KR20240031012A - An anode comprising Lithium-Lanthanum alloy and a lithium ion secondary battery comprising the same - Google Patents

Abstract

It is a negative electrode containing a lithium-lanthanum alloy, and the negative electrode can be applied to a negative electrode for lithium-sulfur batteries. As described above, lithium-sulfur batteries with alloy negative electrodes have improved lifespan characteristics and improved electrochemical efficiency.

Description

An anode comprising Lithium-Lanthanum alloy and a lithium ion secondary battery comprising the same}

The present invention relates to a lithium-sulfur battery with improved battery performance such as output and capacity.

As the scope of application of lithium secondary batteries expands not only to portable electronic devices but also to electric vehicles (EVs) and energy storage systems (ESS), demand for lithium secondary batteries with high capacity, high energy density, and long life is increasing.

Among various lithium secondary batteries, lithium-sulfur batteries use a sulfur compound containing a sulfur-sulfur (S-S) bond as a positive electrode active material, lithium metal, a carbon-based material capable of intercalating/deintercalating lithium ions, and lithium. It is a battery system that uses silicon or tin, which forms an alloy with metal, as a negative active material.

Lithium-sulfur batteries have the advantage of being cheap, non-toxic, and environmentally friendly as sulfur, the main material of the positive electrode active material, has a low atomic weight and is a very abundant resource.

In addition, lithium-sulfur batteries use a conversion reaction of lithium ions and sulfur at the anode (S ₈ +16 Li ⁺ +16 e ^- 8 Li ₂ S), the theoretical specific capacity is 1,675 mAh/g, and when lithium metal is used as the cathode, the theoretical energy density is 2,600 Wh/kg. Because the theoretical energy density of lithium-sulfur batteries is much higher than that of other battery systems (Ni-MH batteries: 450 Wh/kg, Li-FeS batteries: 480 Wh/kg, Li-MnO ₂ batteries: 1,000 Wh/kg) kg, Na-S battery: 800 Wh/kg, lithium-ion battery: 250 Wh/kg), lithium-sulfur battery is attracting attention among secondary batteries developed so far because it is a high-capacity, eco-friendly, and inexpensive lithium secondary battery. .

In addition, in the case of lithium-sulfur batteries, when lithium metal is used as the negative electrode active material, the theoretical specific capacity is very high at 3,860 mAh/g, so the standard hydrogen electrode (SHE) is also -3.045 V. It is very low, making it possible to implement batteries with high capacity and high energy density, so many studies are being conducted on next-generation battery systems.

However, lithium metal, which is a negative electrode active material, has high chemical/electrochemical reactivity and easily reacts with electrolyte solution, so a solid electrolyte interface layer (SEI layer), a type of protective film, is formed on the surface of the negative electrode. The solid electrolyte interfacial layer formed in this way can secure a certain level of stability for the negative electrode active material containing lithium metal by suppressing the direct reaction between the electrolyte and lithium metal, so conventionally, such an SEI layer can be applied stably and uniformly to the surface of lithium metal. Methods of forming have been attempted.

However, in the case of a lithium-sulfur battery, when the negative electrode active material is lithium metal, it is difficult to keep the SEI layer constant because the electrochemical reaction of the battery continues to occur on the surface of the lithium metal even if the SEI layer is formed as described above. In addition, because the SEI layer formed by the reaction of electrolyte and lithium metal has weak mechanical strength, the structure collapses as the battery charges and discharges, causing a local current density difference and forming lithium dendrites on the lithium metal surface. . In addition, the lithium dendrites formed in this way cause internal short circuits of the battery and inactive lithium (dead lithium), which not only increases the physical and chemical instability of the lithium secondary battery, but also reduces battery capacity and cycle life. In addition, the positive electrode active material is dissolved in the form of lithium polysulfide (LiPS) and moves to the negative electrode to form lithium sulfide by-products, which may cause loss of positive electrode active material/passivation of the negative electrode and unwanted side reactions.

Due to the high instability of lithium metal and the problem of lithium dendrite formation, many attempts have been made to solve these problems.

For example, in Korean Patent Publication No. 2016-0034183, a protective layer is formed on the surface of the negative electrode active material layer containing lithium metal and lithium alloy with a polymer matrix that can accumulate electrolyte while protecting the negative electrode, thereby preventing loss of electrolyte and dendrites. It is disclosed that the creation of can be prevented.

Korean Patent Publication No. 2016-0052351 discloses that the stability and lifespan characteristics of lithium secondary batteries can be improved by suppressing the growth of lithium dendrites by introducing an absorbing material for lithium dendrites into the polymer protective film formed on the surface of lithium metal. there is.

These prior technologies suppressed the reaction between electrolyte and lithium metal or the formation of lithium dendrites to some extent, but the effect was not sufficient. In addition, there is a problem of deterioration, such as hardening or expansion of the protective layer as the charging and discharging of the battery progresses.

Accordingly, in the present invention, a lithium-lanthanum alloy anode was used directly as an anode for a lithium-sulfur battery to stabilize anode plating/elution to improve cell efficiency and lifespan.

The purpose of the present invention is to provide a negative electrode that prevents precipitation/elution during battery operation. Another object of the present invention is to provide a lithium ion secondary battery including the negative electrode. It will be readily apparent that other objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof.

The first aspect of the present invention relates to an anode for a lithium secondary battery comprising a Li-M alloy containing lithium and a lanthanum group metal as a negative electrode active material.

A second aspect of the present invention is that in the first aspect, the lanthanide group metal is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), and samarium (Sm). , europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). It includes one or more selected types.

A third aspect of the present invention is that, in the second aspect, the lanthanum group metal includes lanthanum (La).

A fourth aspect of the present invention, in any one of the first to third aspects, is that the content of the lanthanide group metal is less than 15 wt% compared to 100 wt% of the Li-M alloy.

A fifth aspect of the present invention is that in any one of the first to fourth aspects, the content of the lanthanide group metal is 1 wt% to 10 wt% relative to 100 wt% of the Li-M alloy.

The sixth aspect of the present invention, in any one of the first to fifth aspects, is that the negative electrode contains 95 wt% or more of the Li-M alloy out of 100 wt% of the negative electrode active material.

A seventh aspect of the present invention, according to any one of the first to sixth aspects, is that the negative electrode includes Li-M alloy in the form of a metal thin film as a negative electrode active material layer.

An eighth aspect of the present invention is that, in the seventh aspect, the negative electrode further includes a current collector.

The ninth aspect of the present invention relates to a lithium ion secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is according to one aspect of the present invention.

A tenth aspect of the present invention is that according to the ninth aspect, the lithium secondary battery is a lithium-sulfur battery in which the positive electrode active material includes sulfur (S) or a sulfur (S) compound.

An eleventh aspect of the present invention is a method for manufacturing a negative electrode for a lithium secondary battery according to any one of the first to eighth aspects,

Obtaining a first melt by melting metallic lithium;

Obtaining a second melt by adding a lanthanide metal to the lithium melt obtained above;

alloying the second melt by maintaining the temperature above 200°C; and

It includes the step of obtaining a lithium-lanthanide alloy by cooling the second melt obtained in the alloying step.

The lithium-lanthanum alloy negative electrode according to the present invention can be applied as a lithium-sulfur battery negative electrode. The lithium-sulfur battery incorporating the lithium-lanthanum alloy as the negative electrode has the effect of improving lifespan characteristics and coulombic efficiency. When a lithium-lanthanum alloy is used as a negative electrode, uniform electrochemical plating/elution of lithium is induced, thereby effectively suppressing the decomposition of LiPS and lithium salt due to interfacial side reactions.

The drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to better understand the technical idea of the present invention together with the contents of the above-described invention, so the present invention is limited only to the matters described in such drawings. It is not interpreted as such. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer description.
Figure 1 confirms the cycle characteristics of the batteries manufactured in the above examples and comparative examples.
Figures 2 and 3 show the coulombic efficiency of the batteries manufactured in the above examples and comparative examples.

Hereinafter, the present invention will be described in more detail.

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

Throughout the specification of the present application, when a part is said to “include” or “have” a certain component, this does not exclude other components but may further include other components unless specifically stated to the contrary. it means.

In addition, the terms "about", "substantially", etc. used throughout the specification of the present application are used as meanings at or close to the numerical value when manufacturing and material tolerances inherent in the mentioned meaning are presented, and to aid understanding of the present application. It is used to prevent unscrupulous infringers from unfairly exploiting disclosures in which precise or absolute figures are mentioned.

Throughout this specification, the description of “A and/or B” means “A or B or both.”

In the present invention, “specific surface area” is measured by the BET method, and can be specifically calculated from the amount of nitrogen gas adsorption under liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

The term “polysulfide” used in this specification refers to “polysulfide ion (Sx ^2- , x = 8, 6, 4, 2)” and “lithium polysulfide (Li ₂ S _x or LiS _x ^- , x = 8). , 6, 4, 2)”.

The term “composite” as used herein refers to a material that combines two or more materials to form physically and chemically different phases while exhibiting more effective functions.

The term “porosity” used in this specification refers to the ratio of the volume occupied by pores to the total volume in a structure, and vol% is used as its unit, and can be interchanged with terms such as porosity and porosity. You can use it.

In the present invention, “particle diameter D ₅₀ ” refers to the particle size based on 50% of the cumulative volumetric particle size distribution of the particles. The particle size D ₅₀ can be measured using a laser diffraction method. For example, after dispersing the particles in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measurement device (e.g. Microtrac MT 3000), irradiated with ultrasonic waves at about 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. , can be measured by determining the particle size corresponding to 50% of the volume accumulation.

In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of explanation, so the present invention is not necessarily limited to what is shown. In the drawing, the thickness is enlarged to clearly express various layers and areas. And in the drawings, for convenience of explanation, the thicknesses of some layers and regions are exaggerated.

cathode

The first aspect of the present invention relates to a negative electrode active material for an electrochemical device and a negative electrode containing the same.

The negative electrode contains an alloy (Li-M) containing a lanthanide metal and lithium as a negative electrode active material.

In one embodiment of the present invention, the alloy containing the lanthanide group metal and lithium may be stoichiometrically expressed as xLi-yM. Here, x is the molar ratio of Li in the alloy, M is one or more selected from lathanum group metals, and y is the molar ratio of M in the alloy. In one embodiment of the present invention, x and y may each independently exceed 0. For example, x+y may be 0 or more.

The lanthanide group metal (M) is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), and terbium. (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The metal (M) preferably contains lanthanum.

In one embodiment of the present invention, the alloy Li-M may contain lanthanide metal M in a range of 1 wt% or more based on 100 wt% of the total alloy. Meanwhile, the lanthanide group metal may be included in an amount of less than 15 wt%. Meanwhile, in terms of improving lifespan characteristics and coulombic efficiency, the lanthanide metal M may be included in more than 3 wt%, more than 5 wt%, and more than 7 wt% in the alloy. On the other hand, if an excessively large amount of lanthanide metal M is included in the alloy, the coulombic efficiency appears unstable and the average efficiency value may be lowered compared to a lithium metal anode to which no alloy is applied, so less than 15wt%, less than 14wt%, less than 13wt. % or less, 12wt% or less, 11wt% or less, 10wt% or less, 7wt% or less, 5wt% or less, or 3wt% or less. The upper and/or lower limit of the metal M may be controlled to an appropriate range in consideration of the electrochemical characteristics of the battery to which the negative electrode is ultimately applied.

Additionally, in one embodiment of the present invention, the negative electrode may include 95 wt% or more of the Li-M alloy as the negative electrode active material. For example, the negative electrode may include the Li-M alloy as the negative electrode active material.

Meanwhile, the negative electrode according to the present invention can be applied to a battery by manufacturing the Li-M alloy in the form of a thin film. That is, in the present invention, a Li-M alloy thin film can be used as the negative electrode active material layer. In one embodiment of the present invention, the thickness of the negative electrode active material layer may be 0.1 μm or more and 200 μm or less in terms of providing a sufficient lithium source for battery operation and realizing high energy density. For example, the thickness of the Li-M alloy thin film may be 180 μm or less, or 160 μm or less, 150 μm or less, 140 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, or 100 μm or less. Meanwhile, the thickness of the negative electrode active material layer is 0.1 ㎛ or more, 0.5 ㎛ or more, 2 ㎛ or more, 5 ㎛ or more, 10 ㎛ or more, 20 ㎛ or more, 30 ㎛ or more, 50 ㎛ or more, 70 ㎛ or more, 75 ㎛ or more, 90 ㎛ or more. You can. In one embodiment of the present invention, the negative electrode may be formed solely from the Li-M thin film without a current collector, or may be formed by bonding a current collector and a Li-M alloy thin film.

In one embodiment of the present invention, the Li-M alloy may be monolithic. The monolithic (moholithic) means that there is no concentration gradient of metal M in the Li-M alloy according to the present invention. Furthermore, Li-M alloys according to the present invention can be substantially homogeneous throughout the alloy. Li-M alloys according to the invention can be homogeneous throughout the alloy. The Li-M alloy according to the invention is a substantially homogeneous bulk material, wherein the entire bulk material is homogeneous in a continuous phase. That is, all of the metal M is melted and the entire bulk is substantially or completely homogeneous in a continuous phase with lithium.

In one embodiment of the present invention, as the negative electrode current collector, negative electrode current collectors commonly used in the art may be used, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, Surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode current collector may typically have a thickness of 3㎛ to 500㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials. For example, when a current collector in the form of a metal thin film is used, the current collector may have a thickness of 1 μm to 20 μm.

Meanwhile, the method of forming the Li-M thin film is not particularly limited, and any method of forming a layer or film commonly used in the art can be used. For example, methods such as compression and coating methods can be used.

The Li-M thin film includes the steps of a) melting metallic lithium to obtain a lithium melt (first melt); b) adding metal M to the lithium melt obtained in step a) to obtain a lithium-metal M melt (second melt); c) maintaining the lithium-metal M melt obtained in step b) at a temperature of 200° C. or higher; and d) cooling the lithium-metal M melt obtained in step c) to obtain a lithium-metal M ingot; and e) producing a lithium-metal M alloy thin film from a lithium-metal M alloy ingot. In step c), alloying of lithium and metal M may be achieved.

The manufacturing method may include placing a solid piece of lithium, such as a lithium ingot, together with a solid piece, such as a metal M pellet, in a suitable heating means (eg, vessel). The heating means may further include a stirring means for stirring the melt of the two metals and a means for providing an inert gas atmosphere to the heating means. The step a) of providing metal lithium and metal M may not include a sputtering step such as DC sputtering. Rather, melting in step b) may involve stirring the melt. This method is a more cost-effective method to provide an improved lithium-metal M alloy foil with a much more homogeneous distribution of metal M.

The melting may include heating metallic lithium together with metal M at a temperature of 200°C to 500°C.

Cooling in step d) may be to room temperature.

In one embodiment of the present invention, the method for producing the lithium-metal M thin film may include a method of obtaining the lithium-metal M thin film including roll pressing a lithium-lithium-metal M alloy ingot. The roll press may include applying heat and pressure simultaneously, and may be performed using a hot roll press or the like.

Meanwhile, in one embodiment of the present invention, the electrode manufacturing method according to the present invention may further include the following step f) of laminating/adhering the lithium-metal M thin film obtained above with a current collector.

secondary battery

A second aspect of the present invention relates to a lithium ion secondary battery including the negative electrode.

Anode (lithium-sulfur battery)

The lithium ion secondary battery may be a lithium-sulfur battery.

The positive electrode according to the present invention includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector.

The current collector may be any material used in the art that has electrical conductivity and is used as a current collecting component. For example, the positive electrode current collector may include stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum. Alternatively, a stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector may typically have a thickness of 3㎛ to 500㎛, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder material. The positive electrode active material layer may contain 80 to 97 wt% of the positive electrode active material, 2 to 10 wt% of the conductive material, and 2 to 10 wt% of the binder based on the total weight of the positive electrode active material, conductive material, and binder material.

In the present invention, the positive electrode active material includes a sulfur-carbon complex. Preferably, the positive electrode active material may contain 80 wt% or more of a sulfur-carbon complex, preferably 90 wt% or more, based on 100 wt% of the positive electrode active material, and more preferably, the positive electrode active material may include only the sulfur-carbon composite. In addition, it is preferable that the sulfur content is 70% by weight or more compared to 100% by weight of the sulfur-carbon composite.

In one embodiment of the present invention, the sulfur-carbon composite may be complexed by simply mixing the sulfur and the carbon material, or may have a coating or support form of a core-shell structure. The coating form of the core-shell structure is one in which either sulfur or a carbon material coats another material. For example, the surface of the carbon material may be covered with sulfur or vice versa. The carbon material has a porous structure with pores on the inside and surface of the body, and may have sulfur filled inside pores. The form of the sulfur-carbon composite can be used as long as it satisfies the content ratio of the sulfur-based compound and the carbon material described below, and is not limited in the present invention. Meanwhile, in the present invention, it is preferable that the sulfur content is 70% by weight or more based on the total weight of the positive electrode active material.

Since the sulfur alone has no electrical conductivity, it is used in combination with a carbon material.

In one embodiment of the present invention, the sulfur is inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole (2,5-dimercapto -1,3,4-thiadiazole), 1,3,5-trithiocyanuic acid (1,3,5-trithiocyanuic acid), disulfide compounds, organosulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n , x=2.5 to 50, n≥2). Preferably, it may contain inorganic sulfur (S ₈ ).

The carbon material has a porous structure containing a large number of irregular pores on the surface and inside, and serves as a carrier to provide a framework on which sulfur can be uniformly and stably immobilized, and compensates for the low electrical conductivity of sulfur to provide electricity. This is to ensure that the chemical reaction proceeds smoothly. In particular, in sulfur-carbon composites, when the carbon material that acts as a support for sulfur has a large BET specific surface area and an appropriate particle size (D ₅₀ ), the amount of sulfur supported is high, but the irreversible capacity is low and energy density is increased, leading to an electrochemical reaction. The market utilization rate can be increased.

In one embodiment of the present invention, the BET specific surface area of the carbon material may be at least 100 m ² /g or more, and may be at most 3000 m ² /g. Together or independently, the carbon material may have a primary particle diameter (D ₅₀ ) of 1 μm to 50 μm.

When the BET specific surface area and particle size (D ₅₀ ) of the carbon material satisfies the above range, sulfur can be uniformly dispersed on the inner and outer surfaces of the carbon material and the electrochemical reactivity of sulfur can be increased by lowering the irreversible capacity. In addition, the use of carbon materials improves the electrochemical reactivity, stability, and electrical conductivity of the sulfur-carbon composite, which not only improves the capacity and lifespan characteristics of the lithium-sulfur battery, but also reduces the loss or volume change of sulfur during charging and discharging. Even if this occurs, optimal charging and discharging performance is achieved.

When the primary particle particle size (D ₅₀ ) exceeds 50㎛, it is difficult to move lithium ions into the particle due to restrictions on material movement, making it difficult to efficiently use sulfur located at the carbon center. If the primary particle diameter (D ₅₀ ) is less than 1㎛, it is difficult to increase the solid content because a large amount of solvent is required during the electrode slurry production process, and there is a problem of reduced output due to insufficient pores between particles.

In the sulfur-carbon composite of the present invention, the carbon material used as a support for sulfur can generally be manufactured by carbonizing precursors of various carbon materials.

Meanwhile, in one embodiment of the present invention, the pores of the carbon material may have a diameter ranging from 0.5 nm to 200 nm based on the longest diameter. The carbon material may be used without limitation as long as it is spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped and is commonly used in lithium-sulfur secondary batteries.

The carbon material may be any carbon-based material that has porous and conductive properties and is commonly used in the art. For example, graphite; graphene; Carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); Carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); Graphites such as natural graphite, artificial graphite, and expanded graphite; Carbon nanoribbon; It may include one or more types selected from the group consisting of carbon nanobelts, carbon nanorods, and activated carbon.

In the sulfur-carbon composite according to the present invention, the sulfur is located on at least one of the pore inner and outer surfaces of the carbon material, wherein the sulfur is less than 100% of the entire inner and outer surface of the carbon material, preferably 1 to 10%. It may be present in the range of 95%, more preferably 60 to 90%. When the sulfur is within the above range on the surface of the carbon material, the maximum effect can be achieved in terms of electron transfer area and electrolyte wettability. Specifically, since sulfur is thinly and evenly impregnated on the surface of the carbon material in the above range, the electron transfer contact area can be increased during the charging and discharging process. If the sulfur is located on 100% of the entire surface of the carbon material, the carbon material is completely covered with sulfur, which reduces the wettability of the electrolyte and reduces contact with the conductive material contained in the electrode, so it cannot receive electron transfer and participate in the reaction. There will be no more.

Additionally, in one embodiment of the present invention, the sulfur-carbon composite can be obtained by the following manufacturing method.

The manufacturing method of the sulfur-carbon composite according to the present invention is not particularly limited and is commonly known in the art, and can be manufactured by a composite method consisting of the steps of (S1) mixing carbon material and sulfur, and then (S2) compounding. there is.

The mixing in step (S1) is to increase the degree of mixing between sulfur and carbon materials and can be performed using a stirring device commonly used in the art. At this time, mixing time and speed can also be selectively adjusted depending on the content and conditions of the raw materials.

The complexation method of step (S2) is not particularly limited in the present invention, and methods commonly used in the art may be used. For example, methods commonly used in the industry, such as dry compounding or wet compounding such as spray coating, can be used. For example, a method may be used in which the mixture of sulfur and carbon material obtained after mixing is heat treated so that the molten sulfur can be evenly coated on the inner and outer surfaces of the carbon material. Meanwhile, in one embodiment of the present invention, a process of pulverizing the mixture of sulfur and carbon material by a method such as ball milling may be performed before the heat treatment. In one embodiment of the present invention, the heat treatment may be performed for about 20 minutes to 24 hours at a temperature of 120°C to 160°C, and a heating device such as an oven may be applied.

The sulfur-carbon complex manufactured through the above-mentioned manufacturing method has a structure that has a high specific surface area, a high amount of sulfur supported, and improved sulfur utilization, so not only does the electrochemical reactivity of sulfur improve, but it also improves accessibility and contact with the electrolyte solution. The capacity and lifespan characteristics of lithium-sulfur batteries can be improved.

Other cathode materials

In one embodiment of the present invention, the positive electrode active material may be composed of only the sulfur-carbon composite. In addition, in addition to the sulfur-carbon composite, it may further include one or more additives selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

In a specific embodiment of the present invention, the positive electrode active material layer may include a lithium transition metal complex oxide represented by the following [Chemical Formula 1].

[Formula 1]

Li _a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 1, M ¹ may be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

The M ² is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, and preferably one selected from the group consisting of Zr, Y, Mg, and Ti. It may be more than one, more preferably Zr, Y, or a combination thereof. The M ² element is not necessarily included, but when included in an appropriate amount, it can promote grain growth during firing or improve crystal structure stability.

conductive material

The conductive material is used to provide conductivity to the negative electrode, and can be used without particular restrictions in the battery being constructed as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, etc., of which one type alone or a mixture of two or more types may be used. The conductive material may typically be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

binder materials

The binder material serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene. Copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone , polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof. , one type of these may be used alone or a mixture of two or more types may be used.

electrode assembly

Another aspect of the present invention relates to an electrode assembly including the cathode. The cathode may be according to the above description. The positive electrode may include the above-described sulfur-carbon complex as a positive electrode active material. The electrode assembly includes a cathode, an anode, and a separator interposed between the cathode and the anode. For example, the separator may be laminated between the cathode and the anode to form a stacked or stacked/folded structure, or may be wound to form a jelly-roll type structure. In addition, when forming the jelly-roll structure, a separator may be additionally disposed on the outside to prevent the cathode and anode from contacting each other.

separator

The separator is disposed within the electrode assembly in such a way that it is interposed between the cathode and the anode. The separator separates the negative electrode from the positive electrode and provides a passage for lithium ions, and can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. Specifically, the separator is a porous polymer film, for example, a porous film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. A polymer film or a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a separator coated with a coating layer containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength.

battery

Another aspect of the present invention relates to an electrochemical device including the electrode assembly. The electrochemical device is one in which an electrode assembly and an electrolyte are stored together in a battery case. The battery case may be an appropriate battery case, such as a pouch type or a metal can type, as long as it is commonly used in the field of technology, without any particular restrictions. The shape of the battery is not particularly limited and can be of various shapes such as cylindrical, stacked, and coin-shaped.

electrolyte

In the present invention, the electrolyte may include an organic solvent and a lithium salt.

organic solvent

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The organic solvent may be any solvent commonly used in lithium secondary battery electrolytes without limitation. For example, ether, ester, amide, chain carbonate, cyclic carbonate, etc. may be used alone or in combination of two or more. there is. Among these, ether-based compounds may be representatively included.

The ether-based compound may include acyclic ether and cyclic ether.

For example, the acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, ethylene glycol ethylmethyl ether, diethylene glycol dimethyl. Ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetra It may be one or more selected from the group consisting of ethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ethyl ether.

For example, the cyclic ether is 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl- 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1 ,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl- 1,3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene and isosorbide dimethyl ether. ether), furan, 2-methyl furan, 3-methyl furan, 2-ethyl furan, 2-butyl furan, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethyl furan, pyran, 2- Methylpyran, 3-methylpyran, 4-methylpyran, benzoburan, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2- It may be one or more selected from the group consisting of butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, but is not limited thereto.

Examples of esters of the above organic solvents include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ -valerolactone, ε -caprolactone, and mixtures of two or more of them may be selected from the group, but are not limited thereto.

Specific examples of the linear carbonate compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or mixtures of two or more thereof. Any one selected from the group may be mentioned, but it is not limited thereto.

In addition, specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2 , 3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and their halides, or mixtures of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

lithium salt

The lithium salt is a compound that can provide lithium ions in the electrolyte. These lithium salts include LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiCH ₃ SO ₃ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiC ₄ BO ₈ , LiCl, LiBr, LiB ₁₀ Cl ₁₀ , LiI or LiB(C ₂ O ₄ ) ₂ , etc. may be used. In the present invention, in terms of increasing the availability of sulfur and implementing a high-capacity and high-voltage battery, it is preferable to include Li-TFSI as the lithium salt. More preferably, the lithium salt may include LiN(CF ₃ SO ₂ ) ₂ (Li-TFSI) in an amount of 80 wt% or more, or 90 wt% or more, or 100% based on 100 wt% of the total lithium salt.

The concentration of the lithium salt is in the range of 0.1 to 2.0 M, preferably 0.5 to 1 M, and more preferably 0.5 to 0.75 M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively. If the concentration of the lithium salt is less than the above range, it may be difficult to secure ionic conductivity suitable for battery operation, and if it exceeds the above range, the viscosity of the electrolyte increases, causing a decrease in the mobility of lithium ions, or a decomposition reaction of the lithium salt itself. As this increases, battery performance may deteriorate.

In a specific embodiment of the present invention, in an electrolyte containing a first solvent, a second solvent, and a lithium salt, the molar ratio of the lithium salt, the second solvent, and the first solvent is 1:0.5 to 3:4.1 to 15. It can be. Additionally, in one embodiment of the present invention, the molar ratio of the lithium salt, the second solvent, and the first solvent may be 1:2:4 to 13 or 1:3:3 to 10 or 1:4:5 to 10. In the electrolyte included in the lithium-sulfur battery of the present invention, the first solvent containing a fluorine-based ether compound may be included in a higher content ratio than the second solvent containing a glyme-based compound.

Other additives

In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. For example, the additives include nitric acid compounds, nitrous acid compounds, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme ( glyme), hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy Ethanol or aluminum trichloride can be used alone or in combination. The additive may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

In a specific embodiment of the present invention, the electrolyte may include a nitric acid compound and/or a nitrous acid-based compound as an additive. The nitric acid/nitrite-based compounds described above are effective in forming a stable film on the lithium metal electrode, which is the negative electrode, and improving charge/discharge efficiency. These nitric acid or nitrite-based compounds include lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), barium nitrate (Ba(NO ₃ ) ₂ ), ammonium nitrate (NH ₄ NO ₃ ), and nitrous acid. Inorganic nitric acid or nitrite compounds such as lithium (LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), and ammonium nitrite (NH ₄ NO ₂ ); Organic nitric acids such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite. or nitrous acid compounds; It may contain at least one selected from the group consisting of organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof. However, it is not limited to this. In a preferred embodiment of the present invention, the additive may include lithium nitrate.

Additionally, the present invention provides a battery module including the lithium-sulfur battery as a unit cell. The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large devices include power tools that are powered by an omni-electric motor; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the attached patent claims.

Example

Preparation of cathode

Li metal was put into a heating furnace and melted by applying heat to a temperature of 200°C to 500°C. Pellets of metal M were added here at the ratio shown in Table 1 below and melted. Afterwards, the heating furnace was maintained at 200°C to 500°C and stirred. The result was cooled to form a Li-M alloy ingot. The ingot was extruded and rolled to a thickness of 60㎛.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Content of metal M in alloy (wt%) 5wt% 10wt% 0wt% 0.5wt% 15wt% 5wt% Types of Metal M La La - La La Al

Manufacturing of batteries

Carbon nanotubes and sulfur were evenly mixed and placed in an oven at 155°C for 30 minutes to prepare a sulfur-carbon composite. The sulfur content in 100 wt% of the sulfur-carbon composite was 75 wt%. A slurry for producing a positive electrode was prepared by mixing 96 wt% of the prepared sulfur-carbon composite and 4 wt% of styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC 7:3 weight ratio) as a binder. The concentration of solid content in the slurry was 25 wt%. The slurry was applied on both sides of a 20㎛ thick aluminum current collector, dried at 50°C for 12 hours, and pressed using a roll press machine to prepare a positive electrode. The loading amount of the positive electrode active material was 4.00 mAh/cm ² and the porosity was 72 vol%.

The electrolyte was 1M concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1wt% in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME=1:1 (volume ratio)). A mixed solution in which lithium nitrate (LiNO ₃ ) was dissolved was used.

The prepared positive electrode and the negative electrode are positioned to face each other, and polyethylene with a thickness of 16 ㎛ and a porosity of 68% is placed between them as a separator, then charged into a pouch, injected with the prepared electrolyte, and then sealed to produce a lithium-sulfur battery. did. In the battery, a total of 7 positive electrodes and 8 negative electrodes were stacked and folded with the separator interposed. The manufactured battery was operated at 25°C at 0.2C charge/0.3C discharge to check cycle characteristics and efficiency.

Evaluation results

Figure 1 confirms the cycle characteristics of the batteries manufactured in the above examples and comparative examples. According to this, it was confirmed that the batteries of Examples 1 and 2 had superior cycle characteristics to the battery of Comparative Example 1. In particular, Example 2, in which the lanthanum content in the cathode was 10 wt% by weight, showed better cycle characteristics than Example 1. Meanwhile, in Comparative Example 2, similar to Comparative Example 1, no improvement in cycle characteristics was confirmed. Additionally, in Comparative Example 4, similar to Comparative Example 1, no improvement in cycle characteristics was confirmed.

Figures 2 and 3 show the coulombic efficiency of the batteries manufactured in the above examples and comparative examples. Referring to this, it was confirmed that the average coulombic efficiency of the batteries of Examples 1 and 2 was increased compared to the battery of Comparative Example 1. In particular, it was confirmed that the battery of Example 2 (10 wt% La) achieved a higher average efficiency value than the battery of Example 1 (5 wt% La). Meanwhile, as a result of checking the battery of Comparative Example 3, it was confirmed that when 15 wt% or more of lanthanum was applied, the coulombic efficiency was greatly unstable and the average efficiency value was also lowered compared to the battery of Comparative Example 1.

Claims (12)

A negative electrode for a lithium secondary battery containing a Li-M alloy containing lithium (Li) and a lanthanum group metal (M).
According to paragraph 1,
The lanthanide group metals include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), and terbium (Tb). , dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
According to paragraph 2,
A negative electrode for a lithium secondary battery, wherein the lanthanum group metal includes lanthanum (La).
According to paragraph 1,
A negative electrode for a lithium secondary battery, wherein the content of lanthanum group metal is less than 15 wt% compared to 100 wt% of the Li-M alloy.
According to paragraph 1,
A negative electrode for a lithium secondary battery, wherein the content of lanthanide metal is 1 wt% to 10 wt% relative to 100 wt% of the Li-M alloy.
According to paragraph 1,
The negative electrode is a negative electrode for a lithium secondary battery in which the Li-M alloy is 95 wt% or more out of 100 wt% of negative electrode active material.
According to paragraph 1,
The negative electrode is a negative electrode for a lithium secondary battery comprising a Li-M alloy in the form of a metal thin film as a negative electrode active material layer.
In clause 7,
The negative electrode for a lithium secondary battery further includes a current collector.
A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is according to any one of claims 1 to 8.
According to clause 9,
The lithium secondary battery is a lithium-sulfur battery in which the positive electrode active material includes sulfur (S) or a sulfur (S) compound.
In the method for manufacturing a negative electrode for a lithium secondary battery according to any one of claims 1 to 8,
Obtaining a first melt by melting metallic lithium;
Obtaining a second melt by adding a lanthanide metal to the lithium melt obtained above;
alloying the second melt by maintaining the temperature above 200°C; and
A method of manufacturing a negative electrode for a lithium secondary battery comprising: cooling the second melt obtained in the alloying step to obtain a lithium-lanthanide alloy.
According to clause 11,
The alloy is obtained in the form of an ingot, and the method of manufacturing a negative electrode for a lithium secondary battery further includes the step of thinning it into a plate-like structure with a predetermined thickness.

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