Method for manufacturing lithium metal electrodes and lithium ion electrodes, and lithium ion battery

Abstract

The present invention relates to a lithium metal electrode, in particular for a lithium ion battery, comprising a three-dimensional network of metal fibers, said metal fibers being in direct contact with one another and having a thickness and / or width in the range of 0.25-200 μm, and metallic lithium being provided on a surface of said metal fibers of said three-dimensional network of metal fibers.Furthermore, the present invention relates to a method for producing a lithium metal electrode, comprising the steps of: a) providing a three-dimensional network of metal fibers, said metal fibers being in direct contact with one another and having a thickness and / or width in the range of 0.25-200 μm, and b) providing a layer of metallic lithium on said fibers of said three-dimensional network of metal fibers.

Description

[Technical Field]

[0001] This invention relates to lithium metal electrodes, particularly negative electrodes, for lithium-ion batteries. Furthermore, this invention relates to a method for manufacturing lithium metal electrodes and a battery containing such electrodes. [Background technology]

[0002] Lithium metal anodes for lithium-ion batteries have been under consideration since the 1970s due to their high capacity. Conventional lithium-ion battery anodes utilize an active material in which lithium is embedded. In contrast, lithium metal anodes do not contain such an active material. Instead, metallic lithium is deposited onto a mold. 1~3 However, because lithium is highly reactive and tends to form dendrites, applying pure lithium to electrodes has been difficult. Such dendrites can grow until they puncture the separator, causing internal short circuits. 1 This was overcome in 1985 when Akira Yoshino discovered graphite as a lithium host. For this discovery, he, along with Stanley Whittingham and John Goodenough, was awarded the 2020 Nobel Prize in Chemistry. 4 .

[0003] Because the theoretical capacity of metallic lithium is 3800 mAh / g, significantly higher than that of graphite-based electrodes (372 mAh / g), the idea of ​​using pure metallic lithium instead of graphite has recently attracted renewed attention due to the substantial increase in capacity. Various strategies have been proposed to inhibit lithium dendrite growth and the resulting formation of dead lithium. These strategies include the formation of a dense three-dimensional (3D) negative electrode structure. 5~11 , electrolyte engineering 12、13 Modification of the electrode surface 14 , or separators suited to the purpose 15The inventors believe that in order to overcome the effects of dendrite growth and the resulting formation of dead lithium, it is necessary to deposit lithium in a dense layer or structure that provides a large surface area for the deposited lithium.

[0004] In particular, 3D scaffold structures used for lithium deposition are a focus of research. This is because the porous structure provides sufficient free volume to accommodate volume changes associated with deposition and detachment processes. Furthermore, the high conductivity of this host ensures a uniform potential along the scaffold surface, and consequently, uniform lithium deposition. Such scaffolds can be classified into carbon-based scaffolds and metallic scaffolds. In principle, foamed or fibrous structures can be used for both carbon-based and metallic scaffolds.

[0005] Carbon-based scaffolds typically offer both lightness and good conductivity, making them suitable for fabricating free-standing electrodes. 16、17 While carbon nanotubes, graphene, or graphite fibers are used for such carbon-based structures, they have significant drawbacks when applied to lithium metal negative electrodes. When the electrode is composed of a self-supporting carbon-based electrode, its transition to the outer metal circuit is a major obstacle. The mechanical and electrical connection between the carbon electrode and the outer metal circuit is problematic because welding is impossible, resulting in mechanical instability and high electrical resistance. To improve the connection, highly conductive binders (such as metal lacquer) were applied, but this idea was quickly abandoned due to the large temperature rise at the interconnection during cell charging and discharging.

[0006] In summary, carbon-based materials are difficult to process after obtaining the final hierarchical structure within the electrode, making it impossible to apply common processing methods (soldering, welding, etc.).

[0007] On the one hand, metal structures have excellent conductivity and mechanical and electrochemical stability, but they have a high density. Such metal scaffolds can be applied as three-dimensional foams or fibrous networks. In particular, foams are known to be used in the range of porosity of 90 - 95% and metal strand diameter of 30 - 100 μm. 14、16 。通常、発泡体の気孔が開いていると、足場上にリチウムを連続的に堆積させることができ、これは、表面改質によってさらに改善することができる Generally, when the pores of the foam are open, lithium can be continuously deposited on the scaffold, and this can be further improved by surface modification. 14、18 。銅発泡体に関する研究では、金属発泡体へのリチウム堆積時に、電気化学反応に関与しない「デッドリチウム」が大量に形成されることが示された。したがって、このような発泡体型電極の有効性は、Linら(参考情報)が示すように極めて限定的である In the study on copper foams, it has been shown that a large amount of "dead lithium" that does not participate in the electrochemical reaction is formed during the deposition of lithium on the metal foam. Therefore, the effectiveness of such foam-type electrodes is extremely limited as shown by Lin et al. (reference information). 18 。 。

[0008] In the case of the investigation of fibrous networks, only two different technologies divided by the scale of the fiber strand diameter are known.

[0009] One is to form a network consisting of metal strands with a thickness of 50 μm or more, typically in the range of 1 mm or more, to form a mesh-like network structure. And this mesh can be modified to improve the lithium deposition behavior, but usually, it has the drawback that the volume / surface area ratio is small, and as a result, the weight energy density of the entire electrode decreases. The lithium metal negative electrode described in Li, Q., Zhu, S., Lu, Y., "3D Porous Cu Current Collector / Li-Metal Composite Anode for Stable Lithium-Metal Batteries" Adv. Funct. Mater. 2017, 27, 1606422 is known.

[0010] The second approach is based on a wet chemical process and is used to fabricate Cu nanowires with diameters up to 200 nm. Cu(OH)2 is deposited as nanowhiskers using an alkaline reactant, and then it is thermally reduced in forming gas (AR / H2 or pure H2) or chemically reduced using hydrazine or the like to form metallic copper. 19、20 The resulting fibers typically have a very well - defined thickness (50 - 200 nm) and a characteristically large aspect ratio. Since whisker growth is limited to a high aspect ratio, thick fibers in the range of 0.5 - 50 microns cannot be fabricated by the aforementioned techniques, and copper fibers cannot be drawn smaller than 20 microns by conventional metal fiber drawing methods.

Summary of the Invention

Problems to be Solved by the Invention

[0011] From such a perspective, there is a need to provide a lithium metal electrode, particularly for a lithium - ion battery, that avoids the formation of dendrites and dead lithium and reduces the electrochemical stress during the operation of the corresponding battery.

Means for Solving the Problems

[0012] [[ID=***]] According to the present invention, the above object is solved by the electrode according to claim 1. In particular, this object is solved by a lithium metal electrode, particularly for a lithium - ion battery, comprising a three - dimensional network of metal fibers, wherein the metal fibers are in direct contact with each other; the metal fibers have a thickness and / or width in the range of 0.25 - 200 μm; and metallic lithium is provided on the surface of the metal fibers of the three - dimensional network of the metal fibers.

[0013] In the lithium metal electrode of the present invention, it has been found that the formation of dendrites is suppressed even after several cycles of repetition, so that the life of the corresponding battery is significantly extended. Furthermore, in contrast to the foam material, the formation of dead lithium is not observed, so that the efficiency of such an electrode is as high as in the range of 90 to 100%, and the areal specific capacity and the weight specific capacity are high. In comparison, the foam-like electrode has a much lower efficiency than the metal fiber network-based electrode of the present invention. Without being bound by theory, it is presumed that the growth of dendrites is suppressed by the large surface area provided by the metal fibers having a thickness in the range of 0.25 to 200 μm. Due to the large surface area, the deposition rate per unit area of the electrode decreases for a given current.

[0014] Furthermore, the three-dimensional network structure affects not only the overall cycle performance of the electrodes but also the deposition mechanism and associated overpotential. The potential at which lithium deposition occurs in electrochemical cells is usually given by the intercalation voltage of the electrodes, for example, 0.1V to 0.4V for graphite and 3.5V to 4V for LiNiMnCoO2 (NMC). However, the intercalation rate is limited, meaning that only a predetermined number of Li ions can be intercalated into a given volume of active material in a given time, and faster charging rates lead to overpotential. This overpotential is observed not only at various charging rates but also due to the aging degradation of the electrolyte. In this case, the decomposition of the electrolyte due to the increase in applied voltage leads to the growth of the solid electrolyte interface (SEI), dramatically reducing the rate at which Li ions are transported to the active material. Therefore, the overpotential measured in a given charge-discharge profile is also a way to evaluate the electrochemical stress acting on the electrodes. Moreover, since the overpotential (and its energy (obtained by multiplying the current by the voltage)) is directly converted into heat and lost during the storage process, a reduction in overpotential is highly beneficial. The three-dimensional electrode of the present invention was observed to exhibit lower overvoltage compared to the two-dimensional electrode even in the first cycle. Measurements showed that while the overvoltage observed in the two-dimensional electrode increased significantly after 50 cycles, the three-dimensional electrode of the present invention showed almost no change in overvoltage even after 50 cycles. Therefore, the electrode of the present invention not only suppresses dendrite formation but also reduces the electrochemical stress generated during the operation of the corresponding battery.

[0015] In summary, the lithium metal electrode of the present invention can improve the lifespan and capacity of the corresponding lithium metal-based full cell. In addition, heat generation during the charge-discharge process is largely related to the overvoltage applied during each process. That is, faster charging generates more heat, and generally more heat is generated as the cell ages. This effect could be greatly reduced by using the lithium metal electrode of the present invention. In particular, during the metal stripping process, the observed overvoltage was significantly lower compared to the corresponding 2D electrode.

[0016] The embodiments of the present invention are described in detail below, and these should be considered not only in themselves but also in possible combinations thereof.

[0017] According to the present invention, it is preferable that the electrodes essentially do not contain carbon-based materials. By using metal fibers in the electrodes, it becomes possible to directly sinter the metal fibers with each other, and as a result, conductive contact points are formed between these metal fibers. There is no need to use further carbon-based materials as a binder for the metal fibers and / or as the electrode active material. By eliminating such carbon-based materials, the electrodes can achieve a theoretical capacity close to 3800 mAh / g.

[0018] Preferably, the metal fibers are in direct electrical contact with each other to maximize conductivity. According to the present invention, the metal fibers are preferably directly sintered with each other at the contact points between the metal fibers. In this regard, it is particularly preferable that all of the metal fibers are sintered with other metal fibers, and most preferably directly sintered with other metal fibers, without the need for additional binders, such as polymer binders or solder. Therefore, it is even more preferable that the metal fibers are fixed with each other without the use of polymer binders, because such polymer binders often have poor conductivity and high-temperature performance.

[0019] Preferably, the metal fibers are made of copper, nickel, tin, copper alloys, or nickel alloys, and more preferably copper or copper alloys. Such metal fibers exhibit very high conductivity and very low internal resistance. Furthermore, metal fibers made of copper or copper alloys can take advantage of improved metal-to-metal surface diffusion. Although not bound by theory, in the lithium metal electrode of the present invention, a metal fiber-based, particularly sintered, network acts as a framework for the active material, which is lithium metal according to the present invention. This enables excellent electrical energy transport from the intercalation site to the current collector, while simultaneously providing a large effective diffusion coefficient D in the electrolyte. effThis is achieved. Even with an irregular network of metal fibers, at least some of the fiber orientation is always parallel to the ion flux, so the ion flow within the electrode is enhanced by surface diffusion. At high charging rates, the surface properties of the metal fiber-based network improve, resulting in a smaller concentration gradient in the liquid. Surface diffusion transports more ions from the source (Li) to the "consumer" (network). This effect significantly improves overall performance and is thought to explain the observed low overpotential. The improved surface diffusivity is beneficial even with thin electrodes. However, the effect is even more pronounced with thicker electrodes, especially those with a thickness in the range of 100 μm or more.

[0020] The metal fibers are more preferably copper alloys consisting of copper and a further element selected from the group consisting of at least zinc, boron, aluminum, gallium, indium, thallium, silicon, germanium, tin, lead, arsenic, antimony, bismuth, selenium, and tellurium, particularly zinc, boron, silicon, germanium, tin, arsenic, antimony, and tellurium. More preferably, the copper alloy consists of copper and silicon. Particularly preferred copper alloys are CuSi8 or CuSi4. Compared to metal fibers of pure copper, metal fibers of copper alloys are easier to produce by melt spinning. In particular, to obtain metastable fibers that exhibit an exothermic phenomenon when heated as measured by DSC, it is easier to use copper alloys instead of pure copper. As will be explained below, such a metastable state of the initial fibers can make the network of metal fibers stronger.

[0021] The interaction between the metal fiber surface and metallic lithium is a crucial parameter in the charge-discharge process, and the lithophilicity or lithopophilicity of the network must also be considered. This allows for a significant improvement in network performance by adding silicon to a copper network. To the best of our knowledge, such an effect of silicon as an additive has not been reported previously, although measurements with pure silicon have shown a slight improvement in diffusion rate. 21、22 .

[0022] Alloying copper with silicon, particularly a small amount of silicon (<20 wt%), appears to improve lithium deposition on the fiber surface and enhance the electrode's cycle stability. As a result, the resulting electrodes are far less prone to dendrite formation than copper foil or copper foam, and little to no dead lithium formation is observed. From this viewpoint, the metal fibers are preferably copper alloys containing copper and less than 20 wt% silicon, particularly less than 15 wt%, more preferably copper alloys essentially consisting of copper and less than 20 wt% silicon, particularly less than 15 wt%, and even more preferably copper alloys consisting of copper and less than 20 wt% silicon, particularly less than 15 wt%. With respect to the effect of improving lithium deposition and electrode cycle stability, the amount of silicon in the copper alloy is preferably 0.05 wt% or more, more preferably 0.1 wt% or more. Particularly preferred examples are copper alloys consisting of copper and 0.1 wt% to 15 wt% silicon and optionally further elements.

[0023] The fibers can be sintered together, for example, as described in WO2020 / 016240A1.

[0024] According to the present invention, metal fibers exhibit an exothermic phenomenon when heated by DSC measurement before being fixed to each other, and it is preferable that the exothermic phenomenon releases energy in an amount of 0.1 kJ / g or more, more preferably 0.5 kJ / g or more, even more preferably 1.0 kJ / g or more, and most preferably 1.5 kJ / g or more. The absolute amount depends greatly on the metal or metal alloy used. The degree of the exothermic phenomenon can be determined by comparing the DSC measurements of the metal fibers before and after thermal equilibrium. In other words, metal fibers exhibiting such an exothermic phenomenon are not in thermodynamic equilibrium at ambient temperature. During heating in DSC measurement, the metal fibers can transition from a metastable state to a thermodynamically more stable state through relaxation processes such as crystallization and recrystallization, which reduce defects in the lattice of metal atoms. The exothermic phenomenon observed in metal fibers when heated, such as during DSC measurements, indicates that the metal fibers are not in thermodynamic equilibrium. For example, the metal fibers may be in an amorphous or nanocrystalline state containing defect energy and / or crystallization energy released during heating due to crystallization or recrystallization. Such phenomena can be recognized, for example, using DSC measurements. It has been found that the strength of a network of metal fibers exhibiting such exothermic phenomena improves after the metal fibers are fixed together.

[0025] Preferably, the metal fibers have a non-circular cross-section, particularly a rectangular, square, partially circular, or elliptical cross-section with a major axis and a minor axis. Such cross-sections usually result in fibers that are not in thermal equilibrium, i.e., in a metastable state, which can be beneficial depending on the application. Metal fibers obtained by melt spinning exhibit such non-circular cross-sections, thereby distinguishing them from metal fibers obtained by methods such as bundle stretching.

[0026] In relation to this, it is clear that the value of the minor axis must be smaller than the value of the major axis. If the minor axis has a larger value than the major axis, i.e., a longer length, then the definitions of "minor" and "long" must simply be swapped.

[0027] The ratio of the minor axis to the major axis may preferably be in the range of 1 to 0.05, more preferably in the range of 0.7 to 0.1, and particularly in the range of 0.5 to 0.1. As is generally known, the ratio of the lengths of the minor axis to the major axis of an ellipse is large enough that the ellipse looks like a circle (in which case the ratio would be 1). The smaller the value of the ratio, the flatter the ellipse. Therefore, the ratio of the minor axis to the major axis is particularly less than 1.

[0028] Alternatively, the metal fiber may have a circular cross-section. In the case of such a cross-section, the ratio of the "long" axis to the "short" axis will obviously be exactly 1. A circular cross-section has a more energetically favorable state compared to a cross-section with an aspect ratio less than 1. Therefore, fibers with a circular cross-section are closer to an energetically equilibrium state than fibers with other cross-sectional shapes.

[0029] Preferably, the metal fibers can be obtained by melt spinning. Preferably, the metal fibers used in the electrodes of the present invention are obtained by melting the molten material of the metal fibers, particularly by vertical or horizontal melt spinning. 2 K· min -1 This can be obtained by subjecting the material to the above cooling rate. Such metal fibers produced by melt spinning may contain spatially confined domains in a high-energy state (i.e., a metastable state) due to the rapid cooling applied during the melt spinning process. Rapid cooling in this respect refers to 10 2 K·pro -1 A cooling rate of the above, preferably 10 4 K·pro -1 The above is more comfortable 10 5 K· min -1 This refers to the cooling rate described above. A fast cooling rate allows metal fibers to be obtained in a metastable state, for example by melt spinning, and increases the mechanical strength of the corresponding sintered network of metal fibers.

[0030] Furthermore, fibers obtained by melt spinning often have a rectangular or semi-elliptical cross-section, which is far from equilibrium and therefore preferable in certain application fields. Examples of melt spinning machines capable of producing such fibers are known, for example, from the unpublished international application PCT / EP2020 / 063026 and the published applications WO2016 / 020493A1 and WO2017 / 042155A1, which are incorporated herein by reference.

[0031] In another example, at least some of the metal fibers in a group of metal fibers are amorphous, or at least some of the metal fibers in a group of metal fibers are nanocrystalline. Nanocrystalline metal fibers contain crystalline domains. When nanocrystalline metal fibers are heated to a temperature of about 20-60% of their melting temperature, these domains undergo recrystallization, resulting in an increase in the average size of the crystalline domains compared to the average size of the initial crystalline domains in the nanocrystalline metal fibers before heating. It is also possible to mix non-equilibrium fibers (e.g., nanocrystalline or amorphous fibers) with equilibrium fibers (e.g., annealed fibers). In the context of this invention, "% of the melting temperature" refers to the melting point in degrees Celsius. Therefore, if the melting temperature is, for example, 1000°C, in the context of this invention, 20% of the melting temperature is 200°C, 50% of the melting temperature is 500°C, and 95% of the melting temperature is 950°C. The melting temperature can be determined, for example, by DSC measurement.

[0032] The network may have an average pore diameter selected from the range of 0.1 to 1000 μm, preferably from 0.5 to 500 μm, and particularly from 1 to 100 μm. The average pore diameter can be determined by reproducing the fiber structure using a microcomputer tomograph and then evaluating the average pore diameter using the bubble point method. In the bubble point method, the largest ball diameter that can fit between two fibers is determined and considered as the pore diameter. More specifically, a point is placed at the center between the two fibers, and the radius of the bubble is increased from this point until it contacts the surfaces of both fibers. The diameter of the bubble corresponds to the pore diameter. If, for any given parameters, the bubble diameter contacts only one fiber, the center point is shifted in the direction of the fiber that the bubble did not contact.

[0033] In the electrode according to the present invention, it is preferable that the three-dimensional network of metal fibers contained in the electrode is fixed to each other at contact points that are randomly distributed throughout the network of metal fibers, and is particularly preferable that they are directly fixed. In another aspect of the invention, it is preferable that the contact points are not randomly distributed, but are provided, for example, in the peripheral region of the network of metal fibers, or that the contact points are regular because the metal fibers are regular.

[0034] It is even more preferable that the contact points where the metal fibers are fixed to each other are localized in specific regions and not evenly distributed throughout the entire network of metal fibers. By having contact points where the metal fibers are fixed to each other only in separate regions, the fibers between these regions have high flexibility while simultaneously ensuring mechanical stability and good conductivity.

[0035] Preferably, the spatial orientation of the metal fibers is irregular. In an irregular network, some of the metal fibers are always oriented in the direction of the ion flux. This increases the ion diffusivity on the surface of the metal fibers, allowing for better utilization of the related effects described above.

[0036] Preferably, the spatial orientation of the metal fibers is at least partially regular. Therefore, there is a dominant spatial orientation of the metal fibers in one direction. This allows for an increase in the portion of the metal fibers oriented in the direction of the ion flux, resulting in even higher ion diffusivity. The orientation of the metal fibers can be achieved, for example, by carding the metal fibers before sintering them to form a three-dimensional network of metal fibers.

[0037] Preferably, the contact point density is 1 mm -3 ~5000mm -3 The range is as follows. More preferably, the contact point density is 3 mm -3 ~2000mm -3 A range, more preferably 5 mm -3 ~500mm -3This is the range. At the contact points, the metal fibers are directly fixed to each other and are in electrical contact with each other, so the contact point density can also be considered as the crosslinking density between fibers. Fiber density is 1 mm -3 The above, especially 5mm -3 If the above conditions are met, a uniform distribution of potential is achieved, and harmful effects such as high overvoltage and the formation of localized high-temperature regions due to high resistance are avoided. On the other hand, if the contact point density is 5000 mm -3 The following, especially 2000mm -3 Below, especially 500mm -3 The following conditions are useful for providing flexibility to a three-dimensional network of metal fibers, and as a result, even fairly thick three-dimensional networks, i.e., three-dimensional networks with thicknesses of 100 μm or more, 200 μm or more, 500 μm or more, 550 μm or more, 600 μm or more, 750 μm or more, 5000 μm or more, or 10000 μm or more, can be deformed (e.g., rolled) without breaking the network.

[0038] According to the present invention, the metal fibers preferably have a thickness and / or width in the range of 0.4 to 150 μm, and more preferably in the range of 0.5 to 50 μm. When the thickness and / or width of the metal fibers decreases, the surface area relative to the weight of the metal fibers increases, and as a result, dendrite growth is further suppressed.

[0039] Preferably, the metal fibers have a length of 100 μm or more, particularly 1.0 mm or more. Preferably, the aspect ratio of the length to its thickness and / or width of the metal fibers is in the range of 100:1 or more. With such a length and / or aspect ratio, each fiber can have multiple contact points with other fibers, which lowers the electrical resistance of the three-dimensional network of metal fibers and at the same time makes the network of metal fibers mechanically strong.

[0040] According to the present invention, it is preferable that the three-dimensional network of metal fibers consists of metal fibers made of a copper-silicon alloy, more preferably having a silicon content of less than 20% by weight, a thickness and / or width in the range of 0.5 to 50 microns, and a high aspect ratio (length / diameter) of 100:1 or more.

[0041] The present invention is not particularly limited to electrodes of a specific thickness, but it is preferable that the three-dimensional network of metal fibers has a thickness in the range of 50 μm to 5 mm, particularly 200 μm to 5 mm. More preferably, the thickness of the three-dimensional network of metal fibers is in the range of over 500 μm, particularly over 550 μm, even more particularly over 600 μm, even more particularly over 750 μm, and even more particularly over 5000 μm. With a network having such a thickness, it is possible to provide an ultra-thick electrode. Since the fibers are in contact with each other, preferably sintered, direct electrical conductivity is achieved between the fibers, resulting in high network conductivity in terms of conductivity and ion diffusion. On the other hand, the local potential is uniformly distributed across the volume of the electrode, reducing overvoltage, hot spot formation, and other phenomena that shorten the lifespan of battery components such as the electrolyte. Furthermore, ultra-thick electrodes provide high area capacity and reduce the proportion of inert components, i.e., improve the performance per unit mass of the battery. The thickness of the network is not particularly limited. However, from the viewpoint of a uniform potential distribution throughout the network, the thickness is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

[0042] Preferably, the network conductivity is 1 × 10⁻⁶ 5 S / m or larger, especially 5×10 5 S / m or higher, especially 1 × 10 6 The conductivity is S / m or higher. Such high network conductivity improves the uniform distribution of local potentials, even when the density of the three-dimensional network of metal fibers is low. Network conductivity can be measured using a four-point probe instrument.

[0043] Furthermore, the volume fraction of metal fibers in the three-dimensional network of metal fibers is preferably 0.075 vol% or more, particularly 1.3 vol% or more, and especially 2.0 vol% or more. In networks with lower volume fractions, it may be difficult to uniformly distribute local potentials, which can lead to the formation of hot spots and high overvoltages. Therefore, if the volume fraction of metal fibers in the three-dimensional network of metal fibers is as described above, the battery life can be extended. The volume fraction of metal fibers in the three-dimensional network of metal fibers can be determined by reproducing the fiber structure using a microcomputer tomograph and then evaluating the fraction using the bubble point method described herein. These effects are even more pronounced in thick electrodes where the metal fiber network has a thickness of 200 μm or more.

[0044] Preferably, the lithium metal electrode according to the present invention further comprises a lithophilic substance on at least a portion of the metal fibers. The lithophilic substance is a wetting agent that improves the wettability of the metal fiber surface with lithium. Preferably, the lithophilic substance comprises at least one transition metal, aluminum, or magnesium, particularly a transition metal. More preferably, the lithophilic substance is selected from the group consisting of Sn, ZnO, Al2O, and MgO. A particularly preferred lithophilic substance is ZnO. While such a lithophilic substance is not strictly necessary, it can further improve the suppression of dendrite growth and even facilitate the production of lithium metal electrodes by making it easier for lithium to penetrate the three-dimensional network of metal fibers. In addition to inorganic wetting agents, organic wetting agents can also be used. The organic wetting agent may be a branched or unbranched saturated or unsaturated carboxylic acid having at least 10 carbon atoms, particularly at least 15 carbon atoms, and 30 or fewer carbon atoms, particularly 25 or fewer carbon atoms. Preferred examples of organic wetting agents are abietic acid and oleic acid.

[0045] In addition to or instead of a lithium-philic material, the electrode according to the present invention may also be obtained or can be obtained by providing metallic lithium to the surface of the metal fibers in a three-dimensional network of metal fibers while applying a voltage to the network. Such a voltage electrically induces wettability of the metal fibers with lithium, making it easier to form a uniform coating of metallic lithium on the metal fibers. The lithium can be provided in liquid form, for example, as a molten material, while the voltage is applied. The application of the voltage may be required only for the first deposition cycle or for subsequent cycles.

[0046] Furthermore, the present invention relates to a method for manufacturing a lithium metal electrode, a) A process for providing a three-dimensional network of metal fibers, wherein the metal fibers are in direct contact with each other, and the metal fibers have a thickness and / or width in the range of 0.25 to 200 μm. b) A step of providing a layer of metallic lithium on the metal fibers of the three-dimensional network of metal fibers. Regarding methods including

[0047] To manufacture lithium metal electrodes based on a three-dimensional network of metal fibers, it is necessary to impregnate the network with metallic lithium. This can be achieved through various methods, such as injecting metallic lithium into the network under pressure or impregnating the network with molten lithium. Electrodeposition has been found to be difficult, especially for large-scale applications, because the absence of a lithium source leads to the consumption of lithium in the electrolyte, reducing the overall lithium salt concentration and thus the electrochemical properties of the electrolyte. To overcome this hurdle, metallic lithium must be present within the metal fiber network, and / or the wettability of the metal fibers should be improved, for example, by a lithophilic material or electrowetting, as described above. To achieve this, it has been found that lithium can be injected into the metal fiber network, for example, statically or by a roll press. The hardness of lithium metal is low, only 0.6 Mohs. Injecting metallic lithium into the network has been found to be beneficial for bonding the metal fiber network with each individual lithium metal. Because the mechanical stability of the network is particularly high compared to carbon-based networks (CNTs, graphene, or reduced graphene oxide scaffolds), metal fiber networks are undeformed or hardly deformed during static or pressing such as roll pressing.

[0048] Preferably, liquid lithium, i.e., molten lithium, can be impregnated into the network of metal fibers. To achieve this, it is even more preferable to improve the wettability of the metal fibers with the liquid lithium by providing a lithophilic compound or coating on the metal fibers before impregnating them with the liquid lithium.

[0049] It should be understood that the lithium metal electrodes produced by the method of the present invention are those described in the present invention, i.e., those described above and / or in the appended claims. All aspects of the electrodes of the present invention described above also apply to the method for producing lithium metal electrodes of the present invention.

[0050] Preferably, step a) includes the production of metal fibers by melt spinning, and in particular the molten material of the metal fibers, particularly by vertical or horizontal melt spinning, 10 2 K· min -1 Cooling rate, preferably 10 4 K· min -1 The above is more comfortable 10 5 K· min -1 This is done by subjecting the material to the above cooling rate. As described above, this makes it possible to obtain metal fibers in a metastable state, resulting in a mechanically stronger network that can be advantageous when injecting lithium metal into the network.

[0051] Furthermore, in the method of the present invention, step a) preferably includes dispersion of metal fibers in a liquid, sedimentation of metal fibers, and sintering of metal fibers. The formation of a metal fiber network can be achieved, for example, as described in WO2020 / 016240A1 (which is incorporated herein by reference in its entirety). The resulting network is highly mechanically stable and simultaneously provides a large intrinsic surface area.

[0052] Furthermore, the present invention relates to a lithium-ion battery including a negative electrode which is a lithium metal electrode as described in claim 1. It should be understood that the lithium metal battery of the present invention includes a lithium-ion electrode according to the present invention, i.e., a negative electrode which is described above and / or as described in the appended claims. All aspects described above regarding the method of manufacturing the electrode and / or lithium metal electrode of the present invention also apply to the method of manufacturing the lithium metal electrode of the present invention.

[0053] The positive electrode used in the battery of the present invention is not particularly limited. However, it is preferable that the battery of the present invention further includes a positive electrode comprising a network of metal fibers, particularly a three-dimensional network of metal fibers, wherein the metal fibers are made of aluminum or an aluminum alloy. By using a thick fiber-based positive electrode, a large amount of positive electrode active material can be incorporated into the battery, and the lithium incorporated into the negative electrode network structure can be fully utilized. This enables the achievement of high capacity. In this regard, the details described herein regarding the network of metal fibers of the negative electrode, i.e., the lithium metal-based electrode of the present invention, are similarly applicable to the three-dimensional network of metal fibers of the positive electrode, and the preferred material for the positive electrode is aluminum or an aluminum alloy.

[0054] Any suitable material can be used for the positive electrode active material. Preferably, the positive electrode active material is selected from the group consisting of lithium-nickel-manganese-cobalt oxide (NMC), lithium-nickel-cobalt-aluminum oxide (NCA), lithium-cobalt oxide (LiCoO2), and lithium-iron-phosphate (LFP).

[0055] Preferably, in step b), a portion of metallic lithium is first placed on a three-dimensional network of metal fibers, and then pressure is applied to the metallic lithium provided on the three-dimensional network of metal fibers to press-fit the metallic lithium into the opening structure of the three-dimensional network of metal fibers, thereby providing a layer of metallic lithium on the metal fibers. This is a fairly simple method of introducing lithium into a network structure, taking advantage of the low hardness of lithium.

[0056] In step b) of the method of the present invention, it is even more preferable to provide a lithophilic coating on the metal fibers before providing a layer of metallic lithium on the metal fibers. This improves the wettability of the metal fibers, especially when lithium is applied in liquid form. However, even when solid lithium is injected into the network structure, the lithophilic material may exhibit advantageous effects, particularly during the corresponding battery cycle.

[0057] As described above, the lithium-philic material for the lithium metal electrode of the present invention preferably comprises at least one transition metal, tin, aluminum, or magnesium, particularly a transition metal. More preferably, the lithium-philic material is selected from the group consisting of Sn, ZnO, Al2O, and MgO. Particularly preferred lithium-philic materials are ZnO or Sn, and more preferably ZnO. While such lithium-philic materials are not strictly necessary, they can further improve the suppression of dendrite growth and even facilitate the production of lithium metal electrodes by supporting the penetration of lithium into the three-dimensional network of metal fibers. In addition to inorganic wetting agents, organic wetting agents can also be used. The organic wetting agent may be a branched or unbranched saturated or unsaturated carboxylic acid having at least 10 carbon atoms, particularly at least 15 carbon atoms, and 30 or fewer carbon atoms, particularly 25 or fewer carbon atoms. Preferred examples of organic wetting agents are abietic acid and oleic acid.

[0058] In the method of the present invention, it is preferable in step b) to provide a layer of metallic lithium on the metal fibers while applying a voltage to the three-dimensional network of metal fibers. This makes it possible to achieve electrowetting as described above. The voltage may be applied only to the first deposition cycle or to each deposition cycle of one or more subsequent deposition cycles.

[0059] Furthermore, the present invention relates to an electric machine including a battery according to the present invention. In particular, the battery according to the present invention supplies power to the circuit of the electric machine. Furthermore, it is preferable that the circuit of the electric machine supplies power to a motor for propelling the electric machine, in particular an electric vehicle.

[0060] The present invention will be described in further detail below with reference to the attached drawings and figures, as well as various examples of the network and method of the present invention, but these are merely examples. The drawings show the following: [Brief explanation of the drawing]

[0061] [Figure 1]Figure 1a) is a scanning electron microscope image showing dendrite formation on copper foil. Figure 1b) is a scanning electron microscope image of the sample in Figure 1a) that is further magnified. Figure 1c) is a scanning electron microscope image showing a uniform coating of metallic lithium on the metal fibers of a three-dimensional network of metal fibers in the lithium metal electrode according to the present invention. Figure 1d) is a scanning electron microscope image of the sample in Figure 1c) that is further magnified. [Figure 2] This graph shows a comparison of the Coulomb efficiency of three lithium metal batteries using copper foil as the negative electrode and one sample using a three-dimensional network of metal fibers according to the present invention as the electrode. [Figure 3] This graph shows the change in battery capacity over the number of cycles for the same sample as shown in Figure 2. [Figure 4] These two graphs compare the charge-discharge profiles of a copper foil electrode and an electrode consisting of a three-dimensional network of metal fibers; one graph shows the first cycle, and the other shows the 50th cycle. [Figure 5] This describes a test and control setup for a lithium metal-based negative electrode tested with a CR2032 coil cell assembly, and the test setup corresponds to the present invention. [Figure 6] This is a microcomputer tomography image of a three-dimensional network of metal fibers used in electrodes according to the present invention. [Figure 7] This is a scanning electron microscope image showing the structure of a three-dimensional network of sintered CuSi4 fibers. [Figure 8] This is the fiber diameter distribution of the three-dimensional network of metal fibers in the electrode according to the present invention. [Figure 9] This is a scanning electron microscope image showing the structure of a three-dimensional copper foam used for comparison purposes. [Figure 10] This is a scanning electron microscope image showing a side view of a copper foil having a porous structure on its surface. The porous structure was obtained by reducing Cu(OH)2 to metallic copper whiskers on the surface of the copper foil. [Figure 11]This graph shows a comparison of the Coulomb efficiency between three comparative examples (square, rhombus, and circle) and an embodiment according to the present invention (triangle). [Modes for carrying out the invention]

[0062] Results & Discussion: Forms of electrodeposited lithium on 2D electrodes versus 3D electrodes in a liquid electrolyte: To directly compare the formation (or absence) of dendrites in cells composed of metal fiber network electrodes or 2D metal foil electrodes, half-cells containing lithium foil and a metal counter electrode were fabricated. To deposit lithium on the metal current collector, a negative current was applied to the counter electrode (pure Li foil), electrochemically transferring lithium from the lithium foil to the current collector. As shown in Figures 1a and 1b, the formation of lithium dendrites on the copper foil was easily observed and indicated by white circles.

[0063] However, in the case of metal fiber networks (Figures 1c, 1d), the surface area of ​​the network is significantly larger, and since the currents on both electrodes (2D and 3D electrodes) are constant, the deposition rate per unit area is much lower than that of metal foil. Therefore, the larger the surface area, the lower the lithium deposition rate per unit area. Since dendrites were not observed in the fibrous network, the comparison between the 3D network and its 2D counterpart is quite clear. In addition, since the network material is 96 wt% Cu and 4 wt% Si and exists in a fibrous form, both the network material composition and its morphology are significantly different from that of foil. To investigate the effect of metal composition and this behavior in detail, Cu 96 After preparing foils made of Si4, we tested them and investigated dendrite growth.

[0064] Injection of lithium into a metal fiber network: To fabricate a full cell, metallic lithium must be impregnated into a metal fiber network before assembling the electrochemical cell. Electrodeposition proved unsuccessful for depositing lithium within the metal fiber network. This is because the absence of a lithium source leads to the consumption of lithium in the electrolyte, reducing the overall lithium salt concentration and thus the electrochemical properties of the electrolyte. To overcome this hurdle, metallic lithium must be present within the metal fiber network. A roll press was used to deposit lithium within the metal fiber network. The roll press of lithium metal, with its very low hardness of 0.6 Mohs, proved beneficial for bonding the metal fiber network to each individual lithium metal. Due to the high mechanical stability of the network, the metal fiber network undergoes little to no deformation during roll pressing compared to carbon-based networks (CNTs, graphene, or reduced graphene oxide scaffolds).

[0065] To investigate roll-pressed lithium and copper-silicon networks, a full cell is constructed using NMC cathode material. To compare the performance of lithium-filled networks with that of lithium metal foil, the Coulomb efficiency is shown in Figure 2. As observed from Figure 2, the 2D Li metal foil anode-based cell shows a dramatic decrease in performance after 82-91 cycles, while its 3D metal fiber-based counterpart, i.e., the electrode according to the present invention, remains stable up to 134 cycles, resulting in a 50% increase in cycle performance. Cell collapse occurs due to dendrite growth along the concentration gradient, leading to separator penetration. Subsequently, an electrical connection is formed between the anode and cathode, and the electrodes become inoperable due to an internal short circuit.

[0066] As shown in Figure 3, when comparing a Li metal anode with a CuSi network / Li metal anode, the CuSi network-based electrode shows a significant increase in surface area, allowing for faster deposition of more lithium and thus increased capacity. In addition, this reduces dendrite growth because less lithium is deposited per unit surface area.

[0067] However, CuSi networks affect not only the overall cycle performance of the network but also the deposition mechanism and associated overpotentials. The potential at which lithium deposition occurs in an electrochemical cell is usually given by the intercalation voltage of the electrodes, for example, 0.1V to 0.4V for graphite and 3.5V to 4V for LiNiMnCoO2 (NMC). However, the intercalation rate is limited, meaning that only a predetermined number of Li ions can be intercalated into a predetermined volume of active material in a given time, and faster charging rates lead to overpotentials. This overpotential is observed not only at various charging rates but also due to the aging degradation of the electrolyte. In this case, the decomposition of the electrolyte due to the increase in applied voltage leads to the growth of the solid electrolyte interface (SEI), dramatically reducing the rate at which Li ions are transported to the active material. Therefore, the overpotential measured in a certain charge-discharge profile is also a way to evaluate the electrochemical stress acting on the electrodes. As can be easily seen in Figure 4, similar overpotentials are observed in charging profiles (from 3.6 to 4.4V) where lithium is deposited on the metal anode. However, during the discharge phase (4.4 to 3.6) in which metallic lithium detaches from the CuSi network foil, a larger overvoltage is already observed in the first cycle. This effect becomes even more pronounced at cycle 50, with a significant increase in overvoltage during charging and discharging. Since the overvoltage (and its energy (obtained by multiplying the current by the voltage)) is directly converted into heat and lost during the storage process, reducing the overvoltage is highly beneficial.

[0068] In summary, the 3D metal fiber-based electrodes of the present invention can increase the lifespan and capacity of lithium metal-based full cells. In addition, heat generation during the charge-discharge process is largely related to the overvoltage applied during each process. That is, faster charging generates more heat, and generally more heat is generated as the cell ages. This effect could be greatly reduced by using a 3D CuSi fiber network as the metal framework for Li metal deposition. In particular, the overvoltage is significantly lower in the metal stripping process compared to Li metal foil. This results in faster charge-discharge speeds, which is thought to be because the larger inner surface area of ​​the metal fiber network increases the number of lithium ions that can be deposited within a given time window.

[0069] material: To fabricate the metal fiber network, melt-spun fibers, such as those described in WO2020 / 016240A1, are used. These metal fibers are sintered at 980°C to obtain a connected network. Multiple electrodes with a diameter of 14 mm are punched out from the network. The resulting metal fiber network is used as the negative electrode scaffold of an electrochemical cell without further processing. Unless otherwise specified, pure metallic lithium (Alfa Aesar, 99.95%) was used as the counter electrode. The same lithium quality was used for lithium infiltration.

[0070] Electrochemistry: As current collectors for the lithium metal foil, a metal fiber network and copper foil, the same as those used in the embodiments of the present invention described later, were used. To construct the coin cell (CR2032), the foil and metal fiber network were punched out to a diameter of 14 mm. A Whatman AH grade 680 glass fiber filter was used as a separator, and a 15.6 mm diameter metallic lithium disk was used as the counter electrode. Thus, the experiment was designed according to the schematic diagram in Figure 5.

[0071] A negative current was applied between the two contact points to deposit metallic lithium on the copper foil or within the metal fiber network. Upon application of the negative current, metallic lithium was deposited on the contact point where the negative current was applied, according to reaction 1. Li + + e - → Li 金属 [1]

[0072] Currents of 0.5 mA, 1 mA, and 2 mA were applied for 2 hours, yielding deposition capacities of 1 mAh, 2 mAh, and 4 mAh, respectively. Subsequently, the deposited lithium was completely stripped off at the same current rate under a voltage limit of 1 V.

[0073] The following section compares the performance of batteries based on various electrode materials.

[0074] Examples: As an electrode according to the present invention, a sintered three-dimensional network of metal fibers was fabricated, as described in WO2020 / 016240A1. The material of the metal fibers was CuSi4, a copper-silicon alloy consisting of 96 wt% copper and 4 wt% silicon. A microcomputer tomography image of the network used as an electrode is shown in Figure 6, and a scanning electron microscope image thereof is shown in Figure 7. It can be seen that the individual fibers are directly sintered to each other without the use of further additives such as binders or solder. The term "fiber thickness" is used interchangeably with the term "fiber diameter" when describing the present invention. As can be seen from the Gaussian fit shown in Figure 8, the fiber thickness of the three-dimensional network is approximately 31 μm. Figure 8 shows the fiber diameter estimated from a scan using microcomputer tomography (micro-CT) and a Gaussian fit. According to the present invention, the fiber thickness can be determined by estimating the fiber diameter using micro-CT measurement and performing a Gaussian fit based on the estimated fiber diameter. In this specification, the fiber thickness corresponds to the maximum value of the Gauss fit.

[0075] To manufacture the network according to the present invention, a circular sample of an appropriate size was punched out from a sintered network of metal fibers. Then, lithium was impregnated into the sample by roll-pressing metallic lithium into the sintered network. A full cell was constructed containing the Li-filled metal fiber network and NMC as the active material counterpart on the positive electrode.

[0076] Comparative example: For comparison, further lithium metal negative electrodes and corresponding lithium metal batteries were fabricated as described above. However, instead of a three-dimensional network of sintered metal fibers, planar copper foil, copper foam, and copper foil with a porous structure obtained by reducing Cu(OH)2 to metallic copper whiskers on the surface of the copper foil were used.

[0077] The copper foam was obtained from Xiamen Zopin New Material Limited (Room 602-1, No. 39, Xinchang Road, Haicang District, Xiamen City, Fujian Province, China). A scanning electron microscope image of the copper foam is shown in Figure 9.

[0078] Luo et al. obtained a copper foil having a porous structure by reducing Cu(OH)2 to metallic copper whiskers on the surface of the copper foil. 19 and Guo et al. 20 The sample was prepared according to the following procedure. Figure 10 shows a scanning electron microscope image of copper whiskers on the surface of the copper foil.

[0079] As described in the above examples, flat copper foil, copper foam, and copper foil having a porous structure were used together with lithium metal as the lithium metal anode of a full cell. For this purpose, metallic lithium was supported on the copper foil, copper foam, and copper foil having a porous structure by static pressing or electrochemical plating.

[0080] Table 1 below shows an overview of the characteristics of the electrodes in the comparative example and the example according to the present invention.

[0081] [Table 1]

[0082] Figure 11 shows a comparison of Coulomb efficiency over 50 cycles. Data points obtained with electrodes based on flat copper foil are shown as diamonds (comparative example). Data points obtained with electrodes based on copper foam are shown as circles (comparative example). Data points obtained with electrodes based on porous copper foil are shown as squares (comparative example). Data points obtained with electrodes based on a three-dimensional network of sintered metal fibers are shown as triangles (example according to the present invention).

[0083] The electrode in the above embodiment is in accordance with the present invention, and as shown in the triangle in Figure 11 and the measurement results in Figure 2, it already achieves very high efficiency by the second cycle and maintains this value stably well beyond 100 cycles. In contrast, the comparative example using flat copper foil exhibits considerably unstable behavior before reaching a large number of cycles and suffers from dendrite growth, which can be seen in Figures 1a and 1b. Furthermore, as can be seen in Figure 2, dendrite growth ultimately leads to an internal short circuit after about 90 cycles. In contrast, the electrode of the present invention does not suffer from dendrite growth, as can be seen in Figures 1c and 1d.

[0084] Comparing the embodiments of the present invention with copper foam, it can be seen that the efficiency of the foam structure-based electrode is considerably lower. This is presumed to be related to the formation of dead lithium in the foam structure, but such dead lithium formation is not observed in the metal fiber-based structure.

[0085] With regard to the porous copper foil, relatively high efficiency was observed during the charge-discharge cycle, as can be seen from the square in Figure 11. However, the efficiency remained lower than that of the metal fiber-based electrode in the embodiment of the present invention. Furthermore, the electrode in the embodiment of the present invention exhibited lower overvoltage compared to the porous fiber electrode, indicating less electrochemical stress on the cell components during charge and discharge. This suggests that a longer lifespan can be achieved and less electrolyte degradation occurs.

[0086] References 1. Ghazi, Z. A. et al. Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries. Small 15, 1900687 (2019). 2. Liu, B., Zhang, J.-G. & Xu, W. Advancing Lithium Metal Batteries. Joule 2, 833-845 (2018). 3. Liu, J. et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nat Energy 4, 180-186 (2019). 4. Yoshino, A., Sanechika, K. & Nakajima, T. Secondary battery. (1987). 5. Xu, W. et al. Lithium metal anodes for rechargeable batteries. Energy Environ. Sci. 7, 513-537 (2014). 6. Tarascon, J.-M. & Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 414, 359-367 (2001). 7. Whittingham, M. S. Lithium Batteries and Cathode Materials. Chem. Rev. 104, 4271-4302 (2004). 8. Fang, C., Wang, X. & Meng, Y. S. Key Issues Hindering a Practical Lithium-Metal Anode. Trends in Chemistry 1, 152-158 (2019). 9. Fang, C. et al. Quantifying inactive lithium in lithium metal batteries. Nature 572, 511-515 (2019). 10. Guo, Y., Li, H. & Zhai, T. Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries. Advanced Materials 29, 1700007 (2017). 11. Zhang, S. S. Problem, Status, and Possible Solutions for Lithium Metal Anode of Rechargeable Batteries. ACS Appl. Energy Mater. 1, 910-920 (2018). 12. Shim, J. et al. 2D boron nitride nanoflakes as a multifunctional additive in gel polymer electrolytes for safe, long cycle life and high rate lithium metal batteries. Energy & Environmental Science 10, 1911-1916 (2017). 13. Zhou, W. et al. Plating a Dendrite-Free Lithium Anode with a Polymer / Ceramic / Polymer Sandwich Electrolyte. J. Am. Chem. Soc. 138, 9385-9388 (2016). 14. Qian, J. et al. Lithium Induced Nano-Sized Copper with Exposed Lithiophilic Surfaces to Achieve Dense Lithium Deposition for Lithium Metal Anode. Advanced Functional Materials 31, 2006950 (2021). 15. Wang, W., Hao, F. & Mukherjee, P. P. Mechanistics of Lithium-Metal Battery Performance by Separator Architecture Design. ACS Appl. Mater. Interfaces 12, 556-566 (2020). 16. Jin, S., Jiang, Y., Ji, H. & Yu, Y. Advanced 3D Current Collectors for Lithium-Based Batteries. Advanced Materials 30, 1802014 (2018). 17. Nieto, A., Boesl, B. & Agarwal, A. Multi-scale intrinsic deformation mechanisms of 3D graphene foam. Carbon 85, 299-308 (2015). 18. Lu, Q. et al. Dendrite-Free, High-Rate, Long-Life Lithium Metal Batteries with a 3D Cross-Linked Network Polymer Electrolyte. Advanced Materials 29, 1604460 (2017). 19. Lu, L.-L. et al. Free-Standing Copper Nanowire Network Current Collector for Improving Lithium Anode Performance. Nano Lett. 16, 4431-4437 (2016). 20. Guo, F. et al. Flaky and Dense Lithium Deposition Enabled by a Nanoporous Copper Surface Layer on Lithium Metal Anode. ACS Materials Lett. 2, 358-366 (2020). 21. Ruffo, R., Hong, S. S., Chan, C. K., Huggins, R. A. & Cui, Y. Impedance Analysis of Silicon Nanowire Lithium Ion Battery Anodes. J. Phys. Chem. C 113, 11390-11398 (2009). 22. Polat, B. D. & Keles, O. The effect of copper coating on nanocolumnar silicon anodes for lithium ion batteries. Thin Solid Films 589, 543-550 (2015).

Claims

1. A lithium metal electrode for lithium-ion batteries, Including a three-dimensional network of metal fibers, The above three-dimensional network of metal fibers has a thickness ranging from 50 μm to 5 mm. The above metal fibers are in direct contact with each other. The above metal fiber has a thickness and / or width in the range of 0.4 to 150 μm and a length of 100 μm or more. A lithium metal electrode in which metallic lithium is impregnated into a three-dimensional network of the above-mentioned metal fibers.

2. The lithium metal electrode according to claim 1, wherein the electrode essentially does not contain carbon-based material.

3. The lithium metal electrode according to claim 1, wherein the metal fibers are in direct electrical contact with each other.

4. The lithium metal electrode according to claim 1, wherein the metal fibers are sintered together without the use of additional binders and / or solder.

5. The lithium metal electrode according to claim 1, wherein the metal fibers are directly sintered together at the contact points between the metal fibers.

6. The lithium metal electrode according to claim 1, wherein the metal fibers are made of copper, nickel, tin, a copper alloy, or a nickel alloy.

7. The lithium metal electrode according to claim 1, wherein the metal fibers are made of copper or a copper alloy.

8. The lithium metal electrode according to claim 1, wherein the metal fibers are made of a copper alloy essentially consisting of copper and at least a further element selected from the group consisting of zinc, boron, aluminum, gallium, indium, thallium, silicon, germanium, tin, lead, arsenic, antimony, bismuth, selenium, and tellurium.

9. The lithium metal electrode according to claim 1, wherein the metal fibers are made of a copper alloy essentially consisting of copper and at least a further element selected from the group consisting of zinc, silicon, germanium, tin, antimony, and tellurium.

10. The lithium metal electrode according to claim 1, wherein the metal fibers are made of a copper alloy essentially composed of copper and silicon or tin.

11. The lithium metal electrode according to claim 1, wherein the metal fiber is made of a copper alloy consisting of copper and silicon.

12. The lithium metal electrode according to claim 1, wherein the above metal fiber is made of an alloy of copper and silicon and contains 20 wt% or less of silicon.

13. The lithium metal electrode according to claim 1, wherein the metal fiber is made of a copper-silicon alloy containing 0.05 wt% or more of silicon.

14. The lithium metal electrode according to claim 1, wherein the copper alloy is CuSi8 or CuSi4.

15. The lithium metal electrode according to claim 1, wherein the metal fiber has a thickness and / or width of less than 40 μm.

16. The lithium metal electrode according to claim 1, wherein the metal fiber has a length of 1.0 mm or more.

17. The lithium metal electrode according to claim 1, wherein the metal fiber has an aspect ratio of its length to its thickness and / or width of 100:1 or more.

18. The lithium metal electrode according to claim 1, wherein the metal fiber has a non-circular cross-section.

19. The lithium metal electrode according to claim 1, wherein the three-dimensional network of metal fibers has a thickness in the range of 200 μm to 5 mm.

20. The lithium metal electrode according to claim 1, wherein the thickness of the three-dimensional network of the metal fibers is in the range of more than 500 μm.

21. The conductivity of the above metal fiber network is 1 × 10⁻⁶ ５ A lithium metal electrode according to claim 1, wherein the S / m is greater than or equal to S.

22. The lithium metal electrode according to claim 1, wherein the volume fraction of metal fibers in the three-dimensional network of metal fibers is 0.075 vol% or more.

23. The lithium metal electrode according to claim 1, wherein the porosity of the above three-dimensional network is in the range of 90 vol% to 99.5 vol%.

24. The lithium metal electrode according to claim 1, wherein the spatial orientation of the metal fibers is irregular.

25. The lithium metal electrode according to claim 1, wherein the spatial orientation of the metal fibers is at least partially regular.

26. The density of contact points is 1 mm －３ ~5000mm －３ A lithium metal electrode according to claim 1, which is within the range of claim 1.

27. The lithium metal electrode according to claim 1, wherein the metal fibers are directly sintered together at the contact points between the metal fibers.

28. The lithium metal electrode according to claim 1, wherein the metal fiber is made of a copper-silicon alloy.

29. The lithium metal electrode according to claim 1, wherein the fiber has a lithium-hydrophilic substance on at least a portion of its surface.

30. The lithium metal electrode according to claim 29, wherein the lithium-hydrophilic material comprises at least one transition metal, tin, aluminum, or magnesium.

31. The above lithium-hydrophilic materials are ZnO, tin, and Al. ２ A lithium metal electrode according to claim 29, selected from the group consisting of 0 and MgO.

32. The lithium metal electrode according to claim 29, wherein the above-mentioned lithium-hydrophilic material is ZnO or tin.

33. The lithium metal electrode according to claim 29, wherein the above-mentioned lithium-hydrophilic substance is a carboxylic acid.

34. The lithium metal electrode according to claim 29, wherein the above-mentioned lithium-hydrophilic substance is a carboxylic acid having 10 to 30 carbon atoms.

35. The lithium metal electrode according to claim 29, wherein the above-mentioned lithium-hydrophilic substance is abietic acid and / or oleic acid.

36. The lithium metal electrode according to claim 1, wherein the electrode is obtained or can be obtained by applying a voltage to the three-dimensional network of metal fibers and providing metallic lithium to the surface of the metal fibers in the three-dimensional network of metal fibers.

37. A method for manufacturing lithium metal electrodes, a) A step of providing a three-dimensional network of metal fibers having a thickness in the range of 50 μm to 5 mm, wherein the metal fibers are in direct contact with each other, and the metal fibers have a thickness and / or width in the range of 0.4 to 150 μm and a length of 100 μm or more. b) A step of providing a layer of metallic lithium on the metal fibers of the three-dimensional network of metal fibers. Includes, A method for penetrating a three-dimensional network of metallic lithium fibers.

38. The method according to claim 37, wherein the lithium metal electrode is one of the claims described in any one of claims 1 to 36.

39. The method according to claim 37, wherein step a) includes the production of metal fibers by melt spinning.

40. The method according to claim 37, wherein step a) includes dispersing the metal fibers in a liquid, settling the metal fibers, and sintering the metal fibers together.

41. The method according to claim 37, wherein in step b), the layer of metallic lithium is provided on the metal fibers by first placing a portion of the metallic lithium on the three-dimensional network of metal fibers, and then applying pressure to the metallic lithium provided on the three-dimensional network of metal fibers to press-fit the metallic lithium into the opening structure of the three-dimensional network of metal fibers.

42. The method according to claim 37, wherein, in step b), a lithium-hydrophilic coating is provided on the metal fibers before providing the layer of metallic lithium on the metal fibers.

43. The method according to claim 42, wherein the lithium-hydrophilic material comprises at least one transition metal, tin, aluminum, or magnesium.

44. The above lithium-hydrophilic materials are ZnO, tin, and Al. ２ The method according to claim 42, selected from the group consisting of O and MgO.

45. The method according to claim 42, wherein the lithium-hydrophilic substance is ZnO or tin.

46. The method according to claim 42, wherein the above-mentioned lithium-hydrophilic substance is a carboxylic acid.

47. The method according to claim 42, wherein the lithium-hydrophilic substance is a carboxylic acid having 10 to 30 carbon atoms.

48. The method according to claim 42, wherein the above-mentioned lithium-hydrophilic substance is abietic acid and / or oleic acid.

49. The method according to claim 37, wherein in step b), the layer of metallic lithium is provided on the metal fibers while applying a voltage to the three-dimensional network of metal fibers.

50. The method according to claim 37, wherein the above voltage is applied only to the first deposition cycle.

51. The method according to claim 37, wherein the above voltage is applied to each deposition cycle of a further deposition cycle or a further subsequent lithium deposition cycle.

52. A lithium-ion battery comprising a lithium metal electrode as described in any one of claims 1 to 36 as the negative electrode.

53. The battery according to claim 52, further comprising a positive electrode including a network of metal fibers, wherein the metal fibers are made of aluminum or an aluminum alloy.

54. The battery according to claim 52, wherein the positive electrode further comprises an active material selected from the group consisting of lithium-nickel-manganese-cobalt oxide (NMC), lithium-nickel-cobalt-aluminum oxide (NCA), lithium-cobalt oxide (LiCoO2), and lithium-iron-phosphate (LFP).

55. An electrical machine including the battery described in claim 52.

56. The above-mentioned battery supplies power to the circuit of the above-mentioned electrical machine, as described in claim 55.

57. The electrical machine according to claim 55, wherein the electrical machine is an electric vehicle.

Images