Method for manufacturing a graphene / graphite integrated electorde through electrochemical exfoliation and application method to lithium metal battery electrode

Abstract

One embodiment of the present invention provides a method for manufacturing a separator-integrated electrode. According to an embodiment of the present invention, a separator-integrated electrode having a graphite and graphene layer with a very thin thickness at the bottom can be manufactured, and when the electrode manufactured by this method is applied to a negative electrode for a lithium metal battery, the lithium ion affinity of the electrode is increased and the resistance of the electrode surface is lowered, thereby providing the effect of stable operation of the lithium metal battery.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a separator-integrated electrode, and more specifically, to a method for manufacturing a separator-integrated graphene / graphite electrode through electrochemical exfoliation. Background Technology

[0002] Most currently commercialized lithium secondary batteries use graphite as the anode material, but graphite's low theoretical capacity limits its application in fields requiring high energy density, such as portable electronic devices and electric vehicles. Lithium metal batteries are attracting attention as the most promising next-generation batteries due to their low redox potential and a theoretical capacity of 3,860 mAh / g, which is 10 times that of graphite. However, during the repeated plating and stripping process of lithium metal, the deposition of lithium ions forms lithium dendrites, causing internal short circuits. Furthermore, low lifespan characteristics due to dead-Li and defects in stability caused by volume expansion are being pointed out as problems.

[0003] To address the aforementioned drawbacks of lithium metal anodes, lithium metal surface modification, electrolyte optimization, and the formation of artificial solid electrolyte interface layers are being studied. However, these strategies have the potential to significantly increase battery costs and cause the side effect of increased interfacial resistance, so they cannot serve as a fundamental solution for the commercialization of lithium metal batteries with maximized energy density. Prior art literature

[0004] Published Patent Application 10-2020-0076944 The problem to be solved

[0005] The present invention aims to provide a separator-integrated electrode having excellent resistance characteristics and stable driving performance through a method for manufacturing a separator-integrated electrode of a lithium metal battery using an electrochemical peeling method, as a way to solve the problems of the aforementioned prior art.

[0006] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0007] To achieve the above technical problem, one embodiment of the present invention provides a method for manufacturing a separator-integrated electrode.

[0008] A method for manufacturing a separator-integrated electrode according to one embodiment of the present invention comprises: a preparation step of preparing a two-electrode system having a graphite sheet as an anode in an electrolyte; a peeling step of applying an oxidation current and a reduction current to the two-electrode system to peel off and reduce the graphite sheet; a centrifugation step of dispersing the obtained graphite and graphene in water and then centrifuging the graphite and graphene; and a filtration step of filtering the supernatant containing the graphene and graphite obtained through the centrifugation through a separator for a lithium secondary battery.

[0009] In an embodiment of the present invention, the method for manufacturing a separator-integrated electrode may be characterized in that the electrolyte comprises H2SO4, Na2SO4, KOH, Na2MoO4, (NH4)2SO4, or a combination thereof.

[0010] In an embodiment of the present invention, the method for manufacturing a separator-integrated electrode may be characterized in that the electrolyte comprises sulfuric acid with a concentration of 0.1 to 1 M.

[0011] In an embodiment of the present invention, the peeling step may be a method for manufacturing a separator-integrated electrode characterized by alternately applying the oxidation current and the reduction current.

[0012] In an embodiment of the present invention, the method for manufacturing a separator-integrated electrode may be characterized by applying the oxidation current for 120 to 180 minutes and applying the reduction current for 120 to 180 minutes.

[0013] In an embodiment of the present invention, the filtration step may be a method for manufacturing a separator-integrated electrode characterized by further adding a conductive material and a binder to the supernatant and filtering it.

[0014] In an embodiment of the present invention, the method for manufacturing a membrane-integrated electrode may be characterized in that the filtration is performed by a vacuum filtration method.

[0015] In an embodiment of the present invention, the separator may be composed of one or more materials selected from the group consisting of glass fiber, olefin-based polymer, and polyethylene, and may be in the form of a sheet or nonwoven fabric, thereby forming a method for manufacturing a separator-integrated electrode. Effects of the invention

[0016] According to an embodiment of the present invention, a separator-integrated electrode having a graphite and graphene layer with a very thin thickness at the bottom can be manufactured, and when the electrode manufactured by this manufacturing method is applied to a negative electrode for a lithium metal battery, the lithium ion affinity of the electrode is increased and the resistance of the electrode surface is lowered, thereby having the effect of stable operation of the lithium metal battery.

[0017] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0018] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a separator-integrated electrode according to one embodiment of the present invention. Figure 2 is a voltage and current curve of the response over time when a current of ± is applied at equal intervals. FIG. 3 is a diagram showing a suspension centrifuged by a manufacturing method according to one embodiment of the present invention, the suspension filtered through a separation membrane, and a comparative example. Figure 4 shows the X-ray diffraction (XRD) and Raman spectroscopy results of a graphene and graphite mixture and a comparative example obtained by a manufacturing method according to one embodiment of the present invention. FIG. 5 is a scanning electron microscope image of a separator-integrated electrode manufactured by a manufacturing method according to one embodiment of the present invention. Figure 6 is the result of evaluating electrochemical characteristics through various methods by assembling a separator-integrated electrode manufactured by a manufacturing method according to one embodiment of the present invention into a lithium metal battery coin cell. Specific details for implementing the invention

[0019] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0020] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0021] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0022] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0024] A method for manufacturing a separator-integrated electrode according to one embodiment of the present invention is described.

[0025] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a separator-integrated electrode according to one embodiment of the present invention.

[0026] The inventors confirmed that graphite and graphene are obtained as a result of electrochemically exfoliating and reducing a graphite sheet, and were able to obtain a suspension containing a certain ratio of graphite and graphene when centrifuged with ultrapure water. Furthermore, utilizing the fact that graphite and graphene, which have high electrical conductivity and lithium affinity, can be used as electrode materials for lithium metal batteries, the inventors processed them into a separator-integrated electrode through vacuum filtration, and completed the present invention by confirming improved stability when applied to a battery.

[0027] A method for manufacturing an integrated electrode according to one embodiment of the present invention comprises: a preparation step (S100) of preparing a two-electrode system having a graphite sheet as an anode in an electrolyte; a peeling step (S200) of applying an oxidation current and a reduction current to the two-electrode system to peel off and reduce the graphite sheet; a centrifugation step (S300) of dispersing the obtained graphite and graphene in water and then centrifuging the graphite and graphene; and a filtration step (S400) of filtering the supernatant containing the graphene and graphite obtained through the centrifugation through a separator for a lithium secondary battery.

[0028] First, a two-electrode system is prepared using a graphite sheet as the anode (S100).

[0029] In the above two-electrode system, the electrolyte may be of various types including cations and anions capable of entering between the layered structures of graphite to separate the layered structures of graphite, thereby causing the graphite to expand and form gas. For example, the electrolyte may include a gel electrolyte, a liquid electrolyte, or a combination thereof, and the electrolyte may be one in which a lithium salt is dissolved.

[0030] Specifically, the electrolyte is H2SO4, Na2SO4, KOH, Na2MoO -4 It may include (NH4)2SO4 or a combination thereof. In particular, it may be preferable for the electrolyte to include sulfuric acid (H2SO4) at a concentration of 0.1 M to 1 M.

[0031] In the above two-electrode system, platinum (Pt) can be used as the cathode.

[0033] Next, the graphite sheet is peeled off (S200).

[0034] The above peeling is performed by applying current to the two-electrode system. At this time, an oxidation current (+) and a reduction current (-) may be alternately applied to the two-electrode system. For example, a method may be used in which an oxidation (+) current is applied for 120 to 180 minutes and a reduction (-) current is applied for 120 to 180 minutes.

[0035] The average current density of the above oxidation (+) current is 0.1 to 0.25 A / cm² 2 And, the average current density of the reduction (-) current is -0.1 to -0.25 A / cm² 2 It could be.

[0037] Next, graphite and graphene are obtained, and the graphite and graphene are dispersed in water and then centrifuged (S300).

[0038] The graphene mentioned above refers to a sheet-like crystalline carbon allotrope in which carbon atoms are arranged in two dimensions. The basic unit of the two-dimensional arrangement is a C6 ring, and may further include a C5 ring or a C7 ring. The graphene may be formed as a plurality of layers in which several single-layer sheets are stacked, or it may be formed as a single sheet layer. The graphite dispersed in the supernatant after centrifugation may be graphite with a lower density than the graphite remaining after precipitation, which is due to the graphite expanded during the exfoliation process.

[0039] For water, ultrapure water (Di water) from which ions, etc., have been removed can be used.

[0040] The suspension, which has undergone centrifugation and washing processes using the aforementioned water, is treated with a solvent having a higher specific gravity than conventionally used ethanol, thereby additionally including graphene, graphite with a higher density compared to graphene, and graphite expanded during the exfoliation process in the supernatant used for electrode manufacturing. In particular, the inventors of the present invention have confirmed that the presence of such graphite significantly contributes to the improvement of lithium battery performance.

[0042] Next, the obtained supernatant is filtered through a membrane (S400).

[0043] In the above S400 step, the graphite and graphene of the supernatant are filtered through a separation membrane.

[0044] The above separator may be in the form of a sheet or nonwoven fabric composed of one or more materials selected from the group consisting of glass fibers, olefin-based polymers, and polyethylene.

[0045] The above filtration can preferably utilize a vacuum filtration method.

[0046] An integrated electrode manufactured by a manufacturing method according to one embodiment of the present invention has a graphite and graphene layer having a very thin thickness at the bottom, and when applied to a negative electrode for a lithium metal battery, the electrode lithium ion affinity is increased and the electrode surface resistance is lowered, thereby enabling stable operation of the lithium metal battery.

[0048] The present invention will be explained in more detail below through manufacturing examples, comparative examples, and experimental examples. However, the present invention is not limited to the following manufacturing examples and experimental examples.

[0050] Example 1: Preparation of a separator-integrated electrode

[0051] A two-electrode system was constructed using two graphite sheets as the anode and cathode in 200 mL of 0.1 M sulfuric acid electrolyte. +0.2 A / cm² 2 Current with a current density of - 0.2 A / cm² for 30 seconds 2 A current with a current density was applied alternately in 30-second intervals for a total of 5 hours until all the graphite sheets were peeled off and the voltage was limited.

[0052] The obtained graphite and graphene were dispersed in ultrapure water using an ultrasonic bath, and large graphite chunks and the remaining graphene and graphite were separated using a centrifuge.

[0053] The obtained graphene and graphite suspension was directly vacuum filtered onto glass fibers that can be used as separators for lithium secondary batteries. The separator-integrated electrode, prepared by adsorption onto the separator through the filtration method, was used as the negative electrode of the lithium secondary battery.

[0055] Experimental Example 1: Voltage / Current Curves According to Electrochemical Peeling Method

[0056] Figure 2 is a voltage and current curve of the response over time when a current of ± is applied at equal intervals.

[0057] When performing the electrochemical peeling method according to Example 1 above, time-current and time-voltage curves such as those in Fig. 2 above may be obtained.

[0058] SO4 of sulfuric acid in the corresponding process 2- Ions and OH - Ions were inserted into each layer of the graphite sheet under a (+) current and subsequently reduced to become a gas. During this process, the weak bonds connecting the layers of graphite were broken and exfoliated, synthesizing graphene.

[0059] At this time, 5 cm 2 The time required for all the graphite sheets to be peeled off is approximately 5 hours or more, and when the peeling reaction is finished, the power supply shows a voltage limit of 20 V. The reaction was stopped by assuming that this point in time is the end of the reaction.

[0061] Experimental Example 2: X-ray Diffraction Analysis and Raman Spectroscopy Results

[0062] The graphene and graphite obtained in Experimental Example 1 were separated in ultrapure water using the method of Example 2.

[0063] FIG. 3 is a diagram showing a suspension centrifuged by a manufacturing method according to one embodiment of the present invention, the suspension filtered through a separation membrane, and a comparative example.

[0064] Figure 3 shows samples dispersed in ethanol, 2(A) and 2(B) in which only graphene was separated after dispersion in ethanol to obtain only graphene, and samples dispersed in ultrapure water, 2(C) and 2(D) in which graphite and graphene supernatants were obtained after dispersion in ultrapure water.

[0065] Referring to Figure 3 above, when examining the suspension centrifuged in ethanol and the sample centrifuged in ultrapure water, some interlayer gaps of graphite were found in the supernatant when centrifuged in ultrapure water, and the mass ratio of the included material can be confirmed by referring to Table 1 below.

[0067] Pristine GF separator After filtration Amount of adsorbed material ln 16Ø rGO 204.211mg 209.247mg 5.036mg 0.995mg rGO+Graphite 490.318mg 504.844mg 14.526 mg (ln 36 0.644mg

[0068] Figure 4 shows the X-ray diffraction (XRD) and Raman spectroscopy results of a graphene and graphite mixture and a comparative example obtained by a manufacturing method according to one embodiment of the present invention.

[0069] In the above Figure 4, 4A represents commercial graphite, 4B represents graphene, and 4C represents a mixture of graphite and graphene. Graphite is a commercially purchased powder, and graphene and the mixture of graphite and graphene are samples obtained through Example 2. It can be qualitatively confirmed through the X-ray diffraction analysis results of Figure 4A and the Raman spectroscopy results of Figure 4B that graphite and graphene are mixed in the mixture after centrifugation with ultrapure water.

[0071] Experimental Example 3: Observation of Physical and Electrochemical Properties of the Prepared Electrode

[0072] FIG. 5 is a scanning electron microscope image of a separator-integrated electrode manufactured by a manufacturing method according to one embodiment of the present invention.

[0073] Referring to Figure 5 above, the fabricated electrode can be examined in detail through scanning electron microscope (SEM) images. In Figure 5, a very thin layer of graphene and graphite with a thickness of 1 μm is adsorbed at the bottom of the separator through a simple filtration process, thereby maximizing the lithium plating area above the layer, and it can be seen that the fiber structures within the separator physically prevent the indiscriminate growth of lithium metal.

[0074] Figure 6 is the result of evaluating electrochemical characteristics through various methods by assembling a separator-integrated electrode manufactured by a manufacturing method according to one embodiment of the present invention into a lithium metal battery coin cell.

[0075] In the above Figure 6, 6A and 6B represent the results of electrochemical impedance spectroscopic analysis, 6C represents the constant charge / discharge evaluation, and 6D represents the results of rate capability evaluation, respectively.

[0076] Referring to Figures 6A and 6B, it can be seen that the RSEI of the separator-integrated electrode containing a mixture of graphite and graphene appears very low initially, and it was also confirmed that the Rct value remains significantly low even after many charge-discharge cycles. This indicates that the graphite mixed with graphene acts as a lithium-friendly region through the process of lithium ions being inserted between the layers, which facilitates the even plating of lithium metal and enhances stability. Through Figures 6C and 6D, it can be confirmed that the battery operates normally and exhibits higher performance in terms of rate capability and capacity retention rate compared to when only graphene is used.

[0078] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0079] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A method for manufacturing a separator-integrated electrode, characterized by comprising: a preparation step of preparing a two-electrode system having a graphite sheet as an anode in an electrolyte; a peeling step of applying an oxidation current and a reduction current to the two-electrode system to peel off and reduce the graphite sheet; a centrifugation step of dispersing the obtained graphite and graphene in water and then centrifuging the graphite and graphene; and a filtration step of filtering the supernatant containing the graphene and graphite obtained through centrifugation through a separator for a lithium secondary battery; wherein the water is ultrapure water. Claim 2 A method for manufacturing a separator-integrated electrode according to claim 1, wherein the electrolyte comprises H2SO4, Na2SO4, KOH, Na2MoO4, (NH4)2SO4, or a combination thereof. Claim 3 A method for manufacturing a separator-integrated electrode according to claim 2, characterized in that the electrolyte comprises sulfuric acid with a concentration of 0.1 to 1 M. Claim 4 A method for manufacturing a separator-integrated electrode according to claim 1, wherein the peeling step is characterized by alternately applying the oxidation current and the reduction current. Claim 5 A method for manufacturing a separator-integrated electrode according to claim 4, characterized by applying the oxidation current for 120 to 180 minutes and applying the reduction current for 120 to 180 minutes. Claim 6 A method for manufacturing a separator-integrated electrode according to claim 1, wherein the filtration step is characterized by further adding a conductive material and a binder to the supernatant and filtering. Claim 7 A method for manufacturing a membrane-integrated electrode according to claim 1, characterized in that the filtration is performed by a vacuum filtration method. Claim 8 A method for manufacturing a separator-integrated electrode according to claim 1, wherein the separator is composed of one or more types selected from the group consisting of glass fibers and olefin-based polymers, and is in the form of a sheet or nonwoven fabric. Claim 9 A separator-integrated electrode manufactured by the manufacturing method of claim 1.

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