KR100473352B1 - Polyalkylene oxide Composition for Polymer Electrolytes with Enhanced Lithium Stability - Google Patents

Abstract

The present invention relates to a polyalkylene oxide-based polymer electrolyte composition having improved lithium stability, and more particularly, to a lithium salt and a crosslinking agent having a functional group of at least two phenylalkylene glycol acrylates introduced around a connecting center atom. In the electrolyte composition containing the curable initiator and the non-aqueous polar solvent, a specific lithium surface stabilizer having a polyalkylene oxide functional group which forms a stable protective layer on the lithium surface and makes it easy to maintain the ion conducting path is added. It has the effect of stabilizing the interface between lithium metal and electrolyte during charging and discharging and greatly improving the efficiency of lithium charging and discharging. Therefore, polyalkylene jade useful as electrolyte of lithium metal-polymer secondary battery using metal lithium as a negative electrode It relates to a seed-based polymer electrolyte composition.

Description

Polyalkylene oxide composition for Polymer Electrolytes with Enhanced Lithium Stability}

The present invention relates to a polyalkylene oxide-based polymer electrolyte composition having improved lithium stability, and more particularly, to a lithium salt and a crosslinking agent having a functional group of at least two phenylalkylene glycol acrylates introduced around a connecting center atom. In the electrolyte composition containing the curable initiator and the non-aqueous polar solvent, a specific lithium surface stabilizer having a polyalkylene oxide functional group which forms a stable protective layer on the lithium surface and makes it easy to maintain the ion conducting path is added. It has the effect of stabilizing the interface between lithium metal and electrolyte during charging and discharging and greatly improving the efficiency of lithium charging and discharging. Therefore, polyalkylene jade useful as electrolyte of lithium metal-polymer secondary battery using metal lithium as a negative electrode It relates to a seed-based polymer electrolyte composition.

The metal lithium electrode (theoretical energy density: 3.86 Ah / g) has a higher energy density than the carbon-based negative electrode (theoretical energy density: 0.372 Ah / g) used in conventional lithium ion batteries, and thus is suitable for high capacity batteries. . However, the metal lithium electrode has a high reactivity and easily reacts with a commonly used carbonate-based electrolyte solution to form a non-conductive film on the metal surface. In addition, a non-uniform reaction occurs on the surface of the lithium electrode during charging and discharging, so that a needle-shaped dendrite-shaped lithium electrode is formed on the electrode surface, and the dendrite on the surface of the lithium electrode easily falls off the electrode surface, so-called "dead lithium". Is formed to reduce the charge / discharge cycle life of lithium, which is a direct cause of battery short-circuit, which is a major cause of deterioration of battery safety. Therefore, it is essential to develop a high capacity battery using metal lithium electrodes to suppress lithium dendrite growth to improve the reversible charge and discharge cycle life of lithium and to secure battery stability. .

Currently, polyethylene oxide (PEO) -based solid polymer electrolytes have been studied as suitable electrolytes for metal lithium electrodes. However, due to low ionic conductivity at room temperature and relatively high resistance of the electrolyte / electrode interface, the capacity reduction and low temperature characteristics of the battery at room temperature are low. It is pointed out that there is a very bad disadvantage.

In the case of a metallic lithium secondary battery using a gel polymer electrolyte and a hybrid electrolyte containing a liquid electrolyte, the added liquid electrolyte reacts with a very active lithium metal, resulting in a non-uniform electrode / electrolyte interfacial layer (SEI) on the surface. Layer), and this non-uniform SEI layer is known to not effectively prevent dendrite growth. In addition, polyethylene oxide gel polymer electrolytes are known to somewhat inhibit the growth of dendrite on the surface of lithium [ J. Electroanal. Chem ., Vol. 143 , p. 2187], which is not sufficient for application in metal lithium batteries.

Thus, attempts have been made to increase the stability and charge / discharge efficiency of metallic lithium by introducing a protective layer that stabilizes the surface of lithium and prevents reaction with the electrolyte. For example, a conductive polymer [US Pat. No. 5,460,905] having a conjugated double bond, a crosslinking polymer having an ion conductivity [US Pat. No. 5,961,672] or a ceramic [US Pat. No. 5,314,756] is coated on a metal lithium electrode surface to introduce a protective layer. Methods and the like are known. However, the above-described protective layer coating method may increase the interface resistance to reduce the charge and discharge efficiency of the battery.

As another method of stabilizing the surface of lithium, a method of forming a stable protective layer film on the surface by adding a small amount of organic or inorganic to the electrolyte solution is known, wherein the additive is mainly CO ₂ [ Electrochim Acta , Vol. 42 , p . 2667], HF [J. Electrochem. Soc , Vol. 143 , p. 2187], low molecular weight polyethylene glycol dimethyl ether [ J. Electrochem. Soc. , Vol. 147 , p.813] and the like.

As another method, CO ₂ was added to the gel polymer electrolyte to stabilize the surface of lithium and increase slightly compared to before using the charge and discharge efficiency of lithium [ J. Power Sources , Vol. 81-82 , p.734], the method of using a gaseous additive has the trouble of a manufacturing process.

Therefore, there is an urgent need for the development of new polymer electrolytes that are easier to apply to metal lithium polymer batteries.

On the other hand, the present inventors tried to solve the limitation of the conventional cross-linked polymer electrolyte has a limitation in the application to lithium-polymer battery because it is easily broken due to the lack of properties such as stretching or bending after curing, and as a result A patent application was developed by synthesizing a crosslinking agent having a structure in which two or more phenylalkylene glycol acrylates were introduced into a solid polymer electrolyte material having a three-dimensional network structure [Korean Patent Publication No. 2002-72886]. number].

The present invention is an improved invention of Korean Patent Publication No. 2002-72886 developed by the present inventors. That is, a specific lithium surface that stabilizes the lithium surface in an electrolyte composition containing a crosslinking agent and a lithium salt disclosed in Korean Patent Publication No. 2002-72886 to inhibit dendrite growth on the electrode surface to maximize the charge and discharge efficiency of lithium. The present invention has been completed by preparing a polymer electrolyte composition including a stabilizer.

In the conventional method, although CO ₂ or HF was used as an additive to stabilize the lithium surface, the quantitative control was difficult and the complexity of the manufacturing process could not be avoided, whereas the lithium surface stabilizer used in the present invention is a polyalkylene oxide. It has excellent miscibility with the polymer electrolyte and stabilizes the surface of lithium.

Accordingly, an object of the present invention is to provide a polymer electrolyte composition having excellent mechanical properties and excellent lithium-polymer battery manufacturing process application and improved lithium charge and discharge efficiency.

The present invention is i) 3 to 30% by weight of a lithium salt; Ii) 0.1 to 80% by weight of a crosslinking agent represented by the following formula (1); Iii) 0.01 to 20% by weight of a single or two or more lithium surface stabilizers selected from the compounds represented by the following formulas (2) and (3); V) 0.1 to 90% by weight of single or two or more plasticizers selected from non-aqueous polar solvents; And iii) 0.5 to 5% by weight of a curing initiator.

In Chemical Formula 1: X is , , , or Wherein X ₁ and X ₂ each represent a chain or branched alkyl group having 1 to 10 carbon atoms or a haloalkyl group substituted with a halogen atom; R represents a chain or branched alkyl group having 1 to 10 carbon atoms; R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ each represent a hydrogen atom or a methyl group; R ₈ each represents a chain or branched alkyl group having 1 to 10 carbon atoms; j is an integer of 2 or 3; And p, q and r are each an integer of 0 to 20.

C _i F _{2i + 1} C _j H _2j -Q _1- (CH ₂ CH ₂ O) _k -C _j H _2j -Q ₂ -R ₉

In Formula 2, Q ₁ and Q ₂ are -O-, -OC (O) O-, -OC (O)-or -C (O) O-, respectively, and R ₉ is a hydrogen atom or carbon number as a linking functional group. It is a 1-20 chain or branched perfluorinated alkyl group, i and k are the integers of 1-20, respectively, j is an integer of 0-5;

In Formula 3, D is an aromatic or siloxane-based core atom , , , , , , , , , , , And Is selected from; W is , , And Is selected from; R ₁ is a hydrogen atom or a methyl group; Z is Is; Y is a group connecting the central molecule and the side branch , , , , And J and k are each 0 or a natural number of 1 to 4; R is Where n and m are each 0 or a natural number from 1 to 30; R ² is selected from a hydrogen atom or a methyl group; 1 is a natural number of 1 to 8.

Referring to the present invention in more detail as follows.

The present invention is a polymer containing a lithium surface stabilizer represented by the formula (2) or (3) having a polyalkylene oxide functional group that can not only form a stable protective layer on the surface of the lithium but also easily maintain the ion conduction path It relates to an electrolyte composition. The compound of Formula 2 or Formula 3 is a polyalkylene having a perfluorinated alkyl group, an aromatic group or a cyclic siloxane group capable of forming a stable protective layer with a lithium surface at the center molecule or molecular terminal, and can maintain ion conductivity Since one or more oxide groups are bonded, it is effective as a surface stabilizer of lithium metal.

Referring to each composition component contained in the polymer electrolyte composition according to the present invention in detail.

Iii) lithium salt

In the composition of the present invention, any lithium salt may be used as the lithium salt, as long as it is a lithium salt used for producing a conventional polymer electrolyte. Lithium salts that have been used in the past include, for example, LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N.

The lithium salt is used in the range of 3 to 30% by weight, preferably 5 to 15% by weight based on the total composition, but the amount may be adjusted by an appropriate mixing ratio as necessary.

Ii) crosslinking agent

The composition of the present invention is represented by the formula (1) as a crosslinking agent contains a crosslinking agent having a benzene ring introduced to the center of the crosslinking to improve mechanical properties such as stretching and bending characteristics and to improve the ionic conductivity. That is, the crosslinking agent of the present invention has a structure in which two or more phenyl alkylene glycol acrylates are introduced into the linking molecule, as shown in the general formula (1), so that the polymer electrolyte into which the crosslinking agent is introduced can form a three-dimensional network structure. In particular, the polymer electrolyte in which the crosslinking agent represented by Chemical Formula 1 is introduced is crosslinked by hard segments having two or more benzene molecules to reinforce the mechanical properties of the electrolyte, and also the distance between linear or branched polymer chains. Keep it regular. In the crosslinking agent represented by Formula 1, X is preferably or It is to contain a phosphorus compound.

The crosslinking agent may be contained in the total composition of 0.1 to 80% by weight, preferably 5 to 60% by weight, more preferably in the range of 10 to 50% by weight.

Iii) lithium surface stabilizer

The composition of the present invention contains, as a lithium surface stabilizer, a specific compound having a polyalkylene oxide functional group that can not only form a stable protective layer on the lithium surface but also easily maintain an ion conducting path. As the lithium surface stabilizer, a single or a mixture of two or more selected from an aromatic group or a siloxane compound may be used in the perfluorine-based compound represented by Chemical Formula 2 and the center represented by Chemical Formula 3. The perfluorine compound represented by Chemical Formula 2 used as a lithium surface stabilizer can be easily synthesized by a known method or commercially available as a commercially available product, and the aromatic or siloxane compound represented by Chemical Formula 3 can be known by a known method [ Korean Patent Publication No. 2002-80196] can be easily synthesized. In the lithium surface stabilizer according to the invention, it is particularly preferred to use the following:

, , , , , , , , , , , or Wherein n is an integer from 1 to 20 and m is an integer from 1 to 30.

The lithium surface stabilizer may be contained in the total composition of 0.01 to 20% by weight, preferably 0.01 to 10% by weight, more preferably in the range of 0.05 to 2% by weight.

Iii) plasticizer

The composition of the present invention contains a non-aqueous polar solvent capable of dissociating lithium salts as a plasticizer for improving lithium salt dissociation and conductivity. In general, the conductivity of the polymer electrolyte is largely dependent on the content of the added plasticizer, so that the conductivity increases as the content of the plasticizer increases. However, as the content of the added plasticizer increases, the conductivity increases, but the mechanical properties are greatly reduced, making it impossible to form a thin film or to use it in a battery manufacturing process. In consideration of these matters, the plasticizer may be contained in the total composition in the range of 0.1 to 90% by weight, and may contain up to 0.1 to 80% by weight.

Examples of the non-aqueous polar solvent which the present invention can be used as a plasticizer include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxirane, 4, 4-dimethyl-1,3-dioxirane, gamma -butylolactone, acetonitrile, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol diglycidyl Ethers, polypropylene glycol dimethyl ether and polypropylene glycol diglycidyl ether; Polypropylene glycol / polyethylene glycol copolymer of dibutyl ether terminal; And polyethylene glycol / polypropylene glycol / polyethylene glycol block copolymers at the end of dibutyl ether. The plasticizer may be used alone or in combination of two or more thereof for the purpose of imparting ion conductivity to the polymer electrolyte to be produced.

Iii) Curing initiator

Since the curable initiator is contained in the composition of the present invention, both an initiator and a photoinitiator may be used as the initiator component. Examples of photocurable initiators include ethylbenzoin ether, isopropylbenzoin ether, alphamethylbenzoin ethylether, benzoin phenylether, alphaacyloxime ester, alpha, alpha-diethoxyacetophenone, 1,1-dichloroacetophenone , 2-hydroxy-2-methyl-1-phenylpropan-1-one [Darocur 1173 by Ciba Geigy], 1-hydroxycyclohexyl phenyl ketone [Ciba Geigy Irgacure 184], Darocure 1116, Igacure 907, etc., anthraquinone, 2-ethyl anthraquinone, 2-chloro anthraquinone, thioxanthone, isopropyl thioxanthone, chlorothioxanthone, benzophenone , p-chlorobenzophenone, benzyl benzoate, benzoyl benzoate, mickle ketone and the like. Thermosetting initiators include azoisobutyronitrile-based, peroxide-based and the like.

The initiator is contained in the range of 0.5 to 5.0% by weight in the total composition, the content of which can be adjusted by appropriate mixing ratio with various oligomers or polymers contained together.

Next, a process of manufacturing a polymer electrolyte film using the polymer electrolyte composition as described above will be described as an example. First, a lithium salt, a surface stabilizer, and a plasticizer compound are put into a container at an appropriate ratio, stirred with a stirrer to prepare a solution, and then a crosslinking agent is added and mixed with each other. When the curable initiator is added to the mixed solution and stirred, a mixed solution for preparing a polymer electrolyte is produced. The prepared solution is coated on a support such as a glass plate, polyethylene-based vinyl, or commercial Mylar film to an appropriate thickness to undergo a curing reaction under an irradiation condition such as electron beam, ultraviolet ray, gamma ray or heating conditions. Another manufacturing method for obtaining a film having a constant thickness is to apply the composition mixture on the support, and to fix the spacer for adjusting the thickness (spacer) at both ends of the support and then cover another support thereon, the curing irradiator or Curing reaction using a heat source to produce a polymer electrolyte film.

As described above, the polymer electrolyte composition according to the present invention has enhanced physical properties such as mechanical strength and ionic conductivity, and also improves lithium charge and discharge efficiency, and thus is used in a polymer secondary battery using lithium metal as an anode. It is suitable to

Such a present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Preparation Example: Preparation of Polymer Electrolyte Composition

3 g of bisphenol A polyethoxylate (EO / Phenol = 4) (BPAEO4) and 1.7 g of 1 M LiAsF ₆ are dissolved in 5.3 g of a mixture of ethylene carbonate / propylene carbonate (1/1 weight ratio), and then D4 (n 7.2) 0.01 g and 0.6 g benzoyl peroxide ("BPO") were mixed. The mixed solution was impregnated into the porous polyethylene thin film for 1 hour, sandwiched between a lithium electrode and a nickel electrode, pressed, and vacuum-packed to prepare a cell. The produced cell was cured in an oven at 100 ° C. for 20 minutes to finally complete the tester cell.

Charge and discharge characteristics of the lithium oxide was lithium at a constant current of 0.1 mA / cm ² after plating by reducing the lithium at a constant current for 1000 sec with a 0.1 mA / cm ² current over the nickel electrode. The cut-off voltage during oxidation was 1.0 V, and the lithium charge / discharge efficiency was expressed as a percentage of the total amount of lithium oxide charges relative to the total amount of lithium reduction charges. The charge and discharge efficiency of lithium was more than 90% after 5 charge and discharge cycles.

Example 1 lithium charge and discharge characteristics test

An electrolyte of the present invention obtained in the same manner as in Preparation Example, an electrolyte containing 0.01 g of linear polyethylene glycol dimethyl ether (molecular weight 250) as a surface stabilizer, and an electrolyte containing no surface stabilizer were prepared, respectively. A graph of comparison of charge and discharge efficiency of lithium for each electrolyte is attached to FIG. 1.

Compared to the electrolyte without the surface stabilizer and the electrolyte to which polyethylene glycol dimethyl ether (PEGDME) was added, it can be seen from FIG. 1 that the charge and discharge efficiency of the electrolyte to which the surface stabilizer (D4) proposed in the present invention was greatly increased.

Example 2 lithium charge and discharge characteristics according to the type of surface stabilizer

An electrolyte was prepared in the same manner as in Preparation Example, but the electrolyte was prepared by changing the type of surface stabilizer as shown in Table 1 below. The lithium charge and discharge efficiency of each of the prepared electrolytes was evaluated to show the lithium charge and discharge efficiency according to the charge and discharge cycle.

Surface stabilizer structure Charge / discharge efficiency (%) 10th 30 times 50 times n = 3 78.4 84.6 82.9 n = 7.2 80.8 85.2 83.4 n = 16.3 77.2 80.5 81.2 n = 3 83.9 88.2 86.8 n = 7.2 85.2 88.6 87.2 n = 8, m = 6 82.5 85.3 85.1 n = 8, m = 15 83.0 85.6 85.3 n = 8, m = 23 77.2 75.8 72.2 n = 3 89.2 90.9 87.3 n = 16.3 91.0 92.3 92.5 n = 3 93.5 95.8 95.2 n = 7.2 94.5 96.4 95.2 n = 3 93.2 94.5 94.0 n = 7.2 93.8 95.2 94.3

Table 1. Continue

Surface stabilizer structure Lithium Charge Discharge Efficiency (%) 10th 30 times 50 times n = 3 89.0 90.6 86.8 n = 7.2 88.6 90.4 89.2 n = 16.3 85.5 87.6 85.2 n = 3 90.0 90.5 89.2 n = 7.2 89.1 90.4 91.2 n = 3 91.2 92.3 90.5 n = 7.2 90.7 91.8 91.5 BTC n = 3 89.6 91.3 89.9 n = 7.2 91.2 92.5 92.2 n = 16.3 88.2 89.5 88.0 n = 3 92.5 94.0 93.8 n = 7.2 93.2 95.0 95.1 n = 3 93.0 95.1 94.7 n = 7.2 92.8 95.5 94.8

Example 3: Lithium Charge / Discharge Efficiency According to the Content of Surface Stabilizer

An electrolyte was prepared in the same manner as in Preparation Example, but the surface stabilizer (D4, n = 7.2) was changed from 0.02% to 1% by weight, and the charge and discharge efficiency of lithium was evaluated and attached to FIG. 2.

Example 4 Evaluation of Lithium / Electrolyte Interfacial Resistance According to Surface Stabilizer

In the method of Preparation Example, an electrolyte of the present invention in which 0.01 g of BTC (n = 7.2) was added as a surface stabilizer and an electrolyte containing no surface stabilizer as a comparative example were prepared, respectively. Lithium / electrolyte interfacial resistance according to charge and discharge cycles for each electrolyte was measured and attached to FIGS. 3A and 3B, respectively. When the surface stabilizer was not added, the interfacial resistance continued to increase, but when BTC was added, the interfacial resistance was almost constant even after several charge and discharge cycles, which could be assumed to form a lithium / electrolyte stable protective film.

As described above, the electrolyte composition according to the present invention may not only form a stable protective layer on the surface of lithium, but also add a lithium surface stabilizer having a polyethylene oxide functional group capable of easily maintaining an ion conduction path in a certain content ratio. As a result, the polymer electrolyte composition stabilizes the lithium metal / electrolyte interface during charging and discharging, and has an effect of greatly improving the charging and discharging efficiency.

Simple modifications and variations of the present invention can be easily made by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

1 shows an electrolyte of the present invention containing a siloxane compound (D4) as a surface stabilizer, an electrolyte containing a linear polyethylene glycol dimethyl ether (PEGDME) as a surface stabilizer as a comparative example, and no surface stabilizer. It is a graph comparing the charge and discharge efficiency of lithium for each electrolyte.

2 is a graph showing charge and discharge efficiency of lithium according to the addition amount of the surface stabilizer (D4).

3A and 3B are graphs showing lithium / electrolyte interfacial resistances according to charge / discharge cycles of electrolytes of the present invention including BTC as surface stabilizers and electrolytes containing no surface stabilizer as a comparative example.

Claims (3)

In the polymer electrolyte composition for lithium metal-polymer secondary batteries containing a lithium salt, a cross-linking agent with an unsaturated functional group, a lithium stabilizer, a plasticizer and a curing initiator, i) 3 to 30% by weight of lithium salt; Ii) 0.1 to 80% by weight of a crosslinking agent represented by the following formula (1) after introducing functional groups of two or three phenylalkylene glycol acrylates around the linking central atom; Iii) 0.01 to 20% by weight of a single or two or more lithium surface stabilizers selected from the compounds represented by the following formulas (2) and (3); V) 0.1 to 90% by weight of single or two or more plasticizers selected from non-aqueous polar solvents; And Iii) a polyalkylene oxide polymer electrolyte composition comprising 0.5 to 5 wt% of a curing initiator: [Formula 1] In Chemical Formula 1: X is , , , or Wherein X ₁ and X ₂ each represent a chain or branched alkyl group having 1 to 10 carbon atoms or a haloalkyl group substituted with a halogen atom; R represents a chain or branched alkyl group having 1 to 10 carbon atoms; R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ each represent a hydrogen atom or a methyl group; R ₈ each represents a chain or branched alkyl group having 1 to 10 carbon atoms; j is an integer of 2 or 3; And p, q and r are each an integer of 0 to 20; [Formula 2] C _i F _{2i + 1} C _j H _2j -Q _1- (CH ₂ CH ₂ O) _k -C _j H _2j -Q ₂ -R ₉ In Formula 2, Q ₁ and Q ₂ are -O-, -OC (O) O-, -OC (O)-or -C (O) O-, respectively, and R ₉ is a hydrogen atom or carbon number as a linking functional group. It is a 1-20 chain or branched perfluorinated alkyl group, i and k are the integers of 1-20, respectively, j is an integer of 0-5; [Formula 3] In Formula 3, D is an aromatic or siloxane-based core atom , , , , , , , , , , , And Is selected from; W is , , And Is selected from; R ₁ is a hydrogen atom or a methyl group; Z is Is; Y is a group connecting the central molecule and the side branch , , , , And J and k are each 0 or a natural number of 1 to 4; R is Where n and m are each 0 or a natural number from 1 to 30; R ² is selected from a hydrogen atom or a methyl group; 1 is a natural number of 1 to 8. The crosslinking agent of claim 1, wherein X is or Wherein X ₁ and X ₂ are each a chain or branched alkyl group having 1 to 10 carbon atoms or a haloalkyl group substituted with a halogen atom, respectively. The polyalkylene oxide polymer electrolyte composition according to claim 1, wherein the surface stabilizer is selected from: , , , , , , , , , , or Wherein n is an integer from 1 to 20 and m is an integer from 1 to 30.