JP2003086248A - Non-aqueous electrolytic solution secondary battery and electrolytic solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic solution secondary battery which has a high charge-discharge efficiency, and which is superior in cycle characteristics, and which has a high security, and provide the non-aqueous electrolytic solution used for this. SOLUTION: In the non-aqueous electrolytic solution secondary battery including a negative electrode and a positive electrode in which an occlusion/discharge of lithium is possible, and including the electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent, an organic solvent having 25 or more of dielectric constant occupies 60 wt.% or more of the non-aqueous solvent, and the electrolytic solution contains 0.001 to 10 wt.% of a compound having an electrophilic group conjugated with a carbon-carbon unsaturated bond.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte used therein. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having high charge / discharge efficiency, excellent cycle characteristics, and high safety, and a non-aqueous electrolyte used therein.

[0002]

2. Description of the Related Art With the recent lightening and miniaturization of electric products, the demand for lithium secondary batteries having high energy density is increasing. Further, with the expansion of the application fields of lithium secondary batteries, further improvement of battery characteristics is also demanded. As a solvent used for an electrolytic solution of a non-aqueous electrolytic solution secondary battery, ethylene carbonate having a high dielectric constant is often used. However, the freezing point of ethylene carbonate is 36.4.
It is high at ℃ and solid at room temperature, and it is difficult to handle because it has a high viscosity as a liquid. Therefore, the electrolytic solution using ethylene carbonate is mixed with a low-viscosity solvent such as ethyl methyl carbonate or diethyl carbonate as an auxiliary solvent. However, a low-viscosity solvent generally has a low boiling point and a low dielectric constant.Therefore, when mixed in a large amount, the performance of the electrolytic solution deteriorates due to a decrease in the dissociation degree of the lithium salt, or the salt precipitates due to evaporation of the solvent. There is a problem in terms of safety, such as a decrease in flash point. On the contrary, if only a small amount is mixed, there remain problems in terms of electric conductivity and viscosity at low temperatures.

By the way, in a non-aqueous electrolyte secondary battery using a carbonaceous material such as coke, artificial graphite or natural graphite for the negative electrode, the formation of dendrites is suppressed because lithium does not exist in a metallic state, resulting in an excellent battery life. And is known to show safety. However, when a carbonaceous material having a high degree of crystallinity such as graphite is used for the negative electrode, decomposition of the non-aqueous solvent and exfoliation of the carbonaceous material may occur, and the irreversible capacity may increase.
In particular, when propylene carbonate is used as the non-aqueous solvent and a graphite material is used as the negative electrode, the propylene carbonate undergoes severe decomposition on the surface of the graphite electrode, which causes a problem of deterioration in battery characteristics.

In order to suppress such deterioration of battery characteristics, many studies have been made to include various compounds in the electrolytic solution. For example, chloroethylene carbonate (H. Katayama, J.
Arai, H. Akahoshi, J. PowerSources 1999, 81-82, 70
5-708.), Fluoroethylene carbonate (R. McMilla
n, H. Slegr, ZX Sho, W. Wang, J. Power Sources
1999, 81-82, 20-26.), Ethylene sulfite (GH
Wrodnigg, JO Besenhard, M. Winter, J. Electroch
em. Soc. 1999, 146, 470.) and vinylene carbonate
(J. Barker, F. Gao, US Patent No. 5,712,059 (1998),
Y. Naruse, S. Fujita, A. Omaru, USPatent No. 5,71
4,281 (1998)) and other ethylene carbonate derivatives and analogues have been investigated. It is considered that these compounds are usually reduced at a high electrode potential in the initial charge to form a film on the electrode surface.

[0005]

However, the effects of the above-mentioned additives are insufficient, and further improvement is desired. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having high charge / discharge efficiency, excellent cycle characteristics, and high safety.

[0006]

Means for Solving the Problems As a result of intensive studies made by the present inventors in view of such circumstances, an organic solvent having a relative dielectric constant of 25 or more was selected as a non-aqueous solvent for an electrolytic solution of a non-aqueous electrolytic solution secondary battery. By using this, and by mixing with this a compound having an electron-withdrawing group conjugated with a carbon-carbon unsaturated bond, a non-aqueous electrolyte secondary battery having high charge / discharge efficiency, excellent cycle characteristics, and high safety is obtained. Find that you can
The present invention has been completed.

That is, the present invention provides a non-aqueous electrolyte secondary battery including a negative electrode and a positive electrode capable of inserting and extracting lithium, and an electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. An organic solvent having a dielectric constant of 25 or more occupies 60% by weight or more of the non-aqueous solvent, and the electrolytic solution contains 0.001 of a compound having an electron-withdrawing group conjugated with a carbon-carbon unsaturated bond.
The non-aqueous electrolyte secondary battery is characterized by containing 10 to 10% by weight, and the non-aqueous electrolyte used therein.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the organic solvent having a relative dielectric constant of 25 or more include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and γ-valerolactone. Among them, ethylene carbonate, propylene carbonate, and γ-butyrolactone is preferred. You may use these individually or in mixture of 2 or more types. When two or more organic solvents are mixed, the combination is arbitrary. It is preferable that an organic solvent having a relative dielectric constant of 25 or more accounts for 60% by weight or more, and particularly 85% by weight or more in the non-aqueous solvent. When this ratio is low, when a low-boiling point, low-viscosity solvent is also used, the internal pressure of the battery rises during high temperature storage, and the battery is likely to be deformed or leaked.

Dialkyl carbonate (preferably having an alkyl group having 1 to 4 carbon atoms) carbonate such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, and ethyl methyl carbonate together with the above solvent; tetrahydrofuran, 2-methyltetrahydrofuran, etc. Cyclic ethers; chain ethers such as dimethoxyethane and dimethoxymethane; chain esters such as methyl acetate and ethyl propionate; sulfur-containing organic solvents such as sulfolane and diethyl sulfone; phosphorus-containing such as trimethyl phosphate and triethyl phosphate An organic solvent or the like can be used together.

Examples of the compound having an electron withdrawing group conjugated with a carbon-carbon unsaturated bond include acrylonitrile, methacrylonitrile, N, N-dimethylacrylamide, methyl methacrylate, ethyl 2-cyanoacrylate, and α.
-Methylene-γ-butyrolactone and the like. It is preferable that these compounds are contained in the electrolytic solution in an amount of 0.001 to 10% by weight, particularly 0.01 to 3% by weight.

The non-aqueous solvent may further contain known auxiliary agents such as a film forming agent, an overcharge preventing agent, a dehydrating agent and a deoxidizing agent. For example, as film-forming agents, carbonates such as vinylene carbonate and vinyl ethylene carbonate; sulfites such as ethylene sulfite; sulfonate esters such as propane sultone; carboxylic acid anhydrides such as succinic anhydride, maleic anhydride, phthalic anhydride, etc. 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3
-Methyl-2-oxazolidinone, 1,3-dimethyl-
When a compound selected from the group consisting of nitrogen-containing compounds such as 2-imidazolidinone and N-methylsuccinimide is contained in the electrolytic solution in an amount of 0.01 to 3% by weight, the capacity maintenance characteristics and cycle of the battery are improved. The characteristics are improved.

As an overcharge preventing agent, JP-A-8-203 is known.
560, 7-302614, 9-50822.
Nos. 8-273700, 9-17447, and the like; benzene derivatives described in JP-A-9-106;
No. 835, No. 9-171840, No. 10-32125.
No. 8, No. 7-302614, No. 7-302614,
No. 11-162512, each gazette and patent 2939469.
And the derivatives thereof described in JP-A No. 2963898 and the like; Pyrrole derivatives described in JP-A Nos. 9-45369 and 10-32258, and the like; JP-A Nos. 7-320778 and 7 -3026
Aromatic compounds such as aniline derivatives described in JP-A-14, etc .; Ether-based compounds described in JP-A-2983205, and JP-A-2001-15158
The compounds described in the publication can be mentioned.

Further, in order to improve the wettability with the separator and the electrode material, the electrolytic solution contains 0.01 to 2 of a surfactant.
You may contain so that it may become a weight%. A lithium salt is used as the solute of the electrolytic solution used in the present invention.
Lithium salt can be used any of those that may be used as a solute of the nonaqueous electrolyte solution is known, for example, 1) an inorganic lithium salt: LiPF _6, LiAsF _6, LiB
_{F 4, LiTaF 6, LiAlF 4} , LiAlF 6, LiS
Inorganic fluoride salts such as iF ₆ and perhalogenates such as LiClO ₄ 2) Organic lithium salts: Organic sulfonates such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ S
O ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) and other perfluoroalkyl sulfonic acid imide salts, LiC (CF
Perfluoroalkyl sulfonic acid methide salt such as ₃ SO ₂ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiBF ₂ CF ₃ ) ₂ , Li
LiB (CF ₃ C), which is a salt obtained by substituting a part of fluorine in an inorganic fluoride salt such as BF ₃ (CF ₃ ) with a perfluoroalkyl group.
OO) ₄ , LiB (OCOCF ₂ COO) ₂ , LiB (O
Examples thereof include lithium tetrakis (perfluorocarboxylate) borate salts such as COC ₂ F ₄ COO) ₂ , and these may be used as a mixture.

Among these, LiPF ₆ , LiBF ₄ , and LiBF ₄ , in terms of characteristics such as solubility, ionic dissociation, and electrical conductivity.
LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ ,
LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiPF ₃ (C
_{F 3) 3, LiPF 3 (} C 2 F 5) 3, LiBF 2 (C 2 F 5) 2
LiB (OCOCF ₂ COO) ₂ is preferable, and LiP
F ₆ and LiBF ₄ are more preferable. In particular, the non-aqueous solvent is γ-
If the content of butyrolactone is 60% by weight or more, LiB
It is preferable that F ₄ be 50% by weight or more of the whole lithium salt.

The concentration of the lithium salt in the electrolytic solution is
It is preferably 0.5 to 3 mol / liter. If the concentration is too low, the electrical conductivity of the electrolyte becomes insufficient due to an absolute lack of concentration, and on the contrary, if it is too high, the viscosity of the electrolyte increases and the electrical conductivity decreases, or at low temperatures the lithium salt becomes Easily deposited. As the material of the negative electrode constituting the battery of the present invention, carbonaceous materials such as organic pyrolysates under various conditions, artificial graphite, natural graphite and mixtures thereof; tin oxide, antimony tin oxide, silicon monoxide, Metal oxides such as vanadium oxide; lithium metal; aluminum, silicon,
Metals that can be alloyed with lithium, such as tin, antimony, lead, arsenic, zinc, bismuth, copper, cadmium, silver, gold, platinum, palladium, magnesium, sodium, potassium;
Alloys containing the metals (including intermetallic compounds); Metal oxides, metals that can be alloyed with lithium, and complex alloy compounds of alloys containing the metals and lithium; Lithium metal nitrides such as lithium cobalt nitride; Can be mentioned. The above materials may be mixed and used.

As the carbonaceous material, artificial graphite produced by subjecting easily graphitizable pitch obtained from various raw materials to high temperature heat treatment,
Purified natural graphite and graphite materials obtained by subjecting these graphites to surface treatment with various pitches are preferable. As such a graphite material, a lattice plane (002
The d value (interlayer distance) of the surface is 0.335 to 0.34n
m, especially 0.335 to 0.337 nm is preferable. Ash content is preferably 1% by weight or less, 0.5% by weight
It is more preferable that the amount is below, and it is further preferable that the amount is 0.1 wt% or less. The crystallite size (Lc) determined by X-ray diffraction by Gakshin method is preferably 30 nm or more, more preferably 50 nm or more, and 100 nm.
The above is more preferable.

The median diameter of the carbonaceous material by the laser diffraction / scattering method is preferably 1 to 100 μm, and 3 to
50 μm is more preferable, 5 to 40 μm is still more preferable, and 7 to 30 μm is particularly preferable. The BET method specific surface area is preferably 0.3 to 25.0 m ² / g, and 0.5 to 2
0.0m more preferably ² / g, ^{0.7~15.0m 2} /
g is more preferable, and 0.8 to 10.0 m ² / g is particularly preferable.

The carbonaceous material is 1570 to 1 as determined by Raman spectrum analysis using an argon ion laser beam.
Intensity ratio R = IB / IA of the peak PB (peak intensity IB) the scope of the peak PA (peak intensity IA) and 1300～1400Cm ^-1 of 620 cm ^-1 is 0.01
1.0, particularly 0.1 to 0.7 is preferable, and 1570 to 1
The half-value width of the peak in the range of 620 cm ^-1 is, 26cm ^-1 or less, and particularly preferably between 25 cm ^-1 or less.

The alloy is preferably an alloy of a metal selected from the group consisting of tin, antimony, silver, copper and gold,
It is particularly preferable to use a tin-antimony alloy, a tin-silver alloy, a copper-antimony alloy, or a gold-antimony alloy.
The metal or alloy used for the negative electrode may be one kind or a mixture of two or more kinds. The average particle size is 1 to 1000 n
m is preferable, 10-500 nm is more preferable, and 30
-400 nm is more preferable. If the average particle size is too large, the capacity deterioration due to repeated charge and discharge cycles may increase and the usefulness as an electrode may be impaired.
On the other hand, if it is too small, the surface area increases and the safety of the battery decreases. The particle size distribution is preferably within these ranges.

A negative electrode can be manufactured by a conventional method using these negative electrode materials. For example, a negative electrode can be manufactured by adding a binder, a thickener, a conductive material, a solvent and the like to the negative electrode material as needed to form a slurry, coating the slurry on the substrate of the current collector, and drying. Alternatively, the negative electrode material may be roll-formed as it is to form a sheet electrode, or compression-molded to form a pellet electrode.

Any binder can be used as long as it is a stable material with respect to the solvent or electrolytic solution used in the production of electrodes. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, isoprene rubber and butadiene rubber. As the thickener, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose,
Examples thereof include ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch and casein.

Examples of the conductive material include metallic materials such as copper and nickel, and carbonaceous materials such as graphite and carbon black. Examples of the material for the negative electrode current collector include metals such as copper, nickel, and stainless steel. Among these, copper foil is preferable from the viewpoints of easy processing into a thin film and cost.

Examples of the material for the positive electrode include materials capable of inserting and extracting lithium, such as lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide. The positive electrode can be manufactured according to the manufacturing method of the negative electrode described above. If necessary, a binder, a conductive material, a solvent, etc. are added to the positive electrode material and mixed, and then this is applied to the substrate of the current collector to form a sheet electrode, or press-molded to form a pellet electrode. be able to.

Examples of the material for the current collector for the positive electrode include metals such as aluminum, titanium and tantalum or alloys thereof. Among these, aluminum or alloys thereof is preferable in terms of energy density. The separator used in the battery of the present invention may be any as long as it is stable to an electrolytic solution and has excellent liquid retention, and a porous sheet or nonwoven fabric made of polyolefin such as polyethylene and polypropylene is used. Is preferred.

The battery according to the present invention can be prepared by a conventional method using the above-mentioned negative electrode, positive electrode and non-aqueous electrolyte solution. The battery can be of any shape commonly used. For example, a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type in which an inside-out structure is combined with a pellet electrode and a separator, and a coin type in which pellet electrodes and a separator are stacked are listed.

[0026]

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 as long as the gist thereof is not exceeded. (Example 1) Artificial graphite powder (TIMREX KS6) 9
5 parts by weight of polyvinylidene fluoride and 5 parts by weight of N
-Methyl-2-pyrrolidone was dispersed to make a slurry. This was uniformly applied onto a stainless steel mesh serving as a negative electrode current collector, dried and pressed to give a negative electrode.

In a dry argon atmosphere, 1 part by weight of acrylonitrile was added to 99 parts by weight of propylene carbonate, and 1 part of sufficiently dried LiN (CF ₃ SO ₂ ) ₂ was added thereto.
It was dissolved so as to have a mol / liter to prepare an electrolytic solution.
An electrochemical cell was prepared by filling a glass cell with the electrolytic solution, using the negative electrode as a working electrode, and using lithium metal as a counter electrode and a reference electrode, and at room temperature, a potential scanning rate of 0.05 mV / se.
Cyclic voltammetry was measured under the condition of c.

(Comparative Example 1) L in propylene carbonate
An electrochemical cell was prepared and cyclic voltammetry was measured in the same manner as in Example 1 except that an electrolytic solution in which iN (CF ₃ SO ₂ ) ₂ was dissolved to be 1 mol / liter was used. (Example 2) An electrochemical cell was prepared in the same manner as in Example 1 except that an electrolytic solution prepared by adding 1 part by weight of methacrylonitrile was used in place of the acrylonitrile of Example 1, and a cyclic cell was prepared. Voltammetry was measured.

Example 3 Electrochemistry was carried out in the same manner as in Example 1 except that an electrolytic solution prepared by adding 1 part by weight of α-methylene-γ-butyrolactone was used in place of the acrylonitrile of Example 1. A cell was prepared and cyclic voltammetry was measured. The results of Examples 1 to 3 are shown in FIG.
The results of Comparative Example 1 are shown in FIGS.

In the case of Comparative Example 1, only a large reduction current due to the decomposition of the electrolytic solution is observed in the vicinity of about 0.8 V, and no current due to the occlusion / release of lithium is observed. Example 1
In the case of ~ 3, the current due to the decomposition of the electrolytic solution around 0.8V was not observed, but a large reduction current due to the occlusion of lithium was observed around 0.2V, and the release of lithium around 0V to 0.3V. Oxidation current due to is also observed, and it can be seen that the occlusion and release of lithium proceed smoothly.

[Brief description of drawings]

FIG. 1 shows the first-time potential-current curve measured by cyclic voltammetry of Example 1.

FIG. 2 shows a first potential-current curve measured by cyclic voltammetry in Comparative Example 1.

FIG. 3 shows the first-time potential-current curve measured by cyclic voltammetry of Example 2.

FIG. 4 shows the first potential-current curve measured by cyclic voltammetry of Example 3.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jürgen Otto Bosenhardt             Stremaiaga, Graz, Austria             Se, 16/111 A-8010 Technical             University Graz (72) Inventor Martin Winter             Stremaiaga, Graz, Austria             Se, 16/111 A-8010 Technical             University Graz F term (reference) 5H029 AJ02 AJ05 AJ12 AK03 AL07                       AM00 AM01 AM03 AM04 AM05                       AM07 DJ17 HJ02 HJ13 HJ20                 5H050 AA02 AA07 AA15 BA17 CA07                       CB08 FA19 HA02 HA13 HA19

Claims (6)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and an electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent, in a relative dielectric constant of 25 or more. The organic solvent occupies 60% by weight or more of the non-aqueous solvent, and the electrolytic solution contains 0.001 to 10% by weight of a compound having an electron-withdrawing group conjugated with a carbon-carbon unsaturated bond. Electrolyte secondary battery. 2. The organic solvent having a relative dielectric constant of 25 or more is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and γ-valerolactone. 1. The non-aqueous electrolyte secondary battery according to 1. 3. A compound having an electron-withdrawing group conjugated with a carbon-carbon unsaturated bond is acrylonitrile, methacrylonitrile, N, N-dimethylacrylamide, methyl methacrylate, ethyl 2-cyanoacrylate, and α-methylene. The non-aqueous electrolyte secondary battery according to claim 1 or 2, which is selected from the group consisting of -γ-butyrolactone. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains a carbonaceous material. 5. The carbonaceous material has a d-value of 0.335 to 0.34 on the lattice plane (002 plane) determined by X-ray diffraction by Gakushin method.
The non-aqueous electrolyte secondary battery according to claim 4, wherein the non-aqueous electrolyte secondary battery is a graphite material having a thickness of nm. 6. An electrolytic solution for a non-aqueous electrolytic solution secondary battery used in the non-aqueous electrolytic solution secondary battery according to any one of claims 1 to 5.