KR102234763B1 - Anode material comprising yolk-shell structure bismuth sulfide/carbon composite for sodium ion battery and method for preparing the same - Google Patents

Abstract

The present invention is a porous carbon shell (shell); _{And a plurality of yolk particles including bismuth sulfide (Bi 2} S ₃ ) located inside the carbon shell; for sodium ion batteries, which are bismuth sulfide/carbon composites having a yolk-shell structure including Anode Active Material Accordingly, a sodium ion battery with improved electrochemical properties such as charge/discharge capacity, life, and rate can be provided by applying a stable yoke-shell negative electrode active material for a sodium ion battery to a sodium ion battery.

Description

Anode material for sodium ion battery containing yoke-shell structure bismuth sulfide/carbon composite and its manufacturing method {ANODE MATERIAL COMPRISING YOLK-SHELL STRUCTURE BISMUTH SULFIDE/CARBON COMPOSITE FOR SODIUM ION BATTERY AND METHOD FOR PREPARING THE SAME}

The present invention relates to a negative electrode material for a sodium ion battery and a method for manufacturing the same, and more particularly, to a negative electrode material for a sodium ion battery including a yoke-shell bismuth sulfide/carbon composite and a method of manufacturing the same.

As for energy storage technologies, many technologies have been researched and developed through lithium secondary batteries, and in recent years, many electrode materials having high energy density, power density, and safety have been introduced. These lithium secondary batteries include small electronic devices such as smart phones and laptops, hybrid electrical vehicles (HEVs), electric vehicles (EVs), and large-capacity power storage systems (Energy storage). system, ESS), and the demand is expanding, but in connection with the unstable supply and demand of lithium raw materials, research on a next-generation secondary battery that replaces lithium is urgently required. In particular, many applications have been made in sodium ion battery systems, which have the advantage of being able to supply raw materials indefinitely from seawater.

However, ^{Na +} (1.02 A), which has a larger ionic radius than ^{Li +} (0.76 A), is a serious limitation in the development of negative electrode materials for sodium ion batteries. In particular, there has been a problem that graphite materials or silicon (Si) materials commercialized as anode materials for existing lithium secondary battery systems cannot be applied thereto. Therefore, as an alternative to negative electrode materials for sodium ion batteries, metal materials that have an alloy reaction charge/discharge behavior with sodium ions such as antimony (Sb) and tin (Sn) have a high theoretical capacity of ^{660 and 847 mAh g -1, respectively.} Because of its merit, it has attracted the attention of many researchers. On the other hand, as another alloy-based material, bismuth (Bi) is known to have an advantage in that the material has higher stability against air and moisture at room temperature than the previous two materials, and has a higher capacity per volume. However, there are still problems that greatly impair the life stability of the battery in relation to the problem of extreme volume expansion that occurs during charging/discharging of all alloy materials, the growth of the surface SEI (solid electrolyte interphase) layer, and side reactions of the electrolyte.

Recently _{, there has been a study of synthesizing Bi 2} S ₃ nanorods and applying them as cathode materials for sodium ion batteries, but Bi ₂ S ₃ still undergoes extreme volume expansion during charging/discharging in sodium ion batteries, which is a big limitation as a high-performance anode material. have.

Korean Patent Publication No. 10-2019-0037693

An object of the present invention is a Bi / C York produced by the hydrothermal synthesis reaction by forming a Bi ₂ S ₃ York particles inside the shell through the shell particles the sulfur injection process does not collapse the particulate, first formed Bi / C York -Sulfur evenly penetrates and diffuses into the shell particles to form bismuth sulfide (Bi ₂ S ₃ ) and crystallize to provide a cathode active material for sodium ion batteries, which is a stable yoke-shell bismuth sulfide/carbon complex.

Another object of the present invention is to provide a sodium ion battery with improved electrochemical properties such as charge/discharge capacity, life, and rate by applying the yoke-shell bismuth sulfide/carbon composite to a sodium ion battery.

According to an aspect of the present invention,

Porous carbon shell; _{And a plurality of yolk particles including bismuth sulfide (Bi 2} S ₃ ) located inside the carbon shell; for sodium ion batteries, which are bismuth sulfide/carbon composites having a yolk-shell structure including An anode active material is provided.

Each yoke particle constituting the plurality of yolk particles may be a particle in a form in which a plurality of bismuth sulfide nanoparticles form a cluster.

The bismuth sulfide/carbon composite may be spherical particles.

The bismuth sulfide/carbon composite may have an average particle diameter of 500 to 1000 nm.

The yoke particles including the bismuth sulfide may have an average particle diameter of 50 to 300 nm.

The carbon content in the bismuth sulfide/carbon composite may be 25 to 35 wt%.

The bismuth sulfide/carbon composite may have an orthorhombic structure.

The bismuth sulfide/carbon composite may be in a crystalline form including a (110) crystal plane, a (110) diffraction point, and a diffraction point of (001).

The bismuth sulfide/carbon complex has a peak in the range of 280 to 296 eV of C 1s, 154 to 170 eV of Bi 4f and _{168 to 168.5 eV of C-SO x -C group when analyzed by X-ray photoelectron spectroscopy (XPS).} It may be detected.

According to another aspect of the present invention,

(a) a porous carbon shell according to a one-pot hydrothermal synthesis method; And a plurality of yolk particles including bismuth (Bi) contained in the carbon shell; preparing a yoke-shell bismuth/carbon composite powder including;

(b) mixing the bismuth/carbon composite powder with sulfur (S) powder and infiltrating sulfur into the void of the bismuth/carbon composite; And

(c) sintering the bismuth/carbon composite powder impregnated with sulfur to form bismuth sulfide yoke particles, thereby preparing a yoke-shell structured bismuth sulfide/carbon composite; .

Step (a),

(a-1) dissolving a saccharide, a bismuth precursor, and a surface stabilizer in water and then adding an acid to prepare a mixed solution;

(a-2) obtaining a yoke-shell bismuth/carbon composite powder by heat-treating the mixed solution; And

(a-3) washing and drying the bismuth/carbon composite powder.

In step (a-1), the bismuth precursor and sugar may be used in a weight ratio of 1:1 to 1:5.

The heat treatment in step (a-2) may be performed at 150 to 250°C.

In step (b), the bismuth/carbon composite powder and sulfur powder may be mixed in a weight ratio of 1:3 to 1:10.

The heat treatment in step (b) may be performed at 120 to 200°C.

The sintering of step (c) may be performed by heat treatment at 450 to 700°C.

In step (c), the sintering may be performed under an argon atmosphere.

According to another aspect of the present invention,

A negative electrode for a sodium ion battery including the negative electrode active material for a sodium ion battery is provided.

According to another aspect of the present invention,

A sodium ion battery including the negative electrode active material is provided.

According to another aspect of the present invention,

A device, characterized in that any one selected from a portable electronic device including the sodium ion battery, a mobile unit, a power device, and an energy storage device, is provided.

The anode active material for sodium ion batteries, which is a yoke-shell bismuth sulfide/carbon (Bi ₂ S ₃ /C) composite of the present invention, is a bismuth/carbon (Bi/C) yolk-shell produced by hydrothermal synthesis. _{The particle shape does not collapse by forming Bi 2} S ₃ yoke particles inside the shell through the sulfur injection process, and sulfur uniformly penetrates and diffuses into the Bi/C yoke-shell particles formed earlier, thereby bismuth sulfide (Bi ₂ S ₃ ) is formed and crystallized to have a stable structure, and as a result, electrochemical properties such as charge/discharge capacity, life, and rate can be improved by applying this to a sodium ion battery.

1 is a flowchart sequentially showing a method of manufacturing a negative electrode active material for a sodium ion battery according to the present invention.
2 is a scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) analysis results of Experimental Example 1.
3 is an X-ray diffraction (XRD) and TEM structure analysis result of Experimental Example 2.
4 is a thermogravimetric analysis (TGA) result of Experimental Example 3.
5 is an X-ray photoelectron spectroscopy (XPS) analysis result of Experimental Example 4.
6 is a result of charging/discharging evaluation of Experimental Example 5.
7 is a result of evaluation of charge/discharge cycles in Experimental Example 6.
8 is a result of evaluating rate characteristics of Experimental Example 7.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention.

However, the following description is not intended to limit the present invention to a specific embodiment, and in describing the present invention, when it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. .

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the existence of features, numbers, steps, actions, elements, or combinations thereof described in the specification, but one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, actions, elements, or combinations thereof is not preliminarily excluded.

Hereinafter, an anode active material for a sodium ion battery according to the present invention will be described.

The anode active material for a sodium ion battery of the present invention includes a porous carbon shell; And a plurality of yolk particles including _{bismuth sulfide (Bi 2} S ₃ ) positioned inside the carbon shell. It is characterized in that it is a yoke-shell (yolk-shell) bismuth sulfide / carbon composite comprising a structure.

Composed of the bismuth sulfide plurality of yokes (yolk) particles are bismuth sulfide (Bi ₂ S _3), but the nanoparticles, bismuth sulfide nano-particles is a plurality of clusters a cluster form of the yoke particles comprising (Bi ₂ S ₃₎ And these yoke particles are contained within the porous carbon shell. Since the yoke particles including a plurality of bismuthsulfides have a predetermined size, they are included in the carbon shell to sufficiently secure a space between the particles and the shell.

The yoke-shell structure contains a plurality of yoke particles having a predetermined particle diameter in a shell having a predetermined thickness, so that the particles are not simply clustered in the shell, but a limited number of yoke particles can be accommodated in a limited space within the shell. It is characterized in that the space between the shell and the yoke particles is uniformly formed.

In the case of manufacturing a sodium ion battery including such a negative electrode active material, there is an effect of canceling the volume expansion of the particles generated during charging and discharging through the space between the carbon shell and the particles. On the other hand, when Bi ₂ S ₃ nanoparticles are used as they are and are mixed with carbon materials such as CNTs as in the prior art, it is difficult to suppress the volume expansion or aggregation of the nanoparticles that occur during charging and discharging of sodium ion batteries. Problems arise.

The bismuth sulfide/carbon composite is a spherical particle.

The bismuth sulfide/carbon composite may preferably have an average particle diameter of 500 to 1000 nm, more preferably 600 to 900 nm, and even more preferably 700 to 800 nm.

The yoke particles including the bismuth sulfide may preferably have an average particle diameter of 50 to 300 nm, more preferably 70 to 250 nm, and even more preferably 100 to 200 nm. When the average particle diameter of the yoke particles is less than 50 nm, the density of the yoke particles is high, and the space between the carbon shell and the yoke particles is narrow, so it may be difficult to secure a space between the carbon shell and the particles that can compensate for this during volume expansion. If the average particle diameter of the yoke particles is larger than 300 nm, the specific surface area of the yoke particles is small based on the same weight, thereby reducing the energy density of the active material.

In the bismuth sulfide/carbon composite, the carbon content is preferably 25 to 35 wt%, more preferably 27 to 33 wt%, and even more preferably 29 to 31 wt%.

When the above-described carbon content is lower than 25wt%, it is difficult to stably and uniformly cover the yoke particles contained therein, so that the electrolyte may be eluted, and when the above-described carbon content is greater than 35wt%, the amount of yoke particles is small. The energy density of the active material may decrease.

The bismuth sulfide/carbon composite may have an orthorhombic structure.

The bismuth sulfide/carbon composite may include (110) crystal planes according to HR-TEM and diffraction points of (110) and (001) according to FFT.

If the bismuth sulfide crystallized in the bismuth sulfide/carbon composite is not formed, and bismuth and sulfur remain as they are, the (012) crystal plane and rhombohedral structure of bismuth (Bi) will be clearly observed, and low strength sulfur The XRD peak for is also observed. However, residual sulfur that does not react to the bismuth sulfide/carbon complex of the present invention is completely removed and can exist only in the compound crystallized into bismuth sulfide, and all bismuth is also sulfide, so that no bismuth itself remains.

Bismuth sulfide contained in such a bismuth sulfide/carbon composite has a two-dimensional layered structure capable of storing ^{Na + and ions, thereby exhibiting a very advantageous effect on reversible Na +} charging and discharging, and the anode active material of the present invention is bismuth and By including pure bismuth sulfide without residual sulfur, there is an effect of being stable in reversible charging and discharging and increasing energy density.

The bismuth sulfide/carbon complex has a peak in the range of 280 to 296 eV of C 1s, 154 to 170 eV of Bi 4f and _{168 to 168.5 eV of C-SO x -C group when analyzed by X-ray photoelectron spectroscopy (XPS).} It may be detected.

The carbon shell may have a thickness of 100 to 300 nm, more preferably 150 to 250 nm, and even more preferably 180 to 200 nm.

When the thickness of the carbon shell is less than 100 nm, it is difficult to stably and uniformly cover the yoke particles contained therein, so that the electrolyte may be eluted, and when the carbon content is greater than 300 nm, the ratio of the yoke particles is low. The energy density of may decrease.

In the anode active material for sodium ion batteries, which is a yolk-shell bismuth sulfide/carbon composite of the present invention, the frame of the bismuth/carbon composite is first formed, and then sulfur is injected and heated above the melting point of sulfur to make sulfur uniform. It is diffused, and the final heat treatment is performed above the evaporation point of sulfur, thereby completely removing the remaining sulfur residue without forming bismuth sulfide particles, so that there is little foreign matter in the structure, and it has stability without collapse of the structure.

1 is a flowchart sequentially showing a method of manufacturing a negative electrode active material for a sodium ion battery according to the present invention. Hereinafter, a method of manufacturing a negative electrode active material for a sodium ion battery according to the present invention will be described with reference to FIG. 1.

first, Onepot ( one - pot ) Porous carbon shell according to the hydrothermal synthesis method; And contained within the carbon shell Bismuth (Bi) A plurality of yokes containing ( yolk ) Particles; including yoke-shell structure Bismuth /To prepare a carbon composite powder (step a).

It is preferable that this step is specifically performed in the following order.

First, a saccharide, a bismuth precursor, and a surface stabilizer are dissolved in water, and then an acid is added to prepare a mixed solution (step a-1).

As the saccharide, glucose, sucrose, maltose, lactose, starch, glycogen, and the like may be used.

The bismuth precursor may be nitrate, carbonate, chloride, phosphate, borate, oxide, sulfonate, sulfate, stearate, myristic acid, acetate, and anhydrides of bismuth.

The surface stabilizers are PVP (polyvinyl pyrrolidone), HEMA (2-hydroxyethyl methacrylate), PAA (polyacrylic acid), PSS (polystryrene sulfonate), PEI (Polyehylene imine), PLL (poly-L-lysine), PLSA (poly( lactic-coglycolic acid)), PLA (polylactic acid), and the like.

The acid of may be glacial acetic acid, acetic acid, citric acid, malic acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, perchloric acid, and the like.

The bismuth precursor and the saccharide are preferably used in a weight ratio of 1:1 to 1:5, more preferably 1:2 to 1:4, and even more preferably 1:2.5 to 1:3.5.

Next, the mixed solution is heat-treated to obtain a yoke-shell bismuth/carbon composite powder (step a-2).

The heat treatment is preferably performed at 150 to 250° C. for 1 to 4 hours, more preferably at 180 to 220° C. for 1 to 3 hours, and even more preferably at 190 to 210° C. for 1.5 to 2.5 hours can do.

Thereafter, the bismuth/carbon composite powder is washed and dried (step a-3).

The drying may be performed at 70 to 90°C.

Next, above Bismuth /By mixing carbon composite powder with sulfur (S) powder and then heat treatment Bismuth /The space of the carbon complex ( void ) To infiltrate the sulfur (step b).

The bismuth/carbon composite powder and sulfur powder are preferably mixed in a weight ratio of 1:3 to 1:10, more preferably 1:4 to 1:6, even more preferably 1:4.5 to 1:5.5 It can be mixed in a weight ratio of.

The heat treatment is preferably performed at 120 to 200°C, more preferably 130 to 180°C, and even more preferably at 140 to 160°C.

In addition, the heat treatment may be preferably performed for 8 to 17 hours, more preferably 10 to 15 hours, and even more preferably 11 to 13 hours.

Such heat treatment is performed at a temperature higher than 115.2°C, which is the melting point of sulfur (S), so as to uniformly penetrate into the bismuth/carbon composite structure. Preferably, heat treatment may be performed at 140 to 200°C, more preferably at 150 to 170°C.

Finally, sulfur-infiltrated Bismuth /Carbon composite powder Fire it Bismuth sulfide Yoke particles By forming a yoke-shell structure Bismuth sulfide /To prepare a carbon composite (step c).

The sintering is preferably performed by heat treatment at 450 to 700°C, more preferably 500 to 600°C, and even more preferably at 530 to 570°C.

In addition, the heat treatment may be preferably performed for 2 to 6 hours, more preferably 3 to 5 hours, and even more preferably 3.5 to 4.5 hours.

According to the heat treatment, sulfur diffused in the bismuth/carbon composite frame is chemically bonded to bismuth, that is, sulfurized to form bismuth sulfide (Bi ₂ S ₃ ) yoke particles. In addition, the shape of the frame may be maintained as it is, and the sulfur residue that did not participate in the bonding of _{bismuth sulfide (Bi 2} S _{3) may be vaporized and impurities may not remain as heat treatment is performed at a vaporization point of 444.6°C or higher.}

Accordingly, a yoke-shell bismuth sulfide/carbon composite can be finally prepared.

In the preparation of the anode active material for sodium ion batteries of the present invention, an impregnation process was additionally introduced into the bismuth/carbon (Bi/C) yoke-shell particles made by a one-pot hydrothermal synthesis process. The advantage is that a pre-made bismuth/carbon yoke-shell structure frame can be used. In the present invention, the physical properties of sulfur are utilized, and in particular, sulfur can penetrate uniformly into the void of the yoke-shell structure by utilizing the low melting point of sulfur (115.2°C), and sulfur ions naturally diffuse during the firing process. Bismuth sulfide (Bi ₂ S ₃ ) is formed and crystallized, and the sulfur residue remaining without reaction is vaporized at 444.6°C, which is the evaporation point of sulfur, and is removed, thereby preventing collapse of the structure. Due to the low material price of sodium secondary batteries, it is highly likely to be applied to the development of electrode materials for next-generation batteries for electric vehicles or large-capacity power storage devices.

The present invention provides a sodium ion battery including the negative electrode active material.

In addition, the present invention provides a device that is any one selected from a portable electronic device including a sodium ion battery, a mobile unit, a power device, and an energy storage device.

In particular, although not explicitly described in the following examples, in the method for producing a negative electrode active material for a sodium ion battery according to the present invention, in step (a), the weight ratio of the bismuth precursor and the sugar, the heat treatment temperature range, in step (b) , Bismuth/carbon composite powder and sulfur powder weight ratio, heat treatment temperature range, in step (c), while changing the heat treatment temperature conditions to prepare a negative electrode active material for a sodium ion battery.

The performance was confirmed by performing an electrochemical characteristic test on the thus prepared negative electrode active material for sodium ion batteries. As a result, unlike other conditions and other numerical ranges, only when all of the following conditions were satisfied, the rate characteristics and lifetime characteristics of the sodium ion battery were measured to be remarkably high. Such manufacturing conditions are as follows.

In step (a), the bismuth precursor and the saccharide are used in a weight ratio of 1:1 to 1:5, the heat treatment is performed at 150 to 250°C, and in step (b), the bismuth/carbon composite powder and the sulfur powder are 1 Mixing at a weight ratio of :3 to 1:10, heat treatment is performed at 120 to 200°C, and in step (c), sintering is performed at 450 to 700°C.

Hereinafter, an embodiment according to the present invention will be described in detail.

[ Example ]

Example 1: yoke-shell structure Bi ₂ S ₃ /C composite preparation

(1) Yoke-shell structure Bi/C composite preparation

The Bi/C complex was made by a simple one-pot hydrothermal synthesis method. First, 2.95 g of glucose (glucose, Sigma-Aldrich), 0.98 g of Bi(NO ₃ ) ₃ ·5H ₂ O (Sigma Aldrich), and 0.5 g of PVP (Polyvinylpyrrolidone, Mw. 40,000, Sigma-Aldrich) were added 10 ml of 10 ml. It was dissolved in distilled water for 10 minutes, 5 ml of glacial acetic acid (CH ₃ COOH, Sigma-Aldrich) was added to the above solution and stirred for 30 minutes. The mixed solution was transferred to a 50 ml Teflon container and subjected to a heat treatment process at 200°C for 2 hours in a stainless-steel autoclave. Finally, when a black yoke-shell Bi/C powder was obtained, it was recovered, washed with distilled water and ethanol, and dried in a vacuum oven at 80° C. for 6 hours or more.

(2) S-injected Bi/C composite preparation

After mixing the previously prepared yoke-shell Bi/C composite powder with sulfur powder at a weight ratio of 1:5 (wt.%), heat treatment was performed at 155°C for 12 hours to inject sulfur into the Bi/C structure. I did.

(3) Preparation of yoke-shell Bi ₂ S ₃ /C composite

Thereafter, a sulfurization operation was performed by heat treatment at 550° C. for 4 hours in an Ar gas atmosphere _{to obtain a final yoke-shell structured Bi 2} S ₃ /C powder.

[ Experimental example ]

Experimental example 1: scanning electron microscope ( FE - SEM ) And transmission electron microscope ( TEM ) analysis

In order to confirm the shape and internal microstructure of the structure particles manufactured according to Example 1, FE-SEM and TEM analysis were performed, and the images are shown in FIG. 2.

(a) is the analysis result after the (1) hydrothermal synthesis step of Example 1. Accordingly, it has a spherical shape as shown in the FE-SEM photograph, and as shown in the TEM photograph, yolk particles of 300 nm or less can be observed in the space inside the carbon shell.

(b) is the analysis result after the (2) sulfur injection process of Example 1. According to this, when sulfur is added and heat-treated at 155°C as shown in the FE-SEM picture, sulfur is melted and injected into the Bi yoke particles. The obtained porous carbon shell allows sulfur to easily penetrate into the shell. In addition, as shown in the TEM photograph, sulfur particles are observed among the Bi yoke particles, and as shown in EDS mapping, the sulfur signal can be seen to be evenly distributed where Bi is present. Therefore, it can be confirmed that sulfur was well injected into the shell through heat treatment.

(c) is the analysis result after the (3) firing step, that is, the sulfiding step of Example 1. According to this, as shown in the FE-SEM photograph, the excess sulfur covered on the surface is all evaporated and removed. This is done with the sulfurization process of Bi yoke particles into Bi ₂ S ₃ , and the internal yoke particles are well maintained without deforming the shape as shown in the TEM picture, and Bi and S are located at each particle position as shown in the EDS mapping result. It can be seen that the synthesis was successful while being uniformly distributed.

Experimental example 2: X-ray diffraction ( XRD ) And TEM Structure analysis

In order to examine the change in the crystal structure of the material in each synthesis step, XRD patterns, HR-TEM, and FFT images were obtained for each sample, respectively, and are shown in FIG. 3.

According to this, (a) shows the XRD pattern of the Bi/C yoke-shell structure, and the position of each peak coincides with the rhombohedral structure of Bi corresponding to JCPDS card #85-1331. This can be observed in the arrangement of the lattice fringe of HR-TEM, and the (012) crystal plane of Bi with d-spacing of 0.32 nm clearly appears. In addition, it can be seen that the hydrothermal synthesis process including glucose has sufficient high crystallinity and purity of the Bi phase according to the dot pattern on the (012) crystal plane of the FFT image.

(b) shows the XRD pattern of the sample after the sulfur injection, and even after the heat treatment at 155°C, which is the sulfur injection step, the Bi phase is well maintained, and the XRD peak for low intensity sulfur (JCPDS #08-0247) appears well together can see. In addition, it can be seen that the rhombohedral structure is well maintained as seen in the HR-TEM and FFT images.

_{(c) shows the XRD pattern of the Bi 2} S ₃ /C yoke-shell structure after heat treatment at 550° C., and each peak appears with high intensity at a position consistent with JCPDS card #84-0279. _{It can be seen that the sintering to form an orthorhombic structure of Bi 2} S ₃ without impurities was well completed, and it was confirmed that the reaction with sulfur was well carried out inside the carbon shell without the unreacted material of Bi. _{The (110) crystal plane of Bi 2} S ₃ is well observed in the HR-TEM photograph, and the (110) diffraction point and the (001) diffraction point are also observed in the FFT image. On the other hand, it can be seen that the excess sulfur that was introduced in the sulfur injection process was removed during the high-temperature heat treatment process, so that no trace of this was observed.

Experimental example 3: Thermal weight analysis( Thermogravimetric analysis , TGA )

TGA analysis was performed to determine the quantitative amount of carbon contained in the Bi ₂ S ₃ /C yoke-shell composite, and the results are shown in FIG. 4. According to this, a total weight reduction of 30.44 wt% is achieved between 300 and 400°C, which is calculated as the amount of carbon contained in the _{Bi 2} S _{3 /C yoke-shell composite.} Therefore, it appears that carbon accounts for about 30.44wt% of the total sample, and the carbon content synthesized by glucose added at a ratio of 1:3 to Bi nitrate shows a value that is almost consistent with the TGA result.

Experimental example 4: X-ray photoelectron spectroscopy ( XPS ) analysis

In order to find out the surface composition of the material, _{XPS analysis was performed on the Bi 2} S ₃ /C yoke-shell composite, and the results are shown in FIG. 5.

According to this, the XPS full scan spectrum clearly shows peaks for each element appearing on the surface of the _{Bi 2} S _{3 /C yoke-shell complex.} All peaks are for the elements of Bi, C, and S contained in the sample, and there is no trace of impurities, and the O1s peak is related to _{H 2} O, O ₂ and CO _{2 adsorbed on the surface.} It often appears. The highest peak, C1s, appears between 280 and 296 eV. As shown in the high resolution spectrum, C1s can separate each peak at ~284.6, ~286.1, and ~289.0 eV. These are each of the CC, CO, and C=O bonds. Corresponds. In addition, Bi4f appears at 154~170 eV, and _{peaks corresponding to Bi4f 5 /2} and Bi4f _{7 /2} are clearly found at ~164.3 and ~159.1 eV, respectively. For each of the two S2p peak corresponding to Bi4f and S2p _3/2 S2p _1/2 in the overlap does not appear well ~ Bi4f _5/2 appears at 164.3 eV ~ 164.2, ~ can be isolated from 165.1 eV. It is known that the low peak at ~168.1 eV is for the C-SO _x -C group and appears due to the doping of elemental sulfur into the carbon structure. We predicted that the sulfur injected during the heat treatment was partially diffused toward the carbon shell and formed.

Experimental example 5: charge/discharge evaluation

In _{order to evaluate the electrochemical performance of the Bi 2} S ₃ /C yoke-shell composite, a sodium half-cell was assembled using sodium metal as a counter and reference electrode, and the charge/discharge evaluation results at 25° C. 0.05 C-rate are shown in FIG. 6. Indicated.

According to this, in the case of the first cycle at 0.05 C-rate (1 C-rate = 625 mA g ^-1 ), as shown in (a), the initial charge/discharge capacity of _{Bi 2} S ₃ ^{is 492.1/668 mAh g − 1} and the Coulombic efficiency (CE) was 73.6%. In contrast, _{the charge/discharge capacity of the Bi 2} S ₃ /C yoke-shell composite of ^{(b) is 603/821 mAh g -1} , and the CE is 73.4%, which is ^{the Na +} charge _{of the Bi 2} S ₃ /C yoke-shell. The /discharging process was superior to _{Bi 2} S _{3 showing much less capacity.} It can be seen that diffusion ^{of Na +} is limited in the electrochemical process of _{Bi 2} S ₃ with low electrical conductivity.

Experimental example 6: Charge/discharge cycle evaluation

Fig. 7 shows the life characteristics of the _{Bi 2} S ₃ /C yoke-shell composite and the existing Bi ₂ S ₃ after repetition of charging/discharging 300 times at 0.2 C-rate using the same sodium half battery as in Experimental Example 5.

According to this, initially the CE of both samples is relatively low. However, in the case of the Bi ₂ S ₃ /C yoke-shell composite, CE recovered to ~97% at 0.2 C-rate after 3 charging/discharging at 0.05 C-rate, and 282.4 mAh g ^-1 after 300 cycles. The charging capacity was maintained. On the other hand, the existing Bi ₂ S ₃ exhibits a relatively low CE of about 93% in 0.2C cycling, and shows a serious capacity reduction in which the charging capacity is maintained to ^{only 41.36 mAh g −1 after 300 cycles.} This is thought to be due to particle agglomeration or coarsening due to the change in the volume of the material resulting from the irreversible phase generated by the conversion reaction of _{Bi 2} S ₃ with Na ^{+ and subsequent charging/discharging.} do. In addition, since the Bi ₂ S ₃ /C yoke-shell complex has a relatively large ionic radius, it can be seen that the desorption/insertion process of ^{Na +} _{is easier than the existing Bi 2} S _3. The _{improved performance of the Bi 2} S ₃ /C yoke-shell composite is presumed to be due to the presence of the conductive carbon shell as an electron path and the buffering role of the pore structure of the yoke-shell particle structure on the volume change in cycling.

Experimental example 7: Rate characteristics evaluation

Fig. 8 shows the results of evaluating the rate characteristics using the same sodium half battery as in Experimental Example 5. In order to confirm that the rate characteristics of the material are improved by the well-formed yoke-shell structure, it was performed 3 times each at 0.1, 0.2, 0.5, 1, 2, 5, 10 C-rate, and the last 3 times were 0.1 C-rate. Restored to. _{The charge capacity of the Bi 2} S ₃ /C yoke-shell composite in the third cycle at each C-rate was 664.7, 637.7, 612.2, 572.5, 535.8, 462.8 and 413.0 mAh g ^{- 1} , respectively, and 606.6 in the recovery cycle. It recovered to mAh g ^{- 1.} In contrast, the existing Bi ₂ S ₃ showed relatively low charging capacities of 331.8, 284.7, 251.0, 221.6, 176.4, 76.6 and 13.9 mAh g ^-1 , respectively, and recovered to ^{222.0 mAh g -1} at the last 0.1 C-rate. . Therefore, the Bi ₂ S ₃ /C yoke-shell composite maintains reversibly well the ^{Na +} charge/discharge process at a high current density even though the reversible capacity decreases, which is much more reversible at a higher current density than the _{existing Bi 2} S _3. Keep the capacity. As a result, the improvement in output characteristics of the _{Bi 2} S ₃ /C yoke-shell composite is estimated to be due to the presence of a conductive carbon shell uniformly surrounding the _{Bi 2} S _{3 yoke particles.}

In the above, the embodiments of the present invention have been described, but those of ordinary skill in the art will add, change, delete or add components within the scope not departing from the spirit of the present invention described in the claims. Various modifications and changes can be made to the present invention by means of the like, and it will be said that this is also included within the scope of the present invention.

Claims (19)

Porous carbon shell; And
It is a bismuth sulfide/carbon composite having a yolk-shell structure including a plurality of yolk particles including _{bismuth sulfide (Bi 2} S ₃ ) positioned inside the carbon shell,
The plurality of yolk particles are a form in which a plurality of bismuth sulfide nanoparticles form a cluster, and a space between the carbon shell and the yoke particles is formed,
The yoke particles have an average particle diameter of 50 to 300 nm,
The negative electrode active material for a sodium ion battery, characterized in that the thickness of the carbon shell is 100 to 300nm. delete The method of claim 1,
The bismuth sulfide/carbon composite is a negative active material for a sodium ion battery, characterized in that the spherical particles having an average particle diameter of 500 to 1000 nm. delete The method of claim 1,
The anode active material for a sodium ion battery, characterized in that the carbon content in the bismuth sulfide/carbon composite is 25 to 35 wt%. The method of claim 1,
The bismuth sulfide/carbon composite negative electrode active material for a sodium ion battery, characterized in that it comprises an orthorhombic structure (orthorhombic structure). The method of claim 1,
The bismuth sulfide/carbon composite is a negative active material for a sodium ion battery, characterized in that it is in a crystalline form including a (110) crystal plane, (110) a diffraction point, and a diffraction point of (001). The method of claim 1,
The bismuth sulfide/carbon complex has a peak in the range of 280 to 296 eV of C 1s, 154 to 170 eV of Bi 4f and _{168 to 168.5 eV of C-SO x -C group when analyzed by X-ray photoelectron spectroscopy (XPS).} A negative electrode active material for sodium ion batteries, characterized in that detected. delete (a) a porous carbon shell according to a one-pot hydrothermal synthesis method; And a plurality of yolk particles including bismuth (Bi) contained in the carbon shell; preparing a yoke-shell bismuth/carbon composite powder including;
(b) mixing the bismuth/carbon composite powder with sulfur (S) powder and heat treatment to penetrate sulfur into the void of the bismuth/carbon composite; And
(c) sintering the sulfur-impregnated bismuth/carbon composite powder to form bismuth sulfide yoke particles, thereby preparing a yoke-shell structured bismuth sulfide/carbon composite; Including,
Step (a),
(a-1) dissolving a saccharide, a bismuth precursor, and a surface stabilizer in water and then adding an acid to prepare a mixed solution;
(a-2) obtaining a yoke-shell bismuth/carbon composite powder by heat-treating the mixed solution; And
(a-3) washing the bismuth/carbon composite powder and then drying the powder. delete The method of claim 10,
In step (a-1), the bismuth precursor and the saccharide are used in a weight ratio of 1:1 to 1:5. The method of claim 10,
The heat treatment in step (a-2) is a method for producing a negative active material for sodium ion batteries, characterized in that carried out at 150 to 250 ℃. The method of claim 10,
In step (b), the bismuth/carbon composite powder and the sulfur powder are mixed in a weight ratio of 1:3 to 1:10. The method of claim 10,
The heat treatment in step (b) is a method for producing a negative active material for sodium ion batteries, characterized in that carried out at 120 to 200 ℃. The method of claim 10,
The method for producing a negative active material for sodium ion batteries, characterized in that the sintering of step (c) is performed by heat treatment at 450 to 700°C. The method of claim 10,
The method for producing a negative active material for a sodium ion battery, characterized in that the firing in step (c) is carried out under an argon atmosphere. A sodium ion battery comprising the negative active material for a sodium ion battery according to any one of claims 1, 3, and 5 to 8. A device comprising any one selected from a portable electronic device, a mobile unit, a power device, and an energy storage device including the sodium ion battery of claim 18.

Images