KR20000018428A - High polymer electrolyte using polyacrylronitrile ionomer including ion radical - Google Patents

Abstract

PURPOSE: A high polymer electrolyte using polyacrylronitrile ionomer including ion radical is provided to increase a common use property with a plasticizer, improve an ion conductive characteristic by the increased common use property, and, simultaneously, minimize a leakage of the plasticizer, thereby being improved an interface stability for an electrode. CONSTITUTION: A high polymer electrolyte includes a co-polymer of an acrylronitrile and alkalimetalmetacrylate, a plasticizer, and lithium salt. An ion content is the maximum 11 mole% in the co-polymer of the acrylronitrile and the alkalimetalmetacrylate. A weight ratio between the co-polymer of the acrylronitrile and the alkalimetalmetacrylate and the plasticizer is 1: 1 through 1: 9. A weight ratio between the lithium salt and the plasticizer is 1: 5 through 1: 30.

Description

Polymer electrolyte using polyacrylonitrile ionomer containing ionic group

The present invention relates to a polymer electrolyte using a polyacrylonitrile ionomer containing an ionic group. More specifically, the present invention relates to a polymer electrolyte of a lithium polymer secondary battery composed of a copolymer of acrylonitrile and an alkali metal methacrylate containing an ionic group.

With the rapid development of today's electrical, electronics, telecommunications and computer industries, the demand for high performance and high stability secondary batteries is increasing day by day, especially as the light and short size and portable trend of electric and electronic products is a key component in this field. Phosphorus secondary batteries are also required to be reduced in weight and size. In order to meet such demands, one of the high-performance, next-generation advanced new batteries that are currently receiving the most attention is lithium polymer secondary batteries (LPB). Lithium polymer secondary battery is largely composed of a cathode (cathode), an anode (anode) and a polymer electrolyte, the positive electrode active material is used a transition metal oxide, a metal chalcogen compound, a conductive polymer, and the like, lithium, carbon, etc. Used.

Conventional lithium ion batteries (LIB) using liquid electrolytes have raised their safety problems, and methods of mounting electrode materials and safety devices to supplement them have been developed, but they are expensive and can be applied to large secondary batteries. There is a problem such as not. On the contrary, lithium polymer secondary batteries can be manufactured at a lower cost, can be adjusted in size or shape as desired, have a high energy density per unit weight, and can have high voltage and large capacity by stacking. In order to commercialize such a lithium polymer secondary battery, the polymer electrolyte of the lithium polymer secondary battery should have excellent ion conductivity, mechanical properties, and excellent interfacial stability with the lithium electrode.

From this point of view, most of the research subjects as polymer electrolyte materials for lithium polymer secondary batteries are plasticizers produced using polyacrylonitrile as a host polymer and ethylene carbonate, propylene carbonate, and lithium salt as main components. Polymerized polymer electrolyte. However, the polymer electrolyte has excellent ion conductivity and mechanical properties, but a plasticizer leakage problem occurs due to incompatibility between the polyacrylonitrile and the plasticizer, which are host polymers. This not only degrades the ionic conductivity of the polymer electrolyte over time, but also corrodes the lithium electrode to increase the interface resistance between the lithium electrode and the polymer electrolyte, thereby degrading performance due to long-term use.

The present invention provides a copolymer of an alkali metal methacrylate containing acrylonitrile and an ionic group as a host polymer of a polymer electrolyte in a lithium polymer secondary battery in order to solve the problems of the polyacrylonitrile-based polymer electrolyte as described above. The purpose of the present invention is to increase the compatibility with the plasticizer, to improve the ion conducting properties of the polymer electrolyte due to the increased compatibility, and at the same time to minimize the leakage of the plasticizer to improve the interfacial stability with the electrode.

Figure 1 shows the measurement of the ion conductivity according to the ion content in the ionomer of the polymer electrolyte according to the present invention at various temperatures.

Figure 2 shows the change of the interface resistance value between the polymer electrolyte using the conventional polyacrylonitrile and the electrode according to the storage time of the polymer electrolyte according to the present invention.

The polymer electrolyte of the present invention is composed of a copolymer of acrylonitrile and alkali metal methacrylate, a plasticizer and a lithium salt having a maximum ion content of 11 mol% in the copolymer, wherein the acrylonitrile and alkali metal methacrylate The weight ratio of the copolymer and the plasticizer is 1: 1 to 1: 9, and the weight ratio of the lithium salt and the plasticizer is 1: 5 to 1:30.

In the present invention, the alkali metal methacrylate may be selected from lithium methacrylate, sodium methacrylate and potassium methacrylate.

When the ion content in the copolymer exceeds 11 mol%, there is a problem in that the ionic conductivity and the workability are sharply lowered as the ion population is formed.

As the plasticizer, one or a mixture thereof selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate is used, and preferably ethylene carbonate is used.

The lithium salt is selected from lithium perchlorate, lithium triflate, lithium hexafluorophosphate, lithium tetrafluoroborate and lithium trifluoromethanesulfonylimide, and preferably LiClO ₄ is used.

In the above, the weight ratio of each component is 1: 1 to 1: 9, preferably 1: 3 to 1: 6, and lithium salt to plasticizer is 1: 5 to 1:30, preferably 1:10 to 1. 1:15. When the weight ratio of the host polymer to the plasticizer is less than 1: 1, the room temperature ion conductivity is very low, about 10 ⁻⁷ S / cm or less, and when the ratio is greater than 1: 9, the mechanical properties are not satisfied, and the weight ratio of the lithium salt plasticizer is If less than 1: 5 or greater than 1:30, there is a problem that the room temperature ion conduction properties are also very low.

In the polymer electrolyte of the present invention, acrylonitrile and methacrylic acid monomers are mixed at a constant ratio to synthesize various kinds of acrylonitrile and methacrylic acid copolymers having the structural formula of Formula (1). An aqueous solution of alkali metal (lithium, sodium, potassium) hydroxide may be added to neutralize the acrylonitrile and methacrylic acid comonomer to obtain the acrylonitrile and alkali metal methacrylate copolymer of formula (2).

Formula 1

Formula 2

Hereinafter, the present invention will be described in detail as follows.

Example

A certain amount of acrylonitrile and methacrylic acid were added to the reactor together with tertiary distilled water as a solvent, stirred for 30 minutes under a nitrogen atmosphere, and after completion of the stirring, potassium pesulfate and sodium bisulfide were respectively dissolved in a molar ratio. 0.5% was injected and reacted at 50 ° C. for 6 hours, and the obtained reaction was filtered through a filter to obtain a white powder. In order to remove impurities, for example, an initiator, etc. present in the powder, it was filtered three times with tertiary distilled water at 80 ° C. The filtered white powder was dried for 24 hours in a hood at room temperature for moisture drying, and then dried for 48 hours in a vacuum oven at 80 ° C. to completely remove moisture to obtain a compound of formula (1).

The molar ratio of methacrylic acid present in the polymer synthesized by titration was calculated to make the compound of formula (1), i.e., acrylonitrile and methacrylic acid copolymer, as an ionomer. An aqueous solution of lithium, sodium, potassium) hydroxide was added to neutralize the acrylonitrile and methacrylic acid comonomer to obtain acrylonitrile and the alkali metal methacrylate comonomer of the compound of formula (2).

Examples 1-4

3 mol% of the ion content produced by the aforementioned methods, respectively, and 4 mol%, 7 mol%, and 11 mol% of 14.9% by weight of the nitrile with lithium methacrylate copolymer of acrylic, ethylene carbonate 74.6 wt% LiClO ₄ 10.5 A mixture of wt% was added to the dimethylformamide solvent and stirred at 90 ° C. for 2 hours to obtain a homogeneous solution in which all components were dissolved. The obtained solution was cast in a Teflon container to evaporate the solvent to prepare a polymer electrolyte in the form of a film. The obtained polymer electrolyte was prepared in Examples 1 to 4 to form disk-shaped specimens.

Test Example

In Examples 1 to 4 and Comparative Examples, the ionic conductivity with a stainless steel electrode was measured using a frequency response analyzer for the specimen of the polymer electrolyte containing no ionic group, and is shown in Table 1 below. In addition, the ion conductivity at various temperatures was measured and shown in FIG. 1, and the interface resistance with the lithium electrode was measured and shown in FIG. 2.

Table 1

Ion group type Ion Content (mol%) Room temperature ion conductivity (S / cm) Interface resistance (Ω) Early 35 days later Example 1 lithium 3 1.6 × 10 ^-3 77.75 100.45 Example 2 lithium 4 1.9 × 10 ^-3 104.49 190.36 Example 3 lithium 7 1.7 × 10 ^-3 83.36 93.75 Example 4 lithium 11 5.3 × 10 ^-4 61.00 99.76 Comparative example lithium 0 1.6 × 10 ^-3 63.96 1288.31

As shown in Table 1, the polymer electrolyte according to the present invention had a relatively good ion conductivity, and the interface resistance after 35 days increased slightly compared to the initial interface resistance, whereas the polymer electrolyte of the comparative example had an interface resistance after 35 days. This increased to more than 20 times.

Referring to FIG. 2, which shows an interfacial resistance value according to a storage time to confirm interfacial stability with a lithium electrode, a polymer electrolyte based on polyacrylonitrile that does not contain an ionic group has a resistance value over time. On the other hand, the resistance value of the polymer electrolyte of the present invention (the results of Examples 1 to 4 are not shown separately because they are all within an error range) is almost constant, indicating a very stable interface.

As such, the present invention can provide a polymer electrolyte having excellent ion conducting properties and improved interfacial stability with an electrode by using a copolymer of an alkali metal methacrylate including an acrylonitrile and an ionic group as a host polymer.

Claims (4)

It consists of a copolymer of acrylonitrile and alkali metal methacrylate, a plasticizer and a lithium salt having an ionic content of up to 11 mol%, wherein the weight ratio of the copolymer of acrylonitrile and alkali metal methacrylate and the plasticizer is Is 1: 1 to 1: 9, and the weight ratio of the lithium salt and the plasticizer is 1: 5 to 1:30. The polymer electrolyte of claim 1, wherein the alkali metal methacrylate is selected from lithium methacrylate, sodium methacrylate and potassium methacrylate. The polymer electrolyte according to claim 1, wherein the plasticizer is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate or a mixture thereof. The polymer electrolyte according to claim 1, wherein the lithium salt is selected from lithium perchlorate, lithium triplate, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonylimide.