Method for manufacturing anode electrode of lithium metal battery using light electromagnetic energy irradiation, and anode electrode of lithium metal battery

Abstract

To provide a method for manufacturing an anode electrode of a lithium metal battery, which can prevent the growth of lithium dendrites, improve the stability of the lithium metal anode, and ensure energy efficiency and applicability to a current manufacturing process.SOLUTION: A manufacturing method includes the steps of forming a slurry by mixing one or more of metal nanoparticle precursors, conductive carbon additives, polymer carriers, and solvents, depositing the slurry on a metal current collector using a thin film coating method, sintering the deposited slurry by irradiating with optical electromagnetic energy, and sintering the slurry after irradiating with optical electromagnetic energy to form a three-dimensional metal-based network structure.SELECTED DRAWING: Figure 2b

Description

Technical Field

[0001] The present invention discloses an anode electrode of a lithium metal battery and a method for manufacturing the same.

[0002] Specifically, the method for manufacturing the anode electrode of the lithium metal battery disclosed in the present disclosure includes forming a three-dimensional structure on a substrate by photoelectromagnetic energy irradiation, significantly increasing the surface area of the anode electrode, enhancing lithium ion diffusion, reducing interfacial resistance, and suppressing lithium dendrite growth.

[0003] In one embodiment, the method for manufacturing the anode electrode of the lithium metal battery includes forming a three-dimensional structure on a lithium metal substrate. The three-dimensional structure may be a nanoporous structure of a layer of a conductive polymer nanocomposite material, or may be a three-dimensional structure of a carbon frame. In another embodiment, the method for manufacturing the anode electrode of the lithium metal battery includes forming a three-dimensional porous structure of lithium metal composed of copper-silver carbon nanotubes directly coated on a current collector.

Background Art

[0004] Due to the increasing market demand for high-energy density secondary batteries, new anode materials to replace conventional graphite anodes have been sought. Among various candidate materials, lithium metal is suitable as an anode material for lithium secondary batteries because of its high theoretical specific capacity (3860 mAh / g) and low density (0.59 g / cm 3 ). However, despite having these advantages, the large-scale application of lithium metal anodes to lithium secondary batteries has several important issues such as large volume changes during the lithiation cycle and the growth of lithium dendrites.

[0005] A lithium dendrite is a metal microstructure formed on the anode during charging. Due to different deposition rates of the electrodes, additional lithium ions accumulate on the anode surface and grow during repeated deposition / dissolution, during which lithium dendrites are formed. The growth of lithium dendrites can pierce the separator and short-circuit the inside of the battery, damaging the battery and causing catastrophic failures that can lead to ignition and explosion.

[0006] When lithium plating occurs during battery use, dendrites grow from nucleation sites on the lithium metal surface. Lithium dendrites break and become irreversible lithium, reducing the battery capacity. In extreme cases, when lithium dendrites grow to a certain extent, they can connect the cathode and anode, causing a short circuit, damaging the separator, and leading to ignition and explosion. During charge-discharge cycles, the growth of lithium dendrites and the volume change of the lithium metal anode can cause physical damage, delamination, and breakage of the solid electrolyte interphase (SEI) layer. This causes a continuous reaction between the lithium metal anode and the electrolyte, forming a new SEI layer and consuming the electrolyte.

[0007] The Formation Process of Lithium Dendrites

[0008] To solve the problems related to lithium metal batteries and understand the mechanisms of lithium dendrite formation and growth, researchers have made many efforts. Generally, the cause of lithium dendrite generation is the non-uniform deposition of lithium due to non-uniform charge distribution. For example, the rough surface on the current collector can cause ion flow concentration near the tip of the rough surface, promote the deposition of lithium ions near the peak, and sometimes form dendrites. The growth point of the dendrite (such as the tip of the rough surface) is called the nucleation site.

[0009] Theoretically, there are several models indicating the growth of lithium dendrites. In the Chazlviel model [Chazlviel 1990], it is pointed out that space charge exists due to the depletion of anions near the anode surface, and this leads to the formation of lithium dendrites. This model explains the growth rate of dendrites based on the fluidity of ions and electric fields. The time until the appearance of dendrites follows the Scatchard equation, which states that as the current density increases, the time until the appearance of dendrites decreases.

[0010] Another model proposed by Monroe and Newman [Monroe and Newman 2003] claims that the growth of dendrites depends on the elasticity of the separator and is suitable for lithium metal batteries with solid electrolytes. This model shows that if the mechanical strength of the electrolyte is high enough, the growth of dendrites can be avoided. However, such an electrolyte with a high elastic modulus reduces ionic conductivity and hinders the normal cycle function of the battery, so this solution is not practical.

[0011] Dendrite suppression method: Electrochemically stable electrolyte

[0012] Many of the other models mentioned above have improved on this and provided the basic idea for suppressing the growth of lithium dendrites. One way is to use electrolytes with more stable electrochemical properties, such as anion-bonded mixed electrolytes, especially anion liquid-nanoparticle mixed electrolytes. An example of such an ionic liquid is 1-methyl-3-propylimidazolium (IM)TFSI [Lu et al. 2014]. The above electrolyte has stable electrochemical properties, no flammability, and a high dielectric constant. These electrochemical stabilities are due to a unique structure in which anions are connected to cations and the cations are covalently bonded to inorganic particles and anchored. According to the Scatchard model, in this case, when the anions are fixed, it takes an infinitely long time for dendrites to appear.

[0013] Several techniques have been proposed to prevent or suppress the growth of dendrites in lithium metal anodes, including electrolyte optimization. However, such methods have an adverse effect on the electrochemical properties of the battery. Another way to suppress dendrite growth is to add a protective layer to the surface of the anode to form a stable solid electrolyte interphase (SEI) layer. According to some studies, a three-dimensional structure can regulate consistent growth by uniformly distributing nucleation sites across its surface, thereby inducing uniform deposition of lithium across the anode rather than forming dendrites. It has also been shown from research that this structure reduces the local current density and prevents the formation of lithium dendrites.

[0014] Such three-dimensional structures may be fabricated using a variety of materials, including three-dimensional carbon paper, carbon nanotubes, carbon fibers, conductive polymer nanocomposites, metal fibers, and even lithium metal itself.

[0015] Lithium metal anode electrode, US 10483534B2

[0016] The present application relates to an anode electrode composed of two different layers, namely, a lithium metal layer and a porous conductive layer. First, the porous conductive layer may include two layers, a current collector and a conductive load layer, both of which have a plurality of voids. It can be made of various materials and can form a permeable mesh, a network or rod-like structure, or a combination thereof. The porous conductive layer provides a larger surface area for lithium deposition, forms a stable SEI, and reduces the formation of lithium dendrites. Furthermore, the presence of the porous conductive layer prevents lithium dendrites from growing from the lithium metal surface or approaching the lithium metal surface and the separator. Additionally, the conductivity of the anode becomes more uniform, reducing lithium dendrites.

[0017] In the present application, the basic structure of the three-dimensional structure coated on the lithium metal anode, which can suppress the growth of dendrites and prevent the occurrence of fatal failures, has been described. However, the existence of the three-dimensional conductive structure has not been shown.

[0018] Lithium metal protective layer and its manufacturing method, and battery having the lithium metal protective layer, CN111490252A

[0019] The present application relates to a porous protective layer of a lithium metal anode. The protective layer can generate uniformly dispersed lithium alloy and lithium nitride, improve the lithium ion diffusion ability, and suppress the generation of lithium dendrites. In this method, a lithium metal anode is coated in a slurry using an economical material and then dried to form a protective layer. The material of the protective layer includes a metal compound, a conductive agent, and a binder. The metal compound may be a metal nitride, alumina, aluminum fluoride, or non-lithiated tetraaluminum. In the present application, the process of forming a porous structure on the lithium metal anode has been described in detail, but it is limited to a simple deposition process and a simple drying process of the slurry.

[0020] Surface modification of lithium metal electrode, DE102013114233A1

[0021] In the present application, in order to suppress the growth of lithium dendrites, it has been proposed to directly modify the surface structure of a lithium metal anode (or other metal anodes). In this process, grooves of various geometric shapes, that is, blind hole-shaped grooves and tapered grooves, are formed on the surface of the metal anode. The cross-section of the groove is rectangular, trapezoidal, dome-shaped, or triangular. During forming, a rolling roll is used to generate the desired groove shape by a micro needle roll or a laser. When using a soft metal such as lithium metal, grooves are formed on both sides of the groove by a special method during forming.

[0022] The grooves formed on the metal anode increase the surface area of the electrode. By increasing the surface area, the discharge rate, charge rate, and cycle stability are improved, and finally the interfacial resistance is reduced. Furthermore, the improvement of cycle stability leads to the suppression of the growth of dendrites.

[0023] Surface modification of lithium metal electrode, KR100449765B1

[0024] This application relates to a lithium metal anode composed of an integrated separator layer, current collector layer, and protective film layer. The separator layer may be composed of porous polyethylene, polypropylene, or a multilayer structure thereof. Since the exudation rate of the electrolyte is low, the protective film layer between the separator and the lithium metal layer has high lithium ion conductivity. The protective film may contain organic materials and inorganic materials.

[0025] This application relates to a lithium metal electrode having an integrated separator layer and protective layer. However, the manufacture of the protective layer does not include post-treatment for improving the material properties of the raw materials.

[0026] Ti 2 Anode for lithium metal battery including C thin film, its manufacturing method, and lithium metal battery including the anode for lithium metal battery, KR 20190102489A

[0027] In this application, it is proposed to form a stable SEI and suppress the formation of lithium dendrites by forming a Ti 2 C thin film on the lithium metal anode. The Ti 2 C thin film can induce rapid and stable diffusion of lithium ions and prevent the formation of lithium dendrites. It can also prevent unnecessary galvanometer reactions between the lithium metal and the electrolyte and improve the stability of the SEI. Furthermore, this application also relates to a method of forming a Ti 2 C thin film on a substrate using a solution containing dispersed Ti 2 C powder, the Langmuir-Blodgett scooping (LBs) method, and a method of transferring the formed Ti 2 C thin film to the surface of the lithium metal anode.

[0028] This application has proposed an effective method for suppressing the growth of dendrites. However, the formation of the Ti 2 C thin film and its transfer to the lithium metal anode involve an etching process of the lithium metal anode, which is time-consuming and costly.

[0029] Coated lithium electrode, US6955866B2

[0030] This application relates to an electrochemical cell using a lithium metal anode, wherein the anode is a ternary alloy layer composed of lithium and two other metals. In particular, the first metal other than lithium provides a matrix for accommodating volume changes during the lithium cycle, and the second metal is alloyed with lithium and the first metal. The first metal may be copper, and the second metal may be tin. The lithium metal anode coated with the ternary alloy layer exhibits higher anode stability and lithium cycle efficiency. However, this method necessarily involves alloying lithium with other metals.

[0031] Interfacial Engineering of Stabilized Lithium Anodes, US10256448B2

[0032] This application relates to an electrochemical cell using a lithium metal anode comprising an interfacial layer that can control the reactivity of the lithium metal with respect to the electrolyte and accommodate significant volume changes during the lithiation cycle. The interfacial layer allows lithium ions to pass through its walls. Also, a stable solid electrolyte interphase (SEI) can be formed on one side of the interfacial layer to isolate the deposition and dissolution of the lithium metal on the other side. The interfacial layer has a space between the interfacial layer and the lithium metal anode to accommodate the volume change of the lithium metal anode and is loosely attached to the lithium metal anode.

[0033] The interfacial layer includes a two-dimensional atomic crystalline layered material composed of graphene and h-BN (hexagonal boron nitride). These are chemically inert to the electrolyte and lithium metal, and are robust and highly durable. Furthermore, they have the characteristics of small pore diameter, ultrathin, and excellent flexibility. However, since h-BN is insulating, it cannot be used as it is without graphene.

[0034] This application proposes a method for mechanically and chemically effectively controlling the reactivity of lithium metal. However, since forming the interfacial layer between graphene and h-BN requires a high temperature (1000 °C) and a controlled environment, it is an expensive process.

[0035] Lithium metal anode of lithium metal polymer secondary battery including spacer and its forming method, KR100582558B1

[0036] This application relates to a lithium metal anode separated by a lattice-shaped spacer. The spacer is laminated on the current collector and is thicker than the lithium metal film. The openings between the spacers may be polygonal, circular, or elliptical, and the spacers are manufactured mainly from glass-reinforced fibers, carbon fibers, or alumina.

[0037] During the lithiation cycle, in the gap between the spacers, the volume of the separated lithium metal film increases. Thereby, the volume of the lithium metal anode can be changed without changing the volume of the actual battery, thereby maintaining the SEI and improving the stability of the lithium metal battery.

[0038] In the methods described above, various methods have been proposed to suppress the formation of dendrites and improve the stability of the lithium metal anode in lithium secondary batteries. However, although these methods have improved the battery stability to some extent, they are not an economical solution for mass production.

[0039] Prior art documents

[0040] Patent documents

[0041] (Document 001) US 10,483,534 B2

[0042] (Document 002) CN 111490252 A

[0043] (Document 003) DE 102013114233 A1

[0044] (Document 004) KR 10-0449765 B1

[0045] (Document 005) KR 2019-0102489 A

[0046] (Document 006) US 6,955,866 B2

[0047] (Document 007) US 10,256,448 B2

[0048] (Document 008) KR 10-0582558 B1

[0049] Non-Patent Literature

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[0051] (Document 002) L, Li, S. Li, and Y. Lu, Chemical Communication, 2018, 54, 6648 - 6661. (Chemical Communications)

[0052] (Document 003) C. Monroe and J. Newman, J. Electrochem. Soc., 2003, 150, A1377 (Journal of the Electrochemical Society)

[0053] (Document 004) Y. Lu, K. Korf, Y. Kambe, Z. Tu and L. A. Archer, Angew. Chem., Int. Ed. Engl., 2014, 53, 488 - 492. (Angewandte Chemie International Edition (English))

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[0055] (Reference 006) C. Monroe and J. Newman, J. Electrochem. Soc., 2005, 152, A396 - A404 (Journal of the Electrochemical Society)

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[0059] (Reference 010) J. Xiang, Z. Cheng, Y. Zhao, B. Zhang, L. Yuan, Y. Shen, Z. Guo, Y. Zhang, J. Jiang and Y. Huang, Adv. Sci., 2019, 6, 1901120. (Advanced Science)

[0060] (Document 011) H. Zhang, X. Liao, Y. Guan, Y. Xiang, M. Li, W. Zhang, X. Zhu, H. Ming, L. Lu, J. Qiu, Y. Huang, G. Cao, Y. Yang, L. Mai, Y. Zhao, H. Zhang, Nature Communications, 2018, DOI: 10.1038 / s41467-018-06126-z. (Nature Communications)

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Summary of the Invention

Problems to be Solved by the Invention

[0065] The present disclosure proposes a method for manufacturing an electrode different from conventional manufacturing methods. The proposed method forms a three-dimensional nanoporous structure based on photoelectromagnetic energy irradiation, thereby preventing the growth of lithium dendrites, improving the stability of the lithium metal anode, and ensuring energy efficiency and applicability to the current manufacturing process.

[0066] The present disclosure provides a method that contributes to suppressing the growth of lithium dendrites and improving the stability of the lithium metal anode in a lithium secondary battery. By applying photoelectromagnetic energy, a three-dimensional structure can be formed in a short time. The three-dimensional porous structure on the lithium metal anode provides a space for accommodating the volume change of the lithium metal anode. The three-dimensional porous structure is related to the lithium plating layer and has a uniform distribution, so it can prevent the growth of lithium dendrites and maintain a stable SEI.

[0067] The present disclosure proposes a conductive nanoporous coating made of a nanocomposite material applied to the surface of a lithium metal anode. By irradiating a used mixture containing a polymer matrix, a conductive additive, and an evaporation additive having a low melting point with photoelectromagnetic energy (for example, intense pulsed light (IPL)), a conductive nanoporous composite material is generated.

[0068] The present disclosure proposes a three-dimensional structure of carbon nanotubes applied to the surface of a lithium metal anode. By irradiating a mixture of randomly dispersed carbon nanotubes with a high aspect ratio and a metal oxide solution with photoelectromagnetic energy (for example, IPL), a three-dimensional framework of carbon nanotubes is generated.

[0069] The present disclosure proposes a three-dimensional structure of a lithium metal anode integrated with a current collector based on three-dimensional shaped copper, silver, and carbon nanotubes. By electroplating lithium onto the current collector, a three-dimensional structure of the lithium metal anode is generated. The surface of the current collector is pretreated using the three-dimensional structures of copper, sintered ore, and carbon nanotubes, and the surface of the current collector is sintered by irradiation with electromagnetic energy (e.g., IPL) to obtain carbon nanotubes.

[0070] The present disclosure proposes a cooling system for dissipating waste heat accumulated during electromagnetic energy irradiation from the lithium metal.

[0071] Furthermore, the present disclosure also describes surface treatment of the lithium metal anode using sandblasting technology to increase the adhesion of the protective coating material and reduce the contact resistance.

[0072] In one embodiment, the anode electrode of the lithium metal battery includes a current collector, a lithium metal layer provided on the current collector, a protective layer provided on the lithium metal layer and having a three-dimensional continuous bubble porous structure, and a lithium alloy metal provided on the surface of the protective coating.

[0073] The lithium metal layer may have an engineered surface texture.

[0074] The protective coating may be a polymer nanocomposite layer including a continuous bubble nanoporous polymer matrix, a conductive carbon additive, and a structural support material.

[0075] The protective coating may include a carbon nanofiber mattress having a three-dimensional continuous bubble porous structure.

[0076] The protective coating may include a carbon nanotube network having a three-dimensional continuous bubble porous structure including a lithiumophilic metal oxide.

[0077] The carbon nanotube network may have a top layer of sparsely lithiophilic carbon nanotubes and a bottom layer of a parent lithiophilic metal oxide-carbon nanotube composite material.

[0078] The parent lithiophilic metal oxide may include zinc oxide, iron oxide, manganese oxide, and titanium oxide.

[0079] The lithium alloy metal may be a low melting point metal selected from indium, tin, bismuth, gallium, silver, gold, zinc, aluminum, platinum, germanium, and field metal.

[0080] In another embodiment, the anode electrode of a lithium metal battery includes a metal current collector and a three-dimensional network structure coated on the metal current collector, and the three-dimensional network structure is a metal-based structure or a carbon-based structure.

[0081] The anode electrode may further include a lithium metal layer formed on the surface of the three-dimensional network structure.

[0082] In one embodiment, a method for manufacturing an anode electrode of a lithium metal battery includes the steps of providing a lithium metal layer on a current collector, forming a protective coating having a three-dimensional continuous bubble porous structure on the lithium metal layer, and forming a lithium alloy metal layer on the surface of the protective coating, wherein at least one of the two steps of forming the protective coating and forming the lithium alloy metal coating includes photoelectromagnetic energy irradiation.

[0083] The step of forming the protective coating is

[0084] Preparing a slurry containing a first polymer, a second polymer having a lower boiling point than the first polymer, a conductive carbon additive, a structural support additive, and a solvent; applying the slurry onto a lithium metal layer and drying to form an intermediate coating; forming a protective coating using a thin film coating, irradiating the intermediate coating with electromagnetic energy, and evaporating the second polymer in the intermediate coating to form nanopores.

[0085] The first polymer and the second polymer may be selected from polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polydiacetylene (PDA), polypropylene, polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), glycerol, sucrose, cellulose, and lignin. The conductive carbon additive may be selected from single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes, graphene, graphene oxide, graphene nanoplatelets (GNP), and carbon dots. The structural support additive may be selected from hexagonal boron nitride (hBN), silicon nanowires (SiNW), and alumina.

[0086] The step of forming the protective coating includes manufacturing a nanofiber precursor solution, electrospinning the nanofiber precursor solution to produce a nanofiber mat made of a polymer nanocomposite material, applying electromagnetic energy to the polymer nanocomposite material nanofibers to carbonize the polymer nanocomposite material nanofibers and form a carbon nanofiber mat, and attaching the carbon nanofiber mat to a lithium metal anode.

[0087] The nanofiber precursor solution may include a polymer, a conductive carbon additive, and a solvent. The polymer may include one or more of polyamide (PA), polyacrylamide (PAAm), polyurethane (PU), polybenzimidazole (PBI), polycarbonate (PC), polyethylene (PE), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyethylene oxide (PEO), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinyl pyrrolidone (PVP), collagen, and cellulose acetate (CA). The conductive carbon additive may be composed of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes, graphene, graphene oxide, graphene nanoplatelets (GNP), and carbon dots. The solvent may include one or more of water, acetone, formic acid, chloroform, isopropanol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF).

[0088] The step of attaching the carbon nanofiber mattress includes applying thermal stress and compressive stress simultaneously to attach the carbon nanofiber mattress to the lithium metal layer, and the thermal stress and compressive stress may be applied by a rolling mill, a compression molding machine, and a hot press.

[0089] The step of forming the protective coating includes mixing a nanof composite precursor of a lithiumophilic metal oxide and a lithium-phobic carbon nanotube in a solvent, and

[0090] Depositing a nanocomposite material of a lithiumophilic metal oxide and a lithium-phobic carbon nanotube on a lithium metal layer using a thin film coating method, and applying photoelectromagnetic energy to form a carbon nanotube network having gradient lithiumophilic-lithium-phobic properties, wherein the carbon nanotube network has a lithium-phobic carbon nanotube as the top layer and a lithiumophilic metal oxide-carbon nanotube composite material as the bottom layer.

[0091] The step of forming a lithium alloy metal coating may include depositing a powdered lithium alloy metal on the protective coating. In this way, the powdered lithium alloy metal is introduced into the protective coating using a rolling process, irradiated with photoelectromagnetic energy to melt the powdered lithium alloy metal, and then the molten lithium alloy metal is applied to the surface of the protective coating based on capillary action.

[0092] The method may further include forming an engineered surface texture on the lithium metal layer using sandblasting.

[0093] In another embodiment, a method for manufacturing an anode electrode of a lithium metal battery includes forming a slurry composed of one or more of a mixture of a metal nanoparticle precursor, a conductive carbon additive, and a polymer carrier and a solvent, depositing the slurry on a metal current collector using the thin film coating method, irradiating with photoelectromagnetic energy to sinter the deposited slurry, and sintering the slurry after photoelectromagnetic energy irradiation to form a three-dimensional metal-based network structure.

[0094] The metal nanoparticle precursor may include a copper-based nanoparticle precursor, and the copper-based nanoparticle precursor may be one or more selected from copper, copper acetate, copper oxide, and copper formate tetrahydrate.

[0095] The method may further include electroplating lithium on the metal current collector having the three-dimensional metal-based network structure.

[0096] In another embodiment, a method for manufacturing an anode electrode of a lithium metal battery includes: preparing a slurry by mixing a carbon precursor, a conductive carbon additive, and a solvent; depositing the slurry on a metal current collector using the thin film coating method; and applying photoelectromagnetic energy to the deposited slurry to carbonize the slurry and form a three-dimensional carbon-based network structure.

[0097] The carbon precursor may be selected from asphaltene, mesophase pitch, cellulose, cellulose nanocrystal, and lignin.

[0098] The method may further include performing lithium plating on the metal current collector having the three-dimensional carbon-based network structure.

Brief Description of the Drawings

[0099]

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Modes for Carrying Out the Invention

[0100] According to the drawings, several aspects according to the present disclosure are described in detail by way of example and not limitation.

[0101] This disclosure mainly proposes a novel method for suppressing the growth of lithium dendrites by forming a three-dimensional structure using the irradiation of electromagnetic energy such as intense pulsed light (IPL). By depositing a material on a substrate by a method such as the casting method and irradiating electromagnetic energy, these procedures can be applied to the current mass-production process of batteries using a roll-to-roll process. The process proposed in this disclosure is advantageous because it is shorter in time and higher in energy efficiency compared to other processes described below. The material coating absorbs the electromagnetic energy after irradiation to form a three-dimensional structure. Furthermore, by irradiating electromagnetic energy for a short time, it is possible to prevent waste heat from being transferred from the coating to the lithium metal, and avoid performance degradation due to direct heating of the lithium metal substrate. Furthermore, this disclosure also proposes a novel cooling device for preventing the thermal decomposition of lithium metal.

[0102] As the demand for lithium secondary batteries with higher energy density increases, new materials to replace conventional graphite anodes have attracted attention. Among various candidate materials, lithium metal anodes are expected as promising materials because they have a high theoretical capacity (3860 mAh / g), a low electrochemical potential (-3.04 V), and a low density (0.534 g / cm 3 3) [Guo et al., 2017].

[0103] However, the scientific community has discovered that there are several inherent problems in the commercialization of lithium metal batteries, which directly threaten the safety of the batteries [Whittingham 2004]. When the charge-discharge cycle is repeated, lithium metal rapidly forms lithium dendrites. Lithium dendrites often break, forming irreversible lithium fragments in the electrolyte, leading to a decrease in battery capacity. In more severe cases, the lithium dendrites become sharp and penetrate the separator, causing a short circuit, which may lead to a fire or, in some cases, an explosion.

[0104] Furthermore, the low electrochemical potential of lithium metal is also a double-edged sword. While it provides a higher voltage for the battery, it readily reacts with any organic electrolyte and also with the products generated from cathode materials (such as polysulfides in lithium-sulfur batteries). These reactions are irreversible, increasing the battery impedance, decreasing the total capacity, and increasing the degradation rate of lithium metal batteries [Li et al., 2019]. In addition to the above problems, the large volume change of lithium metal during the lithiation cycle, electrolyte consumption, and unstable solid electrolyte interphase (SEI) layer also cause degradation of the lithium metal anode.

[0105] To address the issues associated with lithium metal anodes, it is desirable to apply a protective coating. The present disclosure provides three different protective coatings for lithium metal anodes and one protective coating for current collectors. The protective coatings have a three-dimensional continuous bubble nanoporous structure but are composed of different materials. However, their manufacturing processes are similar, and the processes used can be easily applied to roll-to-roll manufacturing processes including photoelectromagnetic energy application techniques. Examples for manufacturing protective coatings for lithium metal anodes are described in detail below.

[0106] Sandblasting of lithium metal anode

[0107] Before applying a protective coating to the lithium metal anode, it is preferable to produce a lithium metal anode surface with an engineered surface texture. The engineered surface texture may be produced on the lithium metal surface by various methods including processes such as polishing with sandpaper, machining, micro needles, femtosecond lasers, or sandblasting. The microstructures formed by these processes increase the contact surface area, improve the adhesion of the coating material, reduce the contact resistance, and improve the ion diffusion rate (see Figure 1).

[0108] Figure 1 schematically shows a blasting process for forming an engineered surface texture 115 on a lithium metal layer 110 coated on the anode electrode of a lithium metal battery. In the present disclosure, the lithium metal layer is generally referred to as a lithium metal anode. Also, Figure 1 schematically shows an example of a protective coating 120 formed on a lithium metal layer 110a having an engineered surface texture.

[0109] Sandblasting utilizes the impact of a stream of abrasive particles on a target surface to create abrasion and surface deformation. The shape, size, hardness, velocity, and contact angle of the abrasive affect the effectiveness of the sandblasting method. The final velocity of the abrasive is controlled by the magnitude of the pressure applied by a pump, the type of nozzle, and the distance from the target surface.

[0110] The abrasive particles may include, but are not limited to, alumina, crushed silica, and chemically inert soda-lime glass beads. The average diameter of the abrasive particles may range from 500 nm to 10 μm. In this example, the abrasive particles used are spherical, and the carrier gas used must be an inert gas rather than the commonly used compressed air in order to minimize the chemical reaction between lithium metal and moisture.

[0111] In this exemplary embodiment, a lithium metal surface with an average surface roughness R a of 1 - 100 μm is produced using sandblasting. The desired average surface roughness R a may be achieved using a series of different process parameters. In one example, alumina particles with an average diameter of 50 μm are injected with compressed argon gas at a contact angle of 15° and a pressure of 80 psi. The diameter of the blasting area is 2 cm, and the blasting speed onto the surface is 1 cm / s, and this is repeated twice. The sandblasting is performed inside a glove box filled with argon gas, and the humidity inside the glove box is set to 0.1 ppm. Ten different points on the surface are measured using a contact profilometer (Mitutoyo SJ.201P), and the average surface roughness R aDetermine the average value. The measured average surface roughness R a is 67.4 μm.

[0112] The sandblasting process includes forming a rough surface, i.e., an engineered surface texture 115, on the lithium metal anode 110 to increase the contact area, improve the adhesion of the conductive protective coating 120, and reduce the interfacial resistance.

[0113] Protective coating having three - dimensional continuous bubble foam structure

[0114] The development of a protective coating with a three-dimensional continuous bubble foam porous structure can meet the needs of various applications. First, its complex structure provides abundant nucleation sites, and instead of lithium dendrites growing intensively at a small number of nucleation sites, lithium can be uniformly plated at these nucleation sites. Second, the surface area of the three-dimensional structure is much larger than that of a flat surface, reducing the local current density at the lithium metal anode and retarding the growth of dendrites [Monroe and Newman 2005]. Furthermore, the structure in the submicron region induces a uniform charge distribution and reduces the growth of dendrites [Yang et al., 2015].

[0115] The low density of the three-dimensional continuous bubble foam porous structure also contributes to stress relaxation due to the volume expansion of the lithium metal. Lithium plating is carried out inside the three-dimensional structured protective coating without increasing the volume of the lithium metal anode. Whether it is internal deformation or external deformation caused by volume change, the three-dimensional structure may mechanically absorb the deformation without generating additional stress.

[0116] In this example, three different protective coatings with a three-dimensional continuous bubble foam porous structure are described. Among them, a nanoporous polymer nanocomposite coating, a carbon nanotube network with a metal oxide coating, and a carbon fiber mattress are included.

[0117] Nanoporous polymer nanocomposite coating

[0118] Due to its material properties and ease of handling, the polymer material is suitable as a candidate material for the protective coating of lithium metal anodes. Polymer materials are commonly used in various parts of lithium-ion batteries, such as separators, electrode binders, and polymer gel electrolytes in solid lithium batteries. Polymers may have different properties depending on their components, structures, and functional groups.

[0119] The polymer for coating the lithium metal anode is electrochemically stable with respect to both lithium metal and electrolyte, homogenizes the flux of lithium ions near the electrode surface, inhibits the formation of lithium dendrites, reduces direct contact between the lithium metal and the electrolyte, and can maintain contact with the electrode even against large volume changes. Furthermore, the polymer can be easily coated on the lithium metal anode using conventional methods such as spin coating, spray coating, coating methods, and doctor blade film formation methods. Since the coating method is simple, the efficiency of large-scale processing is ensured and the control of the coating thickness is easy.

[0120] Examples of polymer materials for coating the lithium metal anode may include one or more of polyethylene oxide (PEO), polyethersulfone (PES), poly(dimethylsiloxane) (PDMS), poly(ethylene-vinyl alcohol-β-acrylonitrile ether) (EBC), polyvinyl alcohol (PVA), and polydopamine (PDA). Since the above polymers have polarities (for example, oxygen groups in PEO, cyano groups in EBC, and hydroxy groups in PVA), strong electrostatic interactions exist between them and lithium ions.

[0121] Even without a three-dimensional structure, poly(dimethylsiloxane) (PDMS) thin films [Zhu et al., 2017] and other high-viscosity polymers have already been used for the stabilization of lithium metal anodes in lithiation cycles. Furthermore, polyethylene oxide (PEO) coatings have been shown to form stable polar oligomers and generate a stabilized SEI layer during the first electrochemical cycle of lithium metal anodes [Assegie et al., 2018].

[0122] Another interesting example of a polymer coating for lithium metal anodes is the use of poly(vinylidene fluoride) (PVDF) in the β-phase. PVDF in the β-phase has strong dielectric properties due to its unique crystal structure, and a piezoelectric potential is generated in the coating by the action of stress (i.e., stress due to the volume expansion of the lithium metal anode). The piezoelectric potential serves as a lithium ion pump, promoting the diffusion of lithium ions on the coating and thus improving the charging rate and the uniformity of the lithium ion flux [Xiang et al., 2019].

[0123] Figures 2a and 2b schematically show a method for forming a polymer nanoporous composite coating on a lithium metal layer. Figure 2a shows a lithium foil coated with a slurry, and Figure 2b shows a polymer nanoporous composite coating formed on the lithium metal layer by applying photoelectromagnetic energy.

[0124] In this example, the lithium metal layer 110 coated on the anode electrode of a lithium metal battery may be a lithium foil. The lithium metal layer 110 is provided on a metal current collector (e.g., a copper current collector). The slurry mixture includes a high-boiling-point first polymer 121, a low-boiling-point second polymer 122 having a lower boiling point than the first polymer 121, and a conductive carbon additive 123. The slurry is deposited on the lithium metal layer 110 and dried in a vacuum oven to form a coating 120 (see Figure 2a).

[0125] Furthermore, electromagnetic energy can be applied by the IPL irradiation device 201 to heat the coating 120 and evaporate the second polymer 121 with a low boiling point. Through this process, finally, nanopores 122a are left in the polymer nanocomposite material, so that a continuous bubble porous structure in the form of continuous voids can be formed through the nanopores 122a (see Fig. 2b).

[0126] In this embodiment, a novel manufacturing method for forming a nano-composite coating having a continuous bubble porous structure on the lithium metal layer 110 is proposed. In this method, rapid evaporation of the low-boiling material in the protective coating 120 is utilized to form a continuous bubble porous structure. The nano-composite coating is composed of a main polymer matrix, a conductive carbon additive, a structural support additive, and a second polymer material having a boiling point significantly lower than that of the main polymer.

[0127] The main polymer (first polymer) matrix is the main body of the porous membrane structure. The boiling point of the second polymer is very low, and during rapid evaporation, the second polymer is released from the thin film by the action of electromagnetic energy, thereby creating voids. Examples of polymers used as the first and second polymers include polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polydiacetylene (PDA), polypropylene, polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), glycerol, sucrose, cellulose, or lignin. Among these, multiple types of polymers with a boiling point difference of 10 °C or more or 20 °C or more can be selected as the main polymer and the second polymer.

[0128] Carbon-based conductive nanomaterials form a conductive network within the polymer matrix and function as absorbers of photoelectromagnetic energy. Examples of carbon-based conductive nanomaterials include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes, graphene, graphene oxide, graphene nanoplatelets (GNP), or carbon dots.

[0129] For the structural support additive, materials with high mechanical strength and electrochemical inertness are used. The additive can improve the mechanical strength and durability of the porous polymer nanocomposite. Examples of structural support additives include hexagonal boron nitride (hBN), silicon nanowires (SiNW), and alumina.

[0130] The above components are mixed with a suitable solvent for the polymer used in the mixture to form a slurry, and then the slurry is applied onto the surface of the lithium metal anode using a thin-film coating technique (e.g., doctor blade coating method, bar coating, spray coating, or solution casting) to form a thin film. Then, the thin film is dried in a vacuum oven. When the dried thin film is irradiated with photoelectromagnetic energy to rapidly evaporate the low-boiling-point second polymer and release the evaporation gas from the thin film, a continuous bubble porous structure is formed.

[0131] CNT network containing metal oxide

[0132] Carbon conductive materials have high conductivity and high mechanical strength, so they are widely used in various fields. Among carbon conductive materials, carbon nanotubes (CNT) are known for their high aspect ratio due to their nanoscale diameter and micron-length. This three-dimensional structure of CNT has the characteristics of a high aspect ratio, high conductivity, and a lithium-phobic material, so it can form a suitable interfacial layer on the lithium metal anode, prevent the formation of lithium dendrites, and form a stable SEI layer while promoting the diffusion of lithium ions.

[0133] However, due to the poor lithium wettability of CNTs, it becomes difficult to adhere CNT-based structures to lithium metal anodes. Zhang et al. [Zhang et al., 2018] reported a lithium metal anode with an interfacial layer having gradient lithiumophilic-lithiophobic properties. CNTs containing various zinc oxides (ZnO) were dropped layer by layer onto a lithium foil to form a lithiumophilic bottom layer and a lithiophobic top layer. The gradient lithiumophilic-lithiophobic layer coated on the lithium metal foil is compared with the lithium metal foil coated only with CNTs. Compared with the lithium metal foil coated only with CNTs, the gradient lithiumophilic-lithiophobic layer showed higher cycle stability in the symmetric cell test conducted at a constant current density of 1 mA·cm -2 In the symmetric cell test, the lithium foil sample is placed inside the button cell as both the anode and the cathode. Then, charge-discharge cycles are performed at a constant current density. The amplitude of the charge-discharge voltage is maintained constant. An increase in the voltage amplitude indicates that lithium dendrites are beginning to form inside the battery. The gradient lithiumophilic-lithiophobic layer showed stability over a cycle time of up to 500 hours, while the sample coated only with CNTs showed instability with an increase in the voltage amplitude after 200 hours of cycle time.

[0134] The gradient lithiumophilic-lithiophobic interfacial layer is a feasible method for suppressing the growth of lithium dendrites in lithium metal batteries. However, the method proposed by Zhang et al. requires a complex manufacturing process. For example, to form the gradient layer, solutions of CNTs and zinc oxide with various concentrations have to be prepared. These are deposited layer by layer on the lithium foil, and thus a drying process is required between the two depositions of each layer, resulting in an increase in the manufacturing time. Since the melting point of lithium metal is low (180 °C), the solvent cannot be rapidly dried at high temperatures.

[0135] Figure 3 schematically shows a method of forming a three-dimensional structure of carbon nanotubes on a lithium metal layer.

[0136] In this embodiment, the lithium metal layer 310 may be a lithium foil. A slurry containing a solvent 321, randomly dispersed carbon nanotubes 325, and a metal oxide is deposited on the surface of the lithium metal layer and dried in a vacuum oven to form a coating 320 (see FIG. 3a).

[0137] The coating 320 is heated by IPL photoelectromagnetic energy irradiation to evaporate the solvent 321, leaving a complex three-dimensional network in which the carbon nanotubes 325a and the metal oxide 322 are interconnected (see FIG. 3b).

[0138] In the present disclosure, a novel method of using photoelectromagnetic energy is proposed. The gradient of the parent lithium-phobic lithium layer is formed by the photoelectromagnetic energy effect rather than by layer-by-layer deposition. Instead of using a plurality of solutions containing various concentrations of CNT and zinc oxide, a slurry mixture of CNT, metal oxide, a small amount of polymer binder, and a solvent is deposited on a lithium metal foil and irradiated with photoelectromagnetic energy. The photoelectromagnetic energy evaporates the polymer coating, reduces the topmost metal oxide, and leaves a hydrophobic lithium CNT layer on the top. Since the irradiated photoelectromagnetic energy is applied from above, less energy is transmitted to the depth of the coating slurry, and the parent lithium metal oxide and the polymer binder remain in the bottom layer.

[0139] The parent lithium metal oxide may include, but is not limited to, one or more of zinc oxide, iron oxide, manganese oxide, and titanium oxide. The carbon nanotubes may include, but are not limited to, single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), multi-walled CNTs (MWCNTs), functionalized CNTs, or short carbon nanofibers. The solvent may include, but is not limited to, water, ethanol, hexane, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or a combination thereof.

[0140] FIG. 4 schematically shows a lithium metal foil or a metal current collector cooling system.

[0141] The cooling system shown in FIG. 4 shows the transfer of waste heat that can accumulate in the lithium metal layer 110 or the metal current collector in FIGS. 2b and 3b during electromagnetic energy irradiation.

[0142] The cooling system includes a holder plate 401 with a thermally conductive metal, a refrigerant inlet 410 provided on one side of the holder plate, a heat exchange flow path 420 extending from the refrigerant inlet into the holder plate, and a refrigerant outlet 430 provided on one or the other side of the holder plate and connected to the heat exchange flow path 420.

[0143] The holder plate 401 includes a metal plate with extrusion fixing means to fit a lithium metal anode of a specific size. The metal plate has a thickness sufficient to fix the heat exchanger system, and the material of the metal plate may include, but is not limited to, copper and aluminum.

[0144] The refrigerant inlet 410 and outlet 430 can be connected to a refrigerant pump or the like. Also, a Peltier element may be replaced in the heat exchange flow path through which the refrigerant flows.

[0145] A refrigerant such as cooling water passes through the heat exchange flow path 420 made of a high thermal conductivity material. For example, aluminum in contact with the lithium metal anode can take away the extra heat absorbed by the lithium metal anode due to electromagnetic energy irradiation.

[0146] Carbon nanofiber / fiber mat Less

[0147] The carbon fiber matrix is another porous carbon structure suitable for lithium metal anodes, which can suppress the formation of lithium dendrites and provide the space necessary for lithium deposition during charging. The production of carbon fiber is a relatively mature process. However, stabilizing and carbonizing the carbon precursor material usually requires long processing times and high-temperature heating. When processed at high temperatures, the carbon fiber matrix can be manufactured alone and attached to the lithium metal anode. The temperature and pressure required to attach the carbon fiber matrix to lithium metal are usually lower than the melting point of lithium metal (180.5 °C).

[0148] In 2017, Liu et al. formed an independent hollow carbon fiber structure on a lithium metal anode by carbonizing commercially available cotton. Lithium deposition was observed to occur on the outer surface of the carbon fiber, filling the space between multiple carbon fibers, and also on the inner surface of the carbon fiber, filling the hollow space inside the carbon fiber. By maximizing the surface area and porous structure, the lithium metal anode coated with the hollow carbon fiber structure showed stability in more than 600 cycles of symmetric cell tests, while the bare lithium foil began to become unstable after 180 cycles under the same conditions [Liu et al., 2017]. Another study conducted by Zhang et al. is to coat the carbon fiber with lithium-philic silver by electroplating silver directly onto the carbon fiber. This facilitates the injection of lithium and results in a lithium metal anode with the same stability as pure lithium metal [Zhang et al., 2017].

[0149] The present disclosure proposes a novel method for forming a three-dimensional carbon fiber structure on a lithium metal anode to suppress dendrite growth and maintain stability. The method performs carbonization using photoelectromagnetic energy irradiation to improve energy efficiency and shorten the processing time. To compensate for the insufficient depth of energy reach, polymer nanocomposite nanofibers containing carbonaceous nanoparticles may be produced by electrospinning. The nanofibers with a small diameter and the carbonaceous nanoparticles with a high energy absorption rate lower the energy threshold required for carbonization.

[0150] A horizontal electrospinning apparatus can be used to spin polymer nanocomposite nanofibers. The electrospinning apparatus is connected to a needle attached to a syringe pump using a high-voltage power supply. The bases of the pump and the drum are grounded. The drum rotates at a constant speed, and the base is connected to a resistor with a high resistance (about 100 MΩ), thereby maximizing the deposition amount on the drum while minimizing the deposition amount of fibers at other positions. The flow rate into the system is set to hold a single droplet at the tip of the needle. The syringe pump is mounted on an XY platform programmed to perform an oscillatory motion to uniformly deposit fibers across the entire drum. Electrospinning is a cost-effective and convenient alternative method that can be used for the production of nanofibers and nonwoven mats at the nanoscale. By electrospinning, the porosity and surface area of the fiber matress can be controlled.

[0151] Using the electrospinning method, a mixture of a polymer, a carbonaceous nanocomposite material, and a solvent can be spun. Applicable polymers include one or more of polyamide (PA), polyacrylamide (PAAm), polyurethane (PU), polybenzimidazole (PBI), polycarbonate (PC), polyethylene (PE), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyethylene oxide (PEO), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinyl pyrrolidone (PVP), collagen, and cellulose acetate (CA).

[0152] The conductive carbon additive may include one or more of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNT), graphene, graphene oxide, graphene nanoplatelets (GNP), and carbon dots.

[0153] The solvent may include, but is not limited to, a combination of water, acetone, formic acid, chloroform, isopropanol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF), depending on the polymer used.

[0154] Once the electrospinning is complete, the polymer nanocomposite nanofibers can be carbonized using photoelectromagnetic energy. In this process, the spun fibers are placed on a substrate different from the lithium metal anode, and a high-intensity IPL is applied to the spun fibers while irradiating them with photoelectromagnetic energy, so that the carbon fiber mattress can be completely carbonized from both the front and back sides. When the polymer nanocomposite nanofibers are carbonized to form a carbon fiber mattress, they are transferred to the lithium metal anode using hot press technology under heat and pressure conditions.

[0155] Application of photoelectromagnetic energy by intense pulsed light (IPL)

[0156] The most important step in forming a three-dimensional continuous bubble porous structure on the coating film or current collector of a lithium metal anode is the energy application step. In conventional methods, the application of thermal energy by thermal decomposition was the most common, but generally, it was necessary to consume a lot of energy and time. Furthermore, since this process requires applying energy to the coating film of the lithium metal anode, thermal decomposition at high temperatures (400 - 800 °C) cannot be used because the melting point of lithium metal is low (180.5 °C). In the present disclosure, a method of applying electromagnetic energy (i.e., IPL, etc.) that applies energy without damaging the lithium metal anode is utilized.

[0157] Intense pulsed light (IPL) utilizes high-speed electromagnetic waves generated from a xenon lamp. By applying a high-intensity electrical pulse to a xenon-charged lamp, after the xenon gas is excited to a high-energy state and then returns to a low-energy state, photon irradiation occurs. Compared with other electromagnetic energy application processes such as lasers and microwaves, the advantage of IPL technology is that it can cover a large surface area in a short time (a few milliseconds).

[0158] Furthermore, the pulse spectrum of IPL is wide, generally ranging from 200 nm to 1100 nm, while the wavelength spectra of laser and microwave technologies are more specific. Modern IPL devices generate IPL using a group of capacitors controlled by a computer, and the pulse duration, pulse interval, number of pulses, and intensity are all controllable. The fluence (the radiant energy received by the surface per unit area) is related to the distance from the energy source to the target surface, the angle of the reflector, and the absorption rate of the target surface.

[0159] As described above, a carbon additive having a high absorption rate in a wide spectral range is present in the mixture encapsulating the active material, converting the absorbed energy into thermal energy to form a nanoporous structure. This means that the energy efficiency of the IPL process is much higher and much faster than that of the thermal decomposition process. This method is more suitable for the mass production process of batteries involving the existing roll-to-roll manufacturing process because of its high energy efficiency and short processing time.

[0160] Considering a general IPL system, the diffusion depth of IPL irradiation is limited to a range of about 1 μm from the surface. When processing bulk materials, this limited diffusion depth may not be desirable. However, in the present disclosure, it is sufficient to send energy to the thin film to bring about the desired effect on the coating. Also, since energy is not transmitted to the layer below the surface or the influence on the layer below the surface is extremely small, damage to the lithium metal anode below the coating can be avoided. According to the description when forming a gradient lithiumophilic-lithiophobic layer of carbon nanotubes and metal oxides, there are also interesting effects such as generating a gradient effect in this case.

[0161] Anode - free copper current collector having three - dimensional structure

[0162] A protective coating having a three-dimensional continuous bubble-foamed porous structure is formed on the lithium metal anode to prevent excessive external stress caused by dendrite growth and volume changes associated with the lithiation cycle. However, since the lithiation process of the lithium metal anode is electrodeposition of lithium ions, there has been a problem of whether a lithium metal layer is necessary. Lithium ions are derived from the cathode, and the anode only needs to store lithium ions in the form of electrodeposited lithium. From this, it can be concluded that the "anode-free" current collector can serve as the anode of the lithium metal battery.

[0163] For the "anode-free" current collector to operate properly, a rack or structure capable of storing lithium ions during lithiation is required. Therefore, it becomes necessary again to form a three-dimensional continuous bubble-foamed porous structure on the current collector. The three-dimensional continuous bubble-foamed porous structure on the current collector has the same advantages as the protective coating of the lithium metal anode. In the lithiation cycle, it provides abundant nucleation points and space for lithium deposition, prevents volume changes, and prevents internal stress from becoming excessive. Furthermore, due to the large surface area of the highly conductive material, uniform charge distribution is promoted and dendrite formation is reduced. When mechanical stress exists inside or outside, the three-dimensional structure of the current collector can absorb the stress as a structural support.

[0164] Many studies have already been conducted on the fabrication of three-dimensional structures and racks for anode-free current collectors. These studies include the formation of surfaces with high surface roughness, chemical and mechanical etching of the current collector surface, and the construction of additional structures using polymeric, metallic, or carbonaceous materials.

[0165] For example, the three-dimensional structure of a copper-carbon frame constructed on a copper current collector [Chen et al., 2020] is exemplified. A melamine-formaldehyde foam is thermally decomposed to form a carbon frame, and copper plating is applied onto this carbon frame to form a three-dimensional structure. This achieves a good conductivity, increases the surface area, imparts a stable SEI, reduces dendrites, and as a result of its battery tests, can maintain 99.85% of its capacity even after more than 300 cycles. However, to fabricate the carbon frame, it is necessary to heat it at 900 °C in an N 2 atmosphere for 2 hours and then electroplate it for 10 minutes using a CuSO 4 (copper sulfate) electrolyte, which is a toxic electrolyte.

[0166] In another example, foamed copper was produced as a current collector, and reduced graphene oxide (rGO) was attached thereto [Yu et al., 2019]. In this method, the manufacturing process includes immersing foamed copper in a liquid containing a graphene oxide suspension for 12 hours to obtain reduced graphene oxide (rGO) coated on the foamed copper. In a half-cell test using foamed copper coated with rGO as the anode of a lithium metal battery, it was shown that the Coulombic efficiency (CE) was maintained at 98.5% or more even after 350 cycles. The process is simple, but it requires a long processing time (12 hours) and expensive low-density foamed copper.

[0167] Metal - based three - dimensional structure of current collector

[0168] The present disclosure proposes a three-dimensional structure of a metal-based network realized by a method of performing a sintering process using photoelectromagnetic energy after coating a metal conductive ink. The three-dimensional structure is composed mainly of a conductive metal and a small amount of additives.

[0169] FIG. 5 schematically shows the process of fabricating a three-dimensional structure of a conductive metal on a current collector, taking a copper-based conductive ink as an example. In particular, FIG. 5 shows a method of forming a copper-silver-carbon three-dimensional structure on a copper current collector 510. Thereafter, lithium plating is performed during charging to form a lithium metal anode.

[0170] In this example, the current collector is made of copper. A conductive ink mixture is applied to the current collector and dried in a vacuum oven (see FIG. 5a). In this example, the conductive ink mixture includes, but is not limited to, a solvent carrier, copper nanoparticles 511, silver nanoparticles 512, and a conductive carbon additive 513. For specific applications, various materials can be used in different ratios.

[0171] For example, the IPL irradiation device 501 irradiates photoelectromagnetic energy to sinter copper nanoparticles and forms a three-dimensional conductive network composed of copper nanoparticles 511, silver nanoparticles 512a, and a conductive carbon additive 513 on the current collector 510.

[0172] The three-dimensional conductive network formed on the current collector may itself be an anode electrode. During charging, lithium plating can be applied to the current collector on which the three-dimensional conductive network is formed, and a lithium metal anode electrode with a three-dimensional structure can be formed (see Fig. 5b).

[0173] The conductive metal nanoparticles are mainly copper-based nanoparticles, including, but not limited to, pure copper nanoparticles, copper formate, copper oxide, copper nitrate, copper nitrite, copper acetate nanoparticles, tin, or coated nanoparticles with a polymer protective layer. Although they are not conductive by themselves, when exposed to a critical amount of energy, the metal nanoparticles instantaneously melt and form a conductive bridge.

[0174] The polymer carrier includes, but is not limited to, diethylene glycol (DEG) and / or poly(N-vinylpyrrolidone) (PVP), and both are common conductive ink carriers. There are two types of additives: metal additives and non-metal additives, and each additive is added for a specific purpose. The protective layer and additives surround the main metal conductor (i.e., copper nanoparticles) and fill the gaps between the nanoparticles. Furthermore, improvements in conductivity, removal or suppression of oxidation, reduction of the energy required for sintering, improvement of energy absorption, improvement of solderability and adhesiveness, reliable protection from corrosion and wear, and improvement of self-healing properties are also achieved. These additives include materials of various dimensional specifications such as silver salts, tin, manganese, gallium, indium tin oxide, bismuth, zinc, lead, antimony, gold, silver, palladium, platinum, microfibers, carbon nanofibers, metal fibers, graphene, graphene nanoplatelets, and carbon nanotubes, but are not limited to these.

[0175] The mixture is manufactured by stirring and ultrasonic treatment. Since the solvent and the carrier polymer cannot dissolve some of the main materials, ultrasonic treatment using ultrasonic frequency is required to enhance the dispersibility of the materials. After manufacturing the conductive ink mixture, it can be applied to the current collector by various coating methods (including, but not limited to, bar coating, spray coating, doctor blade film forming method, etc.). Once the mixture is applied, the remaining solvent is removed by evaporation through low-temperature (<50°C) vacuum drying.

[0176] The deposited conductive ink particles form a loose layer with gaps between the conductive metal particles, so conductivity cannot be obtained immediately in the dry state. Application of energy (typically in the form of heat) can partially melt the nanoparticles to form conductive bridges between the nanoparticles. There are both conventional and pioneering techniques for nanoparticle sintering technology.

[0177] Conventional metal nanoparticle sintering methods had to be carried out in an inert gas environment at 150°C to 300°C. Furthermore, it took time to achieve such temperature and gas environment, and expensive equipment and a base resistant to high temperature were required. Due to these conditions, the conventional sintering method cannot be expected to have practical effects.

[0178] In the present disclosure, photoelectromagnetic energy is applied to sinter the metal particles. The method of applying photoelectromagnetic energy includes irradiating one or more of IPL (intense pulsed light), laser, IR (infrared light), and microwave. The method of applying photoelectromagnetic energy has several advantages compared with conventional thermal decomposition or thermal application. The most important one is that higher energy efficiency is ensured by the application of photoelectromagnetic energy. In other heating methods, it is necessary to raise the temperature of the entire heating chamber, but the application of photoelectromagnetic energy is different from directly acting energy on the target surface. Furthermore, by adding a carbon additive, the energy absorption efficiency can be further improved and the power consumption can be reduced.

[0179] Furthermore, the method of applying photoelectromagnetic energy only relates to short-time energy irradiation. The IPL method utilizes the flash of a xenon lamp and can cover the surface of a large area in just a few milliseconds. For each irradiation area, although it may take several seconds in the case of laser or microwave methods, a high supply throughput can be achieved in a roll-to-roll manufacturing process. The required power may be high, but due to the short processing time, the total amount of required energy is much lower than that of conventional thermal application processes. The most important thing is that the method of applying photoelectromagnetic energy does not require any chamber or inert environment, so there is no need to significantly modify the existing anode manufacturing equipment.

[0180] Formation of carbon - based three - dimensional structure of copper current collector using industrial by - products

[0181] Carbon has the characteristics of high conductivity, hard structure, and being easy to form a three-dimensional structure, so it is an ideal material for fixing to the three-dimensional structure of the anode current collector.

[0182] Various carbon sources are considered as potential candidates. For example, Aruna Zhamu and Bor Z. Jang of the Universal Graphene Group have described an anode electrode composed of a lithium metal layer and a graphene porous conductive layer. The porous conductive layer increases the surface area of lithium deposition, forms a stable SEI, and reduces the formation of lithium dendrites. The conductivity of the anode also becomes more uniform, and the lithium dendrites are reduced. This technology applies the basic structure of a three-dimensional structure to a lithium metal anode to prevent the growth of dendrites and fatal failures, but it does not include an efficient manufacturing process for forming the structure.

[0183] As another example, Zhaohui Liao, Chariclea Scordilis-Kelley, and Yuriy Mikhaylik proposed a porous protective layer for lithium metal anodes in 2012 that can produce uniformly dispersed lithium alloys and / or lithium nitride. This can improve the diffusion ability of lithium ions and prevent the formation of lithium dendrites. This method uses a high-cost-performance material to coat the lithium metal anode in a slurry, and then performs a drying process to form a protective layer. The material of the protective layer consists of a metal compound, a conductive agent, and a binder, and the metal compound may be a metal nitride, alumina, or aluminum fluoride. This method includes the formation of a porous structure, but is limited to the slurry deposition and drying processes. Furthermore, the drying process takes 720 hours, resulting in poor time efficiency.

[0184] Another promising carbon precursor for porous carbon structures are industrial by-products such as asphaltenes, pitch, cellulose, and lignin. Asphaltenes, an industrial by-product of crude oil, are often removed because they have a high viscosity and high carbon content, which has an adverse effect on fuel production and energy efficiency. Asphaltenes have been treated as waste in the oil and gas industry and are therefore inexpensive and abundantly supplied. The production of advanced lithium-ion batteries using asphaltenes has economic and environmentally friendly advantages. Pitch is a high-carbon-content industrial by-product extracted from petroleum, coal tar, or wood. Cellulose and lignin are high-carbon substances contained in plants and are also agricultural and forestry by-products such as rice husks, wheat, straw, and sawdust.

[0185] The advantages of asphaltenes that form a three-dimensional structure on the current collector as a carbon source have also been discovered. Wang et al. fabricated a high-capacity lithium metal battery for ultra-fast charging using asphaltenes [Wang et al., 2017]. In this study, untreated hard pitch was used as the carbon precursor. Hard pitch is a naturally occurring black solid lightweight material with a high asphaltene content. The untreated hard pitch was pretreated at 400 °C under argon gas filling for 3 hours, and then ground in a mortar using potassium hydroxide (KOH). After heating the mixture at 850 °C for 1 hour, it was filtered, washed with water, and dried at 110 °C for 12 hours. The KOH-pretreated hard pitch mixture, graphene nanoribbon (GNR), and polyvinylidene fluoride (PVDF) were mixed in a mortar at a mass ratio of 4.5:4.5:1, and then an N-methyl-2-pyrrolidone (NMP) solvent was added to form a slurry. After applying this slurry to a copper foil, it was dried overnight in a vacuum at 50 °C to obtain a high-porosity carbon structure called the Asp-GNR-Li anode.

[0186] It was discovered that the Asp-GNR-Li anode exhibits a high specific capacity over the entire current density range compared to the conventional copper lithium anode. Furthermore, as a result of repeating charge-discharge cycles at a constant current density of 0.5C, the Asp-GNR-Li anode was able to maintain 90% of its specific capacity even after 130 cycles, while the specific capacity of the conventional copper lithium anode decreased to 75% or less after 130 cycles. This trend indicates that the specific capacity of the conventional copper lithium anode decreases rapidly as the number of cycles increases.

[0187] The idea of utilizing asphaltenes with a high carbon content as a precursor for the carbon structure is highly anticipated, especially because of its high cost performance and sufficient supply. However, the manufacturing process proposed in the study by Wang et al. involves many steps and requires high temperatures and long processing times.

[0188] The present disclosure proposes a novel manufacturing technique using photoelectromagnetic energy irradiation to form an anode-free current collector having a porous carbon structure on a copper foil. As described above, the method of applying photoelectromagnetic energy has the advantages of energy saving and time saving compared to the conventional heating process using a melting furnace. The method of applying photoelectromagnetic energy does not require any melting furnace, chamber, or inert environment, and can be immediately applied to a mass production process involving a roll-to-roll process.

[0189] In the method, a slurry-like mixture of a carbon precursor, a conductive carbon additive, and a solvent is produced. The carbon precursor includes industrial by-products with a high carbon content such as asphaltene, mesophase pitch, cellulose, cellulose nanocrystals, and lignin. The conductive carbon additive enhances the structural rigidity, improves the conductivity, and increases the energy absorption of photoelectromagnetic energy. These include one or a combination of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, functionalized carbon nanotubes, graphene, and graphene nanoplatelets. The slurry-like mixture is deposited on the copper foil using a thin film coating method. After drying the slurry on the copper foil, photoelectromagnetic energy is applied to carbonize the slurry and form a three-dimensional carbon-based network structure. During charging, lithium plating is performed on the surface of the three-dimensional carbon-based network structure.

[0190] Low - melting - point lithium alloy metal coating

[0191] The addition of a low-melting-point lithium alloy metal coating contributes to the stabilization of the solid electrolyte interphase (SEI) layer. Such a metal coating can be applied to any of the lithium metal layer, the protective layer, or the anode-free current collector. The SEI layer is stabilized by utilizing three different characteristics: high conductivity, rapid alloying reaction with lithium ions, and self-healing.

[0192] Lithium alloy metals often have a higher electrical conductivity compared to copper and silver. By applying this to the lithium metal layer, the contact resistance between the electrolyte and the anode can be reduced, and the charge transport rate can be improved. It has been revealed that applying indium to a lithium metal anode significantly reduces the electrical contact resistance between the electrolyte and the anode [Choudhury et al., 2017].

[0193] Also, research has shown that indium can rapidly diffuse lithium ions through surface diffusion. Calculations using density functional theory indicate that indium has few diffusion barriers on the surface. Lithium ions bind weakly to the indium plating layer and rapidly pass through the indium plating layer to electrodeposit on the underlying lithium metal layer [Choudhury et al., 2017]. Moreover, rapid ion conduction can reduce the formation of dendrites.

[0194] Finally, metals such as indium have self - healing capabilities and can maintain the SEI in cycles of volume change due to lithiation and delithiation. In a liquid electrolyte environment, a trace amount of metal salt can be added to the electrolyte to perform metal plating, and the damaged metal plating layer can be repaired during this process. This is possible because indium is inert to common electrolytes, preventing side reactions and enabling the maintenance of an energy capacity exceeding 90% of the original energy capacity even after 250 charge - discharge cycles [Choudhury et al., 2017].

[0195] In a solid electrolyte environment, a lithium alloy metal coating performs self - repair by taking advantage of its low melting point. The field metal is an alloy of bismuth, indium, and tin. While the melting points of these metals are relatively high at 271.4 °C, 156.6 °C, and 231.9 °C respectively, the melting point of the alloy is only 62 °C. The low melting point enables the self - repair of the metal coating by passively utilizing the heat generated from the internal resistance of the battery or actively using the battery's Joule heating system (commonly used to control the temperature of the battery in cold environments). This self - repair ability can stably maintain the SEI layer, reduce dendrites, and maintain the electrolyte and active material when the charge - discharge cycle is repeated.

[0196] Figure 6 schematically shows an example of a method of applying a lithium metal layer using a lithium alloy metal to improve lithium ion affinity and stabilize the SEI. As shown in Figure 6, crushed lithium alloy metal powder 620 is directly placed on the lithium metal layer 610. Then, photoelectromagnetic energy is irradiated to sinter the lithium alloy metal powder. The flash sintering process can uniformly apply the partially melted lithium alloy metal to the surface of the lithium metal anode 610 to form a lithium alloy metal coating 620a.

[0197] Figure 7 schematically shows an example of a method of applying a three - dimensional structure using a lithium alloy metal to improve lithium ion affinity and stabilize the SEI. As shown in Figure 7, crushed lithium alloy metal powder 620 is placed on the three - dimensional structure 710 coated on the lithium metal layer 610. Then, the lithium alloy metal powder 620 is rolled to apply the three - dimensional structure 710 to the lithium metal anode. Photoelectromagnetic energy is applied to sinter the lithium alloy metal powder. The flash sintering process can uniformly apply the partially melted lithium alloy metal to the surface of the three - dimensional structure 710 to form a lithium alloy metal coating 620a.

[0198] The low melting point lithium alloy metal coating may be directly applied onto the lithium metal layer as shown in Fig. 6, or may be applied onto the three-dimensional continuous bubble porous protective coating on the lithium metal layer as shown in Fig. 7.

[0199] An example of applying a lithium alloy metal onto the lithium metal layer or the three-dimensional protective coating shown in Fig. 7 will be described below. In this example, while minimizing the thermal influence on the lithium metal layer under the lithium alloy metal powder, photoelectromagnetic energy is irradiated to melt the lithium alloy metal powder in a short time, and the melted lithium alloy metal powder is applied onto the lithium metal layer or the three-dimensional protective coating. This method is different from the conventional hot melt dip coating and electrodeposition metal coating.

[0200] In this embodiment, a process for forming a low melting point lithium alloy metal coating by a simple method utilizing rolling, application of photoelectromagnetic energy, and capillary action is described. First, a powdery low melting point lithium alloy metal is produced. The low melting point lithium alloy metal may include, but is not limited to, indium, tin, bismuth, gallium, silver, gold, zinc, aluminum, platinum, germanium, and eutectic alloys (e.g., field metal). Since these metals and metalloids have high ductility, it may be necessary to perform cryogenic grinding to make them into fine powder.

[0201] The metal powder can be randomly deposited on the surface of the three-dimensional protective coating and can be rolled by applying pressure and heat to penetrate into the voids of the three-dimensional protective coating. When photoelectromagnetic energy is applied, the metal powder melts and wets through the three-dimensional structure by capillary action. Since these metals have a low melting point and do not damage the substrate (i.e., the lithium metal layer with a protective layer) at the desired temperature, this method is feasible.

[0202] To observe the effect of suppressing lithium dendrite formation, a sample of a three-dimensional structured CNT network containing metal oxide was prepared. Carboxylic acid-modified CNTs (ACNTs), zinc oxide, and PVDF were dissolved in an NMP solvent at a weight ratio of 2:3:5 to form a mixture. After stirring the mixture with a planetary ball stirrer for 30 minutes, it was applied to a copper foil using a thin film coating. Two samples with different coating thicknesses (70 μm and 100 μm) were prepared and dried in a vacuum oven at 40 °C for 2 hours. Then, the dried samples were irradiated with an IPL at a power of 2.3 kV to form a nanoporous structure.

[0203] Figures 8a and 8b show the porosity of the porous nanocomposite thin film samples. In the scanning electron microscope (SEM) images, it is shown that the thicknesses of the samples are 70 μm (a) and 100 μm (b). The SEM images of the sample surfaces show the nanopores and micropores of the two samples with different thicknesses.

[0204] As shown in Figure 8a, the maximum diameter of the voids in the 70-μm-thick sample is 15 μm. As shown in Figure 8b, the major diameter of the voids in the 100-μm-thick sample is 20 μm.

[0205] Figure 9 shows the porosity of the porous nanocomposite thin film samples obtained from gas pycnometer analysis. As shown in Figure 9, in the porosity analysis using a gas pycnometer, the porosity of the 100-μm-thick sample is 41%, which is larger than that of the 70-μm-thick sample, which is 36% (see Figure 8). Although the compositions of the two samples are the same, the porosities are different because of the different thicknesses. The increase in porosity due to the increase in thickness may be related to the drying process, in which some solvent may remain in the thicker sample, potentially increasing the porosity.

[0206] As shown in Fig. 10, tests were conducted using a symmetric cell test on a nano-composite coating sample on a lithium metal anode. In the symmetric cell test, instead of an anode and a cathode, a pair of lithium metal electrodes 1010a and 1010b are arranged. A single separator 1020 is provided between the pair of lithium metal electrodes 1010a and 1010b. A spacer 1030, a spring 1040, and an upper lid 1050 are continuously arranged on one of the lithium metal electrodes 1010a, and a lower lid 1060 is arranged under the other lithium metal electrode 1010b. The voltage that changes over time throughout the charge-discharge cycle at a constant current density is monitored. When the voltage amplitude increases and reaches the critical limit, it is determined that lithium dendrites are formed and the battery has failed.

[0207] Figs. 11a and 11b show the results of the lithium metal anode stability analysis of the porous nano-composite thin film samples. Analysis is performed using a symmetric cell test on samples of various thicknesses (70 μm and 100 μm) composed of PVDF, ZnO, and CNT.

[0208] As shown in Figs. 11a and 11b, in the voltage diagrams, two samples of different thicknesses (70 μm and 100 μm) show stable cycles at a density of 0.5 mA / cm 2 This clearly shows that both of these two samples effectively suppress the formation of lithium dendrites. Different from the 70-μm-thick sample in Fig. 11a, in the 100-μm-thick sample in Fig. 11b, the voltage amplitude increased (about 15% increase), and the stability is the same as that of the 70-μm sample. The increase in the voltage amplitude indicates that the porosity and volume of the 100-μm-thick sample are higher than those of the 70-μm sample, indicating that the energy capacity of the sample is high.

[0209] As an example, copper nanoparticles (Cu NPs) with an average diameter of 100 nm (Tekna) were used in silver nitrate (AgNO 3 ), poly(vinylpyrrolidone) (PVP, MW: 40000 g / mol), diethylene glycol (DEG), graphene nanoplatelets (GnP, specific surface area: 500 m 2 / g) and formic acid (HCOOH). To conduct the test, the ink is deposited on a substrate made of acrylonitrile-butadiene-styrene (ABS) 3D printed using the doctor blade film forming method. The coating film is dried in a vacuum oven at 50 °C for 1 hour to remove the residual solvent. Then, the conductive ink film is sintered using IPL treatment to form a conductive network between the deposited particles. The intense light pulses from a xenon flash tube (cerium A type) sinter the sample with two different square pulses. The durations are 1 ms and 2.5 ms respectively, and the energy density is 1.07 - 3.66 J / cm 2 is.

[0210] Figures 12a and 12b show the comparison results of the surface morphology of the copper-based metal conductive ink before and after photoelectromagnetic energy irradiation by a scanning electron microscope (SEM).

[0211] As shown in Figure 12a, before applying IPL, on the surface of the applied copper-based metal conductive ink, there are only aggregated metal nanoparticles and crystallized metal oxides other than nothing. However, as shown in Figure 12b, after applying IPL, the metal oxide is reduced to metal, and a thin sintered copper conductive network with a highly porous three-dimensional structure is formed.

[0212] The subject matter of the present disclosure may be summarized as follows.

[0213] An anode electrode of a lithium metal battery having a function of suppressing dendrite growth, maintaining a stable SEI, and withstanding internal stress due to volume change of lithium metal during repeated charge and discharge cycles, comprising: i. a copper current collector layer; ii. a lithium metal layer disposed on the surface of the current collector layer; iii. a protective layer in a three-dimensional structure having continuous bubble voids; and iv. a low melting point lithium alloy metal coating.

[0214] The lithium metal layer has an engineered surface texture that can enhance the adhesion to the protective layer.

[0215] The engineered surface texture is formed by spraying abrasive particles onto the lithium metal layer using a sandblasting method.

[0216] The abrasive particles include, but are not limited to, one or more of alumina, crushed silica, and chemically inert soda lime glass beads.

[0217] The protective layer is composed of a polymer nanocomposite material including a continuous bubble nanoporous polymer matrix, a carbon-based conductive nanomaterial, and a structural support material.

[0218] The present disclosure provides a method for forming a polymer nanocomposite material layer having a continuous bubble nanopore structure, including: i. mixing precursor materials of the polymer nanocomposite material to form a slurry; ii. applying the slurry onto the lithium metal layer using a thin film coating method and drying it; iii. applying photoelectromagnetic energy to evaporate the low melting point polymer in the slurry and form three-dimensional continuous bubble nanopores.

[0219] The mixture of the polymer nanocomposite material slurry includes a plurality of polymers having different boiling points, a conductive carbon additive, a structural support material, and a solvent. The plurality of polymers having different boiling points are selected without limitation from polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonic acid (PEDOT:PSS), polydiacetylene (PDA), polypropylene, polystyrene (PS), polyurethane (PU), polyethylene oxide (PEO), polyethylene terephthalate (PET), styrene-ethylene-butylene-styrene (SEBS), glycerol, sucrose, cellulose, and lignin.

[0220] The structural support additive includes materials with high mechanical strength and electrochemically inert materials such as hexagonal boron nitride (hBN), silicon nanowires (SiNW), and alumina.

[0221] The conductive carbon additive is arbitrarily selected from single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphene, graphene oxide, graphene nanoplatelets (GNP), and carbon dots.

[0222] The solvent includes, but is not limited to, water, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or a combination thereof.

[0223] The protective layer includes a carbon nanofiber mattress having a three-dimensional continuous bubble porous structure.

[0224] The method for forming a carbon nanofiber mattress having a continuous bubble nanoporous structure includes: i. a step of manufacturing a nanofiber precursor solution; ii. a step of electrospinning a nanofiber mattress made of a polymer nanocomposite; iii. a step of applying photoelectromagnetic energy to carbonize the polymer nanocomposite nanofibers to form carbon nanofibers; and iv. a step of thermocompression bonding the polymer nanocomposite nanofiber mattress to a lithium metal anode.

[0225] The nanofiber precursor solution includes a mixture of one or more polymers suitable for electrospinning, a conductive carbon additive, and a solvent.

[0226] The polymer is arbitrarily selected from polyamide (PA), polyacrylamide (PAAm), polyurethane (PU), polybenzimidazole (PBI), polycarbonate (PC), polyethylene (PE), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polydiacetylene (PDA), polypropylene (PP), polystyrene (PS), polyethylene oxide (PEO), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinyl pyrrolidone (PVP), collagen, and cellulose acetate (CA).

[0227] The conductive carbon additive includes, but is not limited to, one or more of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphene, graphene oxide, graphene nanoplatelets (GNPs), and carbon dots.

[0228] The solvent includes, but is not limited to, one or more of water, acetone, formic acid, chloroform, isopropanol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF).

[0229] The electrospinning process uses a horizontal electrospinning device with a high-voltage power supply that forms a voltage difference between a syringe needle attached to a syringe pump and a drum.

[0230] In the step of attaching the carbon nanofiber mattress, thermal stress and compressive stress are simultaneously applied to attach the carbon nanofiber mattress to the lithium metal layer, and the thermal stress and compressive stress are applied without limitation by a rolling mill, a compression molding machine, and a hot press.

[0231] The protective layer is composed of a carbon nanotube network coated with a metal oxide and has a three-dimensional continuous bubble porous structure.

[0232] A method for forming a carbon nanotube network coated with a metal oxide includes: i. mixing a nano-composite material precursor of a parent lithiumophilic metal oxide and a lithium-phobic carbon nanotube; ii. depositing a nano-composite material of the parent lithiumophilic metal oxide and the lithium-phobic carbon nanotube on a lithium metal layer using a thin film coating method; and iii. applying photoelectromagnetic energy to form a carbon nanotube network having gradient parent lithiumophilic-lithium-phobic characteristics, wherein the carbon nanotube network has a top layer of lithium-phobic carbon nanotubes and a bottom layer of a parent lithiumophilic metal oxide-carbon nanotube composite material.

[0233] The mixture of the nano-composite precursor consists of a parent lithiumophilic metal oxide for attaching carbon nanotubes to the lithium metal anode to maintain the network structure and lithium-phobic carbon nanotubes for forming a conductive network.

[0234] The parent lithiumophilic metal oxide may include, but is not limited to, zinc oxide, iron oxide, manganese oxide, and titanium oxide.

[0235] The carbon nanotubes may include, but are not limited to, single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), multi-walled CNTs, functionalized CNTs, or short carbon nanofibers.

[0236] The solvent may include, but is not limited to, water, ethanol, hexane, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or combinations thereof.

[0237] A current collector having a function of suppressing dendrite growth, maintaining a stable SEI, and withstanding internal stress due to volume change of lithium metal during repeated charge and discharge cycles, comprising: i. a copper metal current collector layer; and ii. a three-dimensional network structure coated on the copper metal current collector layer, wherein the three-dimensional network structure is a copper-based structure or a carbon-based structure.

[0238] A method for forming a three-dimensional copper-based network structure, comprising: i. forming a slurry by mixing copper, silver, a conductive carbon additive, a polymer carrier, and a solvent; ii. depositing the slurry on a copper metal layer using a thin film coating method; and iii. sintering the deposited slurry photoelectromagnetically to form a three-dimensional copper-based network structure.

[0239] The slurry includes copper-based nanoparticles, a silver salt, a polymer carrier, a conductive carbon additive, and a solvent.

[0240] The copper-based nanoparticles are composed of one or more selected without limitation from copper, copper acetate, copper oxide, and copper formate tetrahydrate.

[0241] The silver salt is composed of one or more selected without limitation from silver, silver nitrate, silver nitrite, and silver acetate.

[0242] The polymer carrier includes polyethylene glycol in which polyvinylpyrrolidone is dissolved.

[0243] The conductive carbon additive is composed of one or more selected from carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, functionalized carbon nanotubes, graphene, and graphene nanoplatelets.

[0244] A method for forming a three-dimensional continuous bubble carbon-based network structure, comprising: i. forming a slurry by mixing a carbon precursor, a conductive carbon additive, and a solvent; ii. depositing the slurry on a copper metal layer using a thin film coating method; and iii. applying photoelectromagnetic energy to carbonize the slurry to form a three-dimensional carbon-based network structure.

[0245] The mixture includes one or more of a carbon precursor, a conductive carbon additive, and a solvent.

[0246] The carbon precursor includes industrial by-products such as asphaltene, mesophase pitch, cellulose, cellulose nanocrystals, and lignin.

[0247] The conductive carbon additive consists of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, functionalized carbon nanotubes, graphene, graphene nanoplatelets, or combinations thereof.

[0248] The low melting point lithium alloy metal coating has self-healing ability and can be applied to the surface of a lithium metal anode, a protective coating, or an anode-free current collector to stabilize the solid electrolyte interface layer.

[0249] A method of forming a lithium alloy metal coating on a lithium metal anode protective coating, comprising: i. adding a pulverized powder of a lithium alloy metal onto a lithium metal layer, a protective coating, or an anode-free current collector; and ii. applying photoelectromagnetic energy to sinter a thin lithium alloy metal on the lithium target surface.

[0250] This pulverized powder contains one or more of a low melting point lithium alloy metal and a metalloid.

[0251] The low melting point lithium alloy metal and the metalloid are arbitrarily selected from indium, tin, bismuth, gallium, silver, gold, zinc, aluminum, platinum, germanium, and field metal.

[0252] A method for depositing a material using a thin film coating method includes applying a slurry mixture of a nanocomposite material with a coater (which may be a wire coater or a doctor coater), placing the applied slurry in a vacuum oven to dry, and evaporating all solvents in the slurry.

[0253] A method of applying photoelectromagnetic energy includes evaporating a low boiling point material and inducing carbonization of a polymer and a carbon precursor material, and sintering conductive metal nanoparticles.

[0254] The application of photoelectromagnetic energy includes applying high energy in a short time and absorbing the applied energy with a high absorption rate by a carbon additive.

[0255] The application of photoelectromagnetic energy only includes applying energy to the irradiated surface.

[0256] The application of photoelectromagnetic energy includes irradiation by intense pulsed light (IPL), microwave, laser, plasma, or infrared furnace.

[0257] A cooling device for cooling a substrate during the application of photoelectromagnetic energy, which reduces the temperature of the substrate in contact with a material (e.g., a lithium metal layer or a copper current collector layer) under direct irradiation of photoelectromagnetic energy and prevents damage to the substrate due to overheating.

[0258] The cooling device includes i. a holder plate with a thermally conductive metal and ii. a heat exchanger system such as a Peltier element or a heat exchanger system, enabling the refrigerant to be pumped to the heat exchanger after passing through the holder plate.

[0259] The holder plate includes a metal plate with extrusion fixing means to fit a lithium metal anode of a specific size. The metal plate has a thickness sufficient to fix the heat exchanger system, and the material of the metal plate includes, but is not limited to, copper or aluminum.

Claims

1. A method for manufacturing a positive electrode of a lithium metal battery, comprising the steps of: forming a slurry of one or more of a metal nanoparticle precursor, a conductive carbon additive, a polymeric carrier, and a solvent; depositing the slurry onto a metal current collector using a thin film coating method; irradiating the deposited slurry with optical electromagnetic energy to sinter the deposited slurry; and sintering the slurry after exposure to optical electromagnetic energy to form a three-dimensional metal-based network structure.

2. The metal nanoparticle precursor comprises a copper-based nanoparticle precursor and a silver salt; wherein the copper-based nanoparticle precursor is one or more selected from copper, copper acetate, copper oxide, and copper formate tetrahydrate; wherein the silver salt comprises one or a combination of silver, silver nitrate, silver nitrite, silver acetate, and nanoparticles comprising a silver salt; wherein the conductive carbon additive comprises one or more combinations of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, functionalized carbon nanotubes, graphene, and graphene nanoplatelets; wherein the polymeric carrier comprises a combination of polyvinylpyrrolidone (PVP) dissolved in polyethylene glycol (PEG); 10. The method of claim 1, wherein the solvent comprises a combination of one or more of water, deionized water, ethanol, formic acid, nitric acid, or sulfuric acid.

3. Further comprising applying a lithium alloy metal onto the three-dimensional metal-based network structure; The step of applying a lithium alloy metal onto the three-dimensional metallic network structure includes:

2. The method of claim 1, comprising the steps of depositing powdered lithium alloy metal on a three-dimensional metal-based network structure, utilizing a rolling process to infiltrate the powdered lithium alloy metal through the porous structure into the three-dimensional metal-based network structure, irradiating with light electromagnetic energy to melt the powdered lithium alloy metal, and then coating the molten lithium alloy metal on the surface of the three-dimensional carbon-based network structure based on capillary action.

4. A method for manufacturing a positive electrode of a lithium metal battery, comprising the steps of: mixing a carbon precursor, a conductive carbon additive, and a solvent to prepare a slurry; depositing the slurry onto a metal current collector using a thin film coating method; applying optical electromagnetic energy to the deposited slurry to carbonize the slurry and form a three-dimensional carbon-based network.

5. the carbon precursor is selected from asphaltene, mesophase pitch, cellulose, cellulose nanocrystals, and lignin; wherein the conductive carbon additive comprises one or more combinations of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, functionalized carbon nanotubes, graphene, and graphene nanoplatelets; 5. The method of claim 4, wherein the solvent comprises a combination of one or more of water, deionized water, and ethanol.

6. The method further includes applying a lithium alloying metal onto the three-dimensional carbon-based network structure; The step of applying a lithium alloy metal onto the three-dimensional metallic network structure includes:

5. The method according to claim 4, comprising the steps of depositing powdered lithium alloy metal on the three-dimensional metal-based network structure, utilizing a rolling process to infiltrate the powdered lithium alloy metal through the porous structure into the three-dimensional metal-based network structure, irradiating with light electromagnetic energy to melt the powdered lithium alloy metal, and then coating the molten lithium alloy metal on the surface of the three-dimensional carbon-based network structure based on capillary action.

7. A cooling device for cooling a substrate when applying optical electromagnetic energy according to the method of any one of claims 1 to 6, comprising: The cooling device is configured to reduce the temperature of a substrate in contact with the material under direct irradiation of optical electromagnetic energy to prevent damage to the substrate due to overheating, and the cooling device is configured to: i. a holder plate with a thermally conductive metal; ii. A heat exchanger system selected from a Peltier element or a heat exchanger system in which a coolant is pumped through the heat exchanger and passes through the holder plate.

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