JP2003017066A - Electrode surface film forming agent. - Google Patents

Abstract

(57) [Summary] To improve the thermal stability of a battery. SOLUTION: Formula (I): (Wherein, R ¹ and R ² are each independently an alkyl group having 1 to 5 carbon atoms or a fluorine-containing alkyl group, and at least one of R ¹ and R ² is CF ₃ , CF ₃ CH ₂ Or (CF ₃ ) ₂ CH.) An electrolytic solution and / or an electrode surface film forming agent containing at least one member selected from the group consisting of compounds represented by the following formula:

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrode surface film forming agent using a fluorine-containing carbonic acid ester.

[0002]

2. Description of the Related Art Demand for so-called lithium-ion batteries having a negative electrode provided with lithium metal, an alloy thereof, or a compound capable of occluding and releasing lithium ions is greatly expanding due to its high energy density.

On the other hand, a lithium-ion battery may generate heat due to internal / external short-circuiting, external heat generation, etc., which may cause the battery to ignite or emit smoke. Electrolysis at high temperature may improve the safety of the lithium-ion battery. It is required to improve the stability of the liquid.

The 67th Electrochemical Society (April 4-6, 2000, Proceedings 24, 2B21) and the 41st Battery Symposium (November 20-22, 2000, Proceedings 29)
On page 6, 2C10), difluoroacetic acid methyl ester was reported to enhance the thermal stability of lithium batteries. In addition, the present inventor reported in Japanese Patent Application No. 2000-31293 that dimethyldifluoromalonate can contribute to the improvement of thermal stability of a lithium ion battery. According to it, normally, the electrolytic solution used for the battery starts to generate heat at the melting point of lithium metal (180 ° C.) or lower, while methyl difluoroacetate and dimethyldifluoromalonate are mixed with lithium metal in the presence of lithium metal, respectively.
It was shown that an exotherm did not occur up to 50 ° C and 280 ° C. In these compounds, since it is known that the introduction of fluorine increases the reactivity with lithium metal, this effect has the effect that a film of methyl difluoroacetate or dimethyldifluoromalonate is formed on the surface of lithium metal and it is stable. It is considered that the film became a protective film and the thermal stability was improved.

In general, in order to obtain high battery performance, ethylene carbonate (EC), γ-butyrolactone (GBL), propylene carbonate (PC) and dimethyl carbonate (DMC), which have a high dielectric constant and are usually used as electrolytes. It is necessary to mix it with such as. However, when the content of dimethyldifluoromalonate in the electrolytic solution is reduced, the effect of suppressing heat generation is significantly reduced. This is a protective film formed by lithium metal and dimethyldifluoromalonate EC, GB
It is considered that it was dissolved by a solvent such as L, PC and DMC, and part or most of the protective film was peeled off.

[0006] Further, in JP-A-10-116629, the thermal stability of an electrolytic solution using methyl 2,2,2-trifluoroethyl carbonate and LiCoO ₂ as a positive electrode active material is evaluated. It is believed that the reaction between the negative electrode and the electrolytic solution occurs prior to the reaction with the positive electrode, which triggers the temperature rise of the battery, which causes ignition and smoking of the battery.

Therefore, even in the coexistence of an organic solvent-based non-aqueous electrolytic solution having a high dielectric constant, which is used in practically used batteries, it strongly acts as a protective film on the surface of the negative electrode, and the thermal stability of the battery is improved. There is a need for an electrode surface film forming agent that enhances the property.

The present invention relates to a fluorine-containing compound capable of forming a surface protective film which suppresses heat generation of a negative electrode at high temperatures.

The present invention also relates to a method of manufacturing a battery having improved thermal stability.

[0010]

The present inventors have found that the high thermal stability of an electrolytic solution is obtained even in the presence of an organic solvent-based non-aqueous electrolytic solution having a high dielectric constant as used in practically used batteries. As a result of studying to obtain a battery having high performance, it was found that the fluorinated carbonic acid ester can suppress the reaction between the electrolytic solution and the electrode, particularly the negative electrode such as lithium and contribute to the improvement of the thermal stability of the battery. It was

The present invention relates to an electrode surface film forming agent, particularly to a fluorine-containing carbonic acid ester which acts as an electrode surface film forming agent for protecting the surface of a negative electrode, and to a battery manufacturing method using the same.

That is, the present invention relates to the following items 1 to 6.

Item 1, Formula (I):

[0014]

[Chemical 2]

(In the formula, R ¹ and R ² independently of each other have 1 carbon atoms.
~ 5 alkyl group or fluorine-containing alkyl group, at least one of R ¹ and R ² is CF ₃ , CF ₃ CH ₂ or (CF ₃ ).
It is ₂ CH. ) An electrolytic solution and / or an electrode surface film forming agent containing at least one selected from the group consisting of compounds represented by

Item 2, The electrode surface film forming agent according to Item 1, which acts as a protective film on the surface of the electrode material when the battery is prepared and / or used.

Item 3, The electrode surface coating forming agent according to Item 2, wherein the electrode is a negative electrode made of lithium metal, a lithium intercalate compound or a lithium alloy.

A method for producing a battery, which comprises using an electrolytic solution containing at least one compound of items 4 and 1.

A method for producing a battery, characterized in that the negative electrode is treated with at least one of the compounds of items 5 and 1 before or during the production of the battery.

Item 6, The method for producing a battery according to Item 4 or 5, wherein the negative electrode is lithium metal, a lithium intercalate compound or a lithium alloy.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The electrolytic solution and / or the electrode film forming agent of the present invention can be used in any of primary batteries and secondary batteries such as lithium primary batteries and lithium secondary batteries.

In the above formula (I), R ¹ and R ² are each independently an alkyl group having 1 to 5 carbon atoms or a fluorine-containing alkyl group, and at least one of R ¹ and R ² is CF. ₃ , CF ₃
CH ₂ or (CF ₃ ) ₂ CH.

Examples of the alkyl group represented by R ¹ and R ² include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and t-butyl.
Examples thereof include linear or branched C1-C5, preferably C1-C4, and especially C1-C3 alkyl groups such as butyl, n-pentyl, and isopentyl.

R¹And R²Fluorinated alkyl group represented by
For example, CH₂F, CHF₂, CF ₃, C₂H_FourF, C₂H₃F₂,
CF₃CH₂, C₂F_FourH, C₂F_Five, C₃H₆F, C₃F₆H, CF₃CF₂CH₂, (C
F₃)₂CH, C₃F₇, C_FourH₈F, C_FourH₈Cl, C₃F₇CH₂, C_FourF₉, C_FiveF₁₁
Fluorine-containing C 1-5 having straight or branched chain such as
Examples include a rukyl group.

A preferred compound of the present invention is methyl 2,2,2-trifluoroethyl carbonate (CH ₃ -OC
_{OO-CH 2 CF 3),} 2,2,2- trifluoroethyl carbonate _{(CF 3 CH 2 -O-CO} -O-CH 2 CF 3) and the like. The exothermic temperature and calorific value of these compounds and Comparative Example dimethyldifluoromalonate were measured using a differential scanning calorimeter (DSC7) manufactured by Perkin Elmer. The result is shown in Figure 1.
~ 3.

FIGS. 1 to 3 show the compound of the present invention or dimethyldifluoromalonate and 1M LiPF ₆ / EC + DMC = 1: 1 (vol%) electrolyte at a volume ratio of 1: 1 and mixed with 1.3 mg of lithium metal. , DSC measurement. Therefore, dimethyldifluoromalonate has a melting point of lithium metal of 180 ° C.
Exothermic heat starts in the vicinity, and large exothermic heat is observed in the vicinity of 213 ° C., but the compound of the present invention exceeds that, for example, the heat generation of methyl 2,2,2-trifluoroethyl carbonate is mild heat generation from the melting point of lithium. However, a large amount of heat generation is suppressed up to 300 ° C., and thermal stability is improved. These results indicate that the compound of the present invention further improves the thermal stability of the lithium ion battery.

Fluorine-containing carbonic acid esters such as methyl 2,2,2-trifluoroethyl carbonate form a stronger protective film on the lithium metal surface than dimethyl malonate, and thus high heat is generated in the presence of lithium metal. It is considered that stability was obtained. Even when a lithium intercalate compound, that is, a carbon material or various metal oxides is used as the negative electrode, metallic lithium may be deposited due to rapid charging or overdischarging. The above compound is effective in enhancing the thermal stability and safety.

The fluorine-containing carbonic acid ester used in the electrode surface coating forming agent of the present invention may be used alone, but is usually 0.1 to 80 relative to the organic solvent type electrolytic solution which is usually used.
It is contained in an amount of about 5% by weight, preferably about 1 to 50% by weight, more preferably about 5 to 30% by weight.

In the present invention, the organic solvent-based electrolyte used as the electrolyte of the non-aqueous electrolyte secondary battery together with the fluorine-containing carbonic acid ester includes cyclic carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate, diethyl carbonate and dimethyl carbonate. Examples thereof include chain carbonates such as methyl ethyl carbonate and the like. Furthermore, γ-butyrolactone, tetrahydrofuran, dimethoxyethane, diethoxyethane,
Dimethyl sulfoxide, sulfolane and the like can also be used, but are not limited thereto. These may be used alone as a mixture with a fluorine-containing carbonate, or 2
More than one type of organic solvent-based electrolytic solution may be used.

The organic solvent-based electrolytic solution containing at least one of these fluorine-containing carbonic acid esters may be used as an electrode surface film-forming agent for a battery in which the following lithium salt is dissolved, and particularly as a negative electrode surface film-forming agent prior to battery production. It may be used to treat the negative electrode at a stage or in the process of manufacturing the battery. Examples of the method for treating the negative electrode include a method of immersing the negative electrode in an organic solvent containing at least one fluorine-containing carbonate, a method of atomizing and spraying, a method of coating the negative electrode surface with a brush or the like. During processing, cooling or heating may be performed.

A preferred electrolyte for use in a lithium ion (primary or secondary) battery is composed of the above non-aqueous solvent containing a fluorine-containing carbonate and an organic solvent, and a lithium salt dissolved in the solvent.

As the lithium salt, LiPF ₆ , LiPF ₄ (C
F ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (C ₃ F ₇ ) ₂ , LiAsF ₆ , LiBF ₄ , L
iClO ₄ ,, LiCF ₃ SO ₃ ,, LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LIN (C ₂ F ₅
SO ₂ ) ₂ , LiN (C ₄ F ₉ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF
₃ SO ₂ ) ₃ etc. can be used.

The above-mentioned electrolyte can be used as a non-aqueous electrolyte having lithium ion conductivity and as a gel electrolyte in which it is fixed with a polymer matrix.

The lithium-ion battery of the present invention is characterized by using the above-mentioned electrolytic solution, and other conditions such as the shape and constituent elements of the lithium-ion battery are not particularly limited, and known techniques can be used.

Examples of the shape of the battery include a cylindrical shape, a square shape, a coin shape, and a film shape.

Examples of the negative electrode material include lithium metal and its alloys, carbon materials and polymer materials capable of doping / dedoping lithium, and lithium intercalating compounds such as metal oxides.

As the positive electrode material, LiCoO ₂ , LiNiO ₂ , LiMn
Examples thereof include composite oxides of lithium and transition metals such as ₂ O ₄ and LiMnO ₂ , and polymer materials.

As the separator, a porous film of a polymer material such as polyethylene or polypropylene, or a polymer material (so-called gel electrolyte) which occludes and immobilizes the electrolytic solution of the present invention can be used.

The material of the current collector is copper, aluminum, stainless steel, titanium, nickel, tungsten steel,
Carbon material is used, and its shape is foil, mesh, non-woven fabric,
Examples include punched metal.

[0040]

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 For the DSC measurement, DSC7 manufactured by Perkin Elmer was used. Also,
The sample for measurement is 1M LiPF ₆ / EC + in a titanium pressure tight container.
DMC = 1: 1 (vol%) electrolyte 5 ml, fluorinated carbonate 5 ml
Was mixed with 1.3 mg of lithium metal to prepare a mixture. The heating rate is 5
The reaction was carried out at a temperature of ° C / min to measure the exothermic reaction peak temperature. The results measured using various fluorinated carbonic acid esters are shown in FIGS.
Shown in.

[0041]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide an electrode surface film forming agent and a battery manufacturing method capable of improving the thermal stability of a battery. This improves safety even during rapid charging,
Further, it becomes possible to provide a safe battery using lithium metal for the negative electrode.

[Brief description of drawings]

FIG. 1 shows the measurement results of the exothermic temperature and exothermic amount of dimethyldifluoromalonate, which is a comparative example with the compound of the present invention.

FIG. 2 shows the measurement results of the exothermic temperature and exothermic amount of methyl 2,2,2-trifluoroethyl carbonate which is the compound of the present invention.

FIG. 3 shows the measurement results of exothermic temperature and exothermic amount of 2,2,2-trifluoroethyl carbonate which is a compound of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) H01M 6/16 H01M 6/16 A 10/40 10/40 AF term (reference) 5H024 AA00 AA02 AA09 AA12 BB07 BB08 BB10 CC20 DD17 EE09 FF14 5H029 AJ12 AK03 AK16 AL02 AL06 AL12 AL16 AM02 AM03 AM04 AM05 AM07 CJ08 CJ13 CJ22 DJ08 EJ11 HJ02 5H050 AA03 AA15 BA06 BA16 BA17 CA24 FA22 GA10 FA02 EA07 GA12 CB12 FA20 CB12 FA10 CB12 FA20 EA12 EA07

Claims (6)

[Claims] 1. Formula (I): (In the formula, R ¹ and R ² are each independently an alkyl group having 1 to 5 carbon atoms or a fluorine-containing alkyl group, and at least one of R ¹ and R ² is CF ₃ , CF ₃ CH ₂ Or (CF ₃ ) ₂ CH.) An electrolytic solution and / or electrode surface film forming agent containing at least one selected from the group consisting of compounds represented by the formula: 2. A battery is produced and / or used,
The electrode surface film forming agent according to claim 1, which acts as a protective film on the surface of the electrode material. 3. The electrode surface coating forming agent according to claim 2, wherein the electrode is a negative electrode made of lithium metal, a lithium intercalate compound or a lithium alloy. 4. A method for producing a battery, which comprises using an electrolytic solution containing at least one compound of the formula (I) according to claim 1. 5. A method for producing a battery, which comprises treating a negative electrode with at least one compound of formula (I) according to claim 1 before or during the production of the battery. 6. The battery manufacturing method according to claim 4, wherein the negative electrode is a lithium metal, a lithium intercalate compound or a lithium alloy.