Current collector with coating layer, anode-free lithium battery comprising current collector and manufacturing method thereof

Abstract

The present disclosure relates to a current collector having a coating layer, an anode-free lithium battery including the same and a method for manufacturing the current collector. The current collector shows high lithium-ion conductivity while providing excellent mechanical properties, such as flexibility and mechanical strength. In addition, the current collector shows high adhesive property and low swelling property based on chemical / electrochemical stability in an organic electrolyte.

Description

CURRENT COLLECTOR WITH COATING LAYER, ANODE-FREE LITHIUM BATTERY COMPRISING CURRENT COLLECTOR AND MANUFACTURING METHOD THEREOF

[0001] The present disclosure relates to a current collector having a coating layer, an anode-free lithium battery including the same and a method for manufacturing the current collector.

[0002] Fossil fuels are the most widely used energy resources worldwide, but they are gradually running out of resources and cause environmental pollution. For these reasons, importance of studies about various regenerable energy sources, such as solar energy, has been spotlighted. To integrate such regenerable energy to electric grids, large-scale energy storage systems are essentially required. In addition, use of secondary batteries among various energy storage technologies is promising in terms of high energy conversion efficiency and simple maintenance and repairing.

[0003] Lithium-ion batteries have remarkable advantages in terms of stability and energy density. Since lithium-ion batteries were commercialized, the market related therewith has been increased rapidly. Although graphite has been used actively as an electrode material of such lithium-ion batteries, graphite anodes are problematic in that they have a low capacity per weight and are difficult to be applied to development of light-weight batteries by nature.

[0004] As an alternative, among various electrode materials, lithium metal having a high theoretical capacity (3860 mAh g-1) and low redox potential (-3.04 V vs. standard hydrogen electrode (SHE)) has been used most ideally as an anode of a lithium battery. However, a lithium metal anode causes dendrite growth due to the ionization and dissolution of lithium metal after repeating charge / discharge cycles, and thus shows low deposition / dissolution reversibility and poor life characteristics. When such a lithium dendrite phase grows continuously, formation of 'dead lithium', volumetric swelling and electrolyte consumption occur, resulting in low coulombic efficiency and poor life. In addition, when a lithium dendrite phase is grown to a large size and penetrates through a separator, it may result in an internal short-circuit and fire / explosion. Although the mechanism of lithium dendrite crystal growth is not fully understood yet due to the complicated reactions in the lithium metal anode, it is known that the mechanism is closely related with a solid electrolyte interphase (SEI) formed on the lithium metal surface after lithium metal is in contact with a liquid electrolyte. Therefore, development of some technologies for inhibiting dendrite growth, such as designing of a lithium protection film for the purpose of uniform lithium-ion deposition or lithium surface modification for the purpose of functioning as an artificial solid electrolyte interphase (SEI) layer, have been conducted. However, such alternatives cause another problem, such as degradation of ion conductivity or flexibility, or generation of a swelling phenomenon.

[0005] Meanwhile, lithium metal anodes according to the related art not only have low reversibility but also are problematic in that a high risk exists in a battery manufacturing process and use of thick lithium metal causes a drop in energy density. To solve such problems, a lithium-free (Li-free) or anode-free system has been given attentions. Since such a lithium-free (Li-free) or anode-free system is manufactured while not including an excess of lithium metal in the anode, it is possible to significantly reduce a risk in a battery manufacturing process and to realize the maximum energy density by virtue of the absence of thick lithium metal in the anode. However, the lithium-free (Li-free) or anode-free system shows significant degradation of lithium metal deposition / dissolution reversibility during the charging of a battery due to the nucleation of lithium metal on the anode current collector and provides poor life characteristics due to the absence of extra lithium metal at the anode.

[0006] Under these circumstances, some studies about formation of a protective film have been conducted in order to increase the lithium deposition / dissolution reversibility in the lithium-free (Li-free) or anode-free system. In the case of an ideal protective film, it should satisfy all of the conditions of: a) high lithium-ion conductivity, b) excellent physical properties (flexibility and mechanical strength), c) chemical / electrochemical stability in an organic electrolyte, and d) high adhesive property and low swelling property in an organic electrolyte. However, most current studies about protective films show low ion conductivity, a difficulty in ensuring flexibility and physical strength at the same time, and insufficient consideration about swelling in an organic electrolyte, and thus still provide low lithium metal deposition / dissolution reversibility. In addition, most studies include formation of a coating layer having a large thickness, and thus result in a loss of energy density. Therefore, there is an imminent need for developing a technology about an anode or current collector for a lithium-free (Li-free) or anode-free system which can realize all of the above-described effects of a) to d).

[0007]

[0008] [References]

[0009] [Patent Documents]

[0010] Patent Document 1. Korean Patent Publication No. 10-2197880

[0011] The present disclosure is designed to solve the above-mentioned problems, and therefore the present disclosure is directed to providing a current collector including: a current collecting substrate; and a coating layer formed on the current collecting substrate and including nanocellulose.

[0012] The present disclosure is also directed to providing a lithium battery including the current collector.

[0013] In addition, the present disclosure is directed to providing a system including the lithium battery, the system being any one selected from communication systems, transport systems and energy storage systems.

[0014] Further, the present disclosure is directed to providing a method for manufacturing a current collector, including step (A) of applying a coating solution including nanocellulose introduced to a solvent to a current collecting substrate to form a coating layer.

[0015] In one aspect, there is provided a current collector including: a current collecting substrate; and a coating layer formed on the current collecting substrate and including nanocellulose.

[0016] The current collecting substrate may include at least one selected from the group consisting of copper (Cu), nickel (Ni), lithium (Li), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn).

[0017] The nanocellulose may include at least one selected from the group consisting of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs).

[0018] The nanocellulose may have a diameter of 1 nm to 100 μm.

[0019] The nanocellulose may have a length of 50 nm to 100 μm.

[0020] The nanocellulose may have at least one functional group selected from the group consisting of hydroxyl (-OH), carboxyl (-COOH), amine (-NH2), phosphate (-PO4), ammonium (-NH4) and sulfate (SO42-).

[0021] The nanocellulose may include at least one selected from the group consisting of H+, Li+, Na+, Mg2+, K+and Ca2+, as a counter cation of the functional group.

[0022] The coating layer may further include at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite.

[0023] The coating layer may have a thickness of 5 μm or less.

[0024] In another aspect, there is provided a lithium battery including the current collector.

[0025] The lithium battery may be an anode-free lithium battery.

[0026] In still another aspect, there is provided a system including the lithium battery, the system being any one selected from communication systems, transport systems and energy storage systems.

[0027] In yet another aspect, there is provided a method for manufacturing a current collector, including step (A) of applying a coating solution including nanocellulose introduced to a solvent to a current collecting substrate to form a coating layer.

[0028] The solvent may include water and an alcohol.

[0029] The solvent may be a mixed solvent containing water and an alcohol, wherein the alcohol may be present in an amount of 1 to 20 wt% based on 100 wt% of the total weight of the mixed solvent.

[0030] The solvent may include a first solvent, an alcohol and a non-solvent.

[0031] The solvent may be a mixed solvent containing a first solvent, an alcohol and a non-solvent, wherein the weight ratio of the first solvent, the alcohol and the non-solvent may be 72 to 90 : 1 to 10 : 9 to 20.

[0032] The alcohol may include at least one selected from the group consisting of ethanol, isopropyl alcohol (IPA), tert-butanol (TBA), methanol, butanol and n-propyl alcohol.

[0033] The solvent may further include a non-solvent, wherein the non-solvent may be present in an amount of 3 to 22 wt% based on 100 wt% of the total weight of the solvent.

[0034] The method for manufacturing a current collector may further include step (B) of dipping the current collecting substrate having a coating layer in a non-solvent.

[0035] The non-solvent may include at least one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc) and N-methyl-2-pyrrolidone (NMP).

[0036] The coating solution may include the nanocellulose in an amount of 0.1 to 2 wt%.

[0037] The coating solution may further include at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite.

[0038] The coating solution may be applied trough at least one process selected from the group consisting of doctor blade coating, roll coating, bar coating, slot die coating, comma coating, knife coating, gravure coating, micro-gravure coating, dip coating, flow coating, spin coating and spray coating.

[0039] The method for manufacturing a current collector may further include a step of drying the coating solution at 50 to 100°C for 0.5 to 10 minutes, after the coating solution is applied to the current collecting substrate.

[0040] The coating layer may have a thickness of 5 μm or less.

[0041]

[0042] The current collector according to the present disclosure shows high lithium-ion conductivity while providing excellent mechanical properties, such as flexibility and mechanical strength. In addition, the current collector according to the present disclosure shows high adhesive property and low swelling property based on chemical / electrochemical stability in an organic electrolyte.

[0043] Further, the current collector according to the present disclosure can realize functions as an anode even with no anode active material, while significantly improving a phenomenon of degradation of lithium metal deposition / dissolution reversibility occurring in the conventional anode-free lithium batteries, and thus can solve safety-related problems and overcome a limitation in energy density.

[0044] The effects of the present disclosure are not limited to the above-mentioned effects. It should be understood that the effects of the present disclosure include all effects that can be inferred from the following description.

[0045]

[0046] FIG. 1 is a schematic view illustrating a change in the surface of the current collector, caused by the charge / discharge of an anode-free lithium battery using the current collector according to an embodiment of the present disclosure.

[0047] FIG. 2 is a photographic image illustrating the coating solution obtained from Example 1 according to the present disclosure.

[0048] FIG. 3 shows photographic images illustrating the coating layer obtained from each of (a) Example 1 (water) and (b) Example 2 (water + an alcohol) according to the present disclosure.

[0049] FIG. 4 shows scanning electron microscopic (SEM) images illustrating the coating layer formed on the surface of the current collector obtained from each of (a) Example 2 (water + an alcohol) and (b) Example 3 (water + an alcohol + a non-solvent) according to the present disclosure.

[0050] FIG. 5 shows an SEM image illustrating the section of the current collector obtained from Example 3 according to the present disclosure.

[0051] FIG. 6 shows SEM images illustrating the surface of each of (a) the current collector (TOCN∥Cu) obtained from Example 3 according to the present disclosure and (b) a bare copper (Cu) current collector having no coating layer, after an anode-free Li∥Cu cell using each current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0052] FIG. 7 shows SEM images illustrating the surface of the current collector obtained from Example 3 according to the present disclosure, after an anode-free Li∥Cu cell using the current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0053] FIG. 8 shows SEM images illustrating the section of the current collector obtained from Example 3 according to the present disclosure, after an anode-free Li∥Cu cell using the current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0054] FIG. 9 shows graphs illustrating the coulombic efficiency depending on cycle number in an anode-free Li∥Cu cell using each of the current collector (TOCN∥Cu_v1, TOCN∥Cu_v2 and TOCN∥Cu) obtained from Example 3 according to the present disclosure and a bare copper (Cu) current collector having no coating layer, under the conditions of (a) 1 mA cm-2and 1 mAh cm-2, (b) 1 mA cm-2and 5 mAh cm-2and (c) 1 mA cm-2and 10 mAh cm-2.

[0055] FIG. 10 is a graph illustrating the capacity retention and coulombic efficiency depending on cycle number in an LFP∥Cu cell using each of the current collector (TOCN∥Cu) obtained from Example 3 according to the present disclosure and a bare copper (Cu) current collector having no coating layer.

[0056] FIG. 11 shows the current collector obtained from Example 3 according to the present disclosure, dipped in a carbonate-based electrolyte and ether-based electrolyte for 1 month, wherein (a) is a photographic image of the current collector after dipping, (b) is a surface analysis image before and after dipping, and (c) is a graph illustrating a change in dimension.

[0057] The advantages and features of the present disclosure and methods of achieving them will become clear with reference to the embodiments described hereinafter in detail with the accompanying drawings. However, the present disclosure is not limited to the embodiments described hereinafter and will be implemented in various different forms, the embodiments described hereinafter are provided only to ensure that the present disclosure is complete and to fully inform those skilled in the art to which the present disclosure pertains the scope of the present disclosure, and the present disclosure is only defined by the scope of the claims.

[0058] In the specification, if it is determined that detailed description of a related known technology may unnecessarily obscure the gist of the present disclosure, the detailed description thereof is omitted. If "including", "having", "formed of" or the like mentioned in the present specification is used, other parts may be added unless "only" is used. In addition, terms such as "including" or "having" are intended to specify that there is a feature, number, step, element or combination thereof described in the specification, and should not be understood as excluding the existence or the possibility of addition of one or more other features, numbers, steps, elements, or combinations thereof. Further, the case of expressing an element in a singular form includes the case of including the plural unless otherwise stated.

[0059] As used herein, 'anode-free lithium battery' refers to a battery in which a lithium metal layer is excluded on the anode current collector during the battery assemblage (before charge / discharge), the anode includes the current collector alone during the battery assemblage, and a lithium metal layer is deposited on the anode during charge. However, it is obvious that, as the anode current collector, addition of a separate coating layer or other thin film not including lithium metal is not limited.

[0060] In addition, the term 'anode-free lithium battery' may not be construed as limiting the presence of a lithium-containing cathode active material, limiting the presence of a material layer formed on the anode current collector and capable of inducing stable lithium metal deposition due to high lithium metal affinity, or limiting the presence of a lithium metal or a lithium-containing compound grown on the anode current collector according to charge / discharge.

[0061]

[0062] In one aspect of the present disclosure, there is provided a current collector including: a current collecting substrate; and a coating layer formed on the current collecting substrate and including nanocellulose.

[0063] The current collecting substrate may include at least one selected from the group consisting of copper (Cu), nickel (Ni), lithium (Li), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn), preferably at least one selected from the group consisting of copper (Cu), nickel (Ni), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn).

[0064] Particularly, according to an embodiment of the present disclosure, the current collecting substrate may not include lithium (Li), and such a current collector can enhance stability and maximize energy density when being applied to an anode-free lithium battery in which no lithium metal is present.

[0065] Since a synthetic polymer used for a current collector coating layer according to the related art does not form a porous structure but is swollen in an organic electrolyte to conduct lithium ions, it causes degradation of physical properties after swelling, thereby making it difficult to maintain its structure during repeated lithium deposition / dissolution processes.

[0066] However, the current collector according to the present disclosure includes nanocellulose having a nano-sized porous structure in the coating layer, and thus facilitates infiltration of an organic electrolyte through the pores.

[0067] The nanocellulose may be at least one selected from the group consisting of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs).

[0068] The nanocellulose may have a diameter of 1 nm to 100 μm, preferably 5 nm to 10 μm, more preferably 10 nm to 5 μm, and most preferably 10 nm to 1 μm.

[0069] When the diameter of the nanocellulose is less than the lower limit, physical stability may be degraded. On the other hand, when the diameter of the nanocellulose is larger than the upper limit, the coating layer has a non-uniform thickness, resulting in degradation of electrochemical performance.

[0070] The nanocellulose may have a length of 50 nm to 100 μm, preferably 100 nm to 10 μm, more preferably 500 nm to 5 μm, and most preferably 1 μm to 5 μm.

[0071] When the length of the nanocellulose satisfies the above-defined range, there is an advantage in that the coating layer has more improved uniformity.

[0072] The nanocellulose may have at least one functional group selected from the group consisting of hydroxyl (-OH), carboxyl (-COOH), amine (-NH2), phosphate (-PO4), ammonium (-NH4) and sulfate (SO42-), and preferably at least one functional group selected from hydroxyl (-OH) and carboxyl (-COOH). Particularly, the hydroxyl (-OH) and carboxyl (-COOH) groups show excellent adhesive property to the current collecting substrate, and thus can form an interfacial layer with the current collecting layer stably despite repeated lithium deposition / dissolution. In addition, the carboxyl (-COOH) group accelerates decomposition of salts used for the electrolyte of a lithium battery, thereby accelerating formation of an inorganic material-based stable solid electrolyte interphase on the surface of the current collector.

[0073] The nanocellulose may be one oxidized by an N-oxyl compound, preferably by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) or a derivative thereof. Particularly, when the nanocellulose is one oxidized by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) or a derivative thereof, there is an advantage in that a high content of hydroxyl (-OH) and carboxyl (-COOH) groups is present, which improves the adhesion with the current collecting substrate.

[0074] The nanocellulose may include at least one selected from the group consisting of H+, Li+, Na+, Mg2+, K+and Ca2+, preferably Li+, as a counter cation of the functional group. Particularly, when the nanocellulose includes Li+as a counter cation, use of the nanocellulose in an anode current collector increases the Li+concentration on the anode surface, thereby inducing uniform lithium metal deposition advantageously.

[0075] The coating layer may further include at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite in order to maximize lithium-ion conduction property by using a known phenomenon, such as a space charge layer.

[0076] The coating layer may have a thickness of 5 μm or less, preferably 1 μm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and most preferably 50 nm to 110 nm.

[0077] When the thickness of the coating layer is larger than the upper limit, the over-voltage in the battery is increased, resulting in a drop in the charge / discharge capacity of the battery.

[0078] When the coating layer has a thickness of less than 50 nm, the coating layer cannot retain its physical properties during repeated lithium metal deposition / dissolution, thereby making it difficult to maintain the current collector-coating layer interface stably. Therefore, the lower limit of the coating layer thickness may be 50 nm.

[0079] Particularly, when the coating layer has a thickness of 50 nm to 110 nm, there is an advantage in that the coating layer may have a minimized deviation in thickness even after charging / discharging a lithium battery using the coating layer repeatedly, and may improve the energy density to the maximum limit by virtue of such a small coating thickness.

[0080] In another aspect of the present disclosure, there is provided a lithium battery including the current collector.

[0081] The lithium battery may be an anode-free lithium battery.

[0082] As described above, lithium batteries according to the related art use an anode active material, requires a high cost, increases the battery volume, and shows a limitation in increasing the energy density of the battery. Particularly, when using lithium metal as an anode active material, dendrite growth occurs to cause low deposition / dissolution reversibility and poor life characteristics, as well as a high risk of fire / explosion.

[0083] However, the current collector according to the present disclosure has a nanocellulose-containing coating layer on the surface, and thus can realize functions as an anode even with no use of an anode active material and can be used for an anode-free lithium battery. Moreover, the current collector according to the present disclosure has high lithium-ion conductivity while realizing excellent mechanical properties, such as flexibility and physical strength, and shows high adhesive property and low swelling property based on chemical / electrochemical stability in an organic electrolyte, thereby significantly improving the technical limitations appearing in the anode-free lithium batteries according to the related art.

[0084] FIG. 1 is a schematic view illustrating a change in the surface of the current collector, caused by the charge / discharge of an anode-free lithium battery using the current collector according to an embodiment of the present disclosure.

[0085] As shown in FIG. 1, the current collector according to the present disclosure is applied as an anode current collector of an anode-free lithium battery, and no lithium metal layer is formed during the assemblage of a battery. However, during charge / discharge, lithium migrating from the cathode is deposited on the anode current collector to allow of the growth of a lithium metal layer on the current collecting substrate of the current collector. Particularly, since the current collector according to the present disclosure has a nanocellulose-containing coating layer, the lithium metal layer and LiF form a rich stable solid electrolyte interphase to allow realization of the functions as an anode, while significantly improving lithium deposition / dissolution reversibility, which otherwise is limited when using anode active materials according to the related art.

[0086] The lithium battery may be a lithium-ion battery or a lithium metal battery.

[0087] As described, the lithium battery may be obtained by forming a coating layer containing nanocellulose on a current collecting substrate to prepare a current collector, using the current collector as an anode and stacking a cathode, the anode and a separator interposed between the cathode and the anode to form a cell assembly, and then injecting an electrolyte thereto, in a conventional manner. Herein, the lithium battery may conform to the conventional constitution and manufacturing method of an anode-free lithium battery, except that the current collector according to the present disclosure is used.

[0088] The electrolyte of the lithium battery may be a liquid electrolyte or a solid electrolyte.

[0089] When the electrolyte of the lithium battery is a liquid electrolyte, it may include an organic solvent and a lithium salt.

[0090] The organic solvent functions as a medium through which the ions participating in the electrochemical reactions of the battery migrate, and any organic solvent may be used with no particular limitation as long as it is one that may be used for a lithium battery.

[0091] The lithium salt is dissolved in the organic solvent and functions as a lithium-ion source, allows the fundamental functions of the battery and functions to accelerate migration of lithium ions between the cathode and the anode, and any lithium salt may be used with no particular limitation as long as it is one that may be used for a lithium battery.

[0092] Meanwhile, when the electrolyte of the lithium battery is a solid electrolyte, any solid electrolyte may be used with no particular limitation as long as it is one that may be used for a lithium battery.

[0093] The cathode may be obtained by mixing a cathode active material and a polymer binder, optionally with a conductive material, a filler, or the like, in a solvent to prepare a slurry, and applying the slurry to a cathode current collector. However, the scope of the present disclosure is not limited thereto.

[0094] In the case of the cathode active material, any cathode active material may be used with no particular limitation as log as it is capable of reversible lithium-ion intercalation / deintercalation.

[0095]

[0096] In still another aspect of the present disclosure, there is provided a system including the lithium battery, the system being any one selected from communication systems, transport systems and energy storage systems.

[0097]

[0098] In yet another aspect of the present disclosure, there is provided a method for manufacturing a current collector, including step (A) of applying a coating solution including nanocellulose introduced to a solvent to a current collecting substrate to form a coating layer.

[0099] The solvent may include water alone, preferably water and an alcohol, and more preferably water, an alcohol and a non-solvent.

[0100] The alcohol may include at least one selected from the group consisting of ethanol, isopropyl alcohol (IPA), tert-butanol (TBA), methanol, butanol and n-propyl alcohol, preferably at least one selected from the group consisting of ethanol and isopropyl alcohol (IPA).

[0101] When the solvent is a mixed solvent of water with an alcohol, there is an advantage in that it reduces the surface tension of water to allow homogeneous dispersion in the solution and formation of a thin film coating layer.

[0102] Particularly, when the solvent is a mixed solvent of water with an alcohol, the alcohol may be present in an amount of 1 to 20 wt%, preferably 3 to 15 wt%, more preferably 4 to 15 wt%, and most preferably 4 to 12 wt%, based on 100 wt% of the total weight of the mixed solvent.

[0103] When the solvent is a mixed solvent of water with an alcohol but the content of the alcohol in the mixed solvent is less than the lower limit, the surface tension of water cannot be reduced sufficiently to form a coating layer having a large thickness. On the other hand, when the content of the alcohol is larger than the upper limit, the resultant coating layer may have defects and reduced mechanical strength.

[0104] The method for manufacturing a current collector according to the present disclosure includes forming a coating layer through a non-solvent induced phase separation (NIPS) process, wherein a uniform and less dense porous structure is formed in the coating layer to provide significantly improved lithium-ion conduction property. Particularly, nanocellulose forms a dense porous structure due to the strong hydrogen bonding between nanocellulose materials, and such a porous structure has a limitation in improving ion conductivity. However, when the coating layer is formed through the non-solvent induced phase separation process, the porous structure formed by the nanocellulose materials is converted into a uniform and less dense structure, thereby providing significantly improved ion conductivity.

[0105] When the coating layer is formed through the non-solvent induced phase separation process, the solvent may further include a non-solvent, or the method may further include step (B) of dipping the current collecting substrate having a coating layer in a non-solvent.

[0106] The non-solvent may include at least one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc) and N-methyl-2-pyrrolidone (NMP).

[0107] When the solvent further includes a non-solvent, the non-solvent may be present in an amount of 3 to 22 wt%, preferably 5 to 20 wt%, more preferably 10 to 19 wt%, and most preferably 13 to 17 wt%, based on 100 wt% of the total weight of the solvent (mixed solvent of water with a non-solvent, or mixed solvent of water, an alcohol and a non-solvent).

[0108] When the content of the non-solvent is les than the lower limit, the porous structure cannot be formed sufficiently in the coating layer, thereby making it difficult to expect an effect of increasing lithium-ion conductivity. On the other hand, when the content of the non-solvent is larger than the upper limit, the nanocellulose coating solution has decreased dispersibility, thereby making it difficult to form a uniform coating layer.

[0109] When the solvent is a mixed solvent of water, an alcohol and a non-solvent, the weight ratio of water, the alcohol and the non-solvent may be 72 to 90 : 1 to 10 : 9 to 20, preferably 75 to 86 : 2 to 8 : 12 to 17, and more preferably 78 to 83 : 4 to 6 : 13 to 16. When the weight ratio of water, the alcohol and the non-solvent satisfies the above-defined range, there is a particular advantage in that no cracking and defects are generated in the coating layer even after repeating a rapid change in temperature of the resultant current collector from high temperature to low temperature at least 10 times.

[0110] The nanocellulose may be at least one selected from the group consisting of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs).

[0111] The nanocellulose may have a diameter of 1 nm to 100 μm, preferably 5 nm to 10 μm, more preferably 10 nm to 5 μm, and most preferably 10 nm to 1 μm.

[0112] The nanocellulose may have a length of 50 nm to 100 μm, preferably 100 nm to 10 μm, more preferably 500 nm to 5 μm, and most preferably 1 μm to 5 μm.

[0113] The nanocellulose may have at least one functional group selected from the group consisting of hydroxyl (-OH), carboxyl (-COOH), amine (-NH2), phosphate (-PO4), ammonium (-NH4) and sulfate (SO42-).

[0114] The nanocellulose may be one oxidized by an N-oxyl compound, preferably by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) or a derivative thereof.

[0115] The coating solution may include the nanocellulose in an amount of 0.1 to 2 wt%, preferably 0.15 to 1.5 wt%, more preferably 0.2 to 1.3 wt%, and most preferably 0.3 to 1 wt%.

[0116] When the content of the nanocellulose in the coating solution is less than the lower limit, it is difficult to form a uniform coating layer. On the other hand, when the content of the nanocellulose is larger than the upper limit, it is difficult to form a thin film coating layer due to the high solid content, resulting in an electrode having an excessively large thickness and degradation of energy density.

[0117] The coating solution may further include at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite.

[0118] The current collecting substrate may include at least one selected from the group consisting of copper (Cu), nickel (Ni), lithium (Li), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn), preferably at least one selected from the group consisting of copper (Cu), nickel (Ni), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn).

[0119] The coating solution may be applied trough at least one process selected from the group consisting of doctor blade coating, roll coating, bar coating, slot die coating, comma coating, knife coating, gravure coating, micro-gravure coating, dip coating, flow coating, spin coating and spray coating.

[0120] In the method for manufacturing a current collector according to the present disclosure, the coating solution may be applied to the current collecting substrate in step (A) and then dried to form a coating layer, or the current collecting substrate having a coating layer, dipped in the non-solvent and obtained from step (B) may be dried to form a coating layer.

[0121] The drying may be carried out at 50 to 100°C for 0.5 to 10 minutes, preferably at 55 to 70°C for 1 to 3 minutes.

[0122] When any one of the temperature and time of the drying step is less than the lower limit, the coating layer may not be formed sufficiently. On the other hand, when any one of the temperature and time of the drying step is larger than the upper limit, the coating layer uniformity may be degraded.

[0123] The coating layer may have a thickness of 5 μm or less, preferably 1 μm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and most preferably 50 nm to 110 nm.

[0124] According to the most preferred embodiment of the present disclosure, (1) the method further includes a step of drying the coating solution at 50 to 100°C for 0.5 to 10 minutes, after the coating solution is applied to the current collecting substrate; (2) the solvent is a mixed solvent of water, an alcohol and a non-solvent, wherein the weight ratio of water, the alcohol and the non-solvent is 78 to 83 : 4 to 6 : 13 to 16; (3) the non-solvent includes at least one selected from dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP); (4) the nanocellulose is one oxidized by TEMPO; (5) the nanocellulose may have a diameter of 5 nm to 10 μm and a length of 100 nm to 10 μm; (6) the coating solution includes the nanocellulose in an amount of 0.1 to 2 wt%, (7) the current collecting substrate is copper (Cu); and (8) the coating layer has a thickness of 50 nm to 110 nm.

[0125] In the method for manufacturing a current collector according to the present disclosure, a current collector was obtained while changing the above-mentioned conditions of (1) to (8), an anode-free lithium battery was obtained by using the resultant current collector in a conventional manner, and the battery was charged / discharged 300 times. Then, after 300 charge / discharge cycles, the peel strength between the current collecting substrate and the coating layer was tested by using a peel strength tester at a peel rate of 305 mm / min and at an angle of 180° according to the method of ASTM D903-4 (peel test). As a result, it is shown that when satisfying all of the conditions of (1) to (8), the peel strength is maintained with no significant difference after 300 charge / discharge cycles, thereby providing higher binding force. However, if any one of the conditions of (1) to (8) is not satisfied, it is observed that the peel strength is degraded after 300 charge / discharge cycles.

[0126]

[0127] Hereinafter, the present disclosure will be explained in more detail with reference to Examples, but the scope of the present disclosure cannot be construed as being limited thereto or reduced thereby.

[0128]

[0129] Example 1: Current collector using water as solvent

[0130] Preparation of coating solution

[0131] Prepared was 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-oxidized nanocellulose (TOCN) having a diameter of 10 nm, and a length of 5 μm, containing hydroxyl and carboxyl groups as functional groups and having Li+as a counter cation of the carboxyl group.

[0132] The TEMPO-oxidized nanocellulose was introduced to water to prepare a coating solution, wherein 0.5 wt% of TEMPO-oxidized nanocellulose was present based on 100 wt% of the total weight of the coating solution.

[0133]

[0134] Manufacture of current collector

[0135] The coating solution was applied to a copper (Cu) current collecting substrate having a thickness of 20 μm by using a bar (#4) and dried at 60°C for 1 minute to form a coating layer having a thickness of 100 nm.

[0136]

[0137] Example 2

[0138] Preparation of coating solution

[0139] A coating solution was prepared by introducing the same TEMPO-oxidized nanocellulose as used in Example 1 to a mixed solvent containing water and an ethanol mixed at a weight ratio of 95 : 5, wherein 0.5 wt% of TEMPO-oxidized nanocellulose was present based on 100 wt% of the total weight of the coating solution.

[0140]

[0141] Manufacture of current collector

[0142] The coating solution was applied to a copper (Cu) current collecting substrate having a thickness of 20 μm by using a bar (#4) and dried at 60°C for 1 minute to form a coating layer having a thickness of 100 nm.

[0143]

[0144] Example 3

[0145] Preparation of coating solution

[0146] A coating solution was prepared by introducing the same TEMPO-oxidized nanocellulose as used in Example 1 to a mixed solvent containing water, an ethanol and N-methyl-2-pyrroliidone mixed at a weight ratio of 80 : 5 : 15, wherein 0.5 wt% of TEMPO-oxidized nanocellulose was present based on 100 wt% of the total weight of the coating solution.

[0147]

[0148] Manufacture of current collector

[0149] The coating solution was applied to a copper (Cu) current collecting substrate having a thickness of 20 μm by using a bar (#4) and dried at 60°C for 3 minutes to form a coating layer having a thickness of 100 nm.

[0150]

[0151] Example 4

[0152] Lithium metal was deposited on a copper current collecting substrate having a thickness of 20 μm to a thickness of about 5 μm. Then, a coating layer was formed on lithium metal in the same manner as Example 2 by using the same coating solution as Example 2.

[0153]

[0154] Test Example 1. Evaluation of coating solution dispersibility and coating layer surface

[0155] To evaluate the dispersibility of the coating solution using water alone as a solvent according to Example 1, a photographic image is shown in FIG. 2.

[0156] FIG. 2 is a photographic image illustrating the coating solution obtained from Example 1 according to the present disclosure.

[0157] Referring to FIG. 2, it can be seen that the coating solution according to Example 1 includes nanocellulose dispersed homogeneously therein.

[0158] In addition, to evaluate the coating layer surface depending on whether any cosolvent is used or not in the coating solution, photographic images of the coating layer surface of the current collector obtained according to each of Example 1 using water alone as a solvent and Example 2 using a solvent containing an alcohol further added as a cosolvent are shown in FIG. 3.

[0159] FIG. 3 shows photographic images illustrating the coating layer obtained from each of (a) Example 1 (water) and (b) Example 2 (water + an alcohol) according to the present disclosure.

[0160] As shown in FIG. 3, in the case of Example 1 using no cosolvent, it can be seen that coating uniformity is low and surface defects are generated. On the contrary, in the case of Example 2 using a cosolvent, it is observed that the coating layer surface is uniform, and any defect or agglomeration is not generated.

[0161]

[0162] Test Example 2. Scanning electron microscopy (SEM) analysis

[0163] To analyze the thickness and lithium morphology of the coating layer formed on the surface of the current collector according to each of Examples 2 and 3, scanning electron microscopy (SEM) analysis was carried out. The results are shown in FIG. 4 and FIG. 5. Herein, the analysis was analyzed by using a scanning electron microscope (SEM) available from Hitachi Co., and sectional processing was carried out by using a cooling CP device available from JEOL Co. for the purpose of sectional scanning electron microscopy (SEM) analysis.

[0164] FIG. 4 shows scanning electron microscopic (SEM) images illustrating the coating layer formed on the surface of the current collector obtained from each of (a) Example 2 (water + an alcohol) and (b) Example 3 (water + an alcohol + a non-solvent) according to the present disclosure.

[0165] As shown in FIG. 4, after analyzing the surface morphology of the coating layer formed on the surface of the current collector according to each of Examples 2 and 3 by using scanning electron microscopy (SEM), it can be seen that Example 3 to which a non-solvent induced phase separation (NIPS) process using a non-solvent is introduced shows a uniform nanoporous pore structure, and thus can realize higher lithium-ion conductivity.

[0166] FIG. 5 shows an SEM image illustrating the section of the current collector obtained from Example 3 according to the present disclosure.

[0167] As shown in FIG. 5, after analyzing the morphology of the section of the coating layer formed on the surface of the current collector according to Example 3, it can be seen that a thin and uniform ultrathin film coating layer is formed with a thickness of about 100 nm.

[0168]

[0169] Test Example 3. Scanning electron microscopy (SEM) analysis of coating layer surface right after lithium deposition

[0170] To compare the lithium reversibility of the current collector using a copper current collecting substate alone with that of the current collector according to Example 3, a 2032 coin-type cell was used to obtain an Li∥Cu cell. More particularly, the Li∥Cu cell used a polyethylene separator (thickness 20 um) and an electrolyte including 1 M LiTFSI in 1,3-dioxolan (DOL) / 1,2-dimethoxyethane (DME) (1 / 1, v / v) with 2 wt% LiNO3. Then, a PNE charger was used to carry out a test for evaluating coulombic efficiency. The results and the scanning electron microscopic (SEM) image of the current collector after the test are shown in FIG. 6 and FIG. 7.

[0171] FIG. 6 shows SEM images illustrating the surface of each of (a) the current collector (TOCN∥Cu) obtained from Example 3 according to the present disclosure and (b) a bare copper (Cu) current collector having no coating layer, after an anode-free Li∥Cu cell using each current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0172] As shown in FIG. 6, after the anode-free Li∥Cu cell using each of the current collector (TOCN∥Cu) according to Example 3 and a bare copper (Cu) current collector having no coating layer is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2, and then the surface morphology of the current collector was analyzed by using a scanning electron microscope (SEM), the current collector (TOCN∥Cu) according to Example 3 shows a decrease in surface area of lithium deposition as compared to the bare copper (Cu) current collector having no coating layer due to the introduction of the nanocellulose coating layer. It can be seen from the above results that dense lithium with a small surface area is deposited in the case of the current collector according to the present disclosure, and thus side reactions with the electrolyte can be reduced and lithium deposition / dissolution reversibility can be improved.

[0173] The SEM image illustrating the anode according to Example 3 after lithium deposition was used to further analyze the surface and sectional morphology. The results are shown in FIG. 7 and FIG. 8.

[0174] FIG. 7 shows SEM images illustrating the surface of the current collector obtained from Example 3 according to the present disclosure, after an anode-free Li∥Cu cell using the current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0175] FIG. 8 shows SEM images illustrating the section of the current collector obtained from Example 3 according to the present disclosure, after an anode-free Li∥Cu cell using the current collector is subjected to lithium deposition under the condition of 1 mA cm-2and 1 mAh cm-2.

[0176] As shown in FIG. 7 and FIG. 8, in the case of the current collector including a nanocellulose coating layer introduced thereto according to Example 3, it can be seen that the nanocellulose coating layer retains the same structure as its initial structure on the lithium surface even after lithium deposition, thereby providing high stability.

[0177]

[0178] Test Example 4. Evaluation of electrochemical performance in application to Li∥Cu cell

[0179] To evaluate lithium deposition / dissolution reversibility, a test for evaluating the coulombic efficiency of the Li∥Cu Cell according to Example 3 was carried out. The results are shown in FIG. 9. Herein, the TOCN∥Cu_v2 cell shown in FIG. 9 uses the same current collector as obtained from Example 3 in order to evaluate reproducibility.

[0180] FIG. 9 shows graphs illustrating the coulombic efficiency depending on cycle number in an anode-free Li∥Cu cell using each of the current collector (TOCN∥Cu_v1, TOCN∥Cu_v2 and TOCN∥Cu) obtained from Example 3 according to the present disclosure and a bare copper (Cu) current collector having no coating layer, under the conditions of (a) 1 mA cm-2and 1 mAh cm-2, (b) 1 mA cm-2and 5 mAh cm-2and (cc) 1 mA cm-2and 10 mAh cm-2.

[0181] As shown in FIG. 9, the bare copper (Cu) current collector having no coating layer shows degradation of coulombic efficiency as the cycle number is increased, and particularly a rapid drop in coulombic efficiency is observed from the 170thcycle. On the contrary, it can be seen that the current collector including a nanocellulose coating layer introduced thereto according to Example 3 shows improved lithium deposition / dissolution reversibility, and thus realizes significantly improved cyclability.

[0182]

[0183] Test Example 5. Evaluation of electrochemical performance in application to Li∥Cu cell

[0184] The current collector according to Example 3 was used to obtain a pouch-type cell, wherein LFP / Carbon black / PVDF (90 / 10 / 10 (w / w / w)) were mixed to form a cathode (3.5 mAh cm-2), and 1M LiTFSI in 1,3-dioxolan (DOL) / 1,2-dimethoxyethane (DME) (1 / 1, v / v) with 2 wt% LiNO3was used as an electrolyte to obtain an anode-free full-cell (LFP∥Cu cell, Li-free system). Then, the LFP∥Cu cell was evaluated in terms of cyclability to test lithium deposition / dissolution reversibility. The results are shown in FIG. 10.

[0185] FIG. 10 is a graph illustrating the capacity retention and coulombic efficiency depending on cycle number in an LFP∥Cu cell using each of the current collector (TOCN∥Cu) obtained from Example 3 according to the present disclosure and a bare copper (Cu) current collector having no coating layer.

[0186] As shown in FIG. 10, it can be seen that the current collector including a nanocellulose coating layer introduced thereto according to Example 3 shows significantly improved cyclability as compared to the bare copper (Cu) current collector having no coating layer, and thus realizes excellent performance even in an anode-free battery system.

[0187]

[0188] Test Example 6. Evaluation of swelling resistance

[0189] The current collector obtained from Example 3 was dipped in a carbonate-based electrolyte and ether-based electrolyte used as an electrolyte of a lithium battery for 1 month. Then, it is observed whether swelling occurs or not. The results are shown in FIG. 11. Herein, as the carbonate-based electrolyte, 1 M LiPF6dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used. In addition, as the ether-based electrolyte, 1 M LiTFSI dissolved in a mixed solvent of 1,3-dioxolan (DOL) and 1,2-dimethoxyethane (DME) was used.

[0190] FIG. 11 shows the current collector obtained from Example 3 according to the present disclosure, dipped in a carbonate-based electrolyte and an ether-based electrolyte for 1 month, wherein (a) is a photographic image of the current collector after dipping, (b) is a surface analysis image before and after dipping, and (c) is a graph illustrating a change in dimension.

[0191] As shown in FIG. 11, it can be seen that the current collector of Example 3 according to the present disclosure is not dissolved after being dipped in carbonate and ether and shows no change in dimension, and thus has excellent swelling resistance.

[0192]

[0193] Test Example 7. Evaluation of change in cell volume after charge / discharge

[0194] To evaluate a change in cell volume after charge / discharge in the current collector according to each of Examples 1 to 4, an LFP∥Cu cell was obtained by using the current collector according to each of Examples 1 to 4. Then, the cell was subjected to charge / discharge for 100 cycles by being charged to 4.8 V at 1 mA (C / 5 rate) and being discharged to 3.0 V. After that, a change in thickness of the LFP∥Cu cell was determined. As a result, the LFP∥Cu cells using the current collectors obtained from Examples 1 to 4 show a change in thickness of 15%, 6%, 2% and 23%, respectively. Therefore, it can be seen that Examples 1 to 3 using no lithium metal shows significant improvement of the problem of a change in cell volume caused by a change in anode thickness, as compared to Example 4 using lithium metal introduced thereto. It can be also seen that among Example 1 to 3 of application to an anode-free battery, the current collector obtained from Example 3 shows the highest level of improvement of a cell volume change phenomenon.

[0195]

[0196] Test Example 8

[0197] An LFP∥Cu cell was obtained by using the current collector according to each of Examples 1 to 4 in the same manner as described above. Then, the cell was fully charged to SOC 100%, subjected to a nail penetration test at a penetration rate of 80 mm / min by using a nail having a diameter of 3.0 mm, and evaluated according to the following criteria:

[0198] L1: no change, L2: slight heat emission, L3: liquid leakage, L4: fuming, L5: fire ignition, L1 to L3: pass, L4 and L4: fail

[0199] As a result, fuming (L4) is observed in the cell using the current collector according to Example 4, while the cells using the current collectors according to Examples 1 to 3 are judged as liquid leakage (L3), slight heat emission (L2) and no change (L1), respectively. Therefore, it can be seen that the current collector according to the present disclosure significantly reduces electrification even when an internal short-circuit occurs due to external impact, inhibits rapid ignition and explosion of a battery by reducing the heat accumulation of the battery caused by the flow of a lot of electric current, and thus significantly improves the battery stability.

[0200]

[0201] The present disclosure has been described in detail with reference to specific examples. However, it should be understood by those skilled in the art that the various changes and modifications can be without departing from the scope of the present disclosure defined by the following claims through the addition, modification, elimination or supplement of a constitutional element, and that such changes and modifications also fall within the scope of the present disclosure.

Claims

1.A current collector comprising:a current collecting substrate; anda coating layer formed on the current collecting substrate and comprising nanocellulose.2.The current collector according to claim 1, wherein the current collecting substrate comprises at least one selected from the group consisting of copper (Cu), nickel (Ni), lithium (Li), stainless steel (SUS), silver (Ag), gold (Au) and tin (Sn).3.The current collector according to claim 1, wherein the nanocellulose comprises at least one selected from the group consisting of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs).4.The current collector according to claim 1, wherein the nanocellulose has a diameter of 1 nm to 100 μm.5.The current collector according to claim 1, wherein the nanocellulose has a length of 50 nm to 100 μm.6.The current collector according to claim 1, wherein the nanocellulose comprises at least one functional group selected from the group consisting of hydroxyl (-OH), carboxyl (-COOH), amine (-NH2), phosphate (-PO4), ammonium (-NH4) and sulfate (SO42-).7.The current collector according to claim 6, wherein the nanocellulose comprises at least one selected from the group consisting of H+, Li+, Na+, Mg2+, K+and Ca2+, as a counter cation of the functional group.8.The current collector according to claim 1, wherein the coating layer further comprises at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite.9.The current collector according to claim 1, wherein the coating layer has a thickness of 5 μm or less.10.A lithium battery comprising the current collector as defined in any one of claims 1 to 9.11.The lithium battery according to claim 10, which is an anode-free lithium battery.12.A system comprising the lithium battery as defined in claim 10 or 11, the system being any one selected from communication systems, transport systems and energy storage systems.13.A method for manufacturing a current collector, comprising step (A) of applying a coating solution comprising nanocellulose introduced to a solvent to a current collecting substrate to form a coating layer.14.The method for manufacturing a current collector according to claim 13, wherein the solvent comprises water and an alcohol.15.The method for manufacturing a current collector according to claim 13, wherein the solvent is a mixed solvent containing water and an alcohol, and the alcohol is present in an amount of 1 to 20 wt% based on 100 wt% of the total weight of the mixed solvent.16.The method for manufacturing a current collector according to claim 13, wherein the solvent comprises a first solvent, an alcohol and a non-solvent.17.The method for manufacturing a current collector according to claim 13, wherein the solvent is a mixed solvent containing a first solvent, an alcohol and a non-solvent, and the weight ratio of the first solvent, the alcohol and the non-solvent is 72 to 90 : 1 to 10 : 9 to 20.18.The method for manufacturing a current collector according to any one of claims 14 to 17, wherein the alcohol comprises at least one selected from the group consisting of ethanol, isopropyl alcohol (IPA), tert-butanol (TBA), methanol, butanol and n-propyl alcohol.19.The method for manufacturing a current collector according to claim 13, wherein the solvent further comprises a non-solvent, and the non-solvent is present in an amount of 3 to 22 wt% based on 100 wt% of the total weight of the solvent.20.The method for manufacturing a current collector according to claim 13, which further comprises step (B) of dipping the current collecting substrate having a coating layer in a non-solvent.21.The method for manufacturing a current collector according to any one of claims 16, 17, 19 and 20, wherein the non-solvent comprises at least one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc) and N-methyl-2-pyrrolidone (NMP).22.The method for manufacturing a current collector according to claim 13, wherein the coating solution comprises the nanocellulose in an amount of 0.1 to 2 wt%.23.The method for manufacturing a current collector according to claim 13, wherein the coating solution further comprises at least one inorganic substance selected from the group consisting of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum phosphate oxide (LAGP), alumina (Al2O3), silica (SiO2), titania (TiO2) and zeolite.24.The method for manufacturing a current collector according to claim 13, wherein the coating solution is applied trough at least one process selected from the group consisting of doctor blade coating, roll coating, bar coating, slot die coating, comma coating, knife coating, gravure coating, micro-gravure coating, dip coating, flow coating, spin coating and spray coating.25.The method for manufacturing a current collector according to claim 13, which further comprises a step of drying the coating solution at 50 to 100°C for 0.5 to 10 minutes, after the coating solution is applied to the current collecting substrate.26.The method for manufacturing a current collector according to claim 13, wherein the coating layer has a thickness of 5 μm or less.

Images