JPH01107474A - Lithium ion conductive polymer electrolyte - Google Patents

Abstract

PURPOSE:To obtain a polymer electrolyte showing good lithium ion conductivity even at room temperature by using a specified polymer prepared by vinyl- polymerizing allyl polyether glycol as an organic polymer for the polymer electrolyte. CONSTITUTION:A polymer, as shown in the formula I, prepared by vinyl- polymerizing allyl polyether glycol is used as an organic polymer for a polymer electrolyte. In the formula I, R shows H or CH3, m is 3-360, and n is 2-40. Hydrocarbon in a principal chain decreases the glass transition temperature of the polymer to make ion movement easy. Oxygen forming ether bonding in the side chain forms a complex with a lithium salt to form a lithium ion carrier, and polyether glycol in the side chain decreases the crystallinity of the polymer. The polymer electrolyte showing good lithium ion conductivity even at room temperature is obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is a lithium ion conductive material used in electrolytes such as lithium batteries and electrochromic displays, lithium ion concentration sensors, and lithium ion separation membranes. Concerning polymer electrolytes.

[Conventional technology]

Lithium ion conductive electrolytes for lithium batteries include liquid electrolytes such as LiCl0a/propylene carbonate, Li, and N.

Solid electrolytes such as Lil A11as are known, but recently attempts have been made to use polymer electrolytes based on organic polymers that can be easily formed into a flexible film.

If this type of polymer electrolyte is applied to lithium batteries, which require ultra-thin film and miniaturization, it will be advantageous in terms of workability for battery production and reliability of sealing, and will also be low cost. It also has some useful benefits. In addition, due to its flexibility, it can be used as a lithium ion separation membrane, and is also useful as an electrolyte for electrochromic displays and as a lithium ion concentration sensor.

Conventionally, as one of such polymer electrolytes, a composite of polyethylene oxide and lithium salt using polyethylene oxide as an organic polymer has been known (Gast Ion Transport in 5-solids).
P, 131 (1979)).

[Problem that the invention seeks to solve]

However, although the above polyethylene oxide-lithium salt polymer electrolyte melts at high temperatures of 60"C or higher and exhibits relatively good lithium ion conductivity, it has low lithium ion conductivity at room temperature of about 25"C. However, when applied to lithium batteries, which are mostly used at room temperature, and the various uses mentioned above, there was a problem in that the performance was not fully satisfactory.

Therefore, the present invention aims to provide a polymer electrolyte that exhibits good lithium ion conductivity even at room temperature by using a specific polymer different from the above-mentioned polyethylene oxide as an organic polymer in a lithium ion conductive polymer electrolyte. purpose.

[Means for solving problems]

As a result of intensive research to achieve the above object, the inventors discovered that polyether glycols such as polyethylene glycol, polypropylene glycol, and ethylene oxide-propylene oxide copolymers were used as organic polymers constituting the polymer electrolyte. It was discovered that a polymer electrolyte that exhibits good lithium ion conductivity even at room temperature can be obtained when a polymer obtained by vinyl polymerizing allylated polyether is used, and the present invention was completed.

That is, the present invention provides a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, in which the organic polymer has the general formula (1) (wherein R is H or CH, where m is 3 to 360,
n is 2 to 40) The present invention relates to a lithium ion conductive polymer electrolyte characterized by being a polymer represented by:

In the polymer represented by the above general formula (1), the hydrocarbon in the main chain lowers the glass transition temperature of the polymer and facilitates lithium ion movement, and the oxygen constituting the ether bond of the polyether glycol in the side chain lowers the glass transition temperature of the polymer. By forming a complex with a lithium salt, it forms a carrier for lithium ions, and the polyether glycol in the side chain lowers the crystallinity of the polymer, resulting in a temperature of around 60°C as seen in polyethylene oxide-based polymer electrolytes. This makes it possible to provide a polymer electrolyte that prevents significant changes in ionic conductivity across the range and exhibits good lithium ion conductivity even at room temperature.

Furthermore, among the polymers represented by the above general formula (1), those that are liquid at room temperature can be crosslinked with a crosslinking agent without reducing the good ionic conductivity of the liquid (but not in the solid state). It is possible to obtain a polymer electrolyte that exhibits particularly good lithium ion conductivity even at room temperature.

The polymer represented by the above general formula (I) has the following general formula (II) (CHg=CHCHg(OCHCH*)mOH)
It is obtained by vinyl polymerization of the allylated polyether glycol represented by (If). 40 to 100°C in the presence of a polymerization initiator such as potassium, t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl hydroperoxide, etc.
This is done by heating to a certain degree.

The polyether glycol in the allylated polyether glycol preferably has a number average molecular weight of 200 to 10,000, particularly preferably 300 to 2.000. The reason why the number average molecular weight of polyether glycol is particularly preferable in the range of 300 to 2,000 is that when the number average molecular weight of polyether glycol exceeds 2,000, the polymer tends to crystallize when vinyl polymerized, becomes solid at room temperature, and has a low ionic conductivity. If the number average molecular weight is less than 300, the distance between the crosslinking points becomes short when a vinyl polymerized polymer is crosslinked, making it difficult for lithium ions to move, resulting in a decrease in lithium ion conductivity. be.

The degree of polymerization of the allylated polyether glycol by vinyl polymerization, that is, the value of n, is set to 2 to 40 as described above. When the above n is less than 2, it is an allylated polyether glycol monomer, which is not preferable because it has reactivity with lithium and is difficult to solidify by crosslinking. This is because the molecular weight of the main chain hydrocarbon increases, which is undesirable because the lithium ion conductivity decreases.

In addition, m in the general formula (1) is from 3 to 360, which corresponds to the molecular weight of the polyether glycol described above. If m is less than 3, the molecular chain of the polyether is too short and the molecule This is because the chain becomes difficult to move.
Moreover, if m exceeds 360, the polyether in the side chain becomes solid and ionic conductivity decreases.

As a crosslinking agent for crosslinking the polymer represented by the general formula (1), an organic substance having bifunctionality that causes an addition/condensation reaction with a hydroxyl group in the polymer is used. Examples of such bifunctional organic substances include diisocyanates, diamines, dicarboxylic acids, dicarboxylic acid chlorides, methylol compounds, and epichlorohydrin. and,
As the diisocyanate, for example, hexamethylene diisocyanate, 2,4-)lylene diisocyanate, methylene bis(4-phenylisocyanate), xylylene diisocyanate, etc. are used, and as the diamine, for example, ethylene diamine, tetra Methylene diamine etc. are used. As the dicarboxylic acid, for example, Scheller's acid, malonic acid, succinic acid, phthalic acid, isophthalic acid, terephthalic acid, etc. are used, as the dicarboxylic acid chloride, for example, succinel chloride is used, and as the methylol compound, for example, dimethyl Urea etc. are used.

The polymer electrolyte can be prepared by preparing a solution in which a polymer represented by the general formula (1) and a lithium salt are dissolved in an appropriate organic solvent, and then removing the organic solvent by evaporation, or
) is crosslinked with a crosslinking agent by immersing the crosslinked polymer in an appropriate organic solvent solution of a lithium salt, allowing the lithium salt solution to permeate into the polymer, and then evaporating and removing the organic solvent. By dissolving such a polymer and lithium salt in an organic solvent or by immersing a crosslinked polymer in a lithium salt solution, the lithium salt forms a complex and binds to the ether oxygen (-0-) of the polymer, and after the solvent is removed, Also, the above-mentioned bonds are retained and a composite of the organic polymer and the lithium salt is obtained.

As the above-mentioned lithium salt, any of those used in conventional polymer electrolytes can be used, and specific examples include LICF, SO3, t, 1CFsso!
, LiBr% Li I, LISCN, LiBF
m, LiCl0a, LiAsF=, etc.,
As the organic solvent for dissolving the lithium salt, an organic solvent that sufficiently dissolves the lithium salt and does not react with the polymer, such as acetonitrile, dioxolane, 1,2-dimethoxyethane, tetrahydrofuran, methanol, acetone, etc., is used. Regarding the amount of lithium salt used, the ether in the polymer side chain represented by general formula (1) increases the carrier concentration of lithium ions due to an increase in the lithium salt, and decreases the mobility of lithium ions due to an increase in the lithium salt. This is because the lithium ion conductivity increases within the above range.

The form of the polymer electrolyte is determined as appropriate depending on its intended use. For example, if it is used as an electrolyte for a lithium battery and also functions as a separator between the positive and negative electrodes, the polymer electrolyte may be formed into a sheet shape. To obtain this sheet-like polymer electrolyte, an organic solvent solution of the polymer represented by the general formula (1) and a lithium salt is cast onto a suitable substrate, and the organic solvent is evaporated off, or the general formula The sheet may be formed by forming a crosslinked polymer represented by (1) into a sheet, immersing the sheet-like crosslinked polymer in an organic solvent solution of lithium salt, and removing the organic solvent by evaporation after immersion. It is possible to produce extremely thin materials on the order of microns, commonly called films.

In addition, when applying the polymer electrolyte of the present invention to a positive electrode of a lithium battery, a positive electrode active material or the like is added at a predetermined ratio to an organic solvent solution of the polymer represented by general formula (1) and a lithium salt, and the organic solvent is evaporated. Either by removing it and then molding it, or by adding a polymer, a crosslinking agent, a positive electrode active material, etc. in a predetermined ratio, and then crosslinking the polymer.
After molding, the obtained molded body may be immersed in a solution of a lithium salt in an organic solvent, and after the immersion, the organic solvent may be removed by evaporation.

By doing so, a rod in which the polymer electrolyte and the positive electrode active material are mixed can be obtained.

Figure 1 shows an example of a lithium battery using the above-mentioned polymer electrolyte of the present invention. A shallow rectangular dish-shaped negative electrode current collector plate made of stainless steel with a flat peripheral part 2a in the same direction as the bent main surface, 3 denotes opposing peripheral parts 1a and 2a of the bipolar current collector plate 1.2 This is an adhesive layer that seals the gap.

4 is a polymer electrolyte of the present invention, a positive electrode active material, etc. arranged on the side of the positive electrode current collector plate 1 in a space 5 formed between the two electrode current collector plates 1.2, and formed into a sheet shape by the method described above. 6 is a negative electrode made of lithium or lithium alloy loaded on the negative electrode current collector plate 2 side in the space 5; 7
is a separator formed by molding the polymer electrolyte of the present invention interposed between a positive electrode 4 and a negative electrode 6 into a sheet shape.

In addition, the above-mentioned positive electrode 4 may be formed into a sheet by mixing a positive electrode active material with a binder such as polytetrafluoroethylene powder or an electron conduction aid, depending on the case. As the positive electrode active material, for example, Ti1t
, Mo Stx V6O13, V t Os , V S
e % N I P S s % One or more types of polyaniline, polypyrrole, polythiophene, etc. are used.

In the lithium battery constructed in this way, the separator 7 is a sheet-like material made of the polymer electrolyte, and the positive electrode 4 is a similar sheet-like material containing the polymer electrolyte, so that the battery can be made thinner. In addition to having various advantages such as being able to contribute to improvements in workability for battery work, reliability of sealing, etc., and essentially not having to worry about leakage unlike liquid electrolytes, the above-mentioned electrolytes Due to its excellent ionic conductivity, it has very excellent discharge characteristics as a secondary battery and charge/discharge cycle characteristics as a secondary battery.

〔Effect of the invention〕

As described above, according to the present invention, by using the polymer represented by the general formula (I) obtained by vinyl polymerizing allylated polyether glycol as the organic polymer constituting the complex with the lithium salt, it is possible to maintain the property even at room temperature. A polymer electrolyte exhibiting excellent lithium ion conductivity can be provided.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example 1 Allylated polyethylene glycol with number average molecular weight 450 (CHt=CHCHz(OCHtCHz)*OH)1
0 g and 0.1 g of azobisisobutyronitrile were placed in an Erlenmeyer flask and reacted at 60° C. for 400 hours to obtain polyallylated polyethylene glycol having a number average molecular weight of 5,000.

5 g of the obtained polyallylated polyethylene glycol and 2
．． 4-) Put 0.87 g of lylene diisocyanate into an Erlenmeyer flask, stir with a magnetic stirrer, drop the resulting viscous solution mixture onto an aluminum plate, and heat at 80°C on a hot plate in an argon gas flow. The mixture was reacted for 8 hours to obtain a crosslinked product (referred to as a crosslinked polymer). The obtained crosslinked polymer was peeled off from the aluminum plate and dipped in acetone to remove unreacted 2,4-tolylene diisocyanate by dissolving it in acetone.6 Next, it was dipped in ethanol to remove unreacted NGO. The group was reacted with ethanol. The crosslinked polymer was then mixed with LiCFs at a concentration of 3% by weight.
LiCFiSO was immersed in SOs acetone solution for 8 h.
After the S solution was infiltrated into the crosslinked polymer, acetone was removed by evaporation to obtain a sheet-like polymer electrolyte with a thickness of 50 μm.

Example 2 Allylated polyethylene glycol with number average molecular it 200 (CHI-CHCH!(OCRlCH,)30H)
10 g and 0.1 g of azobisisobutyronitrile were placed in an Erlenmeyer flask and reacted at 60° C. for 400 hours to obtain polyallylated polyethylene glycol having a number average molecular weight of 6.000. 5 g of this polyallylated polyethylene glycol and 2.2 g of 2.4-)lylene diisocyanate were reacted in the same manner as in Example 1, and thereafter the same operations as in Example 1 were performed to obtain a polymer electrolyte.

Example 3 Allylated polyethylene glycol with number average molecular weight II 720:
I-ru(CHg-C)(CHg(OCHzCH*)ts
OH) and 0.1 g of azobisisobutyronitrile were placed in an Erlenmeyer flask and reacted at 60°C for 400 hours to obtain polyallylated polyethylene glycol having a number average molecular weight of 6.000. 5g of this polyallylated polyethylene glycol and 2,4-tolylene diisocyaner)0
．． 58 g was reacted in the same manner as in Example 1, and thereafter the same operations as in Example 1 were performed to obtain a polymer electrolyte.

Example 4 Allylated polyethylene glycol (CHm = CHG Hz (OCHtCHz)s) with a number average molecular weight of 1, 380
. OH) 10g and azobisisobutyronitrile 0.1g
were placed in an Erlenmeyer flask and reacted at 60° C. for 8 hours to obtain polyallylated polyethylene glycol having a number average molecular weight of 8,000. This polyallylated polyethylene glycol was immersed in a 3% by weight LtCF3SOs acetone solution for 8 hours to infiltrate the LiCFsSOi solution into the polymer, and then the acetone was removed by evaporation to obtain a polymer electrolyte.

Comparative Example 1 Polyethylene oxide Ig having a number average molecular weight of 600.000 and 0.326 g of Li CFsSOs were dissolved in 5 ml of acetonitrile and stirred with a magnetic stirrer to uniformly dissolve. This solution mixture was dropped onto a glass substrate, left for 5 hours under normal pressure in an argon gas flow, and then vacuumed at I
was treated for 10 hours to remove acetonitrile by evaporation to obtain a sheet-like polymer electrolyte with a thickness of 20 μm.

In order to examine the performance of the polymer electrolytes of Examples 1 to 4 and Comparative Example 1, the following ionic conductivity test and battery internal resistance test were conducted.

Ionic conductivity test> Each of the polymer electrolytes of Examples 1 to 4 was sandwiched between Au plates, and the polymer electrolyte of Comparative Example 1 was sandwiched between Au plates.
<L-shaped electrodes were formed by vapor deposition, AC impedance between the electrodes was measured, and complex impedance analysis (Cole-C
ole plot) to determine the ionic conductivity at room temperature (25°C). The results are shown in Table 1.

Table 1 Further, the results of measuring the ionic conductivity under various temperature conditions in the same manner as above are shown in FIG. Second
In the figure, the vertical axis is ionic conductivity (S/cm),
The horizontal axis is the reciprocal of absolute temperature 10'/T (K-1),
Also, curve 2a is the result of Example 1, and curve 2b is the result of Example 2.
As a result, curve 2c is the result of Example 3, curve 2d is the result of Example 4, and curve 2e is the result of Comparative Example 1.

(Battery internal resistance test) The total thickness of the structure shown in FIG. 1 using the polymer electrolytes of Examples 1 to 4 and Comparative Example 1 as a separator was 0.5 s + w.
, - A square thin lithium battery with a side length of 15 mm was produced.

An alloy of lithium and aluminum was used as the negative electrode, and a sheet-shaped molded product containing a polymer electrolyte having the same composition as in Examples 1 to 4 and Comparative Example 1 and titanium disulfide (TIS) was used as the positive electrode.

For these lithium batteries, 25℃, 60℃, 10℃
Table 2 shows the results of measuring the internal resistance at 0°C.

As is clear from the test results in Table 2 and above, the polymer electrolytes of Examples 1 to 4 of the present invention have a 1. .6X1G-
'~1. OXIG-F showed a high ionic conductivity of about S/cm, but the polymer electrolyte of Comparative Example 1 containing polyethylene oxide as a polymer component had an ionic conductivity of 1.0 x 1 G-''S/cm at room temperature. The ionic conductivity was inferior to that of the polymer electrolytes of Examples 1 to 4 of this invention.

Furthermore, as shown in Table 2, lithium batteries using the polymer electrolytes of Examples 1 to 4 of the present invention were prepared at room temperature (25°C).
The internal resistance was 55.6 to 8.900Ω,
The internal resistance of the lithium battery using the polymer electrolyte of Comparative Example 1 at room temperature (25°C) was as large as 89.000Ω.

In particular, the polymer electrolytes of Examples 1 to 3, which used crosslinked polymers with a small molecular weight crosslinked with a crosslinking agent as polymer components, had high ionic conductivity (and the lithium batteries using them as electrolytes at room temperature The internal resistance was very small compared to the others.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of a lithium battery using the lithium ion conductive polymer electrolyte of the present invention. FIG. 2 is a diagram showing the relationship between ionic conductivity and temperature of lithium ion conductive polymer electrolytes of the present invention and comparative lithium ion conductive polymer electrolytes. 7...Separator (polymer electrolyte) Patent applicant Hitachi Maxell, Ltd. Figure 1 Figure 2 Figure 103/T (k-')

Claims (2)

[Claims] (1) In a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, the above organic polymer has the general formula (I) obtained by vinyl polymerizing allylated polyether glycol ▲ Numerical formula, chemical formula, table, etc. ▼(I) (In the formula, R is H or CH_3, and m is 3 to 360
, n is 2 to 40) A lithium ion conductive polymer electrolyte is a polymer having the following formula. (2) In a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, the above organic polymer has the general formula (I) obtained by vinyl polymerizing allylated polyether glycol ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼(I) (wherein R is H or CH_3, m is 3-360
, n is 2 to 40) A lithium ion conductive polymer electrolyte is a crosslinked polymer obtained by crosslinking a polymer represented by the following formula with a crosslinking agent.