KR20080082239A - Method of improving ionic conductivity of polymer electrolyte using supercritical fluid - Google Patents

Abstract

A method for improving the ion conductivity of a polymer electrolyte is provided to increase the low ion conductivity of a polymer electrolyte such as polyethers, etc. due to high crystallinity by using a supercritical fluid. A method for improving the ion conductivity of a polymer electrolyte comprises the step of treating a polymer solid electrolyte with a supercritical fluid. Preferably the supercritical fluid is a carbon dioxide supercritical fluid, and the treatment is carried out at a temperature of 40-100 deg.C and at a pressure of 5-20 MPa. Preferably the method comprises the steps of putting the prepared species into a high pressure reactor and transferring a carbon dioxide gas; leaving it alone under the temperature and pressure condition in a carbon dioxide gas; and rapidly cooling the reactor in liquid N2 to a temperature of 30 deg.C or less and discharging the remaining carbon dioxide gas.

Description

Method for improving ionic conductivity of polymer electrolyte using supercritical fluid

1 is a schematic configuration diagram of a supercritical CO ₂ treatment apparatus used in the supercritical CO ₂ treatment method of the present invention polymer electrolyte.

2 is a graph showing how the polymer electrolyte affects the ionic conductivity of the supercritical CO ₂ treatment conditions (temperature, pressure).

3 is a graph showing how the ion conductivity and glass transition temperature of the polymer electrolyte change depending on Li ⁺ concentration in the polymer electrolyte before and after the treatment of supercritical CO ₂ .

4 is a graph showing whether the ion conductivity before and after the supercritical CO ₂ treatment changes with time.

The present invention is to improve the low ionic conductivity of the polymer solid electrolyte, and more particularly, to a method for improving the ion conductivity of the polymer solid electrolyte by performing an additional treatment for a conventional polymer solid electrolyte, such as a polyether polymer.

Since polymer electrolyte has material properties that are not expressed in inorganic electrolyte, it can be applied to various fields such as polymer battery, ion sensor, fuel cell, display device, bio cell, capacitor, drug delivery system such as lithium polymer battery as portable power source. Material. However, for example, polyether-based polymer electrolytes have high crystallinity and very low ion conductivity. In particular, polyether-based polymer electrolytes do not show satisfactory ionic conductivity at room temperature.

Since the 1970s, many kinds of polyether derivatives have been synthesized in an effort to obtain high ion conductive polymer materials. In particular, plasticizers are added to polyether electrolytes, or organic / inorganic fillers are introduced and blended to increase conductivity at room temperature. Various studies have been attempted to improve the ion conductivity, such as the introduction of copolymerized and bulky side chain groups, hybridization of polyether-metal salts and introduction of inert ionic liquids.

However, satisfactory results were not obtained even by the above methods for increasing ion conductivity.

SUMMARY OF THE INVENTION An object of the present invention is to improve low ion conductivity due to high crystallinity of a polymer electrolyte, such as a conventional polyether.

An object of the present invention is to provide a method of forming a polymer electrolyte having improved ion conductivity by performing further treatment on a polymer material.

The method for improving the polymer electrolyte ion conductivity of the present invention for achieving the above object is characterized by treating the polymer solid electrolyte with a supercritical fluid.

In the present invention, as the polymer solid electrolyte, a polymer having a methacrylate derivative represented by the following Chemical Formula 1 as a monomer, lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), With lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethansulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethansulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ) Complexes of at least one ionic lithium salt selected from the group consisting of can be used.

[Formula 1]

CH ₂ = C (CH ₃ ) -COO (CH ₂ CH ₂ O) _n -H

In the present invention, the supercritical fluid may be a supercritical fluid of carbon dioxide,

The treatment using the supercritical fluid for the polymer solid electrolyte may be performed for 10 to 120 minutes at a temperature of 40 to 100 ° C. and a pressure of 5 to 20 MPa.

In the present invention, the polymer solid electrolyte may be used in a battery such as a lithium polymer battery.

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

First, the supercritical state, which constitutes an important element of the method of the present invention, is outlined. The material may be present in a state exhibiting intermediate physical properties of liquid and gas above the critical pressure P _c and the critical temperature T _c . The fluid material in the state showing the intermediate characteristics of liquid and gas is called supercritical fluid.

Supercritical fluids have higher densities than gases, lower viscosities than liquids, and superior diffusivity. These physical properties of supercritical fluids are advantageous for mass transfer, dissolution or plasticization of materials. In addition, the physical properties of supercritical fluids change with temperature and pressure. Therefore, it is possible to control the thermodynamic or mass transfer properties of the supercritical fluid by varying the temperature and pressure.

In particular, carbon dioxide reaches a critical state (critical pressure P _c = 7.4 MPa, critical temperature T _c = 31 ° C) at relatively low temperatures and pressures compared to other materials and has the advantages of abundant sources, environmental stability and economy. According to these advantages and characteristics, supercritical carbon dioxide can be used as a solvent for extraction and separation in a process.

The present invention utilizes the characteristics of such a supercritical fluid and is intended to increase the ion conductivity of the polymer electrolyte. When the polymer electrolyte is treated with a supercritical fluid, the solute inside the polymer matrix may be redistributed or the polymer chain may be rearranged due to the high diffusivity and plasticity of the supercritical fluid. This phenomenon appears to be due to the interaction between the molecules forming the supercritical fluid and polar atom groups such as ether or carbonyl groups in the polymer chain. Accordingly, the glass transition temperature (T _g ) and the local viscosity of the portion constituting the polymer-salt composite of the polymer matrix may also be changed.

In the present invention, when the supercritical fluid is applied to the polymer electrolyte, the material forming the polymer matrix structure is diffused and redistributed. As a result, the microstructure of the polymer matrix is changed, and the rearrangement of the polymer chains enables a more advantageous migration path for ion transfer, which is essential for battery operation.

The supercritical fluid treatment method of the following embodiments is commonly as follows.

Supercritical CO ₂ treatment comprises a supercritical CO ₂ extraction system consisting of a delivery pump: 10, a pressure regulator 20, a stainless high pressure reactor (SUS reactor: 30), and the like, as shown in FIG. JASCO Co.) was used. The prepared specimen was placed in a high pressure reactor (30), and the CO ₂ gas was transferred at a rate of 10 ml / min through the transfer pump 10, and then treated for 30 minutes under the conditions of a constant pressure and temperature shown in the examples. . After the treatment, the reactor was placed in liquid nitrogen, quenched to 30 ° C. or lower, and the residual CO ₂ gas was discharged. The treated specimens were vacuum dried at 30 ° C. for 24 hours to remove residual CO ₂ molecules in the matrix.

(Example 1)

Oligo: oxyethylene glycol methacrylate (methacrylate: CH ₂ = C (CH ₃ ) -COO (CH ₂ CH ₂ O) so that the concentration of Li ⁺ to 2.5 mol% of oxyethylene in anhydrous methanol 10 g of _8- H, MEO) and 0.624 g of lithium trimethane sulfonate (LiCF ₃ SO ₃ ) were dissolved to prepare a homogeneous solution, followed by addition of 1.0 wt.% (0.106 g) of AIBN radical initiator. After reacting at 70 ° C. for 4 hours to produce a PMEO-Li salt composite film, a specimen was prepared by vacuum drying at 30 ° C. for 24 hours. The prepared specimens were treated with supercritical CO ₂ at 40 ° C. for 30 minutes under pressure conditions of 5 MPa, 10 MPa, 15 MPa, and 20 MPa, respectively.

The ion conductivity of the specimens treated in this way was measured using the 4192A LF Impedance Analyzer (Hewlett-Packard) in the frequency range of 100 Hz to 13 MHz, and the complex impedance method from 30 ° C. to 100 ° C. at a heating rate of 2.0 ° C./min. Measured by

(Example 2)

The same procedure as in Example 1 was conducted except that the mixture was treated with supercritical CO ₂ at 60 ° C.

(Example 3)

They were treated at 80 ℃ with supercritical CO _2, except as in Example 1.

(Comparative Example 1)

Seconds, except that no treatment with the critical CO ₂ as the first embodiment.

The measured values of Examples 1-3 and Comparative Example 1 are shown in FIG.

As shown in FIG. 2, it can be seen that the ion conductivity of the present polyether electrolyte treated with supercritical CO ₂ is significantly higher than that before the treatment, and the electrolyte having a higher ion conductivity is treated with a temperature of 40 ° C. and a pressure of 10 MPa. It can be seen that it provides.

(Example 4)

Specimen preparation method is the same as in Example 1. The fabricated specimens were treated with supercritical CO ₂ for 30 minutes at three different temperature conditions (40, 60, 80 ° C) under different pressure conditions (5, 10, 15, 20Mpa). The ion conductivity of the specimens thus treated was measured by a complex impedance method using a 4192A LF Impedance Analyzer (Hewlett-Packard) from 30 ° C to 100 ° C at a heating rate of 2.0 ° C / min in the frequency range of 100 Hz to 13 MHz It was.

The glass transition temperature T _g was measured using a differential scanning calorimeter (DSC), and measured under a nitrogen gas atmosphere with a DSC-50 of Shimadzu, with TA-50WS attached. The measurement range was measured while raising the temperature at a rate of 10 ° C / min from -100 ° C to 200 ° C.

(Example 5)

The same procedure as in Example 4 was conducted except that a homogeneous solution was prepared by dissolving MEO and lithium trifluoride methanesulfonate in anhydrous methanol so that the concentration of Li ⁺ was 5.0 mol% with respect to oxyethylene.

(Example 6)

The same procedure as in Example 4 was conducted except that a homogeneous solution was prepared by dissolving MEO and lithium trifluoride methanesulfonate so that the concentration of Li ⁺ was 10 mol% with respect to oxyethylene in anhydrous methanol.

(Example 7)

The same procedure as in Example 4 was conducted except that a homogeneous solution was prepared by dissolving MEO and lithium trifluoride methanesulfonate in anhydrous methanol so that the concentration of Li ⁺ was 20 mol% with respect to oxyethylene.

(Comparative Example 2)

Seconds, except that no treatment with the critical CO ₂ as described in Examples 4.

(Comparative Example 3)

Seconds, except that no treatment with the critical CO ₂ as described in Examples 5.

(Comparative Example 4)

Seconds, except that no treatment with the critical CO ₂ as in Example 6.

(Comparative Example 5)

Seconds, except that no treatment with the critical CO ₂ as in Example 7.

The measured values (ion conductivity: measured at 90 ° C.) and T _g ) of Examples 4 to 7 and Comparative Examples 2 to 5 are shown in FIG. 3. In all concentration ranges of Li ⁺ , the glass transition temperature T _g is lowered by supercritical CO ₂ treatment, and the ion conductivity is increased.

In particular, the polymer electrolyte sample having a concentration of 10 mol% showed the highest ion conductivity before and after treatment, and the synergistic effect of the ion conductivity by the treatment of supercritical CO ₂ was high in the high concentration range of 20 mol%.

The reason why the increase in ion conductivity and the glass transition temperature decrease by the supercritical CO ₂ treatment can be explained as follows.

In general, salts having a predetermined concentration or more present in the polyether-based polymer matrix form coordination bonds with ether-based oxygen atoms in the polymer. The effects of these salts, which occur above the appropriate salt concentration, lower the segmental mobility of the polymer chain, which in turn leads to an increase in T _g and lower the ionic conductivity.

However, the supercritical CO ₂ treatment disperses and redistributes salts in the form of ionic aggregates present in the polymer matrix. Salts evenly dispersed in the polymer matrix lose their role as crosslinkers and the dissociation of the salts is high. Therefore, it is thought that loss of role as a crosslinking agent and increase in dissociation degree of salt have the effect of lowering glass transition temperature and increasing ion conductivity of polymer.

In order to confirm whether the series of ionic conductivity improvement effects due to supercritical CO ₂ treatment is not only one-time, but also the long-term electrochemical stability, the samples of Examples 5 and 7, 7, and 3 and 5 Ion conductivity (measured at 40 ° C.) was measured over three months. As shown in FIG. 4, the change in ion conductivity over time was insignificant.

Using the polymer solid electrolyte treatment method of the present invention can significantly improve the ionic conductivity of the polymer electrolyte.

Claims (7)

A method of improving the ionic conductivity of a polymer electrolyte in which the polymer solid electrolyte is treated with a supercritical fluid. The method of claim 1, The supercritical fluid is a method of improving ion conductivity of a polymer electrolyte, characterized in that the supercritical fluid of carbon dioxide. The method of claim 2, The treatment is a method of improving the ion conductivity of the polymer solid electrolyte, characterized in that the temperature range 40 to 100 ℃, pressure range 5 to 20MPa conditions. The method of claim 3, wherein The treatment is a step of putting the produced specimen in a high pressure reactor to transfer carbon dioxide (CO ₂ ) gas, Leaving the specimen in the carbon dioxide gas for 10 to 120 minutes in the temperature range and the pressure range, And quenching the reactor in liquid nitrogen to 30 ° C. or less, and then discharging the residual carbon dioxide gas. The method of claim 4, wherein Method of improving the ion conductivity of the polymer solid electrolyte, characterized in that further comprising the step of vacuum drying the specimen at 30 ℃ one hour. The method of claim 1, The polymer solid electrolyte is a polymer having a methacrylate derivative represented by the following formula (1) as a monomer, lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (lithium hexafluorophosphate, LiPF ₆ ), lithium trifluoromethansulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethansulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ) Method for improving the ion conductivity of a polymer solid electrolyte, characterized in that the composite of at least one ionic lithium salt CH ₂ = C (CH ₃ ) -COO (CH ₂ CH ₂ O) _n -H (Wherein n is a number from 0 to 20). The method of claim 1, The polymer solid electrolyte is a method of improving the ion conductivity of the polymer solid electrolyte, characterized in that the electrolyte of the lithium polymer battery.

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