KR20220057059A - Lithium Alloy Anode For Lithium Metal Battery And Manufacturing Methods Thereof - Google Patents

Abstract

The present invention relates to a lithium alloy negative electrode of a lithium secondary battery. The present invention relates provides a negative electrode for a lithium secondary battery, which includes an xLi-yIn alloy (wherein, x is the molar ratio of Li in the alloy, y is the molar ratio of In in the alloy, x>0, y>0, x+y<=1), and the x/y is more than 1.5.

Description

Lithium Alloy Anode For Lithium Metal Battery And Manufacturing Methods Thereof

The present invention relates to a negative electrode of a lithium metal battery or a lithium all-solid-state battery, and more particularly, to a lithium alloy negative electrode of a lithium metal battery or a lithium all-solid-state battery.

A lithium secondary battery is largely composed of a positive electrode, an electrolyte, and a negative electrode. A commonly commercialized lithium secondary battery has a structure in which a polymer separator with a thickness of 15 to 25 μm is added in a liquid electrolyte composed of an organic solvent ^and lithium salt. The generated electrons also move from the cathode to the anode, and vice versa during charging. The driving force of such Li ⁺ ion migration is generated by chemical stability according to the potential difference between the two electrodes. The amount of Li ⁺ ions moving from the negative electrode to the positive electrode and from the positive electrode to the negative electrode determines the capacity (Ah) of the battery.

A lithium metal battery is a battery that uses metallic lithium or lithium alloy as an anode material and a non-aqueous solvent as an electrolyte. Since lithium has a low standard reduction potential, high voltage expression is possible when combined with a positive electrode, so batteries with high energy density are being developed. At this time, as the negative electrode, a lithium electrode such as lithium foil is attached to the current collector and used. When the battery is driven, non-uniform current distribution is induced on the surface of the negative electrode, so lithium is electrodeposited only on a specific part of the negative electrode, so lithium is a dendritic precipitate. There is a problem in that the growth of dendrites occurs excessively, thereby deteriorating the lifespan characteristics of the battery.

To solve this problem, a method of optimizing the electrolyte composition and additives to control the composition of the surface film SEI (solid electrolyte interphase), a method of applying a protective film to improve mechanical properties, and lithium dendrite through surface modification of the separator Methods such as inhibiting growth, inhibiting lithium dendrite growth by securing mechanical properties with an organic-inorganic composite protective film, and introducing metal-based or CNT-based three-dimensional porous structures to reduce local effective current density There have been attempts

On the other hand, in lithium all-solid-state batteries, recent attempts have been made to use an In-Li alloy with a high molar ratio of lithium as an anode. . According to this method, it is possible to obtain excellent lifespan characteristics due to improved interfacial stability while having almost the same voltage as compared to a battery using only lithium. However, when an In-Li alloy with a low molar ratio of In or lithium is used as the negative electrode, the lifespan characteristics are improved due to the improvement of interfacial stability, but there is a disadvantage in that the energy density is decreased due to the potential loss (~0.6V) due to In.

(1) Korean Patent Publication No. 2020-50560 A

In order to solve the problems of the prior art, an object of the present invention is to provide an indium alloy anode for a lithium metal battery or a lithium all-solid-state battery that improves interfacial stability with an electrolyte and suppresses dendritic growth of lithium.

Another object of the present invention is to provide an indium alloy negative electrode for a lithium metal battery or a lithium all-solid-state battery having high interfacial stability while minimizing potential loss due to In.

Another object of the present invention is to provide a lithium metal battery having the above-described indium alloy negative electrode.

Another object of the present invention is to provide an all-solid lithium metal battery having the above-described indium alloy negative electrode.

Another object of the present invention is to provide a method for manufacturing the above-described lithium metal battery or an indium alloy negative electrode for a lithium all-solid-state battery.

The present invention in order to achieve the above technical problem, in the negative electrode for a lithium secondary battery, the negative electrode is an xLi-yIn alloy (where x is the molar ratio of Li in the alloy, y is the molar ratio of In in the alloy, x>0, y> 0, x+y≤1), and provides a negative electrode for a lithium secondary battery, characterized in that x/y>1.5.

In the present invention, x and y may satisfy the following relationship, that is, 1.5 < x/y < 4.3. Also, x and y may satisfy the relation of x/y ≥ 4.3. At this time, it is preferable that x/y ≤ 12.

Also, in the present invention, the xLi-yIn alloy may include an InLi ₃ phase or an In ₃ Li ₁₃ phase. In addition, the xLi-yIn alloy may include an In ₃ Li ₁₃ phase and a Li phase.

In the present invention, the alloy of the negative electrode comprises at least one third element selected from the group consisting of Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn and La. may include more. In this case, it is preferable that the molar ratio z of the third element in the negative electrode is z/(x+y+z) < 0.1.

In order to achieve the above other technical problem, the present invention provides a Li powder and an In powder x: y (where x and y are the molar ratios of Li and In in the alloy, respectively, x>0, y>0, x+y≤1 , x/y>1.5) mixing in a molar ratio; And it provides a method of manufacturing a negative electrode for a lithium secondary battery comprising the step of molding the mixed mixture.

In the present invention, x and y may satisfy the relation of 1.5 < x/y < 4.3 or satisfy the relation of x/y ≥ 4.3.

In addition, the present invention may further include the step of alloying the molded mixture by heat treatment in an inert gas atmosphere.

According to the present invention, it is possible to provide an indium alloy negative electrode for a lithium metal battery or a lithium all-solid-state battery that improves interfacial stability with the electrolyte and suppresses dendrite growth of lithium.

In addition, according to the present invention, it is possible to provide an indium alloy negative electrode for a lithium metal battery or a lithium all-solid-state battery having high interfacial stability while minimizing potential loss due to In.

Further, according to the present invention, it is possible to provide a lithium metal battery or a lithium all-solid-state battery having an indium alloy negative electrode by mixing the powder without using a method such as electrodeposition or deposition.

1 is a Li-In binary phase equilibrium diagram.
FIG. 2 is a graph illustrating voltage-capacity characteristics measured according to the progress of electrochemical lithium lithiation into In.
3A to 3D are electron micrographs of the surface state of the working electrode manufactured according to an embodiment of the present invention.
4A to 4C are electron micrographs of cross-sections of the tested working electrodes.
5A and 5B are graphs of measuring capacity characteristics and cycle characteristics of an all-solid-state battery cell manufactured according to an embodiment of the present invention, respectively.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the drawings.

The present invention provides a lithium metal battery using a metal or metal alloy capable of inserting Li as an anode material. The characteristics of the negative electrode required in the present invention will be described with reference to the drawings.

1 is a Li-In binary phase equilibrium diagram. This phase equilibrium diagram is published in "Phase equilibria and thermodynamic investigation of the In-Li system" (Computer Coupling of Phase Diagrams and Thermochemistry 70 (2020) 101779).

1 shows a phase equilibrium diagram of a high temperature region of 400 K or higher. In the region rich in Li near this temperature, it can be seen that In ₄ Li ₅ , In ₂ Li ₃ , LnLi ₂ , InLi ₃ , In ₃ Li ₁₃ and Li phases exist as the content of Li increases. Although FIG. 1 shows a phase near 400 K and omits a phase at room temperature, each phase line in each composition may extend to room temperature. That is, in the Li-rich region near room temperature, In ₄ Li ₅ , In ₂ Li ₃ , InLi ₂ , InLi ₃ , In ₃ Li ₁₃ , and Li phases may exist as stable or metastable phases. In these listed phases, two or more phases may coexist, and in this case, the fraction of each phase in the thermodynamic equilibrium may be determined by a lever rule according to the fraction of Li.

Conventionally, a Li-In alloy having a low Li content has been used due to the instability of Li at the interface in contact with the electrolyte. However, alloys with low Li content lead to significant dislocation losses. The negative electrode of the present invention has a high Li content, preferably a Li-In alloy having a composition in a region in which the mole fraction of Li, that is, the mole fraction of Li with respect to the total of Li and In, is 0.5 or more, and exhibits high interfacial stability. .

FIG. 2 is a graph illustrating voltage-capacity characteristics measured according to the progress of electrochemical lithium lithiation into In.

This test was performed using lithium as a counter/reference electrode, In as a working electrode, and 1M LiTFSI in DOL/DME + 1wt% LiNO ₃ as an electrolyte. For maximum lithium lithiation, an additional 1 mAh/cm ² of lithium was additionally inserted at a voltage below 0V. After the working electrode was collected, SEM analysis was performed.

Referring to FIG. 2 , the state of the working electrode is largely divided into five sections according to the degree of lithium insertion. The alloy composition of each section is as follows.

In the section a, an InLi phase starts to be generated in In, and the In phase and the InLi phase may coexist. This section is a section in which a voltage that is about 0.55-0.6 V lower than that of the lithium counter electrode can be realized.

In section b, an InLi single phase may be present. This section is a section in which a voltage 0.35 to 0.55 V lower than that of the lithium counter electrode can be realized.

In section c, the InLi phase and the In ₄ Li ₅ phase may coexist. This section is a section in which a voltage 0.3V to 0.35V lower than that of the lithium counter electrode can be realized.

In section d, one of the In ₄ Li ₅ , In ₂ Li ₃ , and In ₃ Li ₁₃ phases may exist, or two or more phases may coexist. At the end of this section, an In ₃ Li ₁₃ compound corresponding to the solid solution limit of Li, which is the solid solution limit, is generated. This section is a section in which a voltage 0.03 V lower than that of the lithium counter electrode can be realized.

In section e, the In ₃ Li ₁₃ phase and the Li phase may coexist. In this section, lithium starts to precipitate out of the solid solution limit into the Li phase, and the same voltage as that of the lithium counter electrode can be realized. The photo on the right of FIG. 2 is an optical micrograph of the sample recovered in section e.

Each of the above-described sections may be expressed as a ratio of the mole fraction (x) of Li and the mole fraction (y) of In in the lithium alloy expressed as xLi-yIn, and the ratio (x/y) in each section is as follows.

- Interval a : x/y < 1

- Section b : x/y ~ 1

- Interval c : 1.0 < x/y ≤ 1.125

- Interval d : 1.125 ≤ x/y ≤ 4.33

- Interval e: 4.33 < x/y

3A to 3D are electron micrographs of the tested working electrode surfaces.

First, FIG. 3A is a photograph of the surface state of In before lithium insertion, and the upper and lower portions are photographs taken at different magnifications, respectively. It shows that the surface of the indium metal is maintained in a smooth state before lithium insertion.

Next, FIG. 3b is an electron micrograph of the surface of the working electrode in a fully inserted state corresponding to section d, and FIG. 3c is an electron micrograph of the surface of a state in which lithium of 1 mA/cm ² is inserted in excess. . As can be seen from FIGS. 3B and 3C , it can be seen that curves were formed on the surface in the fully-inserted state or over-inserted state of lithium, and no dendrite-like shape was found.

4a to 4c are electron micrographs of cross-sections of the tested working electrodes, respectively, corresponding to lithium before (Presstine In), fully inserted (Full Li plating), and over inserted (Full Li plating+1mAh) state, respectively. do.

From FIGS. 4A to 4C , it can be confirmed that even when lithium is sufficiently inserted into In and additional lithium is added, only the thickness is increased due to alloying, lithium dendrites are not seen on the surface, and surface undulations are formed. Through this, it can be confirmed that even when lithium is sufficiently stored in the indium base, lithium dendrites are not formed.

The lithium metal battery or lithium all-solid-state battery of the present invention uses a metal material including alloyed lithium or lithium added as a mixture as an anode. The negative electrode material may be provided in the form of a lithium-indium alloy or a lithium-indium metal mixture.

In the present invention, Li and In in the negative electrode alloy or negative electrode mixture are xLi-yIn (where x is the molar ratio of Li in the alloy, y is the molar ratio of In in the alloy, x>0, y>0, x+y≤1) It may be expressed as , preferably x/y > 1.5, 1.5 < x/y < 4.3 or x/y > 4.3.

In addition, the present invention further comprises at least one third element selected from the group consisting of Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn and La as a cathode. may include In this case, it is preferable that the molar ratio z of the third element in the negative electrode is z/(x+y+z) < 0.1.

Meanwhile, as the positive electrode active material in the present invention, a conventional positive electrode active material used in an all-solid-state battery may be used. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or LiNi _x Co _y MnzO ₂ (where x, y, z are composition ratios; hereinafter referred to as NCM), such as LiMO ₂ (herein, M is a metal) layered oxide system represented by , LiFePO ₄ such as LiMPO ₄ (where M is a metal) olivine-based, LiMn ₂ O ₄ such as LiM ₂ O ₄ spinel-based composite metal chalcogen (chalcogen) compounds are represented, and these compounds are exemplified. A cogen compound may be mixed as needed.

In addition, as the positive electrode binder in the present invention, a fluorine-containing binder such as PTFE or PVDF may be used.

In addition, in the present invention, as the cathode conductive material, carbon black (CB), conductive graphite, ethylene black, carbonized carbon fiber (Vertically-aligned Carbon Fiber), and carbon nanotubes (carbon) nanotube, CNT) may be used.

The electrolyte usable in the present invention may be a solid electrolyte or a liquid electrolyte. As the solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof may be used.

The oxide-based solid electrolyte may be lithium oxide having a perovskite structure represented by LiBO ₃ . For example, the oxide of the perovskite structure may include Li _3x La _2/3-x TiO ₂ . In addition, as the oxide-based solid electrolyte, lithium oxide having a garnet structure may be used. For example, Li ₅ LaB′ ₂ O ₁₂ (where B′ is at least one element selected from the group consisting of Bi, Sb, Na and Ta) or Li ₇ La ₃ B″ ₂ O ₁₂ (where B″ is Zr, at least one element consisting of Hf and Sn) may be used. LLZO represented by Li ₇ La ₃ Zr ₂ O ₁₂ in the present invention has high thermal stability. In addition, as the solid electrolyte, LiM ₂ (PO ₄ ) (where M is one element selected from the group consisting of Ti, Ge, and Ge) LISICON, Li _1+x M _2-x M' _x (PO4) _{3 (} where x≥0, M is at least one element selected from the group consisting of Ti, Ge, and Hf, and M' is at least one element selected from the group consisting of Al, B and Sn) element) may be used.

Examples of the sulfide solid electrolyte include a combination of Li ₂ S with Al ₂ S ₃ , SiS ₂ , GeS ₂ , P ₂ S ₃ , P ₂ S ₅ , As ₂ S ₃ , Sb ₂ S ₃ or a mixture thereof. That is, as the sulfide solid electrolyte material, Li ₂ S-Al ₂ S ₃ material, Li ₂ S-SiS ₂ material, Li ₂ S-GeS ₂ material, Li ₂ SP ₂ S ₃ material, Li ₂ SP ₂ S ₅ material, Li ₂ S-As ₂ S ₃ material, Li ₂ S-Sb ₂ S ₃ material, and Li ₂ S-material are mentioned, and Li ₂ SP ₂ S ₅ material is particularly preferable.

In addition, Li ₃ PO ₄ , halogen, or a halogen compound may be added to these solid electrolyte materials to be used as a solid electrolyte material. For example, Li ₂ SP ₂ S ₅ -LiX-based compound (wherein X is one selected from the group consisting of F, Cl, Br, I, Se, and Te), a compound represented by the following Chemical Formula 1, or combinations thereof can, but is not limited thereto.

<Example 1>

Lithium insertion was performed in In using lithium as a counter/reference electrode, In as a working electrode, and 1M LiTFSI in DOL/DME + 1wt% LiNO ₃ as an electrolyte. For maximum lithium intercalation (lithiation), an In-Li alloy was fabricated by additionally inserting 1 mAh/cm ² lithium at a voltage below 0V. In this way, an all-solid-state battery cell was manufactured using an In-Li alloy in a state of excess lithium in the electrochemical method. To fabricate the all-solid-state battery, Li ₆ PS ₅ Cl (LPSCl) was used as the solid electrolyte and LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (NCM622) + LPSCl composite was used as the positive electrode, and the cell was heated using a pressure cell. produced.

5A and 5B are graphs measuring the capacity characteristics and cycle characteristics of the prepared all-solid-state battery cells, respectively. It can be seen from FIGS. 5A and 5B that the voltage characteristic is greatly improved and the lifespan is also stably driven.

<Example 2>

Instead of the electrochemically prepared negative electrode of Example 1, an all-solid-state battery cell was prepared by mixing In powder:Li powder in a molar ratio of 1:5 to serve as the negative electrode. Other materials and manufacturing conditions of the positive electrode and the solid electrolyte were the same as in Example 1.

The prepared battery cell exhibited almost similar properties to those of Example 1. Therefore, it can be seen that the anode made of the non-alloyed Li-In mixture is easily alloyed by lithium intercalation during operation.

A method for manufacturing a Li-In anode using an electrochemical method and a mechanical mixing method has been described above. However, in the present invention, it is easy to see that the method of uniformly coating In on the lithium surface using equipment such as an evaporator or sputter, and a method of bonding In and Li foils in a molar ratio and then laminating them through compression can exhibit the same effect. can be inferred.

In addition, although the above-described embodiment exemplifies a case in which a simple metal mixture is used, the present invention is not limited thereto. For example, the metal mixture or alloy may be manufactured through a heat treatment process in a non-oxidizing atmosphere such as Ar atmosphere or an inert atmosphere at a temperature of 150 to 300°C. This is expected to enable more uniform alloying. On the other hand, although the present invention exemplifies the use of an anode of a Li-In binary metal or alloy, the present invention is applicable to other metals or metal compounds that have solubility with lithium and can form a solid solution in the same principle. It will be apparent to any person skilled in the art upon encountering the present invention.

As mentioned above, although the embodiment of the present invention has been described in detail, the scope of the present invention is not limited thereto, and various modifications and improvements that can be made by those skilled in the art using the basic concept of the present invention defined in the following claims In addition, it will be well understood that it falls within the scope of the present invention.

Claims (11)

In the negative electrode for a lithium secondary battery,
The negative electrode includes an xLi-yIn alloy (where x is the molar ratio of Li in the alloy, y is the molar ratio of In in the alloy, x>0, y>0, x+y≤1),
The negative electrode for a lithium secondary battery, characterized in that the x / y > 1.5. According to claim 1,
A negative electrode for a lithium secondary battery, characterized in that 1.5 < x / y < 4.3. According to claim 1,
A negative electrode for a lithium secondary battery, characterized in that x/y ≥ 4.3. According to claim 1,
The xLi-yIn alloy is an anode for a lithium secondary battery, characterized in that it comprises an InLi ₃ phase or an In ₃ Li ₁₃ phase. According to claim 1,
The xLi-yIn alloy is an anode for a lithium secondary battery, characterized in that it comprises an In ₃ Li ₁₃ phase and a Li phase. According to claim 1,
The alloy of the negative electrode further comprises at least one third element selected from the group consisting of Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, and La An anode for a lithium secondary battery, characterized in that it is an alloy. 7. The method of claim 6,
The anode for a lithium secondary battery, characterized in that the molar ratio z of the third element in the anode is z/(x+y+z) < 0.1. Li powder and In powder are mixed in a molar ratio of x: y (where x and y are the molar ratios of Li and In in the alloy, respectively, x>0, y>0, x+y≤1, x/y>1.5) step; and
A method of manufacturing a negative electrode for a lithium secondary battery comprising the step of molding a mixed mixture. 9. The method of claim 8,
1.5 < x/y < 4.3, characterized in that the manufacturing method of a negative electrode for a lithium secondary battery. 9. The method of claim 8,
A method of manufacturing a negative electrode for a lithium secondary battery, characterized in that x/y ≥ 4.3. 8. The method of claim 7,
Method of manufacturing a negative electrode for a lithium secondary battery, characterized in that it further comprises the step of alloying the molded mixture by heat treatment in an inert gas atmosphere.

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