Lithium metal negative electrode and electrochemical device including the same

Abstract

The present invention relates to a lithium metal anode including a lithium metal layer and an oxide layer located on at least one side of the lithium metal layer, the oxide layer having a cracked portion and a non-cracked portion, and a method for manufacturing the same. The formation of a cracked portion in the oxide layer located on at least one side of the lithium metal layer can improve the life of the battery.

Description

Technical Field

[0001] The present invention relates to a lithium metal negative electrode and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0004911 filed on January 12, 2022, and all of the contents disclosed in the specification and drawings of the application are incorporated into this application.

Background Art

[0003] Recently, as interest in energy storage technology has increased, the research and development of electrochemical devices has been gradually increasing as the application fields have expanded to mobile phones, tablet PCs, laptop computers, camcorders, and even to the energy of electric vehicles (EVs) and hybrid electric vehicles (HEVs). Electrochemical devices are the most prominent fields in this regard, and recently, research and development related to new electrode and battery designs have been connected in order to improve the capacity density and specific energy in developing such batteries.

[0004] Among such electrochemical devices, lithium metal secondary batteries that use lithium metal as a negative electrode, such as lithium-sulfur batteries (Li-S batteries), have a very high theoretical capacity of 3,862 mAh / g and are attracting attention as next-generation high-capacity batteries by using light lithium metal as a negative electrode active material. In a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge. At this time, sulfur forms lithium polysulfide (LiPS) with a linear structure from S8 with a cyclic structure. Such a lithium-sulfur battery is characterized by showing a stepwise discharge voltage until the polysulfide is completely reduced to Li2S.

[0005] However, lithium metal secondary batteries such as lithium-sulfur batteries have a decrease in charge / discharge efficiency during the charge / discharge process and deterioration of battery life due to reasons such as side reactions of the electrolyte (deposition of by-products due to decomposition of the electrolyte) and instability of lithium metal (growth of dendrites on the lithium metal negative electrode resulting in short circuits).

[0006] In particular, lithium metal, which is the negative electrode active material, easily forms large-area dendrites, reacts with salts and additives in the electrolyte to form SEI (solid electrolyte interphase), and continuously consumes the salts and additives in the electrolyte, ultimately promoting battery deterioration.

[0007] Therefore, in order to use lithium metal as the negative electrode, it is necessary to develop technologies to suppress the growth of dendrites and prevent the consumption of salts and additives in the electrolyte.

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a lithium metal negative electrode and an electrochemical element including the same, in which the formation of an oxide layer having crack portions on the surface improves the desorption of lithium, enables uniform electrodeposition, and suppresses dendrite growth.

[0009] Another object of the present invention is to provide a method for manufacturing a lithium metal negative electrode in which the formation of an oxide layer having crack portions on the surface improves the desorption of lithium, enables uniform electrodeposition, and suppresses dendrite growth.

Means for Solving the Problems

[0010] To achieve the above problems, according to one aspect of the present invention, a lithium metal negative electrode of the following embodiments is provided.

[0011] According to a first embodiment, a lithium metal negative electrode is provided, which includes a lithium metal layer and an oxide layer located on at least one surface of the lithium metal layer, and the oxide layer has a cracked portion and an uncracked portion.

[0012] According to a second embodiment, in the first embodiment, the oxide layer having the cracked portion has a cracked portion and an uncracked portion, and the area ratio of the cracked portion to the uncracked portion can be 2:8 to 9:1.

[0013] According to a third embodiment, in the first embodiment or the second embodiment, the thickness of the oxide layer having the cracked portion can be 50% or less based on the maximum thickness of the oxide layer.

[0014] According to a fourth embodiment, in any one of the first to third embodiments, the thickness of the oxide layer having the cracked portion can be 10 nm to 10 μm.

[0015] According to a fifth embodiment, in any one of the first to fourth embodiments, the thickness of the lithium metal layer can be 1 μm to 200 μm.

[0016] According to a sixth embodiment, a method for manufacturing a lithium metal negative electrode includes a lithium metal layer and an oxide layer formed on at least one surface of the lithium metal layer, and a method for manufacturing a lithium metal negative electrode according to any one of the first to fourth embodiments including a step of forming a cracked portion in the oxide layer is provided.

[0017] According to a seventh embodiment, in the sixth embodiment, the step of forming the cracked portion may include a step of heat-treating the lithium metal negative electrode in a vacuum atmosphere at a pressure of 0.001 to 1 Torr.

[0018] According to an eighth embodiment, in the sixth embodiment or the seventh embodiment, the step of forming the cracked portion may include a step of heat-treating the lithium metal negative electrode in an inert atmosphere.

[0019] According to the ninth embodiment, in any one of the sixth to eighth embodiments, the step of forming the crack portion may include heat-treating the lithium metal anode at 40°C to 120°C.

[0020] According to the tenth embodiment, in any one of the sixth to ninth embodiments, the step of forming the crack portion may include heat-treating the lithium metal anode at 65°C to 85°C.

[0021] According to the eleventh embodiment, an electrochemical device including a lithium metal anode in any one of the first to fifth embodiments is provided.

[0022] According to the twelfth embodiment, in the eleventh embodiment, the electrochemical device may include a lithium secondary battery.

[0023] According to the thirteenth embodiment, in the twelfth embodiment, the lithium secondary battery may include a lithium-ion battery, a lithium-sulfur battery, a lithium-lithium symmetric cell, or two or more of these.

Advantages of the Invention

[0024] In a lithium metal anode according to an embodiment of the present invention, cracks are formed in the oxide layer on the surface of the lithium metal, so that the desorption of lithium is improved by such crack portions, uniform electrodeposition is possible due to an increase in the surface area of the lithium metal, and the growth of dendrites can be suppressed.

[0025] An electrochemical device including a lithium metal anode according to an embodiment of the present invention has an improved lifespan by including a lithium metal anode having an oxide layer with crack portions on the surface.

[0026] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventor himself must interpret them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that he can appropriately define the concept of the terms in order to explain the invention in the best way.

[0029] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, there may be various equivalents and modifications that can replace them at the time of this application.

[0030] When lithium metal is exposed to the atmosphere, an oxide layer such as Li2CO3, Li2O, LiOH, etc. is formed on the surface of the lithium metal depending on the type of gas present in the atmosphere. Such an oxide layer not only makes the current density on the surface of the lithium metal non-uniform and reduces the surface area required for the dissolution and deposition of lithium, but also acts as a resistance layer and reduces the ionic conductivity. In addition, there is a problem that lithium is deposited non-uniformly due to such an oxide layer.

[0031] The form of the deposited lithium is related to the charge-discharge current density, the type of electrolyte, and the growth of lithium in the form of dendrites, moss, and spheres. A part of the lithium growing in the form of dendrites breaks during discharge and forms dead lithium, which is electrochemically impossible to charge and discharge but has strong chemical reactivity. When such dead lithium is formed and lithium metal is used as the negative electrode, the reversible charge and discharge of lithium becomes difficult. As a result, even in a non-aqueous electrolyte, the electrode life characteristics of lithium metal are not good and the thermal stability is also poor.

[0032] Therefore, the inventor of the present invention has found that the above-described problems can be solved by forming crack portions in the oxide layer present on the surface of lithium metal, and has completed the present invention.

[0033] The lithium metal negative electrode according to one aspect of the present invention includes a lithium metal layer and an oxide layer located on at least one surface of the lithium metal layer, and the oxide layer is characterized by having crack portions and non-crack portions.

[0034] The lithium metal may be lithium or a lithium alloy. At this time, the lithium alloy may contain an element that can be alloyed with lithium. Specifically, it may be an alloy of lithium and one or more selected from the group consisting of Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, and Al.

[0035] The lithium metal negative electrode may further include a current collector on one side of the lithium metal layer. The current collector may be a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, it may be selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver. As the alloy, an aluminum-cadmium alloy can be used. In addition, fired carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer can also be used. Usually, a copper foil plate is applied as the negative electrode current collector.

[0036] Also, its form can be various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. with fine irregularities formed / not formed on the surface. Further, the negative electrode current collector may have a thickness range of 3 to 500 μm. When the thickness of the negative electrode current collector satisfies the above-described range, the current collection effect can be ensured, and it can be easily ensured that the workability is also achieved when the cell is folded and assembled.

[0037] The lithium metal layer may be in the form of a sheet or foil, and in some cases, it may be in a form where lithium or a lithium alloy is deposited or coated on the current collector by a dry process, or in a form where particulate lithium or a lithium alloy is deposited or coated by a wet process or the like.

[0038] The lithium metal may be exposed to oxygen or react with a lubricant component during the process of rolling the lithium metal negative electrode, forming a thick oxide layer on the surface of the lithium metal.

[0039] The lithium metal negative electrode according to one aspect of the present invention includes a lithium metal layer and an oxide layer located on at least one surface of the lithium metal layer, and the oxide layer has crack portions and non-crack portions.

[0040] As used herein, the "crack portion" of the oxide layer may refer to a region where the thickness of the oxide layer is thinner compared to the "non-crack portion" of the adjacent oxide layer. For example, the "non-crack portion" refers to a region where the oxide layer is thick, and the "crack portion" may refer to a region where the oxide layer is thinner compared to the adjacent "non-crack portion". Specifically, the "crack portion" may refer to a region that is 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less based on the maximum thickness in the thickness of the oxide layer of the "non-crack portion", that is, the oxide layer of the lithium metal. Or, the "crack portion" may refer to a region where the lithium metal layer is exposed due to the absence of the oxide layer.

[0041] FIG. 10 is a cross-sectional view of a lithium metal negative electrode according to an embodiment of the present invention, and FIG. 11 is a more specific cross-sectional view of a lithium metal negative electrode according to an embodiment of the present invention.

[0042] Referring to FIGS. 10 and 11, an oxide layer 20 is located on one surface of the lithium metal layer 10, and the oxide layer 20 has a crack portion 30 and a non-crack portion 40. The crack portion 30 may be a portion that is 50% or less based on the maximum thickness in the thickness of the oxide layer of the lithium metal. Also, the crack portion 30 may refer to a region where the lithium metal layer 10 is exposed due to the absence of the oxide layer. On the other hand, since it is impossible for the surface of the oxide layer to be completely flat, a portion having a fine height difference on the surface of the oxide layer may not be regarded as a crack portion. For example, the non-crack portion 50 has a lower height compared to the thickest portion of the oxide layer, but is distinguished from the crack portion 30.

[0043] Since FIGS. 10 and 11 show a cross-section of a lithium metal negative electrode according to an embodiment of the present invention, the lithium metal negative electrode according to the present invention is not limited to the structure of FIGS. 10 and 11. For example, FIGS. 10 and 11 show a case where an oxide layer is located on one surface of the lithium metal layer, but according to another embodiment of the present invention, oxide layers may be located on both surfaces of the lithium metal layer.

[0044] In this specification, the "crack portion" may include a recess, hole, opening, trench pit, etc. formed on the surface of the oxide layer. And the depth of the crack portion may mean the height difference perpendicular to the surface of the lithium metal from the highest thickness of the oxide layer formed on the surface of the lithium metal to the lowest point of the crack portion. For example, when the highest thickness of the oxide layer formed on the surface of the lithium metal is 100 nm and the thickness of the oxide layer remaining in the crack portion is 5 nm, the depth of the crack portion may be 95 nm.

[0045] And since it is impossible for the surface of the oxide layer to be completely flat, the crack portion may not mean a portion having a fine height difference on the surface of the oxide layer. That is, the crack portion may mean only when it has a depth of at least 20 nm or more, or 30 nm or more.

[0046] Further, the depth of the crack portion can be 60% or more, 70% or more, 80% or more, or 90% or more of the thickness of the oxide layer. Also, in the crack portion, the oxide layer may be completely removed and not present. At this time, the depth of the club portion can be 100% of the thickness of the oxide layer.

[0047] In this specification, the "crack portion" may refer to a region where no oxide is present in an image observed with a scanning electron microscope (SEM) at a magnification of 30,000 times. Alternatively, the "crack portion" may refer to a region shown in a darker color than a region shown in black or an adjacent "non-crack portion" in an image observed with a scanning electron microscope (SEM) at a magnification of 30,000 times. On the other hand, the "non-crack portion" may be shown in a lighter color than white or an adjacent crack portion. At this time, the scanning electron microscope (SEM) photography can be performed immediately after heat treatment, immediately after battery formation, or immediately before battery cycling, but is not limited thereto. Also, the SEM observation is to observe the surface of the lithium metal negative electrode from above and in the vertical direction (top-down) of a plane parallel to the oxide layer and the lithium metal. The "crack portion" and the "non-crack portion" can be visually observed in the SEM image, and a region relatively darker than a black or adjacent region can be determined as the crack portion, and a region relatively lighter than a white or adjacent region can be determined as the non-crack portion.

[0048] The crack portion and the non-crack portion can be more reliably distinguished by converting the image observed by SEM into a binary image. Specifically, the image observed by SEM can be converted to be dichotomized into white and black to clearly distinguish the crack portion and the non-crack portion.

[0049] For example, the raw image observed by SEM can be converted into a binary image by thresholding. Here, the thresholding can be global thresholding, Otsu thresholding, or adaptive thresholding.

[0050] The global threshold processing is to process the pixel value to black when it exceeds the threshold and to white when it does not exceed the threshold after determining the threshold.

[0051] The Otsu binarization is to create a binary image using the Otsu algorithm. When converting to a binary image, the Otsu algorithm arbitrarily determines a threshold, divides the pixels into two categories, and repeatedly obtains the brightness distributions of the two categories. Thereafter, the threshold value when the brightness distributions of the two categories are the most uniform among all cases is selected. The Otsu algorithm has the advantage that the optimal threshold value is automatically searched.

[0052] The adaptive threshold processing is to obtain the threshold value when converting to a binary image by using only the pixel values around the image after dividing the image into a plurality of regions. When the background color in the original image varies or the hue is diverse, and it is difficult to obtain a vivid binary image with a single threshold value, an excellent quality binary image can be created by using the adaptive threshold processing.

[0053] In one embodiment of the present invention, the area ratio between the crack part and the non-crack part can be calculated using an image obtained by observing the surface of the oxide layer with SEM. For example, after distinguishing the crack part and the non-crack part by the method described above, a boundary line between the crack part and the non-crack part is set, the areas of the crack part region and the non-crack part region are derived, and the area ratio between the crack part region and the non-crack part region can be calculated. At this time, as the boundary line between the crack part and the non-crack part, a boundary part where the white or bright part and the black or dark part are surely distinguished in the SEM image can be set. On the other hand, even within the non-crack part region which is the oxide layer, there are very bright parts and slightly bright parts in the non-crack part due to minute height differences of the oxide layer, etc. However, since the crack part as meant in the present invention means a part that is below a certain ratio compared to the thickness of the oxide layer in the non-crack part, even if very bright parts and slightly bright parts are observed in the non-crack part, this is a difference caused by minute height differences in the non-crack part. Therefore, the slightly bright parts are also regarded as the non-crack part and are not regarded as the crack part as relatively not bright.

[0054] In one embodiment of the present invention, the non-crack part may form one or more "oxide islands" which are non-crack parts formed surrounded by the crack part. At this time, the said oxide island (non-crack part) may refer to a region having the same thickness as the maximum oxide layer thickness within the region surrounded by the crack part, or a region having a thickness of 90% or more, 80% or more, 70% or more, 60% or more, or 50% or more. For example, the "oxide island" may be an oxide layer region (non-crack part) having a thickness of 100 to 120 nm and surrounded by an oxide region (crack part) having a thickness of 5 nm or less.

[0055] In one embodiment of the present invention, the "oxide island (i.e., non-crack part)" region may be shown in a white or brighter color compared to the crack part of adjacent sites in an image observed with a scanning electron microscope (SEM) at a magnification of 30,000. On the other hand, the region where there is insufficient oxide surrounding the "oxide island" (i.e., the crack part) may be shown in a black or darker color compared to the non-crack part of adjacent sites. At this time, the SEM observation can be performed immediately after heat-treating the lithium metal negative electrode, immediately after manufacturing the battery, or immediately before cycling the battery, but is not limited thereto. Also, the SEM observation is to observe the surface of the lithium metal negative electrode from above, and is an observation in the vertical direction (top-down) of a plane parallel to the oxide layer and the lithium metal.

[0056] In one embodiment of the present invention, the oxide layer can be a lithium oxide layer. Also, the oxide layer can be a natural oxide layer. The natural oxide layer is formed by the reaction of a metal with atmospheric components and is formed on the metal surface. The natural oxide layer of lithium is usually formed in a two-layer structure. In the two-layer structure, the inner layer becomes lithium oxide (Li2O), and the outer layer can become lithium hydroxide (LiOH) and lithium carbonate (Li2CO3). Also, lithium metal reacts with nitrogen to form lithium nitride (Li3N), and thus the natural oxide layer of lithium may contain lithium nitride. However, the constituent materials of the lithium oxide layer are not limited to the above substances and can be composed of various substances applicable to ordinary technicians.

[0057] According to one embodiment of the present invention, in the lithium metal anode, due to the presence of crack portions in the oxide layer formed on the surface of such lithium metal, all or part of the oxide layer present on the surface of the lithium metal can be removed or destroyed. Such crack portions remove or destroy all or part of the thick oxide layer that acts as a resistance to lithium desorption, exposing the lithium metal, or the oxide layer becomes thinner, reducing the overvoltage required for lithium desorption, thereby improving lithium desorption. During the electrodeposition process, the crack portions can be used as nucleation sites for lithium, and as the surface area of the lithium metal increases due to the crack portions, the electric field on the surface decreases, suppressing dendrite growth, so that the electrodeposition becomes uniform.

[0058] In one embodiment of the present invention, the oxide layer may have crack portions and non-crack portions, and the area ratio of the crack portions to the non-crack portions may be 2:8 to 9:1, or 4:6 to 6:4. When the area ratio of the crack portions to the non-crack portions satisfies the above-mentioned range, it becomes easier to improve lithium desorption, achieve uniform electrodeposition, and suppress dendrite growth, and the battery life can be improved. The areas of the crack portions and the non-crack portions can be calculated from an image obtained by observing the oxide layer with a scanning electron microscope (SEM).

[0059] In one embodiment of the present invention, at least a part or all of the crack portions have an elongated shape, and the average width of the crack portions can be 1 to 500 nm, 10 to 400 nm, or 50 to 300 nm.

[0060] In one embodiment of the present invention, at least a part or all of the crack portions have an elongated shape, and the average length of the crack portions can be 2.5 μm or more, or 3 μm or more.

[0061] In one embodiment of the present invention, the vertical cross-section of the crack portions has an elongated shape at least in part or in whole, and the ratio of the average width to the average length of the crack portions can be 0.001 to 0.2, 0.01 to 0.2, or 0.03 to 0.2.

[0062] In this specification, the "long shape" should be understood in a broad sense as a non-spherical shape, that is, a shape having different diameters in different vertical directions such as an elliptical shape. Further, it is not limited to an elliptical shape, not limited to shapes such as a rectangular shape or a curved form, and may include irregular shapes.

[0063] The length of the crack portion is the distance between the two farthest points of the crack portion, and can be determined from an image obtained by observing the lithium metal on which the oxide layer is formed with a scanning electron microscope (SEM). Specifically, when the surface of the electrode is observed with an SEM, it can be determined from the image of the crack portion observed on the surface.

[0064] The width of the crack portion means the distance between the oxide layers existing on one side and the other side of the crack portion in a direction perpendicular to an imaginary line connecting the two farthest points of the crack portion, and can be determined from an image obtained by photographing the lithium metal on which the oxide layer is formed with a scanning electron microscope (SEM). Specifically, it can be determined from the image obtained by observing the surface of the electrode with an SEM. Specifically, when the surface of the electrode is observed with an SEM, it can be determined from the image of the crack portion observed on the surface.

[0065] In one embodiment of the present invention, the total thickness of the oxide layer may be 10 nm to 10 μm, or 20 nm to 1 μm. That is, for example, the thickness of the non-crack portion of the oxide layer may satisfy the above range. When the thickness of the oxide layer satisfies the above-described range, it is possible to easily prevent the occurrence of deterioration during the storage process of the lithium metal, and it is possible to more easily prevent the problem that the resistance is high and the desorption of lithium does not occur.

[0066] In one embodiment of the present invention, the lithium metal layer may be in the form of a sheet, foil or thin film. And the thickness of the lithium metal layer may be 1 to 200 μm, or 5 to 100 μm. When the thickness of the lithium metal layer satisfies the above-described range, it provides a sufficient lithium source for battery driving and makes it easier to realize a high energy density.

[0067] The lithium metal negative electrode according to an embodiment of the present invention can be manufactured by, but is not limited to, the following method.

[0068] According to one aspect of the present invention, a method for manufacturing a lithium metal negative electrode including a lithium metal layer and an oxide layer formed on at least one surface of the lithium metal layer includes a step of forming a crack portion in the oxide layer.

[0069] The lithium metal negative electrode according to an embodiment of the present invention can form a crack portion in the oxide layer formed on the surface of the lithium metal by heat-treating the lithium metal. During the process of heat-treating the lithium metal, the volume of the lithium metal expands, so that crack portions can occur in the oxide layer existing on the surface of the lithium metal.

[0070] In one embodiment of the present invention, the lithium metal can be heat-treated at 40°C to 120°C, 60°C to 100°C, or 65°C to 85°C to form a crack portion in the oxide layer formed on the surface of the lithium metal. When the temperature condition for heat-treating the lithium metal satisfies the above conditions, crack portions are sufficiently formed in the oxide layer on the surface of the lithium metal, and the problems of lithium evaporation and reduction in the thickness of the lithium metal and reduction in the lithium negative electrode active material can be more effectively prevented, whereby the life of the electrochemical element including the same can be further improved.

[0071] In one embodiment of the present invention, the lithium metal can be heat-treated in a vacuum atmosphere at a pressure of 0.001 to 1 Torr to form a crack portion in the oxide layer formed on the surface of the lithium metal. By heat-treating the lithium metal under the above-described pressure conditions and in a vacuum atmosphere, it is possible to more easily prevent the residual gas from reacting with the surface of the lithium metal to further form an oxide layer. Further, crack portions are generated during the heat-treatment process, and it is possible to more easily prevent the lithium metal exposed by the crack portions from immediately reacting with the residual gas to reform the oxide layer.

[0072] In another embodiment of the present invention, the lithium metal can be heat-treated in an inert atmosphere to form crack portions in the oxide layer formed on the surface of the lithium metal. Here, the inert gas forming the inert atmosphere means a gas that does not cause a chemical reaction, such as argon or nitrogen, but is not limited to the above gases and includes all gases applicable to ordinary technicians. By heat-treating the lithium metal in an inert atmosphere, it is possible to more easily prevent residual gas from reacting with the surface of the lithium metal to further form an oxide layer. Further, during the heat-treatment process, crack portions are generated, and it is possible to more easily prevent the lithium exposed in the crack portions or the thinned oxide layer from immediately reacting with the residual gas to further form an oxide layer.

[0073] In one embodiment of the present invention, the lithium metal can be heat-treated at 40°C to 120°C, or 60°C to 100°C, in a vacuum atmosphere at a pressure of 0.001 to 1 Torr to form cracks in the oxide layer formed on the surface of the lithium metal.

[0074] In another embodiment of the present invention, the lithium metal can be heat-treated at 40°C to 120°C, or 60°C to 100°C, in an inert atmosphere to form cracks in the oxide layer formed on the surface of the lithium metal.

[0075] The electrochemical element according to one embodiment of the present invention includes a lithium metal negative electrode having an oxide layer with cracks on its surface, so that the lifespan can be improved.

[0076] The electrochemical element of the present invention includes all elements that undergo an electrochemical reaction, specifically, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements.

[0077] In one embodiment of the present invention, the electrochemical element is all lithium secondary batteries commonly used in the industry that use lithium metal as the negative electrode, among which it can be a lithium-ion battery, a lithium-sulfur battery, or a lithium-lithium symmetric cell.

[0078] An electrochemical device according to an embodiment of the present invention includes a positive electrode, a lithium metal negative electrode, a separator, and a non-aqueous electrolyte. The electrochemical device can be manufactured by a process of facing the positive electrode to the negative electrode, interposing a separator therebetween, and then injecting a non-aqueous electrolyte.

[0079] Hereinafter, in the electrochemical device according to an embodiment of the present invention, the positive electrode, the separator, and the non-aqueous electrolyte will be described in more detail.

[0080] The positive electrode includes a positive electrode active material, a binder, a conductive material, and the like. The positive electrode active material can be applicable to ordinary electrochemical devices. For example, it may contain a lithium nickel cobalt manganese-based compound (lithium NCM-based compound). It may also contain elemental sulfur (S8), a sulfur-based compound, or a mixture thereof. Specifically, the sulfur-based compound is Li2S n (n≧1), an organic sulfur compound, or a carbon-sulfur composite ((C2S x ) n: It can be, for example, x = 2.5 to 50, n ≥ 2, etc. Further, the positive electrode active material may contain a sulfur-carbon composite. Since the sulfur substance alone has no electrical conductivity, it can be used in combination with a conductive material. The carbon material (or carbon source) constituting the sulfur-carbon composite may have a porous structure or a high specific surface area, and any one may be used as long as it is commonly used in the art. For example, the porous carbon material may be graphite; graphene; carbon black such as Denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); activated carbon; or two or more of these, but is not limited thereto. Its form may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk form, and is not particularly limited as long as it is applicable to an electrochemical element.

[0081] Further, pores are formed in the carbon material, and the porosity of the pores can be 40 to 90%, or 60 to 80%. When the porosity of the pores satisfies the above-mentioned range, lithium ion transfer is likely to occur normally, and the problem of reduced mechanical strength can be more easily prevented. The pore size of the carbon material can be 10 nm to 5 μm, or 50 nm to 5 μm. When the pore size of the carbon material satisfies the above-mentioned range, the permeation of lithium ions becomes easy, and problems such as battery short circuit and safety due to contact between electrodes can be more easily prevented.

[0082] The binder is a component that helps bind the positive electrode active material and the conductive material, etc., and also helps bind to the current collector. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, styrene - butadiene rubber, acrylonitrile - butadiene rubber, ethylene - propylene - diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene - butylene rubber, fluorine rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or two or more of these can be used, but it is not necessarily limited to these.

[0083] The binder can usually be added in an amount of 1 to 50 parts by weight, or 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. When the content of the binder satisfies the above - mentioned range, it becomes easy to ensure the adhesion force between the positive electrode active material and the current collector, and it may also become easy to ensure the battery capacity.

[0084] The conductive material contained in the positive electrode is not particularly limited as long as it does not induce side reactions in the internal environment of the electrochemical element and has excellent electrical conductivity without inducing chemical changes in the battery. Typically, graphite or conductive carbon can be used. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, and lamp black; carbon-based substances with a crystal structure of graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; or two or more of these can be used, but it is not necessarily limited to these.

[0085] The conductive material can usually be added in an amount of 0.5 to 50 parts by weight, or 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. When the content of the conductive material satisfies the above-mentioned range, it becomes easy to improve the electrical conductivity, easily prevent the deterioration of the electrochemical characteristics, and easily ensure the capacity and energy density of the positive electrode.

[0086] The method of including the conductive material in the positive electrode is not particularly limited, and ordinary methods known in the art, such as coating the positive electrode active material, can be used. Further, if necessary, the addition of the conductive material as described above can be replaced by adding a conductive second coating layer to the positive electrode active material.

[0087] In addition, a filler can be selectively added to the positive electrode of the present invention as a component for suppressing its expansion. Such a filler is not particularly limited as long as it does not induce chemical changes in the battery and can suppress the expansion of the electrode. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fibers and carbon fibers; etc. can be used.

[0088] The positive electrode can be manufactured by dispersing and mixing a positive electrode active material, a binder, a conductive material, etc. in a dispersion medium (solvent) to form a slurry, applying the slurry onto a positive electrode current collector, and then drying and rolling. As the dispersion medium, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof can be used, but are not necessarily limited thereto.

[0089] As the positive electrode current collector, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, and those obtained by surface-treating the surface of aluminum (Al) or stainless steel with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) can be used, but are not necessarily limited thereto. The form of the positive electrode current collector can be in the form of a foil, film, sheet, punched material, porous body, foam, etc.

[0090] A normal separator can be interposed between the positive electrode and the negative electrode. Any physical separator that has the function of physically separating the separator electrode and is used as a normal separator can be used without particular limitation. In particular, those with low resistance to ion movement of the electrolyte and excellent impregnation ability of the electrolyte are desirable. Further, the separator separates or insulates the positive electrode and the negative electrode from each other and enables the transport of lithium ions between the positive electrode and the negative electrode. Such a separator can be porous and made of a non-conductive or insulating material. The separator can be an independent member such as a film, or a coating layer added to the positive electrode and / or the negative electrode.

[0091] Examples of polyolefin-based porous membranes that can be used as the separation membrane include membranes formed from polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, either alone or as a mixture of these polymers. Examples of non-woven fabrics that can be used as the separation membrane include non-woven fabrics formed from polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc., either alone or as a mixture of these polymers. Such non-woven fabrics are in the form of fibers that form a porous web and may include a spunbond or meltblown form composed of staple fibers.

[0092] The thickness of the separation membrane is not particularly limited, but it can be 1 to 100 μm, or 5 to 50 μm. When the thickness of the separation membrane satisfies the above-mentioned range, the mechanical properties can be maintained, and the problem of deterioration of battery performance due to the separation membrane acting as a resistance layer can be easily prevented. The pore size and porosity of the separation membrane are not particularly limited, but the pore size is 0.1 to 50 μm, and the porosity can be 10 to 95%. When the pore size of the separation membrane satisfies the above-mentioned range, it is easy to prevent the separation membrane from acting as a resistance layer, and the mechanical properties of the separation membrane can be easily maintained.

[0093] The non-aqueous electrolyte may include a first solvent containing a heterocyclic compound that contains one or more double bonds or does not contain any, and contains one or more of either an oxygen atom or a sulfur atom, a second solvent containing one or more of an ether compound, an ester compound, an amide compound, and a carbonate compound, a lithium salt, and lithium nitrate.

[0094] Hereinafter, the first solvent, the second solvent, the lithium salt, and lithium nitrate contained in the non-aqueous electrolyte according to one embodiment of the present invention will be specifically described respectively.

[0095] First solvent The first solvent contains a heterocyclic compound that contains one or more double bonds or does not contain any, and contains one or more of either an oxygen atom or a sulfur atom. Because of the property of being difficult to dissolve salts due to the delocalization of the lone pair electrons of the heteroatom (oxygen atom or sulfur atom), the formation of a polymer protective film (solid electrolyte interphase; SEI layer) on the surface of the lithium metal by the ring opening reaction of the heterocyclic compound at the initial discharge stage of the battery can suppress the generation of lithium dendrites. Furthermore, the life characteristics of the electrochemical element can be improved by reducing the decomposition of the electrolyte on the surface of the lithium metal and the side reactions caused thereby.

[0096] That is, the heterocyclic compound of the present invention may contain one or more double bonds in order to form a polymer protective film on the surface of the lithium metal, and necessarily contains one or more heteroatoms (oxygen atom or sulfur atom) so as to exhibit effects such as making it polar and increasing the affinity with other solvents in the electrolyte.

[0097] The heterocyclic compound may be a 3- to 15-membered ring, or a 3- to 7-membered ring or a 5- to 6-membered ring heterocyclic compound. Further, such a heterocyclic compound may be a heterocyclic compound substituted or unsubstituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO2), an amine group (-NH2), and a sulfonyl group (-SO2). Further, the heterocyclic compound may be a polycyclic compound of a heterocyclic compound and one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0098] When the heterocyclic compound is substituted with an alkyl group having 1 to 4 carbon atoms, the radical can be stabilized to suppress side reactions with the electrolytic solution. Further, when substituted with a halogen group or a nitro group, a functional protective film can be formed on the surface of the lithium metal. At this time, the formed functional protective film can be stable as a compressed (compact) form of the protective film. Further, uniform deposition of the lithium metal may be enabled. In particular, when the electrochemical element is a lithium-sulfur battery, side reactions between polysulfide and lithium metal can be suppressed.

[0099] Specific examples of the heterocyclic compound include 1,3-dioxolane, 4,5-diethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 4-methyl-1,3-dioxane, 2-methyl-1,3-dioxane, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-Nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiphene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene, etc.

[0100] The first solvent containing such a heterocyclic compound can be contained in a volume ratio of 5 to 50 with respect to 100 volume ratios of the total organic solvents (i.e., the first solvent + the second solvent) contained in the non-aqueous electrolyte according to an embodiment of the present invention (the remainder is the second solvent). When the content of the first solvent satisfies the above-described range, the problem that the protective film is not completely formed on the surface of the lithium metal can be easily prevented, and the problems of the reduction in the capacity and life of the battery due to the increase in the surface resistance of the electrolyte and the lithium metal can be easily prevented.

[0101] In particular, when the positive electrode active material is sulfur, the problem that the ability to reduce the elution amount of polysulfide decreases and it becomes difficult to suppress the increase in the resistance of the electrolyte can be easily prevented.

[0102] Second solvent The second solvent contains one or more of an ether compound, an ester compound, an amide compound, and a carbonate compound, and not only dissolves the lithium salt so that the electrolyte has lithium ion conductivity, but also plays a role in eluting the positive electrode active material to smooth the electrochemical reaction with lithium. In particular, when the positive electrode active material is sulfur, it can play a role in eluting sulfur, which is the positive electrode active material, to smooth the electrochemical reaction with lithium.

[0103] The carbonate compound can be a linear carbonate compound or a cyclic carbonate compound.

[0104] Specific examples of the ether compound include, but are not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, 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, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, or two or more thereof.

[0105] Examples of the ester compound include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, or two or more thereof.

[0106] The amide compound can be a normal amide compound used in the industry.

[0107] Examples of the linear carbonate compound include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or two or more thereof.

[0108] Examples of the cyclic carbonate compound include, but are not limited to, 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, halides thereof (such as fluoroethylene carbonate (FEC)), or two or more of these.

[0109] The second solvent may be contained in a volume ratio of 50 to 95 with respect to 100 volume ratios of the total organic solvents (i.e., the first solvent + the second solvent) contained in the non-aqueous electrolyte according to an embodiment of the present invention. When the content of the second solvent satisfies the above-described range, the lithium salt can be sufficiently dissolved, the problem of poor lithium ion conductivity can be easily prevented, and the problem of precipitation exceeding the concentration at which the positive electrode active material can be dissolved can be easily prevented. In particular, when the positive electrode active material is sulfur, the problem of precipitation exceeding the concentration at which sulfur as the positive electrode active material can be dissolved can be easily prevented, and the problem of excessive elution of sulfur, which causes a severe shuttle phenomenon between lithium polysulfide and the lithium metal negative electrode and reduces the life, can be easily prevented.

[0110] On the other hand, the organic solvent containing the first solvent and the second solvent may be contained in an amount of 60 to 99.5% by weight, or 60 to 99% by weight, or 60 to 98% by weight, or 60 to 95% by weight with respect to 100% by weight of the total non-aqueous electrolyte according to an embodiment of the present invention. When the organic content satisfies the above-described range, the problems of increased viscosity of the electrolyte and decreased ion conductivity or incomplete dissolution of the lithium salt and additives in the electrolyte can be easily prevented, and the problem of decreased ion conductivity due to a low concentration of the lithium salt in the electrolyte can be easily prevented.

[0111] Lithium salt The lithium salt is used as an electrolyte salt for increasing ionic conductivity. Examples of this include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (SO2F)2NLi (i.e., LiFSI), (CF3SO2)2NLi (i.e., LiTFSI), (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylate having 4 or less carbon atoms, lithium 4-phenylborate, lithium imide, or two or more of these.

[0112] The lithium salt concentration can be determined in consideration of ionic conductivity and the like, and can be, for example, 0.2 to 2 M or 0.5 to 1 M. When the concentration of the lithium salt satisfies the above-mentioned range, ionic conductivity suitable for battery driving can be easily ensured, and it is possible to prevent the viscosity of the electrolyte from increasing and the mobility of lithium ions from decreasing, or the decomposition reaction of the lithium salt itself from increasing.

[0113] Lithium nitrate The non-aqueous electrolyte according to one embodiment of the present invention may contain lithium nitrate (LiNO3). Lithium nitrate reacts with the lithium metal negative electrode to form a lithium affinity protective film such as lithium nitride (Li3N) and lithium oxynitride (LiON) on the surface of the lithium metal negative electrode, suppress the growth of lithium dendrites, prevent the decomposition of the electrolyte components, and improve the battery life and efficiency.

[0114] Also, if necessary, it may further contain lanthanum nitrate (La(NO3)3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium nitrate (Mg(NO3)2), barium nitrate (Ba(NO3)2), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), or two or more of these.

[0115] The lithium nitrate may be contained in an amount of 0.1 to 7% by weight, or 0.5 to 5% by weight, or 0.5% to 1.5% by weight based on 100% by weight of the entire non-aqueous electrolyte. When the content of lithium nitrate satisfies the above-described range, it is possible to easily prevent the problem that the Coulomb efficiency rapidly decreases, and it is possible to easily prevent the phenomenon that the viscosity of the electrolyte increases.

[0116] The non-aqueous electrolyte according to one embodiment of the present invention may contain 1,3-dioxolane as the first solvent, dimethoxyethane as the second solvent, (CF3SO2)2NLi as the lithium salt, and lithium nitrate. The 1,3-dioxolane and dimethoxyethane have a high lithium polysulfide solubility and can stabilize the lithium metal negative electrode. Thereby, when the non-aqueous electrolyte contains the above-described substances, it becomes possible to exhibit optimal electrochemical device characteristics.

[0117] On the other hand, the lithium secondary battery according to one embodiment of the present invention can be suitably used not only for a battery cell used as a power source for a small device, but also particularly preferably for a unit cell of a battery module which is a power source for medium and large devices. Also, in this regard, the present invention provides a battery module in which two or more electrochemical devices are electrically connected (in series or in parallel). The number of electrochemical devices included in the battery module can of course be variously adjusted in consideration of the use and capacity of the battery module. Furthermore, the present invention provides a battery pack in which the battery module is electrically connected by ordinary techniques in the art. The battery module and the battery pack can be used as a power source for one or more of medium and large devices such as power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric trucks; electric commercial vehicles; or power storage systems, but are not necessarily limited thereto.

[0118] Hereinafter, examples will be given for a detailed explanation to facilitate the understanding of the present invention. However, the examples according to the present invention can be deformed in various forms, and the scope of the present invention is not limited to the following examples. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0119] Example 1-1 Lithium metal with a thickness of 35 μm was heat-treated at a temperature of 40 °C for 4 hours in a vacuum atmosphere with a pressure of 0.01 Torr using a convection oven, and then it was rolled on one side onto a copper current collector to produce a lithium metal negative electrode.

[0120] Example 1-2 A lithium metal negative electrode was produced in the same manner as in Example 1-1, except that the heat treatment was performed at a temperature of 60 °C.

[0121] Example 1-3 A lithium metal negative electrode was produced in the same manner as in Example 1-1, except that the heat treatment was performed at a temperature of 80 °C.

[0122] Example 1-4 A lithium metal negative electrode was produced in the same manner as in Example 1-1, except that the heat treatment was performed at a temperature of 100 °C.

[0123] Example 1-5 A lithium metal negative electrode was produced in the same manner as in Example 1-1, except that the heat treatment was performed at a temperature of 120 °C.

[0124] Comparative Example 1-1 Lithium metal with a thickness of 35 μm was used as a lithium metal negative electrode without any treatment.

[0125] Examples 2-1 to 2-5 and Comparative Example 2-1: Production of Lithium-Lithium Symmetric Cells First, 1 wt% of lithium nitrate was added to an organic solvent obtained by mixing 1,3-dioxolane (the first solvent) and dimethoxyethane (the second solvent) at a volume ratio (v / v) of 1:1, and it was dissolved so that the concentration of (CF3SO2)2NLi (LiTFSI) (lithium salt) became 1 M to produce a non-aqueous electrolyte.

[0126] The lithium metal anodes produced in Examples 1-1 to 1-5 and Comparative Example 1-1 were used identically for the anode and the cathode, and at this time, the lithiums were positioned so as to face each other. Subsequently, after interposing a porous polyethylene (PE) separator with a thickness of 16 μm between the anode and the cathode, the non-aqueous electrolytes produced above were each injected and sealed to produce coin cell type lithium-lithium symmetric cells.

[0127] Examples 3-1 to 3-5 and Comparative Example 3-1: Fabrication of Lithium-Sulfur Batteries First, 87.5 parts by weight of a sulfur-carbon (CNT) composite (S / C 75:25 weight ratio) as a cathode active material, 5 parts by weight of Denka black as a conductive material, and 7.5 parts by weight of styrene-butadiene rubber / carboxymethyl cellulose (SBR / CMC 7:3) as a binder were mixed to produce a cathode slurry composition. Then, it was applied to one side of a current collector (Al foil), dried at 80 °C, and rolled with a roll press device to produce a cathode (at this time, the load amount was 4.5 mg / cm 2 was made).

[0128] Subsequently, the produced cathode and the lithium metal anodes produced in Examples 1-1 to 1-5 and Comparative Example 1-1 were positioned so as to face each other. After interposing a porous polyethylene (PE) separator therebetween, the non-aqueous electrolytes produced in Examples 2-1 to 2-5 and Comparative Example 2-1 were each injected and sealed to produce coin cell type lithium-sulfur batteries.

[0129] Evaluation Example 1: Surface Observation of Lithium Metal Anode The surfaces of the lithium metal anodes produced in Examples 1-3 and the lithium metal anode produced in Comparative Example 1-1 were observed by scanning electron microscopy (SEM) and are shown in FIGS. 1 and 2, respectively. At this time, the SEM observation of the lithium metal anodes produced in Examples 1-3 was performed immediately after the heat treatment. The SEM equipment used was JEOL JSM-7200F, the magnification was set to 30,000x, and the acceleration voltage was set to 5 kV. Also, since the resolution of the equipment used is 1 nm at 20 kV and 1.6 nm at 1 kV, it is 1-1.6 nm at 5 kV.

[0130] As can be confirmed from FIG. 2, it was confirmed that the lithium metal anode produced in Comparative Example 1-1 had its lithium metal surface covered with a native oxide without crack portions.

[0131] On the other hand, as can be confirmed from FIG. 1, it was confirmed that the lithium metal anodes produced in Examples 1-3 had crack portions formed in the oxide layer present on the surface of the lithium metal.

[0132] Evaluation Example 2: Calculation of the area ratio of the crack portions and non-crack portions of the lithium metal anode Using the images obtained by observing the surfaces of the lithium metal anodes produced in Examples 1-1 to 1-5 and Comparative Example 1-1 by SEM, the area ratio of the crack portions and non-crack portions was calculated. Here, the SEM equipment used was JEOL JSM-7200F, the magnification was set to 30,000x, and the acceleration voltage was set to 5 kV. Also, since the resolution of the equipment used is 1 nm at 20 kV and 1.6 nm at 1 kV, it is 1-1.6 nm at 5 kV.

[0133] Specifically, in the image observed by the SEM, the non-crack part was shown relatively brightly because the surface was rough and protruding, while the crack part was shown darkly because the surface was smooth. To utilize such properties, the SEM image was binary-processed into black and white using "ImageJ" software, and the colors of the processed image were inverted so that the non-crack part appeared dark and the crack part appeared bright to maximize the brightness contrast. Thereafter, the area ratio was calculated using the areas of the regions shown as the crack part and the non-crack part, and the results are shown in Table 1 below.

[0134]

Table 1

[0135] Evaluation Example 3: Cycle Life Evaluation of Lithium-Lithium Symmetric Cell The lithium-lithium symmetric cells manufactured in Examples 2-1 to 2-5 and Comparative Example 2-1 were subjected to discharge (-1V lower limit) and charge (+1V upper limit) cycles at a current density of 1.5 mA / cm 2 at a temperature of 25 °C, and the potential over time (cycles) was measured to evaluate the cycle life, as shown in Table 2 and Figures 3 to 8 below. When the lithium negative electrode operates smoothly during the driving of the symmetric cell, the overvoltage is at the 0.1V level. However, when the lithium negative electrode deteriorates, a larger overvoltage is required to desorb lithium. When an overvoltage of -1V is required, it means that lithium is difficult to desorb at the lithium negative electrode, which may mean that the lithium negative electrode cannot operate normally. Table 2 shows the cell life based on the case where the overvoltage required for lithium desorption reaches -1V.

[0136]

Table 2

[0137] As can be confirmed from Table 1, Table 2, and FIGS. 3 to 8, the lithium-lithium symmetric cells manufactured in Examples 2-1 to 2-5 induced uniform electrodeposition due to the formation of crack portions in the oxide layer on the surface of the lithium metal, and it was confirmed that the lifespan was improved compared to the lithium-lithium symmetric cell manufactured in Comparative Example 2-1 in which no crack portion was formed in the oxide layer on the surface of the lithium metal. In particular, it was confirmed that the battery lifespan was further improved from the lithium-lithium symmetric cells manufactured in Examples 2-2 to 2-4 where the heat treatment temperature was 60°C to 100°C.

[0138] Evaluation Example 4: Cycle Life Evaluation of Lithium-Sulfur Battery For the lithium-sulfur batteries manufactured in Examples 3-1 to 3-5 and Comparative Example 3-1, CC mode charge / discharge cycles at a temperature of 25°C were performed in a voltage range of 1.8V to 2.5V with 0.2C charge / 0.3C discharge, and the capacity-potential due to the charge / discharge cycles was measured (after an initial 0.1C / 0.1C 2.5 cycles and a stabilization process of 0.2C / 0.2C 3 cycles, driven at 0.3C / 0.5C from the 7th cycle), and the results are shown in Table 3 and FIG. 9 below.

[0139]

Table 3

[0140] As can be confirmed from Table 3 and FIG. 9, the lithium-sulfur batteries manufactured in Examples 3-1 to 3-5 including an oxide layer with crack portions formed on the surface of the lithium metal had an improved lifespan compared to the lithium-sulfur battery manufactured in Comparative Example 3-1 in which no crack portion was formed in the oxide layer on the surface of the lithium metal. And in the case of the lithium-sulfur batteries manufactured in Examples 3-2 to 3-4 where the heat treatment temperature was 60°C to 100°C, it was confirmed that the battery lifespan was further improved. In particular, it was confirmed that the lifespan of the lithium-sulfur battery manufactured in Example 3-3 where the heat treatment temperature was in the range of 70 to 90°C was far superior.

Claims

1. A lithium metal layer, and a lithium metal oxide layer located on at least one surface of the lithium metal layer, wherein the lithium metal oxide layer has a cracked portion and a non-cracked portion, the thickness of the lithium metal oxide layer in the cracked portion is 50% or less of the maximum thickness of the lithium metal oxide layer, and the area ratio of the cracked portion to the non-cracked portion is 2:8 to 9:1, characterized in that it is a lithium metal negative electrode.

2. The lithium metal negative electrode according to claim 1, characterized in that the thickness of the lithium metal oxide layer is 10 nm to 10 μm.

3. The lithium metal negative electrode according to claim 1, characterized in that the thickness of the lithium metal layer is 1 μm to 200 μm.

4. A method for manufacturing a lithium metal negative electrode including a lithium metal layer and a lithium metal oxide layer located on at least one surface of the lithium metal layer, including the step of forming a cracked portion in the lithium metal oxide layer, wherein the thickness of the lithium metal oxide layer in the cracked portion is 50% or less of the maximum thickness of the lithium metal oxide layer, and the area ratio of the cracked portion to the non-cracked portion is 2:8 to 9:1, which is a method for manufacturing the lithium metal negative electrode of claim 1.

5. The step of forming the cracked portion includes the step of heat-treating the lithium metal negative electrode in a vacuum atmosphere at a pressure of 0.001 to 1 Torr, characterized in that it is a method for manufacturing the lithium metal negative electrode according to claim 4.

6. The step of forming the cracked portion includes the step of heat-treating the lithium metal negative electrode in an inert atmosphere, characterized in that it is a method for manufacturing the lithium metal negative electrode according to claim 4 or 5.

7. The step of forming the cracked portion includes the step of heat-treating the lithium metal negative electrode at 40°C to 120°C, characterized in that it is a method for manufacturing the lithium metal negative electrode according to claim 4 or 5.

8. The step of forming the cracked portion includes the step of heat-treating the lithium metal negative electrode at 65°C to 85°C, characterized in that it is a method for manufacturing the lithium metal negative electrode according to claim 4 or 5.

9. An electrochemical element including the lithium metal negative electrode according to any one of claims 1 to 3.

10. The electrochemical element according to claim 9, characterized in that the electrochemical element includes a lithium secondary battery.

11. The electrochemical element according to claim 10, wherein the lithium secondary battery includes a lithium ion battery, a lithium sulfur battery, a lithium-lithium symmetric cell, or two or more of these.

Images