JPH1083807A - Nonaqueous lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous lithium secondary battery with excellent cycle property, high Coulomb efficiency of charging and discharging, and high capacity. SOLUTION: In a nonaqueous lithium secondary battery having a lithium salt as an electrolytic substance and an anode and a cathode, a molded body produced by heating a mixture of thermosetting resin and a metal salt and containing a carbon material with 0.001-0.03 atomic ratio (N/C) of nitrogen atom and carbon atom, 3.65-4.00Ålattice plane distance (d002 ) by x-ray diffraction, 12m<2> /g specific surface area by BET method, and 0.03-0.3ml/g total fine pore volume as the anode and a molded body containing activated carbon with 500m<2> /g or higher specific surface area by BET method as the cathode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous lithium secondary battery.

[0002]

2. Description of the Related Art With the development of electronic equipment, the importance of a backup power supply other than a main power supply battery has been highlighted, and the development of a highly reliable small power supply has been desired.

As backup secondary batteries, batteries using activated carbon for the positive electrode and lithium metal for the negative electrode have been known (Japanese Patent Application Laid-Open Nos. 60-17871 and 61-61).
No. 270072). In these cases, since lithium is used for the negative electrode, a secondary battery for an energy source having a high voltage and a large capacity and energy density can be obtained. However, when lithium is used for the negative electrode, there is a problem that the charge / discharge cycle life is short because repetition of charge / discharge generates dendrite.

In order to solve the above problem, B
An activated carbon secondary battery using a lithium alloy in which lithium is occluded in a fusible gold in which heavy metals such as i, Pb, Sn and Cd are combined has been proposed (JP-A-60-281).
70, JP-A-62-143371. However, these secondary batteries have a problem that the energy density is small because of using an alloy.

Further, an activated carbon secondary battery using graphite or graphitized carbon fiber for the negative electrode has been proposed (Japanese Patent Application Laid-Open No. Sho.
0-182670). However, since the degree of graphitization of this negative electrode is too high, there is a problem that the graphite crystals are destroyed with repeated use, and sufficient durability cannot be obtained to withstand practical use. The negative electrode has a lattice spacing (d ₀₀₂ ) in X-ray diffraction of 3.38 to 3.56.
(2) An activated carbon secondary battery using a composite in which lithium has been previously absorbed in a molded article of carbon fiber or a molded article of carbon powder has been proposed (Japanese Patent Application Laid-Open No. 64-14882).
However, there is a problem that the coulomb efficiency of charging and discharging is not sufficient.

Further, a heat treatment product of an aromatic condensed polymer comprising carbon, hydrogen and oxygen as a negative electrode, wherein a polyacene-based polymer having an atomic ratio (H / C) of hydrogen atoms to carbon atoms of 0.05 to 0.5 is used. A secondary battery has been proposed in which lithium is supported on an insoluble and infusible substrate having a skeletal structure and activated carbon having a polyacene skeletal structure is used as a positive electrode (Japanese Patent Application Laid-Open No. 5-28986). . However, also in this case, the capacity was not sufficient.

The negative electrode is a carbonized polyimide polymer, and has an atomic ratio (N / C) of nitrogen atoms to carbon atoms.
Is from 0.001 to 0.100, and a carbon material having a lattice spacing (d ₀₀₂ ) of 3.58 to 4.10 ° in X-ray diffraction is used.
^A secondary battery using activated carbon of ² / g or more has been proposed (Japanese Patent Application No. 7-122326). However, also in this case, there is room for improvement in the capacity and the Coulomb efficiency of charging and discharging.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous lithium secondary battery having good cycle characteristics and high charge / discharge coulomb efficiency and high capacity.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the specific surface area of the negative electrode having a specific surface area of 500 m ² by the BET method was used. A non-aqueous lithium secondary battery using a molded body containing activated carbon of at least / g has been found to achieve the above object, and has reached the present invention.

That is, the gist of the present invention is to provide a non-aqueous lithium secondary battery having a lithium salt as an electrolyte and a negative electrode and a positive electrode, wherein a mixture of a thermosetting resin and a metal salt is heat-treated, Atomic ratio to carbon atom (N /
C) is 0.001 to 0.03, lattice spacing (d ₀₀₂ ) in X-ray diffraction is 3.65 to 4.00 °, specific surface area by BET method is 1 to 25 m ² / g, and total pore volume is 0. .03
A molded article containing a carbon material having a specific surface area of not less than 500 m ² / g by a BET method is used for a positive electrode. It is a water lithium secondary battery.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the nonaqueous lithium secondary battery of the present invention, the lithium salt used as the electrolyte includes, for example, LiCl
O ₄ , LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiA
sF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiAlC
l ₄ , LiCl, LiBr and the like.

The solvent constituting the electrolyte solution is not particularly limited, but an aprotic organic solvent is preferably used. Examples of the aprotic organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl isovalerate, ethyl isovalerate, acetonitrile,
Benzonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolan,
One or two organic solvents such as triethyl phosphite, dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, dimethoxyethane, polyethylene glycol, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, and aromatic hydrocarbons such as toluene and xylene. Mixtures of more than one species can be used.

The concentration of the lithium salt in the electrolyte solution is preferably from 0.2 to 3.0 mol / liter,
2.0 mol / l is more preferred. If it is less than 0.2 mol / liter, the conductivity tends to be insufficient,
If it exceeds 3.0 mol / l, it is not economical.

When an electrolyte solution is used, a separator is used. As the separator, a separator having low resistance to ion migration of a lithium salt in the electrolyte solution and excellent in solution retention is used. , A glass fiber filter, a polymer pore filter such as polyester, polytetrafluoroethylene, and polypropylene, or a nonwoven fabric made of glass fiber and these polymers.

In addition, a solid component (solid electrolyte) can be used as a component in place of the electrolyte solution and the separator. As the solid electrolyte, for example, in the case of an inorganic material, lithium ion conductive glass, LiI and the like can be mentioned. In the organic system, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylamide, or the like is used as a polymer matrix, and a complex in which the above-mentioned electrolyte salt is dissolved in the polymer matrix, or a gel cross-linked body thereof, low molecular weight polyethylene oxide, crown Examples thereof include a solid polymer electrolyte in which an ion dissociating group such as ether is grafted to the polymer main chain, or a gel polymer solid electrolyte in which the above-mentioned electrolytic solution is contained in a high molecular weight polymer.

The carbon material used to obtain the negative electrode in the present invention is obtained by heat-treating a mixture of a thermosetting resin and a metal salt in an inert atmosphere. Examples of the thermosetting resin include a polyimide polymer, a phenol resin, a furfuryl alcohol resin, and an epoxy resin.
Polyimide-based polymers and phenolic resins are preferred, and polyimide-based polymers are more preferred. As the polyimide-based polymer, one having a repeating unit represented by the formula (1) as a structural unit is preferable.

[0017]

Embedded image

In the formula (1), n represents an integer of 2 or more, preferably 10 to 500, more preferably 30 to 300, and R represents a tetravalent aromatic residue having at least one aromatic ring. And is characterized by two divalent bonds to adjacent carbon atoms in the aromatic ring, and specific examples include the following.

[0019]

Embedded image

R is most preferably as follows.

Embedded image

R ′ is 2 ′ having 1 to 4 aromatic rings.
It is a valent aromatic residue, and specific examples thereof include the following.

[0022]

Embedded image

The following are most preferred as R '.

[0024]

Embedded image

Examples of the metal salt include lithium hydroxide, sodium hydroxide, potassium hydroxide, zinc chloride, calcium chloride and the like. Among them, lithium hydroxide, sodium hydroxide, potassium hydroxide and zinc chloride are preferred. Lithium, sodium hydroxide and potassium hydroxide are more preferred.

The metal salt is dry-blended with the thermosetting resin, the metal salt is dissolved in a solvent, the thermosetting resin is dispersed and then dried, or added during the synthesis of the thermosetting resin. Can be mixed using the method described in The mixing ratio of the thermosetting resin and the metal salt is 99/1 to 1 by weight.
50/50 is preferred. Outside this range, the capacity is undesirably reduced.

As a method for obtaining a carbon material used for the negative electrode, a thermosetting resin mixed with a metal salt is heated at 500 to 1500 ° C., preferably 800 to 1300 ° C. in an inert atmosphere (including a vacuum state). More preferably, 900-1
It is obtained by gradually heating to a temperature range of 200 ° C. and performing heat treatment. When the heat treatment temperature is out of the range of 500 to 1500 ° C., the cycle characteristics, the coulomb efficiency of charge and discharge,
The capacity tends to decrease.

Heating and heat treatment are performed in an inert atmosphere. As the inert atmosphere, for example, nitrogen, argon, helium, neon, carbon dioxide, atmosphere such as vacuum,
Nitrogen and vacuum atmospheres are preferred, and such inert atmospheres can be stationary or flowing.

The carbon material used for the negative electrode has an atomic ratio of nitrogen atoms to carbon atoms (N / C) of 0.001 to 0.03, preferably 0.002 to 0.025. More preferably, it is 0.003 to 0.020. The lattice spacing (d ₀₀₂ ) in X-ray diffraction is 3.65 to 4.00 °
, Preferably 3.70 to 3.95 °, more preferably 3.75 to 3.90 °. The specific surface area by the BET method is 1 to 25 m ² / g, preferably 3 to 20 m ² / g, more preferably 5 to 18 m ² / g.
² / g. The total pore volume is 0.03-0.30 ml /
g, preferably 0.035 to 0.20 ml / g
And more preferably, 0.04 to 0.10 ml / g.
It is.

In a carbon material, the atomic ratio between nitrogen atoms and carbon atoms (N / C), the lattice spacing in X-ray diffraction (d
₀₀₂ ), when the specific surface area and the total pore volume are outside the above ranges, the cycle characteristics, the Coulomb efficiency of charge and discharge, and the capacity are undesirably reduced. The atomic ratio between nitrogen and carbon (N / C) was determined by elemental analysis (CHN-O-RAPID, Foss Heraeus)
Calculated from the results obtained by the company. The lattice spacing (d ₀₀₂ ) was measured using RAD-rB (manufactured by Rigaku Corporation) and using CuKα as X-rays. The specific surface area and total pore volume were measured using BELSORP28 (manufactured by Nippon Bell Co., Ltd.).

The carbon material and the resin for the binder are mixed or kneaded to obtain a molded body. As the resin for the binder, for example, those commonly used for battery electrodes such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polypropylene are used. The weight ratio of the carbon material to the resin for the binder in the molded body is preferably 98/2 to 60/40, and more preferably 95/5 to 80/20. If the weight ratio of the resin for the binder is less than 2, it is difficult to obtain a molded body, and if it exceeds 40, the characteristics of the electrode tend to be deteriorated.

The molded body obtained in this way is used for a negative electrode. Further, when lithium is supported on the above-mentioned molded body, a negative electrode which can be used for a battery with higher energy can be obtained. Examples of a method of supporting lithium on the molded body include an electrolytic method, a gas phase method, a liquid phase method, and a method of directly contacting a lithium foil with a molded body in an electrolytic solution, but are not limited thereto.

In the present invention, a molded article containing the following activated carbon is used for the positive electrode. The activated carbon used for the positive electrode has a specific surface area of 500 m ² / g or more, preferably 1000 m ² / g or more, more preferably 1500 m ² / g or more by a BET method. Specific surface area is 500m
If it is smaller than ² / g, the capacity is undesirably reduced. The upper limit of the specific surface area is not limited. The specific surface area was measured using BELSORP28 (manufactured by Nippon Bell Co., Ltd.).

The activated carbon and the resin for the binder are mixed or kneaded to obtain a molded article. As the resin for the binder, for example, those commonly used for battery electrodes such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polypropylene are used.

The weight ratio of the activated carbon to the resin for the binder in the molded article for the positive electrode is preferably 98/2 to 60/40 for the activated carbon / the resin for the binder, and 95/5.
~ 80/20 is more preferable. If the weight ratio of the resin for the binder is less than 2, it is difficult to obtain a molded body, and if it exceeds 40, the characteristics of the electrode tend to be deteriorated. In order to improve conductivity, Ketjen Black,
Acetylene black, metal powder and the like can be added within a range that does not impair the effects of the present invention.

The form of the battery is not particularly limited, but may be various forms such as a coin type, a sheet type, a cylindrical type and a square type.

[0037]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Reference Example (a) Production of Carbon Material A carbon material used for a negative electrode was produced as follows.
15.0 g of 4,4'-diaminodiphenyl ether was added to 300 ml of N, N-dimethylacetamide (DMAc).
Dissolved in water and pyromellitic dianhydride (PMDA)
16.4 g was added, and the mixture was stirred at 30 ° C. for 1 hour. When this solution was added to 1000 ml of chloroform with stirring, polyamic acid powder was precipitated. After the powder was filtered off, it was washed three times with 1000 ml of methyl alcohol,
Drying under reduced pressure at a temperature of 2 ° C. gave 29.9 g of polyamic acid powder. The obtained polyamic acid powder is placed in a vacuum at 200 ° C., 2
By heat treatment for 4 hours and imidization, 20 g of a polyimide-based polymer powder was obtained. After dry-blending the obtained polyimide-based polymer powder and LiOH.H ₂ O at a weight ratio of 92/8, the mixture was placed in a vacuum firing furnace (manufactured by Fuji Denki Kogyo KK) and heated at a rate of 100 ° C./h. The temperature was raised to each temperature shown in Table 1, and heat treatment was performed at this temperature for 5 hours to obtain carbon materials 1 to 5. Table 1 shows the physical property values of the carbon materials 1 to 5.

(B) Production of molded body for negative electrode 10 parts by weight of polytetrafluoroethylene powder was added to 90 parts by weight of carbon materials 1 to 5 and kneaded sufficiently, and a preformed sheet having a predetermined thickness was formed using a roller. Was prepared. After punching the preformed sheet into a predetermined size, the preformed sheet was pressed against a stainless steel wire mesh to obtain a negative electrode molded body.

(C) Production of molded body for positive electrode Activated carbon (M20, manufactured by Osaka Gas Chemical Company, specific surface area: 20)
00m ² / g) 80 parts by weight, Ketjen Black (EC
After adding 10 parts by weight of polytetrafluoroethylene powder to 10 parts by weight of 600 JD (Ketjen Black International) and sufficiently kneading, a preformed sheet having a predetermined thickness was prepared using a roller. After punching the preformed sheet into a predetermined size, it was press-molded to obtain a molded body for a positive electrode.

Example 1 A molded article for a positive electrode (15.0 mm in diameter, 0.46 mm in thickness,
(Weight: 54 mg) was adhered to the positive electrode can using a conductive paint (GP31660, manufactured by Acheson Japan). A glass fiber filter paper (GC50, manufactured by ADVANTEC) impregnated with an electrolyte solution (1M LiClO ₄ propylene carbonate + toluene (volume ratio 9: 1) solution) is used as a separator, and carbon material 3 is used as described above. Molded body for a negative electrode (with wire mesh) (diameter 15.0 mm, thickness 0.
35mm, weight 133mg) and lithium foil (6.4m
g) was incorporated into a CR2016 type coin cell so as to be in contact with the inside of the battery can, thereby producing a secondary battery. Then,
With this rechargeable battery, 1 m in a voltage range of 2.0 v to 3.3 v
A charge / discharge cycle test was performed at a constant current of A. Table 2 shows the results
Shown in

Example 2 A secondary battery was produced in the same manner as in Example 1 except that the carbon material 2 was used, and a test was conducted in the same manner. Table 2 shows the results.

Example 3 A secondary battery was produced in the same manner as in Example 1 except that the carbon material 4 was used, and a test was conducted in the same manner. Table 2 shows the results.

Example 4 A secondary battery was prepared in the same manner as in Example 1 except that activated carbon (YP-17, manufactured by Kuraray Chemical Co., Ltd., specific surface area: 1800 m ² / g) was used for the positive electrode, and a test was performed in the same manner. went. Table 2 shows the results.

Example 5 A secondary battery was prepared and tested in the same manner as in Example 1 except that activated carbon (M-15, manufactured by Osaka Gas Chemical Company, specific surface area: 1500 m ² / g) was used for the positive electrode. Was done. Table 2 shows the results.

Example 6 A secondary battery was prepared and tested in the same manner as in Example 1 except that a 1M LiPF ₆ propylene carbonate + toluene (volume ratio: 9: 1) solution was used as an electrolytic solution. Table 2 shows the results.

Example 7 A secondary battery was prepared in the same manner as in Example 1 except that a 1M LiClO ₄ ethylene carbonate + propylene carbonate + diethyl carbonate (volume ratio 1: 1: 2) solution was used as an electrolyte. Was tested. Table 2 shows the results.

Comparative Example 1 A secondary battery was produced in the same manner as in Example 1 except that the carbon material 1 was used, and a test was conducted in the same manner. Table 2 shows the results.

Comparative Example 2 A secondary battery was produced in the same manner as in Example 1 except that the carbon material 5 was used, and a test was conducted in the same manner. Table 2 shows the results.

Comparative Example 3 A secondary battery was produced in the same manner as in Example 1 except that activated carbon having a specific surface area of 450 m ² / g was used for the positive electrode, and a test was conducted in the same manner. Table 2 shows the results.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

The non-aqueous lithium secondary battery of the present invention has good cycle characteristics and high charge / discharge coulomb efficiency and capacity. Therefore, the nonaqueous lithium secondary battery of the present invention can be suitably used as a backup secondary battery.

Claims (1)

[Claims] 1. A non-aqueous lithium secondary battery having a lithium salt as an electrolyte and a negative electrode and a positive electrode, wherein a mixture of a thermosetting resin and a metal salt is heat-treated, and an atomic ratio of nitrogen atoms to carbon atoms is obtained. (N / C) is 0.001 to 0.0
3. The lattice spacing (d ₀₀₂ ) in X-ray diffraction is 3.65.
~ 4.00Å, specific surface area by BET method is 1 ~ 25m ²
/ G, a molded body containing a carbon material having a total pore volume of 0.03 to 0.3 ml / g as a negative electrode, and a molded body containing activated carbon having a specific surface area of 500 m ² / g or more by a BET method A non-aqueous lithium secondary battery comprising: