KR20190110348A - Method for Preparing Anode and Anode Prepared Therefrom - Google Patents

Abstract

The present invention provides a method for manufacturing a lithium secondary battery, and a lithium secondary battery manufactured therefrom. The method comprises the steps of: (S1) preparing a preliminary negative electrode by coating negative electrode slurry including a negative electrode active material, a conductive material, a binder, and a solvent on at least one surface of a current collector, and drying and rolling to form a negative electrode active material layer; (S2) disposing pieces of lithium metal foil on a surface of the negative electrode active material layer of the preliminary negative electrode and then coating the same; (S3) manufacturing a pre-lithiated negative electrode by impregnating the preliminary negative electrode coated with the lithium metal pieces in an electrolyte; and (S4) assembling the negative electrode manufactured in the step (S3) together with the positive electrode and the separator.

Description

Method for preparing a cathode and a cathode prepared therefrom {Method for Preparing Anode and Anode Prepared Therefrom}

The present invention relates to a method of manufacturing a negative electrode, and more particularly, to a method of manufacturing a pre-lithiated negative electrode that can improve the initial efficiency of the negative electrode.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low discharge rate have been commercialized and widely used.

The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode to separate them, and an electrolytic solution in electrochemical communication with the positive electrode and the negative electrode.

Such lithium secondary batteries are typically manufactured using a compound containing lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , in the positive electrode, and a material in which lithium, such as carbon or Si, is not inserted in the negative electrode. During charging, lithium ions inserted into the positive electrode move to the negative electrode through the electrolyte, and during discharge, lithium ions move from the negative electrode to the positive electrode. Lithium, which moves from the anode to the cathode during the charging reaction, reacts with the electrolyte to form a solid electrolyte interface (SEI), which is a kind of passivation film on the surface of the cathode. This SEI can stabilize the structure of the negative electrode by inhibiting the movement of electrons required for the reaction between the negative electrode and the electrolyte solution, thereby preventing the decomposition reaction of the electrolyte, and also leads to the consumption of lithium ions because it is an irreversible reaction. That is, lithium consumed by the formation of SEI does not return to the positive electrode in the subsequent discharge process, thereby reducing the capacity of the battery, and this phenomenon is called irreversible capacity. In addition, since the charge and discharge efficiency of the positive electrode and the negative electrode of the secondary battery is not 100% completely, as the number of cycles proceeds, consumption of lithium ions occurs, which leads to a decrease in electrode capacity, resulting in a decrease in cycle life. In particular, when a Si-based material is used for the purpose of high capacity as a cathode, a problem of low initial efficiency due to lithium depletion due to high initial irreversible capacity has been raised.

Therefore, as a technique for reducing the initial irreversibility of the negative electrode, pre-lithiation, i.e., before the battery is manufactured, the reversible reaction of the negative electrode is performed in advance, or the lithium is slightly charged into the negative electrode to secure initial reversibility. Attempts have been made to improve electrochemical performance.

For example, in the prelithiation, lithium metal is attached to a negative electrode material or a negative electrode layer including the same by deposition or powder coating, and a battery cell is assembled by interposing a negative electrode, a positive electrode, and a separator therebetween. After the electrolyte is injected. As such, when the electrolyte is injected after cell assembly, lithium is ionized by the reaction of the lithium metal attached to the negative electrode layer and the electrolyte solution and is inserted into the negative electrode layer, and the position where the lithium ions escape from the lithium metal remains as an empty space inside the cell. do. As a result, the phenomenon of lifting of the positive electrode / separator / negative electrode constituting the cell is caused, and charging and discharging are not smooth.

In addition, since lithium metal used for prelithiation is expensive, it is economically disadvantageous when it is attached to the entire negative electrode, and due to excess lithium, the reduction reaction of the electrolyte increases during prelithiation due to excess lithium, consuming excessive electrolyte and by-products. May cause electrochemical side effects.

Accordingly, the present invention is to solve the above problems, an object of the present invention is an economical method without waste of lithium metal in the prelithiation process for compensating the irreversible capacity of the negative electrode in the production of a lithium secondary battery To provide a method capable of improving contact between the positive electrode / separator / negative electrode after battery production.

Another object of the present invention is to provide a lithium secondary battery produced by the above method.

According to an aspect of the invention, (S1) to prepare a negative electrode by coating a negative electrode slurry containing a negative electrode active material, a conductive material, a binder and a solvent on at least one surface of the current collector, dried and rolled to form a negative electrode active material layer step; (S2) disposing pieces of lithium metal foil on the surface of the negative electrode active material layer of the preliminary negative electrode and then coating them; (S3) preparing a pre-lithiated negative electrode by impregnating a preliminary negative electrode coated with the lithium metal foil pieces in an electrolyte; And (S4) there is provided a method of manufacturing a lithium secondary battery comprising the step of assembling the negative electrode prepared in the step (S3) with a positive electrode and a separator.

In the step (S2), the coating may be carried out in a compression method under a temperature of 10 to 200 ℃ and linear pressure conditions of 0.2 to 30 kN / cm.

In the step (S3), the electrolyte solution impregnation may be performed for 2 to 48 hours.

In the step (S3), after the impregnation of the electrolyte may further comprise the step of washing and drying the pre-lithiated anode.

The electrolyte may include a lithium salt and an organic solvent.

The negative electrode active material layer may include Si-based material, Sn-based material, carbon-based material, or a mixture of two or more thereof.

According to another aspect of the present invention, there is provided a lithium secondary battery manufactured by the manufacturing method as described above.

The initial efficiency and capacity retention rate of the lithium secondary battery may be 85% or more, respectively, and after charging and discharging, an area spaced at least 1 μm between the negative electrode and the separator may be 5% or less of the total area of the negative electrode.

According to an aspect of the present invention, during the fabrication of a lithium secondary battery, a cathode, which is preliminarily pre-lithiated, is immersed in an electrolyte after dispersion coating and pressing are cut into several pieces of lithium metal foil on the surface of the anode active material layer. By assembling together with the separator, it is possible to induce uniform prelithiation on the electrode as compared with the case of attaching the lithium metal foil at one time, to ensure the initial reversibility without waste of lithium metal, lithium metal is ionized The distance to be diffused to the cathode is relatively short, which may shorten the prelithiation time. In addition, as the negative electrode is immersed in the electrolyte solution prior to battery assembly, the pre-lithiation of lithium metal is inserted into the negative electrode in advance, thereby minimizing the lifting phenomenon between the positive electrode / separator / cathode generated by the prelithiation after battery assembly. can do.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.
1 schematically illustrates a manufacturing process of a lithium secondary battery according to an embodiment of the present invention.
2 and 3 are photographs showing negative electrodes applied in the manufacture of the lithium secondary battery in Examples 1 to 2 and Comparative Example 1, respectively.

Hereinafter, the terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors properly define the concept of terms in order to explain their invention in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can.

One embodiment of the present invention relates to a method of manufacturing a lithium secondary battery, Figure 1 schematically shows a manufacturing process of a lithium secondary battery according to an embodiment of the present invention.

First, as shown in FIG. 1A, a negative electrode active material layer 14 is formed on at least one surface of the current collector 12 to prepare a preliminary negative electrode (S1).

The negative electrode active material layer 14 of the preliminary negative electrode may be formed by coating a negative electrode slurry obtained by dispersing a negative electrode active material, a conductive material, and a binder in a solvent on at least one surface of the current collector 12, followed by drying and rolling.

The negative electrode active material may include a Si-based material, a Sn-based material, a carbon-based material, or a mixture of two or more thereof.

In this case, the carbonaceous material is a group consisting of crystalline artificial graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, ketjen black, super P, graphene, and fibrous carbon. It may be one or more selected from, preferably crystalline artificial graphite, and / or crystalline natural graphite. The Si-based material may be Si, SiO, SiO ₂ and the like, the Sn-based material may be Sn, SnO, SnO ₂ and the like.

The negative electrode active material, in addition to the above materials, for example, Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me ': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 <x≤1;1≤y≤3; 1 Metal composite oxides such as ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and Bi ₂ O ₅ Metal oxides such as; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

The negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode slurry.

The binder is a component that assists the bonding between the conductive material and the active material or the current collector, and is typically included in an amount of 0.1 to 20 wt% based on the total weight of the negative electrode slurry composition. Examples of such binders include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate ( polymethylmethacrylate), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), etc. Can be mentioned. The carboxymethyl cellulose (CMC) may be used as a thickener to adjust the viscosity of the slurry.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon such as carbon black, acetylene black, ketjen black, channel black, farnes black, lamp black, and thermal black may be used. black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as fluorocarbon, aluminum and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. The conductive material may be added in an amount of 0.1 to 20 wt% based on the total weight of the negative electrode slurry composition.

The solvent may include an organic solvent such as water or NMP (N-methyl-2-pyrrolidone), and in an amount that becomes a desirable viscosity when the negative electrode slurry contains a negative electrode active material, and optionally a binder and a conductive material. Can be used. For example, it may be included so that the solid content concentration in the negative electrode slurry is 50 to 95% by weight, preferably 70 to 90% by weight.

The current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon, nickel on the surface of copper or stainless steel , Surface treated with titanium, silver, or the like, aluminum-cadmium alloy, or the like can be used. The thickness of the current collector is not particularly limited, but may have a thickness of 3 to 500 μm that is commonly applied.

In addition, the coating method of the negative electrode slurry is not particularly limited as long as it is a method commonly used in the art. For example, a coating method using a slot die may be used, and in addition, a Mayer bar coating method, a gravure coating method, an immersion coating method, a spray coating method, or the like may be used.

Next, as illustrated in FIG. 1B, the preliminary negative electrode is coated by dispersing lithium metal foil pieces 16 at regular intervals on the surface of the negative electrode active material layer 14 (S2). In this case, the preliminary negative electrode may be punched out according to the size of a battery to be manufactured before coating the pieces of lithium metal foil, and the preliminary negative electrode may be supplied in a roll-to-roll manner.

The coating may be carried out by cutting the lithium metal foil to a desired size, and then pressing it on a surface of the negative electrode active material layer at a predetermined interval. In this case, the pressing may be performed at a temperature of 10 to 200 ° C. and a linear pressure of 0.2 to 30 kN / cm in consideration of the adhesive force between the negative electrode active material layer and the lithium metal foil. In addition, the lithium metal foil may have a thickness of 5 to 200 μm, but is not limited thereto.

As such, when dispersing and coating the lithium metal foil into several pieces, it is possible to induce uniform prelithiation on the negative electrode as compared to attaching the lithium metal foil at once, and to prevent waste of expensive lithium metal. In addition, when lithium metal is attached to the entire negative electrode, excess lithium causes the reduction reaction of the electrolyte during prelithiation, resulting in excessive consumption of the electrolyte and overcoming problems of electrochemical side effects caused by by-products. In addition, since lithium is ionized in each of the lithium metals dispersed and compressed on the negative electrode and inserted into the negative electrode, the distance from which lithium ions diffuse to the negative electrode is relatively shortened, thereby reducing the prelithiation time that proceeds during subsequent electrolyte immersion. Can be.

Subsequently, as illustrated in FIG. 1C, the preliminary negative electrode coated with the lithium metal foil pieces is impregnated in the electrolyte to prepare the pre-lithiated negative electrode 10 (S3).

During the impregnation of the preliminary negative electrode, the lithium metal foil coated with the flakes reacts with the electrolyte to cause lithium to ionize, and the resulting lithium ions are pre-lithiated to be inserted into the negative electrode layer, whereby the lithium metal foil disappears. . Therefore, the pre-lithiation process of the negative electrode is performed before battery assembly, so that good contact can be maintained after the battery assembly without lifting up between battery components.

Therefore, when the electrolyte is injected after assembly of the battery in the conventional prelithiation method, a spot that is left after the lithium ionization due to the reaction between the lithium metal and the electrolyte is lifted, thereby overcoming the disadvantage of inhibiting charge and discharge.

The electrolyte solution impregnation is advantageously performed for 2 to 48 hours at room temperature for uniform and stable prelithiation of the entire negative electrode.

The electrolyte includes a lithium salt and an organic solvent for dissolving it as an electrolyte.

The lithium salt may be used without limitation so long as those lithium salts are conventionally used in the electrolyte for secondary batteries. For example, as anions of the lithium salt, F ⁻ , Cl ⁻ , 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 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, One kind selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- can be used.

The organic solvent included in the electrolyte may be used without limitation as long as they are conventionally used, and typically propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide One or more types selected from the group consisting of aside, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran can be used.

After fabricating the pre-lithiated cathode 10, as shown in FIG. 1D, the electrode assembly 100 is formed through the cathode 10, the anode 20, and a separator 30 therebetween. (S4).

 The positive electrode is a mixture of a positive electrode active material, a conductive material, a binder and a solvent to prepare a slurry and then directly coated it on a metal current collector, or cast on a separate support and laminating the positive electrode active material film peeled from the support to a metal current collector To produce a positive electrode.

The active materials used for the positive electrode include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO _4, and LiNi _1-xyz Co _x M1 _y M2 _z O ₂ (M1 and M2 are independently of each other Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z independently of each other as the atomic fraction of the elements of the oxide composition 0 = x <0.5, 0 ≤ = y <0.5, 0 = z <0.5, 0 <x + y + z = 1) may include any one of the active material particles or a mixture of two or more thereof.

Meanwhile, the conductive material, the binder, and the solvent may be used in the same manner as used in the production of the negative electrode.

The separator is a conventional porous polymer film used as a conventional separator, for example, polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer The prepared porous polymer films may be used alone or in a lamination thereof. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, etc. may be used, but is not limited thereto.

Thereafter, the electrode assembly may be placed in, for example, a pouch, a cylindrical battery case, or a rectangular battery case, and then injected with an electrolyte to complete a lithium secondary battery. Alternatively, the lithium secondary battery may be completed by stacking the electrode assembly and then impregnating it in an electrolyte, and sealing the resultant into a battery case.

As the lithium secondary battery of the present invention includes the pre-lithiated negative electrode as described above, the irreversible capacity of the negative electrode can be compensated to satisfy excellent initial efficiency and capacity retention rate, such as 85% or more initial efficiency and capacity retention rate. In addition, the lithium secondary battery of the present invention minimizes the lifting phenomenon between the positive electrode / separator / cathode generated by the progress of prelithiation, and when measuring the thickness of the negative electrode and the separator bonded by disassembling the electrode assembly after charge and discharge An area of 1 μm or more spaced apart between the negative electrode and the separator may satisfy 5% or less of the total area of the negative electrode.

According to an embodiment of the present invention, the lithium secondary battery may be a stack type, a wound type, a stack and folding type or a cable type.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells. Preferred examples of the medium-to-large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like, and are particularly useful for hybrid electric vehicles and renewable energy storage batteries, which require high power. Can be used.

Hereinafter, examples will be described in detail to help understand the present invention. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

<Examples 1 to 2 and Comparative Examples 1 to 3: Preparation of a lithium secondary battery>

Example 1:

Step 1:

92% by weight of a mixture of graphite and SiO (7: 3) as a negative electrode active material, 3% by weight of carbon black (Denka black, conductive material), 3.5% by weight of SBR (binder), and 1.5% by weight of CMC (thickener) as solvent Was added to give a negative electrode slurry. The slurry was coated on one surface of a copper current collector, dried and rolled to form a negative electrode active material layer, thereby preparing a preliminary negative electrode.

Step 2:

The preliminary negative electrode was punched out according to the cell size, and a 40 μm thick piece of lithium metal foil (2.3 cm ² ) was distributed in 9 equal intervals on the active material layer of the negative electrode, and then dispersed at regular intervals. Squeezed by linear pressure.

Step 3

The preliminary negative electrode in which the lithium metal foil pieces were dispersed and compressed was impregnated into an electrolyte solution in which 1M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed at a volume ratio of 50:50. After 24 hours, the negative electrode was taken out, washed with DMC, and dried to prepare a pre-lithiated negative electrode.

Step 4

After interposing a polyolefin separator between the pre-lithiated cathode and LiCoO ₂ electrode used as a positive electrode, 1M LiPF ₆ in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed at a volume ratio of 50:50. An electrolyte solution in which the solution was dissolved was injected to prepare a coin-type both battery.

Example 2

In Step 2 of Example 1, a coin-type both battery was prepared in the same manner as in Example 1 except that 20 μm thick lithium metal foil pieces (4.6 cm ² ) were used in equal parts.

Comparative Example 1:

Step 1

92% by weight of a mixture of graphite and SiO (7: 3) as a negative electrode active material, 3% by weight of carbon black (Denka black, conductive material), 3.5% by weight of SBR (binder), and 1.5% by weight of CMC (thickener) as solvent Was added to give a negative electrode slurry. The slurry was coated on one surface of a copper current collector, dried and rolled to form a negative electrode active material layer, thereby preparing a preliminary negative electrode.

Step 2

One piece of lithium metal foil (2.3 cm ² ) having a thickness of 40 μm was placed on the center of the active material layer of the preliminary negative electrode, and pressed at a linear pressure of 5 kN / cm at room temperature.

Step 3

The preliminary negative electrode to which the lithium metal foil was pressed was immersed in an electrolyte solution in which 1M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed in a volume ratio of 50:50. After 24 hours, the negative electrode was taken out, washed with DMC, and dried to prepare a pre-lithiated negative electrode.

Step 4

After interposing a polyolefin separator between the pre-lithiated cathode and LiCoO ₂ electrode used as a positive electrode, 1M LiPF ₆ in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed at a volume ratio of 50:50. An electrolyte solution in which the solution was dissolved was injected to prepare a coin-type both battery.

Comparative Example 2:

A coin-type both battery was prepared in the same manner as in Example 1, except that Step 3 of Example 1 was not performed.

Comparative Example 3:

92% by weight of a mixture of graphite and SiO (7: 3) as a negative electrode active material, 3% by weight of carbon black (Denka black, conductive material), 3.5% by weight of SBR (binder), and 1.5% by weight of CMC (thickener) as solvent Was added to give a negative electrode slurry. The negative electrode was prepared by coating the slurry on one surface of a copper current collector, drying and rolling to form a negative electrode active material layer.

After the polyolefin separator was interposed between the negative electrode and the LiCoO ₂ electrode used as the positive electrode, an electrolyte solution in which 1M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed at a volume ratio of 50:50 was prepared. Injection was performed to produce both coin-type cells.

Experimental Example 1: Evaluation of life characteristics according to charge and discharge

Charge and discharge of the batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were performed using an electrochemical charger. At this time, charging was performed by applying a current at a current density of 0.1 C-rate up to a voltage of 4.2V, and discharging was performed at a voltage of 2.5V at the same current density. After 100 times of such charging and discharging, the initial efficiency (%) and capacity retention rate (%) were calculated as follows, and the values are shown in Table 1 below.

Initial efficiency (%) = (discharge capacity of one cycle / charge capacity of one cycle) x 100

Capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity of one cycle) x 100

Experimental Example 2: Evaluation of Lifting Between Cathode and Separator

In order to evaluate the degree of lifting for the batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 3, the assembled cells were disassembled and the positive electrode was removed, and then a state in which the negative electrode and the separator were bonded was obtained. After measuring the thickness of the bonded cathode and the separator using a non-contact laser thickness meter, and measuring the thickness using a contact tick thickness meter, the area where the difference is 1 μm or more as a percentage of the total area of the cathode The calculation is shown in Table 1.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial Efficiency (%) 86.1 88.6 81.7 83.5 72.7 Capacity retention rate (%) 87 89 82 83 71 Lifted area between cathode and separator (%) 2 2 3 12 One

As can be seen in Table 1, the lithium metal foils were cut into pieces and pressed onto the negative electrode layer (see FIG. 2), and the batteries of Examples 1 and 2 to which the negative electrodes, which were preliminarily pre-lithiated by immersion in electrolyte, were applied. Showed the best initial efficiency and cycle performance (capacity retention), while at the same time the level of excitation between the cathode and the separator was low. This is obtained from the result that uniform prelithiation proceeded on the negative electrode in Examples 1 and 2 and the nonuniform volume expansion of the negative electrode was alleviated at the time of prelithiation. Furthermore, as each lithium metal dispersed and compressed in the negative electrode active material layer is ionized and inserted into the negative electrode, the distance from which lithium ions are diffused to the negative electrode is relatively shorter than that of Comparative Example 1 in which lithium metal is attached in a single piece. It can also shorten the fire time.

In Comparative Example 1, since the lithium metal foil was not fragmented and adhered at once (see FIG. 3), uniform prelithiation was not performed on the electrode, resulting in poor battery performance compared to Example 1. In Comparative Example 2, the lithium metal foil was dispersed in pieces and adhered, but since lithium electrolyte was injected after the battery was assembled, the lithium metal was ionized and inserted into the negative electrode. This phenomenon occurs due to the phenomenon of lifting in the space, and as a result, resistance is increased and smooth charging and discharging are not performed, and thus battery performance is deteriorated.

On the other hand, in the case of Comparative Example 3, the lithium metal did not adhere to the negative electrode used at the time of battery manufacturing, showing the poorest battery performance.

Claims (8)

(S1) preparing a preliminary negative electrode by coating a negative electrode slurry including a negative electrode active material, a conductive material, a binder, and a solvent on at least one surface of a current collector, and drying and rolling to form a negative electrode active material layer;
(S2) disposing pieces of lithium metal foil on the surface of the negative electrode active material layer of the preliminary negative electrode and then coating them;
(S3) preparing a pre-lithiated negative electrode by impregnating a preliminary negative electrode coated with the lithium metal foil pieces in an electrolyte; And
(S4) Method of manufacturing a lithium secondary battery comprising the step of assembling the negative electrode prepared in the step (S3) with a positive electrode and a separator. The method of claim 1,
In the step (S2), the coating is a method of manufacturing a lithium secondary battery is carried out in a compression method under a temperature of 10 to 200 ℃ and linear pressure conditions of 0.2 to 30 kN / cm. The method of claim 1,
In the step (S3), the electrolyte solution impregnation method of manufacturing a lithium secondary battery is performed for 2 to 48 hours. The method of claim 1,
In the step (S3), and further comprising the step of washing and drying the pre-lithiated negative electrode after the electrolyte solution impregnation. The method of claim 1,
The electrolyte solution manufacturing method of a lithium secondary battery containing a lithium salt and an organic solvent. The method of claim 1,
The negative electrode active material layer is a method of manufacturing a lithium secondary battery comprising a Si-based material, Sn-based material, a carbon-based material, or a mixture of two or more thereof. A lithium secondary battery prepared by the manufacturing method according to claim 1. The method of claim 7, wherein
An initial efficiency and a capacity retention rate of the lithium secondary battery are each 85% or more, and after charging and discharging, a lithium secondary battery having an area of 1 μm or more spaced apart from the negative electrode and the separator 5% or less of the total area of the negative electrode.

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