KR102288786B1 - Method for manufacturing a diameter-controllable spinel lithium manganese oxide nanofiber via electrospinning, and spinel lithium manganese oxide nanofiber manufactured by the same - Google Patents

Abstract

The present invention prepares spinel lithium manganese oxide nanofibers using electrospinning, and controls the viscosity, electrical conductivity and surface tension of a spinning solution containing PVP, lithium precursor and manganese precursor to produce nanofibers having a diameter of 35-50 nm. It relates to a manufacturing method of spinel lithium manganese oxide nanofiber, characterized in that it is manufactured, and to a spinel lithium manganese oxide nanofiber prepared thereby. The spinel lithium manganese oxide nanofiber of the present invention can be used as an excellent lithium adsorbent capable of selectively separating lithium ions from brine and seawater.

Description

Method for manufacturing a diameter-controllable spinel lithium manganese oxide nanofiber via electrospinning, and spinel lithium manganese oxide nanofiber manufactured by the same}

The present invention relates to a method for producing a spinel lithium manganese oxide nanofiber whose diameter is controlled through electrospinning, and to a spinel lithium manganese oxide nanofiber prepared thereby, and more particularly, to a viscosity, electrical conductivity, The present invention relates to a method for producing a spinel lithium manganese oxide nanofiber whose diameter is controlled by controlling solution chemical properties such as surface tension, and to a spinel lithium manganese oxide nanofiber prepared thereby.

The demand for lithium resources is increasing in many industries around the world. However, existing resources for lithium are very limited, and the low quality and/or complexity of the feedstock makes it more difficult to obtain. Therefore, much effort has been devoted to obtaining lithium from aqueous lithium sources. Several methods have been proposed to recover lithium from aqueous lithium sources, such as solar evaporation, co-precipitation and solvent extraction, but their use is limited. It is time consuming and requires conditions such as temperature, pH and Mg/Li ratio. Lithium ion-sieve (LIS) materials are considered excellent lithium adsorbents due to their unique chemical structure that can selectively separate lithium ions from brine and seawater. In addition, its low toxicity, low cost, and excellent chemical stability make LIS suitable for lithium recovery from aqueous lithium sources. Spinel hydrated manganese oxide (HMn ₂ O _{4 ) derived from spinel lithium manganese oxide (LiMn 2} O ₄ ) after extraction of lithium from the spinel structure by acid treatment is the most widely studied.

Spinel lithium manganese oxide has the characteristics of easy access of lithium ions and high selectivity to lithium in its structure, so it is applied to cathode materials for lithium secondary batteries and adsorbents for lithium recovery. Spinel lithium manganese oxide is manufactured in various forms to increase the efficiency of lithium ions in and out. In particular, one-dimensional (1D) with high specific surface area such as spherical nanoparticles, tubular nanoparticles, nanowires, rod-shaped nanoparticles, and nanofibers. Nanostructures are attracting attention. When the length/width ratio is small, such as spherical nanoparticles, tubular nanoparticles, and rod-shaped nanoparticles, the characteristics of the one-dimensional nanostructure with a high specific surface area may be deteriorated due to the characteristics of the nanoparticles, due to the nature of the nanoparticles, the one-dimensional nanostructure with a high specific surface area may be deteriorated. Because the /width ratio is very large, it does not agglomerate and exists in the form of a mat, so that it can fully have the characteristics of a one-dimensional nanostructure.

Spinel lithium manganese oxide nanofibers were first manufactured in 2005. Since then, research has been conducted as the characteristics of the one-dimensional nanostructure of nanofibers have emerged, but due to difficulties in manufacturing, nanofibers in a broken form or nanofibers in which nanoparticles are inserted into a polymer support have been manufactured. Although spinel lithium manganese oxide nanofibers have been manufactured up to now, ultrafine spinel lithium manganese oxide nanofibers in a stable form have not yet been developed.

The problem to be solved by the present invention is to provide a method for manufacturing a spinel lithium manganese oxide nanofiber having a small diameter in a stable form.

In order to solve the above problems, the first aspect of the present invention is to prepare a spinel lithium manganese oxide nanofiber using electrospinning, but the viscosity, electrical conductivity and surface tension of a spinning solution containing PVP, a lithium precursor and a manganese precursor Controlled to provide a method for producing a spinel lithium manganese oxide nanofiber, characterized in that for producing a nanofiber having a diameter of 50 nm or less.

In one embodiment of the present invention, the viscosity of the spinning solution is adjusted to 80 ~ 100cp, the electrical conductivity is adjusted to 2.5 ~ 4.0mS / cm, the surface tension is adjusted to 15 ~ 25 dynes / cm.

In one embodiment of the present invention, the concentration of the PVP is adjusted to 3 to 10% by weight.

In one embodiment of the present invention, the voltage during electrospinning is 12 to 16 kV, the working distance is 5 to 20 cm, the collecting plate rotation speed is 200 to 600 rpm, and the spinning flow is controlled to 0.1 to 1 ml/h.

In one embodiment of the present invention, the nanofibers are sintered at 300 to 500° C. for 3 to 5 hours, and then sintered at 550 to 700° C. for 3 to 5 hours to be mineralized.

A second aspect of the present invention provides a spinel lithium manganese oxide nanofiber manufactured by the manufacturing method of the present invention and having a diameter of 50 nm or less.

In one embodiment of the present invention, the spinel lithium manganese oxide nanofiber may be used as a lithium adsorbent for recovering lithium from seawater.

According to the present invention, spinel lithium manganese oxide nanofibers having a diameter of 50 nm or less can be prepared in a stable form.

The spinel lithium manganese oxide nanofiber of the present invention can be advantageously used as an adsorbent for lithium recovery having a high adsorption rate due to an increase in a specific area due to an increase in specific surface area due to a small diameter and an increase in an activated adsorption site. In particular, it can be used as an excellent lithium adsorbent capable of selectively separating lithium ions from brine and seawater.

1 schematically shows a spinel lithium manganese oxide nanofiber manufacturing process according to the present invention.
Figure 2 shows the relationship between the content of the solution components and _{the viscosity of LiNO 3} /Mn(CH ₃ CO ₂ ) ₃ /PVP spinning solution.
3 shows the relationship between the content of the solution components and _{the electrical conductivity of LiNO 3} /Mn(CH ₃ CO ₂ ) ₃ /PVP spinning solution.
4 shows the relationship between the content of solution components and _{the surface tension of LiNO 3} /Mn(CH ₃ CO ₂ ) ₃ /PVP spinning solution.
5 shows the relationship between the content of the solution components and the diameter of the LiNO ₃ /Mn(CH ₃ CO ₂ ) ₃ /PVP electrospinning solution.
_{6 is an FE-SEM image of LiMn 2} O ₄ nanofibers calcined twice at (a)550, (b)600, (c)650, and (d)700° C. for 4 hours (the heating rate of calcination is 2 ℃ min _^-1. LMO Nanofibers were prepared under 5% PVP and 0.5% BYK-377).
_{7 is an XRD pattern of calcined LiMn 2} O ₄ nanofibers as a function of temperature (LMO nanofibers were prepared under 5% PVP and 0.5% BYK-377).
_{8 is an FE-SEM image of LiMn 2} O ₄ nanofibers calcined at 600° C. for 4 hours with different diameters according to the results of DOE and metal salt concentration ((a) PVP 7%; (+--), (b) ) PVP 5% and BYK-377 0.5%; (--+), PVP 5% and BYK-377 0.5% (c) metal salt concentration 50%, (d) metal salt concentration 25%).
_{9 is a cumulative distribution diagram of the diameters of LiMn 2} O ₄ nanofibers having different diameters according to the results of DOE and metal salt concentration (PVP 7%; (+++), PVP 5% and BYK-377 0.5%; (-) -+), metal salt concentration 50% and 25% under PVP 5% and BYK-377 0.5%.The mean diameter of nanofiber is 203.1±50.9, 147.2±36.3, 88.9±19.8, 44.3±11.7 nm).
10 is an XRD pattern of _{LiMn 2} O ₄ and extracted HMn ₂ O _{4 nanofibers.}
11 shows the lithium ion absorption capacity of _{HMn 2} O ₄ nanofibers having different diameters.

Hereinafter, the present invention will be described in detail with reference to the drawings. The embodiments introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like reference numerals refer to like elements throughout.

The present inventors identified the solution chemistry of the electrospinning solution and conducted systematic studies to set the conditions in order to produce a small and stable spinel lithium manganese oxide nanofiber, and the diameter of the spinel lithium manganese oxide nanofiber was determined through experimental design. We found that it could be tuned from 40 nm to 200 nm by controlling the solution properties. In addition, since the lithium adsorption capacity exhibits an inverse linear relationship with the diameter of the nanofiber, it was found that the lithium adsorption performance could be improved by reducing the diameter of the nanofiber. The present invention is based on this.

The present invention is characterized in that the spinel lithium manganese oxide nanofibers having a diameter of 50 nm or less are prepared by controlling the solution chemical properties such as viscosity, electrical conductivity, and surface tension of the spinning solution during electrospinning of lithium manganese oxide nanofibers. .

In the present invention, the electrospinning solution includes PVP, a lithium precursor, and a manganese precursor.

In the process of sintering the nanofiber, as an organic material such as PVP serving as a support is burned, the shape of the nanofiber having a small diameter may become unstable. Therefore, in order to manufacture nanofibers with a small diameter, it is important to control the composition of the electrospinning solution precursor and PVP.

In the present invention, the concentration of PVP is adjusted to 3 to 10% by weight. The PVP concentration can significantly affect the diameter of the nanofibers. This is because the viscosity of the solution increased as the PVP concentration increased (see Fig. 2).

Also, as the viscosity of the solution increased, the diameter of the nanofibers increased (see Table 2). In the present invention, when the concentration of PVP exceeds 10% by weight, the nanofiber having a diameter of 50 nm to be obtained by the present invention cannot be obtained, and when it is less than 3% by weight, electrospinning may not be performed well.

In the present invention, the viscosity of the spinning solution is preferably adjusted to 80 ~ 100cp.

The lithium precursor may be any one selected from the group consisting _{of LiOH, LiNO 3} , Li ₂ CO ₃ , Li ₂ SO ₄ and LiCH ₃ CO _{2 , but is not limited thereto.}

The manganese precursor may be any one selected from the group consisting _{of MnSO 4} , Mn(NO ₃ ) ₂ , Mn(CH ₃ COO) ₂ and MnCl _{2 , but is not limited thereto.} Preferably, manganese acetate (tetrahydrate) (Mn(CH ₃ COO) ₂ .4H ₂ O) can be used.

The present inventors confirmed that as the metal salt concentration in the electrospinning solution decreased, the electrical conductivity was rapidly decreased, and as a result, the diameter of the nanofiber was decreased (see Table 3).

In the present invention, the electrical conductivity of the spinning solution is adjusted to 2.5 ~ 3.5mS / cm.

The electrical conductivity of the spinning solution can be controlled by adjusting the amount of the precursor (metal salt) of the _{LiNO 3} /Mn(CH ₃ CO ₂ ) _{3 /PVP spinning solution.} As shown in Table 2, the electrical conductivity of the spinning solution was rapidly decreased as the concentration of the metal salt decreased, and as a result, it can be seen that the diameter of the nanofiber was decreased.

In the present invention, the metal salt concentration is preferably controlled to 20 to 40%.

In the present invention, 100% of the metal salt concentration represents _{0.183 mol/L of LiNO 3 in PVP/ethanol solution.} The molar ratio of Li:Mn in all solutions is fixed at 1:2.

In the present invention, the surface tension of the spinning solution is adjusted to 15 ~ 25 dynes / cm. Although the surface tension does not affect the diameter of the nanofibers, decreasing the surface tension may decrease the bead density (see Table 2).

In the present invention, the voltage during electrospinning is 12 to 16 kV, the working distance is 5 to 20 cm, the rotation speed of the collecting plate is 200 to 600 rpm, and the spinning flow is controlled to 0.1 to 1 ml/h.

In the present invention, the nanofibers are sintered at 300 to 500° C. for 3 to 5 hours, and then sintered at 550 to 700° C. for 3 to 5 hours to be mineralized. In the first sintering process, the PVP polymer is removed, and in the second sintering process, the Li/Mn precursor is crystallized into _{LiMn 2} O _{4 nanofibers.}

According to the manufacturing method of the present invention, a spinel lithium manganese oxide nanofiber having a diameter of 50 nm or less, preferably 30 to 50 nm can be manufactured.

The spinel lithium manganese oxide may be used as a lithium adsorbent for recovering lithium from seawater.

It was confirmed that the nanofiber having a diameter of 44.3 nm prepared according to the present invention exhibited an adsorption capacity reaching 89.1% of the theoretical adsorption capacity value (FIG. 11). Therefore, the spinel lithium manganese oxide of the present invention can be advantageously used as a lithium adsorbent for recovering lithium from seawater.

Hereinafter, a method for manufacturing a spinel lithium manganese oxide nanofiber according to the present invention will be described through a preferred embodiment of the present invention. However, these are presented as preferred examples of the present invention and cannot be construed as limiting the present invention in any sense. Content not described here will be omitted because it can be technically inferred sufficiently by those skilled in the art.

Materials and Methods

For _{the synthesis of LiMn 2} O ₄ nanofibers (hereinafter, LMO nanofibers), lithium nitrate (LiNO ₃ , Sigma-Aldrich, Reagentplus), manganese acetate tetrahydrate (Mn(CH ₃ CO ₂ ) ₃ .4H ₂ O, Sigma-Aldrich, 99% or more), polyvinylpyrrolidone (PVP, Mw ~ 1,300,000 g/mol) was used.

A pyridinium formate buffer (PF, Fluka analysis, HPLC), BYK-377 (BYK Korea, LLC) was used to show the solution electrical conductivity and surface tension.

Lithium hydroxide (LiOH, Sigma-Aldrich, = 98%) was used for the lithium adsorption test. Highly deionized water was used for all experiments.

The solution properties of LiNO ₃ /Mn(CH ₃ CO ₂ ) ₃ /PVP were characterized using a viscometer (Brookfield, LVDV2T-CP), a conductivity meter (Thermo scientific, Orion 4), and a tensiometer (SEO, DST60).

Examples 1 to 4: LiMn ₂ O ₄ Manufacturing of Nanofibers

Spinel lithium manganese oxide nanofibers were prepared by using electrospinning technology while controlling solution chemical properties such as viscosity, electrical conductivity, and surface tension of the spinning solution as shown in Table 1 below.

In order for the spinning solution to have the solution chemical properties described in Table 1 above, lithium nitrate, manganese acetate, deionized water and the designated PVP/ethanol solution were mixed in a molar ratio of 1:2. After the mixed solution was stirred for at least 1 hour, additives (ie, electrical conductivity and surface tension modifiers) were added. In addition, the electrical conductivity was controlled by controlling the concentration of _{LiNO 3} /Mn(CH ₃ CO ₂ ) ₃ (metal salt) in the electrospinning solution.

The needle (25G) was placed 12 cm away from the drum collector rotating at 400 rpm. The voltage was 12 kV and the feed rate was 0.4 ml/h. Ambient conditions of electrospinning were maintained at humidity/temperature 20%/30°C.

LiNO ₃ /Mn (CH ₃ CO ₂ ) ₃ /PVP nanofibers were calcined at 400 °C for 4 hours and the heating rate was 1 °C/min. Then, the first calcined nanofiber was calcined at 550 to 700 °C for 4 hours and the heating rate was 2 °C/min. The PVP polymer was removed by the firing process, and the Li/Mn precursor was crystallized _{into LiMn 2} O _{4 nanofibers.}

Experimental Example 1; Design of Experiments (DOE)

_{In order to adjust the diameter of the nanofibers, LiNO 3} /Mn(CH ₃ CO ₂ ) ₃ /PVP nanofibers were systematically prepared by controlling the properties of the spinning solution through the experimental design. Viscosity, electrical conductivity and surface tension were measured under each DOE condition, and the effect of each parameter on solution properties and nanofiber diameter was observed, and the results are summarized in Table 1 below.

2 to 4 show the effects of variables such as solution concentration on solution viscosity, electrical conductivity, and surface tension, respectively. It can be seen that the viscosity increases with increasing PVP concentration. It can be seen that the electrical conductivity mainly increases with the increase of the PF concentration, and the surface tension decreases with the increase of the BYK-377 concentration.

5 shows the effect of a variable such as a concentration of a solution on the diameter of a nanofiber. The PVP concentration had a great effect on the diameter of the nanofibers, that is, the diameter of the nanofibers increased with the increase of the PVP concentration. This is because the viscosity of the solution increased as the PVP concentration increased. Also, electrical conductivity has a small effect on the diameter. Although surface tension does not affect diameter, Table 1 shows that decreasing the surface tension decreases the bead density.

From the results in Table 2, it was confirmed that the diameter of the nanofiber tends to decrease as the electrical conductivity of the solution decreases.

Table 2 below shows the changes in the conductivity and diameter of the nanofiber according to the metal salt concentration.

As shown in Table 3, as the metal salt concentration decreased, the electrical conductivity was sharply decreased, and as a result, it could be seen that the diameter of the nanofiber was decreased.

Experimental Example 2: LiMn ₂ O ₄ Analysis of the shape and size of nanofibers

_{FE-SEM imaging of the second calcined LiMn 2} O ₄ nanofibers at 550-700° C. for 4 hours is shown in FIG. 6 . The nanofibers calcined at 650°C were unstable to maintain the shape of the nanofiber, and the shape was not maintained at 700°C. Nanofibers fired at 550° C. still appear to have polymers remaining.

The crystal structure and crystal size _{of the LiMn 2} O ₄ nanofibers were analyzed by X-ray diffraction analysis (XRD, PANalytical X'pert Pro Powder). 7 shows the XRD pattern of _{LiMn 2} O ₄ nanofibers according to the calcination temperature. The nanofibers calcined at 550°C had low crystallinity of LMO due to residual polymer. All crystallinity of LMO can be observed at 600°C. As a result, the second calcination temperature was determined at 600 °C.

Figure 8 shows nanofibers with four diameters ((a) PVP 7%; (b) PVP 5% and BYK-377 0.5%; PVP 5% and BYK-377 0.5% (c) metal salt concentration 50%, ( d) The form of metal salt concentration 25%) is shown. 9 shows the cumulative distribution of the diameters of the nanofibers of FIG. 8, and it can be seen that when the concentration of the metal salt is 25%, the nanofibers having a diameter of less than about 50 nm are obtained.

Experimental Example 3: Lithium ion adsorption experiment

The improved lithium ion adsorption properties of _{HMn 2} O ₄ nanofibers with different diameters in a lithium liquid resource were investigated.

The nanofibers used in the adsorption experiments as adsorbents were delithiated from 0.5 M HCl, and _{the XRD pattern of HMn 2} O ₄ is shown in FIG. 10 . The HMO peak is shifted slightly to the right, indicating that hydrogen ions have been replaced at lithium ion sites.

The lithium ion adsorption properties of samples (10 mg) in 200 ppm LiOH solution (10 ml) at room temperature were evaluated according to diameter. The sample maintained an equilibrium state of lithium after 24 h of adsorption. All adsorption experiments were performed on all samples for 24 h at pH 12 with stirring at 100 rpm. The lithium ion concentration of the lithium solution after adsorption was measured using an inductively coupled plasma emission spectrometer (ICPOES; Thermo Scientific ICAP 7000 series), and the results are shown in FIG. 11 .

As shown in FIG. 11 , the nanofibers of 203.1, 147.2, 88.9 and 44.3 nm had adsorption capacities of 20.44, 27.05, 31.15 and 34.21 mg/g, respectively. In theoretical calculations, _{1 g of LiMn 2} O ₄ contains 38.38 mg of lithium. In conclusion, it can be seen that the nanofiber having a diameter of 44.3 nm prepared according to the present invention can exhibit an adsorption capacity reaching 89.1% of the theoretical adsorption capacity value.

In the above, preferred embodiments of the present invention have been illustrated and described, but the present invention is not limited to the specific embodiments described above, and it is common in the technical field to which the present invention pertains without departing from the gist of the present invention as claimed in the claims. Various modifications may be made by those having the knowledge of, of course, and these modifications should not be individually understood from the technical spirit or perspective of the present invention.

Claims (7)

A spinel lithium manganese oxide nanofiber was prepared using electrospinning,
By controlling the viscosity, electrical conductivity, and surface tension of the spinning solution containing PVP, lithium precursor and manganese precursor, the concentration of the PVP is controlled to 3 to 10% by weight, and the metal salt concentration is controlled to 20 to 40%. to prepare a nanofiber having a diameter of 30-50 nm through and
Method of producing a spinel lithium manganese oxide nanofiber, characterized in that the diameter of the nanofiber is reduced as a result of rapidly reducing the electrical conductivity of the spinning solution by reducing and controlling the concentration of the metal salt, which is a precursor of the spinning solution. delete delete The spinel lithium according to claim 1, wherein the electrospinning voltage is 12-16 kV, the working distance is 5-20 cm, the collecting plate rotation speed is 200-600 rpm, and the spinning flow rate is 0.1-1ml/h. A method for manufacturing manganese oxide nanofibers. The method of claim 1 , wherein the nanofiber is sintered at 300 to 500° C. for 3 to 5 hours, and then sintered at 550 to 700° C. for 3 to 5 hours to be mineralized. A spinel lithium manganese oxide nanofiber, characterized in that it has a diameter of 30 to 50 nm manufactured by the method of any one of claims 1, 4 and 5. The spinel lithium manganese oxide nanofiber according to claim 6, wherein the spinel lithium manganese oxide is used as a lithium adsorbent for recovering lithium from seawater.

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