KR102587972B1 - Method for Preparing Anode and Anode Prepared Therefrom - Google Patents

Abstract

The present invention includes the steps of (S1) preparing a preliminary negative electrode by coating at least one side of a current collector with a negative electrode slurry containing a negative electrode active material, a conductive material, a binder, and a solvent, drying, and rolling to form a negative electrode active material layer; (S2) placing lithium metal foil pieces on the surface of the negative electrode active material layer of the preliminary negative electrode and then coating them; (S3) preparing a pre-lithiated anode by impregnating the preliminary anode coated with the lithium metal foil pieces in an electrolyte solution; and (S4) assembling the negative electrode prepared in step (S3) together with the positive electrode and a separator, and a lithium secondary battery manufactured therefrom.

Description

Method for manufacturing an anode and an anode manufactured therefrom {Method for Preparing Anode and Anode Prepared Therefrom}

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

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

A 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 electrolyte solution that electrochemically communicates with the positive electrode and the negative electrode.

These lithium secondary batteries are typically manufactured using a compound in which lithium is inserted, such as LiCoO ₂ or LiMn ₂ O ₄ , for the positive electrode, and using a material in which lithium is not inserted, such as carbon-based or Si-based, for the negative electrode. During charging, lithium ions inserted into the positive electrode move to the negative electrode through the electrolyte, and during discharging, lithium ions move again 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), a kind of passivation film, on the surface of the cathode. This SEI can stabilize the structure of the cathode by preventing the decomposition reaction of the electrolyte by suppressing the movement of electrons required for the reaction between the cathode and the electrolyte, but it also causes consumption of lithium ions because it is an irreversible reaction. In other words, the lithium consumed due to the formation of SEI does not return to the positive electrode during the subsequent discharge process, thereby reducing the capacity of the battery. This phenomenon is called irreversible capacity. In addition, because the charging and discharging efficiency of the positive and negative electrodes of a secondary battery is not completely 100%, lithium ions are consumed as the number of cycles progresses, causing a decrease in electrode capacity and ultimately shortening cycle life. In particular, when Si-based materials are used as cathodes for the purpose of high capacity, the problem of low initial efficiency due to lithium depletion is increasingly emerging due to the high initial irreversible capacity.

Accordingly, as a technology to reduce the initial irreversibility of the negative electrode, pre-lithiation, that is, performing an irreversible reaction of the negative electrode in advance before manufacturing the battery, or slightly charging the negative electrode with lithium in advance to secure initial reversibility, improves the capacity and capacity of the battery. Methods to improve electrochemical performance are being attempted.

For example, the pre-lithiation involves attaching lithium metal to a negative electrode material or a negative electrode layer containing the same by deposition or powder coating, and assembling a battery cell by interposing the negative electrode and positive electrode manufactured therefrom and a separator between them. This is done by injecting electrolyte solution. In this way, when electrolyte is injected after cell assembly, lithium is ionized and inserted into the cathode layer due to a reaction between the lithium metal attached to the cathode layer and the electrolyte, and the place where the lithium ions escape from the lithium metal remains as an empty space inside the cell. do. This causes the anode/separator/cathode constituting the cell to float, making charging and discharging not smooth.

In addition, the lithium metal used in pre-lithiation is expensive, so attaching it to the entire cathode is not only economically disadvantageous, but also the excess lithium increases the reduction reaction of the electrolyte during pre-lithiation, resulting in excessive consumption of electrolyte and by-products. It may cause electrochemical side effects.

Therefore, the present invention is to solve the above problems, and one object of the present invention is to perform a pre-lithiation process to compensate for the irreversible capacity of the negative electrode during the manufacture of lithium secondary batteries in an economical manner without wasting lithium metal. The aim is to provide a method to improve the contact between the anode/separator/cathode after battery manufacturing.

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

According to one aspect of the present invention, (S1) preparing a preliminary 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 side of the current collector, drying, and rolling to form a negative electrode active material layer. step; (S2) placing lithium metal foil pieces on the surface of the negative electrode active material layer of the preliminary negative electrode and then coating them; (S3) preparing a pre-lithiated anode by impregnating the preliminary anode coated with the lithium metal foil pieces in an electrolyte solution; and (S4) assembling the negative electrode manufactured in step (S3) together with the positive electrode and a separator.

In step S2, the coating may be performed by compression under conditions of a temperature of 10 to 200° C. and a linear pressure of 0.2 to 30 kN/cm.

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

In step S3, the step of washing and drying the pre-lithiated anode after impregnating the electrolyte may be further included.

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

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

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

The initial efficiency and capacity retention rate of the lithium secondary battery are each 85% or more, and the area separated by more than 1 μm between the anode and the separator after charging and discharging may be 5% or less of the total area of the anode.

According to one aspect of the present invention, when manufacturing a lithium secondary battery, a negative electrode that has previously been pre-lithiated by cutting a lithium metal foil into several pieces on the surface of the negative electrode active material layer, dispersing coating and pressing it, and then immersing it in an electrolyte solution is used as a positive electrode. By assembling it with a separator, uniform pre-lithiation can be induced on the electrode compared to the case where the lithium metal foil is attached at once, initial reversibility can be secured without wasting lithium metal, and the lithium metal is ionized. The diffusion distance to the cathode is relatively short, which can shorten the pre-lithiation time. In addition, by immersing the cathode in the electrolyte before battery assembly, pre-lithiation, in which lithium metal is inserted into the cathode, is advanced in advance, thereby minimizing the lifting phenomenon between the anode/separator/cathode that occurs during pre-lithiation after battery assembly. can do.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention along with the contents of the above-described invention. Therefore, the present invention is limited to the matters described in such drawings. It should not be interpreted in a limited way.
Figure 1 schematically shows the manufacturing process of a lithium secondary battery according to an embodiment of the present invention.
Figures 2 and 3 are photographs showing the negative electrode applied in manufacturing the lithium secondary battery in Examples 1 and 2 of the present invention and Comparative Example 1, respectively.

Hereinafter, terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor appropriately defines the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

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

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

The negative electrode active material layer 14 of the preliminary negative electrode may be formed by coating at least one side of the current collector 12 with a negative electrode slurry obtained by dispersing a negative electrode active material, a conductive material, and a binder in a solvent, 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 carbon-based 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 the group consisting of crystalline artificial graphite and/or crystalline natural graphite. The Si-based material may include Si, SiO, SiO _{2 ,} etc., and the Sn-based material may include Sn, SnO, SnO ₂ , etc.

In addition to the above materials _{, the} negative electrode active material _may include, for example _, Li _x Fe ₂ O _{3 (} 0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3; 1 ≤z≤8) and other metal complex oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; 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, etc. can be used.

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

The binder is a component that assists in 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% by weight based on the total weight of the negative electrode slurry composition. Examples of such binders include polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidenefluoride (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 carboxymethylcellulose (CMC) can also be used as a thickener to control the viscosity of the slurry.

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

The solvent may include an organic solvent such as water or NMP (N-methyl-2-pyrrolidone), and is used in an amount to achieve a desirable viscosity when the negative electrode slurry includes a negative electrode active material and optionally a binder and a conductive material. can be used For example, the solid content concentration in the anode slurry may be 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, fired carbon, carbon or nickel on the surface of copper or stainless steel. , surface treated with titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The thickness of the current collector is not particularly limited, but may have a commonly applied thickness of 3 to 500 ㎛.

Additionally, the coating method of the cathode slurry is not particularly limited as long as it is a method commonly used in the field. For example, a coating method using a slot die may be used, and in addition, a Mayer bar coating method, a gravure coating method, a dip coating method, a spray coating method, etc. may be used.

Next, as shown 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). At this time, the preliminary negative electrode can be punched to fit the size of the battery to be manufactured before coating the lithium metal foil pieces, and the preliminary negative electrode can be supplied in a roll-to-roll manner.

The coating can be performed by cutting the lithium metal foil to a desired size, placing it on the surface of the negative electrode active material layer at regular intervals, and pressing it. At this time, the compression may be performed at a temperature of 10 to 200° C. and a linear pressure of 0.2 to 30 kN/cm, considering the adhesive force between the negative electrode active material layer and the lithium metal foil. Additionally, the lithium metal foil may have a thickness of 5 to 200 ㎛, but is not limited thereto.

In this way, when the lithium metal foil is dispersed and coated in several pieces, uniform prelithiation can be induced on the cathode compared to the case where the lithium metal foil is attached at once, and waste of expensive lithium metal can be prevented. In addition, when lithium metal is attached to the entire negative electrode, the reduction reaction of the electrolyte increases during pre-lithiation due to the excess lithium, thereby overcoming the problem of excessive consumption of the electrolyte and causing electrochemical side effects due to by-products. In addition, since lithium is ionized from each lithium metal dispersed and compressed on the cathode and inserted into the cathode, the distance for lithium ions to diffuse into the cathode is relatively short, and this shortens the pre-lithiation time that occurs when immersed in the electrolyte solution. You can.

Next, as shown in FIG. 1C, the pre-lithiated anode 10 is manufactured by impregnating the preliminary anode coated with the lithium metal foil pieces into an electrolyte solution (S3).

While the preliminary cathode is immersed in the electrolyte solution, the lithium metal foil coated in pieces reacts with the electrolyte solution to ionize lithium, and the generated lithium ions are pre-lithiated to be inserted into the cathode layer, thereby causing the lithium metal foil to disappear. . Therefore, since the pre-lithiation process of the negative electrode is performed before battery assembly, good contact can be maintained without lifting phenomenon between battery components after battery assembly.

Therefore, in the existing pre-lithiation method, when electrolyte is injected after battery assembly, the reaction between lithium metal and electrolyte causes the site left after lithium ionization to become excited, thereby overcoming the disadvantage of impeding charging and discharging.

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

The electrolyte solution contains lithium salt as an electrolyte and an organic solvent for dissolving it.

The lithium salt may be used without limitation as long as it is commonly used in electrolytes for secondary batteries. For example, anions of the lithium salt include 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 type selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- can be used.

The organic solvent contained in the electrolyte solution may be any commonly used solvent without limitation, and representative examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, and dimethyl sulfoxide. One or more types selected from the group consisting of side, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

After manufacturing the pre-lithiated cathode 10, as shown in FIG. 1D, an electrode assembly 100 is formed using the cathode 10, the anode 20, and a separator 30 between them. Do it (S4).

The positive electrode is prepared by mixing the positive electrode active material, conductive material, binder, and solvent to prepare a slurry, and then coating it directly on the metal current collector, or casting it on a separate support and lamination of the positive electrode active material film peeled from this support to the metal current collector. Thus, the anode can be manufactured.

Active materials used in 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 selected from Al, Ni, Co, is any one selected from the group consisting of Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are each independently the atomic fraction of the oxide composition elements, 0=x<0.5, 0≤ =y<0.5, 0=z<0.5, 0<x+y+z=1) or a mixture of two or more of them.

Meanwhile, the conductive material, binder, and solvent may be used in the same manner as those used in manufacturing the anode.

The separator is a conventional porous polymer film used as a separator, for example, a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The prepared porous polymer film can be used alone or by stacking them. Additionally, a thin insulating film with high ion permeability and mechanical strength can 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, conventional porous nonwoven fabrics, for example, nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., can be used, but are not limited thereto.

Thereafter, the electrode assembly is placed in, for example, a pouch, a cylindrical battery case, or a square battery case, and then an electrolyte is injected to complete the lithium secondary battery. Alternatively, a lithium secondary battery can be completed by stacking the electrode assemblies, impregnating them with an electrolyte, and sealing the resulting product in 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 is compensated to satisfy excellent initial efficiency and capacity maintenance rate, for example, initial efficiency and capacity maintenance rate of 85% or more. In addition, the lithium secondary battery of the present invention minimizes the phenomenon of lifting between the anode/separator/cathode that occurs during pre-lithiation, and when the electrode assembly is dismantled after charge and discharge and the thickness of the bonded cathode and separator are measured, The area separated by more than 1㎛ between the cathode and the separator may satisfy 5% or less of the total area of the cathode.

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

The lithium secondary battery according to the present invention can not only be used in battery cells used as a power source for small devices, but can also be preferably used as a unit cell in medium to large-sized battery modules containing 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, etc., and are particularly useful for hybrid electric vehicles and batteries for renewable energy storage, which are areas requiring high output. It can be used effectively.

Hereinafter, the present invention will be described in detail through examples to aid understanding. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

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

Example 1:

Step 1:

As a negative electrode active material, 92% by weight of a mixture of graphite and SiO (7:3), 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) are mixed with water as a solvent. was added to obtain a cathode slurry. A preliminary negative electrode was prepared by coating the slurry on one side of a copper current collector, drying and rolling to form a negative electrode active material layer.

Step 2:

The preliminary negative electrode was punched to match the cell size, and 40㎛ thick pieces of lithium metal foil (2.3cm ² ) were divided into 9 equal parts and distributed at regular intervals on the active material layer of the punched negative electrode, and then 5 kN/cm at room temperature. It was compressed with linear pressure.

Step 3

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

Step 4

After interposing a polyolefin separator between the pre-lithiated cathode and the LiCoO ₂ electrode used as the anode, 1M LiPF ₆ was added to a solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (DEC) at a volume ratio of 50:50. A coin-type double-sided battery was manufactured by injecting the dissolved electrolyte solution.

Example 2

In Step 2 of Example 1, a coin-type double-sided battery was manufactured by carrying out the same process as Example 1, except that 9 equal pieces of lithium metal foil (4.6 cm ² ) with a thickness of 20 μm were used.

Comparative Example 1:

Step 1

As a negative electrode active material, 92% by weight of a mixture of graphite and SiO (7:3), 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) are mixed with water as a solvent. was added to obtain a cathode slurry. A preliminary negative electrode was prepared by coating the slurry on one side of a copper current collector, drying and rolling to form a negative electrode active material layer.

Step 2

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

Step 3

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

Step 4

After interposing a polyolefin separator between the pre-lithiated cathode and the LiCoO ₂ electrode used as the anode, 1M LiPF ₆ was added to a solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (DEC) at a volume ratio of 50:50. A coin-type double-sided battery was manufactured by injecting the dissolved electrolyte solution.

Comparative Example 2:

A coin-type double-sided battery was manufactured by performing the same process as Example 1, except that step 3 of Example 1 was not performed.

Comparative Example 3:

As a negative electrode active material, 92% by weight of a mixture of graphite and SiO (7:3), 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) are mixed with water as a solvent. was added to obtain a cathode slurry. A negative electrode was manufactured by coating the slurry on one side of a copper current collector, drying and rolling to form a negative electrode active material layer.

After interposing a polyolefin separator between the cathode and the LiCoO ₂ electrode used as the anode, an electrolyte solution containing 1M LiPF ₆ dissolved in a solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (DEC) in a volume ratio of 50:50 was added. Coin-type double-sided batteries were manufactured by injection.

Experimental Example 1: Evaluation of life characteristics according to charging and discharging

The batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 3 were charged and discharged using an electrochemical charger and discharger. At this time, charging was performed by applying a current at a current density of 0.1C-rate up to a voltage of 4.2V, and discharging was performed up to a voltage of 2.5V at the same current density. After performing such charging and discharging 100 times, the initial efficiency (%) and capacity maintenance 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) × 100

Capacity retention rate (%) = (Discharge capacity after 100 cycles / Discharge capacity after 1 cycle) × 100

Experimental Example 2: Evaluation of excitation between cathode and separator

In order to evaluate the degree of lifting of the batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 3, the assembled cells were disassembled, the positive electrode was removed, and the negative electrode and the separator were bonded to each other. After measuring the thickness of the bonded cathode and separator using a non-contact laser thickness gauge and measuring the thickness using a contact tick thickness gauge, the area where the difference is more than 1㎛ is calculated as a percentage of the total area of the cathode. The calculations are 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 maintenance rate (%) 87 89 82 83 71 Lifting area between cathode and separator (%) 2 2 3 12 One

As can be seen in Table 1, the batteries of Examples 1 and 2 were equipped with a negative electrode in which lithium metal foil was cut into several pieces and pressed onto the negative electrode layer (see FIG. 2), and pre-lithiation was then immersed in an electrolyte solution. showed the best initial efficiency and cycle performance (capacity maintenance rate), and at the same time, the level of excitation between the cathode and the separator was low. This was obtained from the results in Examples 1 and 2, where uniform pre-lithiation was carried out on the cathode, and the uneven volume expansion of the cathode was alleviated during pre-lithiation. Moreover, as each lithium metal dispersed and compressed in the negative electrode active material layer is ionized and inserted into the negative electrode, the distance for lithium ions to diffuse into the negative electrode becomes relatively shorter compared to Comparative Example 1 in which the lithium metal was attached as a single piece, resulting in total lithium. The burn time can also be shortened.

In the case of Comparative Example 1, the lithium metal foil was attached at once without being cut into pieces (see FIG. 3), resulting in uniform pre-lithiation on the electrode, resulting in poorer battery performance compared to Example 1. In Comparative Example 2, the lithium metal foil was dispersed and attached into pieces, but since electrolyte was injected after battery assembly to induce pre-lithiation, the lithium metal was ionized and inserted into the cathode, leaving the remaining lithium metal in place (empty). It is believed that the battery performance deteriorated somewhat as the resistance increased and smooth charging and discharging did not occur.

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

Claims (8)

(S1) preparing a preliminary negative electrode by coating at least one side of a current collector with a negative electrode slurry containing a negative electrode active material, a conductive material, a binder, and a solvent, followed by drying and rolling to form a negative electrode active material layer;
(S2) dispersing lithium metal foil pieces at regular intervals on the surface of the negative electrode active material layer of the preliminary negative electrode and then coating them;
(S3) preparing a pre-lithiated anode in which the lithium metal foil disappears by impregnating the preliminary anode coated with the lithium metal foil pieces in an electrolyte solution for 2 to 48 hours; and
(S4) A method of manufacturing a lithium secondary battery comprising the step of assembling the negative electrode manufactured in step (S3) together with the positive electrode and a separator. According to paragraph 1,
In the step (S2), the coating is performed by compression under conditions of a temperature of 10 to 200 ° C and a linear pressure of 0.2 to 30 kN / cm. delete According to paragraph 1,
In the step (S3), the method of manufacturing a lithium secondary battery further includes the step of washing and drying the pre-lithiated negative electrode after impregnating the electrolyte solution. According to paragraph 1,
The electrolyte solution is a method of manufacturing a lithium secondary battery containing a lithium salt and an organic solvent. According to paragraph 1,
The anode active material layer is a method of manufacturing a lithium secondary battery including a Si-based material, Sn-based material, carbon-based material, or a mixture of two or more thereof as an active material. A lithium secondary battery manufactured by the manufacturing method according to any one of claims 1, 2, and 4 to 6. In clause 7,
A lithium secondary battery in which the initial efficiency and capacity retention rate of the lithium secondary battery are each 85% or more, and the area separated by more than 1㎛ between the negative electrode and the separator after charging and discharging is less than 5% of the total area of the negative electrode.

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