JP2013232436A - Negative electrode active material of self-supporting metal sulfide-based two-dimensional nanostructure and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material of high crystallinity, high uniformity and high purity self-supporting metal sulfide-based two-dimensional nanostructure applicable to a secondary battery, and to provide a production method therefor.SOLUTION: The negative electrode active material grows directly, as a metal sulfide-based two-dimensional nanostructure, on a metal substrate by peeling an aggregate composed of a metal sulfide-based material. The production method thereof includes a step for producing an aggregate composed of a metal sulfide-based material, a step for inserting the aggregate into a tube in an electric furnace for pulse laser vapor deposition, a step for inserting a metal substrate into a tube and locating the metal substrate separately from the aggregate, a step for lowering the pressure in the tube to vacuum state and raising the temperature of the electric furnace to 590-610°C, and a step for peeling the aggregate by injecting pulse laser into the tube. The metal sulfide-based material is grown, as a two-dimensional nanostructure, directly on the metal substrate.

Description

  The present invention relates to a negative electrode active material of a self-supporting metal sulfide-based two-dimensional nanostructure having high crystallinity, high uniformity, and high purity applicable to a secondary battery, and a method for manufacturing the same.

  Recently, along with the rapid development of electric vehicles and hybrid vehicles and the trend toward lighter and smaller portable electronic products, there is a continuous demand for technological development that can increase the power supply sources of these products and increase their output. Yes. The power supply source is roughly divided into a primary battery that can be used once, a secondary battery that can be recharged and used multiple times when discharged, a fuel cell that uses hydrogen as fuel, and solar energy. There are solar cells that convert energy.

  Among these, primary batteries include alkaline batteries, mercury batteries, manganese batteries, etc., which are large in capacity but cannot be recycled, so there are disadvantages that are not friendly to the environment, but lead. Secondary batteries such as storage batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium metal batteries, and lithium ion batteries are reusable, so they are environmentally friendly, have a higher driving voltage and higher energy efficiency than primary batteries There is an advantage.

  Furthermore, there are various types of fuel cells, such as phosphoric acid type, proton exchange membrane type, dissolved carbonic acid type, solid oxide type, etc., depending on the driving system, and these have low energy density and are still technical Although there are many problems that have to be solved, secondary batteries have been commercialized in the industrial field as products having high energy density and high output density.

  Among these, a lithium ion secondary battery (or a lithium secondary battery) has an extremely high energy density and output density as compared with other secondary batteries, and is therefore attracting the most attention as a next-generation energy technology.

  Such a lithium secondary battery uses a reversible insertion / desorption reaction that occurs when lithium ions, which are charge transfer mediators, move to a positive electrode active material or a negative electrode active material, and thus a positive electrode that can store lithium ions. The capacity of the active material and the negative electrode active material determines the performance of the battery.

  Initially, a high energy density was achieved using lithium metal as the negative electrode active material, but the surface of the electrode suddenly changed during charge / discharge, the charge / discharge capacity decreased, and the lithium metal dendrite deposited from the negative electrode contacted the positive electrode. Because of the danger of explosion, no further research and development has been done.

  Later, in 1991, Sony made a regular product based on lithium-ion secondary batteries using carbon as the negative electrode active material and lithium oxide as the positive electrode active material, and still contains lithium ions through insertion / extraction reactions. Carbon-based negative electrode active materials are widely used in lithium ion secondary batteries.

  As described above, the carbon-based materials most widely used as the negative electrode active material can be roughly classified into hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), and graphite. . Both hard carbon and soft carbon are non-graphitic carbon, and hard carbon is irregularly arranged with multiple graphitic crystals consisting of multiple layers and cannot be graphitized through a high-temperature heat treatment process. On the other hand, soft carbon can be graphitized through high-temperature heat treatment because crystals of a layered structure have a certain degree of orientation.

  These non-graphitic carbons can have a capacity much larger than that of graphite-based carbon because lithium ions are inserted between layers and carbon internal pores in the layered structure, but have a disadvantage that the irreversible capacity is large ( Non-Patent Documents 1 and 2).

  Accordingly, graphite is the most widely used carbonaceous material, and can be further classified into natural graphite and artificial graphite.

  Typical artificial graphite includes mesocarbon fibers and mesocarbon microbeads. Recently, artificial graphite doped with two kinds of elements has been produced as a negative electrode active material. Mesophase fibers and mesophase carbon microbeads also exhibit significantly lower capacities due to costly and complex processes, despite manufacturing advantages.

  In addition, natural graphite has the advantages of higher charge / discharge capacity and very low irreversible capacity compared to mesophase fibers and mesophase carbon microbeads. However, it is not easy.

  Therefore, in order to solve the above problems, techniques have been developed in which low-cost coke-based artificial graphite is doped with an element such as boron and used as a negative electrode active material (Patent Documents 1 to 4).

  However, all the above carbon-based negative electrode active materials basically have a small theoretical capacity (372 mAh / g), and it is known that the commercialized capacity is even smaller than this. Further, there is a risk of explosion because a side reaction occurs with the electrolyte solution during the charge / discharge process, the irreversible capacity is large, and the reaction voltage is low. Therefore, there is a limit to satisfy the high energy density and the high output density, which are technical trends required for next-generation portable electronic devices and electric vehicles.

An insertion / desorption reaction-based TiO ₂ -based material has attracted attention as a negative electrode active material replacing carbon-based materials. This is advantageous in that it can be charged and discharged at high speed and is safe, but has the disadvantage that the theoretical capacity is small as in the case of carbon-based materials.

  Therefore, unlike the insertion / extraction reaction, research on a method for storing lithium is attracting attention, which can be broadly divided into a conversion reaction and a lithium alloy reaction.

Among them, the above conversion reaction is a method in which transition metal oxides such as CuO, CoO, Fe ₂ O ₃ , NiO, and MnO ₂ store lithium, and react with 3 to 6 lithium ions per atom. High capacity (Non-patent Documents 3 and 4).

Such conversion reactions, specifically _M x _O y + _2yLi⇔xM + _yLi occur as _{2 O (M = transition metal)} , already a transition metal of the reported Li ₂ O that no electrochemical activity nanosize High capacity is expressed while reversibly reacting with the domain.

  However, in the above conversion reaction, aggregation between particles occurs due to a continuous charge / discharge reaction to create a locally non-uniform composition, which impairs cycle characteristics. Further, since the bond between the transition metal and oxygen is cut, there is a problem that the output characteristics are deteriorated due to the characteristics of the conversion reaction for storing lithium (Non-patent Document 5).

In order to improve the disadvantages of the transition metal oxides, research on synthesizing nanostructures and applying them to lithium secondary batteries has been conducted using Co ₃ O ₄ , Fe ₃ O _4, etc. References 6-8). According to this study, nanowires Co ₃ O ₄ and nanotubes Co ₃ O ₄ are one-dimensional nanostructures, but a sudden capacity decrease occurs with the number of cycles, and Fe on the copper current collector in the form of nanorods. _The self-supporting electrode on which ₃ O ₄ is deposited has improved output characteristics due to suppression of polarization, but the process sequence of various stages must be performed.

On the other hand, the alloy reaction is a system in which lithium ions are stored by forming a lithium alloy of Li _x Si, Li _x Ge, and Li _x Sn by a single element material of Si, Ge, and Sn. Since this reacts with a maximum of 4.4 lithium ions per atom, the theoretical capacity is large (Li-Si: 4200 mAh / g, Li-Ge: 1600 mAh / g, Li-Sn: 990 mAh / g). High capacity can be achieved compared to graphite-based materials. However, due to excessive volume expansion during the alloy / dealloying reaction with lithium, there is a problem in that particles are pulverized and an electric isolation phenomenon occurs in which a path for electrons to move is cut. This causes a rapid decrease in properties, which hinders the possibility of commercializing lithium alloy materials (Non-Patent Documents 9 and 10).

  A considerable number of studies have been reported on improving the electrode characteristics by manufacturing the lithium alloy-based negative electrode active material using various types of nanostructures. First, when nanowire Si or nanowire Ge is grown on a metal current collector using chemical vapor deposition, it is not a system in which electrons are transmitted via a conductive material during charge / discharge, so an active material The contact resistance is minimized and high output characteristics can be obtained, but the manufacturing process is complicated and the synthesis temperature is high (Non-patent Documents 11 and 12). In addition, when Sn nanoparticles are injected into a carbon sphere using a liquid phase synthesis method or surrounded by a carbon layer, the cycle characteristics are improved, but the process procedure is difficult (Non-Patent Documents 13 and 14). ).

  Although various alternative negative electrode active materials have been described above, in order to replace existing carbon-based negative electrode materials, not only has high energy density, high output density, and stable cycle characteristics, but also the manufacturing process is simple and large. A new negative electrode active material that can be manufactured over the area is required.

On the other hand, when SnS is used as the negative electrode active material for a lithium ion secondary battery, a conversion reaction (SnS + 2LiSn + Li ₂ S) and a lithium alloy reaction (Sn + 4.4LiLi _4.4 Sn) occur sequentially only in the first discharge process. In the charge / discharge process, only the lithium alloy reaction (Sn + 4.4LiLi _4.4 Sn) occurs. Since this stores lithium by an alloy reaction, the theoretical capacity (782 mAh / g) is high.

In addition, the amorphous Li ₂ S matrix produced during the first discharge becomes inactive for the subsequent reactions and simply surrounds the active material, thus mitigating excessive volume expansion due to the lithium alloy / dealloying reaction. Thus, improvement in cycle characteristics can be expected.

  However, according to the reports so far, the SnS negative electrode active material is inferior in capacity characteristics and the cycle characteristics are also remarkably low (Non-patent Documents 15 and 16). This is due to the problem of particle size and shape, and the disadvantages of existing electrode manufacturing methods using conductive materials and binders.

JP-A-3-165463 JP-A-3-245458 JP-A-5-26680 JP-A-9-63584

R. Alcantara et al., J. Electrochem. Soc. 149 (2002) A201 J. R. Dahn et al., Carbon 37 (1997) 825 P. Poizot et al., Nature 407 (2000) 496 M. Dolle et al., Electrochem. Solid-State Lett. 5 (2002) A18 R. Yang et al., Electrochem. Solid-State Lett. 7 (2004) A496-A499 X. W. Lou et al., Adv. Mater. 20 (2008) 258 Y. Li et al., Nano Lett. 8 (2008) 265 P. L. Taberna et al., Nature Mater. 5 (2006) 567 A. Anani et al., J. Electrochem. Soc. 134 (1987) 3098 W. J. Weydanz et al., J. Power Sources 237 (1999) 81 C. K. Chan et al., Nature Nanotech. 3 (2008) 31 C. K. Chan et al., Nano Lett. 8 (1) (2008) 307 W. M. Zhang et al., Adv. Mater. 20 (2008) 160 M. Noh et al., Chem. Mater. 17 (2005) 1926 X.-L. Gou et al., Mater. Chem. Phys. 93 (2005) 557 Y. Li et al., Electrochim. Acta 52 (2006) 1383

The present invention is for solving the above-described problems, and is a metal sulfide-based two-dimensional nanocrystal that grows directly on a metal substrate having a large area at a low temperature using a pulsed laser deposition method without a catalyst. The object is to provide a negative active material for a structure.
Another object of the present invention is to provide a method for producing the negative electrode active material.
Another object of the present invention is to provide a negative electrode containing the negative electrode active material.
Another object of the present invention is to provide a secondary battery that employs the negative electrode active material.

  In order to achieve the above object, the present invention provides a self-supporting metal characterized in that an aggregate composed of a metal sulfide-based material is peeled off and directly grown as a metal sulfide-based two-dimensional nanostructure on a metal substrate. A negative electrode active material of a sulfide-based two-dimensional nanostructure is provided.

  The present invention also includes a step of producing an agglomerate comprising a metal sulfide-based material, a step of inserting and attaching the agglomerate into a tube in an electric furnace for pulse laser deposition, and a metal substrate being inserted into the tube. A step of separating from the aggregate, a step of lowering the pressure in the tube to a vacuum of 0.01 to 0.03 Torr and raising the temperature of the electric furnace to 590 to 610 ° C., and A self-supporting metal sulfide system, comprising the step of peeling agglomerates by injecting a pulse laser, wherein the metal sulfide material is directly grown as a two-dimensional nanostructure on the metal substrate. A method for producing a negative electrode active material having a two-dimensional nanostructure is provided.

  In the present invention, a metal sulfide-based material is directly grown on a large-area metal substrate using a pulsed laser deposition method without a catalyst at a low temperature, and the negative electrode active of a self-supporting metal sulfide-based two-dimensional nanostructure is developed. By manufacturing the material, the low capacity and low output characteristics, which are the disadvantages of the conventional negative electrode active material, can be solved, and a high crystallinity, high uniformity, and high purity negative electrode active material can be manufactured.

  In particular, since the pulse laser deposition method is used to manufacture the two-dimensional nanostructure negative electrode active material, the process procedure is simple, it can be synthesized at a low temperature, and no separate catalyst is required. Substantial application not only to ion secondary batteries but also to the solar cell field is expected.

It is a field emission scanning electron micrograph of SnS powder used in order to manufacture an aggregate. It is a schematic diagram of process equipment for pulse laser deposition. 3 is a flowchart illustrating a method of manufacturing a self-supporting SnS two-dimensional nanostructure according to the present invention. 2 is a field emission scanning electron micrograph and a large area synthesis of self-supporting SnS nanosheets, thin nanoplates, thick nanoplates, and thin films prepared according to the present invention. 1 is an X-ray diffraction pattern of a self-supporting SnS nanosheet manufactured according to the present invention. It is a transmission electron micrograph of the high magnification and low magnification of the SnS nanosheet manufactured by this invention. It is a graph which shows the capacity | capacitance change according to cycle of the self-supporting SnS nanosheet manufactured by this invention, a thin film, and powder. It is a graph which shows the capacity | capacitance change according to the current density of the self-supporting SnS nanosheet manufactured by this invention, a thin film, and powder.

  In the present invention, a number of embodiments can exist, and in the description of the present invention, duplicate descriptions for the same parts as those of the prior art are omitted.

  The present invention relates to a self-supporting negative electrode active material in which a metal sulfide-based material grows directly on a metal substrate as a two-dimensional nanostructure, and a method for manufacturing the same, and has an excellent lithium storage capacity, a wide specific surface area, Metal sulfide-based two-dimensional nanostructures with short lithium ion / electron diffusion distance and effective stress relaxation properties were grown directly on a stainless steel (SUS) substrate of a metal collector that is not coated with a catalyst. The present invention relates to a negative electrode active material and a manufacturing method thereof.

  In the embodiment of the present invention, tin sulfide (SnS) is presented as the metal sulfide-based material, but the applicable metal sulfide-based material is not limited thereto.

  The nanostructure according to the present invention exhibits a shape having a thin and wide area. This can be observed with a field emission scanning electron microscope (FESEM), a high-resolution transmission electron microscope (FTEM), and a type of phase (synthesized ph). The crystallographic structure can be confirmed using an X-ray diffraction pattern (XRD).

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  According to an embodiment of the present invention, a two-dimensional tin sulfide nanostructure is grown on a high-temperature metal substrate by exfoliating a tin sulfide target with a periodic laser using a pulsed laser deposition method. Let

  Methods for synthesizing tin sulfide nanostructures can be broadly divided into liquid phase methods, solid phase methods, and gas phase methods.

  The liquid phase method has the advantages that a crystalline material is obtained at a low temperature and uniform and small-sized particles can be obtained, but the synthesis procedure is complicated and the crystallinity of the particles is low.

  The solid phase method is advantageous from an economical viewpoint, but has a defect that the particle size is not uniform and the particle size is large.

  On the other hand, the gas phase method has the advantage that the crystallinity of the product is very high and mass production is easy.

  Such a vapor phase method is roughly divided into a chemical vapor deposition method and a physical vapor deposition method, but the electrochemical vapor deposition method has complicated process variables and has a safety problem due to the use of gas. The vapor deposition method has relatively few process variables, simple process procedures, and is relatively safe.

  Among the physical vapor deposition methods, the pulsed laser deposition method is a thin film or nano-structure while maintaining a composition ratio of a material having a complicated composition ratio such as a binary compound or a ternary compound. There is an advantage that it can be manufactured in a structure form.

  In the pulse laser deposition method used in the present invention, SnS powder is manufactured as a cylindrical aggregate, heat-treated at a high temperature, and peeled to manufacture a desired nanostructure. The SnS powder used is dark gray and the shape can be observed by FESEM photographs.

  FIG. 1 is a field emission scanning electron micrograph of SnS powder used to produce an aggregate, and FIG. 2 is a schematic diagram of process equipment for pulsed laser deposition.

  According to FIG. 1, the SnS powder has a layered structure with a weak binding force toward a specific direction.

  A schematic diagram of the equipment used for pulsed laser deposition in the present invention is shown in FIG.

  As shown in FIG. 2, after the SnS aggregate and the SUS (stainless steel) substrate are positioned inside the quartz tube inserted in the electric furnace, the high energy pulse laser is focused with a lens to peel off the SnS aggregate. And vapor-deposited on the substrate. Here, the temperature, pressure, laser energy, cycle, time, height and position of the SnS aggregate, and the position of the SUS substrate when peeling the SnS aggregate are important factors that influence the entire process.

  The pulse laser deposition process used to manufacture the negative electrode active material of the self-supporting SnS two-dimensional nanostructure according to the present invention is schematically illustrated in FIG. 3, and a specific implementation method based on FIG. It is as follows.

  First, SnS powder is weighed and a certain amount is put into a cylindrical mold (mold), and then uniaxial pressure is applied to produce an aggregate form (temporary aggregate). After the temporary agglomerates are inserted and mounted in the quartz tube in the electric furnace, the temperature of the electric furnace is increased to 580 to 600 ° C. while adding hydrogen gas, and heat treatment is performed for 3 to 5 hours.

  If the said temperature is less than 580-600 degreeC, the physical coupling | bonding (the intensity | strength of SnS aggregate) between the powder in SnS aggregate is inadequate, and laser peeling cannot be performed effectively, and exceeds this range. Then, since the SnS aggregate is oxidized to change to yellow and easily broken, it is preferable to maintain a range of 580 to 600 ° C.

  The heat treatment time is preferably about 3 hours.

  As shown in FIG. 2, the SnS aggregate produced as described above is positioned at the center of the electric furnace for pulsed laser deposition, and the height of the SnS aggregate (quartz tube) so that the focused laser can be accurately peeled off. It is important to adjust the size and the size (located 2.0-2.5 cm above the inner wall surface). Next, the SUS substrate not coated with the catalyst is processed into a disk shape and positioned near the SnS aggregate, and the shape of the composite changes depending on the position of the SUS substrate, so that a desired shape can be obtained. It is preferable to adjust the position (distance from the SnS aggregate).

  Here, the range near the aggregate means a section of 14 to 20 cm from the center of the aggregate toward both sides, and means a section corresponding to 200 to 350 ° C. when the temperature is measured by a thermocouple. . By changing the position of the SUS substrate within this section, various structures such as nanosheets, nanoplates, and thin films can be obtained. Therefore, it is important to determine an appropriate position.

  Next, the pressure in the quartz tube is lowered to a vacuum state of 0.01 to 0.03 Torr using a rotary pump, and the temperature of the electric furnace is raised to a range of 590 to 610 ° C. When the above temperature range does not rise to this range, the SnS aggregates do not easily peel off, and the amount of SnS particles reaching the SUS substrate is insufficient. If this range is exceeded, the aggregates are oxidized. This range is preferably maintained because it turns yellow and breaks easily.

Next, with the temperature and pressure maintained in the above ranges, a KrF excimer laser (wavelength: 248 nm) was set to an energy density of 0.8-1 J / cm ² , and then a pulse laser was injected into the quartz tube. The SnS aggregate is stripped at a rate of 3-5 times per second for 25-35 minutes.

  If the peeling rate per second is less than 3 to 5 times, the amount of SnS particles that reach the SUS substrate within a unit time is small, and the density of the nanostructures is reduced. This range is preferably maintained because the amount of particles is too large and a thin film grows in place of the nanostructure.

  Further, if the peeling time is not in the range of 25 to 35 minutes, the density of the nanostructures is reduced or the thin film grows, so this time is preferably maintained. Preferably, the peeling time is about 30 minutes.

  When the laser peeling is finished, the temperature of the electric furnace is lowered while maintaining the pressure range (0.01 to 0.03 Torr) in the quartz tube to complete the process.

  As described above, according to the method presented in the present invention, various shapes such as nanosheets, nanoplates, and thin films can be simultaneously manufactured by simply changing the position of the SUS substrate in a single process, which is observed by FESEM observation. Can be confirmed.

4A, 4B, 4C, and 4D show changes in the shape of the SnS composite depending on the distance between the SUS substrate and the SnS aggregate. As (d) to (a) in FIG. 4, the SUS substrate is separated from the SnS aggregate and the synthesis temperature is lowered. As a result, the SnS composite is sequentially changed into a thin film, a thick nanoplate, a thin nanoplate, and a nanosheet. It can be seen that it is formed. In particular, the nanosheet of FIG. 4A is manufactured with a very thin thickness of 10 to 15 nm, and is synthesized over a large area of 2 × 2 cm ² as shown in FIG. Can do. Hereinafter, the shape of the SnS nanosheet of FIG. 4A will be described.

  FIG. 5 is a drawing showing an X-ray diffraction pattern of a self-supporting SnS nanosheet produced according to the present invention, and FIG. 6 is a high- and low-magnification transmission electron micrograph of the SnS nanosheet produced according to the present invention. .

  The nanosheet is pure SnS grown directly on the SUS substrate, which can be confirmed from the XRD pattern shown in FIG.

  The SnS nanosheet produced in the present invention is crystalline and has an orthorhombic crystal structure, and the specific shape of such a SnS nanosheet can be observed in detail by TEM or HRTEM observation.

  According to the TEM photograph shown in FIG. 6A, the SnS nanosheet extends widely in two directions, and forms a right angle at one point. Further, as can be seen from the HRTEM observation shown in FIG. 6B, the nanosheet is single crystal and grows in the <101> group direction.

  On the other hand, such a self-supporting SnS two-dimensional nanostructure can be used in an energy device, more specifically, a lithium ion secondary battery, a solar battery, or the like in this field.

  Therefore, in order to determine the possibility of the nanosheet as a negative electrode active material of the lithium secondary battery, in particular, the self-supporting SnS two-dimensional nanostructure is manufactured by separately manufacturing a secondary battery electrode. A battery (half-cell) can be constructed and its electrochemical properties can be evaluated.

  In general, in a lithium ion secondary battery, the volume expansion during charging / discharging is suppressed as the number of lithium ions that can be reacted per atom of the negative electrode active material is increased and the contact resistance between the active materials is minimized. The wider the contact interface between the active material and the electrolyte, the better the electrochemical performance.

  First, a self-supporting nanosheet electrode according to the present invention is used as a positive electrode and lithium metal is used as a negative electrode, and an electrolyte and a separator are placed between the two electrodes to complete a half-cell in a glove box.

  Then, in order to measure the cycle characteristics, a current density of 1 C is applied in a voltage interval of 0.01 to 1.3 V, and a charge / discharge reaction is performed for 100 cycles.

  In addition, in order to evaluate the output characteristics, various current densities (for example, 1C, 3C, 5C, 10C, 20C, 40C, and 80C) are added in the voltage range, and 10 cycles of charge / discharge reactions are performed for each current density. The amount of current corresponding to each current density can be calculated by measuring the pure amount of the SnS nanosheet active material, and the pure amount of the active material is determined by the weight of the SUS substrate before the nanosheet is synthesized and the substrate after the synthesis. The weight is quantified to determine the difference between the two.

  Then, in order to evaluate the relative performance of the self-supporting SnS nanosheet negative electrode active material, the electrochemical characteristics of the SnS thin film and the SnS powder are measured.

  In the case of a SnS thin film, it can be used as an electrode as in the case of the self-supporting SnS nanosheet, and SnS powder is produced as an electrode by a production method as described later.

  First, SnS powder, conductive additive, and binder are quantified and dissolved in an inert organic solvent, and the three substances are uniformly mixed by mechanical mixing and ultrasonic treatment. Next, the slurry-like mixture is thinly applied onto the copper current collector to complete electrode production.

  Hereinafter, the present invention will be specifically described with reference to the following examples, and the present invention is not limited to the following examples.

<Example 1>
2 g of glossy dark gray SnS powder was weighed and uniformly injected into a cylindrical mold having a diameter of 1 cm, and then uniaxially molded at a pressure of 600 psi to produce an aggregate.

  The aggregate was placed in a quartz tube inserted in the electric furnace, and then hydrogen gas (100 sccm) was added, and at the same time, the temperature was increased to 580 ° C. at a rate of 3 ° C. per minute and heat treated for 3 hours.

  After the heat treatment was completed, the temperature was lowered to room temperature at a rate of 3 ° C. per minute to complete the production of the aggregate.

<Example 2>
Since a laser focusing operation is necessary before pulsed laser deposition, a focal lens with a focal length of 50 cm was positioned at the portion where the laser was injected. Whether or not the laser was focused at an appropriate size was confirmed by photographic paper, and a quartz tube having a diameter of 28 cm and a length of 80 cm was inserted into the electric furnace for pulse laser deposition.

  Next, the SnS aggregate produced in Example 1 is positioned in a portion located 50 cm away from the focal lens in the quartz tube, and the aggregated laser is effectively peeled off by the focused laser. The height was adjusted appropriately.

  At this time, the height was adjusted using an alumina boat and an alumina plate so that the center of the focused laser reached the center of the aggregate accurately.

  Next, a SUS substrate not coated with a catalyst was manufactured in a disk shape having a diameter of 1 cm, and was placed in a portion 20 cm away from the right side of the SnS aggregate.

  Next, the pressure in the quartz tube was set to a vacuum state of 0.02 Torr using a rotary pump, and the temperature was raised to 590 ° C. at a rate of 20 ° C. per minute.

Then, the energy density of the laser focused at a temperature of 590 ° C. and a pressure of 0.02 Torr was set to 0.9 J / cm ² , and SnS aggregates were applied at a rate of 3 times per second for 30 minutes. It peeled.

  After the laser peeling, SnS two-dimensional nanosheets were manufactured by lowering the temperature of the electric furnace at a rate of 3 ° C. per minute under the pressure of 0.02 Torr.

<Experimental example 1>
In order to evaluate the electrochemical characteristics of the self-supporting SnS two-dimensional nanosheets manufactured according to Examples 1 and 2 as the negative electrode active material for a secondary battery and compare the characteristics with the thin film and the powder electrode as follows: A half-cell was manufactured.

(A) Manufacture of electrode The SnS nanosheet manufactured by the said Examples 1-2 and the SnS thin film which is the control group itself were used as an electrode.

  As another control group, the SnS powder electrode was weighed so that the mass ratio of powder 2 mg, graphite (MMM, Carbon) as a conductive agent, and Kynar 2801 (PVdF-HFP) as a binder was 67:20:13, A slurry was obtained by dissolving in N-methyl-pyrrolidone (NMP), which is an inert organic solvent. The slurry was applied to a copper foil as a current collector and dried in a vacuum oven at 100 ° C. for 4 hours to volatilize the organic solvent, and then pressed into a disk shape by pressing.

(B) Production and measurement of half-cell for electrochemical property evaluation In order to measure the electrochemical properties of the self-supporting SnS two-dimensional nanosheet, the electrode produced in (a) above was used with lithium metal as the negative electrode. A positive electrode was obtained. An electrolyte and a separation membrane (Celgard 2400) were inserted between the two to form a Swagelok type half-cell. At this time, a substance in which LiPF ₆ was dissolved in a solution in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 was used as an electrolyte. The manufacturing process was performed in a glove box filled with argon, an inert gas.

  The manufactured Swagelok type half-cell is manufactured by adding a 1C current density at a voltage of 0.01 to 1.30V using a charge / discharge cycler (WBCS3000, WonA Tech., Korea) of a galvanostatic mode. Cycle charge / discharge.

  Moreover, the current density was changed to 1C, 3C, 5C, 10C, 20C, 40C, and 80C at the same voltage, and a charge / discharge test of 10 cycles was performed for each current density.

  And the voltage transition curve by the capacity | capacitance obtained from the measurement was analyzed, and the electrochemical characteristic was evaluated. At this time, the applied current amount is inversely converted from the theoretical capacity of SnS and the actual weight of the active material.

  The graph of FIG. 7 shows the change in capacity depending on the number of cycles of the self-supporting SnS nanosheet, the thin film, and the powder electrode when a current density of 1 C is applied.

  According to this, the self-supporting SnS nanosheet negative electrode active material has a higher capacity than a thin film or a powder electrode, and has extremely excellent cycle characteristics.

  Further, the graph of FIG. 8 shows the change in capacitance due to the change in current density, comparing the output characteristics between the three electrodes.

  According to FIG. 8, the self-supporting SnS nanosheet electrode exhibits superior capacity characteristics at all current densities compared to the other two electrodes. This is because the self-supporting SnS nanosheet active material is in direct contact with the current collector (SUS substrate) and the electrons are effectively transmitted to form a two-dimensional structure, so that the contact resistance between particles is minimized. .

  The following Table 1 shows the first and 50th discharge capacities of the self-supporting SnS nanosheets synthesized according to Examples 1 and 2 measured at 1 C current density of the thin film and the powder active material. The discharge capacity in the current density of 1C, 3C, 5C, 10C, 20C, 40C, 80C of the electrode is shown.

  According to FIGS. 7 and 8 and Tables 1 and 2, it can be seen that the self-supporting SnS two-dimensional nanosheet expresses much better capacity, output and cycle characteristics than SnS thin film and SnS powder. By minimizing the wide contact area between the electrode and electrolyte, the short diffusion distance of electrons / lithium ions, the effective relaxation of volume expansion, the smooth electron transfer between the current collector and the active material, and the contact resistance between particles.

  The electrode manufactured according to the present invention is a self-supported electrode in which a negative electrode active material and a metal current collector are in direct contact without a conductive additive and a mechanical binder, The isolated resistance and contact resistance between the negative electrode active material are minimized, and effective electron transfer is possible between the current collector and the active material, so that stable cycle characteristics and excellent output characteristics are exhibited.

  In addition, by the pulsed laser deposition method, the present invention can produce two-dimensional nanostructures having various geometric shapes at a low temperature by a simple synthesis process, on a large area non-catalytic metal substrate. It can be synthesized uniformly.

Claims (2)

Aggregates composed of metal sulfide-based materials are peeled off and grown directly on the metal substrate as metal sulfide-based two-dimensional nanostructures. The negative electrode activity of self-supporting metal sulfide-based two-dimensional nanostructures material. Producing an agglomerate comprising a metal sulfide-based material;
Inserting and attaching the agglomerates to a tube in an electric furnace for pulsed laser deposition;
Inserting a metal substrate into the tube and positioning it away from the aggregate;
Lowering the pressure in the tube to a vacuum of 0.01 to 0.03 Torr and raising the temperature of the electric furnace to 590 to 610 ° C .;
Injecting a pulsed laser into the tube to separate the aggregates;
Including
A method for producing a negative electrode active material of a self-supporting metal sulfide-based two-dimensional nanostructure, wherein the metal sulfide-based material is directly grown on the metal substrate as a two-dimensional nanostructure.