KR102514522B1 - gel-polymer electrolyte comprising litium salt and graft copolymer, the manufacturing method of the same - Google Patents

Abstract

The present invention is a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA); It relates to a gel-type polymer electrolyte containing a lithium salt and an organic solvent. It is safe without the risk of leakage, can exhibit high ion conductivity like a liquid electrolyte, and can exhibit excellent performance with excellent thermal stability and low lithium ion movement activation energy. there is.

Description

A gel-type polymer electrolyte comprising lithium salt and a graft copolymer and a manufacturing method thereof {gel-polymer electrolyte comprising litium salt and graft copolymer, the manufacturing method of the same}

The present invention relates to a gel-type polymer electrolyte and a method for preparing the same, and more particularly, to a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA) (PVDC-g- PMMA); It relates to a gel polymer electrolyte containing a lithium salt and an organic solvent and a method for preparing the same.

Recently, as the environmental pollution problem has been steadily becoming an issue, interest in secondary batteries that are efficient, have excellent performance, and can reduce environmental pollution has been continued. An electrolyte commonly plays an important role in a secondary battery, and research is being actively conducted to improve the chemical properties of the electrolyte, such as the mobility of charges inside the electrolyte, a temperature range, and a voltage range.

Currently, commonly used electrolytes are mainly in liquid form, and have the advantage of having high conductivity due to good charge mobility, but have the disadvantage of having a risk of leakage and being usable only in a narrow voltage range in which the solvent is not decomposed.

In order to solve this problem, the disadvantages of liquid electrolytes are improved by adding nano fillers to reduce the crystallinity of polymers and utilizing the hopping effect of electric charges, or by utilizing gel-type electrolytes that are intermediate between liquids and solids.

At this time, the gel-type electrolyte has no risk of leakage compared to the liquid electrolyte and can improve safety, but has a problem in that ion conductivity is still low due to poor charge mobility.

Accordingly, there is a demand for a gel polymer electrolyte for a lithium secondary battery, which exhibits excellent performance by improving ionic conductivity as well as safety of the electrolyte.

An object of the present invention is to provide a gel polymer electrolyte that is safe and exhibits high ion conductivity without the risk of leakage, and exhibits excellent performance due to excellent thermal stability and low lithium ion movement activation energy.

The present invention is a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA); A gel polymer electrolyte containing a lithium salt and an organic solvent is provided.

In addition, the present invention, a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA); A method for producing a gel-type polymer electrolyte containing a lithium salt and an organic solvent,

Provided is a method for producing a gel polymer electrolyte comprising a step of atomic transfer radical polymerization of polyvinylidene chloride and methyl methacrylate.

The gel-type polymer electrolyte of the present invention is safe in a gel-type form without the risk of leakage, can exhibit high ion conductivity like a liquid electrolyte, and can provide a polymer electrolyte with excellent thermal stability and low lithium ion movement activation energy, which has excellent performance. there is.

1 is a schematic diagram showing a process for preparing a PVDC-g-PMMA copolymer using an atom transfer radical polymerization method according to the present invention.
Figure 2 is a graph comparing the structure of the PVDC polymer and PVDC-g-PMMA of the present invention, (a) shows the FT-IR graph of PVDC-g-PMMA, MMA and PVDC, (b) is the PVDC-g-PMMA It shows the ¹ H NMR graph of g-PMMA and PVDC.
3 is a GPC (gel permeation chromatography) graph measuring the molecular weight of PVDC-g-PMMA according to the present invention.
4 is a graph showing the thermal weight % of PVDC-g-PMMA according to the present invention according to temperature.
5 is a graph showing the ion conductivity according to the temperature of the electrolytes of Example 1 and Comparative Example 1.
6 is a graph showing ionic conductivity according to the ratio of propylene carbonate added to the gel polymer electrolyte according to the present invention.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention, a graft copolymer (PVDC-g-PMMA) of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA); It relates to a gel polymer electrolyte containing a lithium salt and an organic solvent.

The graft copolymer of the present invention may be in the form of graft copolymerization of methyl methacrylate (MMA) monomers to polyvinylidene chloride having repeating units derived from vinylidene chloride monomers.

In the present invention, polyvinylidene chloride (PVDC) was used instead of polyvinyl chloride (PVC), which has Cl attached to both ends unlike polyvinyl chloride (PVC) in which Cl is attached to one side, resulting in an atomic radical transfer polymerization reaction. As a result, the aspect in which the methyl methacrylate monomer is grafted can become more diverse.

On the other hand, the graft copolymer of the present invention was graft-copolymerized using a methyl methacrylate monomer having a C=O group more friendly to lithium ions. While the movement is advantageous, the hopping effect can be increased. Accordingly, an electrolyte containing the graft copolymer of the present invention may exhibit more improved ionic conductivity.

In other words, since Cl is attached to polyvinylidene chloride used as the basic skeleton of the copolymer in both directions, polymethyl methacrylate can be randomly bidirectionally or unidirectionally polymerized, and electron-friendly oxygen ions can form polymethylketa. It is contained in acrylate and can be utilized as a lithium ion electrolyte.

The graft copolymer may be prepared by atom transfer radical polymerization (ATRP).

The atom transfer radical polymerization reaction can proceed at a relatively low temperature, and the molecular weight and number of units of the polymer can be easily controlled by controlling time and temperature. In addition, since an atom causing a radical reaction remains at the end of the molecular unit, there is an advantage that the reaction can be continued, and the ratio of the desired functional group can be easily increased by adjusting the ratio of the monomers added.

The weight ratio of polyvinylidene chloride:polymethyl methacrylate in the graft copolymer of the present invention may be 1:1 to 1:8, 1:1 to 1:7, or 1:1 to 1:6, Specifically, it may be 1:1, 1:3, or 1:6, and more specifically, it may be 1:6.

The graft copolymer of the present invention may include three monomers of polymethyl methacrylate per monomer of polyvinylidene chloride.

The graft copolymer of the present invention may have a number average molecular weight of 80,000 g/mol to 250,000 g/mol.

The graft copolymer of the present invention may be included in the gel polymer electrolyte in an amount of 5 to 20% by weight, 5 to 18% by weight, 5 to 15% by weight, 7 to 15% by weight, or 7 to 12% by weight based on the weight of the gelated polymer electrolyte. .

The lithium salt in the gel polymer electrolyte of the present invention is used as a medium for transferring ions in a lithium secondary battery, and any lithium salt used in the electrolyte can be used without limitation.

In one aspect of the present invention, the lithium salt is LiTFSI, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiOH, LiOH·H ₂ O, LiBOB, LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , CF 3 SO ₃ Li, LiC(CF ₃ SO ₂ ) ₃ , LiC ₄ BO ₈ , LiFSI, and LiClO ₄ may be one or more selected from the group consisting of, and more specifically, it may be LiTFSI or LiClO ₄ . In addition, only one type of lithium salt may be included in the electrolyte of the present invention, or two or more types of lithium salts may be included together.

Depending on the type of lithium salt, especially the type of anion other than Li ⁺ , it shows a difference in interaction with methyl methacrylate (MMA), which can show a difference in ionic conductivity, and later, it is used as either an anode or a cathode However, in some cases, an advantageous lithium salt may be selected and used.

The content of the lithium salt may be 10 to 30% by weight, more specifically 10 to 28% by weight, 12 to 28% by weight, 12 to 25% by weight, or 15 to 25% by weight, based on the weight of the graft copolymer. Specifically, it may be 20% by weight.

In the gel-type polymer electrolyte of the present invention, the organic solvent is not limited as long as it can minimize decomposition due to an oxidation reaction or the like during the charging and discharging process of a secondary battery and exhibits desired characteristics together with an additive. For example, the organic solvent is dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), diethyl carbonate (DEC), propylene carbonate (PC) and N-methyl-2-pyrroly It may include one or more selected from the group consisting of pork (NMP), and more specifically, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) or diethyl carbonate (DEC). ), and more specifically, may include dimethylformamide (DMF).

On the other hand, when diethyl carbonate is used as an organic solvent, PVDC does not melt, but the graft copolymer of the present invention after polymerizing MMA melts and can be appropriately used as a solvent for lithium ion batteries later.

Here, the content of the organic solvent may be 3 to 20mL, 3 to 18mL, 5 to 18mL, or 5 to 15mL, specifically 10mL, based on the weight of 1g of the graft copolymer.

The gel polymer electrolyte of the present invention may further include additives in addition to the graft copolymer, lithium salt, and organic solvent. Here, the additive may be used without limitation as long as it is commonly included in the electrolyte, and in one aspect of the present invention, it may be a plasticizer such as propylene carbonate.

The present invention also provides a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA) (PVDC-g-PMMA); A method for producing a gel-type polymer electrolyte containing a lithium salt and an organic solvent, comprising an atom transfer radical polymerization (ATRP) step of polyvinylidene chloride and methyl methacrylate. A manufacturing method is provided.

The atom transfer radical polymerization step may include adding methyl methacrylate, a metal catalyst, and a ligand to a polyvinylidene chloride solution, followed by reacting at 50 to 200° C. for 3 to 15 hours. In one embodiment, the atom transfer radical polymerization step is the step of adding methyl methacrylate, a metal catalyst and a ligand to a polyvinylidene chloride solution, purging with nitrogen gas, and reacting at 80 to 150 ° C. for 5 to 10 hours can include

The polyvinylidene chloride solution may be prepared by sufficiently dissolving polyvinylidene chloride in 20 ml to 80 ml of a solvent for 3 to 24 hours. Here, the solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone).

The weight ratio of polyvinylidene chloride and methyl methacrylate polymerized in the atom transfer radical polymerization step may be 1:1 to 1:8, 1:1 to 1:7, or 1:1 to 1:6, More specifically, it may be 1:1, 1:3, or 1:6, and more specifically, it may be 1:6.

By purging the nitrogen gas, all oxygen inside the reaction vessel may be replaced with nitrogen.

The metal catalyst used in the atom transfer radical polymerization method of the present invention may be CuCl.

The ligand used in the atom transfer radical polymerization method of the present invention is 1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), N,N ,N',N'',N''-pentamethyldiethylenetriamine (N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDETA), 2,2'-bipyridine (2,2 '-bipyridine, bpy), or 4,4'-dimethyl-2,2'-dipyridine (4,4'-dimethyl-2,2'-dipyridine, DMDP), and more specifically, 1, 4,7,10,10-hexamethyltriethylenetetramine (1,1,4,7,10,10-hexamethyltriethylenetetramine, HMTETA) or N,N,N',N'',N''-pentamethyldi It may be ethylenetriamine (N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDETA).

The method for producing a gel polymer electrolyte of the present invention may be prepared by adding a graft copolymer prepared by atom transfer radical polymerization and a lithium salt to an organic solvent.

Here, the content of the organic solvent may be 3 to 20mL, 3 to 18mL, 5 to 18mL, or 5 to 15mL, specifically 10mL, based on the weight of 1g of the graft copolymer.

The content of the lithium salt may be 10 to 30% by weight, more specifically 10 to 28% by weight, 12 to 28% by weight, 12 to 25% by weight, or 15 to 25% by weight, based on the weight of the graft copolymer. Specifically, it may be 20% by weight.

Here, a plasticizer may be additionally added, and an example of the plasticizer may be polypropylene carbonate (PC). The content of polypropylene carbonate may be 10 to 100% by weight based on the weight of the graft copolymer. When such a plasticizer is used, the gel polymer electrolyte of the present invention can be used as an electrolyte for a flexible device later.

In the method for preparing the gel-type polymer electrolyte of the present invention, a non-solid gel form may be obtained by leaving a part of the organic solvent in which the graft copolymer is dissolved and drying the result.

Another aspect of the present invention may provide a lithium secondary battery including the gel-type polymer electrolyte. Here, the secondary battery may include a positive electrode, a negative electrode, and the gel polymer electrolyte interposed between the positive electrode and the negative electrode. The cathode and anode constituting the lithium secondary battery of the present invention may be prepared and used in a conventional manner.

Hereinafter, the present invention will be described in more detail through examples and the like according to the present invention, but the scope of the present invention is not limited by the examples presented below.

Example

<Production Example 1> PVDC- g -Synthesis of PMMA

5 g of PVDC was put into a 100 ml or 250 ml round flask in 40 ml of NMP and sufficiently dissolved for 3 to 24 hours. After completely dissolving PVDC, 0.3 mol of MMA (weight ratio of PVDC:MMA = 1:6), 0.05 g of CuCl, and 0.46 mmol of PMDETA (N,N,N',N'',N''-pentamethyldiethylenetriamine) were added. After putting it in, nitrogen gas was used to replace all the oxygen inside with nitrogen. After purging for more than an hour and a half, the reaction was performed at 90 to 100 °C for 6 to 8 hours. After the reaction was completed, the resulting polymer precipitated in a 1:1 mixed solution of methanol and hexane was dried in a vacuum oven for 24 hours. Accordingly, PVDC- g- PMMA (hereinafter referred to as 'PP') of the present invention was prepared.

<Preparation Example 2> Preparation of the gel polymer electrolyte of the present invention

10% by mass of PVDC- g- PMMA prepared according to Preparation Example 1 was sufficiently dissolved in dimethylformamide (DMF) (1mL per 0.1g of PVDC -g- PMMA), and LiTFSI was 20% by weight compared to PVDC- g- PMMA. melted A gel polymer electrolyte (Example 1) of the present invention was prepared.

<Preparation Example 3> Preparation of propylene carbonate-added gel polymer electrolyte

A gel polymer electrolyte was prepared in the same manner as in Preparation Example 2, except that 10, 40, 70, and 100% by weight of propylene carbonate was added in Preparation Example 2.

<Comparative Example 1>

A gel polymer electrolyte was prepared in the same manner as in Preparation Example 2, except that 10% by mass of PVDC- g- PMMA was changed to 10% by mass of PVDC-g-PMMA of the present invention.

2 to 4 below compare the PP of the present invention prepared according to Preparation Example 1 and the PVDC itself used in Preparation Example 1, and show the results.

Figure 2 shows the results of analyzing the PP prepared according to Preparation Example 1 by FT-IR (Fig. 2 (a)) and NMR (Fig. 2 (b)). As can be seen in (a) of FIG. 2, in PVDC, the strong peak at 650 cm ^-1 is related to the Cl group, and since Cl remains at the end of MMA even after the reaction proceeds, the corresponding part of PP A peak was also present. In the structure of MMA, carboxyl group (C=O), alkene group (C=C), and isher group (COC) are characteristic structures, which show peaks at 1720.5 cm ^-1 , 1638 cm ^-1 , and 1158 cm ^{-1 ,} respectively. You can check. After synthesizing the PVDC- g- PMMA of the present invention, the disappearance of the peak at 1638 cm ⁻¹ indicates that MMA was successfully polymerized to PVDC. In addition, it can be seen that the peak of the carboxyl group has moved from 1720.5 cm ^-1 to 1723.5 cm ^-1 , which means that the C=O bond in the carboxyl group is relatively weak due to steric hinderance in the prepared PP. This is the result of being stronger.

In the ¹ H NMR graph of FIG. 2(b), it can be confirmed that PVDC- g- PMMA was synthesized. In (b) of FIG. 2, peaks of three MMAs are shown, and when the polymerization ratio is calculated, it can be seen that an average of three MMAs are polymerized in one molecule of PVDC. In addition, in the case of PVDC, since there are two Cl groups in one monomer unit, two and one MMA may be attached to each two Cl of one monomer unit of PVDC, or three MMA may be attached to one Cl group. . Since these various cases exist, the PP of the present invention has a wide molecular weight distribution, as can be seen in Figure 3 below.

3 is a graph showing the results of gel permeation chromatography (GPC) of the prepared PVDC- g- PMMA. The molecular weight of PP was 164,229 g/mol, and the molecular weight of PVDC was 56,433 g/mol. It can be confirmed that the PDI value of PVDC- g- PMMA is 5.13, which is much higher than the PDI value of 3.89 of PVDC.

4 is a graph showing thermogravimetric analysis of PVDC- g- PMMA. PVDC started to decompose around 250℃, whereas PP of the present invention started to decompose around 350℃. Therefore, the PP of the present invention had higher thermal stability than the PVDC of Comparative Example 1.

5 is a graph confirming the difference in ion conductivity values and lithium ion movement activation energy of the gel polymer electrolytes of Example 1 and Comparative Example 1. The electrolyte containing the PP of the present invention had higher ionic conductivity and lower lithium ion movement activation energy than the electrolyte containing PVDC.

6 is a graph showing the ionic conductivity according to the ratio of the added propylene carbonate of the gel polymer electrolyte prepared according to Preparation Example 3, the experiment was conducted twice, and the values are shown in FIG. It was confirmed that the ionic conductivity tended to increase as the amount of propylene carbonate added as a plasticizer increased, suggesting that the gel polymer electrolyte of the present invention can be used as an electrolyte for a flexible device in the future.

Claims (10)

a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA) (PVDC-g-PMMA);
Including a lithium salt and an organic solvent,
The graft copolymer is a form in which methyl methacrylate monomers are graft-copolymerized with polyvinylidene chloride,
The weight ratio of polyvinylidene chloride: polymethyl methacrylate in the graft copolymer is 1: 1 to 1: 8 gel polymer electrolyte. According to claim 1,
The graft copolymer is a gel polymer electrolyte prepared by atom transfer radical polymerization (ATRP). delete delete According to claim 1,
The lithium salt is LiTFSI, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiOH, LiOH H ₂ O, LiBOB, LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , CF3SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ , LiC ₄ BO ₈ , LiFSI, and LiClO ₄ At least one selected from the group consisting of, a gel polymer electrolyte. According to claim 1,
The organic solvent is dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), diethyl carbonate (DEC), propylene carbonate (PC) and N-methyl-2-pyrrolidone (NMP) A gel polymer electrolyte comprising at least one member selected from the group consisting of. a graft copolymer of polyvinylidene chloride (PVDC) and polymethylmethacrylate (PMMA) (PVDC-g-PMMA);
A method for producing a gel-type polymer electrolyte containing a lithium salt and an organic solvent,
It includes an atom transfer radical polymerization (ATRP) step of polyvinylidene chloride and methyl methacrylate,
The weight ratio of polyvinylidene chloride: polymethyl methacrylate in the graft copolymer is 1: 1 to 1: 8, the method for producing a gel polymer electrolyte according to claim 1. According to claim 7,
The atom transfer radical polymerization step is a method for producing a gel-type polymer electrolyte comprising adding methyl methacrylate, a metal catalyst and a ligand to a polyvinylidene chloride solution and then reacting at 50 to 200 ° C. for 3 to 15 hours. delete A lithium secondary battery comprising the gel-type polymer electrolyte according to claim 1.

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