KR102475181B1 - 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, in order to improve conductivity while improving adhesion between the negative electrode current collector and the negative electrode active material of a lithium metal battery, an adhesive layer including a binder and a conductive material is formed between the negative electrode current collector and the negative electrode active material. introduced.

Description

Anode for lithium metal battery, manufacturing method thereof, and lithium metal battery including 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 lithium alloy (Li-alloy) is applied, and theoretically has an advantage of having a very high energy capacity.

A negative electrode of a lithium metal battery is generally manufactured by a physical compression method. Specifically, as a method of manufacturing a negative electrode of a lithium metal battery, a thin film of lithium metal (Li-metal) or lithium alloy (Li-alloy) is placed on the negative electrode current collector, and then a roll-press is used to The compression method is known.

In the negative electrode of a lithium metal battery manufactured by the compression method without a binder, the adhesion between the negative electrode current collector and the negative electrode active material is weak, so that the electrolyte solution can penetrate between the negative electrode current collector and the negative electrode active material during battery operation, and the volume of lithium, which is the negative electrode active material, is high. Depending on the change, a gap between the anode current collector and the anode active material may gradually widen.

This is acting as one of the reasons why lithium metal batteries have not yet been commercialized.

In one embodiment of the present invention, an adhesive layer containing a binder and a conductive material is introduced between the anode current collector and the anode active material in order to improve conductivity while improving adhesion between the anode current collector and the anode active material of a lithium metal battery.

Specifically, in one embodiment of the present invention, the negative electrode current collector; an adhesive layer disposed on one side or both sides of the anode current collector and including a binder and a conductive material; It provides a negative electrode for a lithium metal battery comprising a; lithium metal (Li-metal) thin film located on the adhesive layer.

In one embodiment of the present invention, the binder included in the adhesive layer contributes to improving the adhesion between the anode current collector and the anode active material of the lithium metal battery. Accordingly, the negative electrode having improved adhesion can not only improve the lifespan characteristics and safety of the lithium metal battery, but also help realize the lithium metal battery in the form of an all-solid-state battery.

Furthermore, the conductive material included in the adhesive layer contributes to improving the conductivity of the negative electrode. Accordingly, the negative electrode having improved conductivity can lower the initial resistance of the battery and suppress an increase in resistance during the cycle.

1 schematically illustrates a method of manufacturing a negative electrode for a lithium metal battery according to one embodiment of the present invention.
2A is a SEM image of a cross section of the cathode of Example 2.
2B is an SEM image of a cross section of a negative electrode of Comparative Example 4.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated. As used throughout this specification, the terms "about," "substantially," and the like are used at or approximating that value when manufacturing and material tolerances inherent in the stated meaning are given, and do not convey the understanding of this application. Accurate or absolute figures are used to help prevent exploitation by unscrupulous infringers of the disclosed disclosure. The term "step of (doing)" or "step of" as used throughout the present specification does not mean "step for".

In this specification, the term "combination of these" included in the expression of the Markush form means a mixture or combination of one or more selected from the group consisting of the components described in the expression of the Markush form, It means including 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 thereby the present invention is not limited and the present invention is only defined by the scope of the claims to be described later.

Cathode for lithium metal battery

In one embodiment of the present invention, the negative electrode current collector; an adhesive layer disposed on one side or both sides of the negative electrode current collector and including a binder; It provides a negative electrode for a lithium metal battery comprising a; lithium metal (Li-metal) thin film located on the adhesive layer.

In general, when manufacturing a positive electrode or a negative electrode of a lithium ion battery, a binder is used and a slurry coating method is generally used to attach a particulate electrode active material onto an electrode current collector. Specifically, an electrode active material, a binder, and a conductive material are mixed in a solvent to adjust the slurry phase, and the slurry is applied on an electrode current collector and then dried. After that, an electrode mixture layer is formed on the electrode current collector, and the electrode active material, the binder, and the conductive material are all mixed in the electrode mixture layer.

On the other hand, the negative electrode of a lithium metal battery uses pure lithium metal in the form of a thin film rather than particles as an anode active material, so that a negative electrode current collector such as copper foil and a lithium metal (Li-metal) thin film are laminated and then physically compressed. It is common to manufacture

However, in the negative electrode of a lithium metal battery manufactured by the compression method without a binder, the adhesive force between the negative electrode current collector and the negative electrode active material is weak, so that the electrolyte may penetrate between the negative electrode current collector and the negative electrode active material during battery operation, resulting in side reactions. It is accelerated, and the side reaction product may act as a resistance layer and deteriorate the performance of the battery. In addition, as pointed out above, the gap between the anode current collector and the anode active material may gradually widen according to the volume change of lithium, which is an anode active material.

On the other hand, the negative electrode for a lithium metal battery of one embodiment, unlike a generally known negative electrode of a lithium metal battery, is not manufactured using a physical compression method, and an adhesive layer is introduced between the negative electrode current collector and a lithium metal (Li-metal) thin film. By doing so, the adhesion between them is improved. 1 schematically illustrates a method of manufacturing a negative electrode for a lithium metal battery according to one embodiment of the present invention.

More specifically, in the negative electrode for a lithium metal battery of one embodiment, unlike an electrode mixture layer of a lithium ion battery in which an electrode active material, a binder, and a conductive material are all mixed, the electrode active material and the binder are separated, and the negative electrode current collector and the lithium An adhesive layer is positioned between a lithium metal thin film corresponding to an anode active material of a metal battery and an anode current collector, and a binder and a conductive material are included in the adhesive layer.

The binder may have excellent adhesion to the lithium metal thin film as well as to the anode current collector without having reactivity to the anode current collector. Accordingly, the anode current collector and the lithium metal (Li-metal) thin film may be improved through the binder included in the adhesive layer.

The negative electrode having improved adhesion can help to improve lifespan characteristics and safety of lithium metal batteries.

Furthermore, the conductive material can improve the conductivity of the negative electrode, thereby lowering the initial resistance of a lithium metal battery including the same, and suppressing an increase in resistance during cycling.

adhesive layer

The binder included in the adhesive layer is not particularly limited as long as it has adhesion to the lithium metal thin film as well as to the anode current collector.

For example, the binder may include polyvinylidene fluoride (PVDF), a derivative thereof, or a mixture thereof.

Polyvinylidene fluoride (PVDF), a derivative thereof, or a mixture thereof has low reactivity with lithium metal, and thus may be suitable for use as the binder.

On the other hand, in the case of an adhesive layer including a conductive material together with the binder, rather than an adhesive layer composed of the binder, it is advantageous to improve the conductivity of the lithium metal negative electrode and thereby suppress an increase in resistance during operation of the battery.

The conductive material is not particularly limited as long as it is a conductive material, but may include one or a mixture of two or more selected from the group consisting of carbon black, carbon nanotube, natural graphite, artificial graphite, and carbon fiber. .

A weight ratio of the conductive material to the binder (ie, conductive material/binder) may be 1/4 to 4, specifically 1/3 to 3. Since the specific surface area of the conductive material is large, when the conductive material is added in a high ratio, there is a possibility that the adhesive strength is reduced. However, when the weight ratio of the conductive material/binder is set to 1/4 or more to 4 or less, it is possible to secure appropriate adhesive strength and conductivity.

Meanwhile, a thickness ratio of the adhesive layer to the negative current collector may be 1/10 to 1/20, specifically 1/10 to 1/15 (the order of description is the adhesive layer/current collector). In addition, the thickness ratio of the adhesive layer to the lithium metal thin film may be 1/20 to 1/40, specifically 1/30 to 1/40 (the order of description is the adhesive layer/lithium metal thin film). If the thickness of the adhesive layer is excessively thick compared to the thickness of each of the anode current collector and the lithium metal thin film, the adhesive layer may rather act as a resistor. Therefore, each thickness ratio of the adhesive layer/current collector and the adhesive layer/current collector may be limited to the minimum thickness having adhesive properties as described above.

The adhesive layer of the embodiment may be formed on one side of the negative electrode current collector, or may be formed on both sides of the negative electrode current collector. In this regard, the negative electrode for a lithium metal battery of one embodiment has a structure of a negative electrode current collector/adhesive layer/lithium metal thin film in the former case, and a lithium metal thin film/adhesive layer/negative electrode current collector adhesive layer/lithium metal thin film in the latter case. have a structure Compared to the case formed on one side, when formed on both sides, there is an advantage in expanding the capacity of the battery cell, but the embodiment is not limited thereby.

Manufacturing method of lithium metal anode

In another embodiment of the present invention, applying a composition including a binder, a conductive material and a solvent on one side or both sides of the negative electrode current collector; and laminating the anode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween.

In the manufacturing method of the embodiment, as a binder is used to prepare a negative electrode of a lithium metal battery, adhesion between the negative electrode current collector and the negative electrode active material may be improved in preparation for a physical compression method.

In particular, in the manufacturing method of one embodiment, as a wet process is used instead of a dry process, the adhesive strength between the components of the adhesive layer and the negative electrode current collector and the lithium metal thin film through the adhesive layer are strengthened advantageous to

Specifically, according to an experimental example to be described later, it can be confirmed the difference according to the method of forming the adhesive layer. Specifically, when comparing cases using the same adhesive layer components, it is confirmed that when the adhesive layer is formed in a dry method compared to a wet method, the capacity retention rate of the battery is significantly lowered and the resistance is significantly increased.

In the dry process without using the solvent, it is difficult to evenly apply the components of the adhesive layer on the negative electrode current collector, and when the lithium metal thin film is physically pressed on the unevenly applied components of the adhesive layer, the negative electrode current collector and Adhesion between the lithium metal thin films may be inferior. If the negative electrode adhesion is weak, the electrolyte solution may permeate between the negative electrode current collector and the lithium metal thin film during battery operation, thereby accelerating side reactions, and the side reaction products may act as a resistance layer and deteriorate battery performance. .

On the other hand, when the solvent is used, the components of the adhesive layer may be evenly applied on the anode current collector. In addition, in the process of pressing the lithium metal thin film on the evenly applied components of the adhesive layer and then drying, the solvent volatilizes to strengthen the bonding strength between the components of the adhesive layer, as well as to strengthen the bonding strength between the components of the adhesive layer and It is inferred that it enhances the adhesion of the lithium metal thin film. Here, as mentioned above, the strong adhesion of the negative electrode is one of the factors enabling stable driving while minimizing the increase in resistance of the battery.

Of the total amount (100 wt%) of the composition, the binder may be included in an amount of 5 to 40 wt%, specifically 10 to 30 wt%, and the solvent may be included as the remainder. If it is desired to form an adhesive layer further including the conductive material, the material to be added may be included in an amount of 5 to 40 wt%, specifically 10 to 30 wt%, of the total amount (100 wt%) of the composition. This corresponds to a range of 1/10 to 1/6 of the weight of the binder, and a description thereof is omitted as described above.

In the step of applying a composition including a binder and a solvent on one side or both sides of the anode current collector, the coating amount (g) of the composition relative to the cross-sectional area (cm ² ) of the anode current collector is 0.005 to 0.01 g/cm ² can be This can be appropriately controlled in consideration of the thickness of the finally formed adhesive layer.

laminating the anode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween; Previously, drying the applied composition; may further include. In this case, the composition may be applied on the anode current collector, dried in a vacuum at room temperature for 8 to 16 hours, and then the lithium metal thin film may be laminated and compressed.

If the step of removing the solvent in the applied composition is not further included, a lithium metal thin film is placed thereon before the composition dries, dried for 8 to 16 hours in a vacuum at room temperature, and then pressed. have.

laminating the anode current collector and a lithium metal (Li-metal) thin film regardless of whether the applied composition is dried or not; Thereafter, a step of compressing the stacked negative electrode current collector and the lithium metal (Li-metal) thin film may be further included.

The compression may be performed by applying heat, pressure, or both. Specifically, the compression may be performed at a temperature of 50 to 70 °C at a pressure corresponding to a gap corresponding to the total thickness of the anode current collector and the lithium metal (Li-metal) thin film. In addition, when the experiment is performed by applying both heat and pressure during the compression, when heat and pressure are simultaneously applied, the adhesion between the current collector and the lithium thin film can be further improved. However, it is necessary to appropriately select the heat and pressure in each of the above ranges in consideration of the adhesive properties according to the content of the binder and the conductive material to be applied to the desired thickness of the negative electrode for a lithium metal battery and the current collector.

laminating the anode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween; Thereafter, the composition between the stacked anode current collector and the lithium metal (Li-metal) thin film may be converted into the above-described adhesive layer.

lithium metal battery

In another embodiment of the present invention, the aforementioned negative electrode; electrolyte; It provides a lithium metal battery comprising a; and a positive electrode.

The lithium metal battery of one embodiment, as it has the advantages of the negative electrode of one embodiment described above, can have improved lifespan characteristics by suppressing capacity degradation during operation.

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

Meanwhile, the electrolyte of the lithium metal battery may be a liquid electrolyte (ie, an electrolyte solution) or a solid electrolyte.

When the electrolyte of the lithium metal battery is a liquid electrolyte, it includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

Carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used as the non-aqueous organic solvent. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and the ester-based solvent includes methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate , ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like can be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether-based solvent, and cyclohexanone or the like may be used as the ketone-based solvent. have. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and as the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, among which aromatic rings or ether linkages may be included), nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used.

The above non-aqueous organic solvents may be used alone or in combination with one or more of them, and when used in combination with one or more, the mixing ratio may be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the art. It can be.

In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by Chemical Formula 1 may be used.

[Formula 1]

In Formula 1, R ₁ to R ₆ are each independently hydrogen, halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or a combination thereof.

The aromatic hydrocarbon-based organic solvent is benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4 -triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 -Trichlorotoluene, iodotoluene, 1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotoluene, 1,2,3-triiodotoluene, 1,2,4- Triiodotoluene, xylene or combinations thereof may be used.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by Formula 2 below to improve battery life.

[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 difluoro ethylene 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.

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

As the 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 combinations thereof may be used. , but not limited thereto.

In addition, in the electrolyte solution, the concentration of the lithium salt can 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 thereby.

The electrolyte solution may be impregnated with a porous separator positioned between the negative electrode and the positive electrode. Here, the porous separator, which separates the negative electrode and the positive electrode and provides a passage for lithium ions, can be used as long as it is commonly used in lithium batteries. That is, an electrolyte having low resistance to ion movement of the electrolyte and excellent ability to absorb the electrolyte may be used.

For example, it may be selected from glass fibers, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in the form of non-woven fabric or woven fabric. For example, in lithium ion batteries, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used, and coated separators containing ceramic components or polymer materials may be used to secure heat resistance or mechanical strength. structure can be used.

In contrast, when the electrolyte of the lithium metal battery is a solid electrolyte, usable solid electrolytes are not particularly limited.

Regardless of the electrolyte of the lithium metal battery, the positive electrode may include a positive electrode current collector and a positive electrode mixture layer positioned 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, etc. in a solvent to prepare an electrode mixture in a slurry state, 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.

In the case of the cathode active material, as long as it is a material capable of reversibly intercalating and deintercalating lithium ions, it is not particularly limited. metals such as cobalt, manganese, nickel or combinations thereof; and lithium; may include one or more of complex oxides.

For 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-bc 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-bc 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-bc 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-bc 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-bc 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 (wherein 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 combinations 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 combinations thereof.

Of course, one having a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include an oxide, hydroxide, oxyhydroxide of a coating element, oxycarbonate of a coating element, or hydroxycarbonate of a coating element as a compound of a coating element. Compounds 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 mixtures thereof may be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated with a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (eg, spray coating, dipping method, etc.). Since it is a content that can be well understood by those working in the field, detailed explanations will be omitted.

The cathode 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 does not cause chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel. A surface treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics are possible.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples include 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 can be used as a unit cell used as a power source for a small device, and can also be used as a unit cell in a medium or large battery module including a plurality of battery cells. Furthermore, a battery pack including the battery module may be configured.

Hereinafter, preferred embodiments of the present invention, comparative examples in contrast thereto, and test examples for evaluating them are described. However, the following example is only a preferred embodiment of the present invention, but the present invention is not limited to the following example.

Comparative Example 1

(1) Manufacture of cathode

A composition for forming an adhesive layer was evenly applied to a thickness of about 1 μm on a copper current collector having a circular cross section of 1.76 cm ² (thickness: 10 μm). Here, the composition for forming an adhesive layer is obtained by mixing polyvinylidene fluoride (PVdF) described in Table 1 as a binder and mixing it with NMP as a solvent so that it becomes 40.0% by weight of 100.0% by weight of the composition.

In addition, the application of the composition for forming an adhesive layer was performed under the condition of 3 m/min using a doctor blade device.

Before the applied composition for forming an adhesive layer is dried, a lithium foil having a thickness of 20 μm is covered thereon, then roll pressed, and finally heated in a vacuum oven at 60 ° C. for 2 hr, thereby forming a copper house The composition between the whole and the lithium foil was completely hardened and converted into an adhesive layer.

(2) Fabrication of lithium metal battery

Using LiNi _0.8 Mn _0.1 Co _0.1 O ₂ as the positive electrode active material, carbon black as the conductive material, and polyvinylidene fluoride (PVdF ) as the binder, the weight ratio of the positive electrode active material: conductive material: binder was 96:2:2. To the mixed mixture, NMP as a solvent was added to prepare a positive electrode active material slurry.

The cathode active material slurry was coated on one surface of an aluminum current collector to a thickness of 79 μm, dried and rolled, and then punched to a predetermined size to prepare a cathode.

A coin cell was manufactured in which a separator (polypropylene-based porous polymer substrate) was interposed between the negative electrode and the positive electrode of Comparative Example 1. A lithium metal secondary battery was manufactured by injecting an electrolyte in which 1M LiPF ₆ was dissolved in a solvent in which fluoroethylene carbonate (FEC) and ethylmethyl carbonate (EMC) were mixed in a volume ratio of 30:70 was injected into the coin cell.

Comparative Example 2

(1) Manufacture of cathode

Polyvinylidene fluoride (PVdF) was coated on the copper current collector in a dry manner without using a solvent.

Specifically, on a circular (thickness: 10 μm) copper current collector with a cross section of 1.76 cm ² , only polyvinylidene fluoride (PVdF) was applied to a thickness of about 1 μm at 3 m/min using a doctor blade device. applied evenly.

On the coated polyvinylidene fluoride (PVdF), lithium foil (Li foil) having a thickness of 20 μm was covered thereon, then roll pressed, and finally heated in a vacuum oven at 60 ° C. for 2 hr, The PVdF between the copper current collector and the lithium foil was cured and converted into an adhesive layer.

(2) Fabrication of lithium metal battery

A lithium metal secondary battery was manufactured in the same manner as in Comparative Example 1, except that the negative electrode of Comparative Example 2 was used instead of the negative electrode of Comparative Example 1.

Examples 1 to 3

(1) Manufacture of cathode

Instead of Comparative Example 1 described in Table 1 below, each composition for forming an adhesive layer of Examples 1 to 3 was used, and the negative electrodes of Examples 1 to 3 were prepared in the same manner as in Comparative Example 1 with the rest. Specifically, the compositions for forming an adhesive layer of Examples 1 to 3 use polyvinylidene fluoride (PVdF) as a binder and Super-P as a conductive material. However, each composition of Examples 1 to 3 Of 100.0 wt%, the solvent content was the same as 60.0 wt%, but the respective amounts of the binder and the conductive material were varied.

(2) Fabrication of lithium metal battery

Each lithium metal battery of Examples 1 to 3 was manufactured in the same manner as in Comparative Example 1, except that each negative electrode of Examples 1 to 3 was used instead of the negative electrode of Comparative Example 1.

Comparative Example 3

(1) Manufacture of cathode

Polyvinylidene fluoride (PVdF) and Super-P were coated on the copper current collector in a dry manner without using a solvent.

Specifically, on a circular (thickness: 10 μm) copper current collector with a cross section of 1.76 cm ² , only polyvinylidene fluoride (PVdF) was applied to a thickness of about 1 μm at 3 m/min using a doctor blade device. applied evenly.

On the coated polyvinylidene fluoride and Super-P, lithium foil having a thickness of 20 μm was covered on top, then roll pressed, and finally heated in a vacuum oven at 60 ° C. for 2 hr. , curing the PVdF between the copper current collector and the lithium foil to convert it into an adhesive layer.

(2) Fabrication of lithium metal battery

A lithium metal secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode of Comparative Example 3 was used instead of the negative electrode of Example 1.

Examples 4 and 5

(1) Manufacture of cathode

Instead of Comparative Example 1 described in Table 1 below, the negative electrodes of Examples 4 and 5 were prepared using the compositions for forming an adhesive layer of Examples 4 and 5, and the rest was the same as in Comparative Example 1. Specifically, in the compositions for forming an adhesive layer of Examples 4 and 5, polyvinylidene fluoride (PVdF) was used as a binder and CNT was used as a conductive material. However, the solvent content of 100.0 wt% of each composition of Examples 4 and 5 was the same as 60.0 wt%, but the respective amounts of the binder and the conductive material were different.

(2) Fabrication of lithium metal battery

Each lithium metal battery of Examples 4 and 5 was manufactured in the same manner as in Comparative Example 1, except that the negative electrodes of Examples 4 and 5 were used instead of the negative electrode of Comparative Example 1.

Comparative Example 4

(1) Manufacture of cathode

The negative electrode of Comparative Example 4 was prepared in a conventionally commercially available physical compression method without forming an adhesive layer on the negative electrode of Comparative Example 4 (ie , without applying a binder and a conductive material).

Specifically, on a circular (thickness: 10 μm) copper current collector with a cross-sectional area of 1.76 cm ² , a lithium foil (Li foil) having a thickness of 20 μm was covered thereon, and then roll-pressed to obtain copper without an adhesive layer. The current collector and lithium foil were pressed together.

(2) Fabrication of lithium metal battery

A lithium metal battery of Comparative Example 4 was manufactured in the same manner as in Example 1, except that the negative electrode of Comparative Example 4 was used instead of the negative electrode of Example 1.

adhesive layer component Adhesive layer formation method Composition for forming adhesive layer
(Total weight of composition: 100.0% by weight) bookbinder conductive material bookbinder conductive material Solvent (NMP) Comparative Example 1 PVdF - wet 40.0% by weight 0.0% by weight 60.0% by weight Example 1 PVdF Super-P wet 30.0% by weight 10.0% by weight 60.0% by weight Example 2 PVdF Super-P wet 20.0% by weight 20.0% by weight 60.0% by weight Example 3 PVdF Super-P wet 10.0% by weight 30.0% by weight 60.0% by weight Example 4 PVdF CNT wet 20.0% by weight 30.0% by weight 60.0% by weight Example 5 PVdF CNT wet 10.0% by weight 30.0% by weight 60.0% by weight Comparative Example 2 PVdF - deflation 100% by weight 0.0% by weight 0.0% by weight Comparative Example 3 PVdF Super-P deflation 60% by weight 40% by weight 0.0% by weight Comparative Example 4 (No adhesive layer is formed, that is, no binder and conductive material are applied to the negative electrode)

Experimental Example 1 (cross-sectional SEM measurement of lithium metal battery)

SEM images of cross-sections of each cathode of Comparative Example 4 and Example 2 were taken and shown in FIG. 2 .

However, in the case of lithium metal, it is difficult to measure the adhesive strength of the electrode separately because of its high reactivity with air and ductility. Accordingly, in a state where each lithium metal battery of Comparative Example 4 and Example 2 was manufactured and charged with SOC100, the battery was disassembled and the SEM of the cross section of the negative electrode was measured.

Referring to FIG. 2B , in the case of Comparative Example 4, it can be seen that the adhesion between the anode current collector and the lithium metal thin film (ie, lithium foil) is not properly performed, and there is a gap therebetween. On the other hand, referring to FIG. 2A , in Example 2, it can be confirmed that the gap between the anode current collector and the lithium metal thin film is not spread and the adhesion is well made.

Such negative electrode adhesion is a factor that affects the lifespan, internal resistance, and the like of a lithium metal battery. Specifically, when the negative electrode adhesion is lower, resistance is generated as a gap between the negative electrode current collector and the lithium metal thin film is generated during driving of the lithium metal battery including the negative electrode, and the lifespan of the lithium metal battery may be reduced.

In the following experimental examples, except for Comparative Example 4, in which the negative electrode adhesion is low, an adhesive layer is formed between the negative electrode current collector and the lithium metal thin film, but the formation method is different (ie, Examples 1 to 3 and Comparative Example 1 to 3) to compare.

Experimental Example 2 (Evaluation of Life Characteristics of Lithium Metal Battery)

Under the following conditions, each lithium metal battery was cycled, and the characteristics of the capacity after the 30th cycle and the capacity after the 100th cycle were evaluated compared to the initial capacity, and the evaluation results were recorded in Table 1 below.

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

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

Capacity retention rate (%) @ ^30th @ ^100th Comparative Example 1 96.2 83.8 Example 1 97.1 85.2 Example 2 98.3 91.8 Example 3 97.6 89.2 Example 4 96.3 87.8 Example 5 97.2 88.5 Comparative Example 2 89.5 73.2 Comparative Example 3 91.3 75.3

According to Table 2, it can be confirmed that the capacity retention rate of the battery varies depending on whether a conductive material is used, how much is used, or whether the type of conductive material is changed. Specifically, compared to the case where only the binder was used as an adhesive layer component (Comparative Example 1), the capacity retention rate after 100 cycles of the battery was more excellent in the case where a conductive material was added (Examples 1 to 5). This is because the conductive material can offset the resistance caused by the binder.

In addition, in Table 2, the difference according to the method of forming the adhesive layer can be confirmed. Specifically, when comparing cases using the same adhesive layer components (e.g., Comparative Example 1 vs. Comparative Example 2; Examples 1 to 3 vs. Comparative Example 3), the capacity retention rate of the battery when the adhesive layer is formed in a wet versus dry manner found to be markedly reduced.

This is inferred to be a result of resistance being formed by the gap between the anode current collector and the lithium metal thin film (ie, lithium foil) during operation of the battery due to the inferior adhesive strength of the adhesive layer formed by the dry process compared to the wet process.

On the other hand, according to the wet process, it is possible to apply the adhesive layer components evenly on the copper current collector by the solvent, and as the solvent volatilizes in the drying process after pressing the lithium foil, the bonding strength between the adhesive layer components as well as the copper collector through the adhesive layer is improved. It is inferred that stable driving is possible while minimizing the increase in resistance of the battery by strengthening the adhesion between the whole and the lithium foil.

On the other hand, in the case of using Super-P as a conductive material along with a binder as an adhesive layer component, the characteristics of the battery of Example 2 in which the weight ratio of conductive material / binder is 1 are the best, and the conductive material content is reduced ( In Example 1) and in the case of increasing (Example 3), it can be seen that the capacity retention rate is partially lowered.

Of course, Examples 1 and 3 also exhibit excellent capacity retention rates as lithium metal batteries. However, by optimizing the weight ratio of the conductive material and the binder as in Example 2, the capacity of the lithium metal battery can be maintained at about 91.8% compared to the initial capacity even after 100 cycles.

Experimental Example 3 (resistance measurement after driving 100 cycles of lithium metal battery)

Before evaluation of Experimental Example 2 (i.e., before each battery cycle) and after evaluation (i.e., after 100 cycles of each battery), each battery was set to SOC100 at 4.25V/0.05C cu-off. resistance was measured. In each case, it was measured with two instruments (EC lab) and Hioki instrument (Hioki 3555 Battery HiTESTER) using the EIS (electrochemical impedance spectroscopy) method, and recorded in Table 3 below.

resistance characteristics Hioki EIS (1Hz) before cycle after 100 cycles before cycle after 100 cycles Comparative Example 1 0.27 0.33 0.51 0.92 Example 1 0.26 0.31 0.47 0.9 Example 2 0.23 0.29 0.4 0.73 Example 3 0.23 0.3 0.43 0.8 Example 4 0.25 0.31 0.45 0.87 Example 5 0.24 0.3 0.45 0.88 Comparative Example 2 0.35 0.7 0.79 1.53 Comparative Example 3 0.31 0.55 0.68 1.33

In Table 3, it can be confirmed that the resistance characteristics of the battery vary depending on whether a conductive material is used, how much is used, or whether the type of conductive material is changed. Specifically, in contrast to the case of using only the binder as an adhesive layer component (Comparative Example 1), the initial resistance of the battery in the case of adding a conductive material (Examples 1 to 5) is relatively low, and the resistance increase rate is also relatively low. , This is because the conductive material can offset the resistance caused by the binder, which is a component of the adhesive layer.

In addition, in Table 3, the difference according to the method of forming the adhesive layer can be confirmed. Specifically, when comparing cases using the same adhesive layer components (e.g., Comparative Example 1 vs. Comparative Example 2; Examples 1 to 3 vs. Comparative Example 3), the battery initial resistance and resistance when the adhesive layer is formed in a wet versus dry manner It is confirmed that the increase rate increased significantly. This is inferred to be a result of resistance being formed by the gap between the anode current collector and the lithium metal thin film (ie, lithium foil) during operation of the battery due to the inferior adhesive strength of the adhesive layer formed by the dry process compared to the wet process.

On the other hand, in the case of using Super-P as a conductive material along with a binder as an adhesive layer component, the battery of Example 2 in which the weight ratio of the conductive material/binder was 1 had the lowest initial resistance and the lowest resistance increase rate. It can be seen that the initial resistance and resistance increase rate increase when the content of the conductive material is reduced (Example 1) or increased (Example 3).

Of course, Examples 1 and 3 also show initial resistance and increase in resistance suitable for lithium metal batteries. However, by optimizing the weight ratio of the conductive material and the binder as in Example 3, the initial resistance of the battery can be further lowered, and the low resistance can be maintained even after 100 cycles.

Claims (11)

negative current collector;
an adhesive layer disposed on one side or both sides of the anode current collector and including a binder and a conductive material; and
Located on the adhesive layer, a lithium metal (Li-metal) thin film; includes,
The lithium metal (Li-metal) thin film is a lithium foil,
The adhesive layer is formed in a wet manner,
The thickness ratio (adhesive layer/current collector) of the adhesive layer to the negative current collector is 1/10 to 1/15,
The thickness ratio of the adhesive layer to the lithium metal thin film (adhesive layer / lithium metal thin film) is 1/20 to 1/40,
The weight ratio of the conductive material to the binder (conductive material / binder) is 1 to 3, a negative electrode for a lithium metal battery.
According to claim 1.
The binder,
Polyvinylidene fluoride (PVDF), a derivative thereof, or containing a mixture thereof,
Cathode for lithium metal battery.
According to claim 1.
The conductive material,
One or a mixture of two or more selected from the group consisting of carbon black, carbon nanotubes, natural graphite, artificial graphite, and carbon fibers,
Cathode for lithium metal battery.
According to claim 1.
The thickness ratio of the adhesive layer to the lithium metal thin film (adhesive layer / lithium metal thin film),
1/30 to 1/40,
Cathode for lithium metal battery.
According to claim 1,
The negative electrode current collector,
containing copper,
Cathode for lithium metal battery.
coating a composition including a binder, a conductive material, and a solvent on one side or both sides of the negative electrode current collector; and
Laminating the negative electrode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween;
The lithium metal (Li-metal) thin film is a lithium foil,
Of the total amount of the composition (100% by weight), the binder is included in 10 to 30% by weight,
Of the total amount of the composition (100% by weight), the conductive material is included in 10 to 30% by weight,
Method for manufacturing a negative electrode for a lithium metal battery.
According to claim 6,
In the step of applying a composition including a binder, a conductive material, and a solvent on one side or both sides of the negative electrode current collector;
The coating amount (g) of the composition relative to the cross-sectional area (cm ² ) of the negative electrode current collector is 0.005 to 0.01 g / cm ² ,
Method for manufacturing a negative electrode for a lithium metal battery.
According to claim 6,
laminating the anode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween; Before,
Further comprising; drying the applied composition;
Method for manufacturing a negative electrode for a lithium metal battery.
According to claim 6,
laminating the anode current collector and a lithium metal (Li-metal) thin film with the applied composition therebetween; after,
Further comprising: compressing the stacked negative electrode current collector and the lithium metal (Li-metal) thin film.
Method for manufacturing a negative electrode for a lithium metal battery.
According to claim 9,
The compression,
carried out by applying heat, pressure, or both,
Method for manufacturing a negative electrode for a lithium metal battery.
The negative electrode of claim 1,
electrolytes, and
A lithium metal battery comprising a positive electrode.

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