KR20210030000A - Manufacturing method for pouch type secondary battery - Google Patents

Abstract

The present invention relates to a manufacturing method of a pouch type secondary battery, which minimizes the deterioration of output properties of the secondary battery and improves the stability of the battery by controlling the charging and aging conditions in a preliminary charging step and an activation step.

Description

Manufacturing method of pouch type secondary battery {MANUFACTURING METHOD FOR POUCH TYPE SECONDARY BATTERY}

The present invention relates to a method of manufacturing a secondary battery, and more specifically, to a method of manufacturing a secondary battery capable of enhancing electrode stability of a pouch-type secondary battery.

As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution is amplified, the demand for eco-friendly alternative energy sources is increasing. In particular, secondary batteries are also attracting attention as energy sources such as electric vehicles and hybrid electric vehicles, which have been suggested as a solution to air pollution such as existing gasoline vehicles and diesel vehicles using fossil fuels.

As the application fields and products of secondary batteries are diversified in this way, the types of batteries are also diversifying to provide appropriate output and capacity. In addition, batteries applied to the related fields and products are required to be miniaturized and lightweight, and to increase output.

As a method of improving the output characteristics of a secondary battery, for example, the development of a high-content nickel (High-Ni)-based NCM positive electrode active material having a high energy density is drawing attention. However, a secondary battery to which a high-content nickel (High-Ni)-based NCM positive electrode active material is applied has poor cell stability and, in particular, is very vulnerable to exothermic reaction due to an internal short circuit.

Accordingly, there is an increasing need for a technology capable of improving cell stability without impairing the output characteristics of a secondary battery.

Korean Patent Application Publication No. 2015-0031018

An object of the present invention is to provide a method of manufacturing a secondary battery capable of improving battery stability while minimizing deterioration in output characteristics.

In order to achieve the above object, the method of manufacturing a secondary battery according to the present invention,

For the secondary battery in which the electrode assembly and the electrolyte are housed in the battery case,

(a) Pre-charging the secondary battery before the introduction of the activation step, and the pre-charging step includes: (a-1) 5 to 15% of the design capacity of the secondary battery (State Of Charge) 5 -15%) preliminary charging step; And (a-2) a preliminary aging step of aging the secondary battery at an average temperature of 15 to 30°C; And

(b) activating the pre-charged secondary battery (formation); The activating step may include (b-1) a primary charging step of charging the secondary battery to 75 to 95% (SOC 75 to 95%) of the design capacity; (b-2) a primary aging step of aging the secondary battery at an average temperature of 15 to 70°C; And (b-3) a secondary charging step of charging the secondary battery to 95% (SOC 95%) or more of the design capacity.

In one example, the ratio of (a-2) the aging time (T1) of the preliminary aging step and (b-2) the aging time (T2) of the first aging step is in the range of 1: 1.5 to 3.5 (T1: T2) Is satisfied. In a specific example, the (a-2) preliminary aging step is performed for 15 to 30 hours. In addition, the (b-2) first aging step is performed for 45 to 105 hours.

In yet another example, the method of manufacturing a secondary battery according to the present invention has a structure in which a SEI (Solid Electrode Interface) film is formed on all or part of the negative electrode surface of the electrode assembly before the step of (b) activating.

In one example, the preliminary charging step is performed by charging the secondary battery with a constant current in the range of 0.01 to 0.1C, and the primary charging step is performed by charging the secondary battery with a constant current in the range of 0.15 to 0.5C.

In one example, the (b-3) secondary charging step is performed by charging the secondary battery to 95% (SOC 95%) or more of the design capacity and then discharging it to 5% (SOC 5%) or less. .

In yet another example, the method of manufacturing a secondary battery according to the present invention further includes the step of (b) activating, after the step (b-3) of the secondary charging, a second aging step.

In addition, after the step of (b) activating, the secondary battery further includes a step of shipping charge of charging the secondary battery to 40 to 60% of the design capacity (SOC 40 to 60%).

The secondary battery according to the present invention has a structure in which an electrode assembly and an electrolyte are accommodated in a battery case. In one example, the electrode electrode assembly has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the electrolyte solution contains a lithium salt. Specifically, the secondary battery according to the present invention is a pouch-type secondary battery.

The method of manufacturing a secondary battery according to the present invention can increase the stability of the battery while minimizing deterioration in output characteristics of the secondary battery.

1 is a graph comparing and measuring the discharge capacity of secondary batteries according to Comparative Examples and Examples.
2 is a graph measuring a self-discharge reduction rate and a capacity loss increase rate according to the amount of charge in the second charging step.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the present specification and claims are not limited to their usual or dictionary meanings and should not be construed, and the inventors appropriate the concept of terms to describe their own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention on the basis of the principle that it can be defined.

The present invention provides a method for manufacturing a secondary battery. The secondary battery manufacturing method,

For the secondary battery in which the electrode assembly and the electrolyte are housed in the battery case,

(a) Pre-charging the secondary battery before the introduction of the activation step, and the pre-charging step includes: (a-1) the secondary battery at 5 to 15% (SOC 5 to 15%) of the design capacity. Pre-charging step of charging; And (a-2) a pre-aging step of aging the secondary battery at an average temperature of 15 to 30°C; And

(b) activating the pre-charged secondary battery (formation); The activating step may include (b-1) a primary charging step of charging the secondary battery to 75 to 95% (SOC 75 to 95%) of the design capacity; (b-2) a primary aging step of aging the secondary battery at an average temperature of 15 to 70°C; And (b-3) a secondary charging step of charging the secondary battery to 95% (SOC 95%) or more of the design capacity.

The method for manufacturing a secondary battery according to the present invention includes the step of (a) pre-charging before the step of (b) activating the secondary battery, and the step of (a) pre-charging includes (a-2) the secondary battery. It includes a preliminary charging step of charging to 5-15% of the design capacity (SOC 5-15%). That is, in the present invention, in the preliminary charging step (a), the secondary battery undergoes a low-level charging (a-1) of 15% or less SOC, followed by aging (a-2). Through this, before the step of (a) activating the secondary battery, a SEI (Solid Electrode Interface) film is formed on the surface of the negative electrode. The formed SEI film serves to reduce the irreversibility of the secondary battery to a certain level even if it is charged to a high level in the (b) activation step.

In the present invention, (a-1) in the preliminary charging step, the secondary battery is charged to 5 to 15% of the design capacity (SOC 5 to 15%), and (b-1) the secondary battery is charged to the design capacity in the first charging step. It is characterized by charging at 75-95% (SOC 75-95%). Specifically, in the present invention, (a-1) the secondary battery is charged to 8 to 12% of the design capacity in the preliminary charging step, and (b-1) the secondary battery is charged to 75 to 85 of the design capacity in the primary charging step. Charge in %. For example, in the present invention, (a-1) the secondary battery is charged to 10% of the design capacity in the preliminary charging step, and (b-1) the secondary battery is charged to 80% of the design capacity in the first charging step. .

In the present invention, (a-1) charging the secondary battery to a low level in the preliminary charging step is to form an SEI film on the surface of the negative electrode as described above, and further, for example, the electrolyte is ethylene, which is a cyclic carbonate compound series. When it contains carbonate (ethylene carbonate, EC), it is for sufficient reduction of the ethylene carbonate.

In addition, in the present invention, (b-1) charging the secondary battery to a high level in the primary charging step is to improve the voltage stability of the secondary battery to lower the voltage drop level due to self-discharge. In general, during the activation process for the secondary battery, the detection process for defective battery cells is simultaneously performed. One of the methods of detecting a defective battery is a low voltage defect detection process. In the process of detecting a defective low-voltage battery, effective detection is possible by lowering the voltage drop level of the battery. Specifically, the low-voltage defective battery refers to a battery having a large voltage drop compared to a good-quality battery during the activation process. Therefore, lowering the voltage drop of a good battery increases the voltage drop gap with a defective battery, thereby making it easier to detect a defective battery.

However, in the process of activating the secondary battery, when the charging level of the battery is increased, there is a problem that output characteristics are deteriorated. Due to this problem, conventionally, during or before the activation of the secondary battery, the charging level of the secondary battery is limited to 30% or less or 70% or less. However, the present invention prevents a certain level of deterioration in output characteristics of the battery by preliminarily charging the secondary battery (b) before the step (b) of activating the secondary battery.

In one example, in the present invention, the ratio of the aging time (T1) in the (a-2) preliminary aging step and the aging time (T2) in the (b-2) primary aging step is 1: 1.5 to 3.5 (T1 :T2) range is satisfied. Specifically, the ratio of the aging time (T1) in the (a-2) preliminary aging step and the aging time (T2) in the (b-2) primary aging step is 1: 1.5 to 2.5, 1: 1.7 to 2.5, 1 : 2.1~2.5, 1: 1.5~1.9 or 1: 1.8~2.2 (T1:T2). By controlling the ratio of the aging time (T1) of the (a-2) preliminary aging step and the aging time (T2) of the (b-2) primary aging step to the above range, each step is prevented from deteriorating the capacity of the battery. It is possible to minimize the time consuming due to aging.

In a specific example, the (a-2) preliminary aging step is performed for 15 to 30 hours. Specifically, the (a-2) preliminary aging step is performed for 15 to 25 hours or 20 to 30 hours. In another specific example, the (b-2) first aging step is performed for 45 to 105 hours. Specifically, the (b-2) first aging step is performed for 45 to 70 hours, 30 to 60 hours, and 45 to 55 hours.

In another example, the (b-2) first aging step is performed at an average temperature of 15 to 70°C. Specifically, the (b-2) first aging step is performed at an average temperature of 15 to 60°C, 20 to 60°C, 30 to 70°C, or 40 to 70°C. In this case, the time may be changed according to the temperature of the aging step, and it is to be avoided that the operation is performed for a long time at a relatively high temperature.

In yet another example, the method of manufacturing a secondary battery according to the present invention has a structure in which a SEI (Solid Electrode Interface) film is formed on all or part of the negative electrode surface of the electrode assembly before the step of (b) activating. Specifically, in the present invention, (a-1) the SEI film is formed on the surface of the negative electrode in the preliminary charging step, and the SEI film formed in the (a-2) preliminary aging step is stabilized.

In the present invention, a method of charging the secondary battery in each step is not particularly limited. In one example, in the preliminary charging step, the secondary battery is charged with a constant current in the range of 0.01 to 0.1C or 0.05 to 0.1C. In addition, in the first charging step, the secondary battery is charged with a constant current in the range of 0.15 to 0.5C or 0.15 to 0.3C. In the present invention, it was confirmed that the stability of the battery can be improved by performing charging with a low constant current in the preliminary charging step and charging with a relatively high constant current in the first charging step.

In one example, the (b-3) secondary charging step is performed by charging the secondary battery to 95% (SOC 95%) or more of the design capacity and then discharging it to 5% (SOC 5%) or less. . Specifically, the (b-3) secondary charging step is a process of charging the secondary battery to 95 to 99.9% (SOC 95 to 99.9%) of the design capacity and then discharging to 0.1 to 5% (SOC 0.1 to 5%) It is done with. The (b-3) secondary charging step substantially completely charges and completely discharges the secondary battery. In the present invention, the secondary battery is sufficiently activated through the (b-3) secondary charging step.

In yet another example, the method of manufacturing a secondary battery according to the present invention further includes the step of (b) activating, after the step (b-3) of the secondary charging, a second aging step. The secondary aging step is a process of stabilizing a secondary battery that has undergone an activation process. The second aging step can be performed at room temperature or high temperature, for example, it is performed for 3 to 7 days.

In addition, after the step of (b) activating, the secondary battery further includes a step of shipping charge of charging the secondary battery to 40 to 60% of the design capacity (SOC 40 to 60%). In the present invention, the secondary battery undergoes an activation step to perform shipping and charging. The shipping charge means charging the manufactured secondary battery to an appropriate level prior to shipping, and includes the case of shipping and discharging the secondary battery if necessary.

The present invention relates to a method of manufacturing a secondary battery. The secondary battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; An electrolyte solution 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.

The positive electrode has a structure in which a positive electrode active material layer is stacked on one or both surfaces of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder polymer, and if necessary, may further include a positive electrode additive commonly used in the art.

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.

For example, the lithium-containing transition metal oxide is Li _x CoO ₂ (0.5<x<1.3), Li _x NiO ₂ (0.5<x<1.3), Li _x MnO ₂ (0.5<x<1.3), Li _x Mn ₂ O ₄ (0.5<x<1.3), Li _x (Ni _a Co _b Mn _c )O ₂ (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 O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn y O 2 (0.5 <x <1.3, 0 =y<1), Li _x Ni _{1 - y} Mn _y O ₂ (0.5<x<1.3, O=y<1), Li _x (Ni _a Co _b Mn _c )O ₄ (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 O ₄ (0.5<x<1.3, 0<z<2), the group consisting of _{z Co z O 4 (0.5 <} x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and _{Li x FePO 4 (0.5 <x} <1.3) - Li x Mn 2 Any one selected from or a mixture of two or more of them may be used, and the lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition, in addition to the lithium-containing transition metal oxide, sulfide, selenide, and halide may be used.

The positive active material may be included in the range of 94.0 to 98.5 wt% in the positive active material layer. 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 providing sufficient positive electrode conductivity or adhesion between electrode materials.

The current collector used for the positive electrode may be a metal having high conductivity, and any metal that can be easily adhered to the positive electrode active material slurry and not reactive in the voltage range of the electrochemical device may be used. Specifically, non-limiting examples of the current collector for the positive electrode include a foil manufactured by aluminum, nickel, or a combination thereof.

The positive electrode active material layer further includes a conductive material. As the conductive material, a carbon-based conductive material is widely used, and includes a sphere type or a linear carbon-based conductive material.

The point-shaped carbon-based conductive material is mixed with a binder and fills pores, which are empty spaces between active material particles, thereby improving physical contact between active materials, reducing interfacial resistance, and improving adhesion between the lower positive electrode active material and the current collector. The point-type carbon-based conductive material may include carbon black including Denka Black, for example, FX35 (Denka), SB50L (Denka), Super-P, but is not limited thereto. Here, the'sphere type' means having a spherical particle shape and having an average diameter (D50) of 10 to 500 nm, specifically 15 to 100 nm or 15 to 40 nm.

In a sense corresponding to the point-type carbon-based conductive material, there is a needle-type carbon-based conductive material. The linear carbon-based 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 them. I can. Here, the term'needle type' means that a particle shape such as a needle, for example, an aspect ratio (a value of length/diameter) of 50 to 650, specifically 60 to 300 or 100 to 300. .

The point-type carbon-based conductive material has an advantage in that dispersion is advantageous compared to the linear conductive material, and the electrical conductivity is lower than that of the linear carbon-based conductive material, thereby improving the insulating properties of the corresponding layer.

The conductive material may be included in the range of 0.5 to 5% by weight in the positive electrode active material layer. When the content of the conductive material satisfies the above range, there is an effect of providing sufficient conductivity of the positive electrode and lowering the interface resistance between the electrode current collector and the active material.

As the binder polymer, a binder commonly used in the art may be used without limitation. For example, polyvinylidene fluoride-co-hexafluoropropylene (Poly (vinylidene fluoride-co-hexafluoropropylene), PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile ), polymethyl methacrylate, styrene-butadiene rubber (SBR), and carboxyl methyl cellulose (CMC).

The content of the binder polymer is proportional to the content of the conductive material included in the upper positive electrode active material layer and the lower positive electrode active material layer. This is because a binder polymer is needed more when the content of the conductive material is increased, and less binder polymer can be used when the content of the conductive material is decreased.

The negative electrode has a structure in which a negative active material layer is stacked on one or both surfaces 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 if necessary, may further include a negative electrode additive commonly used in the art.

The negative 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. Typical low crystalline carbons include soft carbon and hard carbon, and high crystalline carbons include natural graphite, kish graphite, pyrolytic carbon, and liquid crystal pitch-based carbon fiber. High-temperature calcined carbons such as (mesophase pitch based carbon fiber), mesocarbon microbeads, mesophase pitches, and petroleum orcoal tar pitch derived cokes are typical.

Non-limiting examples of the current collector used for the negative electrode include copper, gold, nickel, or a foil manufactured by a copper alloy or a combination thereof. In addition, the current collector may be used by stacking substrates made of the above materials.

In addition, the negative electrode may include a conductive material and a binder commonly used in the art.

The separator may be used as long as it is a porous substrate used in a lithium secondary battery, and for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.

Examples of the polyolefin-based porous membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, alone or as a mixture of them. There is one membrane.

As the nonwoven fabric, in addition to the polyolefin nonwoven fabric, for example, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, etc., either alone or Nonwoven fabrics formed of polymers obtained by mixing them are exemplified. The structure of the nonwoven fabric may be a sponbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

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

Meanwhile, in order to improve the mechanical strength of the separator composed of the porous substrate and to suppress 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.

The electrolyte solution may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. As the lithium salt, those commonly used in a non-aqueous electrolyte for a lithium secondary battery may be used without limitation. For example is the above lithium salt anion ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF _{^{4 -, (CF 3) 3}} PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - _{, (CF 3 SO 2) 2} N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, CF _{3 (CF 2) 7 SO 3} -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - one selected from the group consisting of two or more kinds of these It may include.

As the organic solvents included in the above-described electrolyte, those commonly used in the electrolyte for secondary batteries can be used without limitation. For example, ether, ester, amide, linear carbonate, cyclic carbonate, etc. can be used alone or in combination of two or more. Can be used. Among them, representatively, a cyclic carbonate, a linear carbonate, or a carbonate compound that is a mixture thereof may be included.

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

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, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, or these A mixture of two or more of them may be representatively used, but is not limited thereto.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are organic solvents of high viscosity and have a high dielectric constant, so that lithium salts in the electrolyte can be more easily dissociated, such as dimethyl carbonate and diethyl carbonate. If a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio and used, an electrolyte solution having a higher electrical conductivity can be prepared.

In addition, as the ether of the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used. , But is not limited thereto.

And esters of the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α -Any one selected from the group consisting of valerolactone and β-caprolactone, or a mixture of two or more of them may be used, but the present invention is not limited thereto.

The injection of the non-aqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

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. The secondary battery includes a cylindrical, rectangular, or pouch-type secondary battery depending on the shape. In one embodiment, the secondary battery to which the manufacturing method of the present invention is applied is a pouch-type secondary battery. The pouch-type secondary battery has a structure in which a stack-type or stack/folding-type electrode assembly is embedded in a pouch-shaped battery case formed of an aluminum laminate sheet. The assembled secondary battery undergoes a cell activation process during the manufacturing process of the battery. The cell activation process is a process of applying a current to a predetermined voltage to an electrode assembly impregnated with an electrolyte.

Hereinafter, the present invention will be described in more detail through examples and the like. However, since the configurations described in the embodiments described in the present specification are only one embodiment of the present invention and do not represent all the technical spirit of the present invention, various equivalents and modifications that can replace them at the time of the present application It should be understood that there may be.

Manufacturing example

As a cathode active material _{NCM (LiNi 0. 8 Co 0} . 1 Mn 0. 1 O 2) 100 parts by weight of a conductive material, carbon black (FX35, Denka) 1.5 part by weight of fluoride polyvinylidene fluoride as a binder polymer (KF9700, Kureha ) 2.3 parts by weight of a positive electrode active material slurry was prepared by adding NMP (N-methyl-2-pyrrolidone) as a solvent. The positive electrode active material slurry was coated on both sides of aluminum foil in a loading amount of ^{640 mg/25cm 2 and then vacuum dried to obtain a positive electrode.}

The negative electrode is 100 parts by weight of artificial graphite (GT, Zichen (China)) as an anode active material, 1.1 parts by weight of carbon black (Super-P) as a conductive material, 2.2 parts by weight of styrene-butadiene rubber, 0.7 parts by weight of carboxy methyl cellulose, water as a solvent After adding to to prepare a negative active material slurry, it was prepared by coating, drying, and pressing once on a copper foil.

Meanwhile, polypropylene was uniaxially stretched using a dry method to prepare a separator having a microporous structure with a melting point of 165° C. and a width of 200 mm on one side, and then interposed between the anode and the cathode to prepare an electrode assembly. , After the electrode assembly was embedded in a pouch-type battery case, a 1M LiPF ₆ carbonate-based solution electrolyte was injected to complete a battery.

Example One

The pouch-type secondary battery assembled according to the manufacturing example was pre-charged with 10% SOC and then pre-aged at room temperature for 1 day. The secondary battery was charged with 75% SOC and then aged at 50° C. for 2 days. Then, the secondary battery was fully charged and completely discharged, and then aged at room temperature for 5 days. The aging secondary battery was charged with 50% SOC to prepare a secondary battery (SOC 75%).

Example 2

The pouch-type secondary battery manufactured according to the manufacturing example was charged with 10% SOC and then aged at room temperature for 1 day. The secondary battery was charged with 85% SOC and then aged at 50° C. for 2 days. Then, the secondary battery was fully charged and completely discharged, and then aged at room temperature for 5 days. The aging secondary battery was charged with 50% SOC (85% SOC).

Comparative example One

For the pouch-type secondary battery manufactured according to the manufacturing example, after SOC 17% was charged, it was aged at 50° C. for 2 days. Then, the secondary battery was fully charged and completely discharged, and then aged at room temperature for 5 days. The aging secondary battery was charged with 50% SOC (17% SOC).

Comparative example 2

For the pouch-type secondary battery prepared according to Preparation Example, after charging with SOC 60%, it was aged at 50° C. for 2 days. Then, the secondary battery was fully charged and completely discharged, and then aged at room temperature for 5 days. The aging secondary battery was charged with 50% SOC (SOC 60%).

Experimental example One

For the pouch-type secondary batteries prepared according to Comparative Examples 1 and 2 and Example 1, the discharge capacity was measured. The measurement of the discharge capacity was performed by a known method. The measurement results are shown in Table 1 and FIG. 1 below.

Example No. Discharge capacity (mAh) Comparative Example 1 3,375 Comparative Example 2 3,345 Example 1 3,352

Referring to the results of Table 1 and FIG. 1, the discharge capacity of Comparative Example 1, which is 17% SOC in the primary charge of the activation step, is at the level of 3,375 mAh, but the discharge of Comparative Example 2, which is 60% SOC in the primary charge of the activation step. It has a capacity of 3,345 mAh. From this, it can be seen that when the primary charge level of the secondary battery is increased in the activation step, the discharge capacity of the secondary battery is reduced by about 9%. In contrast, in Example 1, the secondary battery had a discharge capacity of 3,352 mAh, even though the SOC was charged by 75% in the primary charge of the activation step. This is the increase in the discharge capacity of the secondary battery compared to Comparative Example 2. Through this, it can be seen that a low level of charging (preliminary charging) is performed before the activation step, as in the present invention, and even if the charging level is increased in the activation step of the secondary battery, a decrease in discharge capacity can be minimized.

Experimental example 2

The secondary batteries prepared in Preparation Example were divided into two test groups (test groups 1 and 2) of 10 each. The batteries of each test group were prepared in the same manner as in Example 1, except that the primary charge level of the activation step was different. However, the batteries of test group 1 were pre-charged with SOC 8%, and test group 2 was pre-charged with SOC 12%.

For the pouch-type secondary batteries of each test group, the charging level in the activation step was changed, and aged at 50° C. for 2 days after charging. Then, each secondary battery was fully charged and completely discharged, and then aged at room temperature for 5 days. The aging secondary battery was charged with 50% SOC.

Self Discharge Decreasing (%) and Capacity Loss Increasing (%) were compared and measured for each test group. The comparative measurement is to calculate a relative value with a secondary battery (SOC 30%) having a charge level of 30% in the activation step as a control. The calculation results are shown in FIG. 2.

Referring to FIG. 2, in test groups 1 and 2, the self-discharge reduction rate decreases as the primary charge rate (1st Charge SOC, %) of the activation step increases, but the first charge rate (1st Charge SOC, %) is 70-80%. It decreases sharply in the phosphorus section. At the same time, the rate of increase in capacity loss in that section is not large. Specifically, in the corresponding interval, the increase rate of the dose loss of test group 1 is about 0.5%, and the increase rate of the dose loss of test group 2 is about 0.2%.

In comparison by section, in the case of test group 1, the self-discharge reduction rate decreases by about 20% in the section where the primary charge rate is 70-80%, but the self-discharge reduction rate decreases by about 15% in the section where the primary charge rate is 60-70%. Decreases. In addition, in the case of test group 2, the self-discharge reduction rate decreases by about 20% in the section where the primary charging rate is 70-80%, but the self-discharge reduction rate decreases by about 5% in the section where the primary charging rate is 60-70%. Hits.

Through this, the method of manufacturing a secondary battery according to the present invention, by charging to a low level of 15% or less during preliminary charging and simultaneously controlling the primary charge in the activation step to a level of 75% or more, maximizes the stability of the battery and maximizes the capacity. The reduction was minimal.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (12)

With respect to the secondary battery in which the electrode assembly and the electrolyte are housed in the battery case,
(a) pre-charging the secondary battery before introducing the activation step,
The preliminary charging step,
(a-1) a preliminary charging step of charging the secondary battery to 5 to 15% of the design capacity (SOC 5 to 15%); And
(a-2) a preliminary aging step of aging the secondary battery at an average temperature of 15 to 30°C; including; And
(b) activating the pre-charged secondary battery (formation);
The activating step,
(b-1) a primary charging step of charging the secondary battery to 75-95% (SOC 75-95%) of the design capacity;
(b-2) a primary aging step of aging the secondary battery at an average temperature of 15 to 70°C; And
(b-3) a secondary charging step of charging the secondary battery to 95% (SOC 95%) or more of the design capacity;
Method of manufacturing a secondary battery comprising a. The method of claim 1,
(a-2) The ratio of the aging time (T1) in the preliminary aging step to the aging time (T2) in the (b-2) primary aging step is 1: 1.5~3.5 (T1:T2) Method of manufacturing. The method of claim 1,
(a-2) The method of manufacturing a secondary battery, characterized in that the preliminary aging step is performed for 15 to 30 hours. The method of claim 1,
(b-2) The method of manufacturing a secondary battery, characterized in that the first aging step is performed for 45 to 105 hours. The method of claim 1,
(b) prior to the step of activating,
A method of manufacturing a secondary battery having a structure in which a SEI (Solid Electrode Interface) film is formed on all or part of the surface of the negative electrode of the electrode assembly. The method of claim 1,
In the preliminary charging step, the secondary battery is charged with a constant current in the range of 0.01 to 0.1C,
The primary charging step is a method of manufacturing a secondary battery, characterized in that the secondary battery is charged with a constant current in the range of 0.15 to 0.5C. The method of claim 1,
(b-3) The secondary charging step,
A method of manufacturing a secondary battery, characterized in that the secondary battery is charged to 95% (SOC 95%) or more of the design capacity and then discharged to 5% (SOC 5%) or less. The method of claim 7,
(b) the step of activating,
(b-3) After the secondary charging step, a method of manufacturing a secondary battery further comprising a secondary aging step. The method of claim 8,
(b) after the step of activating,
A method of manufacturing a secondary battery further comprising the step of charging the secondary battery at 40-60% (SOC 40-60%) of the design capacity. The method of claim 1,
The electrode assembly has a structure including an anode, a cathode, and a separator interposed between the anode and the cathode,
The method of manufacturing a secondary battery, characterized in that the electrolyte contains a lithium salt. The method of claim 1,
The method of manufacturing a secondary battery, characterized in that the secondary battery is a pouch-type secondary battery. In the secondary battery manufactured by the manufacturing method according to claim 1, wherein the electrode assembly and the electrolyte are accommodated in a battery case,
The electrode assembly has a structure including an anode, a cathode, and a separator interposed between the anode and the cathode,
The electrolyte solution contains a lithium salt, and the secondary battery is a pouch-type secondary battery.

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