KR102464823B1 - Anode for lithium metal battery, manufacturing method of the same, lithium metal battery including the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium metal battery, a manufacturing method thereof, and a lithium metal battery including the same.
Specifically, in one embodiment of the present invention, a lithium metal (Li-metal) negative electrode; and a lithium nitride (Li ₃ N) thin film positioned on one or both surfaces of the lithium metal (Li-metal) negative electrode.

Description

Anode for lithium metal battery, manufacturing method thereof, and lithium metal battery comprising the same

The present invention relates to a negative electrode for a lithium metal battery, a manufacturing method thereof, and a lithium metal battery including the same.

A lithium metal battery is a battery to which an anode active material of lithium metal (Li-metal) or a lithium alloy (Li-alloy) material is applied, and has the advantage of theoretically having a very high energy capacity.

However, the lithium metal battery, despite its advantages, is difficult to drive stably and has not reached the commercialization stage. Specifically, lithium metal or lithium alloy is a material having high (electro)chemical reactivity with an electrolyte containing a carbonate-based organic solvent. For this reason, as the driving cycle of the lithium metal battery proceeds, a resistance layer is formed on the surface of the negative electrode due to a side reaction with the electrolyte, and the electrodeposition/desorption of lithium ions on the surface of the negative electrode on which the resistance layer is formed becomes non-uniform, and gradually The battery capacity is reduced, and eventually, the battery has no choice but to stop.

In this regard, various materials and methods for forming a protective film on the surface of a lithium metal negative electrode have been proposed. However, the materials and methods proposed so far have stabilized the interface between the negative electrode and the electrolyte and uniform electrodeposition/desorption of lithium ions from the surface of the negative electrode. There is a limit to sustain.

In embodiments of the present invention, in order to maintain the uniform electrodeposition/desorption of lithium ions on the surface of the anode, dip coating ( dip coating) or a spray coating method, a technique for forming a lithium nitride (Li ₃ N) material protective film to a level of several nm to several hundreds of μm is proposed.

Specifically, in one embodiment of the present invention, a lithium metal (Li) negative electrode; and a lithium nitride (Li ₃ N) thin film positioned on one or both surfaces of the metal plate of the lithium metal (Li) negative electrode.

In another embodiment of the present invention, by a dip coating or spray coating method, on one or both surfaces of a lithium metal (Li) negative electrode, forming a lithium nitride (Li ₃ N) thin film; It provides a method of manufacturing a negative electrode for a lithium metal battery, comprising a.

In another embodiment of the present invention, the negative electrode of the embodiment; an electrolyte comprising a carbonate-based organic solvent and a lithium salt dissociated into the carbonate-based organic solvent; and a positive electrode; provides a lithium metal battery comprising.

According to the embodiments of the present invention, uniform electrodeposition/desorption of lithium ions from the surface of the anode can be sustained while stabilizing the interface between the lithium metal anode and the electrolyte (especially, the electrolyte including the carbonate-based organic solvent), and ultimately can improve the lifespan characteristics of a lithium metal battery.

1 shows the capacity retention rate according to 90 cycle driving of each lithium metal battery of Examples 1 to 2 and Comparative Examples 1 to 4;

In the present specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. As used throughout this specification, the terms "about," "substantially," and the like are used in a sense at or close to the numerical value when presented with manufacturing and material tolerances inherent in the stated meaning, and are intended to enhance the understanding of this application. To help, precise or absolute figures are used to prevent unfair use by unscrupulous infringers of the stated disclosure. The term "step of" or "step of" to the extent used throughout this specification does not mean "step for".

In the present specification, the term "combination of these" included in the expression of the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush form, and the components It means to include one or more selected from the group consisting of.

Based on the above definition, embodiments of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Anode for lithium metal battery

In one embodiment of the present invention, a lithium metal (Li) negative electrode; and a single-layer lithium nitride (Li ₃ N) thin film positioned on one or both sides of the lithium metal (Li) negative electrode and having a thickness of greater than 20 nm and less than or equal to 400 μm; .

protective film ( lithium nitride pellicle)

As described above, various techniques for forming a protective film on the surface of a lithium metal anode have been proposed, but the techniques proposed so far have limitations in stabilizing the interface between the anode and the electrolyte while maintaining uniform electrodeposition/desorption of lithium ions from the surface of the anode. there was

Specifically, a multilayer protective film of Li ₃ N and LIBON has been proposed. However, this has a problem of lowering the lifespan characteristics of the lithium metal battery due to the Li ₃ N and LiBON interface resistance and the LiBON and the electrolyte solution interface resistance. In addition, when the surface of the lithium metal (Li metal), which is the base material, is not uniform, the Li ₃ N layer and the LiBON layer coated on the surface are also non-uniformly generated, and there is a problem of non-uniform electron density on the surface of the anode. .

On the other hand, in terms of method, a technique for forming a protective film on the surface of the negative electrode of a lithium metal battery by using sputtering has also been proposed, but it is difficult to form a protective layer on both sides of the electrode by sputtering, and there is a problem in the process, so it is difficult to manufacture a stacked cell. .

In this regard, even in the comparative examples to be described later, when the cathode protective film is not formed at all, as well as when the cathode protective film of the Li ₃ N single layer or the Li ₃ N-LIBON double layer is formed by sputtering, the capacity of the lithium metal battery It can be seen that the deterioration is extreme. In this regard, since it is difficult to construct a double-sided electrode by the sputtering method and it is possible only in a closed chamber substituted with nitrogen gas, the roll to roll process is difficult, making it difficult to apply to large-capacity, large-area stacked batteries. can

On the other hand, in the case of the dip coating method used in the embodiments to be described below, or the spray coating method capable of implementing similar physical properties, a roll to roll process is possible, so a lithium metal ion battery having a high energy density suitable for

Therefore, for the commercialization of lithium metal batteries, it is necessary to appropriately select a protective film material, structure, and formation method that can sustain the uniform electrodeposition/desorption of lithium ions on the surface of the anode while stabilizing the interface between the anode and the electrolyte.

In this regard, in one embodiment, a single layer of a single layer of a protective film made of a lithium nitride (Li ₃ N) material is formed using a method other than a sputtering method to form a single layer having a level of several nm to several hundred μm, specifically 20 nm Provided is a negative electrode of a lithium metal battery formed into a thin film exceeding 400 μm or less, such as 40 nm or more and 200 μm or less.

The negative electrode protective film of the embodiment is made of lithium nitride, which suppresses the reactivity of the lithium metal negative electrode and the solvent compared to LIBON to form a protective film on the surface of the lithium metal negative electrode, so that a stable negative electrode-electrolyte interface can be formed.

Furthermore, the cathode protective film of one embodiment uses a lithium nitride (Li ₃ N) material capable of forming a stable cathode-electrolyte interface to form a single layer protective film, and furthermore, a thin film by using a method other than the sputtering method. Since it is formed as a (thin film), there is an advantage in that the uniform electrodeposition/desorption of lithium ions on the surface of the anode (with a protective film formed) can be maintained.

Therefore, the negative electrode protective film of the embodiment stabilizes the interface between the negative electrode and the electrolyte in preparation for other materials such as LIBON, a multi-layer structure with more than a double layer, and a thickness formed when a sputtering method is used, while uniform electrodeposition of lithium ions on the surface of the negative electrode / There are advantages of a material that can sustain desorption (Li ₃ N), a structure (single layer), and a uniform surface treatment. These advantages can ultimately contribute to suppressing a decrease in capacity during driving of a lithium metal battery and improving its lifespan characteristics.

On the other hand, the negative electrode protective film of the embodiment may be formed on one surface of the lithium metal plate, or may be formed on both surfaces as in the embodiment to be described later.

lithium metal ( Li -metal) cathode

Meanwhile, the lithium metal (Li-metal) negative electrode is not particularly limited as long as it is generally applied to the negative electrode of a lithium metal battery. For example, a copper (Cu) current collector having a thickness of 5 to 300 μm; A thin film disposed on one or both surfaces of the copper (Cu) current collector and including a lithium metal (Li-metal) or a lithium alloy (Li-alloy) may be cut into an appropriate shape.

In this case, the lithium nitride thin film may be positioned on the thin film including the lithium metal (Li-metal) or lithium alloy (Li-alloy).

Manufacturing method of negative electrode for lithium metal battery

In another embodiment of the present invention, by a dip coating or spray coating method, on one or both sides of the lithium metal plate, forming a single-layer lithium nitride (Li ₃ N) thin film; It provides a method of manufacturing a negative electrode for a lithium metal battery, including.

This is by using a dip coating or spray coating method to form a lithium nitride (Li ₃ N) thin film having a level of several nm, which cannot be achieved by a sputtering method, on the surface of the lithium metal plate. It is a method that can finally obtain one negative electrode.

Hereinafter, with respect to the manufacturing method of the embodiment, process characteristics will be described in detail, and accordingly, the description of the anode finally obtained will be omitted because it overlaps with the above.

Coating method 1 (dip coating)

The forming of the lithium nitride (Li ₃ N) thin film may be performed by the dip coating method, as in an embodiment to be described later. Specifically, the lithium metal plate may be immersed in a coating solution containing lithium nitrate (LiNO ₃ ).

Coating solution according to coating method 1 (dip coating)

During the dip coating, a coating solution including a first lithium salt, an ether-based solvent, and lithium nitrate (LiNO ₃ ) may be used. When such a coating solution is used, lithium nitride (Li ₃ N) may be deposited on the surface of the lithium metal plate according to the following reaction formula.

LiNO ₃ + 8Li ⁺ + 8e ^- → Li ₃ N + 3Li ₂ O

In the coating solution, the content of lithium nitrate (LiNO ₃ ) may be 0.5 to 30% by weight. In other words, the weight of the lithium nitrate (LiNO _{3 ) in the total amount (100% by weight) of the coating solution including the lithium salt, the ether-based solvent, and lithium nitrate (LiNO 3 )} is 0.5 to 30% by weight can

In the coating solution, the ether-based solvent is not particularly limited as long as it contains an ether functional group in its molecular structure. For example, tetraethylene glycol dimethyl ether (TEGDME), dioxolane (DOL), and dimethyl ether (Dimethyl ether, DME), an ether containing at least one selected from the group consisting of A solvent may be used.

The first lithium salt is not particularly limited as long as an anion capable of dissociating in the etheric solvent and a lithium cation are combined. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 ) SO ₂ ) (where x and y are natural numbers), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) 1 selected from the group consisting of Lithium salts comprising more than one species may be used.

When preparing the coating solution, the molar concentration of the first lithium salt may be 0.8 to 5 M, but the present invention is not limited thereto.

Process conditions according to coating method 1 (dip coating)

On the other hand, by controlling the dip coating process conditions, specifically, the immersion time, the thickness of the lithium nitride thin film finally formed can be adjusted.

Coating Method 2 (Spray Coating)

Meanwhile, the forming of the lithium nitride (Li ₃ N) thin film may be performed by the spray coating method, unlike the embodiments to be described later. Specifically, a coating solution containing lithium nitrate (LiNO ₃ ) may be sprayed on the surface of the lithium metal plate.

The coating solution, in the same manner as used in the dip coating method, a first lithium salt, an ether-based solvent, and lithium nitrate (LiNO ₃ ) It may be used. When the coating solution is sprayed on the surface of the lithium metal plate, lithium nitride (Li ₃ N) may be deposited on the surface of the lithium metal plate by the same reaction as the above-described reaction formula. Accordingly, the overlapping description of the coating solution will be omitted.

On the other hand, by controlling the spray coating process conditions, specifically, the spraying time, the thickness of the lithium nitride thin film finally formed can be adjusted.

lithium metal battery

Another embodiment of the present invention, the above-described negative electrode; an electrolyte including a carbonate-based organic solvent and a second lithium salt; and a positive electrode; provides a lithium metal battery comprising.

cathode and electrolyte compatibility (Lifetime characteristics of lithium metal batteries)

In research on lithium metal batteries known to date, an electrolyte solution containing an ether-based solvent has been mainly used. Although the carbonate-based organic solvent has excellent oxidation stability and excellent characteristics in a 4V class high voltage battery, dendrites are formed during operation due to the reactivity of the negative electrode material and the electrolyte when in contact with the negative electrode made of lithium metal or lithium alloy material Thus, the use of a carbonate-based organic solvent is avoided, and an ether-based solvent having a low reactivity with the lithium metal has been used, but its use has been limited to a battery having a low driving voltage due to poor oxidation stability. .

However, the negative electrode of one embodiment described above uses an ether-based electrolyte and lithium nitrate as the protective film material to form a lithium nitride layer on the surface of the lithium metal, thereby suppressing direct reactivity with lithium metal when in contact with a carbonate-based solvent. .

Therefore, in the lithium metal battery of one embodiment, in spite of using the electrolyte containing the carbonate-based solvent, the negative electrode-electrolyte interface can be stably formed by applying the negative electrode of the above-described embodiment, and the carbonate-based solvent can take advantage

In addition, as the lithium metal battery of the embodiment has the advantages of the negative electrode of the embodiment described above, a decrease in capacity during driving thereof is suppressed, and thus, it can have improved lifespan characteristics.

The lithium metal battery of the embodiment may be manufactured by impregnating the electrolyte into an electrode assembly including a porous separator between the positive electrode and the negative electrode.

The description of the negative electrode applied to the lithium metal battery of the embodiment is the same as described above, and below, battery components other than the negative electrode will be described in detail.

carbonate organic solvent

In the electrolyte solution of the lithium metal battery, as the carbonate-based organic solvent, one or more carbonate-based organic solvents widely known in the field of batteries may be used alone or in mixture of one or more, and when one or more are mixed The mixing ratio can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art.

In general, carbonate-based organic solvents widely known in the battery field include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), propylene carbonate (PC), butylene carbonate (BC), fluorine and fluoroethylene carbonate (FEC).

When manufacturing the lithium metal battery, the carbonate-based organic solvent may be used by mixing a cyclic carbonate and a chain carbonate.

electrolyte additive

In addition, the electrolyte of the lithium metal battery may further include one or more additives widely known in the field of batteries in order to improve battery life. For example, vinylene carbonate (VC), or an ethylene carbonate-based compound represented by the following Chemical Formula 2 may be further included.

[Formula 2]

In Formula 2, R ₇ and R ₈ are each independently hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), or a C1 to C5 fluoroalkyl group, and at least one of R ₇ and R ₈ is a halogen group, a cyano group (CN), a nitro group (NO ₂ ), or a C1 to C5 fluoroalkyl group.

Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like. can When the vinylene carbonate or the ethylene carbonate-based compound is further used, the lifespan can be improved by appropriately adjusting the amount used.

secondary lithium salt

In the electrolyte solution of the lithium metal battery, the second lithium salt is dissolved in the carbonate organic solvent, and serves as a source of lithium ions to enable the basic operation of the lithium metal battery of the embodiment, and between the positive electrode and the negative electrode It can play a role in promoting the movement of lithium ions.

As the second lithium salt, a lithium salt widely applied to an electrolyte may be used. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F _{2y + 1} ) SO ₂ ) (where x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB), or a combination thereof may be used, but , but not limited thereto.

In addition, in the electrolyte, the concentration of the second lithium salt may be controlled within the range of 0.1 to 5.0M. Within this range, the electrolyte may have appropriate conductivity and viscosity, and lithium ions may effectively move within the lithium metal battery of the embodiment. However, this is only an example, and the present invention is not limited thereto.

porous separator

The electrolyte may be impregnated in a porous separator positioned between the negative electrode and the positive electrode. Here, the porous separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and any one commonly used in lithium batteries may be used. That is, a material having low resistance to ion movement of the electrolyte and excellent moisture content of the electrolyte may be used.

For example, it may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for lithium ion batteries, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and optionally single-layer or multi-layer structure can be used.

anode

The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector.

The positive electrode is prepared by mixing an active material and a binder, in some cases, a conductive material, a filler, and the like in a solvent to form an electrode mixture in a slurry phase, and applying the electrode mixture to each electrode current collector. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein.

The positive active material is not particularly limited as long as it is a material capable of reversible insertion and deintercalation of lithium ions. metals of, for example, cobalt, manganese, nickel, or combinations thereof; and lithium;

As a more specific example, a compound represented by any one of the following formulas may be used as the cathode active material. Li _a A _{1 -b} R _b D ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0 ≤ _b ≤ 0.5); Li _a E _{1 -b} R _{b O 2 -c} D _{c (} wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE _{2 -b} R _b O _{4 - c} D _c (wherein 0 ≤ _b ≤ 0.5 and 0 ≤ c ≤ 0.05); Li _a Ni _{1 -b- c} Co _b R _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li _a Ni _{1 -b- c} Co _b R _c O _{2 -α Z α ( wherein} 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _{1 -b- c} Co _b R _c O _{2 -α} Z _{2 (} wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _1-bc Mn _b R _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li _a Ni _{1 -b- c} Mn _b R _c O _{2 -α Z α ( wherein} 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _{1 -b- c} Mn _b R _c O _{2 -α} Z _{2 (} wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); and LiFePO ₄ .

In the above formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer is a coating element compound, and may include oxide, hydroxide, oxyhydroxide of a coating element, oxycarbonate of a coating element, or hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, dipping, etc., for this Since it is a content that can be well understood by those engaged in the field, a detailed description will be omitted.

The positive electrode current collector is generally made to have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated on the surface of the can be used. The current collector may increase the adhesive force of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body are possible.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The lithium metal battery of one embodiment may be used not only in a battery cell used as a power source for a small device, but also as a unit cell in a medium/large battery module including a plurality of battery cells.

Hereinafter, preferred examples of the present invention, comparative examples, and test examples for evaluating them are described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited thereto.

< Example >

Example One

(1) Preparation of negative electrode

As shown in Table 1 below, a lithium nitride (Li ₃ N) thin film having a thickness of 40 nm was formed on both sides of the lithium metal plate by a dip coating method.

Specifically, the manufacturing process of the coating solution and the dip coating process are as follows.

Coating solution : In a solvent in which TEGDME, DOL, and DME were mixed in a volume ratio of 1:1:1, LiTFSI, a lithium salt, was dissolved at a concentration of 2M, and LiNO ₃ was added to prepare a coating solution. Here, the content of LiNO ₃ in the total amount (100% by weight) of the prepared coating solution was 3 weight.

Dip coating : At room temperature, by dipping a lithium metal anode (lithium cross section 20 μm, Cu 10 μm) in the coating solution for 2 hours, 40 nm thick lithium nitride (Li ₃ N) A thin film was formed.

(2) Preparation of lithium metal batteries

As shown in Table 1 below, the lithium metal plate formed on both sides of the lithium nitride (Li ₃ N) thin film as an anode, and an electrolyte containing a carbonate-based solvent (1M LiPF ₆ in EC/EMC 1:1 (v/v) ), VC 0.5%), and a positive electrode (positive electrode active material: LiCoO ₂ ) were used. A separator was interposed between the prepared positive electrode and the negative electrode, placed in a pouch, sealed, and the prepared non-aqueous electrolyte was injected into the cell to prepare a lithium metal secondary battery.

Specifically, the manufacturing process of the electrolyte solution, the manufacturing process of the positive electrode, and the cell assembly process are as follows.

Electrolyte : In a carbonate-based solvent in which EC and EMC are mixed in a volume ratio of 3:7, LiPF ₆ , a lithium salt, is dissolved at a concentration of 1M, and VC is added as an additive, An electrolyte solution was prepared. Here, the content of the additive (VC) in the total amount of the prepared electrolyte solution (100 wt%) was 0.5 wt% (1M LiPF ₆ in EC/EMC 1:1 (v/v), VC 0.5%).

Example 2

By changing the immersion time of Example 1 to 24 hours, as shown in Table 1 below, a negative electrode having a protective film thickness of 200 μm was prepared.

A pouch-type lithium metal battery was manufactured in the same manner as in Example 1 except for the negative electrode.

< comparative example >

comparative example One

As shown in Table 1 below, a pouch-type lithium metal battery was prepared in the same manner as in Example 1 except for the negative electrode using a lithium metal negative electrode that was not coated at all.

comparative example 2

As shown in Table 1 below, using a lithium metal negative electrode that is not coated at all, the electrolyte solution containing LiNO ₃ in the electrolyte solution of Example 1 was used as the electrolyte solution, and the rest except for the negative electrode and the electrolyte solution were the same as in Example 1. , a pouch-type lithium metal battery was prepared.

Specifically, the manufacturing process of the electrolyte solution is as follows.

Electrolyte : In a carbonate-based solvent in which EC and EMC are mixed in a volume ratio of 3:7, LiPF ₆ , a lithium salt, is dissolved at a concentration of 1M, and VC is added as an additive, LiNO ₃ was also added to prepare an electrolyte solution (1M LiPF ₆ in EC/EMC 1:1 (v/v), VC 0.5%, LiNO ₃ 1%).

comparative example 3

(1) Preparation of negative electrode

As shown in Table 1 below, by a sputtering method, on one side of the lithium metal negative electrode, a lithium nitride (Li ₃ N) thin film having a thickness of 20 nm (ie, 0.02 μm) and a thickness of 200 nm (ie, 0.2 μm) of LIBON thin films were sequentially formed.

Specifically, the sputtering process is as follows.

A lithium nitride (Li ₃ N) thin film (thickness: 0.02 μm) is formed on one side of a lithium metal plate (thickness: 20 μm) by a reactive sputtering method in which nitrogen (N ₂ ) gas is exposed for 5 minutes at 0.1 Pa in a vacuum chamber. And, by continuously leaving the lithium metal plate on which the lithium nitride thin film is formed in the vacuum chamber as it is, Li ₂ BO ₃ In a reactive sputtering method using as a target, Li _{3 . 09} BO _{2 .} A _LiBON thin film (thickness: 0.2 μm) having a composition of ₅₃ N _0.52 was formed.

(2) Preparation of lithium metal batteries

As shown in Table 1 below, a lithium metal negative electrode in which a double layer of the lithium nitride (Li ₃ N) thin film and the LiBON thin film was formed on both sides was used, and the rest except for the negative electrode was the same as in Example 1, and a pouch-type lithium metal battery was prepared.

comparative example 4

In Comparative Example 3, a lithium metal negative electrode in which only a lithium nitride thin film was formed was used, and except for the negative electrode, a pouch-type lithium metal battery was prepared in the same manner as in Example 1.

cathode cell With or without a shield
(coating method) protective film material protective film thickness electrolyte Example 1 you
(dip coating) Li ₃ N 40 nm 1M LiPF ₆ in EC/EMC 3:7, VC 0.5% Example 2 200 μm Comparative Example 1 radish - - Comparative Example 2 radish - - 1M LiPF ₆ in EC/EMC 3:7, VC 0.5%, LiNO ₃ 1% Comparative Example 3 you
(sputtering) Li ₃ N, LiBON
(double layer) 0.02 μm (Li ₃ N),
0.2 μm (LiBON) 1M LiPF ₆ in EC/EMC 3:7, VC 0.5% Comparative Example 4 you
(sputtering) Li ₃ N 0.02 μm (Li ₃ N)

Experimental example 1 (Evaluation of electrochemical properties of lithium metal batteries)

The cycle of each lithium metal battery is performed under the following conditions, and the characteristics of the capacity after the 30th cycle and the capacity after the 90th cycle are evaluated compared to the initial capacity, and the evaluation results are recorded in Table 2 below, 1 is shown.

Charge: 0. 1C, CC/CV, 4.25V, 1/20C cut-off

Discharge: 0.5C, CC, 3.0V, cut-off

Capacity retention rate (%) @ 30 ^th @ 80 ^th Example 1 99.41 95.89 Example 2 98.84 97.40 Comparative Example 1 90.52 78.43 Comparative Example 2 94.48 77.64 Comparative Example 3 38.55 - Comparative Example 4 96.9% 53.93

According to Table 2 and FIG. 1 , in the lithium metal battery, the material, structure, and thickness of the negative electrode protective layer, and the importance of the formation method thereof can be grasped.

Specifically, except for Comparative Example 2, the electrolyte composition commonly applied to all lithium metal batteries (1M LiPF ₆ in EC/EMC 3:7, VC 0.5%) is avoided in the lithium metal battery field, but ( It is an electrolyte composition including a carbonate-based solvent that is widely used in the field of lithium ion batteries (not using a lithium metal negative electrode).

1) In Comparative Example 1, a lithium metal negative electrode having no protective film was applied together with an electrolyte containing the carbonate-based solvent, and the capacity retention rate after 80 cycles was found to be only 78.4%.

On the other hand, in Comparative Example 2, as a result of using the electrolyte in which lithium nitrate was added to the electrolyte of Comparative Example 1, the capacity retention rate after 80 cycles was 77.6%, which was rather lower than in Comparative Example 1.

As a result, it can be confirmed that the lithium metal negative electrode in which the protective film is not formed at all reacts with the carbonate-based solvent to accelerate and deplete the consumption of the lithium metal, thereby gradually reducing the capacity during battery cycle driving.

2) Comparative Example 3 is a continuous sputtering method, in which lithium nitride (Li ₃ N) and LiBON are sequentially coated on one surface of a lithium metal negative electrode, and the thickness of each layer is 0.02 μm (Li ₃ N) and 0.2 μm ( LiBON) formed with a double layer protective film was applied as a cathode. The battery of Comparative Example 3 to which such a negative electrode was applied could not be charged and discharged until 80 cycles, and it was found that the capacity retention rate after 30 cycles was already only 38.5%.

Meanwhile, in Comparative Example 4, the step of coating LIBON in Comparative Example 3 was omitted, and a single layer lithium nitride (Li ₃ N) protective film having a thickness of 0.02 μm was formed by a sputtering method as a cathode. The battery of Comparative Example 4 to which the negative electrode was applied had improved capacity retention compared to Comparative Example 3, but it was confirmed that the capacity retention rate after 80 cycles was rather lower than those of Comparative Examples 1 and 2 in which no protective film was formed.

Accordingly, when the Li ₃ N and LiBON layers are physically stacked on the lithium metal anode, the resistance increases at the interface between the metal and Li ₃ N, Li ₃ N and LiBON, and LiBON and the electrolyte, which further increases the capacity during battery cycle driving. It can be seen that there is a problem of slowing down.

It can be seen that the lithium metal battery capacity retention rate of Comparative Example 4 is improved compared to Comparative Example 3, and when the lithium nitride (Li ₃ N) material rather than LiBON is in direct contact with the carbonate-based solvent, the surface side reaction itself is lowered. However, as a limitation of using the sputtering method as a coating method, a protective layer cannot be coated on both sides of the lithium metal negative electrode, so battery capacity is limited, and air must be replaced with nitrogen during the sputtering process. It is difficult to manufacture a large-area electrode.

3) On the other hand, in Examples 1 and 2, a single-layer thin film made of a lithium nitride (Li ₃ N) material was formed by a dip coating method in common.

In common, they were able to achieve the level of commercial lithium-ion batteries with a capacity retention rate of 98% or more after 30 cycles and a capacity retention rate of 95% or more after 90 cycles.

This is compared with the previous comparative examples, a lithium nitride (Li ₃ N) material that stabilizes the negative electrode-electrolyte interface by suppressing side reactions, as a single layer, it also has a thickness of several nm to several hundred μm, and is uniform It can be seen as a result of forming a thin film having one surface.

4) On the other hand, in Examples 1 and 2, a lithium metal (Li-metal) negative electrode including a lithium metal (Li-metal) thin film is used only on one surface of the copper current collector on a laboratory scale, and the lithium metal (Li- A so-called mono-cell is realized by forming a single-layer thin film made of lithium nitride (Li ₃ N) material only on the metal) thin film.

However, in the actual production process, when dip coating or similar spray coating is used as in Examples 1 and 2, double-sided coating is easy, and large-area coating is possible because coating can be performed in the air. Therefore, dip coating or similar spray coating as in Examples 1 and 2 is useful for realizing large-area and/or double-sided negative electrodes, and the large-area double-sided negative electrode thus prepared is applied to a stacked cell. can

Claims (14)

lithium metal (Li-metal) negative electrode; and located on one or both sides of the lithium metal (Li-metal) negative electrode, having a thickness of more than 20 nm and 400 μm or less, and a single layer, including a first lithium salt, an ether-based solvent, and lithium nitrate (LiNO ₃ ) A cathode comprising; a lithium nitride thin film made of lithium nitride (Li ₃ N) and Li ₂ O formed using a coating solution to
An electrolyte comprising a carbonate-based organic solvent and a second lithium salt, and
A lithium metal battery comprising a positive electrode.
According to claim 1,
The thickness of the lithium nitride thin film is,
40 nm or more and 200 μm or less,
lithium metal battery.
According to claim 1,
The lithium metal (Li-metal) negative electrode,
current collector; and
It is located on one side or both sides of the current collector, and a thin film containing lithium metal (Li-metal) or lithium alloy (Li-alloy);
lithium metal battery.
4. The method of claim 3,
The lithium nitride thin film,
Which is located on a thin film containing the lithium metal (Li-metal) or lithium alloy (Li-alloy),
lithium metal battery.
A method for manufacturing a lithium metal battery according to claim 1, comprising:
One surface of a lithium metal (Li-metal) negative electrode by dip coating or spray coating using a coating solution containing a first lithium salt, an ether-based solvent, and lithium nitrate (LiNO ₃ ) or on both sides, forming a lithium nitride thin film made of lithium nitride (Li ₃ N) and Li ₂ O to prepare an anode;
A method for manufacturing a lithium metal battery.
6. The method of claim 5,
Forming the lithium nitride (Li ₃ N) thin film; is performed by the dip coating method,
The dip coating method is to immerse the lithium metal negative electrode in the coating solution,
A method for manufacturing a lithium metal battery.

delete 6. The method of claim 5,
The content of lithium nitrate (LiNO ₃ ) in the coating solution is,
0.5 to 30% by weight of the total amount of the coating solution (100% by weight),
A method for manufacturing a lithium metal battery.
6. The method of claim 5,
The ether-based solvent is
Tetraethylene glycol dimethyl ether (Tetraethylene glycol dimethyl ether, TEGDME), dioxolane (Dioxolane, DOL), and dimethyl ether (Dimethyl ether, DME) comprising at least one selected from the group consisting of,
A method for manufacturing a lithium metal battery.
6. The method of claim 5,
The first lithium salt is
LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ )( Here, x and y are natural numbers), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) includes at least one selected from the group consisting of that is,
A method for manufacturing a lithium metal battery.
delete According to claim 1,
The carbonate-based organic solvent,
Ethyl carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl Propyl carbonate (MPC), ethyl propyl carbonate (Ethyl propyl carbonate, EPC), propylene carbonate (Propylene carbonate, PC), and butylene carbonate (Butylene carbonate, BC to containing at least one selected from the group consisting of ~ ,
lithium metal battery.
According to claim 1,
The second lithium salt is
LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ )( where x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) or a combination thereof,
lithium metal battery.
The method of claim 1 .
The anode is
A metal of cobalt, manganese, nickel, or a combination thereof. and at least one positive electrode active material among lithium composite oxides,
lithium metal battery.

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