Ion-conductive lithiated polymer binder and lithium-sulfur battery usable in lean electrolyte comprising same

Abstract

The present invention relates to an ion conductive lithiated polymer binder and a lithium-sulfur battery usable in a lean electrolyte and, more specifically, to a lithium-sulfur battery exhibiting high performance even in a lean electrolyte, manufactured using a sulfur positive electrode material including an ion conductive lithiated polymer binder in which a tragacanth polymer is lithiated by ion exchange with LiOH.

Description

Lithium-sulfur battery usable in ion-conducting lithiated polymer binder and lean electrolyte containing same

[0001] The present invention relates to a lithium-sulfur battery usable in an ion-conductive lithiated polymer binder and a lean electrolyte, and more particularly, to a lithium-sulfur battery that exhibits high performance even in a lean electrolyte manufactured using a sulfur cathode material including an ion-conductive lithiated polymer binder.

[0002]

[0003] Among next-generation secondary battery technologies capable of achieving high energy densities, lithium-sulfur secondary batteries are attracting attention due to their high commercialization potential compared to other technologies. A lithium-sulfur secondary battery is a battery system that uses sulfur as the positive active material and lithium metal as the negative active material. When a lithium-sulfur secondary battery discharges, the sulfur in the positive electrode accepts electrons and is reduced, while the lithium in the negative electrode is oxidized and ionized. This electrochemical reaction achieves a theoretical energy density of 2,600 Wh / kg, 10 times that of lithium-ion batteries. However, many issues remain, including the high solubility of lithium polysulfide, poor cycle life and output characteristics, low electrical conductivity of sulfur, and reduced stability due to the use of lithium metal.

[0004] A feasible alternative is to maximize sulfur utilization under lean electrolyte conditions. However, maximizing sulfur utilization requires overcoming the interface between sulfur and carbon, electrolyte, and binder components. To date, efforts have been made to address this interfacial issue through doping with heteroatoms, metal oxides, phosphides, nitrides, and sulfides. To more effectively increase the energy density of lithium-sulfur batteries, the role of the active binder in ion balance in multicomponent interfacial engineering is crucial when designing efficient sulfur anodes.

[0005] Ion-conducting polymers exhibit attractive advantages of ionic environment and ion conduction at the sulfur-binder-electrolyte interface through lithium ion hopping across adjacent polymer chains. Several unique lithium-ion conducting polymers, including polyethylene oxide (PEO), sulfonated tetrafluoroethylene copolymer (Nafion), polyacrylic acid (PAA), polyquaternium-10, and lithiated-PAA, have been reported for lithium-sulfur and lithium-ion batteries, with the adoption of these conducting polymers demonstrating high ionic conductivity in the range of 3–8 mg / cm. 2 Although the accessibility to sulfur particles was clearly improved even at high sulfur contents, the problem of excessive use of a large amount of electrolyte, which negatively affects the energy density of lithium-sulfur batteries, occurred. Designing an active ion-conducting polymer for lithium-sulfur batteries should focus on providing excellent ion transport, limiting the diffusion of polysulfides, mitigating volume changes, and making it mechanically robust. Therefore, the presence of an appropriate ionic environment at the sulfur interface through an active ion-conducting binder can provide additional ion conduction paths in thick electrodes and replenish the lithium ions that are lacking in lean electrolyte conditions.

[0006] Accordingly, based on the above background technology, the inventors of the present invention have completed the present invention of manufacturing a sulfur electrode including a novel ion-conductive lithiated polymer binder and using the same to manufacture a lithium sulfur battery capable of supplementing lithium ions in a lean electrolyte state.

[0007]

[0008] An object of the present invention is to provide an ion-conductive lithiated polymer binder characterized in that the tragacanth polymer is lithiated by ion exchange with LiOH.

[0009]

[0010] It is also an object of the present invention to provide a lithium-sulfur battery usable in a lean electrolyte comprising an ion-conductive lithiated polymer binder as a sulfur cathode material.

[0011]

[0012] The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0013]

[0014] To solve the above problems, the present invention provides an ion-conductive lithiated polymer binder characterized in that the tragacanth polymer is lithiated by ion exchange with LiOH.

[0015] The above ion-conductive lithiated polymer binder is characterized in that it comprises 85 to 95 parts by weight of the tragacanth polymer and 5 to 15 parts by weight of the LiOH, based on 100 parts by weight of the total of the ion-conductive lithiated polymer binder.

[0016]

[0017] The present invention also provides a lithium-sulfur battery usable in a lean electrolyte comprising an ion-conductive lithiated polymer binder as a sulfur cathode material.

[0018] The above sulfur cathode material is characterized in that it comprises 75 to 85 parts by weight of a sulfur / carbon composite, 10 to 20 parts by weight of a conductive material, and 1 to 10 parts by weight of the ion-conductive lithiated polymer binder, based on 100 parts by weight of the total sulfur cathode material.

[0019] The above sulfur anode material has a thickness of 30 to 350 ㎛ and a sulfur loading amount of 0.5 to 20 mg / cm 2 It is characterized by including.

[0020] The above lithium-sulfur battery is characterized in that continuous lithium ion release or donation is possible during discharge by the ion-conductive lithiated polymer binder, and subsequent lithium ion replenishment is possible through charging.

[0021] The lithium-sulfur battery has a sulfur loading of 7 to 9 mg / cm in the lean electrolyte. 2 When using 55 to 65% of sulfur in a thick sulfur cathode material, it is characterized by exhibiting a capacity of 950 to 1100 mAh / g.

[0022] The above lean electrolyte is characterized by an electrolyte / sulfur ratio of 5 to 7 μl / mg.

[0023] The above lithium-sulfur battery can be manufactured into a pouch cell, and the manufactured pouch cell is characterized by exhibiting an energy density of 300 to 400 Wh / kg.

[0024] The lithium-sulfur battery manufactured with the above pouch cell has a sulfur loading amount of 4 to 6 mg / cm in a lean electrolyte with an electrolyte / sulfur ratio of 4 to 5 μl / mg. 2 It is characterized by being.

[0025]

[0026] By means of solving the above problem, the present invention can provide an ion-conductive lithiated polymer binder characterized in that the tragacanth polymer is lithiated by ion exchange with LiOH.

[0027] The present invention also provides a lithium-sulfur battery usable in a lean electrolyte comprising an ion-conductive lithiated polymer binder as a sulfur cathode.

[0028]

[0029] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0030]

[0031] FIG. 1 is a conceptual diagram of the interface, sulfur reactivity, electrochemical cycling, and manufacturing of a thick ICLP / sulfur anode material manufactured according to a manufacturing example of the present invention.

[0032] Figure 2 is a graph analyzing lithium ion dissolution of a sulfur cathode material manufactured using an ion-conductive active binder manufactured according to a manufacturing example of the present invention.

[0033] Figure 3 is a graph analyzing the electrochemical characteristics of a sulfur cathode material manufactured according to thickness using an ion-conductive active binder manufactured according to a manufacturing example of the present invention.

[0034] FIG. 4 is a graph analyzing the effects of continuous Li donation and excess sulfur reaction at various E / S ratios on the cycling performance of an ICLP / sulfur battery manufactured according to a manufacturing example of the present invention.

[0035] Figure 5 is a graph comparing and analyzing the mechanical and chemical properties of ICLP / sulfur cathode materials and PVDF / sulfur cathode materials manufactured according to a manufacturing example of the present invention.

[0036] FIG. 6 is a graph analyzing the electrochemical characteristics of a lithium-sulfur pouch cell usable in a lean electrolyte manufactured according to a manufacturing example of the present invention.

[0037]

[0038] The terms used in this specification will be briefly explained, and the present invention will be described in detail.

[0039] The terms used in this invention have been selected from widely used, common terms, taking into account their functions. However, these terms may vary depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. Therefore, the terms used in this invention should be defined based on their meaning and the overall content of the invention, rather than simply their names.

[0040] When a part of a specification is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0041] Below, with reference to the attached drawings, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0042] Specific details, including the problems to be solved, means of solving them, and the effects of the invention, are included in the embodiments and drawings described below. The advantages and features of the present invention, and methods for achieving them, will become clearer with reference to the embodiments described below in detail, along with the accompanying drawings.

[0043] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0044]

[0045] The present invention provides an ion-conducting lithiated polymer binder (ICLP binder) characterized in that a tragacanth (TG) polymer is lithiated by ion exchange with LiOH.

[0046] The ion-conductive lithiated polymer binder preferably comprises 85 to 95 parts by weight of the tragacanth polymer and 5 to 15 parts by weight of the LiOH, based on 100 parts by weight of the total of the ion-conductive lithiated polymer binder, but more preferably comprises 90 parts by weight of the tragacanth polymer and 10 parts by weight of the LiOH.

[0047] The above tragacanth (TG) polymer may use one kind of tragacanth gum selected from the group consisting of Astragalus parrowianus, Astragalus gossypinus, Astragalus rabensis, Astragalus fluccosus, Astragalus microcephalus, and Astragalus compactus.

[0048] The above tragacanth polymer can be dissolved in an aqueous solvent for 11 to 13 hours and then swelled to form a gel.

[0049] The above ion-conductive lithiated polymer binder is preferably lithiated by adding the LiOH solution to the tragacanth polymer formed into the gel and stirring at 19 to 21°C for 1 to 3 hours, but it is more preferably lithiated by adding the LiOH solution to the tragacanth polymer formed into the gel and stirring at 20°C for 2 hours.

[0050] The above ion-conductive lithiated polymer binder preferably includes a process of obtaining the above lithiated tragacanth polymer by drying it at 60 to 70° C., but more preferably, the above ion-conductive lithiated polymer binder may include a process of obtaining the above lithiated tragacanth polymer by drying it at 65° C.

[0051]

[0052] The present invention also provides a lithium-sulfur battery usable in a lean electrolyte comprising an ion-conductive lithiated polymer binder as a sulfur cathode material.

[0053] The above sulfur cathode material preferably comprises 75 to 85 parts by weight of a sulfur / carbon composite, 10 to 20 parts by weight of a conductive material, and 1 to 10 parts by weight of the ion-conductive lithiated polymer binder, based on 100 parts by weight of the total sulfur cathode material, but it is more preferably comprised of 80 parts by weight of a sulfur / carbon composite, 15 parts by weight of a conductive material, and 5 parts by weight of the ion-conductive lithiated polymer binder.

[0054] It is preferable that the above sulfur / carbon complex be a mixture of sulfur and carbon in a mass ratio of 7:3.

[0055] The above-mentioned conductive material may be selected from the group consisting of graphene, multi-walled carbon nanotubes (MWCNTs), porous carbon, and mixtures thereof, but multi-walled carbon nanotubes (MWCNTs) are preferably selected.

[0056] The above sulfur / carbon complex can be melted and infiltrated under an inert gas atmosphere, and the inert gas can be selected from nitrogen, argon and helium, and nitrogen is preferably selected.

[0057] The above melting and infiltration is preferably performed at 150 to 160°C for 11 to 13 hours, but is more preferably performed at 155°C for 12 hours.

[0058] The above ion-conductive lithiated polymer binder can be prepared as a viscous slurry by dispersing it in deionized water.

[0059] It is preferable that the above-mentioned sulfur cathode material be manufactured by casting a slurry containing the above-mentioned manufactured sulfur / carbon composite, the above-mentioned conductive material, and the above-mentioned ion-conductive lithiated polymer binder on an aluminum current collector.

[0060] The above aluminum current collector is preferably 16 to 18 μm thick, but is more preferably 17 μm thick.

[0061] The above-mentioned sulfur anode material is preferably dried at 60 to 80°C for 11 to 13 hours in a vacuum oven, but more preferably, it can be dried at 70°C for 12 hours.

[0062] The above sulfur anode material has a mass of 1.1 to 1.3 mg / cm 2 It could be.

[0063] The above sulfur anode material has a thickness of 30 to 350 ㎛ and a sulfur loading amount of 0.5 to 20 mg / cm 2 It is preferable to include a thickness of 100 to 300 ㎛ and a sulfur loading of 1.2 to 15 mg / cm 2 It is more desirable to include this.

[0064] The above lithium-sulfur battery may be capable of continuous lithium ion release or donation during discharge by the ion-conductive lithiated polymer binder, and subsequent lithium ion replenishment may be possible by charging.

[0065] The lithium-sulfur battery has a sulfur loading of 7 to 9 mg / cm in the lean electrolyte. 2 When using 55 to 65% sulfur in a thick sulfur cathode material, it is desirable to exhibit a capacity of 950 to 1100 mAh / g.

[0066] The above lean electrolyte preferably has an electrolyte / sulfur ratio of 5 to 7 μl / mg, but more preferably has an electrolyte / sulfur ratio of 6 μl / mg.

[0067] The above lithium-sulfur battery can be manufactured into a pouch cell, and the manufactured pouch cell can exhibit an energy density of 300 to 400 Wh / kg.

[0068] The lithium-sulfur battery manufactured with the above pouch cell has a sulfur loading amount of 4 to 6 mg / cm in a lean electrolyte with an electrolyte / sulfur ratio of 4 to 5 μl / mg. 2 It could be.

[0069] The above pouch cell may be a stack composed of a sulfur cathode material including the ICLP, a lithium metal anode material, and a polypropylene separator.

[0070] The above pouch cell may be 6 to 7 cm in length and 1 to 2 cm in width, and preferably 6.5 cm in length and 1.5 cm in width.

[0071]

[0072] Hereinafter, to aid understanding of the present invention, examples will be given in detail. However, the following examples are intended only to illustrate the scope of the present invention and are not intended to limit its scope. These examples are provided to more fully explain the present invention to those of average skill in the art.

[0073]

[0074] <Manufacturing Example 1> Fabrication of ion-conducting lithiated polymer binder (ICLP binder)

[0075] An ion-conducting lithiated polymer binder (ICLP binder) was prepared by ion-exchange with a tragacanth polymer binder and LiOH. Tragacanth (TG) powder was dissolved in an aqueous solvent at room temperature for approximately 12 hours to prepare a tragacanth solution. The dissolved tragacanth became a homogeneous, viscous gel over time, and a LiOH solution (10 wt.% LiOH based on the polymer mass) was slowly added to the tragacanth polymer gel. The mixture was stirred at 20°C for approximately 2 hours and dried at 65°C under vacuum to recover the ICLP binder solid particles. ICLP binders were prepared with various lithium (Li) contents depending on the Li / TG weight ratio (10:90, 20:80, 30:70, and 40:70).

[0076]

[0077] <Manufacturing Example 2> ICLP / Sulfur Cathode Manufacturing

[0078] Sulfur and carbon were mixed in a mass ratio of 7:3 and melt-infiltrated at 155°C for 12 hours under a nitrogen flow (100 ml / min) to prepare a sulfur / carbon (S / C) composite. The S / C composite thus prepared, multi-walled carbon nanotubes (MWCNTs), and the ICLP binder of Preparation Example 1, which was dispersed in deionized water to prepare a viscous slurry, were mixed in a mass ratio of 80:15:5 to prepare a viscous slurry. The prepared slurry was cast on a washed aluminum (17 μm) current collector, and thin or thick sulfur cathodes were prepared by controlling the lamination thickness. The electrodes were dried in a vacuum oven at 70°C for 12 hours and then fabricated into electrodes of the desired size. The mass of the tragacanth / ICLP-based sulfur electrode (ICLP / S) was 1.1–1.3 mg / cm. 2 am.

[0079]

[0080] <Comparative Example 1> Manufacturing of PVDF / sulfur anode material

[0081] A PVDF / sulfur cathode material was manufactured using the same method as in Manufacturing Example 2 above, but using a PVDF binder. At this time, the PVDF binder was dispersed in N-methylpyrrolidone (NMP) and used, and the mass of the manufactured PVDF / sulfur cathode material was approximately 0.9 to 1.1 mg / cm 2 am

[0082]

[0083] <Comparative Example 2> Preparation of a non-lithiated tragacanth-sulfur electrode

[0084] A non-lithiated tragacanth-sulfur electrode was manufactured using the same method as in Manufacturing Example 2 above, but using a non-lithiated tragacanth polymer binder.

[0085]

[0086] <Example 1> Evaluation of electrode characteristics

[0087] The surface morphology and cross-sectional characteristics of the electrodes manufactured according to the above manufacturing examples and comparative examples were observed through a field emission scanning electron microscope (FESEM, TESCAN MIRA3), and the changes in various electrochemical polysulfides and lithium ion environments related to the state of discharge (DOD) and state of charge (SOC) were tested through a UV-Vis spectrometer, a SCINCO Neosys-2000 spectrometer, and a 7Li nuclear magnetic resonance (NMR, Bruker AV-500) spectrometer. The internal morphology and microstructure of the sulfur electrode were imaged through a focused ion beam scanning electron microscope (FIB-SEM, TESCAN AMBER) using Ga as an ion source, and the chemical composition and functional groups of the polymer were characterized in the spectral range 4000-500 cm -1FT-IR, Perkin Elmer UATR2 spectrometer was used for the analysis. Contact angle measurements were performed with a contact angle meter (Phoenix 300, SEIO) using an ether-based electrolyte at 25°C, and changes in the valence state and chemical environment of the sulfur cathode material during electrochemical cycling were analyzed by an X-ray photoelectron spectrometer (XPS, Thermo Ficher Scientific, NEXSA) equipped with Al Kα (hν = 1486.6 eV) radiation with a pass energy of 50 eV, and the XPS data were acquired using AVANTAGE software, and each deconvolution and fitting were performed in Origin 9.0 graphics and analysis software.

[0088]

[0089] <Manufacturing Example 3> Manufacturing of a pouch-type Li-S cell

[0090] The pouch-type Li-S cell is composed of a single stack of the ICLP / S cathode material of Manufacturing Example 2, a triple-layer polypropylene separator, and an expanded Li anode material. To fabricate the pouch-type Li-S cell, the stack was placed inside a prefabricated aluminum laminate package, the tabs were pulled out, and the side of the aluminum laminate package was sealed using a heat press. Then, an amount of electrolyte (1 M LiTFSI in DOL:DME containing 2% LiNO3) calculated based on the electrolyte / sulfur (E / S) ratio was permeated into the stack, and the other side of the aluminum laminate package was sealed again using a heat press to complete the pouch-type Li-S cell. The fabricated pouch-type Li-S cell had a size of approximately 6.5 cm x 1.5 cm (cm in length x cm in width).

[0091]

[0092] <Example 2> Electrochemical Characteristics Analysis

[0093] To evaluate the electrochemical performance, a coin-type CR2032 cell or a pouch-type cell of the above-mentioned manufacturing example 3 was used. The cells were assembled and disassembled in an argon-filled glove box with O2 and H2O controlled to less than 0.5 ppm. Typically, the assembly of a coin cell is fabricated in a pattern using a manufactured sulfur electrode as a positive electrode material and a pure Li foil with the oxide film removed as a negative electrode material, separated through a polypropylene separator. The stack (positive electrode material, negative electrode material, separator) contains electrolyte and a sulfur (S) ratio (E / S: 4 to 15 μL / mg s) was used to infiltrate and press the liquid electrolyte based on the mass of sulfur determined through the electrochemical cell ion exchanger. The electrolyte, consisting of 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, was dissolved in a mixture of anhydrous solvents 1,3 dioxolane (DOL) and 1,2-dimethoxymethane (DME) in a 1:1 (v / v) ratio and 2% LiNO3 as an additive. The assembled coin cells were aged at room temperature for approximately 2 h and then electrochemically tested, and all electrochemical characterizations were performed in a humidity- and temperature-controlled chamber maintained at 25°C. Additionally, galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), and galvanostatic intermittent titration technique (GITT) for electrochemical performance evaluation were performed on an automatic multichannel battery cycler (WBCS3000, WonATech), and electrochemical impedance spectroscopy (EIS) tests were performed on a modular galvanostat / potentiostat (PGSTAT204, METROHM) at an open-circuit voltage in the frequency range of 1 MHz to 0.01 Hz at an AC amplitude of 5 mV. GCD experiments were recorded over a voltage range of 1.7 V to 2.8 V at each current rate relative to the mass of sulfur (1 C = 1675 mAh / g). Cyclic voltammetry tests were performed over a voltage window of 1.7 V to 2.8 V at a scan rate of 0.1 mV / s, and GITT tests were performed at OCV with a lower cutoff voltage of 1.7 V for discharge and at 2.8 V for charge, with 5-minute intervals and 1-minute delay.

[0094]

[0095] <Experimental Example 1> Characteristics of a sulfur electrode containing an ion-conductive lithiated polymer binder (ICLP)

[0096] In order to confirm the role of lithium ions in the ICLP binder manufactured according to the above Manufacturing Example 1, a constant current discharge-charge experiment was performed at an E / S ratio of 8 μL / mg and a current rate of 0.3 C (1 C = 1675 mAh / g), and the results were analyzed as shown in Fig. 2a. The discharge-charge profile for the ICLP / sulfur cathode material of the above Manufacturing Example 2 showed a reliable high-voltage plateau up to 2.05 V, which means that the S8→Li2S4 (solid→liquid) conversion consumed about 60.85% (20.24% of the total) of sulfur, which is equivalent to a specific capacity of 255 mAh / g (theoretical capacity of S8→Li2S4 = 419 mAh / g). In contrast, the PVDF / sulfur cathode material of Comparative Example 1 exhibited a short-lived S8→Li2S8 followed by a limited Li2S8→Li2S4 conversion utilizing about 27.44% of the active sulfur, which was 55% lower than that of the ICLP / sulfur cathode material. After that, the PVDF / sulfur cathode material consumed about 28.02% of sulfur in the Li2S4→Li2S (liquid→solid, theoretical capacity=1256 mAh / g) conversion, resulting in a specific capacity of 352 mAh / g, whereas the ICLP / sulfur cathode material consumed about 45.46% of sulfur, resulting in a specific capacity of 571 mAh / g compared to the theoretical capacity of 74.98%. Additionally, the charging process of the ICLP / sulfur cathode material follows a high sulfur reconversion with excellent reversibility of 93%, and the charge overpotential of the ICLP / sulfur cathode material is 2.35 V, which indicates that the solid Li2S precipitate is tightly bound to the polymer backbone, thereby keeping the electrode surface largely exposed to the charging process.

[0097] In addition, the dissolution of polysulfides during discharge (S8→Li2S6→Li2S4→Li2S2→Li2S) or charge (Li2S→Li2S4→Li2S6→Li2S8 / S8) for various depths of discharge (DOD) and states of charge (SOC) was tested and shown in Figs. 2b and 2c. The electrochemically induced polysulfides for the recovered ICLP / sulfur cathode material of Preparation Example 2 exhibited a faint yellow color, confirming that the disulfide dissolution was well controlled in a series of DOD and SOC conditions. The PVDF / sulfur cathode material of Comparative Example 1 showed a faint yellow color that became darker as S8→Li2S4 and Li2S increased, and this continued during the charging process. In addition, the UV spectroscopy result of Fig. 2c shows that the ICLP of Preparation Example 1 can still bind with polysulfides.

[0098] Figure 2d shows the reversible lithium ion release and replenishment during electrochemical cycling in lean electrolyte, and to confirm this, the DOD corresponding to the plateau at high S8→Li2S4 and low Li2S4→Li2S and the SOC at Li2S→Li2S4 and Li2S4→Li2S8 / S8 for the recovered ICLP / sulfur cathode material. 7 Analysis was performed using Li NMR, and is shown in Fig. 2e. The ICLP exhibited a single lithium resonance peak located at 0 ppm and an electron-shielding Li nuclei peak located at -0.46 ppm, and it can be confirmed that the integrated intensity of the NMR peak is directly proportional to the amount of lithium in the polymer and the recovered electrode.

[0099] As shown in Fig. 2f, the lithium content of the DOD decreased by approximately 6.21% as the conversion from S8 to Li2S progressed, and then the Li concentration increased to 3.83% until the SOC was semi-charged to 2.63 V while the conversion from Li2S to Li2S8 / S8 progressed. The results indicate the reversible provision and participation of lithium ions that promote the discharge-charge process of the ICLP / sulfur electrode in a lean electrolyte.

[0100]

[0101] <Experimental Example 2> Evaluation of the electrochemical correlation between thick ICLP / sulfur anode materials and lean electrolytes

[0102] Manufactured as in the above manufacturing example 2, but manufactured with ICLP / sulfur anode materials of various thicknesses to measure electrochemical properties. 7 Li was analyzed using NMR and electrochemical impedance spectroscopy (EIS).

[0103] As shown in Fig. 3a, the manufactured ICLP / sulfur cathode material has a thickness of 100 to 300 μm and an active sulfur mass of 1.2 to 15 mg / cm 2 was manufactured with.

[0104] As shown in Fig. 3b and Fig. 3f, the thin ICLP / sulfur cathode material (1.2 mg / cm) was prepared under E / S ratios of 4, 6, and 8 μL / mg and excess conditions (approximately 15 μL / mg). 2 ) have charge transfer resistances (Rct) of 253.46, 218.02, 196.07, and 109.59 Ω / cm. 2 as As it appears It was found that the Rct gradually decreased. This is a typical characteristic of thick sulfur electrodes in general dilute electrolytes, but the Rct differences between E / S ratios of 4, 6, and 8 μL / mg and excess conditions (approximately 15 μL / mg) were 57.39 and 86.48 Ω / cm, respectively. 2It was confirmed that the ICLP / sulfur anode material remained closer to the substrate, indicating a favorable and reduced ion transport resistance within the ICLP / sulfur anode material.

[0105] Also 1.2, 2.2, 3.8, 5.1 mg / cm 2 The resistance characteristics of thick ICLP / sulfur anode materials with active sulfur content were tested at various E / S ratios of 4, 6, and 8 μL / mg, and are shown in Figs. 3c, 3d, and 3e. At an E / S ratio of 4 μL / mg, The Rct of ICLP / sulfur anode material is 256.12, 375.6, 439.16, and 520.01 Ω / cm 2 It showed a high resistance value.

[0106] However, as shown in Fig. 3g, when the E / S ratio increases to 6 and 8 μL / mg, the Rct value tends to decrease, indicating that the liquid electrolyte is sufficiently permeated. When the E / S ratio is 6 and 8 μL / mg, the Rct values ​​are approximately 457.4 and 464.2 Ω / cm, respectively. 2 , with a high sulfur content of 5.1 mg / cm 2 The values ​​of Rct at different E / S ratios are similar due to the penetration of the liquid electrolyte into the DOD, which is caused by the continuous supply of lithium ions by the spatially located active ICLP binder, alleviating the resistance caused by the lean electrolyte, and the donation of lithium ions by the lithiated polymer is maintained uniformly across the sulfur electrode regardless of the electrode thickness.

[0107] Also, R according to the E / S ratio of 4, 6, and 8 μL / mg of the ICLP / sulfur cathode material ion (ionic resistance) was analyzed and shown in Fig. 3h. The above R ion silver Sulfur mass is 1.2 mg / cm 2The E / S ratio of the ICLP / sulfur electrode was 10.30 and 9.98 Ω / cm at 6 μL / mg and 8 μL / mg, respectively. 2 , but at a low E / S ratio of 4 μL / mg, the ionic resistance was 23.84 Ω / cm. 2 In particular, in the thick ICLP / sulfur cathode material, the E / S ratio was 9.98 Ω / cm at 8 μL / mg. 2 As R ion A sharp decrease was observed, which indicates the maximum utilization of lithium ion donation in ICLP, and the ratio of active sulfur to Li ions utilized in ICLP tends to be more efficient at E / S 8 μL / mg due to the relatively excess liquid electrolyte volume than at E / S ratios of 4 and 6 μL / mg. Therefore, as shown in Fig. 3i, lithium ions must be provided to the electrolyte from within the thick sulfur cathode material in order to continuously utilize the Li ions of the ICLP binder in zone II.

[0108]

[0109] <Experimental Example 3> Effects of Continuous Li Donation and Excess Sulfur Reaction on the Cycling Performance of Lithium-Sulfur Batteries at Various E / S Ratios

[0110] The effect of lithium donation on the cycling performance of lithium-sulfur batteries at various E / S ratios was analyzed by electrochemical cross-sectional tomography through constant current discharge-charge experiments.

[0111] As shown in Fig. 4a, the voltage polarization of the ICLP / sulfur cathode material of Manufacturing Example 2 was confirmed according to various E / S (4, 6, 8, and 10 μL / mg) at current rates C / 3 and 1C. At a low current rate C / 3, the polarization of all ICLP / S electrodes was less than 0.28 V, and the difference between the E / S ratios of 6 and 8 μL / mg was 0.02 V. In addition, as the current rate increased to 1C, the polarization of the ICLP / S electrode was confirmed to increase to approximately 0.38 V, 0.41 V, and 0.43 V.

[0112] Figure 4b is Q H The specific capacity values ​​derived in relation to (high stability) were measured as E / S dependent capacity, Q H It was confirmed that the capacity increased from 272 mAh / g at 4 μL / mg of E / S to 338 mAh / g at 8 μL / mg of E / S.

[0113] Figure 4c shows the long-term cycling stability of the ICLP / sulfur cathode materials for various E / S ratios tested at a current rate of C / 3. The ICLP / sulfur cathodes for all various E / S ratios exhibited excellent cycling stability until the end of 150 discharge-charge cycles, and especially at a limited electrolyte volume of 4 μL / mg E / S, the capacity trend increased over the initial few cycles compared to the capacity decay typically observed at excessive electrolyte volume due to the persistent wettability. At a current rate of C / 3, the sulfur utilization rates followed the trend of 8 > 6 > 4 μL / mg, and the specific capacities were 811, 776, and 661 mAh / g, respectively. Additionally, the sulfur utilization remained relatively stable even with increasing cycles, remaining at 42.93%, 41.41%, and 37.83% at the end of 150 cycles. The specific capacities at an E / S ratio of 4 μL / mg were confirmed to be almost maintained at 115 mAh / g and 150 mAh / g, respectively, compared to E / S ratios of 6 and 8 μL / mg.

[0114] In Fig. 4d, all ICLP / sulfur cathodes with various E / S ratios of 4–8 μL / mg at a high current rate of 1C exhibited similar capacity increase trends up to cycles 86, 46, and 32, which is due to the continuous and wettability-dependent kinetics. The amounts of sulfur utilized during the initial cycles were about 28.82%, 24.65%, and 24.11%, corresponding to capacities of 483 mAh / g and 413 mAh / g for E / S ratios of 8, 6, and 4 μL / mg, respectively, and the sulfur utilization was maintained at a fairly high level for more than 500 cycles with low capacity decay rates of 0.024%, 0.014%, and 0.018% per cycle, respectively.

[0115] Lithium ion exchange capacity at high sulfur loading of 3.7 mg / cm 2 ~ 8.1 mg / cm 2Further experiments were performed on the ICLP / sulfur anode material as shown in Fig. 4e. The E / S ratio was 3.7 mg / cm at 6 μL / mg. 2 , 5.3 mg / cm 2 and 8.1 mg / cm 2 of The thick sulfur cathode exhibited specific capacities of 793, 964, and 1021 mAh / g, and sulfur utilizations of 47.34%, 57.55%, and 60.89% of the theoretical limit (when 1675 mAh / g is 100%).

[0116] In order to confirm the influence of ion exchange on improved electrochemical performance, the PVDF / sulfur cathode material of Comparative Example 1, the non-lithiated tragacanth / sulfur cathode material of Comparative Example 2, and the ICLP / sulfur cathode material were tested as shown in Fig. 4f. At an E / S ratio of 8 μL / mg, the sulfur utilization was the highest at approximately 47.8% for the ICLP / sulfur cathode material, followed by the PVDF / sulfur cathode material at 17.98%.

[0117] In addition, the sulfur utilization rates of the PVDF / sulfur anode material of Comparative Example 1 and the ICLP / sulfur anode material were confirmed at E / S ratios of 12 and 8 μL / mg in FIG. 4g, and the PVDF / sulfur anode material showed sulfur utilization rates of 35.17% and 17.98%, respectively, which were confirmed to be 48.43% lower than the sulfur utilization rate of the ICLP / sulfur anode material.

[0118] Figures 4h, 4i, and 4j were analyzed using FIB-SEM to confirm the internal pore space, voids, and micro-nano-structural changes of the ICLP / sulfur cathode material under discharge conditions. The cross-sectional FIB-SEM image of the fresh ICLP / sulfur cathode material, which has a significant pore space and voids essential for electrolyte filtration and wetting, was confirmed, as was the FIB-SEM image of the cycled ICLP / sulfur cathode material (at a current rate of C / 3). In addition, the degree of liquid electrolyte access and sulfur reactivity in the internal changes of the ICLP / sulfur cathode material before and after discharge were confirmed. The distribution pattern showed that the electrode was partially wetted, and compositional changes occurred in the subsequent region due to discharge, but some regions in contact with the current collector still did not react. This shows that the ICLP / sulfur cathode material exhibits microstructural characteristics favorable for electrolyte wetting related to the utilization of the Li ion environment of the lithiated polymer.

[0119]

[0120] <Experimental Example 4> Analysis of mechanical and chemical properties of PVDF binder or ICLP binder and cathode materials manufactured using them, respectively.

[0121] The adhesion and mechanical stability of the PVDF binder of Comparative Example 1 and the ICLP binder of Manufacturing Example 1 are compared, as shown in FIGS. 5a and 5b. The ICLP binder remained stable in an ether-based electrolyte, and a smooth, crack-free surface was exposed when the electrolyte solvent was completely evaporated. In contrast, the PVDF binder developed micrometer cracks when the electrolyte solvent was completely removed, which may have adverse effects during electrochemical cycling.

[0122] In addition, when the PVDF binder and the ICLP binder were dissolved in the respective solvents N-methyl pyrrolidone (NMP) and water, the ICLP binder retained the inherent characteristics of a lithiated slurry form, and when the solvents of both binders were removed, the same results as in the above-described Fig. 5a were shown. This indicates that the ICLP binder is more suitable for developing a solid and very thick sulfur cathode material.

[0123] In addition, the contact angles of the sulfur cathode materials manufactured using the PVDF binder and the ICLP binder were measured and shown in Fig. 5c. The ICLP / sulfur cathode materials showed contact angles of 21°±2° and 8°±1° for aqueous media and electrolyte solutions, respectively, demonstrating excellent wettability, which is an essential characteristic for hydrophilicity of the modified binder for polysulfide capture.

[0124] In addition, the surface chemical composition of the lithiated polymer of the ICLP binder and the successful lithiation of the ICLP binder were investigated using Fourier transform infrared spectroscopy (FT-IR) and 7 Li NMR analysis was performed and shown in Fig. 5d and Fig. 5e. 1630 cm -1 The peak observed in the vicinity corresponds to the carboxylate group and shows a notable high wavenumber shift in the lithiated polymer. This is due to Li + Cations and COO - This is because the dissociation of the anion is enhanced, and this high mobility is due to Li + This is due to the ion-dipole interaction between the cation and carboxyl oxygen, which shows that the lithiation of the polymer was successful. The lithiation of the ICLP binder has a middle 0 ppm peak and -(negative value) ppm due to the electron shielding around the lithium peak and single lithium resonance. 7This was confirmed through Li NMR analysis. This shows that the ICLP binder exists as -COOLi and that a lithium environment is donated during electrochemical cycling.

[0125] The surface structures, such as morphology and pore structure, of the ICLP binder and PVDF binder films were examined using FE-SEM. As shown in FIGS. 5f and 5g, the ICLP binder film exhibited a smooth, continuous network, whereas the PVDF binder film was stiff and comprised of large pores. Meanwhile, the sulfur cathode material manufactured using the PVDF binder had exposed wide cracks, whereas the sulfur cathode material manufactured using the ICLP binder exhibited a smooth, crack-free surface. The smooth, crack-free electrode of the sulfur cathode material manufactured using the ICLP binder demonstrates the robustness of the ICLP required to cope with the volume change of active sulfur particles during electrochemical cycling.

[0126] The cross-sections of the new and cycled state electrodes of the thin and thick ICLP / sulfur electrodes were confirmed by FE-SEM, as shown in Fig. 5h. The microscope images of the thin and thick ICLP / sulfur electrodes showed a solid structure, and 1.2 mg / cm 2 , 2.2 mg / cm 2 and 5.1 mg / cm 2 The sulfur masses were included and showed electrode expansions of about 16.27%, 10.33%, and 4.91%, respectively. The volume change tends to be lower as the sulfur mass increases, which may be due to the excess porosity that can help accommodate the volume expansion more efficiently.

[0127] The deconvoluted S 2p and Li of the ICLP / sulfur electrode and the PVDF / sulfur electrode in the discharge and charge states were compared using X-ray photoelectron spectroscopy (XPS), as shown in Fig. 5i. During the discharge process, the deconvoluted S 2p on the surface of the PVDF / sulfur electrode showed relative intensities of terminal (ST) and cross-linked (SB) sulfur and polythionate, whereas the surface of the ICLP / S electrode showed lower intensities of ST and SB, indicating control of polysulfide. As a result, polythionate [SO4] 2- is dominant in the PVDF / sulfur electrode during charging, but [SO4] in the ICLP / sulfur electrode. 2- is significantly reduced [SO3] 2- The relative amount of polysulfides and sulfur was generated from low to high levels during charging, [SO3] 2- The presence of, especially [SO3] - The existence of Li in the above ICLP + Due to the re-donation of cation species (Li + ) favors ion hopping.

[0128]

[0129] <Experimental Example 5> Evaluation of the Electrochemical Characteristics of Lithium-Sulfur Pouch Cells Usable in Dilute Electrolytes

[0130] A lithium-sulfur pouch cell usable in a lean electrolyte was manufactured using an ICLP binder as in Manufacturing Example 3 above (Fig. 6a), and its electrochemical characteristics were evaluated.

[0131] Sulfur cathode materials were manufactured using unlithiated tragacanth polymer binder (pristine), the ICLP binder lithiated with 10 wt% LiOH of Preparation Example 1 (ICLP), and the ICLP binder lithiated with 20 wt% (ICLP-x) or 30 wt% (ICLP-y) of LiOH, and lithium-sulfur pouch cells usable in a lean electrolyte were manufactured including the same, and their specific capacities were compared. As shown in Fig. 6b, the lithium-sulfur pouch cell usable in a lean electrolyte including the unlithiated tragacanth polymer binder exhibited a sulfur utilization of 14.9% (249 mAh / g), whereas the lithium-sulfur pouch cell usable in a lean electrolyte including the ICLP binder of Preparation Example 1 exhibited a sulfur utilization of 46.32% (776 mAh / g), indicating that the specific capacity of sulfur was superior. Additionally, lithium-sulfur pouch cells usable in lean electrolytes containing the ICLP binder lithiated at 20 wt% (ICLP-x) or 30 wt% (ICLP-y) showed higher sulfur utilization than lithium-sulfur pouch cells usable in lean electrolytes containing the non-lithiated tragacanth polymer binder, but the reduced amount of hydrophilic -COOH and -OH groups was found to pose a risk for polysulfide cross-over and mechanical integrity of the binder.

[0132] Sulfur content 3.1 mg / cm 2The lithium-sulfur pouch cell usable in the lean electrolyte, which was fabricated with an ICLP / sulfur cathode material containing , N / P (negative-to-positive): 2, E / S (electrolyte / sulfur): 4.3 μL / mg, and measuring approximately 6.5 cm × 1.5 cm, can display a digital image of the open circuit (Fig. 6c) and illuminate an array of light-emitting diodes (LEDs) (Fig. 6d). In addition, the lithium-sulfur pouch cell usable in the lean electrolyte showed stable cycling performance at a high current rate of C / 5 (typically tested at C / 10 or C / 20), and the capacity was 635 mAh / g even in the last 40 cycles. s The specific capacity of the ICLP / sulfur cathode material was shown (Fig. 6e). In addition, in a lean electrolyte, the specific capacity of the ICLP / sulfur cathode material showed similar results in both coin cells and pouch-type lithium-sulfur cells.

[0133] The ion concentrations and specific capacities of the ICLP / sulfur electrode of the above-described Manufacturing Example 2 and the PVDF / sulfur electrode of the above-described Comparative Example 1 according to thin or thick electrodes or various electrolyte capacities E / S ratios of 4, 6, and 8 μL / mg are compared in FIGS. 6g and 6h. During continuous sulfur conversion, it was confirmed that the lithium-sulfur cell capacity was improved in the limited electrolyte capacity of the E / S ratio of 4 to 8 μL / mg due to the participation of excess lithium ions through the donated lithium ions. In addition, at the E / S ratio of 4 μL / mg, the number of ions available in the electrolyte and sulfur cathode material was 2.408×10 , as shown in FIG. 6h. 18 and 3.01×10 20 It was confirmed that when E / S increases to 8 μL / mg, the ion concentration is 3.058×10 20 It increases to 18.066×10, which is the ion concentration limit under excess conditions. 18This has been shown to approach . This can lead to additional specific capacity by improving the overall sulfur reactivity even with minimal utilization of the ions present in the lithiated polymer.

[0134] Also, as shown in Fig. 6i, the energy density of various electrodes was compared, and the energy density of the ICLP / sulfur cathode material of Manufacturing Example 2 was 1323 Wh / kg, and the energy densities of the tragacanth / sulfur cathode material and the PVDF / sulfur cathode material were 498 Wh / kg and 225 Wh / kg, respectively.

[0135] Also, as shown in Fig. 6j, E / S: 4.3 μL / mg, N / P: 2, sulfur mass 3.1 mg / cm 2 The total energy density of the lithium-sulfur pouch cell including the above was confirmed to be 202 Wh / kg and 324 Wh / kg at current ratios of C / 5 and C / 10.

[0136]

[0137] <ICLP 바인더를 포함하는 두꺼운 황 양극재 지속적인 리튬-이온 방출 및 폴리설파이드(polysulfide) 포획>

[0138] When operating Li-S batteries in a lean electrolyte, the effective utilization of active sulfur is significantly limited by the thick sulfur cathode. Sulfur propagation varies with electrolyte dosage, and the viscosity, ionic conductivity, and deteriorated polarization of the electrolyte inevitably change under lean electrolyte conditions. Typically, the solubility of lithium polysulfides (LiPSs) in lean electrolytes is limited to 8 mols / L, which corresponds to an electrolyte-to-sulfur (E / S) ratio of 3.8 μL / mg, and hinders the active activation of polysulfides in a series of electrochemical reactions involving the liquid-based S8 (solid) → Li2S4 (liquid) → Li2S (solid) transformation. Therefore, the presence of added lithium ions can promote ion transport within the thick sulfur cathode, and the small availability of Li ions from the active polymer binder can be obtained through the lithiated active polymer in the limited ionic environment of the lean electrolyte (Figure 1c). The estimated ion concentration available through the liquid electrolyte is approximately 10 in dilute electrolyte (E / S: 4–8 μL / mg). 18 In the case of PVDF / sulfur anode materials, the dissolution of polysulfide and the oxidation-reduction reaction of sulfur were not sufficiently promoted. In contrast, the ion concentration of the sulfur electrode through the lithiated active polymer was 10 times higher than that of the lean electrolyte. 18 About 10 is added, which is almost twice the ion concentration of 20was reached (Fig. 1d). Consequently, the ions provided from the active polymer as well as those solvated in the electrolyte promote efficient and maximum sulfur electrokinetics in the sulfur electrode applying the lithiated polymer compared to the conventional sulfur electrode. Considering the triple interface of sulfur-binder-electrolyte (Fig. 1e), the lithiated polymer-based cathode material can release lithium ions at the miscibility limit of lithium in the active binder and the electrolyte. This is due to the activation of the lithiated polymer in the spatial environment, which leads to preferential release of lithium ions and their sustained release upon wetting of the electrolyte, and to the enhanced utilization and ion transport of active sulfur in the sulfur electrode (Fig. 1f). The difference in specific capacity during reduction (discharge, △d) and oxidation (charge, △c) of sulfur was about 361 mAh / g for the ICLP / sulfur electrode and 303 mAh / g for the PVDF / sulfur electrode. Additionally, lithiated polymers can be a great advantage in ion exchange strategies as they allow the fabrication of crack-free thick sulfur cathodes (Fig. 1g, h).

[0139]

[0140] While specific aspects of the present invention have been described in detail above, it should be apparent to those skilled in the art that these specific descriptions are merely preferred implementation examples and are not intended to limit the scope of the present invention. Therefore, the actual scope of the present invention is defined by the appended claims and their equivalents. The scope of the present invention is set forth in the claims below, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. An ion-conductive lithiated polymer binder characterized in that the tragacanth polymer is lithiated by ion exchange with LiOH.

2. In paragraph 1, The above ion-conducting lithiated polymer binder, For 100 parts by weight of the total ion-conducting lithiated polymer binder, An ion-conductive lithiated polymer binder characterized by comprising 85 to 95 parts by weight of the tragacanth polymer and 5 to 15 parts by weight of the LiOH.

3. A lithium-sulfur battery usable in a lean electrolyte containing the ion-conductive lithiated polymer binder of paragraph 1 as a sulfur cathode material.

4. In paragraph 3, The above sulfur anode material is, For 100 parts by weight of the above sulfur anode material, A lithium-sulfur battery usable in a lean electrolyte, characterized in that it comprises 75 to 85 parts by weight of a sulfur / carbon composite, 10 to 20 parts by weight of a conductive material, and 1 to 10 parts by weight of the ion-conductive lithiated polymer binder.

5. In paragraph 3, The above sulfur anode material has a thickness of 30 to 350 ㎛ and a sulfur loading amount of 0.5 to 20 mg / cm 2 A lithium-sulfur battery usable in a lean electrolyte, characterized in that it comprises:

6. In paragraph 3, The lithium-sulfur battery is a lithium-sulfur battery usable in a lean electrolyte, characterized in that continuous lithium ion release or donation is possible during discharge by the ion-conductive lithiated polymer binder, and subsequent lithium ion replenishment is possible during charging.

7. In paragraph 3, The lithium-sulfur battery has a sulfur loading of 7 to 9 mg / cm in the lean electrolyte. 2 A lithium-sulfur battery usable in a lean electrolyte, characterized in that it exhibits a capacity of 950 to 1100 mAh / g by utilizing 55 to 65% sulfur in a thick sulfur cathode material.

8. In paragraph 3, A lithium-sulfur battery usable in a lean electrolyte, wherein the lean electrolyte has an electrolyte / sulfur ratio of 5 to 7 μl / mg.

9. In paragraph 3, The above lithium-sulfur battery It can be manufactured with pouch cells, A lithium-sulfur battery usable in a lean electrolyte, characterized in that the above-mentioned manufactured pouch cell exhibits an energy density of 300 to 400 Wh / kg.

10. In paragraph 9, The lithium-sulfur battery manufactured with the above pouch cell has a sulfur loading amount of 4 to 6 mg / cm in a lean electrolyte with an electrolyte / sulfur ratio of 4 to 5 μl / mg. 2 A lithium-sulfur battery usable in a lean electrolyte characterized by:

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