KR100722835B1 - Lithium-ion battery including polymer electrolyte composite material - Google Patents

Abstract

The present invention relates to a lithium ion battery including clay, and specifically, to improve electrical and mechanical properties of a polymer electrolyte for a lithium ion battery, a polymer in which a cation is substituted with lithium ions is introduced into the polymer electrolyte to make a conventional polymer electrolyte. The present invention relates to a polymer composite material of a lithium polymer battery that provides a migration path of lithium ions and improves ion conductivity, together with the reduction of the crystalline region.

Through this, it is possible to reduce the size and power consumption of components aiming at miniaturization of portable electronic devices, continuous use for a long time.

Polymer electrolyte composites, fillers, clays, lithium ion batteries

Description

Lithium ion battery containing polymer electrolyte composite material {LITHIUM-ION BATTERY INCLUDING POLYMER ELECTROLYTE COMPOSITE MATERIAL}

FIG. 1 is a graph showing XRD results of a polymer electrolyte composite material with addition of clay. FIG. 1A is a graph showing a change in interlayer space ratio in an MMT region and FIG. 1B in a PEO region.

Figure 2 is a graph showing the DSC measurement results of the polymer electrolyte composite material with the addition of clay.

3A and 3B are graphs showing a change in impedance resistance according to a frequency change of an AC potential for measuring the impedance resistance of a polymer electrolyte composite material according to the addition of clay at room temperature.

4 is a graph showing a change in ion conductivity of a polymer electrolyte composite material at various temperature ranges.

The present invention relates to a lithium ion battery containing clay, and more particularly, to improve the electrical and mechanical properties of a polymer electrolyte for a lithium ion battery, by introducing a clay in which a cation is substituted with lithium ions to a polymer compound, The present invention relates to a polymer composite material of a lithium polymer battery, which reduces the crystalline region, provides a migration path for lithium ions, and improves ion conductivity.

Recently, due to the serious environmental protection and pollution problem, alternative energy development is being done to solve this problem. The secondary battery, which is one of such alternative energy developments, is used as a small-scale, high-performance energy source for large-capacity power storage batteries such as electric vehicles, batteries and power storage systems, and portable electronic devices such as mobile phones, camcorders, laptops, and PDAs. Lithium polymer battery as a secondary battery can be an alternative to the problems of the stability of the battery, the electrolyte leakage, which is a disadvantage of the lithium ion battery. In addition, since the adhesion between the electrode and the electrolyte can be improved, the energy density can be improved.

The solid polymer electrolyte used in the lithium polymer battery is classified into a gel solid polymer electrolyte and an intrinsic solid electrolyte. Gel-type polymer solid electrolyte refers to a polymer electrolyte obtained by gelling a polymer by impregnating a large amount of organic liquid electrolyte, and an intrinsic solid electrolyte forms a complex by coordinating a polar molecule present in the polymer to an alkali metal cation to form a complex. It refers to the electrical conductivity by moving the polymer in the dissociated state. Intrinsic solid electrolytes mainly use PEO-based electrolytes.

PEO-based polymer electrolytes have very low ionic conductivity of 10 ^-8 S / cm at room temperature due to high crystallinity. To solve this problem, liquid plasticizers and fillers such as TiO ₂ , Al ₂ O ₃ , SiO ₂ and activated silica are used. Among these methods, the method of adding a plasticizer results in the improvement of the ionic conductivity of the polymer electrolyte, but there is a problem in that the mechanical properties of the electrolyte are reduced and react with the positive electrode.

On the other hand, the method of adding the filler has an effect of improving ion conductivity, mechanical properties, and adhesion between the anode and cathode interfaces. As an example, Korean Patent Laid-Open Publication No. 2001-25311 and US Patent No. 5965299 use plasticizers and inorganic ceramic particles or surface-modified inorganic ceramic particles as fillers to improve electrical and mechanical properties of polymer electrolytes. It discloses how to. However, the above method has an advantage that there is no fear of leakage of electrolyte at room temperature, but the ion conductivity of the polymer electrolyte is low at room temperature, making it difficult to miniaturize electronic devices.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned problems, and an object of the present invention is to introduce a crystalline region of a conventional polymer by introducing clay having a layered structure in a polymer electrolyte of a lithium ion battery and having a cation substituted with lithium ions. It is to provide a lithium ion battery having the characteristics of improving the electrical and mechanical properties of the polymer electrolyte by reducing and improving the ion conductivity by providing a mobile passage of lithium ions.

In order to achieve the technical object of the present invention, the present invention provides a lithium secondary battery having a layered structure and including a clay in which a cation is substituted with lithium ions.

The clay is preferably pyrophylite-talc, montmorilonite (MMT), hectorite, saponite, laponite, vermiculit ), Illite, mica and brittle mica are used, and more preferably, montmorillonite is used.

The interlayer spacing of the layered structure is preferably about 5 to 30 m 3, and the lithium ion is preferably lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), or lithium hexafluorophosphate (LiPF ₆ ). And those derived from any one or more lithium salts selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ) and lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ).

The polymer electrolyte of the lithium ion battery of the present invention includes 100 parts by weight of a polymer compound, 10 to 100 parts by weight of a plasticizer, 2 to 50 parts by weight of clay in which the cation of the substrate is replaced with lithium ions, and an organic solvent.

The high molecular compound preferably comprises at least one functional group selected from the group consisting of ethylene oxide, propylene oxide and glycidol.

The plasticizer is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, gamma butyrolactone, sulfolane, methyl acetate and methyl propionate It is preferable that it is any one or more.

The organic solvent is preferably 50 to 400 parts by weight based on 100 parts by weight of the polymer compound, and from the group consisting of ethanol, methanol, isopropyl alcohol, acetone, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone It is better to use one or more selected.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a lithium ion battery having a layered structure and including clay in which a cation is substituted with lithium ions.

In general, a polymer electrolyte composite material of a lithium ion battery is prepared by mixing a high molecular compound including a functional group such as polyethylene oxide, a filler composed mainly of a lithium salt, a plasticizer and silica in an organic solvent in an appropriate ratio. However, the polymer electrolyte composite material of the conventional lithium ion battery has stability against the leakage and explosion risk of the electrolyte, but the ion conductivity at room temperature and the lithium ion transport rate are low, and thus the lithium ion battery is applied to the electronic device. There was a limit in pursuing the miniaturization, light weight, and thinning of.

On the other hand, clay is a kind of interlayer compound in which functional groups are introduced between layers of inorganic structures. These clays are silica minerals of silicate layer structure, and are composed of a combination of silica tetrahydral sheet and alumina octahydral sheet. According to the degree of the negative charge of the (illite), vermiculite (vermiculite), mica (mica) and smectite (mica). Among the clay, smectite is a typical layered silicate, which has a cationic substitution on the tetrahedral and octahedral structures to balance the charges, and the cations inserted between the layers are called exchangeable ions. The molecular layer of cations has a regular layered structure, and cations are inserted between the layers to change the properties of the clay.

The present invention has been devised in view of the cation substitution ability of the clay, a problem that the polymer electrolyte composite material of the conventional lithium ion battery described above using a clay in which a cation is substituted with a lithium ion as a filler of a polymer electrolyte in a lithium ion battery. Overcome it. More specifically, as the high molecular compound polyethylene oxide is embedded in the layers of the clay, the crystallinity of the polyethylene oxide is reduced and the amorphous region is expanded, and the enlargement of the amorphous region provides an ion channel for lithium ions and consequently increases ion conductivity. By improving the electrical and mechanical properties of the polymer electrolyte composite material (see FIGS. 1 to 4).

The clay used in the present invention is not limited as long as it has a cation substitution ability, preferably pyrophylite-talc, montmorilonite (MMT), hectorite, saponite ( saponite, laponite, vermiculit, illite, mica and brittle mica are used, more preferably Uses montmorillonite in which the interlayer cations of clay are filled with sodium ions. The montmorillonite has a silicate layer having a thickness of 10 mm 3 and a length of 2800 mm 3, and has a high aspect ratio and a plate-like morphology, so that the cation substitution ability is excellent.

The method of replacing the interlayer cations of clay with lithium cations is not particularly limited, but preferably, after mixing the clay and the lithium salt from which impurities are removed, stirring for 1 to 4 days and then performing centrifugation and centrifugation. To the separated filtrate, an aqueous solution of silver nitrate was added to obtain clay in which the interlayer cation was finally replaced with lithium ions.

The layer spacing of the clay is not particularly limited, but preferably, the interlayer spacing of the layered structure is 5 to 30 mm 3. If the interlayer spacing of the clay is less than 5 mm 3, the passage is narrow and ion transmission is difficult. If it exceeds 30 mm, the size of the passage is too large and other materials may move, which is not preferable.

Meanwhile, the lithium salt is not particularly limited as long as it can provide lithium cations to clay, preferably lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), It is cost and efficient to use those derived from any one or more lithium salts selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ) or lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ) Good on the side

The polymer electrolyte of the present invention has high ionic conductivity, excellent electrical and mechanical properties, and is extremely useful for reducing the weight and power consumption of components aiming at miniaturization of portable electronic devices and long-term continuous use.

The polymer electrolyte of the lithium ion battery of the present invention includes 100 parts by weight of the polymer compound, 10 to 100 parts by weight of the plasticizer, and 2 to 50 parts by weight of clay in which the interlayer cation of the substrate is replaced with lithium ions and an organic solvent.

The polymer compound is not particularly limited as long as it is a polymer compound used in a lithium ion battery, but preferably includes any one or more functional groups selected from the group consisting of ethylene oxide, propylene oxide and glycidol. Using the compound is more reactive.

The plasticizer is generally a high molecular compound used in a lithium ion battery, but there is no limitation in the kind, preferably ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, It is preferred to use any one or more compounds selected from the group consisting of gammabutyrolactone, sulfolane, methyl acetate and methyl propionate. Meanwhile, the plasticizer adds 10 to 100 parts by weight based on 100 parts by weight of the polymer compound. If the amount is less than 10 parts by weight, the efficiency of reducing the crystallinity is significantly lowered. If it exceeds 100 parts by weight, the ratio of the plasticizer is too high, resulting in a decrease in mechanical strength and an increase in cost.

Clay in which the interlayer cation of the substrate is substituted with lithium ions plays a role of a filler in the polymer electrolyte composite material, and adds 2 to 50 parts by weight with respect to 100 parts by weight of the polymer compound, preferably 2 to 35 parts by weight, more Preferably 2 to 25 parts by weight is added. If less than 2 parts by weight is added, there is no significance of the addition, 50 When it exceeds the weight part, ion transfer becomes difficult by the aggregation phenomenon between fillers.

The organic solvent is not limited as long as it can dissolve the polymer electrolyte, but is preferably a group consisting of ethanol, methanol, isopropyl alcohol, acetone, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone Any one or more selected from among those used, and the amount of the organic solvent added is preferably 50 to 400 parts by weight based on 100 parts by weight of the polymer compound. If less than 50 parts by weight, it is difficult to completely dissolve the polymer electrolyte, and if it exceeds 400 parts by weight, the solution concentration is too low, making the film difficult.

The method for producing a polymer electrolyte of a lithium ion battery including the clay of the present invention may be any method commonly prepared by those skilled in the art, but preferably 100 parts by weight of the polymer compound, 10 to 100 parts by weight of the plasticizer and the interlayer cation of the substrate. 2 to 50 parts by weight of the clay substituted with lithium ions are mixed with 50 to 400 parts by weight of an organic solvent, followed by stirring to prepare an electrolyte sludge. The electrolyte slurry prepared as described above is applied to a glass container, followed by a vacuum oven at 40 ° C. Drying for 24 hours produces an electrolyte film.

Hereinafter, the present invention will be described in detail by Examples and Experimental Examples. The following examples are merely to illustrate the invention, the scope of the invention is not limited to the following examples.

Synthesis Example Preparation of Filler

Since sodium ions were intercalated between montmorillonite (Southern Clay Products, cation exchange capacity 1.54 meq / g) to be used as a filler, lithium chloride (LiCl, Aldrich) was used to replace it with lithium. In order to remove impurities remaining in montmorillonite, a suspension was prepared by using 1 L distilled water of 20 to 40 g of montmorillonite, which was stirred for 24 hours and then centrifuged. 20 to 40 g of lithium chloride solution and 800 ml of distilled water were added to the montmorillonite from which impurities were removed, and the mixture was stirred for 2 days so that sodium could be completely replaced with lithium. Substituted montmorillonite was obtained. After centrifugation, 0.1N AgNO ₃ aqueous solution was added to the filtrate, and the filtrate was washed and centrifuged until no white precipitate was formed. Drying for 24 hours yielded lithium-montmorillonite (Li-MMT).

<Example 1>

After mixing 1 g of dried polyethylene oxide, 0.5 g of ethylene carbonate and 6 ml of acetonitrile at 24 ° C. for 24 hours, 2 parts by weight of the filler prepared in Synthesis Example was added to the mixed solution, followed by stirring for 24 hours. After casting this in a glass container (cast) was prepared in the form of a film and dried for 24 hours in a vacuum oven at 40 ℃ to prepare an electrolyte film (SPE).

<Example 2>

An electrolyte film was prepared in the same manner as in Example 1, except that 5 parts by weight of the filler prepared in Synthesis Example was added based on polyethylene oxide.

<Example 3>

An electrolyte film was prepared in the same manner as in Example 1 except that 10 parts by weight of the filler prepared in Synthesis Example was added based on polyethylene oxide.

<Example 4>

An electrolyte film was prepared in the same manner as in Example 1, except that 15 parts by weight of the filler prepared in Synthesis Example was added based on polyethylene oxide.

Example 5

An electrolyte film was prepared in the same manner as in Example 1, except that 20 parts by weight of the filler prepared in Synthesis Example was added based on polyethylene oxide.

<Example 6>

An electrolyte film was prepared in the same manner as in Example 1, except that 25 parts by weight of the filler prepared in Synthesis Example was added based on polyethylene oxide.

Comparative Example 1

1 g of polyethylene oxide dried at 50 ° C. for 24 hours was mixed with 6 ml of acetonitrile and stirred for 24 hours, then cast into a glass container to prepare a film, and dried in a vacuum oven at 40 ° C. for 24 hours. An electrolyte film (SPE) was prepared.

Comparative Example 2

An electrolyte film was prepared in the same manner as in Comparative Example 1 except that 0.5 g of ethylene carbonate, which was a plasticizer, and 1 g of PEO were added.

Experimental Example

The physical properties of the electrolyte films prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were performed in the following manners, and the results are shown in Table 1 and FIGS. 1 to 4.

(1) structure and surface crystallinity

Structural analysis of polymer nanocomposites with the addition of ethylene carbonate and clay to polyethylene oxide was carried out through X-ray diffraction analysis (XRD). The differential scanning calorimeter (DSC, Perkin Elmer DSC6) was used to investigate the effect of ethylene carbonate and clay addition on the crystallinity of PEO. DSC was carried out at room temperature up to 125 ℃ at 5 ℃ / min in N ₂ atmosphere. It was. DSC results show a change in the melting point of the polymer electrolyte, which means a decrease in the crystallization region of the polyethylene oxide. Reduction of the crystallization region of the polyethylene oxide can be confirmed through the crystallinity ( χ ) and the crystallinity is calculated in the same manner as in Equation (1).

And △ H _f ^o and T _m is 189 J / g and 65 ℃ each of said polyethylene oxide, △ H _f with the addition of LiClO ₄ and the MCM-41 was determined through a DSC measurement.

(2) AC impedance

AC impedance was measured to measure the ion conductivity of the prepared electrolyte film. The AC impedance measurement is made by sandwiching an electrolyte film on two stainless steel electrodes in the form of a sandwich, the frequency response analyzer (FRA) connected to the frequency response analyzer (FRA) in the frequency range of 10 Hz ~ 10 kHz, temperature range of 25 ~ 80 ℃ It was measured using (potentiostat / galvanostat) (Eco Chemie, Netherlands).

(3) Bulk phase resistance ( R _b ) and ion conductivity (σ)

Bulk resistance ( R _b ) is measured by equivalent circuit analysis using FRA software. On the other hand, the ionic conductivity can be obtained by calculating the bulk resistance in relation to the bulk resistance and the film dimension thereof through Equation 2 below.

Where t is the thickness of the polymer electrolyte and A is the area of the polymer electrolyte.

Melting Point (Tm, ℃) Crystallinity (χ,%) Example 1 52.90 51.98 Example 2 52.74 49.67 Example 3 54.12 48.09 Example 4 52.24 47.74 Example 5 52.49 37.73 Example 6 54.80 38.74 Comparative Example 1 53.50 52.76 Comparative Example 2 53.15 53.96

Table 1 and Figures 1 to 4 it was confirmed that the interlayer space is present through the XRD results of the polymer electrolyte in which the cation is substituted with a lithium ion as a filler filler. This phenomenon occurs as polymer chains are incorporated into the clay having a layered structure. As the filler content increases, the interlayer space ratio is low. Through this, it was confirmed that the production of the nanocomposite material in the case of the polymer electrolyte using the clay in which the cation was substituted with lithium ions as a filler. Further, in the region of 2 θ = 15 ~ 30 ° in the XRD can be observed a unique peak of PEO. These PEO characteristic peaks were observed to have a tendency to decrease the intensity (ie, crystallinity) with the addition of clay. The decrease in crystallinity can also be observed through DSC results, because melting occurs when heat is applied to the polymer, and the crystalline region of the polymer changes from the melting region to the amorphous region. It can be seen that the endothermic reaction occurs from below the melting point due to the change of the area. As a result of DSC measurement, the endothermic peak at the melting point becomes weaker and the endothermic peak at the melting point becomes weaker and moves toward the lower temperature as the clay is added. The decrease in crystallinity decreases the crystal growth of PEO as the polymer chains are incorporated between the layers of clay, and as a result of examining the change in electrical properties according to the addition of clay, it can be observed that the ion conductivity is improved as clay is added. The crystallinity is believed to be influenced by the degree of dispersion of the clay in the polymer. In addition, it was observed that the ionic conductivity increases with increasing temperature, which means that 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. The ionic conductivity is rising.

The present invention can improve the ionic conductivity at room temperature by reducing the crystallinity by manufacturing a polymer electrolyte composite material using a clay substituted with lithium as a filler using a cation exchange reaction of clay.

The improvement of the ion conductivity improves the mechanical and electrical properties of the lithium ion battery and maximizes the efficiency of the polymer electrolyte, thereby reducing the weight and power consumption of components aimed at miniaturization of portable electronic devices and long-term continuous use. It is a very useful invention.

Although the present invention has been described in detail only with respect to the embodiments described, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, and such modifications and variations belong to the appended claims. .

Claims (10)

delete delete delete delete A polymer comprising 100 parts by weight of a polymer compound, 10 to 100 parts by weight of a plasticizer, a layered structure having an interlayer spacing of 5 to 30 mm, 20 to 25 parts by weight of clay in which an interlayer cation is substituted with lithium ions, and an organic solvent. A lithium ion battery containing an electrolyte composite material. The method of claim 5, The polymer compound is a lithium ion battery comprising a polymer electrolyte composite material characterized in that it comprises at least one functional group selected from the group consisting of ethylene oxide, propylene oxide and glycidol. The method of claim 5, The plasticizer is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, gamma butyrolactone, sulfolane, methyl acetate and methyl propionate Lithium ion battery comprising a polymer electrolyte composite material, characterized in that any one or more. The method of claim 5, The organic solvent is a lithium ion battery comprising the polymer electrolyte composite material, characterized in that 50 to 400 parts by weight based on 100 parts by weight of the polymer compound. The method of claim 5, The organic solvent is lithium containing the polymer electrolyte composite material, characterized in that any one or more selected from the group consisting of ethanol, methanol, isopropyl alcohol, acetone, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone Ion battery. The method of claim 5, The clay is pyrophylite-talc, montmorilonite (MMT), hectorite, saponite, laponite, vermiculit, work One selected from the group consisting of illite, mica and brittle mica, and the lithium ion is lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexa Derived from at least one lithium salt selected from the group consisting of fluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) and lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ) A lithium ion battery comprising the polymer electrolyte composite material.

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