KR20190013503A - Sodium ion storage material - Google Patents

Abstract

The present invention relates to a material for storing sodium ions, an electrode material for a sodium ion battery including the same, an electrode material for a seawater battery, an electrode for a sodium ion battery, an electrode for a seawater battery, a sodium ion battery, and a seawater battery. More specifically, the material for storing sodium ions includes one or more material selected from a group consisting of Cu_xS, FeS, FeS_2, Ni_3S, NbS_2, SbO_x, SbS_x, SnS, and SnS_2 (provided that 0 < x <= 2). According to the present invention, the material for storing sodium ions is used to maintain high discharge capacity and when the material is applied to a sodium ion secondary battery, excellent charging and discharging cycle properties can be achieved.

Description

[0001] Sodium ion storage material [0002]

The present invention relates to a sodium ion storage material and an electrode material for a sodium ion battery, an electrode material for a seawater battery, an electrode for a sodium ion battery, an electrode for a seawater battery, a sodium ion battery and a seawater battery.

A lithium secondary battery such as a lithium ion battery or a lithium polymer battery has a high voltage and a high capacity as compared with a nickel cadmium battery and a nickel metal hydride battery and is also lightweight. For this reason, in recent years, it has been expanded to use as a main power source of a mobile communication device, a portable electronic device, an electric bicycle, an electric motorcycle, an electric car, and the like.

For example, in a current lithium ion battery, lithium-containing transition metal composite oxides such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium iron phosphate (LiFePO ₄ ) Graphite, hard carbon, or the like, which is capable of absorbing and releasing lithium (lithium), is used for the negative electrode. The electrolytic solution used in the lithium ion battery is mainly composed of a cyclic carbonate such as propylene carbonate (PC) or ethylene carbonate (EC), a cyclic carbonate such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethanesulfonyl amide _{(LiN (CF 3 SO 2)} 2), may be used by dissolving an electrolyte salt such as trifluoride methanesulfonic acid lithium (LiCF ₃ SO _3).

The major problem posed by lithium ion batteries is that of localized localization of lithium resources. In recent years, research on primary (sea water cells) and secondary batteries using sodium ions instead of lithium ions using non-aqueous electrolytes has been started in recent years. Sodium is abundant in seawater and is the sixth most abundant element on earth, and it is cheap and readily available. In other words, it can be said that it is a very attractive element in view of the tendency of rare earth element free in recent years. In addition, copper foil is used for the lithium ion battery as the collector of the negative electrode, but it is also an advantage that an inexpensive aluminum foil can be used for the sodium ion battery. Further, sodium is an alkali metal element similar to lithium and has similar properties, and the theory itself of a sodium ion battery has been studied for a long time.

For the above-described sodium ion battery, a positive electrode active material mainly NaCrO _2, NaMnO _2, NaFePO ₄ of the oxide-based material such as the _{Na 3 V 2 (PO 4)} 3, NaFePO 4 such polyanion-based, NaxTiS ₂ such as the sulfide Series, fluoride series such as FeF _3, and phosphate series such as NASICON.

However, the study on the anode material of Na ion battery is very limited. The commercial lithium ion battery is a lithium ion battery in which lithium ions move between graphite as a negative electrode active material and lithium-containing transition metal oxide such as LiCoO ₂ as a positive electrode active material and cause intercalation phenomenon to move between molecules of respective materials. (Charge / discharge). Graphite is a layered molecular structure, and the structure of graphite is less likely to be destroyed even when lithium ions enter and leave between these layers. Also, in theory, lithium ions of 372 mAh / g can be occluded. However, the sodium ion is not suitable for sodium storage because it has a large ionic radius and is difficult to enter between the graphite layers.

Therefore, petroleum cokes, carbon black and hard carbon have been mentioned as candidates for the anode material of the sodium ion battery, but the sodium storage capacity is also poor. For example, a hard carbon based material among carbon-based materials has been reported to have a capacity of ~ 300 mAh / g. However, considering the voltage characteristics and low initial efficiency, the practical capacity of the battery is within 180 mAh / g. On the other hand, a material which undergoes an alloy reaction with a negative electrode material may also be used, examples of which include Sn, Sb and P, and the like. However, these materials have a problem of very large volume expansion. For example, Na ₁₅ Sn ₄ has a volume expansion of 525% and Na ₃ P has a volume expansion of 490%. This problem is similarly applied to a sodium ion battery, which is a sodium ion primary battery, and development of a suitable electrode material is required to solve this problem.

Korean Patent Laid-Open Publication No. 10-2015-0088826 (published date 2015.08.03)

It is an object of the present invention to provide a sodium ion storage material capable of exhibiting excellent charge-discharge cycle characteristics while maintaining a high discharge capacity.

Another object of the present invention is to provide an electrode material for a sodium ion battery capable of exhibiting excellent charge-discharge cycle characteristics while maintaining a high discharge capacity.

Another object of the present invention is to provide an electrode for a sodium ion battery capable of exhibiting excellent charge / discharge cycle characteristics while maintaining a high discharge capacity.

It is another object of the present invention to provide a sodium ion battery capable of exhibiting excellent charge / discharge cycle characteristics while maintaining a high discharge capacity.

Still another object of the present invention is to provide an electrode material for a seawater battery including the sodium ion storage material, an electrode for a seawater battery including the same, and a sea water battery including the same.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

According to an embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising _{: a step} of selectively removing ₁ (1) selected from the group consisting of Cu _x S, FeS, FeS ₂ , Ni ₃ S, NbS ₂ , SbO _x , SbS _x , SnS and SnS ₂ And more particularly to a sodium ion storage material comprising more than one species of material.

The material may be a particle having a size of 1 nm to 500 μm, and preferably a particle having a size of 100 nm to 1000 nm.

In the present invention, the material may be a nanoplate, a nanosphere, a nanowire, a hollow nanosphere, a nanobox, a nanodot, and a nanotube. And may have at least one shape selected from the group consisting of

In the present invention, the material may be in the form of a nanoplate.

In the present invention, the nano plate may have a polygonal plate shape.

In the present invention, the nano plate may have a hexagonal plate shape.

In the present invention, the material may be one in which two nanoparticles are cross-oriented with respect to each other. In the present invention, the first nanoparticle of the two nanoparticles is oriented along a {001} plane and the second nanoparticle is oriented along a {100} Plane. &Lt; / RTI &gt;

In the present invention, the diameter of the nano plate may be between 100 nm and 1000 nm.

In the present invention, the thickness of the nano plate may be between 10 nm and 100 nm.

In the present invention, the electrode material for a sodium ion battery or the electrode material for a seawater battery may include the sodium ion storage material as an electrode active material.

In the present invention, the electrode active material may be coated with at least one selected from the group consisting of conductive carbon, noble metal, and metal.

In the present invention, the electrode material may further include a binder.

In the present invention The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid, alginic acid, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, , At least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber and fluorine rubber.

In the present invention, the electrode material may further include a conductive material.

According to another embodiment of the present invention, there is provided an electrode for a sodium ion battery or an electrode for a sea water battery including an electrode material according to the present invention.

According to another embodiment of the present invention, there is provided a sodium ion battery or a sea water battery including an electrode and an electrolyte according to the present invention.

INDUSTRIAL APPLICABILITY The present invention can maintain a high discharge capacity by using a sodium ion storage material and an electrode material for a sodium ion battery or a seawater battery, and can exhibit excellent charge / discharge cycle characteristics when applied to a sodium ion battery as a secondary battery .

1 (a) is an XRD graph of a CuS nanoplate manufactured in Example 1 of the present invention.
FIG. 1 (b) shows an SEM image of the three-dimensional shape of the CuS nanoplate produced in Example 1 of the present invention.
1 (c) and 1 (d) are high-resolution transmission electron microscope (HR-TEM) photographs of the side plane and basal plane of the CuS nanoplate prepared in Example 1 of the present invention will be.
Figure 2 (a) shows the charge and discharge profile of the sodium ion cell prepared in Example 2 of the present invention at 0.2 C for 100 cycles.
FIG. 2 (b) is a graph showing changes in charge capacity, discharge capacity and coulombic efficiency of the CuS nanoplate produced in Example 2 of the present invention at 0.2 C for 150 cycles.
Figure 3 (a) shows a bright field transmission electron microscope (BF-TEM) image of the morphological changes of the CuS nanoplate during the sodiumation reaction.
3 (b) is a graph showing the change in the area of the sodiumated phase projected in the TEM according to the electron beam irradiation time. Here, the light blue color is pure CuS phase, the orange color represents the Na _x CuS during the intercalation reaction, and the blue color represents the Na ₂ S + Cu as the converted phase.
FIG. 3 (c) is a graph showing the rate of change of the total area projected according to the electron beam irradiation time.
FIG. 4 is a photograph of the sodiumation reaction of a CuS nanoplate at high resolution. Fig. (A) of 4 total sodium reaction, (b) is CuS, (c) is _{Na (CuS) 4, (d} ) is _{Na 7 (Cu 6 S 5)} 2, and (e), Na ₃ ( CuS) ₄ , and (f) is a schematic diagram showing Na ₂ S + Cu. Here, the purple arrows in FIG. 4B, the light blue and blue arrows in FIG. 4C indicate the movement path of sodium in each structure.
5 (a) shows a transmission electron microscope (HR-TEM) photograph of the CuS nano-box according to the present invention.
FIG. 5 (b) is a graph showing changes in charge capacity, discharge capacity, and coulombic efficiency with respect to the CuS nanobox at 1 C for 1800 cycles in FIG. 5 (a).
6 (a) shows a transmission electron microscope photograph of CuS having a size of 1 탆 according to the present invention.
FIG. 6 (b) is a graph showing changes in charge capacity, discharge capacity, and coulombic efficiency with respect to CuS at 0.2 C and FIG. 6 (a) for 80 cycles.
FIG. 7 (a) shows a scanning electron microscope (SEM) image of a bulk-sized CuS according to the present invention.
FIG. 7 (b) is a graph showing changes in charge capacity, discharge capacity and coulombic efficiency with respect to CuS in FIG. 7 (a) at 0.2 C for 50 cycles.
8 (a) shows a transmission electron microscope photograph of CuS nano dot according to the present invention.
FIG. 8 (b) is a graph showing changes in charge capacity, discharge capacity and coulombic efficiency with respect to CuS nano dot in FIG. 8 (a) at 3C for 1000 cycles.
FIG. 9 is a graph showing changes in charge capacity, discharge capacity and coulombic efficiency of the CuS nanoplate produced in Example 11 of the present invention at 0.2 C for 20 cycles.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

The inventors of the present invention found that when the sulfide composition is used as a sodium ion storage material, an electrode material of a sodium ion battery, and an electrode material of a sea water battery, excellent charge and discharge cycle characteristics can be obtained while maintaining a high discharge capacity , As well as that the particle size of the sulfide used as the electrode material of the sodium ion storage material and the sodium ion battery exhibits excellent electrochemical performance in the bulk unit as well as the nano unit, leading to the present invention.

According to one embodiment of the present invention, there is provided a sodium ion storage material comprising Cu _x S, FeS, FeS ₂ , Ni ₃ S, NbS ₂ , SbO _x , SbS _x , SnS and SnS ₂ , 2), preferably Cu _x S (0 < x? 2), and more specifically CuS.

The size of the substance related to the sodium ion storage material may be a bulk or nano unit having a size between 1 nm and 500 μm, a particle having a size between 1 nm and 1000 nm when the unit is a nano unit, , At least one shape selected from the group consisting of nanospheres, nanospheres, nanowires, hollow nanospheres, nanoboxes, nanodots, and nanotubes. And may be in the form of a nanoplate.

In the present invention, the " nano plate " means a two-dimensional plate structure which is different from the powder shape or the particle shape.

In the present invention, the term " nanowire " means a wire structure having a cross-sectional diameter of nanometers. For example, the nanowire may have a cross-section diameter between 100 nm and 500 nm and a length between 0.1 and 100 μm. For example, the nanowire may have an aspect ratio of 5 or more, 10 or more, specifically 50 or more, and more specifically 100 or more. The nanowires can be substantially uniform or variable in diameter, and at least a portion of the major axis of the nanowire can be straight, curved or bent, or branched.

In the present invention, the term "nanosphere" means a sphere structure having a diameter of nanometer unit. For example, the diameter of the nanospheres is preferably 100 to 1000 nm, and particularly preferably 200 to 500 nm.

The " hollow nanospheres " in the present invention are nano hollow spheres having a diameter of nanometer units, and are hollow and have only a shell like a ball. At this time, the diameter of the hollow nanospheres is preferably 100 to 1000 nm, and particularly preferably 200 to 500 nm.

In the present invention, the term " nanobox &quot; means a box having a length of nanometer unit, and the length of the nanobox is preferably 100 to 1000 nm, more preferably 100 to 200 nm.

In the present invention, the " nano dot &quot; refers to a point shape having a length of nanometer unit, and the size is preferably 1 to 30 nm.

In the present invention, the term " nanotube " refers to a tube structure having a cylindrical shape of nanometer length. The length of the nanotubes is preferably 100 to 1000 nm, more preferably 100 to 200 nm.

In the present invention, if the nano plate is capable of reversibly intercalating sodium ions during charging and discharging, the crystal structure is not particularly limited, but preferably the nano plate may be in the form of a polygonal plate, For example, it may be a hexagonal, pentagonal, rectangular, triangular, parallel slope or trapezoidal shape, but may be more preferably hexagonal.

In the present invention, the material may be one in which two nanoparticles are cross-oriented with respect to each other, preferably one of the two nanoparticles is oriented in a {001} crystallographic plane, and the second nanoparticle is oriented in { 100} crystallographic plane.

In the present invention, the diameter of the nano plate may be between 100 nm and 1000 nm, and preferably between 100 nm and 500 nm.

Also, in the present invention, the thickness of the nano plate may be between 10 nm and 100 nm, and preferably between 10 nm and 50 nm.

In the present invention, the material of the nano plate has a nano plate shape having a size (diameter or length) between 100 nm and 1000 nm, so that the shape of the nano plate can be maintained at the initial stage of the sodiation process, Can provide a large surface area for extraction, and as the cycling progresses, a large number of crystal grains are produced, and intergranular interfaces facilitate the Na outflow. As a result, the sodium ion storage material of the present invention can have a specific capacity close to the theoretical value as the cycle number increases.

In addition, the present invention provides an electrode material for a sodium ion battery and an electrode material for a seawater battery, wherein the sodium ion storage material is used as an electrode active material, preferably as a negative electrode active material.

In the present invention, the electrode active material may be coated with a conductive material to further improve electrical conductivity. In the present invention, the conductive material may be at least one selected from the group consisting of conductive carbon, noble metal, and metal. Particularly, in the case of covering with conductive carbon, the conductivity can be effectively increased without significantly increasing the manufacturing cost and weight, which is desirable.

In the present invention, the conductive carbon may be at least one selected from the group consisting of carbon black, carbon nanotubes, and graphene, but is not limited thereto.

In the present invention, the conductive carbon may be coated in an amount of more than 2 wt% to 5 wt%, preferably 2.5 wt% to 5 wt%, based on the total weight of the nanoplate. When the amount of the conductive carbon is excessively large, the amount of the nanoplate is relatively reduced, thereby reducing the overall battery characteristics. When the amount is too small, the electric conductivity improving effect can not be exhibited.

In the present invention, the conductive carbon may be applied to the surface of the electrode active material particle, for example, the surface of the electrode active material particle may be coated to a thickness of 0.1 nm to 20 nm.

In the present invention, when the conductive carbon is a primary particle coated with 0.5 to 1.5 wt% based on the total weight of the electrode active material, the thickness of the carbon coating layer may be about 0.1 nm to 2.0 nm.

In the present invention, the electrode material may further include a binder and optionally a conductive material in addition to the electrode active material.

In the present invention, the binder is for adhering the electrode active material particles to each other and improving the bonding of the negative electrode active material to the current collector. The specific kind is not particularly limited, but for example, polyvinylidene fluoride, polyvinyl alcohol, Polyacrylic acid, alginic acid, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter Polymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

In the present invention, the binder may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the electrode active material, but is not limited thereto.

In the present invention, the solvent of the binder is not particularly limited, but for example, N-methylpyrrolidone (NMP), acetone or water may be used.

In the present invention, the solvent is contained in an amount of 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material, so that the work for forming the negative electrode material is easy.

In addition, the electrode material of the present invention may further include a conductive material selectively in order to further improve the electrical conductivity. As the conductive material, any material generally used for a sodium ion battery can be used. Examples of the conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; A conductive polymer such as a polyphenylene derivative, or a conductive material including a mixture thereof. The content of the conductive material can be appropriately adjusted.

In the present invention, the conductive material preferably has a particle size of 2 nm to 1 탆. When the particle size of the conductive material is less than 2 nm, it is difficult to form a uniform slurry in an electrode manufacturing process. When the conductive material has a particle size exceeding 1 탆, the electric conductivity of the electrode can not be improved.

In the present invention, the electrode active material and the conductive material may be contained in a weight ratio of 9: 1 to 99: 1, more preferably 9: 1, but the present invention is not limited thereto.

The term " sodiate " and " sodiation " in the present invention may refer to the process of adding sodium to the electrode material.

The term " desodiate " and " desodiation " in the present invention can refer to the process of removing sodium from the electrode material.

The terms " charge " and " charge " in the present invention can refer to the process of providing electrochemical energy to a battery.

The term " discharge " and " discharge " in the present invention can refer to a process of removing electrochemical energy from a battery, for example, when using the battery to perform a desired operation.

The term " anode " in the present invention can refer to an electrode (sometimes referred to as a cathode) where electrochemical reduction and sodiumation take place during the discharge process.

The term " cathode " in the present invention can refer to an electrode (sometimes referred to as an anode) where electrochemical oxidation and denaturation occurs during the discharge process.

According to another embodiment of the present invention, there is provided a method for preparing an electrode active material according to the present invention, comprising the steps of: (a) reacting cetyl trimethylammonium bromide (CTAB), hexane, n- pentanol) and copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) to form a microemulsion; (b) adding the microemulsion to carbon disulfide; And (c) drying at a temperature of 150 to 200 DEG C for 12 to 24 hours.

In the present invention, a CuS nanoplate having a diameter of 100 nm to 1000 nm and a thickness of 10 nm to 100 nm as an electrode active material can be produced by the above process.

In the present invention, the CuS nanoplate may have a hexagonal shape, a pentagonal shape, a square shape, a triangular shape, a parallel slope shape, or a trapezoid shape, but may be hexagonal .

In the present invention, more specifically, the two nano plates are cross-aligned with each other to have an 'X' shape in cross section. Preferably, the first nano plate among the two nano plates is a {001 } Crystallographic plane, and the second nanoplate can be oriented in a {100} crystallographic plane.

Each step in the present invention will be described in detail as follows.

Step (a): Mixing cetyl trimethylammonium bromide (CTAB), hexane, n-pentanol and copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) To form a microemulsion.

The n-pentanol may be added in an amount of 8.65 mol based on the cetyltrimethylammonium bromide, and the copper nitrate may be added in an amount of 10 molar ratio relative to the cetyltrimethylammonium bromide, but not limited thereto .

Also, the cetyltrimethylammonium bromide may be 0.1 M concentration, and the copper nitrate may be 0.2 M concentration, but the present invention is not limited thereto.

(b): The microemulsion may be added to carbon disulfide.

In the present invention, the carbon disulfide may be added in an amount of 100: 0.7 to 0.9 based on the microemulsion, but the present invention is not limited thereto.

(c): drying at a temperature of 150 ° C to 200 ° C for 12 to 24 hours may be performed.

In the present invention, the drying can be performed in an autoclave, but is not limited thereto.

In the present invention, a black precipitate, that is, a CuS nanoplate can be prepared by the above step (c), and if necessary, washed with a solvent several times and then dried at a temperature of 50 to 70 ° C in a vacuum oven Can be performed.

In the present invention, the surface of the nano plate may be further coated with a conductive material to improve electrical conductivity of the CuS nano-plate.

In the present invention, the conductive material may be at least one selected from the group consisting of conductive carbon, noble metal, and metal. Particularly, in the case of covering with conductive carbon, the conductivity can be effectively increased without significantly increasing the manufacturing cost and weight, which is desirable.

In the present invention, the conductive carbon may be at least one selected from the group consisting of carbon black, carbon nanotubes, and graphene, but is not limited thereto.

In the present invention, the conductive carbon may be coated in an amount of more than 2 wt% to 5 wt%, preferably 2.5 wt% to 5 wt%, based on the total weight of the nanoplate. When the amount of the conductive carbon is excessively large, the amount of the nanoplate is relatively reduced to reduce battery characteristics, and when it is too small, the effect of improving the electron conductivity can not be exhibited.

In the present invention, the conductive carbon may be applied to the surface of the nano plate. For example, the surface of the primary particle may be coated to a thickness of 0.1 nm to 10 nm, the surface of the secondary particle may be coated to a thickness of 0.1 nm to 20 nm Thickness can be coated.

In the present invention, in the case of the primary particles in which the conductive carbon is coated with 0.5 to 1.5 wt% based on the total weight of the nanoplate, the thickness of the carbon coating layer may be about 0.1 to 2.0 nanometers.

According to another embodiment of the present invention, there is provided an electrode for a sodium ion battery and an electrode for a sea water battery including an electrode material according to the present invention. In the present invention, the electrode may be a cathode.

The electrode material may be directly coated on the current collector or may be obtained as an electrode plate by casting on a separate support and laminating an electrode material film peeled off from the support to the current collector. In the present invention, the electrode is not limited to the above-described form, but may be in a form other than the above-described form.

In the present invention, the current collector may generally have a thickness of 3 mu m to 500 mu m. In the present invention, the current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, it may be copper, stainless steel, aluminum, nickel, titanium, Treated with carbon, nickel, titanium, silver or the like on the surface thereof, or may be an aluminum-cadmium alloy. Further, fine unevenness may be formed on the surface to enhance the binding force of the electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

According to another embodiment of the present invention, there is provided a sodium ion battery and a sea water battery including the electrode and the electrolyte according to the present invention. When the electrode according to the present invention is a cathode, the cathode may be prepared by directly coating a cathode material including a cathode active material on the collector, or casting the cathode material on a separate support, and laminating the cathode material film, Can be obtained as a positive electrode plate. In the present invention, the anode is not limited to the above-mentioned form, but may be in a form other than the above-described form.

When the electrode according to the present invention is a cathode, a compound capable of reversibly intercalating and deintercalating sodium (sodium intercalation compound) may be used as the cathode active material. A more specific positive electrode active material is not particularly limited, but a sodium-transition metal composite oxide is preferable. Sodium transitions As the metal composite oxide, for example _{NaMn 2 O 4, NaNiO 2,} NaCoO 2, NaFeO 2, NaNi 0.5 Mn 0.5 O 2, NaCrO 2, Na 0.9 Mg 0.05 Ni 0.5 Mn 0.5 O 2 and Na _0.9 Ca _0.05 Ni _0.5 Mn _0.5 O _2, and the like. In some cases, two or more kinds of positive electrode active materials may be used in combination.

In the present invention, the cathode material may further include a binder, a solvent and optionally a conductive material in addition to the cathode active material layer.

In the present invention, the binder is for adhering the electrode active material particles of the nano plate to each other well and improving the bonding of the electrode active material to the current collector. The specific kind is not particularly limited, but for example, polyvinyl alcohol, , Alginic acid, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, poly But are not limited to, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon.

In the present invention, the binder may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the positive electrode active material, but is not limited thereto.

In the present invention, the type of the solvent of the binder is not particularly limited. For example, N-methylpyrrolidone (NMP), acetone or water may be used.

In the present invention, the solvent is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the cathode active material, so that it is easy to work for forming the cathode material.

In addition, the cathode material of the present invention may further include a conductive material selectively in order to further improve the electrical conductivity. As the conductive material, any material generally used for a sodium ion battery can be used. Examples of the conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; A conductive polymer such as a polyphenylene derivative, or a conductive material including a mixture thereof. The content of the conductive material can be appropriately adjusted.

In the present invention, the conductive material preferably has a particle size of 2 nm to 1 탆. When the particle size of the conductive material is less than 2 nm, it is difficult to form a uniform slurry in an electrode manufacturing process. When the conductive material has a particle size exceeding 1 탆, the electric conductivity of the electrode can not be improved.

In the present invention, the cathode active material and the conductive material may be contained in a weight ratio of 1: 9 to 99: 1, more preferably 1: 1 to 9: 1, but the present invention is not limited thereto.

In the present invention, the current collector may generally have a thickness of 3 mu m to 500 mu m. In the present invention, the current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and may be aluminum, nickel, titanium, sintered carbon, copper or stainless steel, Treated with carbon, nickel, titanium, silver or the like on the surface thereof, or may be an aluminum-cadmium alloy. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In the present invention, the electrolyte includes a liquid electrolyte, a solid electrolyte, or a combination thereof, and the liquid electrolyte includes a sodium salt, an organic solvent, or a combination thereof. The solid electrolyte includes an organic solid electrolyte , An inorganic solid electrolyte, or a combination thereof.

In the present invention, when the electrolyte is a liquid electrolyte, it includes an electrolyte salt and a solvent.

In the present invention, the electrolytic salt is specifically exemplified by a sodium-containing hydroxide such as sodium hydroxide (NaOH), a borate (such as sodium metaborate (NaBO ₂ ), borax (Na ₂ B ₄ O ₇ ) Boric acid (H ₃ BO ₃ ) and the like), phosphates (for example, trisodium phosphate (Na ₃ PO ₄ ), sodium pyrophosphate (Na ₂ HPO ₄ ) and the like), chloric acid (for example, NaClO ₄ ) ₄ , NaAsF ₆ , NaBF ₄ , NaPF ₆ , NaSbF ₆ , NaCF ₃ SO ₃ or NaN (SO ₂ CF ₃ ) ₂ , and any one or a mixture of two or more thereof may be used.

In the present invention, the electrolyte may contain 2 to 5% by weight of the electrolyte salt based on the total weight of the electrolyte.

In addition, in the present invention, the solvent can be used without particular limitation as long as it can act as a medium through which ions involved in an electrochemical reaction of a battery can move. Specifically, the solvent may be an aqueous solvent such as water, alcohol, or the like; Or a nonaqueous system such as an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, or a carbonate solvent. These may be used singly or in combination of two or more.

Particularly preferred solvents in the present invention are esters, and examples thereof include methyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, But are not limited to, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide,? -Valerolactone, mevalonate, Mevalonolactone,? -Caprolactone,? -Valerolactone, or? -Caprolactone, and the like.

More preferred examples of the ether solvents include diethylene glycol dimethyl ether, diglyme, dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, Or tetrahydrofuran, and the like. For comparison, Example 3 and Example 11 in which the electrochemical performance of the CuS nanoplate was tested were compared. In Example 3, an ether-based solvent (diglyme) was used as an electrolyte, and Example 11 was a carbonate- DEC) was used. Comparing the results of the two experiments, it can be seen that the electrochemical performance of Example 3 using an ether-based solvent is much better.

In the present invention, specific examples of the ketone-based solvent include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

Specific examples of the carbonate solvent in the present invention include dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate EPC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) Or fluoroethylene carbonate (FEC).

In the present invention, when the electrolyte is a solid electrolyte, an organic polymer electrolyte such as a polymer compound containing at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain, and a polyoxyalkylene chain may be used have. A so-called gel type in which a non-aqueous electrolyte solution is held in a polymer compound may also be used. In addition, inorganic solid electrolytes such as sulfide electrolytes such as Na ₂ S-SiS ₂ and Na ₂ S-GeS ₂ and NASICON electrolytes such as NaZr ₂ (PO ₄ ) ₃ may be used. When these solid electrolytes are used, there are cases where safety can be further increased.

In the case of using the solid electrolyte in the sodium secondary battery of the present invention, the solid electrolyte may serve as a separator, and in this case, a separator may not be required.

In addition to the above electrolyte components, the electrolyte may further contain an additive (hereinafter, referred to as "other additive") that can be generally used for an electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing reduction in battery capacity, .

In the present invention, 0.1 to 5% by weight of fluorinated ethylene carbonate is preferably added to the electrolyte.

As described above, the sodium ion battery of the present invention may use a solid electrolyte as an electrolyte and may not require a separate separator when the solid electrolyte serves as a separator. However, the sodium ion battery may further include a separator .

In the present invention, the separator separates the negative electrode and the positive electrode, provides a passage for sodium ions, and can be used as long as it is commonly used in a battery using sodium ions. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, it may be a nonwoven fabric or a woven fabric selected from glass fibers, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof. Preferably, a polyolefin-based polymer separator such as polyethylene, polypropylene or the like is mainly used for the sodium secondary battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength. Alternatively, Structure.

In addition, the sodium secondary battery of the present invention may further include FEC (fluoroethylene carbonate), VC (vinylene carbonate), or a combination thereof as an additive.

Hereinafter, the present invention will be described in more detail with reference to Examples. It will be apparent to those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments in accordance with the gist of the present invention .

Example

[Example 1] Production of negative electrode active material (CuS nanoplate)

A three-dimensional structure of CuS nanoplate was synthesized by solvent solvothermal method in a Teflon sealed autoclave. The copper nitrate _{(Cu (NO 3) 2 ·} 3H 2 O), cetyltrimethylammonium bromide (cetyl trimethylammonium bromide, CTAB), hexane (hexane) and n- pentanol (n-pentanol) used for the synthesis is from Sigma-Aldrich Respectively. A microemulsion consisting of water containing 0.1 M CTAB (in hexane), 8.65 (molar ratio to CTAB) n-pentanol, 10 (molar ratio to CTAB) 0.2 M copper nitrate was used. A 0.2 M aqueous copper nitrate solution was added to a mixed solution of pentanol and hexane containing 0.1 M CTAB and stirred until it became transparent. The microemulsion was placed in a 100 ml Teflon-sealed autoclave and 0.8 ml of carbon disulfide was added. The autoclave was placed in an oven and treated at 170 DEG C for 15 hours. The resulting black precipitate was washed several times with acetone and ethanol, and dried at 60 DEG C in a vacuum oven. SEM, FEI, Varios 460 and X-ray diffractometer (XRD, RIGAKU, D / MAX-2500) were used to confirm the three-dimensional structure and crystal structure of the synthesized nanoplate.

[Example 2] In-situ TEM sample preparation

NaF particles and CuS nanoplates were dispersed on a holey carbon Au grid (300 mesh, SPI) coated graphene. A voltage of 200 kV was applied using a conventional transmission electron microscope (TEM) (JEOL, JEM-2100F and ARM-200F) equipped with a charge coupled device (CCD) camera (Orius 1000, Gatan) The reaction was observed in real time. The sodiumation reaction is initiated by electron beam irradiation of a CuS nanoplate adhered to NaF particles as the metal Na is decomposed from NaF. After the sodiumation reaction, energy dispersive spectroscopy (EDS) mapping was performed to confirm the structural change.

[Example 3] Electrochemical cell experiment and ex-situ characterization

CuS NPs, acetylene black (Alfa Aesar) and polyvinylidene fluoride (PVDF, Sigma Aldrich) were mixed in a weight ratio of 8: 1: 1 in 1-methyl-2-pyrrolidone . The prepared slurry was coated on a Cu foil and vacuum dried for 12 hours. As the electrolyte, 1M sodium hexafluorophosphate (NaPF ₆ ) was dissolved in diglyme. After the sodium salt was added to the diglyme, the electrolyte was stirred in a glove box at a temperature of 80 캜 for 2 days under an Ar gas atmosphere. Pure Na foil and glass fiber were used as reference electrode and separator. A half-cell (ECC-STD, EL-CELL) was assembled in a glove box under an Ar gas atmosphere. Electrochemical cell tests were performed using a PARSTAT MC 1000 battery tester (Princeton Applied Research). The charge / discharge cycle profile was evaluated at room temperature from 0.05 to 2.6 V at a rate of 0.2C. For ex-situ experiments, the electrochemical cell was disassembled after several charge / discharge cycles. The active material was thoroughly washed in dimethyl carbonate (DMC) for 3 hours via active sonication and then dispersed on a grid for TEM experiments.

[Example 4] Shape of CuS nanoplate and electrochemical characteristics during sodiumation process

The synthesized CuS nano-plate (space group: P6 ₃ / mmc) had interweaving of two thin plates with a mean diameter of ~ 300 nm and a thickness of ~ 30 nm (Figures 1 (a) and 1 (b)). The plate showed a hexagonal structure with faces exposed to crystallographic {100} and {001} (FIGS. 1 (c) and 1 (d)). These plates not only protect CuS from fractures induced during the sodiumation process, but also provide a large surface area for sodium insertion and extraction. The charge / discharge profile and the capacity performance of the CuS nanoplate are shown in FIGS. 2 (a) and 2 (b). In the first cycle, the highest discharge capacity reached ~ 680 mAh / g, but the capacity was slightly decreased until the 5th cycle. However, the capacity gradually recovered from the 10th cycle to the theoretical capacity level at the 100th cycle Reaching ~ 550 mAh / g known. Partial reduction of capacity in the initial cycle is due to a sharp decrease in sodium kinetic in the Na _x CuS structure, but as the number of cycles increases, the nanoplate breaks into small fragments and provides a short path to sodium, _The capacity could be restored by increasing the number of Na escaped from the _x CuS lattice. Once recovered as described above, the capacity and coulombic efficiency were maintained at ~ 560 mAh / g and ~ 100% for 60 cycles, respectively. The presence of two or more plateaus during the discharge profile indicates that two or more intercalation and conversion reactions occur during the sodiumation reaction. Typically, the intercalation and the conversion reaction can be represented by the following scheme:

Wherein x represents the sodium content. Within the range of 0-0.5 V, the voltage plate corresponds to the conversion reaction. Therefore, it was found that the capacity during the intercalation reaction is very important because it corresponds to half of the cell capacity.

[Example 5] Real-time observation of sodiumation reaction in CuS

In order to analyze the sodiumation reaction of CuS, the sodiumation reaction of the CuS nanoplate was performed in the TEM and the result was observed in real time (Fig. 3 (a)). The NaF particles were decomposed by irradiating an electron beam to generate Na, and a chemical reaction of Na and CuS was performed. The boundary between the intercalated portion and the CuS is indicated by a green line, and the sodiumation reaction proceeds from left to right. Before the end of the process from the front, we could see that the boundary between the intercalation marked by purple and the conversion reaction moved along the first boundary. Through this, it was found that two different reactions occur at the same time. These two areas have different diffraction contrasts to match the areas of intercalation (Na _x CuS) and conversion reactions (Na ₂ S and Cu). The conversion reaction is observed during the CuS sodiumation reaction, during which Na ₂ S matrix and Cu nanoparticles are generated. Through the observed crystalline form of Na ₂ S matrix, the CuS sodiumation reaction was found to be due to the displacement route rather than the general conversion pathway to generate the amorphous Na ₂ S matrix. After the CuS standard electrochemical test, TEM images were taken to analyze the superposition reaction between the intercalation and the conversion reaction. In order to quantitatively analyze the dynamics of the CuS sodiumation reaction, the area difference of various reaction zones was measured through a time-continuous TEM image (FIG. 3 (b)). Intercalation reaction was initiated when sodium was added and intercalation reaction was initiated for 57 seconds and conversion reaction was started at 24 seconds. After 57 seconds, the intercalation rate decreased, but the conversion reaction showed a relatively high area increase rate. Finally, the conversion reaction reached higher than the intercalation reaction and mixed (Figure 3 (c)). Initially, the intercalation reaction proceeded and increased at a constant rate, indicating that the rate of the intercalation reaction was controlled by the reaction of sodium and CuS. Thereafter, as the conversion reaction was initiated and sodium was depleted, the rate of intercalation progression rapidly decreased. The area change rate of the conversion reaction was relatively higher than that of the intercalation. As a result, the boundaries between the two reactions became difficult to distinguish from each other.

[Example 6] Preparation of Na _x Observation of change in CuS

)의 Na(CuS)₄와 유사한 구조로 구조적 변경되어, CuS 격자가 약간 팽창하였다. 삽입된 나트륨은 CuS_x 사면체 기둥(파란색의 사면체)를 붕괴시키고 Na(CuS)₄ 격자의 {001} 면에 위치되었다. As shown in FIG. 2 (a), it can be seen that two or more plateaus exist in the sodium discharge profile of CuS. That is, the CuS nanoplate was found to perform an additional step, rather than two steps of a simple intercalation-conversion reaction. Therefore, in order to confirm the atomic structure in all reactions, the mechanism of CuS sodiumation reaction was analyzed by taking real time high resolution images. During the intercalation reaction, the reaction plane proceeded along the <210> crystal plane. It proceeded with sodium layer inserted parallel to the {100} plane. A high resolution TEM image was taken at different steps in the sodium reaction and the results are shown in FIG. When sodium was added to CuS, various phases were generated. At the first intercalation step, the hexagonal ( P6 _{3 /} mmc ) CuS is the trigonal geometry (

) Structure of Na (CuS) _4, and the CuS lattice was slightly expanded. The inserted sodium disrupts the CuS _x tetrahedral pillar (blue tetrahedron) And was located on the {001} plane of the Na (CuS) ₄ lattice.

During sodium insertion, neighboring Cu atoms were released and rearranged with S atoms. As a result, Cu and S atoms achieved roto-inversion symmetry along the Na surface. Secondary structural deformation occurred when Na was further inserted. Sodium atom Na (CuS) is inserted in the {001} plane of the _four crystals being rearranged in the internal structure, CuS _x tetrahedral also change the structure, and as a result new metastable monoclinic structure _{(P2 / m) Na 7 (} Cu ₆ S ₅ ) ₂ crystals were formed. During this variation, the bond length of Cu and S atoms increased to ~ 12%.

} Na₃(CuS)₄ 면은 {

} Na₇(Cu₆S₅)₂ 면에 해당하였다. CuS_x 사면체는 S 원자 사이 브릿지가 파괴되며 두 S 열 사이가 5.16 Å 로 변화되었다. 그 결과, 더 많은 나트륨 원자가 두 CuS_x 기둥 사이로 삽입되고, 이전에 존재하던 나트륨 원자는 그 위치를 유지하게 되었다. 최종적으로 x_Na = 0.75 이상의 나트륨 삽입은 전환 반응을 통하여 그 구조를 결정성 Na₂S 매트릭스와 Cu 나노입자로 변화시켰다(도 4(e)). As a final step of the intercalation, the Na ₇ (Cu ₆ S ₅ ) ₂ phase changed to an orthorhombic Na ₃ (CuS) ₄ ( Pbam ) crystal. Both structures have high crystallographic similarity, and as shown in Fig. 4 (d), {

} Na ₃ (CuS) ₄ plane is {

} Na ₇ (Cu ₆ S ₅ ) ₂ plane. The CuS _x tetrahedron was destroyed by the bridge between the S atoms and the distance between the two S columns was changed to 5.16 Å. As a result, more sodium atoms were inserted between the two CuS _x columns, and the previously existing sodium atoms remained in place. Ultimately, sodium insertion with x _Na = 0.75 or more changed the structure to a crystalline Na ₂ S matrix and Cu nanoparticles through a conversion reaction (Fig. 4 (e)).

[Example 7] Electrochemical properties of CuS nanobox

FIG. 5 (b) shows the results of changing the charge capacity, the discharge capacity, and the coulombic efficiency for the CuS nanobox shown in FIG. 5 (a).

In the initial cycle, the capacity was slightly decreased, but then the capacity rapidly recovered, reaching ~ 300 mAh / g, which is known as the theoretical capacity level of CuS in the 100th cycle. Once recovered as described above, it was confirmed that the capacity and coulombic efficiency were maintained at ~ 300 mAh / g and ~ 100% for 1800 cycles, respectively.

[Example 8] Electrochemical properties for 1 탆 CuS

Fig. 6 (b) shows the results of changing the charge capacity, the discharge capacity and the coulombic efficiency at 0.2 C for 80 cycles of 1 탆 CuS shown in Fig. 6 (a).

In the initial cycle, the capacity was slightly reduced to 500 mAh / g, but it was confirmed that the capacity was maintained to ~ 550 mAh / g and ~100% coulombic efficiency for 80 cycles after the recovery.

[Example 9] Electrochemical properties of Bulk CuS

Fig. 7 (b) shows the results of changing the charge capacity, discharge capacity and coulombic efficiency at 0.2 C for 50 cycles of bulk-sized CuS shown in Fig. 7 (a).

In the initial cycle, it decreased to ~ 350mAh / g, but it was recovered similarly and it was confirmed that the storage capacity was ~ 410mAh / g and the ~ 100% coulombic efficiency was maintained for 50 cycles.

[Example 10] Electrochemical properties of CuS nanodot

The results of the change in charge / discharge capacity and coulombic efficiency at 0.2 C for 100 cycles with respect to the nanodot type CuS shown in FIG. 8 (a) are shown in FIG. 8 (b) The results of the change of the discharge capacity and the coulombic efficiency are shown in FIG. 8 (c), the results of the change of charge / discharge capacity and coulombic efficiency according to the change of the current density of 0.2 to 3 C are shown in FIG. Respectively.

 As a result, it was confirmed that the storage capacity was reduced to ~ 500 mAh / g at 0.2 C, but recovered within 100 cycles, and the storage capacity was ~ 530 mAh / g and ~100% coulomb efficiency after 100 cycles.

3C, the storage capacity was slightly reduced to ~ 432 mAh / g, but it was recovered to within 505 mAh / g and ~100% coulombic efficiency after ~ 900 cycles. Of the storage capacity and ~ 100% coulombic efficiency.

The reason for the decline in the initial capacity reduction effect at NanoDot is due to the sufficiently large active surface area.

[Example 11]

In Example 3, except for using dimethylcarbonate (DMC) as an electrolyte solvent in the preparation of the electrode, the rest of the production process is the same as in Example 3. It was confirmed that the use of the ether-based electrolyte of Example 3 was superior in the capacity recovery than that using the carbonate-based electrolyte.

Although the present invention has been described in detail with reference to the above results, it is to be understood that the scope of the present invention is not limited to these embodiments and that various modifications and changes may be made without departing from the scope of the present invention. It will be obvious to those of ordinary skill in the art.

Claims (21)

Wherein at least one substance selected from the group consisting of Cu _x S, FeS, FeS ₂ , Ni ₃ S, NbS ₂ , SbO _x , SbS _x , SnS and SnS ₂ material. The method according to claim 1,
Wherein the material is a particle having a size between 1 nm and 500 탆. The method of claim 3,
The material may be selected from the group consisting of nanoplates, nanospheres, nanowires, hollow nanospheres, nanoboxes, nanodots, and nanotubes. A sodium ion storage material having at least one selected shape. The method of claim 3,
The material may be selected from the group consisting of nanoplates, nanospheres, nanowires, hollow nanospheres, nanoboxes, nanodots, and nanotubes. A sodium ion storage material having at least one selected shape. 5. The method of claim 4,
Wherein the material is in the form of a nanoplate. 6. The method of claim 5,
Wherein the nanoplate is in the form of a polygonal plate. The method according to claim 6,
Wherein the nanoplate is in the form of a hexagonal plate. 6. The method of claim 5,
Wherein the material is two nanoplates cross-oriented with respect to each other. 9. The method of claim 8,
Wherein a first nanoplate of the two nanoplates is oriented along a {001} plane and a second nanoplate is oriented along a {100} plane. 6. The method of claim 5,
Wherein the nanoplate has a diameter ranging from 100 nm to 1000 nm. 6. The method of claim 5,
Wherein the thickness of the nanoplate is between 10 nm and 100 nm. An electrode material for a sodium ion battery, comprising the sodium ion storage material of claim 1 as an electrode active material. 13. The method of claim 12,
Wherein the electrode active material is coated with at least one selected from the group consisting of conductive carbon, noble metal, and metal. 13. The method of claim 12,
Wherein the electrode material further comprises a binder. 15. The method of claim 14,
The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid, alginic acid, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, , At least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber and fluorine rubber. 13. The method of claim 12,
Wherein the electrode material further comprises a conductive material. An electrode for a sodium ion battery comprising the electrode material of any one of claims 12 to 16. 17. A sodium ion battery comprising the electrode of claim 17 and an electrolyte. An electrode material for a seawater cell comprising the sodium ion storage material of any one of claims 1 to 11 as an electrode active material. 20. An electrode for a sea water cell comprising the electrode material of claim 19. 20. A sea water cell comprising the electrode of claim 20 and an electrolyte.

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