JP2001093574A - Gel polymer electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel polymer electrolyte secondary battery having improved charging/discharging cycle characteristics. SOLUTION: The battery includes a positive electrode using aluminum as a current collector material; a negative electrode; and a gel polymer electrolyte which also serves as a separator. The gel polymer electrolyte is prepared by impregnating a polymer with a non-aqueous electrolyte formed by dissolving, in a non-aqueous solvent, a lithium salt represented by the formula LiX(SO2R)n, where X is N or C, n=2 if X is N, n=3 if X is C, and R is CF3, C2F5, C3F7 or C4F9. To above non-aqueous electrolyte, phosphotrialkylester is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention uses aluminum as a positive electrode current collector material and has the formula: LiX (SO ₂ R) _n
[Where X is N or C, n = 2 when X is N, n = 3 when X is C, R is CF ₃ , C ₂ F ₅ , C ₃ F ₇ or C ₄
It is an F _9. Non-aqueous electrolyte solution obtained by dissolving a lithium salt represented by a non-aqueous solvent, a polymer electrolyte is impregnated with a gel-like polymer electrolyte used as an electrolyte that also serves as a separator. The present invention relates to an improvement of the above gelled polymer electrolyte for the purpose of improving its charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art
As an electrolyte of the secondary battery, a liquid electrolyte having excellent ion conductivity is used, but the liquid electrolyte has a problem such as liquid leakage.

[0003] For this reason, there is no need to worry about leakage of solid electrolyte,
In particular, polymer solid electrolytes that can be easily formed into a thin film and that are inexpensive have attracted attention.

However, in general, the solid polymer electrolyte has low ionic conductivity. In recent years, polymer solid electrolytes having relatively high ion conductivity, such as siloxane and phosphazene, have been proposed. However, those having ion conductivity enough to withstand practical use have not yet been reported.

Therefore, recently, a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent has been proposed as an electrolyte which has taken advantage of liquid electrolytes and solid polymer electrolytes and eliminated disadvantages.
A gel polymer electrolyte obtained by impregnating a polymer has attracted attention.

As an electrolyte salt for a gel polymer electrolyte having a high ionic conductivity, LiX (SO ₂ R) _n [wherein:
X is N or C; n = 2 when X is N; n = X when X is C
3, R is CF ₃ , C ₂ F ₅ , C ₃ F ₇ or C ₄ F ₉ . ] Is well known (Japanese Patent Application Laid-Open No.
-25384).

[0007] As the positive electrode current collector material of the gel polymer electrolyte secondary battery, stainless steel, gold, platinum, nickel, aluminum, titanium and the like can be used. Aluminum is most suitable from the comprehensive viewpoint of electrochemical stability, economy, workability and the like.

However, as a result of investigations by the present inventors, when the above-mentioned lithium salt is used as an electrolyte salt and aluminum is used as a positive electrode current collector material, a gel polymer electrolyte secondary battery having good charge / discharge cycle characteristics is obtained. It turned out that a battery could not be obtained. It is considered that the above-mentioned lithium salt reacts with aluminum to corrode the aluminum, and as a result, the current collecting ability of the positive electrode current collector decreases.

Accordingly, the present invention provides a gelled polymer electrolyte secondary battery having good charge / discharge cycle characteristics, using aluminum as a positive electrode current collector material and using the above-mentioned lithium salt as an electrolyte salt. Aim.

[0010]

A gel polymer electrolyte secondary battery (battery of the present invention) according to the present invention comprises a positive electrode using aluminum as a current collector material, a negative electrode, and a formula: LiX (SO
₂ R) _n wherein, X is N or C, when X is N n = 2,
When X is C, n = 3, and R is CF ₃ , C ₂ F ₅ , C ₃ F ₇
Or C ₄ F ₉ . A non-aqueous electrolyte solution obtained by dissolving a lithium salt represented by a non-aqueous solvent, and a gel polymer electrolyte serving also as a separator obtained by impregnating the polymer,
Trialkyl phosphate is added to the non-aqueous electrolyte.

The battery of the present invention has good charge / discharge cycle characteristics even when aluminum is used as a positive electrode current collector material and the above-mentioned lithium salt which corrodes aluminum is used as an electrolyte salt. Although the reason is not clear, the trialkyl phosphate (neutral ester) added to the non-aqueous electrolyte reacts with aluminum to form a protective film on the surface of the positive electrode current collector. It is presumed to suppress progress.

The gel polymer electrolyte has the formula: LiX (SO
₂ R) _n wherein, X is N or C, when X is N n = 2,
When X is C, n = 3, and R is CF ₃ , C ₂ F ₅ , C ₃ F ₇
(N- or an iso-) or _{C 4 F 9 (n-, iso-} ,
sec- or tert-). ] Is dissolved in a non-aqueous solvent, and the polymer is impregnated with a non-aqueous electrolyte.

The above-mentioned lithium salt has a high ionic conductivity and does not decompose like LiPF ₆ to generate hydrogen fluoride, so that there is no danger of destroying the polymer.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, chain carbonates such as dimethyl carbonate and diethyl carbonate, ethers such as 1,2-dimethoxyethane and 1,2-ethoxymethoxyethane, Examples thereof include glymes such as methyl diglyme, methyl triglyme, methyl tetraglyme, ethyl glyme, ethyl diglyme, butyl diglyme, sulfolane, dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, and γ-butyrolactone.

As the polymer, polyethylene oxide,
Examples include polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, poly (meth) acrylate oligoethylene oxide, polyethyleneimine, polyalkylene sulfide, polyphosphazenes and polysiloxanes having oligoethylene oxide in the side chain, and copolymers and cross-linked products thereof. You. A polymer having a polyalkylene oxide structure in the molecule is preferable in view of ion conductivity and charge / discharge cycle characteristics.

Specific examples of the trialkyl phosphate include trimethyl phosphate, triethyl phosphate, tri (n- and iso-propyl) phosphate and tri (n-phosphate).
-, Iso-, sec- and tert-butyl). Trimethyl phosphate is most preferred. The reason that alkyl phosphates are limited to trialkyl phosphates is that phosphate monoesters and diesters containing an OH group in the molecule are more unstable than trialkyl phosphates, The active hydrogen of the group is Li
Because it reacts with

The preferable amount of the trialkyl phosphate added depends on the type of the trialkyl phosphate to be added. If the amount of the trialkyl phosphate added is too small, a film is not sufficiently formed on the surface of the positive electrode current collector, whereas if the amount is too large, the viscosity of the non-aqueous electrolyte increases. In any case, the charge / discharge cycle characteristics are degraded. Taking the case of trimethyl phosphate as an example, it is preferable to add 0.1 to 10% by weight to the non-aqueous electrolyte.

[0018]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope of the invention without changing its gist. It is something.

(Experiment 1) A battery of the present invention and a comparative battery were manufactured, and charge / discharge cycle characteristics were examined.

(Example 1) [Preparation of positive electrode] LiCoO ₂ powder 8 as positive electrode active material
NM of 5 parts by weight, 10 parts by weight of carbon powder as a conductive agent, and 5 parts by weight of polyvinylidene fluoride powder as a binder
A P (N-methyl-2-pyrrolidone) solution was mixed, applied to an aluminum current collector to a thickness of about 80 μm by a doctor blade method, and heated at 130 ° C. to obtain a disc-shaped positive electrode having a diameter of 10 mm. Was prepared.

[Preparation of Negative Electrode] A copper current collector was prepared by mixing 95 parts by weight of graphite powder having an average particle size of 10 μm as a lithium ion storage material and an NMP solution of 5 parts by weight of polyvinylidene fluoride powder as a binder. It was applied to a thickness of about 70 μm on the body by a doctor blade method, and heated at 130 ° C. to produce a disk-shaped negative electrode having a diameter of 10 mm.

[Preparation of Gel Polymer Electrolyte] Polyethylene glycol ethyl ether acrylate [CH ₂ = CH-COO- (CH ₂ -CH ₂ -having a number average molecular weight of 360)
_{O) n-CH 2 -CH 3} ; and oligomers], LiN (C
A non-aqueous electrolyte obtained by dissolving ₂ F ₅ SO ₂ ) ₂ in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 at 1 mol / liter was mixed at a weight ratio of 1: 5. Trimethyl phosphate was added to the mixture thus obtained in an amount of 2% by weight with respect to the non-aqueous electrolyte, and then applied to one surface of the positive electrode to a thickness of 25 μm. ： 2Mr
(ad · m / min) to polymerize polyethylene glycol ethyl ether acrylate,
A gel polymer electrolyte membrane also serving as a separator was formed on the positive electrode.

[Preparation of Gel Polymer Electrolyte Secondary Battery] A negative electrode is superposed on the gel polymer electrolyte membrane of the positive electrode having the gel polymer electrolyte membrane formed on one surface as described above to form an electrode body. The battery was housed inside and sealed to produce a flat gel polymer electrolyte secondary battery A1 (battery of the present invention). The capacity ratio of the positive electrode to the negative electrode was set to 1: 1.1, so that the capacity of the battery was regulated by the capacity of the positive electrode.

Example 2 Instead of trimethyl phosphate,
2% by weight of triethyl phosphate relative to non-aqueous electrolyte
A gel polymer electrolyte secondary battery A2 (battery of the present invention) was produced in the same manner as in Example 1 except that it was added.

Example 3 Instead of trimethyl phosphate,
A gel polymer electrolyte secondary battery A3 (battery of the present invention) was produced in the same manner as in Example 1 except that tri (n-butyl) phosphate was added in an amount of 2% by weight relative to the non-aqueous electrolyte.

Example 4 As a non-aqueous electrolyte, LiN was used.
A non-aqueous electrolyte obtained by dissolving (n-CF ₃ SO ₂ ) ₂ in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 at 1 mol / liter was used in the same manner as in Example 1. Thus, a gelled polymer electrolyte secondary battery A4 (battery of the present invention) was produced.

Example 5 As a non-aqueous electrolyte, LiN was used.
_{(N-C 3 F 7 SO} 2) 2 at a volume ratio of ethylene carbonate and diethyl carbonate 1: except for using 1 mole / liter Dissolve obtained non-aqueous electrolyte in a mixed solvent of 1 as in Example 1 Similarly, a gelled polymer electrolyte secondary battery A5 (battery of the present invention) was produced.

Example 6 As a non-aqueous electrolyte, LiN was used.
_{(N-C 4 F 9 SO} 2) 2 at a volume ratio of ethylene carbonate and diethyl carbonate 1: except for using 1 mole / liter Dissolve obtained non-aqueous electrolyte in a mixed solvent of 1 as in Example 1 Similarly, a gelled polymer electrolyte secondary battery A6 (battery of the present invention) was produced.

Example 7 As a non-aqueous electrolyte, LiN was used.
Except that a non-aqueous electrolyte obtained by dissolving (CF ₃ SO ₂ ) (nC ₄ F ₉ SO ₂ ) in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 at 1 mol / liter is used. In the same manner as in Example 1, a gelled polymer electrolyte secondary battery A7 (battery of the present invention) was produced.

Example 8 As a non-aqueous electrolyte, LiC was used.
_{(N-C 3 F 7 SO} 2) 3 the volume ratio of ethylene carbonate and diethyl carbonate 1: except for using 1 mole / liter Dissolve obtained non-aqueous electrolyte in a mixed solvent of 1 as in Example 1 Similarly, a gelled polymer electrolyte secondary battery A8 (battery of the present invention) was produced.

Comparative Example 1 The procedure of Example 1 was repeated except that trimethyl phosphate was not added to the non-aqueous electrolyte.
A gel polymer electrolyte secondary battery B1 (comparative battery) was produced.

Comparative Example 2 As a non-aqueous electrolyte, LiPF
₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 at a ratio of 1 mol / liter, and a non-aqueous electrolyte solution was used. A secondary battery B2 (comparative battery) was produced.

<Discharge Capacity at 1st and 100th Cycles of Each Battery> Each battery was charged at 25 ° C. at a current density of 100 μA / cm ² to 4.2 V, and then charged at a current density of 100 μA / cm ² . The battery was discharged and discharged to 2.75 V for 100 cycles, and the discharge capacity (mAh) at the first cycle and the 100th cycle of each battery was determined. Table 1 shows the results.

[0034]

[Table 1]

Table 1 shows that the battery of the present invention has better charge / discharge cycle characteristics than the comparative battery. Further, the charge / discharge cycle characteristics of the battery A1 of the present invention are different from those of the batteries A2 and A of the present invention.
3 indicates that trimethyl phosphate is preferable as the trialkyl phosphate.

(Experiment 2) A suitable amount of trimethyl phosphate added to the non-aqueous electrolyte was examined.

The amount of trimethyl phosphate added to the non-aqueous electrolyte was 0.1% by weight, 1% by weight, 3% by weight, 5% by weight,
Except having set it as 10 weight% or 15 weight%, it carried out similarly to Example 1, and carried out gel-type polymer electrolyte secondary battery C1-C6.
(Battery of the present invention) was produced. Next, a charge / discharge cycle test under the same conditions as those performed in Experiment 1 was performed.
Discharge capacity (mAh) at the 100th and 100th cycles
I asked. Table 2 shows the results. Table 2 shows the battery A of the present invention.
1 and the result of the comparative battery B1 are also transcribed from Table 1.

[0038]

[Table 2]

Table 2 shows that when trimethyl phosphate is added, it is preferable to add 0.1 to 10% by weight based on the non-aqueous electrolyte.

[0040]

The present invention provides a gelled polymer electrolyte secondary battery having good charge / discharge cycle characteristics.

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Claims (4)

[Claims] 1. A positive electrode comprising aluminum as a current collector material;
Negative electrode and formula: LiX (SO ₂ R) _n [where X is N or C, n = 2 when X is N, n = 3 when X is C, R is C
F ₃ , C ₂ F ₅ , C ₃ F ₇ or C ₄ F ₉ . A non-aqueous electrolyte solution obtained by dissolving a lithium salt represented by a non-aqueous solvent, and a gel polymer electrolyte also serving as a separator obtained by impregnating the polymer, a gel polymer electrolyte secondary battery comprising: A gel polymer electrolyte secondary battery, wherein a trialkyl phosphate is added to the nonaqueous electrolyte. 2. The trialkyl phosphate according to claim 1, wherein the trialkyl phosphate is at least one trialkyl phosphate selected from the group consisting of trimethyl phosphate, triethyl phosphate, tripropyl phosphate and tributyl phosphate. Gel-type polymer electrolyte secondary battery. 3. The gelled polymer electrolyte secondary battery according to claim 1, wherein the trialkyl phosphate is trimethyl phosphate. 4. The gelled polymer electrolyte secondary battery according to claim 3, wherein 0.1 to 10% by weight of trimethyl phosphate is added to the non-aqueous electrolyte.