Hollow cobalt sulfide-carbon microsphere and manufacturing method thereof

Abstract

The present disclosure relates to hollow cobalt sulfide-carbon microspheres and a method for manufacturing the same. A hollow cobalt sulfide-carbon microsphere according to one embodiment of the present disclosure can exhibit excellent electrochemical properties. In addition, the method for manufacturing hollow cobalt sulfide-carbon microspheres according to one embodiment of the present disclosure can completely sulfide cobalt even within a short reaction time and effectively suppress the crystal growth of cobalt sulfide.

Description

Technology Field

[0001] The present disclosure relates to hollow cobalt sulfide-carbon microspheres and a method for manufacturing the same. Background Technology

[0002] Metal sulfides are gaining prominence as key elements in the development of advanced technologies across various fields, including biology, medicine, environmental science, and energy storage, due to their abundant active sites, unique structural features, tunable electronic properties, and flexible composition. To overcome the major challenges facing metal sulfides—namely, limited electrical conductivity and electrochemical stability—significant efforts are being concentrated on fabricating metal sulfide complexes using various synthesis methods, such as hydrothermal methods, precipitation, electrodeposition, and spray pyrolysis.

[0003] One critical aspect of metal sulfide synthesis methods is the need for a cost-effective process featuring a continuous workflow. In this regard, spray pyrolysis is emerging as a viable option for synthesizing various nanostructured materials. This method is advantageous for reducing preparation time and producing nanostructured particles through a continuous workflow. However, synthesizing metal sulfides in a single process is difficult because droplets typically decompose within a short time during spray pyrolysis. To address this issue, methods using spray solutions containing high concentrations of sulfur sources have been proposed; however, this leads to increased overall process costs and introduces new problems, such as significantly increased sulfide crystal growth.

[0004] Therefore, there is a need for research and development on synthesis methods for metal sulfides that enable complete sulfation within a short reaction time and effectively inhibit crystal growth. The problem to be solved

[0005] The object of the present disclosure is to provide hollow cobalt sulfide-carbon microspheres and a method for manufacturing the same. means of solving the problem

[0006] To achieve the above objective, the present disclosure provides a hollow cobalt sulfide-carbon microsphere comprising: cobalt sulfide; heteroatoms; and a conductive carbon material.

[0007] The crystal grain size of the cobalt sulfide according to one example of the present disclosure may be 10 nm to 80 nm.

[0008] According to one example of the present disclosure, the heteroatom may be one or more selected from the group consisting of Ni, Cr, Si, Al, W, Na, Cu, and Fe.

[0009] According to one example of the present disclosure, the conductive carbon material may be one or more selected from the group consisting of carbon nanotubes, graphene, graphene oxide (GO), reduced graphene oxide (rGO), MXene, and carbon black.

[0010] According to one example of the present disclosure, the cobalt sulfide and the conductive carbon material may be uniformly distributed within the hollow cobalt sulfide-carbon microspheres.

[0011] In addition, another aspect of the present disclosure provides a method for manufacturing hollow cobalt sulfide-carbon microspheres, comprising the steps of: ball-milling waste cemented carbide sludge in an aqueous sulfuric acid solution to obtain an aqueous cobalt sulfate solution; adding a conductive carbon material and a water-soluble carbon material to the aqueous cobalt sulfate solution to prepare a spray solution; and spray-pyrolyzing the spray solution.

[0012] According to one example of the present disclosure, the aqueous cobalt sulfate solution may contain heteroatom ions.

[0013] According to one example of the present disclosure, the heteroatom ion may be one or more selected from the group consisting of Ni, Cr, Si, Al, W, Na, Cu, and Fe ions.

[0014] The water-soluble carbon material according to one example of the present disclosure may be one or more selected from the group consisting of sugars, polyols, polyethers, and organic acids.

[0015] According to one example of the present disclosure, the concentration of the water-soluble carbon material in the spray solution may be 0.01 M to 1 M.

[0016] According to one example of the present disclosure, the concentration of the conductive carbon material in the spray solution may be 1 mg / ml to 20 mg / ml.

[0017] According to one example of the present disclosure, the ball milling may be performed at a speed of 50 rpm to 300 rpm for 0.5 hours to 4 hours.

[0018] According to one example of the present disclosure, the spray pyrolysis can be performed at 300°C to 1000°C.

[0019] In addition, another aspect of the present disclosure provides a negative electrode for a potassium ion battery comprising the hollow cobalt sulfide-carbon microspheres.

[0020] In addition, another aspect of the present disclosure provides a potassium ion battery comprising a negative electrode for the potassium ion battery. Effects of the invention

[0021] A hollow cobalt sulfide-carbon microsphere according to one embodiment of the present disclosure can exhibit excellent electrochemical properties.

[0022] A method for manufacturing hollow cobalt sulfide-carbon microspheres according to one embodiment of the present disclosure can completely sulfide cobalt even within a short reaction time.

[0023] A method for manufacturing hollow cobalt sulfide-carbon microspheres according to one embodiment of the present disclosure can effectively suppress the crystal growth of cobalt sulfide. Brief explanation of the drawing

[0024] FIG. 1 is a schematic diagram showing the process of manufacturing hollow cobalt sulfide-carbon microspheres according to one embodiment of the present disclosure. FIG. 2 is a schematic diagram of Example 1, Example 2 and Comparative Example 1 of the present disclosure and an SEM image of the manufactured microspheres. FIG. 3 shows low-magnification and high-magnification SEM images (a, b), TEM images (c, d), HR-TEM images (e), SAED patterns (f), and elemental mapping images (g) of hollow cobalt sulfide-carbon microspheres according to one embodiment of the present disclosure. FIG. 4 is a low-magnification and high-magnification SEM image (a, b) of a microsphere according to Comparative Example 2 of the present disclosure. FIG. 5 shows the XRD pattern (a), Williamson-Hall plot (b), Co 2p XPS spectrum (c), S 2p XPS spectrum (d), and C 1s XPS spectrum (e, f) of the microspheres of Example 1 and Comparative Example 2 of the present disclosure. Figure 6 is a Williamson-Hall plot of the microspheres of Comparative Example 3. FIG. 7 shows the scan rate of Example 3, Comparative Example 4, and Comparative Example 5 of the present disclosure at 0.1 mV s -1 CV curves (a, c, e) and current density 0.2 A g at -1 This is the charge / discharge profile (b, d, f) at. FIG. 8 is a Nyquist plot according to potential (a, d) and resistance (b, e) of Example 3 and Comparative Example 5 of the present disclosure. FIG. 9 shows the rate performance (a), cycle performance (b), long term cycle performance (c, d), Nyquist plot (e, f), and SEM images (g, h) of Example 3, Comparative Example 4, and Comparative Example 5. FIG. 10 shows the CV curves (a, e, i) according to scan rate of Example 3, Comparative Example 4, and Comparative Example 5, the fitting for peaks 1 and 2 (b, f, j), the CV curves showing the capacitance contribution to the total current (c, g, k), and the capacitance contribution according to scan rate (d, h, l). Specific details for implementing the invention

[0025] The present disclosure is described in more detail below. However, the following examples or embodiments are merely references for the detailed explanation of the present disclosure and are not limited thereto, and the present disclosure may be implemented in various forms.

[0026] Additionally, unless otherwise defined, all technical and scientific terms have the same meaning as generally understood by one of the people skilled in the art to which this disclosure pertains.

[0027] The terms used in the description herein are merely for the purpose of effectively describing specific embodiments and are not intended to limit the disclosure.

[0028] Additionally, the singular form used in the specification and the appended claims may be intended to include the plural form unless specifically indicated otherwise in the context.

[0029] Additionally, units used herein without special mention are based on weight, for example, units of % or ratio mean weight % or weight ratio, and weight % means the weight percentage of any one component of the total composition that occupies the composition, unless otherwise defined.

[0030] 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 may include additional components.

[0031] Additionally, the numerical ranges used in this specification may include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined in the specification of this invention, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0033] The present disclosure will be explained in more detail below.

[0034] The present disclosure relates to hollow cobalt sulfide-carbon microspheres and a method for manufacturing the same. The hollow cobalt sulfide-carbon microspheres comprise cobalt sulfide and a conductive carbon material within a carbon matrix and are doped with heteroatoms to exhibit excellent electrochemical properties. Furthermore, the method for manufacturing the same can completely sulfide cobalt within a short reaction time and effectively suppress the crystal growth of cobalt sulfide. Accordingly, the method for manufacturing hollow cobalt sulfide-carbon microspheres of the present disclosure enables the production of cobalt sulfide-carbon microspheres, which can be utilized in various industrial fields, from waste resources such as waste cemented carbide in a single process.

[0035] The present disclosure provides a hollow cobalt sulfide-carbon microsphere comprising cobalt sulfide; heteroatoms; and a conductive carbon material.

[0036] In one example of the present disclosure, the cobalt sulfide is Co x S y It can be represented as such, and the above x and y may be values ​​within the range of 1 to 10, specifically x / y may have a value of 1 or greater, and more specifically, the ratio of x and y (x:y) may be 1:1, 1:2, 9:8, or 4:3.

[0037] In one example of the present disclosure, the grain size of the cobalt sulfide may be 10 nm to 100 nm. Specifically, when the cobalt sulfide is CoS, the CoS grain size may be 30 nm to 100 nm, 50 nm to 90 nm, or 70 nm to 80 nm. Additionally, when the cobalt sulfide is Co9S8, the Co9S8 grain size may be 10 nm to 60 nm, 15 nm to 45 nm, or 20 nm to 30 nm. When satisfying the above ranges, the electrical conductivity and stability of the cobalt sulfide may be improved.

[0038] In one example of the present disclosure, the heteroatom may be one or more selected from the group consisting of Ni, Cr, Si, Al, W, Na, Cu, and Fe, but is not limited thereto as long as the purpose of the present disclosure can be achieved. The heteroatom can improve the charge transfer rate of hollow cobalt sulfide-carbon microspheres and can play a role in inhibiting the crystal growth of cobalt sulfide.

[0039] In one example of the present disclosure, the conductive carbon material may be one or more selected from the group consisting of carbon nanotubes, graphene, graphene oxide (GO), reduced graphene oxide (rGO), MXene, and carbon black, specifically carbon nanotubes, and more specifically multi-walled carbon nanotubes (MWCNT). The conductive carbon material may form a conductive network together with the cobalt sulfide and inhibit the crystal growth of the cobalt sulfide, thereby imparting excellent electrochemical properties to the hollow cobalt sulfide-carbon microspheres.

[0040] In one example of the present disclosure, the diameter of the carbon nanotube may be 5 nm to 30 nm, specifically 10 nm to 20 nm, and the length of the carbon nanotube may be 1 μm to 20 μm, specifically 5 μm to 15 μm, but is not limited thereto.

[0041] In one example of the present disclosure, the cobalt sulfide and the conductive carbon material may be uniformly distributed within the hollow cobalt sulfide-carbon microspheres. This is a result of the crystal growth of the cobalt sulfide being suppressed by the aforementioned configuration and the characteristics of the spray pyrolysis described later; consequently, the hollow cobalt sulfide-carbon microspheres may exhibit excellent electrochemical properties due to the uniformly distributed cobalt sulfide and the conductive carbon material.

[0042] In addition, the present disclosure provides a method for manufacturing hollow cobalt sulfide-carbon microspheres, comprising the steps of: ball-milling waste resources in an aqueous sulfuric acid solution to obtain an aqueous cobalt sulfate solution; adding a conductive carbon material and a water-soluble carbon material to the aqueous cobalt sulfate solution to prepare a spray solution; and spray-pyrolyzing the spray solution.

[0043] The description of the hollow cobalt sulfide-carbon microspheres of the present disclosure described above may be applied in the same way to the method for manufacturing the hollow cobalt sulfide-carbon microspheres of the present disclosure to the extent of overlap.

[0044] The step of obtaining the above-mentioned aqueous cobalt sulfate solution is to ball-mill waste resources in an aqueous sulfuric acid solution to obtain an aqueous cobalt sulfate solution in which cobalt and heteroatoms are dissolved in the aqueous sulfuric acid solution.

[0045] In one example of the present disclosure, the waste resource is not particularly limited as long as it contains cobalt, but it is preferable that it contains other metals in addition to cobalt, and specifically, it may be waste cemented carbide.

[0046] In one example of the present disclosure, the aqueous cobalt sulfate solution may contain heteroatom ions. The heteroatom ions may subsequently be reduced and doped into the hollow cobalt sulfide-carbon microspheres.

[0047] In one example of the present disclosure, the heteroatom ion may be one or more selected from the group consisting of Ni, Cr, Si, Al, W, Na, Cu, and Fe ions, but is not limited thereto.

[0048] In one example of the present disclosure, the ball milling may be performed at a speed of 50 rpm to 300 rpm, specifically 80 rpm to 150 rpm, for 0.5 hours to 4 hours, specifically 1 hour to 2 hours. Additionally, the ball milling may have a Ball-to-Powder Weight Ratio (BPR) of 1:1 to 10:1, specifically 2:1 to 5:1. When the above range is satisfied, the waste resource can be sufficiently powdered so that it can be easily dissolved in an aqueous sulfuric acid solution.

[0049] The step of preparing the above spray solution is to prepare a spray solution to be used for spray pyrolysis by adding a conductive carbon material and a water-soluble carbon material to the above aqueous cobalt sulfate solution.

[0050] In one example of the present disclosure, the concentration of the conductive carbon material in the spray solution may be 1 mg / ml to 20 mg / ml, specifically 5 mg / ml to 10 mg / ml. When the above range is satisfied, the conductivity of the carbon microspheres is improved and the effect of inhibiting the crystal growth of cobalt sulfide is excellent.

[0051] In one example of the present disclosure, the diameter of the carbon nanotube may be 5 nm to 30 nm, specifically 10 nm to 20 nm, and the length of the carbon nanotube may be 1 μm to 20 μm, specifically 5 μm to 15 μm. When the above ranges are satisfied, the degree of dispersion in the aqueous cobalt sulfate solution can be optimized.

[0052] In one example of the present disclosure, the water-soluble carbon material may be one or more selected from the group consisting of sugars, polyols, polyethers, and organic acids. More specifically, examples include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch and dextrin; polyols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; polyethers; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Sucrose may be preferred when considering water solubility and dispersibility, but is not limited thereto.

[0053] The above-mentioned water-soluble carbon material releases CO gas when heat is applied; this CO gas acts as a catalyst to promote the sulfation of cobalt, thereby enabling the conversion of cobalt into cobalt sulfide even within a short reaction time. Additionally, the above-mentioned water-soluble carbon material forms an amorphous carbon matrix through thermal decomposition, allowing for the uniform distribution of cobalt sulfide and conductive carbon material.

[0054] In one example of the present disclosure, the concentration of the water-soluble carbon material in the spray solution may be 0.01 M to 1 M, specifically 0.1 M to 0.5 M, and more specifically 0.15 M to 0.2 M.

[0055] Next, the spray pyrolysis step is to spray the spray solution into droplets and apply heat to produce hollow cobalt sulfide-carbon microspheres.

[0056] In one example of the present disclosure, the spray pyrolysis may be performed at 300°C to 1000°C, specifically at 700°C to 900°C, but is not limited thereto.

[0057] In addition, the present disclosure provides a negative electrode for a potassium ion battery comprising the hollow cobalt sulfide-carbon microspheres.

[0058] In addition, the present disclosure provides a potassium ion battery comprising a negative electrode for the potassium ion battery.

[0059] In one example of the present disclosure, the potassium ion battery may further comprise a positive electrode; a separator; and an electrolyte. The positive electrode, the separator, and the electrolyte are not particularly limited in the present disclosure and may be adopted from those known in the art.

[0061] Preferred embodiments and comparative examples of the present disclosure are described below. However, the following examples are merely preferred embodiments of the present disclosure, and the present disclosure is not limited to the following examples.

[0063] Example 1: Preparation of Hollow Cobalt Sulfide-Carbon Microspheres

[0064] Waste cemented carbide sludge (Wolfram Tech) was washed with deionized water and dried at 100°C for 24 hours to obtain waste cemented carbide powder. The components and composition of the waste cemented carbide powder were as shown in Table 1 below. 1.1 kg of the above waste cemented carbide powder was placed in 1 L of 2 M sulfuric acid solution (95% purity, Junsei) and ball-milled for 2 hours under conditions of BPR 2.5:1 and 90 rpm. After the ball-milling process, the leaching solution was filtered through a nylon membrane filter with a pore size of 0.2 μm to remove the remaining waste cemented carbide powder, thereby obtaining an aqueous cobalt sulfate solution. Next, acid-treated multi-walled CNTs and sucrose were added to the aqueous cobalt sulfate solution to achieve concentrations of 8 mg / ml and 0.2 M, respectively, to prepare a spray solution. The above spray solution was formed into droplets using a 1.7 MHz ultrasonic spray generator. The above droplets were [distributed] at 5 L min -1 Hollow cobalt sulfide-carbon microspheres were produced by transferring the material to a quartz reactor heated to 800°C with a length of 1200 mm and a diameter of 50 mm using a 5% H2 / Ar carrier gas flowing at a speed, and then spray pyrolysis.

[0065] ingredient Composition (weight%) W 77.30 Co 9.28 Ni 0.05 Cr 0.48 Al 0.08 Si 1.72 Fe 0.37 etc 10.72

[0066] Example 2: Preparation of Hollow Cobalt Sulfide-Carbon Microspheres

[0067] Hollow cobalt sulfide-carbon microspheres were prepared in the same manner as in Example 1, except that sucrose was added to make the concentration 0.1 M.

[0069] Example 3: Preparation of a potassium ion battery

[0070] Hollow cobalt sulfide-carbon microspheres from Example 1, carbon black (Super-P), and sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 7:2:1 and uniformly mixed with water solvent in a mortar. A cathode was prepared by coating the well-mixed slurry onto a Cu foil using a doctor blade and drying it in a vacuum oven for 3 hours. Potassium metal was used as the anode, and a microporous polypropylene film was interposed between the cathode and the anode as a separator. A potassium ion battery was prepared by injecting 3 M potassium bis(fluorosulfonyl)imide (KFSI) dissolved in 1,2-dimethoxyethane (DME) as the electrolyte.

[0072] Comparative Example 1

[0073] Porous microspheres were prepared by performing the same procedure as in Example 1, except that CNTs and sucrose were not added to the aqueous cobalt sulfate solution.

[0075] Comparative Example 2

[0076] Hollow carbon microspheres were prepared in the same manner as in Example 1, except that a spray solution was used in which 0.45 M cobalt nitrate hexahydrate (Co(NO3)2·6H2O, Junsei), 0.2 M sucrose, 8 mg / ml acid-treated multi-walled CNTs, and 300 ml of 2 M sulfuric acid (purity 60%, Daejung) were dissolved in 1 L of distilled water.

[0078] Comparative Example 3

[0079] Hollow carbon microspheres were prepared in the same manner as in Example 1, except that CNTs were not added.

[0081] Comparative Example 4

[0082] A potassium ion battery was prepared in the same manner as in Example 3, except that the hollow carbon microspheres of Comparative Example 2 were used.

[0084] Comparative Example 5

[0085] A potassium ion battery was prepared in the same manner as in Example 3, except that the hollow carbon microspheres of Comparative Example 3 were used.

[0087] Experimental Example 1: Observation of Microsphere Morphology

[0088] Figure 2 is a result of comparing the morphology of microspheres obtained in Example 1, Example 2 and Comparative Example 1.

[0089] Through Figures 2 (a), (b), and (c), it can be seen that in the absence of water-soluble carbon material during the spray pyrolysis process, crystal growth is excessive and a hollow structure is not formed. In addition, it can be seen that cobalt does not sulfide within a short reaction time due to the large crystal size and the absence of additional reducing gases (such as CO gas).

[0090] However, through Figures 2(d) to 2(i), it can be seen that hollow microspheres are formed when a water-soluble carbon material is added, which is due to the formation of an amorphous carbon matrix that inhibits crystal growth. Meanwhile, additional reducing gases (such as CO gas) generated by the decomposition of sucrose enable the sulfation of the cobalt component within a short reaction time, and it was confirmed that Example 1, which has a higher concentration of sucrose, achieved more sulfation of cobalt within the same time compared to Example 2.

[0091] Figure 3 shows the results of observing the morphological characteristics of the hollow cobalt sulfide-carbon microspheres obtained in Example 1.

[0092] Through the low-magnification and high-magnification SEM images of Figure 3 (a) and (b), respectively, cobalt sulfide and CNTs uniformly distributed in hollow cobalt sulfide-carbon microspheres with an average diameter of 2.5 μm can be seen.

[0093] Through the TEM images of Figures 3 (c) and (d), hollow cobalt sulfide-carbon microspheres with fine-sized cobalt sulfides distributed therein can be seen, and it can be seen that the CNT components are uniformly distributed inside with almost no exposure on the surface of the microspheres.

[0094] Through the HR-TEM image in Fig. 3(e), lattice stripes of 0.29 nm and 0.26 nm corresponding to the (311) and (102) crystal planes of Co9S8 and CoS, respectively, can be observed. The presence of Co9S8 and CoS phases can be clearly confirmed by the SAED pattern in Fig. 3(f).

[0095] As shown in the elemental mapping results presented in Figure 3 (g), it can be seen that cobalt sulfide is uniformly distributed within hollow cobalt sulfide-carbon microspheres.

[0097] Experimental Example 2: Observation of the Effect of Heteroatoms

[0098] The morphological characteristics of the microspheres prepared in Example 1 and Comparative Example 2 were compared to observe the effect of the presence or absence of heteroatoms.

[0099] Through the low-magnification and high-magnification SEM images of Figures 4 (a) and (b), respectively, it can be confirmed that the microspheres of Comparative Example 2 are also hollow, but the size of the cobalt sulfide crystals is larger compared to Example 1. Through this, it can be seen that heteroatoms have an inhibitory effect on the growth of cobalt sulfide crystals.

[0100] The presence of Co9S8 and CoS phases can be confirmed through the XRD data in Fig. 5(a). In addition, the average crystal size of cobalt sulfide can be calculated using the following Williamson-Hall (WH) equation.

[0101] Williamson-Hall style

[0102]

[0103] The above β is the full width at half maximum of the observed XRD peak, θ is the diffraction angle of the peak, K is the Debye-Scherrer constant (0.94 for spherical nanoparticles), λ is the X-ray wavelength (Cu Kα), D is the average crystal size, and ε is the average microlattice strain.

[0104] Figure 5(b) is a WH plot including error bars obtained for the Co9S8 and CoS nanocrystals in microspheres of Example 1 and Comparative Example 2. The positive slope of the linear fitting indicates the presence of microlattice strain within the cobalt sulfide crystals. In the case of Example 1, high microlattice strain values ​​were observed due to the doping of various heteroatoms. Consequently, despite peak broadening due to the introduction of heteroatoms, the calculated crystal sizes of Co9S8 and CoS in Example 1 were 23 nm and 75 nm, respectively, whereas in Comparative Example 2, they were 55 nm and 105 nm, respectively.

[0105] In addition, through Figures 6(a) and 6(b), it was confirmed that the crystal sizes of Co9S8 and CoS contained in the microspheres of Comparative Example 3 were 28 nm and 90 nm, respectively. Through this, it can be seen that the effect of heteroatom doping in inhibiting cobalt sulfide crystal growth is greater than that of conductive carbon materials.

[0106] Figures 5(c) to 5(f) show the XPS analysis results. Examining the Co 2p spectrum shown in (c), the Co of Example 1 3+ Wa Co 2+ It can be seen that the peak is shifted to a higher binding energy than that of Comparative Example 3, and if we examine the S 2p spectrum shown in (d), S 2- , Sn 2- , SO xThe CS peaks can be observed, and it can also be seen that the peak of Example 1 has shifted to a higher binding energy than that of Comparative Example 2. This implies that heteroatoms influence the local electronic environment of cobalt sulfide. Through the C 1s spectra shown in (e) and (f), peaks corresponding to C=C, CC, CO, and C=O can be observed, indicating the presence of carbon components derived from carbonized sucrose and CNTs.

[0108] Experimental Example 3: Evaluation of Electrochemical Performance of Potassium Ion Battery

[0109] The electrochemical performance of the potassium ion batteries of Example 3, Comparative Example 4, and Comparative Example 5 was evaluated.

[0110] First, cyclic voltammetry (CV) analysis was performed during the first 5 cycles at a scan rate of 0.1 mV / s in a voltage range of 0.001 V to 3.0 V.

[0111] As can be seen in Figures 7 (a), (c), and (e), the CV curves of the electrodes of Example 3, Comparative Example 4, and Comparative Example 5 showed similar trends. During the initial cathode sweep, all electrodes exhibited peaks at 1.2 V and 0.17 V, respectively, attributed to the insertion of potassium ions into the cobalt sulfide nanocrystals and the formation of K2S and Co. Additionally, two additional distinct peaks were observed, corresponding to the formation of a solid electrolyte interface (SEI) layer due to the decomposition of the dimethoxyethane-based electrolyte (0.33 V) and the insertion of potassium ions into the carbon component (0.01 V). During the subsequent charging process, a broad peak at 1.0 V and distinct peaks at 1.7 V and 2.0 V were observed, attributed to the deinsertion of potassium ions and the formation of cobalt sulfide due to the oxidation of metallic Co, respectively.

[0112] As can be seen in Figures 7 (b), (d), and (f), the plateaus observed in the initial discharge and charge curves coincided with the peak pattern identified in the CV curve. The initial discharge and charge capacities of Example 3 were 625 and 495 mA hg, respectively. -1 As such, the initial Coulomb efficiency (ICE) was 79.2%. In addition, Comparative Examples 4 and 5 were 610 and 628 mA hg, respectively. -1 It showed similar discharge capacities, and the ICE values ​​were 74.2% and 75.0%, respectively.

[0113] Electrochemical impedance spectroscopy (EIS) measurements were performed to analyze the resistance and diffusion characteristics of these electrodes during the initial discharge and charging processes.

[0114] As shown in FIG. 8 (a) and (d), the Nyquist plots obtained at various potentials during the initial cycle show the solution resistance (R s ), interface layer resistance (R) associated with the SEI layer sei ), and charge transfer resistance (R ct It shows the effects originating from ).

[0115] Figures 8(b) and 8(e) show the total resistance (R) determined through EIS. tot = R s + R sei + R ctThis represents the change in ). During the initial discharge process, the resistance values ​​of all electrodes decreased significantly. Volume expansion due to the conversion reaction of cobalt sulfide and the formation of a low-electron conductive SEI layer during the initial discharge cycle increase electrode resistance. However, during the initial conversion reaction, cobalt sulfide nanocrystals are transformed into ultrafine nanocrystals, which reduces electrode resistance, resulting in a decrease in the total resistance of the electrode. Comparative Example 4 exhibited a higher resistance value compared to the electrode of Comparative Example 5 during the initial discharge process, despite the presence of conductive CNTs. This is due to the improved charge transfer rate caused by heteroatoms and the reduction in the crystal size of cobalt sulfide. Subsequently, the resistance of the electrode gradually decreased, which is because the non-conductive K2S is converted into more conductive cobalt sulfide and the volume shrinks due to depotassiumation.

[0116] FIG. 9(a) shows the results of comparing the rate performance of the electrodes of Example 3, Comparative Example 4, and Comparative Example 5. The electrode of Example 3 exhibited the best rate performance due to the smallest cobalt sulfide crystal size and improved charge transfer rate resulting from heteroatom doping and the inclusion of CNT components. Specifically, 0.2, 0.5, 1, 2, 3, 4, and 5 A g -1 At current densities, the electrodes of Example 3 were 477, 443, 406, 341, 299, 274, and 253 mA hg, respectively. -1 It showed the reversible discharge capacity. Although the electrode of Comparative Example 4 contained CNTs, its rate performance was slightly inferior to that of the electrode of Comparative Example 5, because the improvement in charge transfer rate promoted by heteroatoms has a greater influence on determining rate performance than that of conductive carbon materials.

[0117] FIG. 9(b) is the result of comparing the cycle performance of the electrodes of Example 3, Comparative Example 4, and Comparative Example 5, 0.2 A g -1At the current density, the electrode of Example 3 exhibited superior cycle performance compared to the other electrodes. During the initial 80 cycles, the reversible discharge capacity of all electrodes gradually increased as the particles were slightly crushed due to electrochemical activation and electrochemical polishing effects, forming a reversible polymer gel-like film on the particle surface. As subsequent cycles progressed, the electrode of Example 3 maintained a reversible discharge capacity of 557 mA hg for over 300 cycles. -1 While exhibiting consistent cycle stability while maintaining the reversible discharge capacity, the electrodes of Comparative Example 4 and Comparative Example 5 showed 190 and 456 mA hg, respectively, during the same cycle range. -1 It maintained a discharge capacity. The hollow cobalt sulfide-carbon microspheres of the present disclosure contain nanoscale cobalt sulfide crystals, in which the growth of cobalt sulfide crystals is inhibited by heteroatoms and conductive carbon materials during the spray pyrolysis process. This effectively controlled stress during the conversion reaction, exhibiting excellent cycle stability. As can be seen from FIG. 9 (c) and (d), the electrodes of Example 3 were 1 and 2 A g, respectively. -1 It can be confirmed that excellent cycle stability is maintained even at current densities.

[0118] Figures 9(e) and 9(f) show the Nyquist plots of the initial electrode and the electrode after 250 cycles, respectively. Unlike the other electrodes, it can be seen that Example 3 maintains structural integrity during repeated cycles, consistently maintaining a low resistance value. The low-magnification and high-magnification SEM images in Figures 9(g) and 9(h) were consistent with these results.

[0119] Figures 10 (a), (e), and (i) show 0.1 to 2.0 mV s⁻¹. -1 These are the results of CV rate tests performed on the electrodes of Example 3, Comparative Example 4, and Comparative Example 5 at various scan speeds.

[0120] Figures 10 (b), (f), and (j) are the results of calculating the value of b by plotting log(v) versus log(i) based on the relationship between the scan speed (v) and the measured current (i) following Equation 1 below.

[0121] log(i) = blog(v) + log(a) Equation (1)

[0122] Among these electrodes, the electrode of Example 3 showed higher b values ​​than the other electrodes for both the reduction process (peak 1) and the oxidation process (peak 2).

[0123] Figures 10 (c), (g), and (k) are the results of verifying the capacitive and diffusion-controlled roles of the electrode for capacitance using the following Equation 2.

[0124] i(V) = k1v + k2v 1 / 2 (2)

[0125] k1v is the surface capacitance contribution, k2v 1 / 2 represents diffusion-controlled processes within the electrode material. 1.5 mV s -1 At scan speeds, the capacitive contributions (purple areas) of Example 3, Comparative Example 4, and Comparative Example 5 were found to be 86%, 65%, and 78%, respectively. Additionally, Figures 10 (d), (h), and (i) show that the electrode of Example 3 exhibits a higher capacitive contribution at various scan speeds, and that the capacitive contribution gradually increases in proportion to the scan speed. This is due to nanoscale cobalt sulfide crystals.

[0127] The features, structures, effects, etc. described in the above-described embodiments are included in at least one embodiment of the present disclosure and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment may be combined or modified and implemented in other embodiments by a person skilled in the art to which the embodiments belong. Accordingly, details regarding such combinations and modifications should be interpreted as being included within the scope of the present disclosure.

[0128] Furthermore, although the above description has focused on the embodiments, this is merely illustrative and does not limit the present disclosure. Those skilled in the art will understand that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the embodiments. For example, each component specifically shown in the embodiments may be modified and implemented. Differences related to such modifications and applications should be interpreted as being included within the scope of the present disclosure as defined in the appended claims.

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A method for manufacturing hollow cobalt sulfide-carbon microspheres, comprising: a step of ball-milling waste cemented carbide sludge in an aqueous sulfuric acid solution to obtain an aqueous cobalt sulfate solution; a step of adding a conductive carbon material and a water-soluble carbon material to the aqueous cobalt sulfate solution to prepare a spray solution; and a step of spray-pyrolyzing the spray solution. Claim 7 In claim 6, the above-mentioned aqueous cobalt sulfate solution comprises a method for producing hollow cobalt sulfide-carbon microspheres containing heteroatom ions. Claim 8 A method for manufacturing hollow cobalt sulfide-carbon microspheres according to claim 7, wherein the heteroatom ions are one or more selected from the group consisting of Ni, Cr, Si, Al, W, Na, Cu and Fe ions. Claim 9 A method for manufacturing hollow cobalt sulfide-carbon microspheres according to claim 6, wherein the water-soluble carbon material is one or more selected from the group consisting of sugars, polyols, polyethers, and organic acids. Claim 10 A method for manufacturing hollow cobalt sulfide-carbon microspheres according to claim 6, wherein the concentration of the water-soluble carbon material in the spray solution is 0.01 M to 1 M. Claim 11 A method for manufacturing hollow cobalt sulfide-carbon microspheres according to claim 6, wherein the concentration of the conductive carbon material in the spray solution is 1 mg / ml to 20 mg / ml. Claim 12 A method for manufacturing hollow cobalt sulfide-carbon microspheres according to claim 6, wherein the ball milling is performed at a speed of 50 rpm to 300 rpm for 0.5 hours to 4 hours. Claim 13 A method for producing hollow cobalt sulfide-carbon microspheres according to claim 6, wherein the spray pyrolysis is performed at 300 ℃ to 1000 ℃. Claim 14 delete Claim 15 delete

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