KR20200013950A - 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 relates to a method for manufacturing a spinel lithium manganese oxide nanofiber via electrospinning, wherein the method for manufacturing a spinel lithium manganese oxide nanofiber controls the viscosity, electric conductivity, and surface tension of a spinning solution comprising PVP, a lithium precursor, and a manganese precursor to manufacture a nanofiber having a diameter of 30 to 50 nm; and a spinel lithium manganese oxide nanofiber manufactured by the same. The spinel lithium manganese oxide nanofiber of the present invention can be an excellent lithium absorbent which can selectively separate lithium ions from salt water 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 preparing spinel lithium manganese oxide nanofibers with a diameter controlled through electrospinning and spinel lithium manganese oxide nanofibers prepared according to the present invention, and more particularly, to the viscosity, electrical conductivity, The present invention relates to a method for preparing spinel lithium manganese oxide nanofibers whose diameter is controlled by adjusting solution chemical properties such as surface tension, and spinel lithium manganese oxide nanofibers prepared accordingly.

The demand for lithium resources is increasing in many industries around the world. However, existing resources for lithium are very limited, and the low and / or complexity of the feedstock makes it more difficult to secure resources. Thus, much effort has been devoted to obtaining lithium from aqueous lithium resources. Several methods have been proposed to recover lithium from an aqueous lithium source, such as solar evaporation, coprecipitation and solvent extraction, but use is limited. This is time consuming and requires conditions such as temperature, pH and Mg / Li ratio. Lithium ion-sieve (LIS) materials are considered good lithium adsorbents because of 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 the recovery of lithium from aqueous lithium resources. 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 oxides are easily applied to lithium ions and have high selectivity to lithium in structure, and thus they are applied to cathode materials of lithium secondary batteries and adsorbents for lithium recovery. Spinel lithium manganese oxide is manufactured in various forms to increase the access efficiency of lithium ions. Especially, spinel lithium manganese oxide has a high specific surface area such as spherical nanoparticles, tubular nanoparticles, nanowires, rod nanoparticles, and nanofibers. Nanostructures are attracting attention. When the length / width ratio is small, such as spherical nanoparticles, tubular nanoparticles, and rod-shaped nanoparticles, agglomeration between particles may easily occur due to the characteristics of the nanoparticles, thereby degrading one-dimensional nanostructure characteristics having a high specific surface area. The / width ratio is very large and can be present in the form of a mat without agglomeration, so that one-dimensional nanostructures can be fully characterized.

Spinel lithium manganese oxide nanofibers were first manufactured in 2005. Subsequently, research was conducted as the characteristics of the one-dimensional nanostructure of the nanofibers emerged. However, nanofibers in which the nanofibers were formed by inserting nanoparticles into the polymer support or the nanofibers that were broken due to difficulties in manufacturing were manufactured. Until now, spinel lithium manganese oxide nanofibers have been manufactured, but stable microfine spinel manganese oxide nanofibers have not been developed.

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

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

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 PVP is adjusted to 3 to 10% by weight.

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

In one embodiment of the present invention, the nanofiber is sintered at 300 ~ 500 ℃ for 3 to 5 hours, and then sintered at 550 ~ 700 ℃ for 3 to 5 hours to be inorganicized.

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

In one embodiment of the present invention, the spinel lithium manganese oxide nanofibers 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 manufactured in a stable form.

Spinel lithium manganese oxide nanofibers of the present invention can be advantageously used as a lithium recovery adsorbent having a high adsorption rate by increasing the specific area and the activated adsorption site by increasing the specific surface area is small diameter. In particular, it can be used as an excellent lithium adsorbent capable of selectively separating lithium ions from brine and sea water.

Figure 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 component 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 component and the electrical conductivity of the LiNO ₃ / Mn (CH ₃ CO ₂ ) ₃ / PVP spinning solution.
4 shows the relationship between the content of the solution component and the surface tension of the LiNO ₃ / Mn (CH ₃ CO ₂ ) ₃ / PVP spinning solution.
5 shows the relationship between the content of the solution component 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 (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 over temperature (LMO nanofibers were prepared under PVP 5% and BYK-377 0.5%).
FIG. 8 is an FE-SEM image of LiMn ₂ O ₄ nanofibers calcined at 600 ° C. for 4 hours at different diameters as a result of DOE and metal salt concentrations ((a) PVP 7%; (+-), (b A) 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 of the diameters of LiMn ₂ O ₄ nanofibers with different diameters as a result of DOE and metal salt concentrations (PVP 7%; (+++), PVP 5% and BYK-377 0.5%; (- -+), 50% and 25% metal salt concentrations under 5% PVP and 0.5% BYK-377.The average diameter of the nanofibers 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.
Figure 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 following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience. Like numbers refer to like elements throughout the specification.

The present inventors conducted a systematic study to determine the solution chemistry of electrospinning solution and set the conditions in order to manufacture a stable and stable spinel lithium manganese oxide nanofiber, and the diameter of the spinel lithium manganese oxide nanofiber was measured through an experimental design. It was found that by controlling the solution properties can be adjusted from 40nm to 200nm. In addition, since the lithium adsorption capacity exhibits an inverse linear relationship with the diameter of the nanofibers, it has been found that the lithium adsorbing performance can be improved by reducing the diameter of the nanofibers. 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 by controlling the solution chemical properties such as the viscosity, electrical conductivity, surface tension of the spinning solution during electrospinning of lithium manganese oxide nanofibers .

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

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

In the present invention, the concentration of PVP is adjusted to 3 to 10% by weight. PVP concentrations can have a significant effect on the diameter of nanofibers. This is because the viscosity of the solution increased with increasing PVP concentration (see FIG. 2).

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

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 inventors confirmed that the electrical conductivity drastically decreased as the metal salt concentration in the electrospinning solution decreased, and as a result, the diameter of the nanofibers 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 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 rapidly decreased as the metal salt concentration decreased, and as a result, the diameter of the nanofibers was reduced.

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. Surface tension does not affect the diameter of the nanofibers, but bead density may decrease as surface tension decreases (see Table 2).

In the present invention, the electrospinning voltage is 12 ~ 16 kV, the working distance is 5 ~ 20 cm, the collecting plate rotation speed is 200 ~ 600 rpm, the spinning flow rate is adjusted to 0.1 ~ 1ml / 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 inorganicized. In the first sintering process, the PVP polymer is removed, and in the second sintering process, the Li / Mn precursor crystallizes into LiMn ₂ O ₄ nanofibers.

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

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

It was confirmed that the nanofibers having a diameter of 44.3 nm prepared according to the present invention exhibited adsorption capacities up to 89.1% of the theoretical adsorption capacity value (FIG. 11). Accordingly, 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 of manufacturing spinel lithium manganese oxide nanofibers according to the present invention through a preferred embodiment of the present invention. However, it is presented as a preferred example of the present invention and should not be construed as limiting the present invention by any means. Details that are not described herein will be omitted because those skilled in the art can sufficiently infer technically.

Materials and methods

LiMn ₂ O ₄ nano fiber nitric acid in the synthesis of (the LMO nanofibers) lithium _{(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.

Pyridinium formate buffer (PF, Fluka assay, HPLC), BYK-377 (BYK Korea, LLC) was used to show 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.

Solution characteristics 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 tension meter (SEO, DST60).

Examples 1-4: LiMn ₂ O ₄  Fabrication of Nanofibers

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

Lithium nitrate and manganese acetate, deionized water, and a designated PVP / ethanol solution were mixed in a 1: 2 molar ratio so that the spinning solution could have the solution chemical properties listed in Table 1 above. The mixed solution was stirred for at least 1 hour and then additives (ie, electrical conductivity and surface tension regulators) were added. In addition, the electrical conductivity was controlled by adjusting 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. The 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. The first fired nanofibers were then fired at 550-700 ° C. for 4 hours and the heating rate was 2 ° C./min. The PVP polymer was removed by the calcination process and the Li / Mn precursor was crystallized with LiMn ₂ O ₄ nanofibers.

Experimental Example 1; Experimental Design (DOE)

In order to adjust the diameter of the nanofibers, the experimental design to control the properties of the spinning solution to prepare a LiNO ₃ / Mn (CH ₃ CO ₂ ) ₃ / PVP nanofibers systematically. Viscosity, electrical conductivity and surface tension were measured under each DOE condition and the results of each parameter on the solution properties and the diameter of the nanofibers were observed and the results are summarized in Table 1 below.

2-4 show the effect of variables such as concentration of solution 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 increasing PF concentration, and the surface tension decreases with increasing BYK-377 concentration.

5 shows the effect of variables such as the concentration of the solution on the diameter of the nanofiber. PVP concentrations had a significant effect on the diameter of nanofibers, ie the diameter of nanofibers increased with increasing PVP concentration. This is because the concentration of the PVP increased and the viscosity of the solution increased. In addition, electrical conductivity has a small effect on the diameter. Surface tension does not affect diameter, but Table 1 shows that decreasing surface tension reduces bead density.

The results of Table 2 confirm that the diameter of the nanofibers tends to decrease as the electrical conductivity of the solution decreases.

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

As shown in Table 3, as the metal salt concentration decreases, the electrical conductivity sharply decreased, as a result, it can be seen that the diameter of the nanofiber is reduced.

Experimental Example 2: LiMn ₂ O ₄  Shape and size analysis 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 nanofibers and the shape was not maintained at 700 ° C. Nanofibers fired at 550 ° C. still appear to have polymer remaining.

The crystal structure and crystal size of 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 with calcination temperature. Nanofibers calcined at 550 ° C. had low crystallinity of LMO due to residual polymer. All crystallinity of the LMO can be observed at 600 ° C. As a result, the second calcination temperature was determined at 600 ° C.

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) form of metal salt concentration 25%). 9 shows the cumulative distribution of the diameters of the nanofibers of FIG. 8, and it can be seen that nanofibers having a diameter of less than about 50 nm are obtained when the metal salt concentration is 25%.

Experimental Example 3: Lithium Ion Adsorption Experiment

The improved lithium ion adsorption characteristics of HMn ₂ O ₄ nanofibers with different diameters in lithium liquid resources were investigated.

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

In a 200 ppm LiOH solution (10 ml) at room temperature, the lithium ion adsorption characteristics of the sample (10 mg) were evaluated according to diameter. The sample maintained the equilibrium of lithium after 24 hours of adsorption. All adsorption experiments were performed on all samples for 24 hours 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, nanofibers of 203.1, 147.2, 88.9 and 44.3 nm were found to have 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 nanofibers having a diameter of 44.3 nm prepared according to the present invention can exhibit adsorption capacities up to 89.1% of the theoretical adsorption capacity value.

While the above has been shown and described with respect to preferred embodiments of the invention, the invention is not limited to the specific embodiments described above, it is usually in the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

Claims (7)

Spinel lithium manganese oxide nanofibers were prepared using electrospinning,
A method for producing spinel lithium manganese oxide nanofibers, comprising: controlling nanoparticles having a diameter of 50 nm or less by controlling the viscosity, electrical conductivity, and surface tension of a spinning solution including PVP, lithium precursor, and manganese precursor. The spinel lithium manganese according to claim 1, wherein the spinning solution has a viscosity of 80 to 100 cps, an electric conductivity of 2.5 to 3.5 mS / cm, and a surface tension of 15 to 25 dynes / cm. Method for producing oxide nanofibers. The method of claim 1, wherein the concentration of PVP is adjusted to 3 to 10% by weight of the spinel lithium manganese oxide nanofiber manufacturing method. The spinel lithium of 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 controlled at 0.1-1 ml / h. Method of manufacturing manganese oxide nanofibers. The method of claim 1, wherein 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 inorganicized. A spinel lithium manganese oxide nanofiber, which is manufactured by the manufacturing method of any one of claims 1 to 5 and has a diameter of 50 nm or less. The spinel lithium manganese oxide nanofiber of claim 6, wherein the spinel lithium manganese oxide is used as a lithium adsorbent for recovering lithium from seawater.

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