Method for activating secondary batteries

Abstract

The present invention relates to a method for activating a secondary battery, and in the activation process, a suitable initial state of charge (SOC) and high-temperature aging time are calculated according to the size of the secondary battery. In the activation process using this method, gas generated inside the electrode assembly during charging is efficiently removed, thereby improving the charging uniformity of the electrodes in the subsequent charging step and increasing the usable capacity of the battery.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0144212 dated October 27, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for activating a secondary battery, and more particularly to a method for discharging gas from within a secondary battery during the activation process of the secondary battery. [Background technology]

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

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

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

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

[0007] Such secondary batteries undergo an activation process in which they are charged and discharged before shipping. The conventional activation process generally proceeds in the order of pre-aging, primary charging, main aging, and defect inspection. However, after the primary charging, a gas trap phenomenon occurs due to gas remaining inside the electrode assembly, which reduces the uniformity of the electrodes and generates high withstand voltage inside the battery. This causes a non-uniform charging phenomenon, which ultimately leads to a decrease in battery performance. This problem occurs particularly in cylindrical or prismatic batteries, in which it is difficult to apply a process for removing residual gas. Therefore, there is a need to develop a secondary battery activation technology that improves the efficiency of the battery by improving the charging method in the activation step during the conventional secondary battery manufacturing process and discharging gas from inside the secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention relates to a method for activating a secondary battery, and aims to provide a new method for activating a secondary battery that can efficiently remove gas remaining inside the secondary battery and ensure the maximum capacity of the secondary battery by providing a method of initially charging the battery within a suitable SOC range and adjusting the conditions for high-temperature aging. [Means for solving the problem]

[0009] The present invention provides a method for activating a secondary battery. In one embodiment, the method for activating a secondary battery includes an initial charging step of charging a manufactured secondary battery, and a degassing step of discharging gas from the charged secondary battery, the degassing step further includes a high-temperature aging process performed at a temperature of 50°C to 80°C, and the SOC charged in the initial charging step is: a) Degas one or more secondary batteries having different initial charge SOCs by performing a high-temperature aging process at a temperature of 50°C to 80°C for 3 to 5 hours; b) A method for activating a secondary battery, comprising evaluating the discharge capacity of the result of a) and determining the one with the largest discharge capacity as the SOC.

[0010] In a specific example, in the activation method of a secondary battery according to the present invention, the execution time of the high temperature aging process in the degassing step is the sum of the temperature rise time for the secondary battery to reach 98% of the maximum temperature and the maintenance time for maintaining 98% to 100% of the maximum temperature of the secondary battery when the secondary battery is charged with a current of 0.15C to 0.25C.

[0011] In another specific example, in the method for activating a secondary battery according to the present invention, the range of the initial charge SOC of one or more secondary batteries different from each other is 1% to 15%.

[0012] In another embodiment, in the method for activating a secondary battery according to the present invention, the discharge capacity is evaluated by discharging the battery to SOC 20% or less after full charge.

[0013] In another embodiment, in the method for activating a secondary battery according to the present invention, the degassing step further includes a room temperature aging process after the high temperature aging process, and the room temperature aging process is performed for 0.5 to 72 hours.

[0014] In another embodiment, in the method for activating a secondary battery according to the present invention, the degassing step further includes a process of charging the battery to an SOC of 60% to 70% after a high-temperature aging process.

[0015] In a specific example, the method for activating a secondary battery according to the present invention further includes, after the degassing step, charging the secondary battery to a SOC range of 70% or more.

[0016] In another embodiment, the method for activating a secondary battery according to the present invention further comprises discharging the secondary battery to a level of SOC 20% or less after charging the secondary battery to a level of SOC 70% or more.

[0017] In another embodiment, the method for activating a secondary battery according to the present invention is such that, prior to an initial charging step of charging an assembled secondary battery, the secondary battery is maintained at an SOC of 0% or more and less than 1%.

[0018] In one embodiment, the method for activating a secondary battery according to the present invention includes a process of forming a solid electrode interface (SEI) film on all or a portion of a negative electrode surface of an electrode assembly prior to a degassing step.

[0019] In another embodiment, in the method for activating a secondary battery according to the present invention, the secondary battery has a structure in which an electrode assembly and an electrolyte are housed in a battery case, the electrode assembly has a structure in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the electrolyte contains a lithium salt.

[0020] In another example, in the method for activating a secondary battery according to the present invention, the secondary battery is any one of a rectangular type, a cylindrical type, and a pouch type. Effect of the Invention

[0021] According to the present invention, there is provided a method for selecting an optimal SOC range during initial charging of a secondary battery, and when this method is applied, a passage for discharging gas generated inside an electrode assembly due to initial charging can be suitably secured.

[0022] In addition, by providing a method for calculating an optimal high-temperature aging time in a degassing step for removing gas generated inside an electrode assembly of an initially charged secondary battery, a secondary battery using this method can prevent a gas trapping phenomenon in the electrode assembly and improve charging uniformity, thereby increasing usable capacity and reducing the battery defect rate. [Brief description of the drawings]

[0023] [Figure 1] The graph shows the results of evaluating the discharge capacity of a 21 mm diameter secondary battery after initial charging at different SOCs. [Diagram 2] The graph shows the results of evaluating the discharge capacity as a function of the high-temperature aging time after initial charging for a secondary battery with a diameter of 21 mm that was initially charged under the condition of an SOC of 7%. [Diagram 3]This shows the temperature change over time during the charging process of a 21 mm diameter secondary battery and a 46 mm diameter secondary battery. [Figure 4] The figures show the results of evaluating the discharge capacity of a 46 mm diameter secondary battery after initial charging at different SOCs. [Diagram 5] The graph shows the results of evaluating the discharge capacity as a function of the high-temperature aging time after initial charging for a secondary battery with a diameter of 46 mm and initially charged under the condition of SOC 9%. [Figure 6] The graph shows the results of evaluating the discharge capacity of a 46 mm diameter secondary battery as a function of the initial charge SOC and high-temperature aging time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described in detail below. Before that, the terms and words used in the specification and claims should not be interpreted limitedly to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of the terms in order to best describe his own invention.

[0025] The present invention relates to a method for activating a secondary battery, which comprises charging at a low SOC (State of charge) level, performing a degassing step including a high-temperature aging process, selecting a suitable SOC range, and calculating the time required for the high-temperature aging process. In the present specification, SOC 0% means a state in which the capacity of the secondary battery is completely consumed, and SOC 100% means a state in which the capacity of the secondary battery is fully filled. The SOC can be measured by selecting at least one of known measurement methods such as a chemical measurement method, a voltage measurement method, a current integration method, and a pressure measurement method.

[0026] The present invention provides a method for activating a secondary battery. In one example, the method for activating a secondary battery according to the present invention may include an initial charging step of charging a manufactured secondary battery, and a degassing step of discharging gas from the charged secondary battery.

[0027] Here, the degassing step may further include a high-temperature aging process carried out at a temperature of 50°C to 80°C.

[0028] In addition, in the SOC to be charged in the initial charging step, one or more types of secondary batteries each having a different initial charging SOC may be degassed by performing a high temperature aging process at a temperature of 50°C to 80°C for 3 to 5 hours, and the discharge capacity of the degassed result may be evaluated, and the SOC at which the discharge capacity is the largest may be determined as the SOC to be charged in the initial charging step.

[0029] Meanwhile, due to the characteristics of secondary batteries, an activation process is essential during the first cycle to activate the positive electrode active material and form 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, the gas remains in a certain space inside the secondary battery, causing a gas trap phenomenon and inducing high withstand voltage. The withstand voltage causes structural deformation of the secondary battery, adversely affecting battery performance such as available capacity and output, and lifespan.

[0030] When initial charging is performed at a predetermined SOC level, gas is generated inside the electrode assembly of the secondary battery, and in order to properly discharge the gas, aging is performed at a high temperature for a predetermined time so that the generated gas is discharged to the outside of the electrode assembly, thereby preventing the gas trapping phenomenon.

[0031] Therefore, it is important to select a suitable SOC level during initial charging. If the suitable SOC range is not met, gas generation will be insufficient and gas may be generated again during subsequent charging stages. On the other hand, if the suitable SOC range is exceeded, the thickness of the positive and negative electrodes will expand more when the battery is charged, making it difficult to ensure a passage for gas removal.

[0032] Furthermore, when the size of the secondary battery increases or decreases, the amount of gas formed inside the secondary battery also differs, so a suitable SOC must be selected in consideration of the size of the secondary battery.

[0033] Meanwhile, when degassing a secondary battery initially charged at an optimal SOC through high-temperature aging, the amount of gas formed inside the secondary battery varies depending on the size of the secondary battery, so it is necessary to appropriately calculate the time required for the high-temperature aging process.

[0034] Therefore, the inventors of the present invention have confirmed that a secondary battery that is aged under suitable conditions required for high-temperature aging, which is one of the degassing steps, effectively discharges gas and at the same time exhibits maximum discharge capacity, thereby improving the electrochemical activity of the battery, thereby arriving at the present invention.

[0035] First, an initial charging step of charging the secondary battery will be described. The initial charging step of charging the secondary battery is a step of primarily charging the secondary battery at a predetermined SOC.

[0036] Specifically, in selecting the SOC at the initial charging stage, one or more types of secondary batteries having different initial charging SOCs are degassed by performing a high-temperature aging process at a temperature of 50°C to 80°C for 3 to 5 hours, and the discharge capacity of the result is evaluated. The SOC at which the discharge capacity is the largest is selected as the initial charging SOC.

[0037] More specifically, in one or more secondary batteries having different initial charge SOCs, the initial charge SOC may be in the range of 1% to 15%. Specifically, the initial charge SOC may be in the range of 3% to 12%, or 5% to 10%. If the initial charge SOC range is too small, gas generation may be insufficient as described above, and gas may be generated again in the subsequent charging stage. Conversely, if the initial charge SOC range is too high, the thickness of the electrodes may expand excessively, resulting in a problem that a gas exhaust passage inside the secondary battery cannot be easily secured.

[0038] Also, the initial charging step may be performed in a constant current (CC) mode. The intensity of the charging current during the initial charging may be suitably controlled within a range of 0.05C to 1C, taking into consideration the time required for the manufacturing process and ensuring charging uniformity.

[0039] In addition, one or more types of secondary batteries having different initial charge SOCs may be degassed by performing a high-temperature aging process at a temperature of 50° C. to 80° C. for 3 to 5 hours.

[0040] The high temperature aging process is a process that promotes the release of gas generated during the initial charging stage to the outside of the electrode assembly. In this case, if the electrolyte has a low viscosity and high fluidity, it is favorable for forming a passage for the gas to be discharged from within the electrode assembly.

[0041] At this time, the high-temperature aging process may be performed at a temperature of 50° C. to 80° C., preferably at a temperature of 55° C. to 70° C. If the temperature is less than 50° C., the electrolyte viscosity is not easily reduced, making it difficult to form gas passages, and if the temperature exceeds 80° C., electrochemical elements such as the electrolyte and electrode active materials may be deteriorated, and side reactions such as oxidation and reduction reactions of the electrolyte may occur.

[0042] The high-temperature aging process may be performed for 3 to 5 hours. The high-temperature aging time may be adjusted appropriately depending on the temperature. If the aging process is performed at a high temperature, it is preferable to proceed for a short period of time so that the electrochemical device is not excessively exposed to high temperatures. However, if the aging time is too short, the gas generated inside the electrode assembly may not be entirely released and may remain there, so it is necessary to ensure a sufficient aging time. Therefore, the aging time may be appropriately set in consideration of the temperature and the release rate of the generated gas.

[0043] In this manner, one or more types of secondary batteries having different initial charge SOCs may be aged at high temperature, and the discharge capacity of the degassed resultant may be evaluated, and the SOC at which the discharge capacity is the largest may be selected as the initial charge SOC.

[0044] Specifically, the discharge capacity evaluation may be a method of discharging to a level of SOC 20% or less after full charge (SOC 100%). As an example, the discharge may be performed to SOC 0%. At this time, the secondary battery may exhibit a voltage of 2V to 46V. Through such charge and discharge steps, the maximum discharge capacity of the secondary battery may be measured, and the initial charge SOC of the secondary battery having the maximum discharge capacity may be selected as the SOC to be charged in the initial charge step of the present invention.

[0045] In one embodiment of the present invention, after selecting an optimal initial charge SOC through the discharge capacity evaluation, a degassing step of discharging gas generated inside an electrode assembly of a secondary battery that has been initially charged at the optimal initial charge SOC may be included.

[0046] The degassing step may further include a high-temperature aging process performed at a temperature of 50° C. to 80° C. At this time, the high-temperature aging process may be performed at a temperature in the range of 50° C. to 80° C. in consideration of the viscosity and fluidity of the electrolyte, as described above.

[0047] Meanwhile, when the size of the secondary battery after the initial charge is increased or decreased, the high temperature aging time required to exhaust the gas formed inside the secondary battery may differ, so it is necessary to calculate a suitable high temperature aging process time.

[0048] Therefore, in one example of the present invention, the execution time of the high temperature aging process in the degassing step may be the sum of the temperature rise time for the secondary battery to reach 98% of the maximum temperature and the maintenance time for the secondary battery to maintain 98% to 100% of the maximum temperature when the secondary battery is charged at a current of 0.15C to 0.25C.

[0049] As described below, it can be seen from the evaluation results of the discharge capacity of a secondary battery that has been subjected to high temperature aging for a time that includes a temperature rise time and a maintenance time, and a secondary battery that has been subjected to high temperature aging for an arbitrary time, that the former case has a larger discharge capacity than the latter case. This has the advantage that when conditions such as the size of the secondary battery are changed, it is possible to measure the temperature rise time and maintenance time during the charging process of the secondary battery and predict a suitable high temperature aging time taking into account the discharge capacity of the battery.

[0050] In another embodiment of the present invention, the degassing step may further include a room temperature aging process after the high temperature aging process, and the room temperature aging process may be performed for 0.5 to 72 hours. Specifically, the room temperature may be performed by storing the secondary battery at a temperature of 20° C. to 30° C., or by storing the secondary battery in a chamber configured to maintain the room temperature.

[0051] In another embodiment of the present invention, the degassing step may further include a process of charging the battery to SOC 60% to 70% after the high temperature aging process, thereby allowing gas that may be generated by additional charging to be discharged through the degassing process, thereby further improving the stability of the battery.

[0052] Meanwhile, the method may further include charging the secondary battery after the degassing process to a SOC of 70% or more. In this step, the secondary battery may be charged to a SOC of 70% or more. Preferably, the secondary battery is charged to a SOC of 70% to 100%, and the battery may be activated to operate normally by such charging.

[0053] The method may further include discharging the secondary battery to a level of SOC 20% or less after charging the secondary battery to a level of SOC 70% or more. The discharging may be performed to SOC 0%. At this time, the secondary battery may exhibit a voltage of 2V to 46V. This discharging step may allow the capacity of the battery to be selected and may prevent non-uniform current density due to non-uniform distribution of the electrode active material.

[0054] On the other hand, in one embodiment of the present invention, the secondary battery to which the initial charging step is applied has not undergone any charging process after electrolyte injection, and this step is the first charging applied after electrolyte injection.

[0055] In one embodiment of the present invention, prior to the initial charging step of charging the assembled secondary battery, the secondary battery may be maintained at an SOC of 0% or more and less than 1%. When the pre-charging is performed as described above, the potential of the negative electrode may be lowered to suppress dissolution of copper used as the negative electrode current collector, which is effective in suppressing the occurrence of low voltage in the battery.

[0056] In another embodiment of the present invention, a process of forming an SEI (Solid Electrode Interface) film on all or part of the negative electrode surface of the electrode assembly before the degassing step may be included. The formed SEI film serves to reduce the irreversibility of the secondary battery to a certain level even when it is charged to a high level in the degassing step. Such an SEI film is formed on the negative electrode surface in the initial charging step. For example, when the electrolyte contains ethylene carbonate (EC), which is a cyclic carbonate compound, the initial charging step is necessary for the SEI film to be sufficiently reduced. In addition, the stabilization of the SEI film can be accelerated through a high-temperature aging process.

[0057] Meanwhile, in the present specification, "activation" refers to a process of supplying a certain amount of electricity to an electrode assembly or battery cell that does not have electrical properties, thereby making the positive and negative electrodes have electrical properties, and may be understood to include all reactions accompanying the initial charging of the electrode assembly or battery cell. Non-limiting examples of reactions accompanying the initial charging include the formation of an SEI film, partial charging of the battery capacity, and activation of the negative electrode, such as lithiation of a carbon-based negative electrode active material.

[0058] In one embodiment of the present invention, the secondary battery used in the activation method may be one or more of the following. The secondary battery has a structure including an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, an electrolyte impregnating the electrode assembly, and a battery case containing the electrode assembly and the non-aqueous electrolyte. The non-aqueous electrolyte is, for example, an electrolyte containing a lithium salt.

[0059] The positive electrode has a structure in which a positive electrode active material layer is laminated on one or both sides of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, a binder polymer, etc., and may further include a positive electrode additive commonly used in the art, as necessary.

[0060] The positive electrode active materials may be the same or different lithium-containing oxides. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used.

[0061] For example, lithium-containing transition metal oxides include 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)およびLi xIt can be any one selected from the group consisting of FePO4 (0.5 < x < 1.3) or a mixture of two or more of these. Further, the lithium-containing transition metal oxide can be coated with a metal or metal oxide such as aluminum (Al). In addition to the lithium-containing transition metal oxide, one or more of sulfide, selenide, and halide can be used.

[0062] The positive electrode active material can be contained in the positive electrode active material layer in the range of 94.0 to 98.5% by weight. When the content of the positive electrode active material satisfies the above range, it is advantageous in terms of manufacturing a high-capacity battery and imparting sufficient conductivity of the positive electrode and adhesion between electrode materials.

[0063] The current collector used for the positive electrode is a metal with high conductivity, which can be easily adhered to the positive electrode active material slurry, and any one can be used as long as it is not reactive within the voltage range of the electrochemical element. 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 contains a conductive material.

[0064] As the conductive material, carbon-based conductive materials are often used, including spherical or needle-shaped carbon-based conductive materials. The spherical carbon-based conductive material fills the pores, which are the empty spaces between the active material particles, in a state mixed with the binder, thereby improving the physical contact between the active materials, reducing the interfacial resistance, and improving the adhesion between the lower positive electrode active material and the current collector.

[0065] Examples of the spherical carbon-based conductive material include carbon black such as Denka black, for example, FX35 (Denka), SB50L (Denka), Super-P, but are not limited thereto. Here, "spherical" means having a spherical particle shape and having an average diameter (D50) in the range of 10 to 500 nm, specifically 15 to 100 nm or 15 to 40 nm.

[0066] The dot-shaped carbonaceous conductive material corresponds to a needle-type carbonaceous conductive material. The linear carbonaceous conductive material may be a carbon nanotube (CNT), a vapor-grown carbon fiber (VGCF), a carbon nanofiber (CNF), or a mixture of two or more of these. Here, "needle type" refers to a needle-like particle shape, for example, an aspect ratio (length / diameter value) in the range of 50 to 650, specifically 60 to 300 or 100 to 300.

[0067] The dotted carbonaceous conductive material has the advantage of being easier to disperse than the linear conductive material, and has the effect of improving the insulating properties of the layer since it has inferior electrical conductivity compared to the linear carbonaceous conductive material.

[0068] The conductive material may be contained in the positive electrode active material layer in an amount of 0.5 to 5% by weight. When the content of the conductive material satisfies the above range, sufficient conductivity of the positive electrode is imparted, and there is an effect of reducing the interfacial resistance between the electrode current collector and the active material.

[0069] The binder polymer may be any binder commonly used in the art without limitation. For example, the binder may be a water-insoluble polymer that is soluble in an organic solvent and insoluble in water, or a water-soluble polymer that is insoluble in an organic solvent and soluble in water. The water-insoluble polymer may be one or more selected from the group including polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene butadiene rubber (SBR), polyacrylate, and derivatives thereof.

[0070] The water-soluble polymer may be one or more selected from the group including various cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), and hydroxypropylmethylcellulose phthalate (HPMCP).

[0071] The binder polymer content is proportional to the conductive material content in the upper and lower positive electrode active material layers, because it provides adhesive strength to the conductive material, which has a relatively small particle size compared to the active material, and because an increase in the conductive material content requires more binder polymer, whereas a decrease in the conductive material content requires less binder polymer.

[0072] The negative electrode has a structure in which a negative electrode active material layer is laminated on one or both sides of a 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, and the like, and may further include a negative electrode additive commonly used in the art, as necessary.

[0073] The negative electrode active material may include a carbon material, lithium metal, silicon, or tin. When a carbon material is used as the negative electrode active material, both low crystalline carbon and high crystalline carbon may be used. Representative low crystalline carbons include soft carbon and hard carbon, and representative high crystalline carbons include natural graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high temperature calcined carbons such as petroleum or coal tarpitch derived cokes.

[0074] Non-limiting examples of the current collector used in the negative electrode include foils made of copper, gold, nickel, copper alloys, or combinations thereof. The current collector may also be used by laminating a substrate made of the above materials.

[0075] The negative electrode may also include conductive materials and binders commonly used in the art.

[0076] The separator may be any porous substrate used in lithium secondary batteries, for example, a polyolefin-based porous membrane or nonwoven fabric, but is not limited thereto.

[0077] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high density polyethylene, linear low density polyethylene, low density polyethylene, and ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0078] Examples of the nonwoven fabric include, in addition to polyolefin-based nonwoven fabric, nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, either alone or in combination. The structure of the nonwoven fabric may be a spunbonded or meltblown nonwoven fabric made of long fibers.

[0079] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0080] Meanwhile, in order to improve the mechanical strength of the separator formed of the porous substrate and to prevent a short circuit between the positive electrode and the negative electrode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one surface of the porous substrate.

[0081] The electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. The lithium salt may be any of those commonly used in non-aqueous electrolytes for lithium secondary batteries without limitation. For example, Li + The anion is F. - , Cl - , Br - , I - , NO 3- , N(CN) 2- , B.F.4- , ClO 4- , AlO 4- , AlCl 4- , P.F. 6- , SbF 6- , AsF 6- , BF2C2O 4- , B.C.4O 8- , (CF3)2PF 4- , (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- , CHCO 2- , SCN - and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of:

[0082] The organic solvent contained in the above-mentioned electrolytic solution may be any organic solvent commonly used in electrolytic solutions for secondary batteries, and may be used without limitation, for example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc., each of which may be used alone or in combination of two or more. Among these, representative carbonate compounds may include cyclic carbonates, linear carbonates, or mixtures thereof.

[0083] Specific examples of the cyclic carbonate compound include any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more of these. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

[0084] In addition, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more of these, but are not limited thereto.

[0085] In particular, among the above carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents with high dielectric constants, and can dissociate lithium salts in the electrolyte more effectively. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants such as dimethyl carbonate and diethyl carbonate, an electrolyte solution having higher electrical conductivity can be produced.

[0086] In addition, the ether among the above organic solvents 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 these, but is not limited thereto.

[0087] Among the above organic solvents, the ester may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and β-caprolactone, or a mixture of two or more of these, but is not limited thereto.

[0088] The injection of the non-aqueous electrolyte may be performed at a suitable stage during the manufacturing process of the electrochemical device depending on the manufacturing process and required properties of the final product, i.e., before assembly of the electrochemical device or at the final stage of assembly of the electrochemical device.

[0089] In this case, the secondary battery includes a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc. The secondary battery may include a cylindrical, rectangular, or pouch-type secondary battery depending on the form.

[0090] The present invention will be described in more detail with reference to the drawings. Since the present invention can be modified in various ways and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, and should be understood as including all modifications, equivalents, or alternatives within the spirit and technical scope of the present invention. EXAMPLES

[0091] [Production Example] Cathode active material (LiNi 0.5 Co 0.2 Mn 0.3 O2), conductive material (carbon black), and binder (PVDF) were mixed in a weight ratio of 96:2:2 into N-methyl-2-pyrrolidine (NMP) to prepare a positive electrode slurry, which was then applied to a 20 μm thick aluminum foil as a positive electrode current collector to obtain a current of 3.1 mAh / cm. 2The positive electrode was prepared by coating with 100% water.

[0092] Artificial graphite, conductive material (carbon black), and binder (PVDF) were mixed in a weight ratio of 96:2:2 into N-methyl-2-pyrrolidine (NMP) to prepare anode slurry, which was then applied to a 20 μm-thick copper foil as anode current collector to obtain a current of 3.1 mAh / cm. 2 The negative electrode was prepared by coating the positive electrode with a capacity of 1.5 M. A separator (polyethylene material, thickness 20 μm) was interposed between the positive electrode and the negative electrode to prepare a jelly roll type electrode assembly. The electrode assembly was inserted into a battery case, and then an electrolyte was injected and the battery case was sealed to prepare a cylindrical secondary battery with a diameter of 21 mm and a cylindrical secondary battery with a diameter of 46 mm. The electrolyte was prepared by adding LiPF6 at a concentration of 1.4 M to an organic solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of 20:20:60. Vinylene carbonate (3 vol%) and succinonitrile (1 vol%) were mixed in the electrolyte. [Experimental Example 1]

[0093] (Cylindrical secondary battery with a diameter of 21 mm) According to the above manufacturing example, a total of six types of secondary batteries (Examples 1 to 5 and Comparative Example 1) with a diameter of 21 mm were manufactured. The activation process of each battery was performed as follows. For the secondary batteries of Examples 1 to 5, a degassing step including an initial charging step, high temperature aging (60°C, 4 hours), and room temperature aging (12 hours) was performed as shown in Table 1 below. In the room temperature aging step, additional charging was performed up to SOC 65%. Then, a step of fully charging to SOC 100% (4.2V) and discharging to SOC 0% (2.5V) was performed. The discharging was performed in 1C CC mode and 0.2C CV mode up to 2.5V. Meanwhile, Comparative Example 1 was performed in the same process as Examples 1 to 5, except that the initial charging step and the high temperature aging and degassing step were not performed, which is an existing process.

[0094] [Table 1]

[0095] Selection of initial charging SOC Fig. 1 is a graph showing the results of evaluating the discharge capacity of Examples 1 to 5 and Comparative Example 1. Referring to Fig. 1, three identical secondary batteries were manufactured for each of Examples 1 to 5 and Comparative Example 1, and the discharge capacity was evaluated. As a result, it was confirmed that the discharge capacity of Example 4, in which the initial charge was performed in the SOC range of 7%, was superior to the other Examples and Comparative Examples. It was confirmed that when the initial charge was performed in the SOC range of 1% or 3%, the discharge capacity was similar to that of no initial charge, and that when the initial charge exceeded the appropriate level, such as in the case of an SOC of 10%, the discharge capacity decreased.

[0096] Evaluation of discharge capacity according to high-temperature aging time FIG. 2 is a graph showing the results of evaluating the discharge capacity according to the high-temperature aging time after initial charging for a secondary battery having a diameter of 21 mm and manufactured under the condition of an initial charge of SOC 7%. Referring to FIG. 2, the discharge capacity according to the high-temperature aging time after initial charging for a secondary battery (Example 4) manufactured under the condition of an initial charge of SOC 7% was evaluated, and the results for the discharge capacity of two identical secondary batteries can be seen in 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. It was confirmed that the maximum discharge capacity exceeded 100% when the aging time was 1 hour and 2 hours. However, when the aging time exceeded 2 hours, deterioration of the battery chemical element and side reactions were caused, and the discharge capacity tended to be lowered. It was also confirmed that the lowest discharge capacity was shown when aging was not performed.

[0097] [Table 2]

[0098] Measurement of temperature rise and maintenance time Figure 3 shows the temperature rise profile of a 21mm diameter secondary battery and a 46mm diameter secondary battery. Referring to Figure 3, it was confirmed that the temperature rise time to reach 98% of the maximum temperature (60°C) when charging a 21mm diameter secondary battery with a current of 0.2C was about 30 minutes, and the maintenance time to maintain 98% to 100% of the maximum temperature (60°C) was about 30 minutes. There was not a large difference between the time (about 1 hour) obtained by adding the temperature rise time and maintenance time and the high temperature aging time (1 hour) when showing the maximum discharge capacity in Table 2 above. [Experimental Example 2]

[0099] (Cylindrical secondary battery with a diameter of 46 mm) According to the above manufacturing example, a total of three types of cylindrical secondary batteries (Examples 6 to 8) with a diameter of 46 mm were manufactured. As shown in Table 3 below, each battery was subjected to an initial charging step and a degassing step including high temperature aging (60°C, 4 hours) and room temperature aging (12 hours). After the room temperature aging step, additional charging was performed up to SOC 65%. Then, a step of fully charging to SOC 100% (4.2V) and discharging to SOC 0% (2.5V) was performed. The above discharging was performed in 1C CC mode and 0.2C CV mode up to 2.5V.

[0100] [Table 3]

[0101] Selection of initial charging SOC Fig. 4 is a graph showing the results of evaluating the discharge capacity of Examples 6 to 8. Referring to Fig. 4, the results of evaluating the discharge capacity of three identical secondary batteries manufactured in each of Examples 6 to 8 show that the discharge capacity of Example 8, in which the initial charge was performed in the SOC range of 9%, was superior to that of the other Examples and Comparative Examples.

[0102] High temperature aging time estimation FIG. 3 is a diagram showing the temperature rise profile of a secondary battery having a diameter of 21 mm and a secondary battery having a diameter of 46 mm. Table 4 below shows the results of estimating the high-temperature aging time from the temperature rise time to reach 98% of the maximum temperature and the maintenance time to maintain 98% to 100% of the maximum temperature. Referring to FIG. 3 and Table 4, it was confirmed that the temperature rise time of the secondary battery having a diameter of 46 mm and a maximum discharge capacity (Example 8) is six times different from that of the secondary battery having a diameter of 21 mm and a maximum discharge capacity (Example 4). In addition, the maintenance time of the secondary battery having a diameter of 21 mm and a maximum discharge capacity (Example 4) was confirmed to be 30 minutes. Thus, the maintenance time of the secondary battery having a diameter of 46 mm and a maximum discharge capacity (Example 8) can be estimated to be three hours, which is six times different from the temperature rise time. This is because as the size of the battery increases, the maintenance time increases proportionally to the increase in the temperature rise time.

[0103] Furthermore, it was confirmed that the difference between the high-temperature aging time showing the maximum discharge capacity and the sum of the temperature rise time and the maintenance time was not large, as described above in Example 1. From this, it can be estimated that the suitable high-temperature aging time for the secondary battery (Example 8) having the maximum discharge capacity and a diameter of 46 mm is 6 hours, which is the sum of the temperature rise time and the maintenance time.

[0104] [Table 4]

[0105] Evaluation of discharge capacity according to high-temperature aging time FIG. 5 is a graph showing the results of evaluating the discharge capacity according to the high-temperature aging time after the initial charge for a secondary battery having a diameter of 46 mm and manufactured under the condition of an initial charge of SOC 9%. Referring to FIG. 5, the discharge capacity according to the high-temperature aging time after the initial charge for a secondary battery (Example 8) manufactured under the condition of an initial charge of SOC 9% was evaluated, and the results for the discharge capacity of two identical secondary batteries can be seen in [Table 5]. Specifically, the aging temperature was 60° C., and the aging time was 0 hours, 1 hour, 2 hours, 4 hours, 6 hours, and 8 hours. According to this, when the aging time was 4 hours, 6 hours, and 8 hours, the average discharge capacity exceeded 100%, and the maximum discharge capacity was shown when the aging time was 6 hours. This confirmed that the high-temperature aging time according to the temperature rise time and maintenance time estimated above was consistent.

[0106] [Table 5]

[0107] Evaluation of discharge capacity according to initial charge SOC and high-temperature aging time Figure 6 is a graph showing the results of evaluating the discharge capacity according to the initial charge SOC and high temperature aging time of a secondary battery with a diameter of 46 mm. Referring to Figure 6, it was confirmed that the initial charge SOC was in the range of 9%, and the secondary battery that had undergone the high temperature aging process for 6 hours had a higher discharge capacity than the secondary battery that had undergone high temperature aging for 2 hours, with the initial charge SOC being in the range of 7% compared to the secondary battery that had not undergone high temperature aging.

[0108] Therefore, when the diameter of the secondary battery changes, the initial charge SOC and high temperature aging time at which the maximum discharge capacity is achieved may differ, and it is necessary to set a suitable initial charge SOC and high temperature aging time. According to the present invention, when the size of the secondary battery is different, a suitable initial charge SOC can be selected by evaluating the discharge capacity, and a suitable high temperature aging time can be predicted by calculating the temperature rise time and maintenance time of the temperature rise profile. The secondary battery that has undergone such an activation process can efficiently discharge gas generated inside the battery and ensure maximum usable capacity.

Claims

1. A method for activating a secondary battery, comprising: an initial charging stage of charging the manufactured secondary battery; A degassing step of discharging gas from the charged secondary battery; The degassing step includes: Further comprising a high temperature aging process carried out at a temperature of 50°C to 80°C; The SOC to be charged in the initial charging stage is: a) degassing two or more types of secondary batteries having different initial charge SOCs by performing a high-temperature aging process at a temperature of 50° C. to 80° C. for 3 to 5 hours; b) Evaluating the discharge capacity of the result of a) The method for activating a secondary battery comprises setting the SOC of a secondary battery having a maximum discharge capacity within a range of 1% to 15% of the initial charging SOC as the SOC to be charged in the initial charging stage.

2. The duration of the high temperature aging process in the degassing step is When the secondary battery is charged with a current of 0.15 C to 0.25 C, the temperature rise time for the secondary battery to reach 98% of the maximum temperature; 2. The method for activating a secondary battery according to claim 1, further comprising a maintenance time for maintaining the secondary battery at 98% to 100% of the maximum temperature.

3. 2. The method for activating a secondary battery according to claim 1, wherein the discharge capacity is evaluated by discharging the battery to an SOC of 20% or less after full charging.

4. The degassing step includes: After the high temperature aging process, a room temperature aging process is further included, 2. The method of claim 1, wherein the room temperature aging process is performed for 0.5 to 72 hours.

5. The degassing step includes: The method of claim 1, further comprising the step of charging the secondary battery to an SOC of 60% to 70% after the high temperature aging step.

6. The method of claim 1 , further comprising the step of charging the secondary battery to an SOC range of 70% or more after the degassing step.

7. The method of claim 6, further comprising discharging the secondary battery to a level of SOC 20% or less after charging the secondary battery to a level of SOC 70% or more.

8. The method of activating a secondary battery according to claim 1 , wherein the secondary battery is maintained at an SOC of 0% or more and less than 1% before an initial charging stage of charging the assembled secondary battery.

9. Prior to the degassing step, The method of activating a secondary battery according to claim 1 , further comprising forming an SEI coating on all or a portion of a surface of a negative electrode of the electrode assembly.

10. The secondary battery has a structure in which an electrode assembly and an electrolyte are housed in a battery case, The electrode assembly has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The method for activating a secondary battery according to claim 1 , wherein the electrolyte contains a lithium salt.

11. The method for activating a secondary battery according to claim 1 , wherein the secondary battery is any one of a rectangular type, a cylindrical type, and a pouch type.

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