KR102496666B1 - Method of manufacturing anode for lithium battery and lithium battery including the same - Google Patents

Abstract

The present invention provides a method for manufacturing a negative electrode for a lithium battery, including the steps of: settling iron powder in a reactor and heat-treating the iron powder; injecting fluorine gas into the reactor to treat the heat-treated iron powder with fluorine; mixing the fluorinated iron powder with liquid lithium to form a liquid lithium-iron powder mixture; rolling the liquid lithium-iron powder mixture to form a negative electrode sheet; and molding the negative electrode sheet to form a negative electrode for a lithium battery.

Description

Method of manufacturing anode for lithium battery and lithium battery including the same}

The present invention relates to a method for manufacturing a negative electrode for a lithium battery and a lithium battery including the same, and more particularly, to a method for manufacturing a negative electrode for a lithium battery in which iron powder is uniformly dispersed and a lithium battery including the same.

In general, a negative electrode for a lithium battery is manufactured by mixing molten lithium with metal powder including iron, titanium, nickel, or alloys thereof that are not reactive with molten lithium. These metal powders have a positive Gibbs free energy, so a strong shear force of several hours must be applied to mix them with molten lithium. When the metal powder is not evenly dispersed and agglomerated in the negative electrode for a lithium battery, performance of the lithium battery is deteriorated, and fire and/or explosion may occur due to a short circuit.

Therefore, in order to manufacture a negative electrode for a lithium battery in which the metal powder is evenly dispersed, it is necessary to improve the wettability of the material surface. Wettability is determined by surface free energy. Surface free energy is defined as the cohesive force per unit area required to attract an internal constituent material to the surface, and metals generally have high surface free energy due to internal metal bonding. Therefore, the wettability of the surface can be improved by weakening the metal bond.

In general, in order to improve wettability of molten lithium, the temperature of molten lithium may be increased. In this case, the relationship between surface tension and temperature can be represented by Equation 1 below.

[Equation 1]

은 용융온도에서 용융 리튬의 표면장력이고,

은 리튬의 용융점이고, T는 용융 리튬의 온도이고,

는 온도 T에서의 표면장력이며,

이다.here,

is the surface tension of molten lithium at the melting temperature,

is the melting point of lithium, T is the temperature of molten lithium,

is the surface tension at temperature T,

am.

In order to improve the wettability of molten lithium, a hetero-atom may be doped. Since the binding force between the heteroatom and lithium is smaller than the binding force of the metallic bond between lithium and lithium, the surface free energy of molten lithium may be reduced by doping a small amount of elemental additives into the metal. At this time, the Gibbs free energy that governs the bonding reaction between lithium and heteroatoms and wettability of molten lithium may have a relationship as shown in Equation 2 below.

[Equation 2]

은 가스-액체 표면 에너지이고,

은 고체-액체 표면 에너지이고,

는 반응이 없을 때의 접촉각이고,

은 반응 후의 접촉각이고,

는 반응에 대한 깁스 자유 에너지이다.here,

is the gas-liquid surface energy,

is the solid-liquid surface energy,

is the contact angle when there is no reaction,

is the contact angle after the reaction,

is the Gibbs free energy for the reaction.

)가 감소(

)하고, 깁스 자유 에너지(

)가 음의 값을 가질 경우,

이 감소하여 용융 리튬의 젖음성이 향상된다.According to Equation 2 above, the gas-liquid surface energy (

) decreases (

), and the Gibbs free energy (

) is negative,

This decreases and the wettability of molten lithium is improved.

Recently, Choi et al. produced lithium-philic nickel oxides (NiO, Ni ₂ O ₃ ), etc. using a high-temperature oxidation method in the air temperature range of 500 ° C to 900 ° C of pure nickel or nickel alloy to produce molten lithium It was confirmed that the impregnation and mixing properties were improved.

1. Korea Registered Patent Publication No. 10-1920851 (November 15, 2018)

However, due to this conventional oxidation reaction, oxides such as iron oxide (Fe ₃ O ₄ ) or alumina (Al ₂ O ₃ ) having a lithium phobic property are generated, and the wettability of molten lithium is rather deteriorated. can

In addition, metals having excellent wettability with molten lithium are alloyed with molten lithium, and metal particles, plates, porous bodies, etc. are not separated, making it difficult to use them as electrode materials. Therefore, a method for manufacturing a negative electrode for a lithium battery capable of improving only the wettability of a metal powder and molten lithium to form a physically homogeneous mixture is required.

An object of the present invention is to solve various problems including the above problems, and to provide a method for manufacturing a negative electrode for a lithium battery in which iron powder is evenly dispersed, and a lithium battery including the same. However, these tasks are illustrative, and the scope of the present invention is not limited thereby.

According to one aspect of the present invention, placing iron powder in a reactor and heat-treating the iron powder, injecting fluorine gas into the reactor to fluorine-treat the heat-treated iron powder, fluorine-treating the iron powder with liquid lithium and mixing to form a liquid lithium-iron powder mixture, rolling the liquid lithium-iron powder mixture to form a negative electrode sheet, and forming the negative electrode sheet to form a negative electrode for a lithium battery, A method for manufacturing a negative electrode is provided.

In one embodiment, the method of manufacturing a negative electrode for a lithium battery may further include injecting an inert gas into the reactor and discharging the inert gas from the reactor before the heat treatment of the iron powder.

In one embodiment, in the step of injecting the inert gas and the step of discharging the inert gas, the pressure change rate of the reactor may be 0.01 to 0.2 bar/min.

In one embodiment, in the step of discharging the inert gas, the inert gas may be discharged such that the pressure of the reactor is less than atmospheric pressure.

In one embodiment, in the heat treatment of the iron powder, the temperature in the reactor may be 20 °C to 50 °C.

In one embodiment, in the step of treating the heat-treated iron powder with fluorine, a pressure change rate of the reactor may be 0.01 to 0.2 bar/min.

In one embodiment, in the fluorine treatment of the heat-treated iron powder, the pressure of the fluorine gas in the reactor may be 0.1 bar to 3.0 bar.

In one embodiment, the fluorine gas is fluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), carbon tetrafluoride (CF ₄ ), carbon trifluoride (CHF ₃ ), carbon octafluoride (C ₃ F ₈ ), tetrafluoride tetra It may include any one of carbon (C ₄ F ₈ ) and mixtures thereof.

In one embodiment, in the fluorine treatment of the heat-treated iron powder, the fluorine gas is mixed with an inert gas and injected, and at this time, the partial pressure of the fluorine gas in the reactor may be 0.1 bar to 3.0 bar.

In one embodiment, in the fluorine treatment of the heat-treated iron powder, the temperature in the reactor may be 20 °C to 100 °C.

In one embodiment, in the fluorine treatment of the heat-treated iron powder, the fluorine treatment may be performed for 24 hours to 48 hours.

In one embodiment, in the forming of the liquid lithium-iron powder mixture, the mass of the fluorine-treated iron powder may be 10% to 25% of the mass of the liquid lithium.

In one embodiment, in the step of forming the liquid lithium-iron powder mixture, the temperature in the mixing vessel may be 200 °C to 400 °C.

According to another aspect of the present invention, there is provided a liquid lithium battery including a negative electrode for a lithium battery manufactured according to any one of the above-described manufacturing methods for a negative electrode for a lithium battery.

Other aspects, features and advantages other than those described above will become apparent from the following drawings, claims and detailed description of the invention.

These general and specific aspects may be practiced using a system, method, computer program, or any combination of systems, methods, or computer programs.

According to one embodiment of the present invention made as described above, it is possible to implement a method for manufacturing a negative electrode for a lithium battery in which iron powder is evenly dispersed, and a lithium battery including the same. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart schematically illustrating a method for manufacturing a negative electrode for a lithium battery according to an embodiment of the present invention.
2a is a photograph of a liquid lithium-iron powder mixture prepared according to a comparative example, and FIG. 2b is a photograph of a liquid lithium-iron powder mixture prepared according to an experimental example.
3 is a diagram schematically illustrating a lithium battery manufactured according to an embodiment of the present invention.
4 to 6 are graphs showing Li oxidation-reduction voltage contrast (vs. Li/Li ⁺ ) according to charge/discharge current density of symmetric cell-type lithium batteries according to Experimental Examples and Comparative Examples.
7 is a graph showing the Li redox voltage comparison (vs. Li/Li ⁺ ) when the charge/discharge current density of lithium batteries according to Experimental Examples and Comparative Examples is 0.2 mA/cm ² .
8 is a graph showing a nucleation energy barrier according to charge/discharge current density of lithium batteries according to Experimental Examples and Comparative Examples.
9 is a scanning electron microscope (SEM) photograph of the surface of an anode after a charge/discharge test of a symmetric cell-type lithium battery according to a comparative example.
10 is a scanning electron microscope photograph of the surface of a negative electrode after a charge/discharge experiment of a symmetric cell-type lithium battery according to Experimental Example.

Since the present invention can apply various transformations and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. Effects and features of the present invention, and methods for achieving them will become clear with reference to the embodiments described later in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and when describing with reference to the drawings, the same or corresponding components are assigned the same reference numerals, and overlapping descriptions thereof will be omitted. .

In this specification, terms such as first and second are used for the purpose of distinguishing one component from another component without limiting meaning.

In this specification, singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as include or have mean that features or elements described in the specification exist, and do not preclude the possibility that one or more other features or elements may be added.

In this specification, when an embodiment is otherwise embodied, a specific process sequence may be performed differently from the described sequence. For example, two processes described in succession may be performed substantially simultaneously, or may be performed in an order reverse to the order described.

In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, since the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, the present invention is not necessarily limited to the illustrated bar.

1 is a flowchart schematically illustrating a method for manufacturing a negative electrode for a lithium battery according to an embodiment of the present invention.

Referring to FIG. 1, a method for manufacturing a negative electrode for a lithium battery according to an embodiment of the present invention includes heat-treating iron powder (S110), treating the iron powder with fluorine (S120), and forming a liquid lithium-iron powder mixture. Step S130, forming a negative electrode sheet (S140), and forming a negative electrode for a lithium battery (Step 2150) are included.

In the step of heat-treating the iron powder (S110), the iron powder may be placed in a reactor and subjected to heat treatment. The iron powder may be any one of a flake type, a sheet type, a fiber type, a fabric type, a porous body type, and a mixture thereof.

In the heat treatment of the iron powder, the temperature in the reactor may be from room temperature to about 50 °C. Room temperature in the present specification may be about 20 ℃. When the iron powder is heat-treated at a temperature lower than room temperature, moisture contained in the iron powder may not be sufficiently removed. The higher the heat treatment temperature, the easier it is to remove the moisture contained in the iron powder, but the amount of moisture contained in the iron powder heat-treated at a temperature exceeding 50 ° C. invisible

Prior to the heat treatment of the iron powder (S110), the step of injecting an inert gas into the reactor and the step of discharging the inert gas from the reactor may further be included.

The inert gas may be a stable material that does not chemically react with iron powder, such as nitrogen (N ₂ ), helium (He), neon (Ne), argon (Ar), or a mixed gas thereof. In the step of injecting the inert gas and the step of discharging the inert gas, the pressure change rate of the reactor may be 0.01 to 0.2 bar/min. If the pressure change rate in the reactor exceeds 0.2 bar/min, the iron powder may be scattered and it may be difficult to collect the iron powder. If the pressure change rate is less than 0.01 bar/min, the process time may increase unnecessarily.

At this time, after the inert gas is discharged, the pressure of the reactor may be lower than atmospheric pressure. By discharging the inert gas so that the pressure in the reactor is lower than atmospheric pressure, moisture and impurities in the reactor can be sufficiently discharged to minimize unintended side reactions. The step of injecting the inert gas and the step of discharging the inert gas may be repeatedly performed a plurality of times.

In the step of treating iron powder with fluorine (S120), fluorine gas may be injected into a reactor carrying the heat-treated iron powder. Fluorine gas is fluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), carbon tetrafluoride (CF ₄ ), carbon trifluoride (CHF ₃ ), carbon octafluoride (C ₃ F ₈ ), carbon octafluoride (C ₄ F ₈ ) and mixtures thereof.

The pressure of the fluorine gas injected into the reactor may be about 0.1 bar to about 3.0 bar. When the pressure of the fluorine gas is less than about 0.1 bar, the adsorption point increases and a sufficient amount of fluorine functional groups may not be introduced into the iron powder. When the pressure of the fluorine gas exceeds 3.0 bar, the amount of fluorine functional groups introduced into the fluorine-treated iron powder does not show a significant difference from that of the fluorinated iron powder when the pressure of the fluorine gas is 3.0 bar.

In one embodiment, fluorine gas may be mixed with an inert gas and introduced into the reactor. The inert gas may be a stable material that does not chemically react with iron powder, such as nitrogen (N ₂ ), helium (He), neon (Ne), argon (Ar), or a mixed gas thereof. When the fluorine gas and the inert gas are mixed and injected into the reactor, the partial pressure of the fluorine gas injected into the reactor may be about 0.1 bar to about 3.0 bar.

When fluorine gas or a mixed gas of fluorine gas and an inert gas is injected into the reactor, a pressure change rate in the reactor may be about 0.01 bar/min to about 0.2 bar/min. If the pressure change rate in the reactor exceeds 0.2 bar/min, the iron powder may be scattered and it may be difficult to collect the iron powder. If the pressure change rate is less than 0.01 bar/min, the process time may increase unnecessarily.

In the step of treating the iron powder with fluorine (S120), the temperature of the reactor may be maintained at room temperature to about 100 °C. When the temperature of the reactor is below room temperature, the adsorption point increases and a sufficient amount of fluorine functional groups may not be introduced into the iron powder. When the reactor temperature exceeds 100 °C, the characteristics of the fluorinated iron powder do not show a significant difference from those of the fluorinated iron powder when the temperature of the reactor is 100 °C.

Fluorine treatment of the iron powder can be performed for about 24 hours to about 48 hours. If the fluorine treatment time of the iron powder is less than 24 hours, a sufficient amount of fluorine functional groups may not be introduced into the iron powder. If the treatment time of iron powder with fluorine exceeds 48 hours, unintended side reactions may occur.

In the step of forming the liquid lithium-iron powder mixture (S130), the molten liquid lithium may be mixed with the fluorine-treated iron powder. In one embodiment, liquid lithium and fluorinated iron powder may be mixed in a stirrer.

In this case, the mass of the fluorine-treated iron powder may be about 10% to about 25% of the mass of the liquid lithium. When the mass of the fluorine-treated iron powder is less than 10% of the mass of the liquid lithium, the aggregated iron powder cannot function as a support layer supporting the liquid lithium. When the mass of the fluorine-treated iron powder exceeds 25% of the mass of liquid lithium, the iron powder hinders the movement of lithium, and thus the performance of the lithium battery may deteriorate.

A temperature at which the liquid lithium and the fluorine-treated iron powder are mixed may be about 200 °C to about 400 °C. When mixing at a temperature of less than 200 ° C., lithium is not sufficiently melted, and the flowability of lithium is low, so mixing may be difficult. When mixed at a temperature exceeding 400 ° C., desorption of fluorine may occur in the fluorine-treated iron powder.

In the step of forming the negative electrode sheet ( S140 ), the negative electrode sheet may be formed by rolling the liquid lithium-iron powder mixture on a heating plate.

In one embodiment, the mold for rolling the liquid lithium-iron powder mixture may include one or more of graphite, magnesium oxide, yttrium oxide and boron nitride. The mold may be heated to prevent the liquid lithium-iron powder mixture from cooling and nitriding.

Then, in the step of forming a negative electrode for a lithium battery (S150), the negative electrode for a lithium battery may be formed by molding the negative electrode sheet.

2a is a photograph of a liquid lithium-iron powder mixture prepared according to a comparative example, and FIG. 2b is a photograph of a liquid lithium-iron powder mixture prepared according to an experimental example.

As an experimental example, first, the process of injecting and exhausting nitrogen gas into the reactor was performed three times. The pressure change rate of the reactor during injection and exhaust of nitrogen gas was 0.2 bar/min, and the pressure of the reactor after nitrogen gas was exhausted became 0.5 bar. Thereafter, the temperature of the reactor in which the iron powder was seated was raised to 50° C., and heat treatment was performed for 1 hour. Fluorine treatment was performed at room temperature by injecting fluorine gas into the heat-treated iron powder. At this time, the pressure of fluorine gas in the reactor was maintained at 1.2 bar. Fluorinated iron powder and molten liquid lithium were mixed in an inert atmosphere in a glove box. At this time, the temperature was maintained at 300° C., and the mass of the fluorine-treated iron powder was mixed to be 12% of the mass of the liquid lithium.

As a comparative example, a liquid lithium-iron powder mixture was prepared without fluorine treatment on the same iron powder as the iron powder used in the experimental example. Iron powder and molten liquid lithium were mixed in an inert atmosphere in a glove box. At this time, the temperature was maintained at 300 °C, and the mass of the iron powder was mixed to be 12% of the mass of the liquid lithium.

So far, only the method for manufacturing a negative electrode for a lithium battery has been mainly described, but the present invention is not limited thereto. For example, a negative electrode for a lithium battery manufactured using the method for manufacturing a negative electrode for a lithium battery and a lithium battery including the same will also fall within the scope of the present invention.

Referring to FIG. 2A, when the liquid lithium-iron powder mixture according to the comparative example is cooled to form an ingot, only lithium exists in area A, and iron powder is separated from liquid lithium and aggregated in area B. can confirm that The Gibbs free energy of pure iron powder is positive, making it very difficult to mix with liquid lithium.

On the other hand, referring to FIG. 2B , when an ingot is formed by cooling the liquid lithium-iron powder mixture according to the experimental example, it can be confirmed that the fluorine-treated iron powder is evenly dispersed in the liquid lithium. This is because the Gibbs free energy of the iron powder has a negative value due to the fluorine functional group introduced to the surface of the iron powder, so that the iron powder can spontaneously mix with the liquid lithium. The fluorine-treated iron powder and liquid lithium are mixed within a few seconds, and the mixing process time, which previously required 3 hours or more, can be reduced to within a few minutes. In addition, due to excellent wettability between liquid lithium and fluorine-treated iron powder, the iron powder can be homogeneously dispersed in liquid lithium as shown in FIG. 2B.

)를 표시하고 있다.Table 1 below shows the Gibbs free energy according to the surface functional groups of liquid lithium and metal powder (

) is displayed.

[Table 1]

Referring to Table 1, the iron powder having a fluorine functional group according to an embodiment of the present invention has a negative Gibbs free energy of -11.74 eV upon reaction with liquid lithium. This is a value close to twice the Gibbs free energy (-6.51 eV) of the NiO functional group known to have excellent wettability when mixed with conventional liquid lithium, and can dramatically improve the homogeneity of the liquid lithium-iron powder mixture.

In addition, the fluorine functional group introduced to the surface of the iron powder reacts with liquid lithium after the initial mixing process to generate lithium fluoride (LiF), and the surface tension of liquid lithium to which fluorine, a heterogeneous element, is added may be further lowered. Accordingly, the fluorine-treated iron powder may be more evenly dispersed in liquid lithium having a lowered surface tension.

3 is a diagram schematically illustrating a lithium battery manufactured according to an embodiment of the present invention. 3 is for schematically illustrating the operation of a lithium battery, and the structure of the lithium battery according to the present invention is not limited thereto. The lithium battery according to the present invention may be a primary battery, a secondary battery, and a thermal battery, and may have various known structures.

Referring to FIG. 3 , a lithium battery including a negative electrode for a lithium battery manufactured according to an embodiment of the present invention may include a negative electrode 10 , an electrolyte 20 and a positive electrode 30 .

The negative electrode 10 may be manufactured according to the method for manufacturing a negative electrode for a lithium battery described above.

Electrolyte 20 may include a lithium salt. Wherein the lithium salt is LiCl, LiBr, LiI, LiC10 ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ S0 ₃ , LiCF ₃ C0 ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ S0 ₃ Li, CF ₃ S0 ₃ Li, LiSCN, LiC(CF ₃ S0 ₂ ) ₃ , (CF ₃ S0 ₂ ) ₂ NLi, (FS0 ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenyl borate lithium and their It may include any one or more of the combinations, but is not limited thereto. In one embodiment, the electrolyte 20 may be a solid electrolyte dissolved by heat. In another embodiment, the electrolyte 20 may be a liquid electrolyte including an organic solvent for dissolving the above-described lithium salt. In another embodiment, the electrolyte 20 may be a gel type electrolyte. The electrolyte 20 may further include additives to improve lifespan and stability of the lithium battery.

The positive electrode 30 may include a material known as a positive electrode material for a lithium battery without limitation. For example, the positive electrode 30 may include at least one of a lithium-phosphate-iron compound, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium copper oxide, a lithium nickel-based oxide, a lithium manganese composite oxide, and a lithium-nickel or manganese-cobalt-based oxide. It may include one or more, but is not limited thereto.

In the negative electrode 10 for a lithium battery manufactured by the manufacturing method according to an embodiment of the present invention, in the process of mixing liquid lithium and fluorine-treated iron powder, a part of the liquid lithium is doped with fluorine, resulting in a small amount of fluorination on the surface. It may contain lithium (LiF). Accordingly, when the negative electrode 10 is discharged, lithium ions in lithium fluoride are oxidized, and fluorine may be ionized at the interface between the negative electrode 10 and the electrolyte 20 . Ionized fluorine can react with the electrolyte 20 to quickly form a solid electrolyte interphase (SEI). The lithium fluoride solid electrolyte interface on the surface of the negative electrode 10 suppresses the generation of lithium dendrite and dead lithium during charging and discharging of the lithium battery, thereby improving coulumic efficiency and cycle characteristics. can Thus, the lifetime of the lithium battery can be increased.

4 to 6 are graphs showing Li oxidation-reduction voltage contrast (vs. Li/Li ⁺ ) according to charge/discharge current density of symmetric cell-type lithium batteries according to Experimental Examples and Comparative Examples.

As an experimental example, a negative electrode for a lithium battery was formed using the liquid lithium-iron powder mixture shown in FIG. 2B, and a symmetric cell-type lithium battery including the negative electrode was manufactured. As a comparative example, a negative electrode for a lithium battery was formed using pure lithium, and a symmetric cell-type lithium battery including the negative electrode was manufactured. The charge/discharge current density was changed to 0.2 mA/cm ^{2 ,} 0.5 mA/cm ² and 1.0 mA/cm ^{2 for} each lithium battery, and a charge/discharge test was performed.

4 to 6, the lithium battery according to the experimental example was first shorted at a charge/discharge current density of 0.2 mA/cm ² , but at a charge/discharge current density of 0.5 mA/cm ² and 1.0 mA/cm ² It was confirmed that the lithium battery according to is more stable than the lithium battery according to Comparative Example. In addition, it was confirmed that the charge and discharge time of the lithium battery according to the experimental example was also increased compared to the charge and discharge time of the lithium battery according to the comparative example.

Under all charge and discharge current density conditions, it was confirmed that the polarization characteristics of the negative electrode for a lithium battery according to Experimental Example were higher than those of the negative electrode for a lithium battery according to Comparative Example. Accordingly, a lithium battery including a negative electrode for a lithium battery manufactured according to embodiments of the present invention has improved charge/discharge performance and low resistance, so that power density and battery efficiency can be improved.

7 is a graph showing the Li redox voltage comparison (vs. Li/Li ⁺ ) when the charge/discharge current density of lithium batteries according to Experimental Examples and Comparative Examples is 0.2 mA/cm ² . FIG. 7 shows a result of calculating a nucleation energy barrier based on the charge/discharge test results of FIG. 4 .

Referring to FIG. 7 , at a charge/discharge current density of 0.2 mA/cm ² , the lithium battery according to Comparative Example had a nucleation energy barrier of 37.3 mV, and the lithium battery according to Experimental Example had a nucleation energy barrier of 33.1 mV. It was confirmed that the nucleation energy barrier of the lithium battery according to the Experimental Example decreased by 4.2 mV compared to the Comparative Example.

Therefore, in the lithium battery including the negative electrode for a lithium battery manufactured according to the embodiments of the present invention, the possibility of generating lithium dendrites during charging and discharging is reduced, and thus the lifespan of the battery may be improved.

8 is a graph showing a nucleation energy barrier according to charge/discharge current density of lithium batteries according to Experimental Examples and Comparative Examples. FIG. 8 shows nucleation energy barriers of lithium batteries according to Experimental Examples and Comparative Examples when charge/discharge current densities are 0.2 mA/cm ^{2 ,} 0.5 mA/cm ² , and 1.0 mA/cm ² .

Referring to FIG. 8 , it was confirmed that the lithium battery according to Experimental Example had a lower nucleation energy barrier than the lithium battery according to Comparative Example at all charge and discharge current densities. In addition, it was confirmed that the difference in nucleation energy barrier between the lithium battery according to the experimental example and the lithium battery according to the comparative example increased as the charge/discharge current density increased.

Therefore, in an environment where a lithium battery is charged and discharged in a high charge/discharge current density environment, a lithium battery including a negative electrode for a lithium battery manufactured according to embodiments of the present invention may have a longer lifespan and higher charge/discharge efficiency. there is.

9 is a scanning electron microscope (SEM) photograph of the surface of a negative electrode after a charge-discharge test of a symmetric cell-type lithium battery according to a comparative example, and FIG. This is an electron microscope picture.

Referring to FIG. 9 , it was confirmed that lithium dendrites were formed on the surface of the negative electrode of the lithium battery according to the comparative example. These dendrites may grow around the lithium nucleus and damage the separator separating the positive electrode and the negative electrode. If the separator is damaged, a short circuit may occur in the lithium battery. Alternatively, due to dendrites, current inside the battery rapidly increases, causing fire or explosion in the lithium battery.

Referring to FIG. 10 , it can be seen that no lithium dendrites are formed on the surface of the anode of the lithium battery according to the Experimental Example. As described above, in the process of mixing the fluorine-treated iron powder and liquid lithium, a portion of lithium is doped with fluorine, and a small amount of lithium fluoride is present on the surface of the negative electrode for a lithium battery according to the experimental example. During charging and discharging of the lithium battery, ionized fluorine forms a lithium fluoride solid electrolyte interface (LiF SEI) at the interface between the anode for the lithium battery and the electrolyte, which can suppress the generation of lithium dendrites.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

10: negative electrode for lithium battery
20: anode
30: electrolyte

Claims (14)

Placing iron powder in a reactor and heat-treating the iron powder;
Injecting fluorine gas into the reactor to treat the heat-treated iron powder with fluorine;
mixing the fluorine treated iron powder with liquid lithium to form a liquid lithium-iron powder mixture;
forming a negative electrode sheet by rolling the liquid lithium-iron powder mixture; and
Forming a negative electrode for a lithium battery by molding the negative electrode sheet; Including,
In the step of forming the liquid lithium-iron powder mixture, at least some of the fluorine functional groups introduced to the surface of the fluorine-treated iron powder react with the liquid lithium to produce lithium fluoride. Method for producing a negative electrode for a lithium battery. According to claim 1,
Prior to the heat treatment of the iron powder,
Injecting an inert gas into the reactor; and
Discharging the inert gas from the reactor; further comprising a method for producing a negative electrode for a lithium battery. According to claim 2,
In the step of injecting the inert gas and discharging the inert gas,
The pressure change rate of the reactor is 0.01 to 0.2 bar / min, a method for producing a negative electrode for a lithium battery. According to claim 2,
The step of discharging the inert gas,
Method for producing a negative electrode for a lithium battery, in which the inert gas is discharged so that the pressure of the reactor is less than atmospheric pressure. According to claim 1,
In the step of heat-treating the iron powder, the temperature in the reactor is 20 ° C to 50 ° C, a method for producing a negative electrode for a lithium battery. According to claim 1,
In the step of fluorine treating the heat-treated iron powder,
The pressure change rate of the reactor is 0.01 to 0.2 bar / min, a method for producing a negative electrode for a lithium battery. According to claim 1,
In the step of fluorine treating the heat-treated iron powder,
The pressure of the fluorine gas in the reactor is 0.1 bar to 3.0 bar, a method for producing a negative electrode for a lithium battery. According to claim 1,
The fluorine gas is fluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), carbon tetrafluoride (CF ₄ ), carbon trifluoride (CHF ₃ ), carbon octafluoride (C ₃ F ₈ ), carbon octafluoride (C ₄ F ₈ ) and a method for producing a negative electrode for a lithium battery comprising any one of mixtures thereof. According to claim 1,
In the step of fluorine treating the heat-treated iron powder,
The fluorine gas is mixed with an inert gas and injected,
At this time, the partial pressure of the fluorine gas in the reactor is 0.1 bar to 3.0 bar, a method for producing a negative electrode for a lithium battery. According to claim 1,
In the step of fluorine treating the heat-treated iron powder,
The temperature in the reactor is 20 ℃ to 100 ℃ method for producing a negative electrode for a lithium battery. According to claim 1,
In the step of fluorine treating the heat-treated iron powder,
A method for producing a negative electrode for a lithium battery in which the fluorine treatment is performed for 24 to 48 hours. According to claim 1,
In forming the liquid lithium-iron powder mixture,
The mass of the fluorine-treated iron powder is 10% to 25% of the mass of the liquid lithium. According to claim 1,
In forming the liquid lithium-iron powder mixture,
The temperature in the mixing vessel is 200 ℃ to 400 ℃ method for producing a negative electrode for a lithium battery. A lithium battery comprising the negative electrode for a lithium battery manufactured according to any one of claims 1 to 13.

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