JP2003086247A - Nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution secondary battery and a nonaqueous electrolytic solution to use this wherein decomposition of the electrolytic solution is less, charge-discharge efficiency is high, and storage characteristics and cycle characteristics in high-temperatures are superior. SOLUTION: In the nonaqueous electrolytic solution secondary battery containing a negative electrode and a positive electrode capable of occluding/ discharging lithium and an electrolytic solution in which a lithium salt is dissolved in the nonaqueous solvent, nitrile compound(s) having carbon-carbon unsaturated bond(s) is made to be contained in the electrolytic solution.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery and an electrolyte used therein. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having a high degree of charge / discharge efficiency, high decomposition efficiency of the electrolyte, excellent storage characteristics and cycle characteristics at high temperatures, and an electrolyte used therein.

[0002]

2. Description of the Related Art With the recent lightening and miniaturization of electric products, development of lithium secondary batteries having a high energy density has been promoted. Further, improvement of battery characteristics is also demanded as the application field of lithium secondary batteries is expanded. 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 as high as 36.4 ° C. and it is a 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, there is a problem that the propylene carbonate undergoes severe decomposition on the surface of the graphite and battery characteristics deteriorate.

In order to suppress such a decomposition reaction, many studies have been made to include various compounds in the electrolytic solution. For example, chloroethylene carbonate (H. Katayama, J. Arai, H.
Akahoshi, J. Power Sources 1999, 81-82, 705-70
8.), Fluoroethylene carbonate (R. McMillan, H.
Slegr, ZX Sho, W. Wang, J. Power Sources 1999,
81-82, 20-26.), Ethylene sulfite (GH Wrodnig
g, JO Besenhard, M. Winter, J. Electrochem. So
c. 1999, 146, 470.), vinylene carbonate (J. Bark
er, F. Gao, US Patent No. 5,712,059 (1998), Y. Nar
use, S. Fujita, A. Omaru, US Patent No. 5,714,281
(1998)) and other ethylene carbonate derivatives and analogues have been investigated. It is generally believed that these compounds are reduced at a high electrode potential during the initial charge to form a film on the surface of the electrode.

[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 which is less likely to decompose an electrolyte, has high charge / discharge efficiency, and has excellent storage characteristics and cycle characteristics at high temperatures.

[0006]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of such circumstances, and as a result, by incorporating a nitrile compound having a carbon-carbon unsaturated bond into the electrolyte of a non-aqueous electrolyte secondary battery, The inventors have found that a non-aqueous electrolyte secondary battery with less decomposition of the electrolyte solution, high charge / discharge efficiency, and excellent storage characteristics and cycle characteristics at high temperatures can be obtained, and completed the present invention.

That is, the gist of the present invention is 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. A non-aqueous electrolyte secondary battery characterized in that the electrolyte contains a nitrile compound having a carbon-carbon unsaturated bond, and a non-aqueous electrolyte used therein.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The nitrile compound having a carbon-carbon unsaturated bond used in the present invention is any compound as long as it has at least one carbon-carbon unsaturated bond and at least one cyano group in the molecule. It may be one. Such compounds include acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile,
3,7-Dimethyl-2,6-octadienenitrile, fumaronitrile, 2-methyleneglutaronitrile, cinnamonitrile, 4-methoxycinnamonitrile, 3-methoxyacrylonitrile, 3-ethoxyacrylonitrile, (1-ethoxyethylidene) Malononitrile, 1-
Cyanovinyl acetate, 2-acetoxy-3-butenenitrile, ethyl 2-cyanoacrylate, ethyl 2
-Cyano-3-methyl-2-butenoate, ethyl 2
-Cyano-2-pentenoate, diethyl dicyanofumarate, ethyl 2-cyano-3-ethoxyacrylate, methyl α-cyanocinnamate, ethyl 2-cyano-3-phenyl-2-butenoate, ethyl 2-
Cyano-3,3-diphenyl acrylate, 2-furonitrile, 2-cyanoethyl acrylate, ethyl 2-
Examples thereof include cyano-3-dimethylamino acrylate. The nitrile compound having a carbon-carbon unsaturated bond is contained in the electrolytic solution in an amount of 0.001 to 10% by weight, particularly 0.1.
It is preferable that the content is 0.1 to 3% by weight.
As the non-aqueous solvent used in the present invention, an alkylene carbonate having an alkylene group having 2 to 4 carbon atoms, a dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms, a cyclic ether, a chain ether, a cyclic ester, a chain ester, It suffices to appropriately select and use from among those that can be used as a solvent of the non-aqueous electrolyte solution, such as a sulfur-containing organic solvent and a phosphorus-containing organic solvent, and these solvents may be mixed and used. As the alkylene carbonate having 2 to 4 carbon atoms in the alkylene group, ethylene carbonate, propylene carbonate,
Butylene carbonate and the like can be mentioned. Of these, ethylene carbonate and propylene carbonate are preferable. Examples of the dialkyl carbonate in which the alkyl group has 1 to 4 carbon atoms include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethylmethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate and the like. . Of these, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are preferred.

Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of chain ethers include dimethoxyethane and dimethoxymethane. Examples of the cyclic ester include γ-butyrolactone and γ-valerolactone.

Examples of the chain ester include methyl acetate, methyl propionate, ethyl propionate and the like.
Examples of the sulfur-containing organic solvent include sulfolane and diethyl sulfone. Examples of the phosphorus-containing organic solvent include trimethyl phosphate and triethyl phosphate.

Of these non-aqueous solvents, alkylene carbonates having an alkylene group having 2 to 4 carbon atoms and dialkyl carbonates having an alkyl group having 1 to 4 carbon atoms are preferable. Particularly preferably, the alkylene group has 2 to 2 carbon atoms.
4 alkylene carbonate and a dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms are 20
It is a mixed solvent containing more than 70% by weight and occupying more than 70% by weight of the whole.

From the viewpoint of high temperature stability, the non-aqueous solvent is
An organic solvent having a relative dielectric constant of 25 or more is used in an amount of 60% by weight or more, particularly 8
It is preferable that the content is 5% by weight or more. When this ratio is low, when a low-boiling point, low-viscosity solvent is used together, the internal pressure of the battery rises during high-temperature storage, and the battery is likely to deform and leak. Examples of the organic solvent having a relative dielectric constant of 25 or more include ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone and the like. These may be used alone or in combination of two or more.

The electrolytic solution may further contain 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. Consisting of nitrogen-containing heterocyclic compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide When the compound selected from the group contains 0.01 to 3% by weight in the electrolytic solution, the capacity maintenance characteristics,
Cycle characteristics are improved.

As an overcharge preventing agent, Japanese Patent Application Laid-Open No. 8-203
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 add so that it may become 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 , L
iBF ₃ (CF ₃₎ salts a part of the fluorine inorganic fluoride salts was replaced by perfluoroalkyl groups such as, LiB (CF ₃
COO) ₄ , LiB (OCOCF ₂ COO) ₂ , LiB
Examples thereof include lithium tetrakis (perfluorocarboxylate) borate salts such as (OCOC ₂ F ₄ COO) ₂ . These may be mixed and used.

Among these, LiPF ₆ , LiBF ₄ , and LiN _{4 in} terms of solubility, ionic dissociation, and electric conductivity characteristics.
_{(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 accounts for 50% by weight or more of the whole lithium salt.

The concentration of the lithium salt in the electrolytic solution is 0.5 to
It is preferably 3 mol / liter. If the concentration is too low, the electrical conductivity of the electrolytic solution becomes insufficient due to an absolute lack of concentration. Conversely, if the concentration is too high, the viscosity increases and the electrical conductivity decreases, and precipitation at low temperatures easily occurs. As materials for the negative electrode constituting the battery of the present invention, carbonaceous materials such as pyrolyzed products of organic materials 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, tin, antimony,
Lead, arsenic, zinc, bismuth, copper, cadmium, silver, gold,
Metals that can be alloyed with lithium such as platinum, palladium, magnesium, sodium, potassium; alloys containing the above metals (including intermetallic compounds); metals that can be alloyed with lithium, and alloys containing the metals and lithium Alloy compounds; lithium metal nitride such as lithium cobalt nitride, and the like. The above materials may be mixed and used.

Of these, artificial graphite, purified natural graphite produced by subjecting easily graphitizable pitches obtained from various raw materials to high temperature heat treatment, and graphite materials obtained by subjecting these graphites to surface treatment at various pitches are preferable. As such a graphite material, the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is 0.335 to 0.34 nm, and particularly 0.
It is preferably 335 to 0.337 nm. Ash content is 1
It is preferably not more than 0.5% by weight, more preferably not more than 0.5% by weight, particularly preferably not more than 0.1% by weight. X according to Gakshin method
The crystallite size (Lc) determined by line diffraction 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
It is more preferably 50 μm or less, further preferably 5 to 40 μm, particularly preferably 7 to 30 μm. 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 argon ion laser light.
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.

As the alloy, an alloy of a metal selected from the group consisting of tin, antimony, silver, copper and gold is preferable,
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 a negative electrode material to form a slurry, applying the slurry to a substrate of a current collector, and drying. it can. Alternatively, the negative electrode material may be roll-formed as it is to form a sheet electrode, or compression molding may be performed to form a pellet electrode.

Any binder can be used as long as it is a material that is stable 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 above-mentioned manufacturing method of the negative electrode. That is, 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 a substrate of a current collector to form a sheet electrode, or press-molded to form a pellet electrode. can do. Examples of the material of the current collector for the positive electrode include metals such as aluminum, titanium and tantalum, and 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 one which is stable to an electrolytic solution and has an excellent liquid retaining property, such as a porous sheet or a non-woven fabric made of polyolefin such as polyethylene or polypropylene as a raw material. It is preferably used. The battery according to the present invention can be manufactured by a conventional method using the above-mentioned negative electrode, positive electrode and non-aqueous electrolyte solution.

The battery can be of any conventional shape. Examples include 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.

[0028]

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, dried and pressed to give a negative electrode.

Under a dry argon atmosphere, 1 part by weight of acrylonitrile was added to 99 parts by weight of propylene carbonate, and LiN (CF ₃ SO ₂ ) ₂ was dissolved to be 1 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 performing cyclic voltammetry at a room temperature potential scanning speed of 0.05 mV / sec. It was measured.

(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.

The results of Example 1 are shown in FIG. 1, the results of Comparative Example 1 are shown in FIG. 2, and the results of Example 2 are shown in FIG. In the case of Comparative Example 1, only a large reduction current due to the decomposition of the electrolytic solution is observed at about 0.8 V, and no current due to the occlusion / release of lithium is observed. In the case of Examples 1 and 2, no current due to the decomposition of the electrolytic solution near 0.8 V was observed, and
A large reduction current due to the occlusion of lithium is observed from the vicinity, and an oxidation current due to the release of lithium is also observed from around 0 V to 0.3 V, which indicates 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.

   ─────────────────────────────────────────────────── ─── 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 AJ04 AJ05 AJ07 AK03                       AL07 AM00 AM03 AM04 AM05                       AM07 DJ17 HJ02 HJ11 HJ13                       HJ20                 5H050 AA02 AA07 AA10 AA13 BA17                       CA08 CA09 CB08 DA13 EA22                       FA19 HA02 HA11 HA13 HA19

Claims (7)

[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 in which a lithium salt is dissolved in a non-aqueous solvent, wherein the electrolyte is carbon- A non-aqueous electrolyte secondary battery comprising a nitrile compound having a carbon unsaturated bond. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte contains 0.001 to 10% by weight of a nitrile compound having a carbon-carbon unsaturated bond. 3. The non-aqueous solvent having an alkylene group having 2 to 2 carbon atoms.
4 alkylene carbonate and dialkyl carbonate having 1 to 4 carbon atoms in the alkyl group account for 20% by weight or more, and these carbonates account for 70% of the total.
The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte secondary battery occupies at least wt%. 4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the non-aqueous solvent contains 60% by weight or more of an organic solvent having a relative dielectric constant of 25 or more. 5. 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. 4. The non-aqueous electrolyte secondary battery according to 4. 6. A negative electrode capable of inserting and extracting lithium has a lattice plane (002) obtained by X-ray diffraction by Gakushin method.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, comprising a graphite material having a surface value d of 0.335 to 0.34 nm. 7. 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 6.