CN118633178A

CN118633178A - Negative electrode for lithium secondary battery, method for producing same, and lithium secondary battery comprising same

Info

Publication number: CN118633178A
Application number: CN202380020651.4A
Authority: CN
Inventors: 金允贞; 金明星; 金起铉; 李度中
Original assignee: Lg Energy Solution
Current assignee: Lg Energy Solution
Priority date: 2022-08-31
Filing date: 2023-08-31
Publication date: 2024-09-10

Abstract

The present invention relates to: a negative electrode for a lithium secondary battery, which comprises a lithium-magnesium-aluminum alloy; a method for producing the same; and a lithium secondary battery, such as a lithium sulfur battery, including the same. Lithium secondary batteries, such as lithium sulfur batteries, comprising the negative electrode according to the present invention exhibit superior battery life characteristics compared to those using a negative electrode from conventional technology.

Description

Negative electrode for lithium secondary battery, method for producing same, and lithium secondary battery comprising same

Technical Field

The present disclosure relates to a negative electrode for a lithium secondary battery, a method of preparing the same, and a lithium secondary battery including the same. The present application claims priority from korean patent application No. 10-2022-0110208, filed on 8-31-2022, korean patent application No. 10-2023-0082211, filed on 26-6-2023, and korean patent application No. 10-2023-0104846, filed on 30-8-2023, the disclosures of which are incorporated herein by reference in their entirety.

Background

As the application range of lithium secondary batteries is extended not only to portable electronic devices but also to Electric Vehicles (EVs) and Electric Storage Systems (ESS), there is an increasing demand for lithium secondary batteries having high capacity, high energy density and long life.

Among various lithium secondary batteries, lithium-sulfur batteries are battery systems using a sulfur-based material containing sulfur-sulfur bonds as a positive electrode active material, and using lithium metal, a carbon-based material capable of inserting/extracting lithium ions, or silicon, tin, or the like alloyed with lithium as a negative electrode active material.

In lithium sulfur batteries, sulfur, which is a main material of a positive electrode active material, has advantages of low atomic weight, very abundant resources and thus easy supply and reception, low price, non-toxicity, and environmental friendliness.

In addition, the lithium ion and sulfur in the positive electrode are converted (S ₈ +16Li⁺ +16e^- 8Li ₂ S), the theoretical specific capacity of the lithium-sulfur battery was 1,675 mAh/g, and when lithium metal was used as the negative electrode, the theoretical energy density was 2,600 Wh/kg. Among the secondary batteries developed so far, lithium-sulfur batteries are attracting attention as high-capacity, environmentally friendly, inexpensive lithium secondary batteries because the theoretical energy density of lithium-sulfur batteries is far higher than that of other battery systems currently under study (Ni-MH battery: 450 Wh/kg, li-FeS battery: 480 Wh/kg, li-MnO ₂ battery: 1,000 Wh/kg, na-S battery: 800 Wh/kg) and lithium ion battery (250 Wh/kg).

In addition, in the case of a lithium sulfur battery, when lithium metal is used as a negative electrode active material, since the theoretical specific capacity is high, 3,860mah/g, and the standard reduction potential (standard hydrogen electrode; SHE) is also low, 3.045V, it is possible to realize a battery of high capacity and high energy density, and thus several studies are being conducted as a next-generation battery system.

However, since lithium metal as a negative electrode active material is easily reacted with an electrolyte due to its high chemical/electrochemical reactivity, a solid electrolyte interface layer (SEI layer), which is a passivation layer, is formed on the surface of a negative electrode. Since the solid electrolyte interface layer formed in this way can ensure a certain level of stability for the anode active material containing lithium metal by suppressing the direct reaction between the electrolyte and lithium metal, there has been an attempt in the related art to stably and uniformly form the SEI layer on the surface of lithium metal.

However, in the case of a lithium sulfur battery, when the anode active material is lithium metal, even if the SEI layer is formed as described above, it is difficult to keep the SEI layer constant since electrochemical reaction of the battery continues to occur on the surface of the lithium metal. In addition, since the mechanical strength of the SEI layer formed by the reaction between the electrolyte and the lithium metal is weak, as the charge and discharge of the battery proceeds, the structure collapses, resulting in a local difference in current density, thereby forming lithium dendrites on the lithium metal surface. In addition, lithium dendrites formed in this way cause internal short circuits and inert lithium (dead lithium) of the battery, thereby causing problems of increased physical and chemical instability of the lithium secondary battery, and reduced battery capacity and cycle life. In addition, the positive electrode active material is dissolved in the electrolyte in the form of lithium polysulfide (LiPS) and moves to the negative electrode to form lithium sulfide byproducts, so that positive electrode active material loss/negative electrode passivation and undesired side reactions may occur.

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

For example, korean patent publication No. 2016-0034183 discloses forming a protective layer on a negative electrode active layer containing lithium metal or lithium alloy, which serves as a polymer matrix capable of accumulating an electrolyte while protecting the negative electrode, thereby being capable of preventing loss of the electrolyte and generation of dendrites.

Korean patent publication No. 2016-0052351 discloses that stability and life characteristics of a lithium secondary battery can be improved by introducing an absorbent material of lithium dendrites into a polymer protective film formed on a surface of lithium metal and thereby inhibiting growth of lithium dendrites.

These prior arts suppress the reaction between the electrolyte and lithium metal or the formation of lithium dendrites to some extent, but the effect is not sufficient. Further, as charge and discharge of the battery proceed, there is a degradation problem such as hardening or swelling of the protective layer.

Disclosure of Invention

Technical problem

Accordingly, there is a need to develop a lithium metal negative electrode for use in a lithium secondary battery, particularly for forming a lithium-based material suitable for improving battery life and efficiency characteristics, which overcomes the drawbacks of the prior art.

Technical proposal

The above problems are solved according to independent items. Other embodiments result from sub-items and/or from the detailed description that follows.

In particular, in order to achieve the above object, in a first embodiment, the present disclosure provides a negative electrode for a lithium secondary battery including a lithium-magnesium-aluminum alloy (Li-Mg-Al alloy). The lithium-magnesium-aluminum alloy may have the form of a foil.

According to a second embodiment of the present disclosure, in the first embodiment, the amount of magnesium (Mg) in the lithium-magnesium-aluminum alloy may be 0.1 to 50 wt% with respect to the total weight (100 wt%) of the lithium-magnesium-aluminum alloy.

According to a third embodiment of the present disclosure, in the first or second embodiment, the amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.01 to 10 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy.

According to a fourth embodiment of the present disclosure, in any one of the first to third embodiments, the weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 2:1 to 20:1.

According to a fifth embodiment of the present disclosure, in any one of the first to fourth embodiments, the lithium-magnesium-aluminum alloy may be a lithium-magnesium-aluminum foil, and the thickness of the lithium-magnesium-aluminum foil may be 0.1 [ mu ] m to 200 [ mu ] m.

According to a sixth embodiment of the present disclosure, in any one of the first to fifth embodiments, the lithium-magnesium-aluminum alloy may have an elastic modulus of at least 400 MPa and/or a tensile strength of at least 1.5 MPa.

According to a seventh embodiment of the present disclosure, in any one of the first to sixth embodiments, the lithium-magnesium-aluminum alloy may have an EM _d value of at least 600 (MPa-cm ³)/g according to the following formula (1),

Wherein EM _Alloy is the elastic modulus of the lithium-magnesium-aluminum alloy, d _Alloy is the density of the lithium-magnesium-aluminum alloy, the density of the alloy is the alloy mass per unit volume of the alloy, and the volume is the apparent volume of the alloy.

According to an eighth embodiment of the present disclosure, in any one of the first to seventh embodiments, the lithium-magnesium-aluminum alloy may be monolithic (monolithic).

According to a ninth embodiment of the present disclosure, in any one of the first to eighth embodiments, magnesium and aluminum may be uniformly distributed in the lithium-magnesium-aluminum alloy.

In addition, in a tenth embodiment, the present disclosure provides a negative electrode for a lithium secondary battery, the negative electrode comprising an alloy made of a combination of lithium and at least one other metal, wherein the alloy has an elastic modulus of at least 400 MPa.

According to an eleventh embodiment of the present disclosure, the present disclosure provides a negative electrode for a lithium secondary battery, the negative electrode comprising an alloy made of lithium and at least one other metal, wherein the alloy has an EM _d value of at least 600 (MPa-cm ³)/g according to the following formula (1),

According to a twelfth embodiment of the present disclosure, in the tenth or eleventh embodiment, the other metal may be at least one of magnesium and aluminum.

According to a thirteenth embodiment of the present disclosure, in any one of the tenth to twelfth embodiments, the at least one other metal may include or consist of magnesium and aluminum, and the weight ratio of magnesium to aluminum may be 2:1 to 20:1.

In addition, according to a fourteenth embodiment, the present disclosure provides a lithium secondary battery including the negative electrode for a lithium secondary battery according to any one of the first to thirteenth embodiments.

In a fifteenth embodiment of the present disclosure, in the fourteenth embodiment, the lithium secondary battery may further include a separator and an electrolyte.

In a sixteenth embodiment of the present disclosure, in the fourteenth or fifteenth embodiment, the lithium secondary battery may be a lithium sulfur battery in which a positive electrode active material contains sulfur (S) and/or a sulfur (S) compound.

Further, in a seventeenth embodiment, the present disclosure provides a method of producing a negative electrode for a lithium secondary battery, wherein the negative electrode for a lithium secondary battery is the negative electrode for a lithium secondary battery according to any one of the first to ninth embodiments. The method comprises the following steps:

Melting lithium metal to obtain a first melt;

Adding metallic magnesium and metallic aluminum to the first melt obtained in the melting step to obtain a second melt;

Alloying the second melt obtained in the adding step by maintaining the second melt at a temperature of at least 200 ℃; and

The second melt obtained in the alloying step is cooled to obtain a lithium-magnesium-aluminum alloy.

In an eighteenth embodiment of the present disclosure, in the seventeenth embodiment, the alloy may be obtained in the form of a ingot, and the method may further include the step of thinning the ingot into a plate structure having a predetermined thickness.

Advantageous effects

Lithium secondary batteries, such as lithium sulfur batteries, comprising the negative electrode according to the present disclosure exhibit superior battery life characteristics compared to such batteries using prior art negative electrodes.

Lithium secondary batteries, such as lithium sulfur batteries, comprising the negative electrode according to the present disclosure exhibit excellent battery efficiency characteristics of such batteries using prior art negative electrodes.

Drawings

The accompanying drawings illustrate preferred embodiments of the present disclosure and together with the foregoing disclosure serve to provide a further understanding of the technical features of the present disclosure, and therefore, the present disclosure is not to be construed as being limited to the accompanying drawings. On the other hand, the shapes, sizes, scales, or ratios of elements in the drawings included in the present application may be exaggerated to emphasize clearer explanation.

Fig. 1 shows the cycle life of pouch-type lithium sulfur batteries based on the specific capacities of example 1 and comparative examples 1, 2, and 3 of the present disclosure.

Fig. 2 shows the coulombic efficiency of the pouch-type lithium sulfur battery of example 1 and comparative examples 1, 2, and 3 of the present disclosure.

Fig. 3 shows the elastic modulus of preparation examples 1 and 4 and comparative example 1 of the present disclosure.

Fig. 4 shows a photographic image of an example of a cutting device for cutting elastic modulus samples.

Fig. 5 shows an SEM image of a cross section of the anode obtained in example 1 of the present disclosure.

Fig. 6 and 7 show EDS elemental analysis results of a cross section of the anode obtained in example 1 of the present invention, wherein fig. 6 shows the distribution of magnesium in the anode and fig. 7 shows the distribution of aluminum in the anode.

Detailed Description

The terms or words used in the present specification and claims should not be construed as being limited to general or dictionary terms, but should be construed in a meaning and concept conforming to the technical ideas of the present disclosure on the basis of the principle that the inventor is able to properly define concepts of terms in order to describe the present invention in the best possible manner.

Unless otherwise limited, the detailed description of the defined or indicated elements may be applied to all inventions and is not limited to the description of specific inventions. That is, the present disclosure also relates to combinations of the embodiments even if they are separately disclosed.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It will be understood that terms such as "comprises" or "comprising," when used in this specification, are intended to specify the presence of stated features, integers, steps, operations, elements, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. The term "comprising" is intended to include, even though not necessarily limited thereby, the meaning of "consisting essentially of" and "consisting of.

The term "consisting essentially of" as used herein means "comprising at least 70%", preferably "comprising at least 80%", most preferably "comprising at least 90%". If reference is made to the amount of an ingredient in a mixture of materials, then% is by weight relative to the total weight of the respective mixture. For example, a material comprising mainly polyethylene comprises polyethylene in an amount of at least 70 wt.%, relative to the total weight of the material.

In addition, the terms "about" and "substantially" as used herein are used in a sense equal to or similar to given the manufacturing and material tolerances inherent in the stated environment and to prevent unscrupulous infringers from unfair ly utilizing the present disclosure where precise or absolute numbers are stated to aid in understanding the present disclosure.

As used herein, "A and/or B" means "A and B, or A or B".

The term "composite" as used herein refers to a material that combines two or more materials to perform more efficient functions while forming the same physically and chemically distinct from each other.

The term "polysulfide" as used herein is a concept that includes both "polysulfide ions (S _x ^2-, x=1-8)" and "lithium polysulfide (Li ₂S_x or LiS _x ^- x=1-8)".

The negative electrode referred to herein may also be referred to as a negative electrode.

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

The present disclosure relates to a negative electrode for a lithium secondary battery including a lithium-magnesium-aluminum alloy. In one embodiment of the present disclosure, the alloy may be introduced into the anode in the form of a foil, i.e., may be a lithium-magnesium-aluminum alloy foil, and the anode may be formed using only the lithium-magnesium-aluminum foil, or the lithium-magnesium-aluminum alloy foil and a current collector are bonded to each other, preferably directly bonded to each other, to form the anode.

The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 0.1wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 0.5wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 1wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 2 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 3 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be at least 4 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. These amounts of Mg in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 50 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be not more than 40 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be not more than 30 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 25 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 20 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 15 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 12.5 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be not more than 10 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 7.5 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be no more than 6 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. These amounts of Mg in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The amount of magnesium in the lithium-magnesium-aluminum alloy may be 0.1 to 50 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be 0.5 to 30 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be 1to 20 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be 2 to 10 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be 3 to 7 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of magnesium in the lithium-magnesium-aluminum alloy may be 4 to 6 wt%, for example about 5 wt%, relative to the total weight of the lithium-magnesium-aluminum alloy. These amounts of Mg in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.01 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.05 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.1 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.2wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.3 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be at least 0.4 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. These Al amounts in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The amount of aluminum in the lithium-magnesium-aluminum alloy may be no more than 5 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not more than 4 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not more than 3 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not greater than 2.5 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not more than 2 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not greater than 1.5 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be no more than 1.25 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not greater than 1 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be no more than 0.75 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be not greater than 0.6 wt% relative to the total weight of the lithium-magnesium-aluminum alloy. These Al amounts in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.01 to 5wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.05 to 3 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.1 to 2 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.2 to 1wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.3 to 0.7 wt% with respect to the total weight of the lithium-magnesium-aluminum alloy. The amount of aluminum in the lithium-magnesium-aluminum alloy may be 0.4 to 0.6 wt%, for example about 0.5 wt%, relative to the total weight of the lithium-magnesium-aluminum alloy. These Al amounts in the alloy are advantageous in view of the lifetime and efficiency of the anode.

The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be from 2:1 to 20:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 3:1 to 17.5:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 4:1 to 16:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 5:1 to 15:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 6:1 to 14:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 7:1 to 13:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy may be 8:1 to 12:1. The weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy is 9:1 to 11:1, for example about 10:1. These ratios of Mg to Al in the alloy are advantageous in view of the elastic modulus of the alloy.

In the case of thinning the lithium-magnesium-aluminum alloy and using the alloy foil as the anode active material layer, the thickness of the alloy foil may be 10 μm to 200 μm. In a specific embodiment, the thickness may be less than 180 [ mu ] m, less than 160 [ mu ] m, less than 150 [ mu ] m, less than 140 [ mu ] m, less than 130 [ mu ] m, less than 120 [ mu ] m, less than 110 [ mu ] m, less than 100[ mu ] m or less than 90 [ mu ] m. The above thickness is advantageous in providing a lithium source sufficient to drive the battery and achieving high energy density.

On the other hand, the thickness of the alloy foil may be at least 0.1 [ mu ] m, at least 0.5 [ mu ] m, at least 1 [ mu ] m, at least 2 [ mu ] m, at least 5 [ mu ] m, at least 10 [ mu ] m, at least 20[ mu ] m, at least 30 [ mu ] m, at least 40 [ mu ] m, at least 45 [ mu ] m, at least 50 [ mu ] m, at least 60 [ mu ] m, at least 70 [ mu ] m, at least 75 [ mu ] m, at least 80 [ mu ] m, at least 85 [ mu ] m, at least 90 [ mu ] m. These lower limits are advantageous in providing a lithium source sufficient to drive the battery and achieving high energy densities.

In a specific embodiment, the thickness of the alloy foil may be 0.1 to 200 [ mu ] m, 1 to 200 [ mu ] m, 50 to 150 [ mu ] m, 50 to 120 [ mu ] m, 60 to 110 [ mu ] m, 60 to 140 [ mu ] m, 70 to 90 [ mu ] m, 70 to 130 [ mu ] m, 80 to 120 [ mu ] m, 90 to 110 [ mu ] m, 75 to 85 [ mu ] m, about 50 to 80 [ mu ] m, or 60 to 80 [ mu ] m, 95 to 105 [ mu ] m, for example about 100 [ mu ] m. When the thickness of the lithium metal satisfies the above-defined range, it is possible to more easily provide a lithium source sufficient to drive the battery and achieve high energy density.

The lithium-magnesium-aluminum alloy may be provided as monolithic. It may be provided that, with respect to the uniform concentration of magnesium or aluminum, there is no concentration gradient according to the alloy position in the entire lithium-magnesium-aluminum alloy. It can be provided that, as regards the concentration of magnesium and aluminum, no concentration gradient exists in the lithium-magnesium-aluminum foil. It may be provided that the lithium-magnesium-aluminum alloy is substantially homogeneous. It may be provided that the lithium-magnesium-aluminum alloy is homogeneous. It may be provided that the magnesium and the aluminum are uniformly distributed in the lithium-magnesium-aluminum alloy. The lithium-magnesium-aluminum alloy may be provided as a bulk material, such as a substantially homogeneous bulk material, wherein the entire bulk material is homogeneous in the continuous phase. That is, both Mg and Al are also melted, so that the entire mass is completely homogeneous in the continuous phase with lithium. That is, a lithium-magnesium-aluminum alloy according to the present disclosure may not include a lithium-based material in a discontinuous phase, for example, in the form of particles with an alloy shell surrounding a metal (Li) core.

Fig. 6 and 7 show EDS surface element analysis results of a cross section of a lithium-magnesium-aluminum alloy of example 1 of the present disclosure, and it can be seen that Mg and Al are uniformly detected in the entire alloy, i.e., magnesium and aluminum are uniformly distributed in the lithium-magnesium-aluminum alloy. On the other hand, the detailed structure of the Li alloy of the present disclosure may vary depending on Mg and Al contents, and in detail, the structure of the Li alloy may exhibit a uniform beta lithium phase of a body-centered cubic (BCC) structure; or substituting Mg or Al for some sites of the lithium lattice of the BCC structure that would have been Li, while substantially maintaining the BCC structure; or the newly formed Li ₉Al₄ phase is uniformly distributed in the alloy matrix in which some of the Li lattice of the BCC structure is replaced by Mg.

The negative electrode may mainly include or consist of the lithium-magnesium-aluminum alloy. The alloy may be present in the negative electrode in the form of a foil having a plate-like structure of a predetermined thickness.

In alternative embodiments, the negative electrode may comprise other components, and in particular may also comprise a current collector (also referred to herein as a "negative electrode current collector"). In one embodiment of the present disclosure, it may be provided that the anode further includes a current collector and an anode active material layer disposed on at least one face of the current collector, and the anode active material layer may further include, mainly include, or consist of the lithium-magnesium-aluminum alloy. The negative electrode may be formed by bonding (pressing process, etc.) of the current collector and the alloy foil, preferably directly, that is, without any other constituent part therebetween; or by depositing the lithium-magnesium-aluminum alloy on at least one face of the current collector.

The anode current collector is used to support the anode active material layer and is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, and sintered carbon may be used; copper or stainless steel surface-treated with carbon, nickel, silver, or the like; aluminum-cadmium alloys, and the like. The current collector may enhance the binding force with a lithium metal thin film as a negative electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam body, and a non-woven fabric body may be used. For example, the current collector may be selected from the group consisting of a copper current collector, a porous current collector, and a plastic current collector. The thickness of the current collector may be in the range of 1 to 60 μm. For example, when the current collector is used in the form of a metal foil, the thickness of the current collector may be 1 to 20 μm. When the thickness of the current collector satisfies the above-defined range, the current collecting effect can be ensured, and workability can be easily ensured even when the battery is assembled by folding.

The lithium-magnesium-aluminum alloy may have an elastic modulus of at least 300 MPa, at least 350 MPa, at least 400 MPa, at least 450 MPa, at least 500 MPa, at least 550 MPa, at least 600 MPa, or at least 650 MPa.

The elastic modulus of the lithium-magnesium-aluminum alloy may be no greater than 1,000 MPa, no greater than 900 MPa, or no greater than 800 MPa.

In a specific embodiment, the elastic modulus of the lithium-magnesium-aluminum alloy may be 300 to 1,000 MPa, 400 to 1,000 MPa, 500 to 900 MPa, 550 to 800 MPa, or 500 to 700 MPa.

In one embodiment of the present disclosure, the modulus of elasticity may be measured according to ASTM D412-B. ASTM D412-B is used to measure the elasticity of a material under tensile deformation and/or to determine the material property profile after load removal. The elastic modulus may be expressed as a relation between stress (σ) and strain (ε), and in detail, the measurement method may be described as the following equation 2.

Stress (σ) =elastic modulus (E) ×strain (ε) (2)

Here, N/mm ² can be used as a unit of stress and elastic modulus. The strain may be calculated by the following equation 3.

Strain (epsilon) =deformation (delta)/length (l) (3)

In one embodiment of the present disclosure, the elastic modulus may be specifically measured by the following method. First, an alloy sample is prepared by punching the alloy to a predetermined size, and then each sample is measured using a Universal Tester (UTM) and a 20N or 100N load cell.

A known UTM device may be used, for example, an Ametek Ls1 UTM device may be used. In one embodiment of the present invention, the sample is preferably sized according to ASTM D412-B. For example, the dimensions of the sample are, lateral lengths 80 mm to 200 mm, longitudinal lengths 10mm to 50 mm, lateral lengths 30 mm to 100 mm of the sample center straight portion, and longitudinal lengths 1mm to 12 mm of the sample center straight portion. Can be appropriately determined within this range. In a more specific embodiment, the sample has a transverse length of about 140 mm, a longitudinal length of about 25mm, a transverse length of about 60 mm in the center straight portion of the sample, and a longitudinal length of 6mm in the center straight portion of the sample according to ASTM D412-B.

The measurements were performed at a single strain rate of 0.01/second (18 mm/min). Fig. 4 shows a photographic image of an example of a punching frame for punching a specimen for measuring the modulus of elasticity. And pressing and stamping the sample by using the stamping frame.

The lithium-magnesium-aluminum alloy may have an EM _d value of at least 450 (MPa-cm ³)/g according to the following formula (1).

Here, EM _Alloy is the elastic modulus of the lithium-magnesium-aluminum alloy measured according to ASTM standards as described herein; d _Alloy is the density of the lithium-magnesium-aluminum alloy. The density of the alloy is the alloy mass per unit volume of the alloy, and the volume is the apparent volume of the alloy.

The term "apparent volume" refers to the size or volume of an object occupying an external space, and refers to the external size or space irrespective of the actual internal structure or density of the material. The apparent volume may generally be calculated using measurements such as length, width, and height. For example, the apparent volume of a rectangular parallelepiped-shaped object can be calculated as length x width x height. The volume of a regularly shaped sample (e.g., cube, cylinder, etc.) can be measured in terms of its size using suitable means known to those skilled in the art, such as a ruler or caliper. For irregularly shaped samples, the volume may be measured by displacement with a known volume of liquid and measuring the change in volume. The change in volume may be equal to the volume of the sample. The skilled artisan can use other methods known in the art to measure the volume of the sample.

According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be at least 500 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be at least 550 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be at least 575 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be at least 600 (MPa-cm ³)/g.

According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be 500 to 750 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be 550 to 700 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be 575 to 700 (MPa-cm ³)/g. According to the formula (1), the EM _d value of the lithium-magnesium-aluminum alloy may be 600 to 650 (MPa-cm ³)/g.

The tensile strength of the lithium-magnesium-aluminum alloy according to the present disclosure may be 5.0 MPa or less, for example 3.0 MPa or less, or 2.5 MPa or less, or 2.1 MPa or less.

The tensile strength of the lithium-magnesium-aluminum alloy according to the present disclosure may be 1.50 or more MPa and 5.0 or less MPa, for example 1.70 or more MPa and 3.0 or less MPa, or 1.90 or more MPa and 2.5 or less MPa, or 1.95 or more MPa and 2.1 or less MPa.

In the present disclosure, the tensile strength may be measured by the same method as the above elastic modulus measuring method.

The method of forming the lithium-magnesium-aluminum metal alloy is not particularly limited, and methods of forming a layer or a film commonly used in the art may be used. For example, methods such as a compression method, a coating method may be used.

It may be provided that the lithium-magnesium-aluminum alloy is obtainable by a method comprising the steps of: a) Melting lithium metal to obtain a lithium melt; b) Adding magnesium metal and aluminum metal to the lithium melt obtained in step a) to obtain a lithium-magnesium-aluminum melt; c) Maintaining the lithium-magnesium-aluminum melt obtained in step b) at a temperature of at least 200 ℃; d) Cooling the lithium-magnesium-aluminum melt obtained in step c) to obtain a lithium-magnesium-aluminum alloy ingot; and e) producing a lithium-magnesium-aluminum alloy from the lithium-magnesium-aluminum alloy ingot, i.e. a lithium-magnesium-aluminum alloy in a desired form, e.g. in foil form.

The method may include providing for placing a solid piece of metallic lithium, e.g., lithium, such as a lithium ingot, with a solid piece of metallic magnesium, e.g., magnesium, solid pieces of metallic aluminum, e.g., aluminum, such as aluminum particles, into a suitable heating mechanism, e.g., a container, or the like. It may be provided that the heating means further comprises stirring means enabling stirring of the melts of the three metals and means for providing an inert gas atmosphere in the heating means. It may be provided that metallic lithium is provided together with metallic magnesium and metallic aluminum without including a sputtering step, such as DC sputtering. Instead, it may be provided that step b) comprises stirring the melt. In this way a more cost-effective way is provided to provide a lithium-magnesium-aluminium alloy with a more improved uniform magnesium and aluminium distribution in the foil.

The melting may include heating the metallic lithium together with the metallic magnesium and the metallic aluminum at a temperature of 200 ℃ to 500 ℃.

The cooling in step d) may be cooling to room temperature.

In one embodiment of the present disclosure, the method of obtaining the lithium-magnesium-aluminum alloy may include the steps of: manufacturing a lithium-magnesium-aluminum alloy from the lithium-magnesium-aluminum alloy ingot, wherein the manufacturing includes rolling the lithium-magnesium-aluminum alloy ingot. The rolling may include the simultaneous application of heat and pressure, which may be performed using a hot roll press or the like.

In another aspect, in one embodiment of the present disclosure, the method further comprises the following step f): the lithium-magnesium-aluminum alloy is deposited on a current collector.

The object is also achieved by a negative electrode for a lithium secondary battery obtainable by the method according to the present disclosure.

The object is also achieved by a negative electrode for a lithium secondary battery comprising an alloy consisting of lithium and at least one other metal in combination, wherein the alloy has an elastic modulus of at least 300 MPa according to the above.

The alloy may have an elastic modulus of at least 300 MPa. The alloy may have an elastic modulus of at least 350 MPa. The alloy may have an elastic modulus of at least 400 MPa. The alloy may have an elastic modulus of at least 450 MPa. The alloy may have an elastic modulus of at least 500 MPa. The alloy may have an elastic modulus of at least 550 MPa. The alloy may have an elastic modulus of at least 600 MPa. The alloy may have an elastic modulus of at least 650 MPa.

The elastic modulus of the alloy may be no greater than 1,000 MPa. The elastic modulus of the alloy may be no greater than 900 MPa. The elastic modulus of the alloy may be no greater than 800 MPa.

The elastic modulus of the alloy may be 300 MPa to 1,000 MPa. The elastic modulus of the alloy may be 400 MPa to 1,000 MPa. The elastic modulus of the alloy may be 500 MPa to 900 MPa. The elastic modulus of the alloy may be 550 MPa to 800 MPa. The elastic modulus of the alloy may be 500 MPa to 700 MPa.

The object is also achieved by a negative electrode for a lithium secondary battery comprising an alloy comprising lithium and a combination of at least one other metal, wherein the alloy has an EM _d value of at least 600 (MPa-cm ³)/g according to the following formula (1),

Here, EM _Alloy is the elastic modulus of the alloy according to ASTM standards; d _Alloy is the density of the alloy. The density of the alloy is the alloy mass per unit volume of the alloy, and the volume is the apparent volume of the alloy.

The alloy may have an EM _d value of at least 500 (MPa-cm ³)/g according to equation (1). The alloy may have an EM _d value of at least 550 (MPa-cm ³)/g according to equation (1). The alloy may have an EM _d value of at least 575 (MPa-cm ³)/g according to equation (1). The alloy may have an EM _d value of at least 600 (MPa-cm ³)/g according to equation (1).

The alloy may have an EM _d value of not more than 750 (MPa-cm ³)/g according to equation (1). The alloy may have an EM _d value according to equation (1) of not more than 700 (MPa-cm ³)/g. The alloy may have an EM _d value of not more than 650 (MPa-cm ³)/g according to formula (1).

The EM _d value of the alloy may be 500 to 750 (MPa-cm ³)/g according to formula (1). The EM _d value of the alloy may be 550 to 700 (MPa-cm ³)/g according to formula (1). The alloy may have an EM _d value of 575 to 700 (MPa-cm ³)/g according to equation (1). The EM _d value of the alloy may be 600 to 650 (MPa-cm ³)/g according to formula (1).

On the other hand, the tensile strength of the alloy according to the present disclosure may be 1.50 MPa or more, preferably 1.70 MPa or more, more preferably 1.90 MPa or more, or 1.95 MPa or more.

The tensile strength of the alloy according to the present disclosure may be 5.0 MPa or less, for example 3.0 MPa or less, or 2.5 MPa or less, or 2.1 MPa or less.

The tensile strength of the alloy according to the present disclosure may be 1.50 MPa or more and 5.0 MPa or less, for example 1.70 MPa or more and 3.0 MPa or less, or 1.90 MPa or more and 2.5 MPa or less, or 1.95 MPa or more and 2.1 MPa or less.

In one embodiment of the present disclosure, the other metal may include magnesium (Mg) and/or aluminum (Al). Preferably, the other metal consists of magnesium (Mg) and aluminum (Al). In the present disclosure, the tensile strength may be measured by the same method as the above elastic modulus measuring method. The object is also achieved by a lithium secondary battery comprising a negative electrode for a lithium secondary battery according to the present disclosure. The lithium secondary battery may further include a positive electrode, a separator, and an electrolyte. The lithium secondary battery may be a lithium sulfur battery.

The lithium sulfur battery according to the present disclosure may further include other constituent parts known in the art, in particular, a positive electrode (=positive electrode), a separator, and an electrolyte, in addition to the negative electrode. In particular, the lithium sulfur battery may include a positive electrode, a negative electrode, and an electrolyte interposed therebetween, wherein the negative electrode is a negative electrode as described herein.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer applied on one or both sides of the positive electrode current collector.

The positive electrode current collector is for supporting a positive electrode active material and as described in the current collector for supporting the negative electrode.

The positive electrode active material layer may contain a positive electrode active material, and may further contain a conductive material, a binder, an additive, and the like.

The positive electrode active material contains sulfur, and specifically may contain at least one selected from the group consisting of elemental sulfur (S ₈) and sulfur compounds. The positive electrode active material may be at least one selected from the group consisting of inorganic sulfur, li ₂S_n (n ≡1), disulfide compounds, organic sulfur compounds, and carbon sulfur polymers ((C ₂S_x) n: x=2.5 to 50, n ≡2). Preferably, the positive electrode active material may be inorganic sulfur (S ₈).

Sulfur contained in the positive electrode active material is used in combination with a conductive material such as a carbon material because it alone does not have conductivity. Therefore, the positive electrode active material may be a sulfur-carbon composite, preferably, the sulfur is contained in the form of a sulfur-carbon composite.

The carbon contained in the sulfur-carbon composite is a porous carbon material and provides a framework capable of uniformly and stably fixing sulfur, and compensates for low conductivity of sulfur, so that electrochemical reaction can be smoothly performed.

The porous carbon materials may generally be prepared by carbonizing various carbonaceous precursors. The porous carbon material may contain non-uniform pores therein, the pores may have an average diameter ranging from 1 to 200 nm, and the porosity may range from 10% to 90% of the total volume of the porous carbon material.

In the present disclosure, the porosity measurement is not limited to a specific method as long as it is a well-known porosity measurement method. For example, porosity may be measured by using mercury porosimetry (mercury porosimeter), or BET (Bruhol-Amite-Teller) measurement using nitrogen, or ASTM D-2873. In addition, the net density of the electrode can be calculated from the density (apparent density) of the electrode, the composition ratio of materials contained in the electrode, and the density of each component; the porosity of the electrode is then calculated from the difference between the apparent density and the net density. For example, the porosity may be calculated by the following equation 1.

The apparent density in equation 1 can be calculated by equation 2 below.

Apparent density, also known as bulk density, is a measure of how much space a material occupies per unit volume, including voids or empty spaces therein. The apparent density takes into account both the solid material present in a given volume and any voids. The apparent density may be calculated by dividing the mass of the material by its total volume, including any pores or voids. The apparent density is calculated as:

apparent density = mass/total volume

The mass of the material can be measured with a balance.

The volume of a regularly shaped sample (e.g., cube, cylinder, etc.) can be measured in terms of its size using suitable means known to those skilled in the art, such as a ruler or caliper. For irregularly shaped samples, the volume may be measured by displacement with a known volume of liquid and measuring the change in volume. The change in volume may be equal to the volume of the sample. The skilled artisan can use other methods known in the art to measure the volume as well as the apparent density of the sample.

The net density, also referred to as true density, may be a measure of the density of a material without regard to any voids or pores within the material. It can be expressed as the mass of solid material divided by the actual volume of solid material that does not include any empty space. The net density can be calculated by dividing the mass of a substance by its unoccupied volume of solids. The net density is calculated as:

net density = mass/solid volume

The net density provides a measure of the inherent density of the material, as opposed to the apparent density, which takes into account the total volume including voids.

The net density may be determined by the methods described above, or by gas gravimetric techniques according to ISO 12154:2014 or other measurement methods known to those skilled in the art.

When the average diameter of the pores is smaller than the above range, the pore size is at the molecular level only, and impregnation with sulfur cannot be achieved. On the other hand, when the average diameter of the pores exceeds the above range, the mechanical strength of the porous carbon material is weakened, which is not preferable for the manufacturing process applied to the electrode.

The porous carbon material is in the form of a sphere, rod, needle, plate, tube or block, and may be used without limitation as long as it is commonly used in lithium sulfur batteries.

The porous carbon material may have a porous structure or a high specific surface area, and may be any porous carbon material conventionally used in the art. For example, the porous carbon material may be, but is not limited to, at least one selected from the group consisting of: graphite; a graphene; carbon blacks such as Danka black (Denka black), acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal 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 graphites, artificial graphites and expanded graphites, and activated carbons. Preferably, the porous carbon material may be Carbon Nanotubes (CNTs).

The sulfur-carbon composite may contain 60 to 90 parts by weight, preferably 65 to 85 parts by weight, more preferably 70 to 80 parts by weight of sulfur based on 100 parts by weight of the sulfur-carbon composite. When the sulfur content is below the above range, since the content of the porous carbon material in the sulfur-carbon composite is relatively increased, the specific surface area is increased, so that the content of the binder is increased at the time of manufacturing the positive electrode. This increase in the amount of binder used eventually increases the sheet resistance of the positive electrode and acts as an insulator preventing electrons from passing therethrough, thereby deteriorating the performance of the battery. In contrast, when the sulfur content exceeds the above range, sulfur that cannot be bound to the porous carbon material is aggregated with each other or re-leached to the surface of the porous carbon material, and thus it is difficult to receive electrons, and cannot participate in electrochemical reaction, resulting in a loss of battery capacity.

In addition, the sulfur in the sulfur-carbon composite is located on the surface of the porous carbon material, particularly at least one of the inner surface and the outer surface of the above porous carbon material, and at this time, may be present on less than 100%, preferably 1% to 95%, more preferably 60% to 90% of the area of the entire inner and outer surfaces of the porous carbon material. When sulfur as described above is present on the inner and outer surfaces of the porous carbon material in the above-described range, the greatest effect can be exhibited in terms of the electron transfer area and wettability with the electrolyte. Specifically, since sulfur is thinly and uniformly impregnated on the inner and outer surfaces of the porous carbon material in the above-described range, the electron transfer contact area can be increased during the charge and discharge process. When sulfur is located in 100% of the area of the entire inner and outer surfaces of the porous carbon material, the carbon material is entirely covered with sulfur, so that wettability to an electrolyte is poor and contact with a conductive material contained in an electrode is poor, so that electrons cannot be received and thus electrochemical reaction cannot be participated.

The method of preparing the sulfur-carbon composite is not particularly limited in the present disclosure, and methods commonly used in the art may be used. For example, a method of simply mixing sulfur and the porous carbon material and then heat-treating them to form a composite may be used.

The positive electrode active material may further contain at least one additive selected from the group consisting of: transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

The transition metal element may include Sc, ti, V, cr, mn, fe, co, ni, cu, zn, Y, zr, nb, mo, tc, ru, rh, pd, os, ir, pt, au, hg, etc., the group IIIA element may include Al, ga, in, tl, etc., and the group IVA element may include Ge, sn, pb, etc.

The sulfur content may be 40 to 95 wt%, preferably 50 to 90wt%, more preferably 60 to 85 wt%, based on 100 wt% total of the positive electrode active material layers constituting the positive electrode. In one embodiment of the present disclosure, when a sulfur-carbon composite is used as the positive electrode active material, the content of the sulfur-carbon composite may be 90 to 97 wt% based on 100 wt% of the positive electrode active material layer. When the content of the positive electrode active material is less than the above range, it is difficult to sufficiently exhibit the electrochemical reaction of the positive electrode. In contrast, when the content exceeds the above range, the contents of the conductive material and the binder described later are relatively insufficient, and thus there are problems that the resistance of the positive electrode increases and the physical properties of the positive electrode decrease.

The positive electrode active material layer may further optionally contain a conductive material that allows electrons to move smoothly within the positive electrode (specifically, positive electrode active material), and a binder for good adhesion of the positive electrode active material to the current collector.

The conductive material is a material that serves as a path for electrons to be transferred from the current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material. The conductive material may be used without limitation as long as it has conductivity.

For example, as the conductive material, it is possible to use either singly or in combination: graphite such as natural graphite or artificial graphite; carbon blacks such as Super P, danka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; carbon derivatives such as carbon nanotubes and fullerenes; conductive fibers such as carbon fibers and metal fibers; a fluorocarbon compound; metal powders such as aluminum powder and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

The conductive material may be contained in an amount of 0.01 to 30 wt% based on 100 wt% in total of the positive electrode active material layers constituting the positive electrode. When the content of the conductive material is less than the above range, it is difficult to transfer electrons between the positive electrode active material and the current collector, thereby reducing voltage and capacity. In contrast, when the content exceeds the above range, the proportion of the positive electrode active material relatively decreases, so that the total energy (charge amount) of the battery may decrease. Therefore, the content of the conductive material is preferably determined to be an appropriate content within the above-described range.

The binder holds the positive electrode active material in the positive electrode current collector and organically connects the positive electrode active material to increase the binding force therebetween, any binder known in the art may be used.

For example, the binder may be any one selected from the group consisting of: fluororesin-based adhesives including polyvinylidene fluoride (PVdF) or Polytetrafluoroethylene (PTFE); rubber-based adhesives including styrene-butadiene rubber (SBR), nitrile rubber, and styrene-isoprene rubber; cellulosic binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; a polyol-based binder; polyolefin-based adhesives, including polyethylene and polypropylene; polyimide-based adhesives; a polyester-based adhesive; and a silane-based adhesive, or a mixture or copolymer of two or more thereof.

The binder may be contained in an amount of 0.5 to 30wt% based on 100 wt% in total of the positive electrode active material layers constituting the positive electrode. When the content of the binder is less than 0.5 wt%, the physical properties of the positive electrode may be deteriorated, and thus the positive electrode active material and the conductive material may be separated. When the content exceeds the above range, the ratio of the positive electrode active material and the conductive material in the positive electrode may be relatively reduced, and thus the capacity of the battery may be reduced. Therefore, the content of the binder is preferably determined to be an appropriate content within the above-mentioned range.

In the present disclosure, the method of manufacturing the positive electrode is not particularly limited, and may be a method known to those skilled in the art or various modifications thereof.

For example, the positive electrode may be prepared by preparing a slurry composition for a positive electrode including the above-described components, and then applying it to at least one surface of the positive electrode current collector.

The positive electrode slurry composition contains the positive electrode active material, the conductive material, and the binder, and may further contain a solvent in addition to the above.

As the solvent, a solvent capable of uniformly dispersing the positive electrode active material, the conductive material, and the binder may be used. Such a solvent may be an aqueous solvent, and most preferably is water, in which case the water may be distilled or deionized water. However, it is not necessarily limited thereto, and a lower alcohol which can be easily mixed with water may be used as needed. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol and butanol, and preferably, they may be used in combination with water.

The solvent contained may be at a level having a concentration that makes it easy to apply, and the specific content varies depending on the application method and apparatus.

The positive electrode slurry composition may contain a material generally used for the purpose of improving the function thereof in the related art, as needed. For example, viscosity modifiers, fluidizers, fillers, etc. are mentioned.

In the present disclosure, the method of applying the slurry composition for positive electrode is not particularly limited in the present disclosure, and for example, methods such as a doctor blade method, a die casting method, a comma coating method, and a screen printing method may be used. In addition, the positive electrode slurry may be applied to the positive electrode current collector by pressing or laminating after being formed on a separate substrate.

After the application, a drying process for removing the solvent may be performed. The drying process is performed at a temperature and for a time at a level capable of sufficiently removing the solvent, and the conditions may vary depending on the type of solvent, and thus are not particularly limited in the present disclosure. Examples of the drying method may include a drying method using warm air, hot air, or low humidity air; a vacuum drying method; and a drying method of irradiation with (far) infrared radiation or electron beam. The drying rate is generally adjusted so that the solvent is removed as quickly as possible within a range of speeds at which cracks are not caused in the positive electrode active material layer due to stress concentration and the positive electrode active material layer is not peeled off from the positive electrode current collector.

In addition, by compressing the current collector after drying, the positive electrode active material density in the positive electrode can be increased. As the pressing method, methods such as molding and rolling are mentioned.

The porosity of the positive electrode, particularly the positive electrode active material layer prepared from the above composition and manufacturing method, may be 50% to 80%, preferably 60% to 75%. When the porosity of the positive electrode is less than 50%, since the filling degree of the slurry composition for positive electrode including the positive electrode active material, the conductive material and the binder is too high, there is a problem in that sufficient electrolyte cannot be maintained between the positive electrode active materials to exert ion conductivity and/or conductivity, thereby possibly deteriorating the output characteristics or cycle characteristics of the battery and making the reduction of the overvoltage and discharge capacity serious. In contrast, when the porosity of the positive electrode exceeds 80% and has an excessively high porosity, there are problems in that physical and electrical connection with a current collector is lowered, thus adhesion is lowered and reaction is difficult, and in that the increased porosity is filled with electrolyte, thus resulting in a decrease in energy density of the battery. Accordingly, the porosity of the positive electrode is appropriately adjusted within the above range.

In addition, the sulfur loading in the positive electrode according to the present disclosure, i.e., the mass of sulfur in the positive electrode active material layer per unit area in the positive electrode, may be 0.5 to 15mg/cm ², preferably 1 to 10 mg/cm ².

The negative electrode is as described above.

The electrolyte contains lithium ions and is intended to cause electrochemical oxidation or reduction reactions in the positive and negative electrodes by the lithium ions.

The electrolyte may be a nonaqueous electrolytic solution or a solid electrolyte that does not react with lithium metal, but is preferably a nonaqueous electrolyte, and contains an electrolyte salt and an organic solvent.

The electrolyte salt contained in the nonaqueous electrolytic solution is a lithium salt. The lithium salt may be used without limitation as long as it is generally used in an electrolyte for a lithium secondary battery. For example, the lithium salt may be LiCl、LiBr、LiI、LiClO₄、LiBF₄、LiB₁₀Cl₁₀、LiPF₆、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、(CF₃SO₂)₂NLi、LiN(SO₂F)₂、 chloroborane lithium, lower aliphatic carboxylic acid lithium, tetraphenyl borate lithium, iminolithium, and the like.

The concentration of the lithium salt may be 0.2 to 2M, preferably 0.4 to 2M, more preferably 0.4 to 1.7M, depending on various factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charge and discharge conditions of the battery, the operating temperature, and other factors known in the lithium battery art. When the concentration of the lithium salt is less than 0.2M, the conductivity of the electrolyte may be lowered, and thus the performance of the electrolyte may be deteriorated. When the concentration of the lithium salt is more than 2M, the viscosity of the electrolyte may increase, and thus mobility of lithium ions may be reduced.

As the organic solvent contained in the nonaqueous electrolytic solution, an organic solvent conventionally used in an electrolytic solution for a lithium secondary battery, for example, ether, ester, amide, linear carbonate, cyclic carbonate, or the like may be used alone or in combination of two or more. Among these compounds, an ether compound may be typically contained.

The ether compound may comprise acyclic ethers and cyclic ethers.

For example, the acyclic ether may be, but is not limited to, at least one selected from the group consisting of: dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methylethyl ether.

For example, the cyclic ether may be, but is not limited to, at least one selected from the group consisting of: 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-dimethyl-1, 3-dioxolane, 2-methoxy-1, 3-dioxolane, 2-ethyl-2-methyl-1, 3-dioxolane, tetrahydropyran, 1, 4-dioxolaneAlkane, 1, 2-dimethoxybenzene, 1, 3-dimethoxybenzene, 1, 4-dimethoxybenzene and isosorbide dimethyl ether.

Examples of the esters of the organic solvents may be, but are not limited to, any one selected from the group consisting of: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, sigma-valerolactone and epsilon-caprolactone, and mixtures of two or more thereof.

Specific examples of the linear carbonate compound may be representatively any one selected from the group consisting of: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl Methyl Carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, or a mixture of two or more thereof.

In addition, a specific example of the cyclic carbonate compound may be any one selected from the group consisting of: ethylene Carbonate (EC), propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate and its halides, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

The electrolyte may further contain a nitric acid or nitrous acid compound as an additive in addition to the above electrolyte salt and the organic solvent. The nitric acid or nitrous acid compound has an effect of forming a stable film on a lithium metal electrode as a negative electrode and improving charge and discharge efficiency.

The nitric acid-based or nitrous acid-based compound is not particularly limited in the present disclosure, but may be at least one selected from the group consisting of: inorganic nitric or nitrous compounds, such as lithium nitrate (LiNO ₃), potassium nitrate (KNO ₃), cesium nitrate (CsNO ₃), barium nitrate (Ba (NO ₃)₂), ammonium nitrate (NH ₄NO₃), lithium nitrite (LiNO ₂), potassium nitrite (KNO ₂), cesium nitrite (CsNO ₂) and ammonium nitrite (NH ₄NO₂), organic nitric or nitrous compounds, such as methyl nitrate, dialkylimidazolesNitrate, guanidine nitrate and imidazoleNitrate, pyridineNitrate, ethyl nitrite, propyl nitrite, butyl nitrite, amyl nitrite and octyl nitrite; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof, preferably lithium nitrate is used.

The injection of the electrolyte may be performed at an appropriate stage of the manufacturing process of the electrochemical device depending on the manufacturing process and the desired properties of the final product. That is, the injection may be performed before the electrochemical device is assembled or at the final stage of the assembly of the electrochemical device.

A separator may be further included between the positive electrode and the negative electrode.

The separator may be made of a porous non-conductive or insulating material that separates or insulates the positive and negative electrodes from each other and enables lithium ions to be transported between the positive and negative electrodes. The separator may be used without particular limitation as long as it is used as a separator in a conventional lithium sulfur battery. The separator may be a separate member, such as a membrane, or may contain a coating added to the positive and/or negative electrode.

Preferably, the separator has excellent wettability to the electrolyte while having low resistance to ion migration of the electrolyte.

The separator may be made of a porous substrate, which is used as long as it is a porous substrate commonly used in lithium-sulfur batteries, and a porous polymer film may be used alone or by stacking it, for example, a high-melting-point nonwoven fabric made of glass fibers, polyethylene terephthalate fibers, or the like, or a polyolefin-based porous film may be used, but is not limited thereto.

The material of the porous substrate is not particularly limited in the present disclosure, and any material may be used as long as it is a porous substrate commonly used in electrochemical devices. For example, the porous substrate may comprise at least one material selected from the group consisting of: polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalates, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, poly (p-phenylene benzobisp-phenylene)Azole), and polyarylates.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the range of the thickness of the porous base material is not particularly limited to the above range, when the thickness is far less than the above lower limit, mechanical properties are deteriorated, so that the separator may be easily damaged during use of the battery.

The average diameter and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 μm to 50 μm and 10% to 95% by volume, respectively.

In addition to the general winding process, the lithium secondary battery according to the present disclosure may be manufactured through lamination, stacking, and folding processes of the separator and the electrode.

The shape of the lithium secondary battery is not particularly limited, and may be various shapes such as a cylindrical shape, a laminate shape, and a coin shape.

The present disclosure also provides a battery module including the above lithium sulfur battery as a unit cell.

The battery module may be used as a power source for medium-to-large devices requiring high temperature stability, long cycle characteristics, high capacity characteristics, and the like.

Examples of such medium-sized devices may include, but are not limited to: a power tool driven and moved by the motor; electric vehicles, including Electric Vehicles (EVs), hybrid Electric Vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles, including electric bicycles (E-bicycles) and electric scooters (E-scooters); an electric golf cart; power storage systems, and the like.

Examples

Hereinafter, specific embodiments of the present disclosure will be described. However, it will be apparent to those skilled in the art that the following embodiments are merely examples of the present disclosure and that various changes and modifications may be made within the scope of the disclosure, and such changes and modifications are within the scope of the appended claims.

Preparation example 1 (preparation of Li-Mg-Al alloy)

And melting the lithium ingot at the temperature of 200 ℃ to obtain a lithium melt. A solid magnesium source (particles) and a solid aluminum source (particles) are added to the lithium melt to obtain a lithium-magnesium-aluminum melt. The amount of magnesium was 5 wt.% relative to the total weight of the lithium-magnesium-aluminum melt. The amount of aluminum was 0.5 wt.% relative to the total weight of the lithium-magnesium-aluminum melt.

The obtained melt was cooled to room temperature (about 22 ℃) to obtain a lithium-magnesium-aluminum alloy ingot. Lithium-magnesium-aluminum alloy (lithium-magnesium-aluminum alloy foil) in the form of foil having a thickness of 80 μm was manufactured from the lithium-magnesium-aluminum alloy ingot by rolling.

Preparation example 2 (preparation of Li-Zn alloy)

And melting the lithium ingot at the temperature of 200 ℃ to obtain a lithium melt. Solid Zn sources (particles) are added to the lithium melt to obtain a lithium zinc melt. The amount of Zn was 5 wt.% relative to the total weight of the lithium zinc melt.

The obtained melt was cooled to room temperature (about 22 ℃) to obtain a lithium zinc alloy ingot. Lithium zinc alloy in the form of foil having a thickness of 80 μm was manufactured from the lithium zinc alloy ingot by rolling.

Preparation example 3 (preparation of Li-Al alloy)

And melting the lithium ingot at the temperature of 200 ℃ to obtain a lithium melt. Solid aluminium sources (particles) are added to the lithium melt to obtain a lithium aluminium melt. The amount of aluminum was 0.5 wt.% relative to the total weight of the lithium aluminum melt.

The obtained melt was cooled to room temperature (about 22 ℃) to obtain a lithium aluminum alloy ingot. A lithium aluminium alloy in foil form with a thickness of 80 μm is manufactured from the lithium aluminium alloy ingot by rolling.

Preparation example 4 (preparation of Li-Mg alloy)

And melting the lithium ingot at the temperature of 200 ℃ to obtain a lithium melt. Solid magnesium sources (particles) are added to the lithium melt to obtain a lithium magnesium melt. The amount of magnesium was 5wt.% relative to the total weight of the lithium magnesium melt.

The obtained melt was cooled to room temperature (about 22 ℃) to obtain a lithium magnesium alloy ingot. Lithium magnesium alloy in the form of foil having a thickness of 80 μm was manufactured from the lithium magnesium alloy ingot by rolling.

Example 1

The lithium-magnesium-aluminum alloy having a thickness of 80 μm prepared in the above preparation example 1 was used as a negative electrode, and a separate current collector was not used.

96 Parts by weight of a sulfur/carbon composite (S/C75:25 parts by weight) as a positive electrode active material was mixed with 4 parts by weight of styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC 7:3) as a polymer binder to obtain a slurry. The slurry was applied to both sides of an aluminum current collector, and then dried at 50 ℃ for 12 hours and rolled, thereby preparing a positive electrode (=positive electrode). The positive electrode loading was 2.70 mAh/cm ² and the porosity was 78% by volume.

As separator a 16 μm polyethylene porous membrane (porosity 68 vol%) was used.

A folded battery was assembled by inserting a total of 7 positive electrodes and 8 negative electrodes and stacking them with the porous polyethylene separator. By inserting the tabs of the positive and negative electrodes into the pouch, electrolyte is injected and sealed, a pouch type battery is manufactured. The manufactured lithium sulfur battery was driven at a temperature of 25C under a condition of 0.3C charge/2.0C discharge to confirm cycle life and efficiency. The electrolyte was prepared by adding 1M of lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and 1 wt% of lithium nitrate (LiNO ₃) to a mixture of 1, 3-dioxolane and dimethyl ether (DOL: dme=1).

Comparative example 1

A lithium sulfur battery was produced in the same manner as in the case of example 1, except that 80 μm lithium foil was used as the negative electrode.

Comparative example 2

A lithium sulfur battery was produced in the same manner as in the case of example 1, except that the 80 μm lithium zinc alloy obtained in production example 2 was used as a negative electrode.

Comparative example 3

A lithium sulfur battery was produced in the same manner as in the case of example 1, except that the 80 μm lithium aluminum alloy obtained in production example 3 was used as a negative electrode.

Experimental evaluation 1: pouch cell evaluation

The lithium sulfur batteries manufactured according to example 1 and comparative examples 1 to 3 were driven at a temperature of 25C under 0.3C charge/2.0C discharge, 1.8V to 2.5V (with respect to Li/li+) to confirm cycle life and efficiency.

The charge and discharge of the battery and the measurement of coulombic efficiency were performed by a battery charger and discharger PNE (Wonik company). The specific capacity is a ratio of the discharge capacity (mAh) of the battery confirmed in the charger and discharger to the weight of sulfur contained in the positive electrode. The coulombic efficiency is a% ratio of the discharge capacity to the charge capacity.

As can be seen from fig. 1, when a lithium-magnesium-aluminum three-phase alloy negative electrode is applied (example 1), the cycle life is superior to that of a lithium-sulfur battery using bare Li as the negative electrode (comparative example 1). In the case of the example, the battery was driven for approximately 280 cycles, but in the case of the comparative example, the driving was stopped before the number of charge-discharge cycles reached 200 cycles.

When a lithium-magnesium-aluminum alloy negative electrode according to the present disclosure was applied (example 1), the cycle life was superior to that of a lithium-sulfur battery using other dissimilar metal-lithium alloy as a negative electrode (comparative examples 2 and 3).

As can be seen from fig. 2, when the lithium-magnesium-aluminum alloy negative electrode according to the present disclosure is applied (example 1), the coulombic efficiency stability is higher than that of Li metal (comparative example 1) and alloys of lithium with other dissimilar metals (comparative examples 2 and 3).

Experimental evaluation 2: modulus of elasticity

As can be seen from fig. 3, the Li metal and the Li-Mg alloy (preparation example 4) have similar elastic moduli, and in the case of the Li-Mg-Al alloy (preparation example 1) according to the present disclosure, the elastic modulus is more than twice as large.

Furthermore, even though the elastic modulus is considered with respect to the density of the material, the mechanical properties of the Li-Mg-Al material of the invention are still significantly better, as shown in table 1.

The elastic modulus and tensile strength were measured by the following methods. First, samples were prepared by punching the alloy obtained in preparation example 1, lithium metal, and the alloy obtained in preparation example 4 to predetermined dimensions, and then each sample was measured using a Universal Tester (UTM) and a 20N or 100N load cell. A single strain rate of 0.01/second (18 mm/min) was applied as a measurement condition. Fig. 4 shows a photographic image of one example of a UTM device for measuring elastic modulus.

Experimental evaluation 3: surface observation

The lithium-magnesium-aluminum alloy foil obtained in preparation example 1 was ion-cut to obtain a cross section, and the cross section was observed using a Scanning Electron Microscope (SEM), as shown in fig. 5. Referring to fig. 5, it was confirmed that the cross section of the obtained alloy foil exhibited a uniform morphology.

The SEM apparatus used was JSM-7200F from JOEL in Korea, resolution 3.0 nm (15 kV, WD 10 mm, probe current 5 nA).

Experimental evaluation 4: EDS measurement results

As a result of EDS analysis of the alloy of preparation example 1, it was confirmed that magnesium and aluminum were distributed over the entire surface of the negative electrode. Fig. 6 is an EDS analysis photograph for confirming the distribution of magnesium in the alloy of preparation example 1, and fig. 7 is an EDS analysis photograph for confirming the distribution of aluminum. For the EDS analysis UlTim Max was used, provided that 15 kv, WD 10mm, and probe current 5 nA. The features disclosed in the foregoing description and in the dependent claims may be used as material for realizing the aspects of the disclosure described in the independent claims in their diverse forms, both separately and in any combination thereof.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising a lithium (Li) -magnesium (Mg) -aluminum (Al) alloy.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein an amount of magnesium (Mg) in the lithium-magnesium-aluminum alloy is 0.1 to 50 wt% with respect to a total weight (100 wt%) of the lithium-magnesium-aluminum alloy.

3. The negative electrode for a lithium secondary battery according to claim 1 or 2, wherein the amount of aluminum in the lithium-magnesium-aluminum alloy is 0.01 to 10% by weight relative to the total weight of the lithium-magnesium-aluminum alloy.

4. The negative electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein a weight ratio of magnesium to aluminum in the lithium-magnesium-aluminum alloy is 2:1 to 20:1.

5. The anode for a lithium secondary battery according to any one of claims 1 to 4, wherein the anode comprises a lithium-magnesium-aluminum alloy in the form of a foil, and the thickness of the anode is 0.1 to 200 μm.

6. The negative electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein the lithium-magnesium-aluminum alloy has an elastic modulus of at least 400 MPa or a tensile strength of at least 1.5 MPa.

7. The negative electrode for a lithium secondary battery according to any one of claims 1 to 6, wherein the lithium-magnesium-aluminum alloy has an EM _d value of at least 600 (MPa cm ³)/g according to the following formula (1),

Wherein EM _Alloy is the elastic modulus of the lithium-magnesium-aluminum alloy measured according to ASTM D412-B, D _Alloy is the density of the lithium-magnesium-aluminum alloy, the density of the alloy is the alloy mass per unit volume of the alloy, and the volume is the apparent volume of the alloy.

8. The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, wherein the lithium-magnesium-aluminum alloy is a single sheet.

9. The negative electrode for a lithium secondary battery according to any one of claims 1 to 8, wherein magnesium and aluminum are uniformly distributed in the lithium-magnesium-aluminum alloy.

10. A negative electrode for a lithium secondary battery, the negative electrode comprising an alloy made of a combination of lithium and at least one other metal than lithium, wherein the alloy has an elastic modulus of at least 400 MPa.

11. A negative electrode for a lithium secondary battery, the negative electrode comprising an alloy made of lithium and at least one other metal than lithium, wherein the alloy has an EM _d value of at least 600 (MPa cm ³)/g according to the following formula (1),

12. A lithium secondary battery, the 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 a negative electrode for a lithium secondary battery according to any one of claims 1 to 11.

13. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is a lithium sulfur battery in which the positive electrode active material contains sulfur (S) and/or a sulfur (S) compound.

14. A method of producing the negative electrode for a lithium secondary battery according to any one of claims 1 to 9, the method comprising:

Melting lithium metal to obtain a first melt;

adding magnesium metal and aluminum metal to the first melt to obtain a second melt;

Alloying the second melt by maintaining the second melt at a temperature of at least 200 ℃; and

After the alloying, the second melt is cooled to obtain a lithium-magnesium-aluminum alloy.

15. The method for producing a negative electrode for a lithium secondary battery according to claim 14, wherein the alloy is obtained in the form of an ingot, and the method further comprises the step of thinning the ingot into a plate structure having a predetermined thickness.