WO2016064187A1 - Multi-layer structured lithium metal electrode and method for manufacturing same - Google Patents

Abstract

The present invention relates to a multi-layer structured lithium metal electrode and a method for manufacturing the same and, specifically, to a multi-layer structured lithium metal electrode comprising: a buffer layer of lithium nitride (Li₃N) formed on a lithium metal plate; and a protective layer of LiBON formed on the buffer layer, and to a method for manufacturing a multi-layer structured lithium metal electrode by continuously forming a lithium nitride buffer layer and a LiBON protective layer on a lithium metal plate through continuous reactive sputtering. The multi-layer structured lithium metal electrode of the present invention can protect the reactivity of the lithium metal from moisture or an environment within a battery, and prevent the formation of dendrites, by forming the protective layer. In addition, the formation of the buffer layer prevents the deterioration of ion conductivity, caused by an oxide layer formed on the lithium metal plate in the process of forming the protective layer.

Description

Lithium metal electrode of multi-layer structure and method of manufacturing same

The present invention relates to a lithium metal electrode having a multi-layer structure and a method of manufacturing the same, and more particularly, to form a buffer layer of lithium nitride (Li ₃ N) on a lithium metal plate, and to form a protective layer of LiBON on the buffer layer. The present invention relates to a method for producing a lithium metal electrode having a multilayer structure, wherein a lithium nitride buffer layer and a LiBON protective layer are successively formed on a lithium metal electrode having a multilayer structure and a lithium metal plate by reactive sputtering.

Starting with mobile phones, a variety of devices requiring batteries are being developed, ranging from wireless home appliances to electric vehicles. With the development of these devices, the demand for secondary batteries is also increasing. In particular, in addition to miniaturization of electronic products, secondary batteries are also becoming lighter and smaller.

In response to this trend, lithium metal secondary batteries (Lithium Metal Battery, LMB) has been in the spotlight. Lithium metal secondary batteries use lithium as a negative electrode. Lithium has a low density and low standard reduction potential of -3.04 V, which is light and has the advantage of producing high energy in secondary battery manufacturing.

Korean Unexamined Patent Publication No. 2013-0043117 discloses a lithium secondary battery using lithium metal oxides such as LiNiCoMnO ₂ , LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , and the like. Generally, lithium oxide is used as a negative electrode in a secondary battery because lithium metal is highly reactive. Lithium metal reacts with moisture in the air to produce by-products such as LiOH, Li ₂ O, Li ₂ CO _3, and the like. In addition, when a lithium metal used as an electrode is exposed to an electrolyte, a resistive material is produced, which significantly degrades the performance of the manufactured battery, and may cause an internal short circuit. In addition, since lithium is a very weak metal, handling is difficult and it is difficult to utilize it as an electrode.

Accordingly, the development of lithium metal electrodes that can solve the reactivity problem of lithium while improving energy efficiency using lithium metal and can simplify the process more.

[Preceding technical literature]

[Patent Documents]

Patent Document 1: Korean Patent Publication No. 2013-0043117 (Published: 2013.04.29)

An object of the present invention is to form a protective layer that can ensure the safety by preventing the violent reaction of moisture and lithium metal in the air during cell fabrication, the oxide is formed by the side reaction of oxygen and lithium in the process of forming the protective layer It is to provide a multi-layered lithium metal electrode having a buffer layer for preventing the ion conductivity is reduced.

An object of the present invention is to provide a method for producing an electrode having excellent processability by sequentially and successively forming a buffer layer and a protective layer on a lithium metal plate in the same chamber by a reactive sputtering method.

In order to achieve the above object, an aspect of the present invention is a lithium metal electrode of a multi-layer structure includes a protective layer consisting of a lithium nitride layer formed on the lithium metal plate and LiBON having a composition of the following formula (1):

LixBOyNz formula (1)

(The x is 0.9 to 3.51, y is 0.6 to 3.2, z is 0.5 to 1.0.)

In the lithium metal electrode of a multilayer structure according to an embodiment of the present invention, the buffer layer may be formed on one side or both sides of the lithium metal plate, and may be preferably formed on the side facing the electrolyte.

In one embodiment of the present invention, LiBON having a composition of Formula 1 is Li _{3 . 09} BO _{2 . 53 N 0 .52, Li 0.90 BO} 0.66 N 0.98, Li _3.51, or _3.03 N _0.52 BO, and the like, but not limited to these.

In one embodiment of the present invention, the thickness of the lithium metal plate may be 30 to 500㎛.

In one embodiment of the present invention, the thickness of the buffer layer lithium nitride layer may be 0.01 to 5㎛.

In one example of the present invention, the thickness of the protective layer LiBON layer may be 0.1 to 10㎛.

In one embodiment of the present invention, the method of manufacturing the lithium nitride buffer layer or LiBON protective layer is not particularly limited, and for example, a method selected from electron beam deposition, organometallic chemical vapor deposition, reactive sputtering, high frequency sputtering, and magnetron sputtering It can be formed as.

Another aspect of the present invention provides a method of manufacturing a lithium metal electrode of a multilayer structure by a reactive sputtering method comprising the following steps.

Providing a lithium metal plate in a vacuum chamber;

Forming a lithium nitride (Li ₃ N) thin film on one or both surfaces of the lithium metal plate by reactive sputtering; And

Forming a LiBON thin film having a composition of Chemical Formula 1 by reactive sputtering in a continuous manner to the lithium nitride thin film.

Another aspect of the present invention is a lithium secondary battery including a negative electrode, a positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode, a lithium secondary using a lithium electrode of a multi-layer structure according to the aspect of the present invention as the negative electrode Provide a battery.

The lithium metal electrode of the multi-layered structure of the present invention can form a protective layer to protect the lithium metal from moisture or reactivity in the battery environment and prevent dendrite formation. In addition, the oxide layer is formed on the lithium metal plate during the formation of the protective layer by the formation of the buffer layer to prevent the problem that the ion conductivity may be reduced.

1 is a schematic diagram of a lithium metal electrode of a multilayer structure according to an embodiment of the present invention.

2 is a flowchart of a method of manufacturing a lithium metal electrode of a multilayer structure according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. At this time, it is noted that the same components in the accompanying drawings are represented by the same reference numerals as possible. In addition, detailed descriptions of well-known functions and configurations that may blur the gist of the present invention will be omitted. For the same reason, in the accompanying drawings, some components are exaggerated, omitted or schematically illustrated.

1 is a view showing a lithium metal electrode of a multilayer structure according to an embodiment of the present invention.

Referring to FIG. 1, in the lithium metal electrode 1000 of the present invention, a buffer layer 1210 and a protective layer 1220 are formed on a lithium metal plate 1100. Although the buffer layer 1210 and the protective layer 1220 are formed on only one surface of the lithium metal plate 1100 in this drawing, both surfaces of the lithium metal plate 1100 may be formed.

In general, when lithium metal is used as a battery negative electrode, the following problems exist. First, lithium is an alkali metal and explosively reacts with water, making it difficult to manufacture and use in a general environment. Second, when lithium is used as a negative electrode, it forms a passivation layer by reacting with electrolyte, water, impurities in the battery, lithium salt, etc., and this layer causes a local current density difference to form dendritic lithium dendrite. . In addition, the dendrite thus formed may grow and cause an internal short circuit directly between the positive electrode and the void of the separator, thereby causing the battery to explode. Third, lithium is a soft metal and its mechanical strength is poor, making it very intractable for use without additional surface treatment.

Thus, in the present invention, by forming the buffer layer 1210 and the protective layer 1220, it is possible to prevent the formation of the passivation layer and the formation of dendrites and to reinforce the mechanical strength. In addition, the buffer layer 1210 blocks handling of the lithium metal in a battery manufacturing environment, thereby making it easier to handle and lowering ion conductivity.

The lithium metal plate 1100 uses a plate metal. The lithium metal plate may be adjusted in width depending on the shape of the electrode to facilitate the manufacture of the electrode. The thickness of the lithium metal plate may be 30 to 500 μm.

The buffer layer 1210 may be formed of lithium nitride (Li ₃ N), and may be formed on both the top and bottom surfaces of the lithium metal plate 1100 or on only one surface of the lithium metal plate 1100 that faces the electrolyte layer. When the buffer layer 1210 is not formed, lithium metal is oxidized in the process of forming the protective layer 1220 to expose to moisture in the air, thereby forming Li ₂ O, thereby lowering the ionic conductivity. Thus, in the present invention, forming the lithium nitride thin film is to prevent oxidation of the electrode rather than to improve battery performance. Therefore, the thickness of the lithium nitride layer is sufficient to be applied only enough to prevent the surface of the lithium electrode from being exposed to moisture or air to be oxidized, and if too thick, it causes an unnecessary increase in thickness of the electrode. May be μm.

The protective layer 1220 may be deposited on the surface of the buffer layer 1210 to prevent the lithium metal plate 1100 from being directly exposed to the electrolyte, thereby preventing the reaction between lithium and the electrolyte. In addition, since the protective layer 1220 of the present invention is made of LiBON and has conductivity, it is possible to smoothly transfer ions to the electrode, thereby increasing battery life and enhancing battery performance.

The LiBON may have a composition of Formula 1 below.

LixBOyNz formula (1)

(The x is 0.9 to 3.51, y is 0.6 to 3.2, z is 0.5 to 1.0.)

The LiBON is especially Li _{3 . 09} BO _{2 . 53} have the following composition when N _{0 .52} ionic conductivity up to 2.3 × 10 ^-6 S / cm, has been reported to exhibit excellent charge-discharge performance compared to conventional LiPON bar.

If the thickness of the protective layer 1220 is too thin, the protective effect on the environment of the moisture or the battery may not be sufficiently exhibited. On the contrary, if the thickness is too thick, relative capacity loss may occur due to unnecessary thickness increase. It may be formed to a thickness of μm.

The method of forming the lithium nitride thin film of the buffer layer 1210 and the LiBON thin film of the protective layer 1220 is not particularly limited. For example, electron beam deposition, organometallic chemical vapor deposition, reactive sputtering, high frequency sputtering, and magnetron sputtering Various vapor deposition methods may be used, but the present invention is not limited thereto. Each of the illustrated deposition methods is a well-known method, and thus a detailed description thereof is omitted herein.

The lithium metal electrode 1000 of the multilayer structure according to the present invention may have various widths and lengths depending on the shape of the battery. If necessary, the lithium metal electrode 1000 manufactured in various widths may be wound and cut if necessary.

2 is a flow chart of a method for manufacturing a lithium electrode of a multi-layer structure according to an embodiment of the present invention.

Referring to FIG. 2, first, a lithium metal electrode is provided in a vacuum chamber (S1).

The next step (S2) is a step of forming a lithium nitride (Li ₃ N) thin film on one or both sides of the lithium metal plate by nitrogen (N ₂ ) gas reactive sputtering method.

The next step (S3) is a step of forming a LiBON thin film having the composition of Chemical Formula 1 by reactive sputtering method while leaving the lithium metal plate on which the lithium nitride thin film is formed in the reaction chamber.

Here, reactive sputtering is a method of forming a thin film using DC power. To form a lithium nitride thin film, a lithium metal is mounted as a target and an argon gas is injected to generate a plasma, and nitrogen may be added as a reactive gas. . In addition, in order to form a LiBON thin film, a lithium metal plate coated with a lithium nitride thin film is targeted in the same vacuum chamber, and boron gas, oxygen gas, and nitrogen gas are added as a reactive gas. Each gas line can be equipped with a Mass Flow Controller (MFC) to control the gas. Only by controlling the amount of the reaction gas precisely, the stoichiometric ratio of the thin film can be matched.

One embodiment of the present invention includes a negative electrode, a positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode, the negative electrode provides a lithium secondary battery which is a lithium electrode of the multi-layer structure described above. Since the secondary battery of the present invention manufactures a negative electrode using lithium metal instead of lithium ions, a battery having a higher capacity and a higher energy density than a conventional secondary battery can be manufactured. In addition, by forming a buffer layer on the lithium metal plate before the cathode is manufactured, a protective layer can be formed on the lithium metal plate while preventing lithium from reacting with moisture in the air.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

( Example  One)

A lithium metal plate (thickness: 20 μm) was exposed to 0.1 Pa of nitrogen (N ₂ ) gas for 5 minutes in a vacuum chamber to form a lithium nitride (Li ₃ N) thin film (thickness: 0.02 μm) by the reactive sputtering method. continuously while still placed a lithium metal plate to form a thin film of lithium in the reaction chamber by reactive sputtering a target of Li ₂ BO ₃ method (reactive sputtering) as Li _{3. 09} BO _{2 . 53} N ₀ LiBON thin film having a composition of _0.52 (thickness: 0.2㎛) was formed. The lithium metal plate on which the coating layer thus prepared was formed was used as a negative electrode.

The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate (mixing volume ratio of EC / EMC = 1/1).

A symmetric cell of the prepared negative electrode was prepared.

The surface of the LiBON thin film prepared in Example 1 was observed with a scanning electron microscope (SEM) photograph, and the result is Korean Patent Application No. 10-2015-0145771 (Application date: October 20, 2015) 3 is shown in FIG.

( Example  2)

A symmetric cell was prepared in the same manner as in Example 1 except that the thickness of the lithium nitride (Li ₃ N) thin film was formed to 0.02 μm in Example 1.

( Example  3)

A symmetric cell was prepared in the same manner as in Example 1 except that the thickness of the lithium nitride (Li ₃ N) thin film was formed in 0.01 μm.

( Example  4)

A symmetric cell was prepared in the same manner as in Example 1 except that the thickness of the LiBON thin film was formed to 0.01 μm in Example 1.

( Example  5)

A symmetric cell was prepared in the same manner as in Example 1 except that the thickness of the LiBON thin film was set to 5 μm in Example 1.

( Example  6)

The LiBON thin film in Example 1 was Li _{0 . 9} BO _{0 . 66} N ₀ to _0.98, and the composition of the embodiment in the same manner as in Example 1, but formed to have a symmetrical cell was prepared.

( Example  7)

The LiBON thin film in Example 1 was Li _{3 . 51} BO _{3 . 03} N ₀ to _0.52, and the composition of the embodiment in the same manner as in Example 1, but formed to have a symmetrical cell was prepared.

( Comparative example  One)

A symmetric cell was prepared in the same manner as in Example 1 except that the lithium nitride (Li ₃ N) thin film and the LiBON thin film were not formed in Example 1.

( Comparative example  2)

A symmetric cell was prepared in the same manner as in Example 1 except that the LiBON thin film was not formed in Example 1.

( Comparative example  3)

A symmetric cell was prepared in the same manner as in Example 1 except that the lithium nitride (Li ₃ N) thin film was not formed in Example 1.

( Comparative example  4)

A lithium metal plate (thickness: 20 μm) was exposed to 0.1 Pa of nitrogen (N ₂ ) gas for 5 minutes in a vacuum chamber to form a lithium nitride (Li ₃ N) thin film (thickness: 0.02 μm) by the reactive sputtering method. continuously while still placed a lithium metal plate to form a thin film of lithium in the reaction chamber by reactive sputtering a target of Li ₃ PO ₄ method (reactive sputtering) by LiPON LiPON thin film having a composition of _{1, 0.33:} (thickness 0.2㎛) was formed. The lithium metal plate on which the coating layer thus prepared was formed was used as a negative electrode.

The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate (mixing volume ratio of EC / EMC = 1/1).

A symmetric cell of the prepared negative electrode was prepared.

The surface of the LiPON thin film prepared in Example 4 was observed with a scanning electron microscope (SEM) photograph, and the result is Korean Patent Application No. 10-2015-0145771 (Application Date: October 20, 2015) 4 is shown in FIG.

( Comparative example  5)

A symmetric cell was prepared in the same manner as in Comparative Example 4 except that the thickness of the LiPON thin film in Comparative Example 4 was 0.1 μm.

( Comparative example  6)

A symmetric cell was prepared in the same manner as in Comparative Example 4 except that the thickness of the LiPON thin film was formed at 2 μm in Comparative Example 4.

[ Experimental Example Manufactured Symmetrical  Performance measurement]

The symmetric cells prepared in Examples and Comparative Examples were charged and discharged at 83% DOD (depth of discharge) and 1C charge and discharge conditions. After the charging and discharging, it was visually observed whether the Li metal was oxidized and whether the LiBON thin film or the LiPON thin film was cracked, and the cycle efficiency (%) was measured. The results are shown in Table 1 below.

Li metal oxidation Cracks in LiBON / LiPON Thin Films Li cycle efficiency (%) Example 1 X X 91 Example 2 X X 81 Example 3 △ △ 69 Example 4 X X 73 Example 5 X X 75 Example 6 X X 89 Example 7 X X 87 Comparative Example 1 none none 68 Comparative Example 2 X none 70 Comparative Example 3 O O Not measurable Comparative Example 4 X O 69 Comparative Example 5 X O 68 Comparative Example 6 X O 71

1) Oxidation standard of Li metal

X: not oxidized

Δ: partial oxidation

-O: all oxidation

2) Crack

-X: no crack

△: intermittent crack

-O: full crack

Referring to Table 1, it can be seen that the optimum thickness of the lithium nitride (Li ₃ N) thin film in Examples 1 to 3 is 0.02㎛. When the thickness is smaller than this, LiBON thin film coating may cause oxidation of Li. When the thickness is larger, the Li efficiency decreases due to the low ion conductivity of the lithium nitride (Li ₃ N) thin film. .

In addition, it can be seen that in Example 1, 4 and 5, the optimum thickness of the LiBON thin film is 0.2 μm. When the thickness is smaller than this, lithium is exposed to the electrolyte due to the breakdown of the LiBON thin film during charge and discharge, and when the thickness is larger, the efficiency decreases due to the resistance.

In addition, in Examples 1, 6 and 7, it can be seen that the efficiency is almost 90%, although slightly different depending on the elemental composition of LiBON.

Meanwhile, in Comparative Example 2, the LiBON thin film is not formed to prevent lithium dendrite formation, and in Comparative Example 3, the lithium nitride (Li ₃ N) thin film is not formed so that the battery is not driven by the formation of LiO ₂ during coating of the LiBON thin film. It can be seen that.

In Comparative Examples 4 to 6, the LiPON thin film was formed instead of the LiBON thin film, but it can be seen that cracks occur on the surface of the LiPON thin film, thereby decreasing efficiency.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented specific examples to easily explain the technical contents and help the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

[Description of the code]

1000: lithium metal electrode 1100: lithium metal plate

1210: buffer layer 1220: protective layer

The present invention relates to a lithium metal electrode having a multi-layer structure and a method of manufacturing the same, the multi-layer structure of forming a buffer layer of lithium nitride (Li ₃ N) on a lithium metal plate, and a protective layer of LiBON on the buffer layer The present invention relates to a method for producing a lithium metal electrode having a multi-layer structure in which a lithium nitride buffer layer and a LiBON protective layer are successively formed on a lithium metal plate by a lithium metal electrode and a reactive sputtering method. The lithium metal electrode may be used as a negative electrode of a lithium secondary battery.

Claims (9)

Lithium metal plate; A buffer layer made of lithium nitride (Li ₃ N) formed on the lithium metal plate; And A lithium metal electrode having a multilayer structure, formed on the buffer layer and including a protective layer made of LiBON having a composition of Formula 1 below: LixBOyNz formula (1) (The x is 0.9 to 3.51, y is 0.6 to 3.2, z is 0.5 to 1.0.) The method of claim 1, The buffer layer is a lithium metal electrode of a multilayer structure, characterized in that formed on the surface facing the electrolyte of the lithium metal plate. The method of claim 1, LiBON having a composition of Formula 1 is Li _{3 . 09} BO _{2 . 53} N _{0 .52,} Li _{0. 90} BO _{0 . 66} N _{0 .98,} and Li _{3.51 3.03} BO, lithium metal electrode of the multi-layer structure, characterized in that any one of selected from the group consisting of N _0.52. The method according to claim 1 or 2, The thickness of the lithium metal plate is 30 to 500㎛, lithium metal electrode of a multi-layer structure. The method according to claim 1 or 2, The lithium nitride layer, which is the buffer layer, has a thickness of 0.01 to 5 µm. The method according to claim 1 or 2, The LiBON layer, which is the protective layer, has a thickness of 0.1 to 10 µm. The method of claim 1, The lithium nitride buffer layer or the LiBON protective layer is formed by a method selected from electron beam deposition method, organometallic chemical vapor deposition method, reactive sputtering, high frequency sputtering method, and magnetron sputtering method, multi-layered lithium metal electrode. Providing a lithium metal plate in a vacuum chamber; Forming a lithium nitride (Li ₃ N) thin film on one or both surfaces of the lithium metal plate by nitrogen (N ₂ ) gas reactive sputtering; And Forming a LiBON thin film having a composition of Chemical Formula 1 by a nitrogen (N ₂ ) gas reactive sputtering method continuously on the lithium nitride thin film; Method for producing a lithium metal electrode of a multi-layer structure, including: LixBOyNz formula (1) (The x is 0.9 to 3.51, y is 0.6 to 3.2, z is 0.5 to 1.0.) A negative electrode, a positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode, wherein the negative electrode is a lithium electrode of a multilayer structure according to claim 1, wherein the lithium secondary battery.

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