KR20210114653A - Surface treatment method of lithium metal and lithium metal battery comprising the lithium metal surface-treated thereby - Google Patents

Abstract

The present invention relates to a lithium metal surface treatment method and a lithium metal battery containing lithium metal surface-treated by the same. According to the present invention, a native oxide film formed on lithium metal is eliminated by using organic acid and an organic film, that can increase stability, is simultaneously formed on a lithium metal surface to stabilize the lithium metal, thereby increasing efficiency of the lithium metal battery.

Description

Surface treatment method of lithium metal and lithium metal battery comprising lithium metal surface-treated thereby

The present invention relates to a secondary battery, and more particularly, to a lithium metal battery.

Studies are underway to use lithium metal, which has a higher theoretical capacity than carbon, which is a commonly used anode material for lithium batteries, as an anode material. Efforts are being made to form various artificial coatings on the surface of lithium metal in order to stably utilize the lithium metal anode.

Conventional lithium metal battery research has mainly made efforts to inhibit dendrite growth of lithium metal by forming a coating layer on the lithium metal surface or modifying the electrolyte. However, there is an indigenous oxide film on the surface of highly reactive lithium metal, and without removing it, there is a limit to performance improvement due to the native oxide film formed in a non-uniform shape. For the development of lithium metal, it is necessary to remove the native oxide film formed on the surface of the lithium metal.

Korean Patent Publication No. 10-2017-0026098

An object of the present invention is to provide a surface treatment method for removing the native oxide film formed on the surface of lithium metal and a lithium metal battery using the surface-treated lithium metal as an anode.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above technical problem, one aspect of the present invention provides a method for surface treatment of lithium metal using an organic acid.

The organic acid may be camphorsulfonic acid.

The organic acid may be used by dissolving it in an organic solvent.

In order to achieve the above technical object, another aspect of the present invention provides a lithium metal battery comprising a lithium metal surface-treated by the surface treatment method.

According to the present invention, the efficiency of a lithium metal battery can be improved by removing the native oxide film formed on the lithium metal by using an organic acid and at the same time forming an organic film that can improve stability on the lithium metal surface to stabilize the lithium metal. have.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a schematic diagram showing a lithium metal battery according to an embodiment of the present invention.
2 is a graph showing the discharge efficiency and discharge capacity retention rate of the lithium metal battery according to the presence or absence of surface treatment of the lithium metal surface-treated through Preparation Example 1 and Comparative Example 1 of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Lithium metal surface treatment method

One aspect of the present invention provides a method for surface treatment of lithium metal.

The surface treatment method of the lithium metal includes the step of immersing the lithium metal in an organic acid.

The organic acid may be camphorsulfonic acid.

The organic acid may be used by dissolving it in an organic solvent.

By immersing the lithium metal in an organic acid for a certain period of time, the native oxide film formed on the surface of the lithium metal is removed, and a new organic film is formed, thereby stabilizing the lithium metal.

lithium metal battery

On the other hand, another aspect of the present invention provides a lithium metal battery.

1 is a schematic diagram showing a lithium metal battery according to an embodiment of the present invention.

1, the lithium metal battery according to the present invention includes a lithium negative electrode 10; a positive electrode 20 including a positive active material; and an electrolyte 30 positioned between the lithium negative electrode 10 and the positive electrode 20 .

Of course, the lithium metal battery according to one embodiment is not limited to this shape, and it is natural that any formation, such as a cylindrical shape, a pouch, etc. that includes the electrolyte according to an embodiment of the present invention and can operate as a battery, is possible.

lithium negative electrode

The lithium negative electrode 10 may be a lithium metal or a lithium alloy surface-treated by the above-described surface treatment method.

As the lithium alloy, an alloy consisting of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn may be used.

A protective film layer 40 may be formed on the surface of the lithium negative electrode 10 .

The protective film layer may be an organic film formed by removing the native oxide film formed on the lithium metal by immersing the lithium metal in a solution in which an organic acid, for example, camphorsulfonic acid is dissolved in an organic solvent for a certain period of time.

The protective layer may improve the efficiency of the lithium metal battery by stabilizing the lithium metal.

anode

The positive electrode 20 may be manufactured by a conventional method known in the art, and may vary depending on the specific type of the lithium secondary battery.

Specifically, when the lithium secondary battery is a lithium ion battery, the positive electrode may contain a positive electrode active material, a binder, and a conductive material. The positive electrode active material of the lithium ion battery may contain a lithium-transition metal oxide or a lithium-transition metal phosphate. The lithium-transition metal oxide may be a composite oxide of lithium and at least one transition metal selected from the group consisting of cobalt, manganese, nickel, and aluminum. Lithium-transition metal oxide is an example, Li(Ni _1-xy Co _x Mn _y )O ₂ (0≤x≤1, 0≤y≤1, 0≤x+y≤1), Li(Ni _{1- xy} Co _x Al _y )O ₂ (0≤x≤1, 0<y≤1, 0<x+y≤1), or Li(Ni _1-xy Co _x Mn _y ) ₂ O ₄ (0≤x≤1) 1, 0≤y≤1, 0≤x+y≤1). The lithium-transition metal phosphate may be a composite phosphate of lithium and at least one transition metal selected from the group consisting of iron, cobalt, and nickel. As an example, the lithium-transition metal phosphate may be Li(Ni _1-xy Co _x Fe _y )PO ₄ (0≤x≤1, 0≤y≤1, 0≤x+y≤1).

When the lithium secondary battery is a lithium sulfur battery, the positive electrode may contain a sulfur compound as a positive electrode active material, and may further contain a binder and a conductive material. The sulfur compound may be solid sulfur (S ₈ ) and/or Li ₂ S.

When the lithium secondary battery is a lithium-air battery, the positive electrode may contain a carbon material, a catalyst for oxidation/reduction of oxygen, or a combination thereof. The carbon material may include carbon black (super P, ketjen black, etc.), carbon nanotubes (CNT), graphite, graphene, porous carbon, or a combination thereof. The catalyst for the redox of oxygen may be a transition metal, a transition metal oxide, or a transition metal carbide. The transition metal is ruthenium (Ru), palladium (Pd), iridium (Ir), cobalt (Co), nickel (Ni), iron (Fe), silver (Ag), manganese (Mn), platinum (Pt), gold (Au), nickel (Ni), copper (Cu), aluminum (Al), chromium (Cr), titanium (Ti), silicon (Si), molybdenum (Mo) tungsten (W), or a combination thereof. have. The transition metal oxide is ruthenium dioxide (RuO ₂ ), iridium dioxide (IrO ₂ ), tricobalt tetraoxide (Co ₃ O ₄ ), manganese dioxide (MnO ₂ ), cerium dioxide (CeO ₂ ), ferric trioxide (Fe ₂ O ₃ ), It may include triiron tetraoxide (Fe ₃ O ₄ ), nickel monoxide (NiO), copper oxide (CuO), a perovskite-based catalyst, or a combination thereof. The transition metal carbide may include a titanium carbide (TiC), silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide (Mo ₂ C)-based catalyst, or a combination thereof.

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 conductivity without causing chemical change in the battery, and is a metal with high conductivity and a metal that the slurry of the positive electrode active material can easily adhere to, and the voltage range of the battery Any of the non-reactive ones can be used. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof.

The solvent for forming the positive electrode includes an organic solvent such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, or water or water, and these solvents are used alone or in two or more types. can be mixed and used.

The amount of the solvent used is sufficient as long as it is capable of dissolving and dispersing the electrode active material, the binder, and the conductive material in consideration of the application thickness of the slurry and the production yield.

The conductive material may be used without limitation as long as it is generally available in the art, for example, artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, carbon fiber, metal fiber, Aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, titanium oxide, polyaniline, poly Thiophene, polyacetylene, polypyrrole, or a mixture thereof may be used.

The binder may be used without limitation as long as it is generally used in the art, for example, polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVdF / HFP), poly( vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene ( PTFE), polyvinyl chloride, polyacrylonitrile, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, ethylene-propylene-diene monomer (EPDM) sulfonated ethylene-propylene-diene monomer, carboxymethylcellulose (CMC) ), regenerated cellulose, starch, hydroxypropyl cellulose, tetrafluoroethylene, or a mixture thereof may be used.

The positive electrode may further add a filler to the mixture, if necessary. The filler is optionally used as a component for inhibiting the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, an olipine-based polymer such as polyethylene or polypropylene; A fibrous material such as glass fiber or carbon fiber is used.

separator

A separator that insulates the electrodes may be used between the positive electrode and the negative electrode, and the separator includes a conventional porous polymer film conventionally used as a separator, for example, ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, A porous polymer film made of a polyolefin-based polymer such as an ethylene/hexene copolymer and an ethylene/methacrylate copolymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a glass fiber having a high melting point, A nonwoven fabric made of polyethylene terephthalate fiber or the like may be used, but is not limited thereto.

electrolyte

The electrolyte is a lithium salt-containing non-aqueous electrolyte, which consists of a non-aqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Rho lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitro Methane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydro An aprotic organic solvent such as a furan derivative, ether, methyl pyropionate, or ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing an ionic dissociation group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _{2 and the like may be used.}

The lithium salt is a material easily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenyl lithium borate, and imide can

In addition, the electrolyte includes, for the purpose of improving charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

battery module

The lithium metal battery according to the present invention can be used not only in a battery module used as a power source for a small device, but also as a unit battery in a medium or large battery pack including a plurality of batteries. The battery module according to another embodiment of the present invention includes the above-described lithium secondary battery as a unit cell, and the battery pack according to another embodiment of the present invention includes the battery module.

Examples of the medium-large device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

The battery case used in the present invention may be adopted that is commonly used in the art, and there is no limitation in the external shape according to the use of the battery, for example, cylindrical, prismatic, pouch type or coin using a can. (coin) type, etc.

Hereinafter, preferred preparation examples and experimental examples are presented to help the understanding of the present invention. However, the following Preparation Examples and Experimental Examples are only for helping understanding of the present invention, and the present invention is not limited by the following Preparation Examples and Experimental Examples.

Manufacturing of lithium metal battery: manufacturing example 1 and comparative example One

<Preparation Example 1: Preparation of lithium metal battery containing surface-treated lithium metal>

A lithium metal foil was supported in a solution of 0.1 wt% of camphorsulfonic acid in tetrahydrofuran (THF) for 1 hour and then dried, and the surface-treated lithium metal foil was used as the negative electrode.

Layered system doped with 2 mol% aluminum [LiNi _{0 . 75} Co _{0 . 10} Mn _{0 . 15} O ₂ ] was used as a positive electrode active material to prepare a positive electrode.

A lithium metal battery was prepared using a lithium salt electrolyte between the positive electrode and the negative electrode.

<Comparative Example 1: Preparation of lithium metal battery containing lithium metal without surface treatment>

A lithium metal battery was manufactured in the same manner as in Preparation Example 1, except that the lithium metal foil was used as the negative electrode without surface treatment.

<Experimental Example 1: Battery charge/discharge test>

The lithium metal batteries prepared in Preparation Example 1 and Comparative Example 1 were subjected to constant current charging and discharging, and the efficiency of charging versus discharging according to the number of cycles and the discharging capacity retention rate were measured and shown in FIG. 2 .

2 is a graph showing the discharge efficiency and discharge capacity retention rate of the lithium metal battery according to the presence or absence of surface treatment of the lithium metal surface-treated through Preparation Example 1 and Comparative Example 1 of the present invention.

As shown in FIG. 2, it can be seen that the lithium metal battery using the lithium metal surface-treated with an organic acid according to the present invention maintains better discharge efficiency and discharge capacity retention rate compared to charging compared to the case where the surface treatment is not performed.

Therefore, according to the present invention, by using an organic acid to remove the native oxide film formed on the lithium metal and at the same time to form an organic film capable of increasing stability on the surface of the lithium metal to stabilize the lithium metal, the efficiency of the lithium metal battery can be improved. can

On the other hand, the embodiments of the present invention disclosed in the present specification and drawings are merely presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

10: lithium negative electrode
20: positive electrode
30: electrolyte
40: protective film layer

Claims (5)

immersing lithium metal in an organic acid for a predetermined time;
removing the native oxide film formed on the surface of the lithium metal; and
A method for surface treatment of lithium metal comprising; forming a new organic film on the surface of the lithium metal. The method according to claim 1,
The organic acid is camphor sulfonic acid surface treatment method of lithium metal. The method according to claim 1,
The method for surface treatment of lithium metal using the organic acid dissolved in an organic solvent. 4. The method according to claim 3,
The organic solvent is tetrahydrofuran surface treatment method of lithium metal. anode;
electrolyte; and
A lithium metal battery comprising the surface-treated lithium metal of claim 1 as an anode.

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