KR100788211B1 - Polymer electrolyte composite materials including organic clay and lithium secondary battery comprising same - Google Patents

Abstract

A solid polymer electrolyte composite material, and a lithium secondary battery containing the solid polymer electrolyte composite material are provided to improve ion conductivity and mechanical strength and to prevent the danger of explosion and leakage. A solid polymer electrolyte composite material comprises 100 parts by weight of a polymer; 1-200 parts by weight of a lithium salt; 0.1-100 parts by weight of a plasticizer; and 1-20 parts by weight of a filler, wherein the filler comprises a clay which is organized with a C1-C30 alkyl ammonium and has an interlayer distance of 15-35 Angstrom. Preferably the clay is any one selected from the group consisting of montmorillonite, bentonite, hectorite, saponite, attapulgite, sepiolite, and vermiculite.

Description

Polymer electrolyte composite material containing an organic clay and a lithium secondary battery comprising the same {POLYMER ELECTROLYTE COMPOSITE MATERIALS INCLUDING ORGANIC CLAY AND LITHIUM SECONDARY BATTERY COMPRISING SAME}

1 shows the results of differential scanning calorimeter (DSC) measurement of the polymer electrolyte composite materials of Comparative Examples 1 and 2 and Examples 1 to 6,

2 shows the results of X-ray diffraction analysis of the polymer electrolyte composite materials of Comparative Examples 1 and 2 and Examples 1 to 6,

3 is a graph showing the AC impedance results of the polymer electrolyte film,

4 shows ionic conductivity of the polymer electrolyte composite materials of Comparative Examples 1 and 2 and Examples 1 to 6. FIG.

The present invention relates to a solid polymer electrolyte composite material used in an electrochemical device such as a lithium polymer secondary battery, and a lithium secondary battery including the same.

With the recent rapid development of high integration and high performance of devices due to the development of the electronic and telecommunication industries, the necessity of high performance small batteries is increasing, and the realization of electric vehicles that can solve the pollution problem by automobiles using fossil fuels. There is a greater demand for secondary batteries than ever before. Among the secondary batteries, lithium secondary batteries using lithium have attracted attention for their long life and high energy density, and researches on secondary batteries using solid electrolytes have been conducted due to stability problems and manufacturing costs in liquid electrolyte batteries. Actively done.

The solid polymer electrolyte used in the lithium polymer battery not only improves the energy density but also increases the stability of the battery, prevents leakage of the electrolyte solution, thereby improving the reliability of the battery, and improves the adhesion of the electrode / electrolyte interface. It is advantageous in high-rate charging and discharging, easy to manufacture thin battery, and has the advantage of making any shape battery is expected to be applied to high-capacity lithium secondary batteries, such as for electric vehicles, along with small lithium secondary batteries for portable electronic devices.

The solid polymer electrolyte is classified into a gel-type solid electrolyte and an intrinsic solid electrolyte. The former is obtained by impregnating a large amount of organic liquid electrolyte into a polymer and gelling the latter. The latter is coordinated with an alkali metal cation by polar molecules present in the polymer. It forms a complex, moves in the polymer in a state in which salts are dissociated in the polymer, and thus is electrically conductive. A polyethylene oxide (PEO) -based electrolyte is mainly used.

The PEO-based polymer electrolyte has a high chemical and electrochemical stability, and particularly has the advantage of using a lithium metal electrode of a high capacity, but has a relatively low ion conductivity at room temperature compared to an electrolyte in an aqueous solution or a gel state. Since the ionic conductivity of the solid polymer electrolyte affects the internal resistance during battery charging and discharging, the efficiency and the rate of the battery, efforts are being made to improve the ionic conductivity. The liquid plasticizer and TiO ₂ , Al ₂ O ₃ Examples are techniques using fillers such as, SiO ₂ and activated silica.

In the above method, the method of adding a liquid plasticizer improves ionic conductivity, but degrades the mechanical properties of the electrolyte and reacts with the electrode (XG Sun et al., Solid State Ionics , 175, p713, 2004).

On the other hand, the method of adding the filler improves the ionic conductivity, mechanical properties and the adhesion between the anode and cathode interfaces, but is very low compared to the ionic conductivity of the liquid electrolyte, and it is necessary to increase it dramatically (F. Croce et al. Nature , 394, p456, 1998 and L. Fan et al., Solid State Ionics, 164, p81, 2003).

Accordingly, an object of the present invention is to provide a solid polymer electrolyte composite material having high electrochemical stability and excellent mechanical properties.

In addition, to provide an efficient and safe lithium secondary battery using the same.

In order to achieve the above object, in the present invention, in the polymer electrolyte composite material containing a polymer, a lithium salt, a plasticizer and a filler, the filler is organicized with alkyl ammonium having 1 to 30 carbon atoms, the clay having an interval of 15 to 35 kPa It provides a solid polymer electrolyte composite material comprising a.

In addition, the present invention provides a lithium battery comprising the solid polymer electrolyte composite material.

Hereinafter, the present invention will be described in detail.

The solid polymer electrolyte composite material of the present invention is characterized in that it comprises an organic clay having a spacing of 15 to 35 kPa as a filler, and by adding the organic clay, a small amount of filler is introduced to increase the compressive strength, impact strength, and the like. Increasing distance and hydrophobicity improves the ion conductivity, and there is no risk of explosion and leakage, which may be usefully used in electrochemical devices such as lithium batteries.

If the interlayer spacing is less than 15 GPa, the effect of improving the ionic conductivity is insignificant. If the interlayer spacing is greater than 35 GPa, the layer is exfoliated and the clay addition effect cannot be exhibited.

In the present invention, the clay is montmorilonite, bentonite, hectorite, saponite, attapulgite, sepiiorite, vermiculite, and the like. Among them, montmorillonite has a silicate layer having a thickness of about 10 mm 3 and a length of 2800 mm, and has a high aspect ratio, and the raw material itself is an inexpensive and environmentally friendly material, and thus may be preferably used.

In the present invention, such clays are organically used with alkyl ammonium having 1 to 30 carbon atoms. For example, dimethyl benzyl hydrogenated tallow quaternary ammonium and dimethyl dihydrogen tallow. Dimethyl dihydrogenated tallow quaternary ammonium, dimethyl hydrogenated tallow 2-ethylhexyl quaternary ammonium, methyl tallow bis-2-hydroxyethyl quaternary ammonium (methyl tallow bis- Organic agents such as 2-hydroxyethyl quaternary ammonium, methyl dihydrogenated tallow ammonium, octylammonium chloride, dodecylammonium chloride, octadecyl ammonium chloride Is available.

The organic clay used in the present invention can be easily prepared by purchasing pure clay and treating it with a desired organic substance.

The polymer used in the polymer electrolyte composite material of the present invention is polyethylene oxide, polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate, polypropylene At least one selected from oxide (polypropyleneoxide), polydimethylsiloxane, polyvinylidene fluoride, polyvinylidenecarbonate, and polyvinyl pyrrolidinone can be used. Preferably polyethylene oxide can be used.

In addition, the lithium salt used in the polymer composite material of the present invention is lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LipF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) And at least one selected from lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ), and the like, and preferably lithium perchlorate can be used.

In addition, the plasticizer used in the polymer composite material of the present invention is ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate ), Dimethyl carbonate, ethyl methyl carbonate, gamma butyrolactone (GBL), sulfolane, methyl acetate, and methyl propionate One or more types can be selected and used, and preferably ethylene carbonate can be used.

In the present invention, the polymer, the lithium salt, the plasticizer and the filler may be used as 100 parts by weight of the polymer, 1 to 200 parts by weight of the lithium salt, 0.1 to 100 parts by weight of the plasticizer, and 1 to 20 parts by weight of the filler.

In the solid polymer electrolyte composite material of the present invention, an organic sludge is mixed with an organic solvent as the polymer, a plasticizer, a lithium salt, and a filler, followed by stirring to prepare an electrolyte sludge, which is poured onto a glass plate or teflon and cast. After drying, the film may be formed into a film. The drying temperature is preferably performed at 20 to 50 ° C. for about 24 hours.

The organic solvent used in the production process may be selected from acetonitrile, ethanol, methanol, isopropyl alcohol, acetone, dimethylformamide, N-methylpyrrolidone, tetrahydrofuran and mixtures thereof.

Thus, the film-formed solid polymer electrolyte composite material of the present invention includes an organic clay as a filler, and thus a high interlayer space ratio is possible as the polymer chain is incorporated into the organic clay having a layered structure. Therefore, the polymer electrolyte composite material according to the present invention can be usefully used in an electrochemical device such as a lithium battery because it has excellent mechanical properties and improves ionic conductivity by increasing interlayer distance and hydrophobicity.

Accordingly, the present invention provides a lithium secondary battery comprising a solid polymer electrolyte composite material containing the organic clay as a filler.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention and do not limit the scope of the present invention.

Hereinafter, in Comparative Examples and Examples, polyethylene oxide was used at 50 ° C., LiClO ₄ at 130 ° C., and montmorillonite was used at 100 ° C. for 24 hours, respectively. As shown in 1.

Comparative Example 1

1.1025 g of polyethylene oxide (weight average molecular weight: 2.0 × 10 ⁵ , Aldrich) dried at 50 ° C. for 24 hours, 0.55 g of ethylene carbonate (Aldrich) as a plasticizer, 0.1675 g of LiClO ₄ (Aldrich) as a lithium salt and acetonitrile (Junsei Chemical; Japan) 5 ml of the mixture was stirred for 24 hours, and then cast into a glass container to prepare a film, and dried for 24 hours in a vacuum oven at 40 ℃ to prepare a polymer membrane.

Comparative Example 2

A polymer electrolyte membrane was prepared in the same manner as in Comparative Example 1, except that 0.11025 g of pure montmorillonite (Southern Clay Products, Inc., USA), which was not organicized, was added as a filler.

Example 1

Montmo, mixed with 1.1025 g of polyethylene oxide (PEO), 0.55 g of ethylene carbonate, 0.1675 g of LiClO ₄ , and 5 ml of acetonitrile, and then organicized with dimethylbenzyl hydrogenated tallow ammonium (125 meq / 100g clay) Lilonite (Southern Clay Products, Inc., USA) was added at 0.11025 g (10 wt% to PEO) and stirred for 24 hours, which was then cast into a glass container to produce a film form and vacuum oven at 40 ° C. After drying for 24 hours, a polymer electrolyte composite membrane according to the present invention was prepared.

Example 2

According to the present invention in the same manner as in Example 1, except that montmorillonite organicated with dimethyl dihydrogenated tallow ammonium (125meq / 100g clay) was added instead of dimethylbenzyl hydrogenated tallow quaternary ammonium as a filler. A polymer electrolyte composite membrane was prepared.

Example 3

According to the present invention in the same manner as in Example 1, except that montmorillonite organicated with dimethyl dihydrogenated tallow ammonium (95 meq / 100 g clay) was added instead of dimethylbenzyl hydrogenated tallow quaternary ammonium as a filler. A polymer electrolyte composite membrane was prepared.

Example 4

As the filler, the montmorillonite organicated with dimethyl hydride tallow 2-ethylhexyl quaternary ammonium (95meq / 100g clay) was added instead of dimethylbenzyl hydride tallow quaternary ammonium. A polymer electrolyte composite membrane according to the invention was prepared.

Example 5

The same method as in Example 1, except that montmorillonite organicated with methyl tallow bis-2-hydroxyethyl quaternary ammonium (90 meq / 100 g clay) was added instead of dimethylbenzyl hydrogenated tallow quaternary ammonium as a filler. The polymer electrolyte composite membrane according to the present invention was prepared.

Example  6

Polymer electrolyte according to the present invention in the same manner as in Example 1, except that montmorillonite organicated with methyl dihydrogenated tung ammonium (90meq / 100g clay) was added instead of dimethyl benzyl hydrogenated tallow quaternary ammonium as a filler Composite membranes were prepared.

Test Example 1: Confirmation of structure and crystallinity

Through differential scanning calorimeter (perkin Elmer DSC6) and X-ray diffraction (XRD), the effect of the addition of organic clay on the crystallinity and structure of polyethylene oxide was investigated.

First, DSC was carried out at a temperature increase rate of 5 ℃ / min from room temperature to 125 ℃ in a nitrogen atmosphere, the results are shown in FIG.

As a result, as shown in FIG. 1, when 10 weight percent of the organic clay was added, it was observed that the endothermic peak at the melting point was weakened and the melting point moved toward the lower temperature, which reduced the crystalline region of the polymer. And the amorphous region is enlarged.

On the other hand, Figure 2 shows the results of X-ray diffraction analysis, the peak characteristic of polyethylene oxide was observed in the region of the diffraction angle 2θ is 15 ~ 30 °, the intensity of the peak (intensity) as the organic clay is added A decrease can be observed. This means that the degree of crystallinity of polyethylene oxide is reduced, since this decrease is caused by the incorporation of polymers, ie, polyethylene oxide chains, between layers of organic clay, thereby reducing the crystal growth of polyethylene oxide.

Test Example  2: Confirmation of Ionic Conductivity

The polymer electrolyte membranes prepared in Comparative Examples and Examples were assembled in the form of the inactive electrode SS (stainless steel) / SPE (solid polymer electrolyte composite material) / SS to measure the ion conductivity of the electrolyte through AC impedance analysis.

Impedance is measured by sandwiching an electrolyte membrane between two stainless steel electrodes in a sandwich form, and the AUTOLAB 30 (potentiostat / galvanostat) connected to a frequency response analyzer (FRA) at a frequency range of 10 Hz to 10 kHz and a temperature range of 20 ° C .; Eco Chemie, Netherlands). The bulk resistance ( R _b ) was measured by equivalent circuit analysis using FRA software, from which the ionic conductivity (σ) was calculated according to the following equation, respectively, and FIG. 3 (AC impedance). ) And FIG. 4 (ion conductivity).

In the above formula, t means the thickness of the polymer electrolyte membrane, A means the area of the polymer electrolyte membrane.

As a result, as shown in FIG. 4, it was found that the ionic conductivity was improved when the organic clay was included. The conduction of ions occurs in the amorphous region and the ionic conductivity below the melting point is affected by the crystallinity of the polymer electrolyte. As shown in Test Example 1, the crystalline region of the polymer is reduced and the amorphous region is added by adding organic clay. Because of this expansion, the ionic conductivity is increased.

As described above, according to the present invention, the solid polymer electrolyte composite material including the clay grouped with a specific group as a filler having an interlayer spacing of 15 to 35 mm 3 has improved ion conductivity and improved mechanical strength as compared to the conventional electrolyte. Because of the risk of explosion, leakage and leakage, it can be usefully used in electrochemical devices such as lithium batteries.

Claims (8)

A polymer electrolyte composite material comprising a polymer, a lithium salt, a plasticizer, and a filler, wherein the filler comprises a clay organicized with alkyl ammonium having 1 to 30 carbon atoms and having an interlayer spacing of 15 to 35 kPa. Electrolyte composite materials. The method of claim 1, Clay from the group consisting of montmorilonite, bentonite, hectorite, saponite, attapulgite, sepiiorite, and vermiculite Polymer electrolyte composite material, characterized in that one selected. The method of claim 1, Alkyl ammonium dimethyl benzyl hydrogenated tallow quaternary ammonium, dimethyl dihydrogenated tallow quaternary ammonium, dimethyl hydrogenated tallow 2-ethylhexyl quaternary ammonium tallow 2-ethylhexyl quaternary ammonium, methyl tallow bis-2-hydroxyethyl quaternary ammonium, methyl dihydrogenated tallow ammonium, octyl ammonium chloride ( octylammonium chloride), dodecylammonium chloride (dodecylammonium chloride), octadecyl ammonium chloride (octadecyl ammonium chloride) A polymer electrolyte composite material characterized in that at least one member selected from the group consisting of. The method of claim 1, Polymer is polyethylene oxide, polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate, polypropyleneoxide, polydimethylsiloxane ), Polyvinylidene fluoride (polyvinylidene fluoride), polyvinylidene carbonate (polyvinylidene carbonate), and polyvinyl pyrrolidinone (polyvinyl pyrrolidinone). The method of claim 1, Lithium salts include lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LipF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) and lithium trifluoromethanesulfonylimide ( LiN (CF ₃ SO ₂ ) ₂ ) A polymer electrolyte composite material characterized in that at least one member selected from the group consisting of. The method of claim 1, The plasticizer is ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate (ethyl methyl carbonate), gamma butyrolactone (GBL), sulfolane (sulfolane), methyl acetate, and at least one member selected from the group consisting of methyl propionate (methyl propionate) Electrolyte composite materials. The method of claim 1, A polymer electrolyte composite material comprising 100 parts by weight of polymer, 1 to 200 parts by weight of lithium salt, 0.1 to 100 parts by weight of plasticizer, and 1 to 20 parts by weight of filler. A lithium secondary battery comprising the solid polymer electrolyte composite material according to any one of claims 1 to 7.

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