for carrying out the present invention

[0101] The invention will be described in detail below. First, the terms and words used in this specification and claims should not be construed as limited to their common or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the scope of the invention, based on the principle that the inventors have appropriately defined the concepts of the terms in order to best describe the invention.

[0102] Manufacturing Example

[0103] The positive electrode active material (LiNi) 0.5 Co 0.2 Mn 0.3O2), conductive material (carbon black), and binder (PVDF) were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 96:2:2 and mixed to prepare a cathode slurry. The prepared cathode slurry was then coated onto a substrate with a capacity of 3.1 mAh / cm³. 2 A 20 μm thick aluminum foil was used to prepare the positive electrode current collector.

[0104] Artificial graphite, conductive material (carbon black), and binder (PVDF) were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 96:2:2 and mixed to prepare an anode slurry. The prepared anode slurry was then coated onto a substrate with a capacity of 3.1 mAh / cm³. 2 A 20 μm thick copper foil was used to prepare the negative electrode current collector. A jelly roll-type electrode assembly was fabricated by placing a separator (polyethylene material, 20 μm thick) between the positive and negative electrodes. After the electrode assembly was loaded into a battery casing, electrolyte was injected, and the battery casing was sealed to fabricate cylindrical secondary batteries with a diameter of 21 mm and 46 mm. The electrolyte was prepared by adding 1.4 M LiPF6 to an organic solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 20:20:60 (volume ratio). Additionally, ethylene carbonate (3 vol%) and succinate (1 vol%) were mixed into the electrolyte.

[0105] Experimental Example 1

[0106] Cylindrical secondary battery with a diameter of 21mm

[0107] Six secondary batteries (Examples 1 to 5 and Comparative Example 1) with a diameter of 21 mm were manufactured using the above manufacturing examples. The activation process for each cell was performed as described below. As shown in Table 1 below, the secondary batteries of Examples 1 to 5 underwent an initial charging phase and a degassing phase including high-temperature aging (60°C, 4 hours) and room-temperature aging (12 hours). During the room-temperature aging phase, an additional charge to 65% SOC was performed. Thereafter, a phase of full charging to 100% SOC (4.2V) and discharging to 0% SOC (2.5V) was performed. Discharging to 2.5V was performed in 1C CC mode and 0.2C CV mode. Meanwhile, in Comparative Example 1, the same process as in Examples 1 to 5 was performed, except that the initial charging phase and the degassing phase via high-temperature aging were not performed as in existing processes.

[0108] [Table 1]

[0109]

[0110] Select initial charge SOC

[0111] Figure 1 This is a graph showing the results of evaluating the discharge capacity of Examples 1 to 5 and Comparative Example 1. (Reference) Figure 1 As a result of evaluating the discharge capacity by manufacturing three identical secondary batteries in each of Examples 1 to 5 and Comparative Example 1, it was confirmed that in the case of Example 4, where the initial charge was performed at a SOC of 7%, the discharge capacity was superior to that of the other examples and comparative examples. When the initial charge was at a SOC of 1% or 3%, the discharge capacity was confirmed to be similar to that without initial charging, and when the initial charge exceeded an appropriate level to reach a SOC of 10%, the discharge capacity was confirmed to decrease.

[0112] Discharge capacity evaluation based on high-temperature aging time

[0113] Figure 2 This is a graph showing the results of evaluating the discharge capacity of a 21mm diameter secondary battery manufactured at an initial charge SOC of 7%, based on high-temperature aging time after the initial charge. (Reference) Figure 2 For the secondary battery prepared under an initial charge SOC of 7% (Example 4), the discharge capacity after initial charging was evaluated based on the high-temperature aging time, and the results for the discharge capacity of two identical secondary batteries could be checked using Table 2. Specifically, the aging temperature was set to 60°C, and the aging time was set to 0 hours, 1 hour, 2 hours, 3 hours, and 4 hours. Accordingly, it was confirmed that the maximum discharge capacity exceeded 100% when the aging time was 1 hour or 2 hours. However, when the aging time exceeded 2 hours, degradation of the electrochemical device or side reactions occurred, resulting in a decreasing trend in discharge capacity. In addition, it was confirmed that the discharge capacity was lowest when no aging was performed.

[0114] [Table 2]

[0115]

[0116] Measure heating time and holding time

[0117] Figure 3 This is a graph showing the temperature rise profiles of a secondary battery with a diameter of 21 mm and a secondary battery with a diameter of 46 mm. (Reference) Figure 3The heating time required to reach 98% of the maximum temperature (60°C) while charging a 21mm diameter secondary battery at a current of 0.2C was approximately 30 minutes, and the holding time required to maintain 98% to 100% of the maximum temperature (60°C) was also confirmed to be approximately 30 minutes. The time obtained by adding the heating time and the holding time (approximately 1 hour) is not significantly different from the high-temperature aging time (1 hour) for the maximum discharge capacity shown in Table 2.

[0118] Experimental Example 2

[0119] Cylindrical secondary battery with a diameter of 46mm

[0120] Three cylindrical secondary batteries (Examples 6 to 8) with a diameter of 46 mm were manufactured using the above manufacturing examples. As shown in Table 3 below, an initial charging phase and a degassing phase, including high-temperature aging (60°C, 4 hours) and room-temperature aging (12 hours), were performed in each secondary battery. During the room-temperature aging phase, an additional charge to 65% SOC was performed. Thereafter, a phase of full charging to 100% SOC (4.2V) and discharging to 0% SOC (2.5V) was performed. Discharging to 2.5V was performed in 1C CC mode and 0.2C CV mode.

[0121] [Table 3]

[0122]

[0123] Select initial charge SOC

[0124] Figure 4 This is a graph illustrating the discharge capacity results for Examples 6 to 8. (Reference) Figure 4 As a result of evaluating the discharge capacity by manufacturing three identical secondary batteries in each of Examples 6 to 8, in the case of Example 8 where the initial charge was performed at a SOC of 9%, its discharge capacity was confirmed to be superior to that of the other examples and comparative examples.

[0125] Estimated high-temperature aging time

[0126] Figure 3 This is a graph illustrating the temperature increase profiles of a secondary battery with a diameter of 21 mm and a secondary battery with a diameter of 46 mm. Table 4 below shows the predicted high-temperature aging execution time, calculated from the heating time required to reach 98% of the maximum temperature and the holding time required to maintain the maximum temperature from 98% to 100%. (Reference) Figure 3As shown in Table 4, a six-fold difference in heating time was confirmed between the secondary battery with a diameter of 46 mm and maximum discharge capacity (Example 8) and the secondary battery with a diameter of 21 mm and maximum discharge capacity (Example 4). Furthermore, the holding time for the secondary battery with a diameter of 21 mm and maximum discharge capacity (Example 4) was confirmed to be 30 minutes. Therefore, the holding time for the secondary battery with a diameter of 46 mm and maximum discharge capacity (Example 8) can be estimated to be 3 hours, which, like the heating time, represents a six-fold difference. This is because, as the battery size increases, the holding time increases proportionally to the increase in heating time.

[0127] Furthermore, as described above in Example 1, it can be confirmed that the difference between the time obtained by adding the heating time and the holding time and the high-temperature aging time representing the maximum discharge capacity is not significant. Therefore, it is possible to estimate that the appropriate high-temperature aging time for a secondary battery (Example 8) with a diameter of 46 mm and the maximum discharge capacity is 6 hours, which is the time obtained by adding the heating time and the holding time.

[0128] [Table 4]

[0129]

[0130] Discharge capacity evaluation based on high-temperature aging time

[0131] Figure 5 This is a graph showing the results of evaluating the discharge capacity of a secondary battery with a diameter of 46 mm and an initial charge condition of 9% SOC, after the initial charge, based on the high-temperature aging time. (Reference) Figure 5 The discharge capacity of a secondary battery (Example 8) manufactured at an initial charge SOC of 9% was evaluated based on the high-temperature aging time after the initial charge, and the results for the discharge capacity of two identical secondary batteries were confirmed by Table 5. Specifically, the aging temperature was set to 60°C, and the aging time was set to 0 hours, 1 hour, 2 hours, 4 hours, 6 hours, and 8 hours. It was confirmed that the maximum discharge capacity exceeded 100% when the aging time was 4 hours, 6 hours, or 8 hours, with the 6-hour aging time exhibiting the highest discharge capacity. This confirms that the high-temperature aging time is consistent with the previously estimated heating and holding times.

[0132] [Table 5]

[0133]

[0134] Discharge capacity evaluation based on initial charge state of charge (SOC) and high-temperature aging time.

[0135] Figure 6This is a graph showing the results of evaluating the discharge capacity of a 46mm diameter secondary battery based on initial charge SOC and high-temperature aging time. (Reference) Figure 6 The initial charge SOC is in the range of 9%, and in the case of a secondary battery that has undergone a high-temperature aging process of 6 hours, together with a secondary battery that has not undergone initial charging and high-temperature aging, it has an initial charge SOC in the range of 7%, and it is confirmed to have a higher discharge capacity than a secondary battery that has undergone high-temperature aging for 2 hours.

[0136] Accordingly, when the diameter of the secondary battery changes, it is necessary to set appropriate initial charge state of charge (SOC) and high-temperature aging time, as the initial charge SOC and high-temperature aging time with maximum discharge capacity may change. According to the present invention, when secondary batteries have different sizes, an appropriate initial charge SOC can be selected through discharge capacity evaluation, and an appropriate high-temperature aging time can be predicted by calculating the heating time and holding time of the temperature increase profile. By efficiently discharging the gas generated inside the battery, the secondary battery that has undergone this activation process can ensure maximum usable capacity.

Claims

1. A method for activating a secondary battery, comprising: The initial charging phase of the manufactured secondary battery; and The degassing stage of the emitted gas from the charged secondary battery. The degassing stage further includes a high-temperature aging process performed at a temperature of 50°C to 80°C. And regarding the SOC charged during the initial charging phase, a) For one or more types of secondary batteries with different initial charge SOCs, degassing is performed by carrying out a high-temperature aging process at 50°C to 80°C for 3 to 5 hours, and b) Evaluate the discharge capacity based on the results of a), wherein the SOC charged during the initial charging phase is the SOC at which the discharge capacity is highest. Among them, one or more types of secondary batteries with different initial charge SOCs have an initial charge SOC range from 1% to 15%.

2. The secondary battery activation method according to claim 1, wherein, The execution time of the high-temperature aging process in the degassing stage is the sum of the following times: The secondary battery reaches 98% of its maximum temperature when charged with a current of 0.15C to 0.25C. and The holding time for maintaining the highest temperature of the secondary battery at 98% to 100%.

3. The secondary battery activation method according to claim 1, wherein, Discharge capacity evaluation is a method of discharging to 20% or lower of the state of charge after a full charge.

4. The secondary battery activation method according to claim 1, wherein, The degassing stage further includes a room temperature aging process following the high-temperature aging process. The room temperature aging process takes 0.5 to 72 hours.

5. The secondary battery activation method according to claim 1, wherein, Following the high-temperature aging process, the degassing stage further includes a process of charging to 60% to 70% of the State of Charge (SOC).

6. The secondary battery activation method according to claim 1, wherein, Following the degassing stage, the process further includes charging the secondary battery to 70% or higher SOC.

7. The secondary battery activation method according to claim 6, wherein, After charging the secondary battery to 70% or higher SOC, the process further includes discharging the secondary battery to 20% or lower SOC.

8. The secondary battery activation method according to claim 1, wherein, Prior to the initial charging phase of charging the assembled secondary battery, the secondary battery is maintained at a state of charge (SOC) of 0% or higher and below 1%.

9. The secondary battery activation method according to claim 1, wherein, Prior to the degassing stage, the process includes forming a solid electrode interface (SEI) film on all or part of the surface of the negative electrode of the electrode assembly of the secondary battery.

10. The secondary battery activation method according to claim 1, wherein, The secondary battery has a structure in which electrode components and electrolyte are stored in a battery casing. The electrode assembly has a structure including a positive electrode, a negative electrode, and a membrane between the positive electrode and the negative electrode, and The electrolyte contains a lithium salt.

11. The secondary battery activation method according to claim 1, wherein, The secondary battery is any one of prismatic, cylindrical, or pouch-shaped.

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