JPH02265174A - Nonaqueous electrolyte energy storage unit - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte energy storage unit having low self discharge rate and long charge-discharge cycle life by constituting a positive electrode with a molding of activated carbon powder or fibers and a negative electrode with the carbonized material of an aromatic condensation polymer and an alkali metal. CONSTITUTION:A positive electrode 1 is made of a molding of activated carbon powder or fibers. A negative electrode 2 is made of the carbonized material of an aromatic condensation polymer and an alkali metal. As the aromatic condensation polymer, phenol resin and furan resin are used. Phenol resin obtained by condensing aromatic hydrocarbon having a phenolic hydoxyl group and aldehyde such as formaldehyde and acetaldehyde is preferable. A nonaqueous electrolyte energy storage unit having low self discharge rate and long chargedischarge cycle life can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a non-aqueous electrolyte energy storage device, particularly a non-aqueous electrolyte energy storage device with little self-discharge and excellent charge/discharge cycle characteristics. .

[Prior Art] In recent years, secondary batteries using alkali metals, particularly lithium, as a negative electrode active material have been attracting attention as small, lightweight, high-energy density, high-performance energy storage devices.

In this case, if an alkali metal is used as a negative electrode as in a lithium secondary battery, the alkali metal will precipitate in the form of dendrites during charging, resulting in internal short circuits in the battery and drop-off of the active material, resulting in a decrease in charging and discharging efficiency. cause

In order to improve these drawbacks, for example, ■ using an alloy of alkali metal and aluminum for the negative electrode, and ■ using a conductive polymer such as polyacetylene as the negative electrode and filling it by doping and dedoping with alkali metal ions. It has been proposed to use an electrochemically generated graphite intercalation compound of an alkali metal using graphite as a negative electrode material to generate a discharge.

On the other hand, as the positive electrode material, ■TiS2. MO32,V
Metal chalcogen compounds such as 2O5 have been proposed.

This utilizes an interlayer compound of alkali metal ions and metal chalcogen compounds, and charges and discharges by electrochemically releasing and inserting alkali metal ions.

In addition, like the negative electrode, a conductive polymer is used as the positive electrode, and ClO4
It has also been proposed to charge and discharge by doping and dedoping anions such as - and BF4-, and to use activated carbon fiber for the positive electrode, which forms an electric double layer on the electrode surface without reacting with the electrolyte. has been done.

[Problem to be Solved by the Invention] However, in the proposal (2) above, the alloy repeatedly absorbs and releases alkali metals due to charging and discharging, which causes the negative electrode to fall off, which causes a reduction in cycle life. It has some drawbacks.

In addition, the proposal (■) has the disadvantage that the discharge state (doped state) is unstable, so the self-discharge as a battery is large (and the cycle characteristics are insufficient.) However, such compounds are unstable and have large self-discharge.
It also has the disadvantage of insufficient cycle characteristics.

Regarding (2), satisfactory characteristics have not yet been obtained, such as generally low battery electromotive force, small capacity, and poor cycle characteristics.

In case (2), the conductive polymer is easily oxidized and the charged state (doped state) is chemically unstable, resulting in large self-discharge and short cycle life.

It is no exaggeration to say that method (2) is far from practical, and has the drawback of a small capacity.

[Means for Solving the Problems] The present inventor has conducted various studies with the aim of eliminating the various drawbacks of these conventional methods and finding a non-aqueous electrolytic energy storage device with less self-discharge and excellent charge-discharge cycle characteristics. ,
As a result of our studies, we found that by using electrodes in which the positive electrode is made of activated carbon powder or a molded fiber, and the negative electrode is made of a carbonized aromatic condensed polymer compound and an alkali metal,
It has been discovered that the above object can be achieved, and this is the gist of the present invention.

In the present invention, the aromatic condensation polymer compound that is the raw material for the negative electrode material that is one electrode of the non-aqueous electrolyte energy storage device includes, for example, phenol resin, furan resin, etc., and phenol, xylenol, cresol, etc. A phenol resin which is a condensation of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde such as formaldehyde or acetaldehyde is preferred.

The negative electrode material is obtained by carbonizing the aromatic condensation polymer compound, and has a hydrogen/carbon atomic ratio of 0.
．． 35 or less, preferably 0.1 or less, and the interplanar spacing of the carbon (002) plane determined by X-ray diffraction method is 3.3.
7 Å or more, preferably 3.40 Å or more and 3.80 Å
The following are suitable. A method for carbonizing an aromatic condensed polymer compound to obtain such a material is to heat-treat the polymer compound in vacuum or in an inert atmosphere such as nitrogen or argon. The temperature of the heat treatment varies depending on the raw material polymer compound, but is preferably 750 to 3000°C.

Furthermore, when using this material, the aromatic condensation polymer compound may be made into a shape suitable for use as a film, plate, cloth, etc., and then carbonized, or the polymer compound may be carbonized and then crushed. The powder may be made into a powder, and if necessary, a binder or the like may be added as appropriate and molded into a desired shape.

As the alkali metal which is another negative electrode material, lithium is particularly preferable.

A method for forming a negative electrode from the material obtained by carbonizing the aromatic condensation polymer compound and an alkali metal may be formed by forming each into a desired shape such as a sheet, plate, or pellet, and then laminating them. However, each powder may be molded into a desired shape by adding an appropriate binder, if necessary.

Next, the positive electrode of the present invention preferably has a specific surface area of 1500
~3500 m2/g of activated carbon powder or fiber, preferably a sheet-like molded product of powder. Raw materials for activated carbon powder having such a specific surface area include coconut husk, sawdust, coal coke, etc., but petroleum coke is particularly preferred since it provides activated carbon powder with a high specific surface area and few impurities.

The positive electrode used in the present invention can also be made by mixing activated carbon powder or fibers with an electrolytic solution to form a paste. However, as an electrode with even better capacity per unit volume and mechanical strength, activated carbon powder is made into a sheet using an adhesive with excellent chemical resistance such as polytetrafluoroethylene (hereinafter abbreviated as PTFE). Examples include electrodes made of For such a sheet-like electrode, first, it is preferable that the activated carbon fine powder contains 1 to
50% by weight, more preferably 5-30% by weight PTF
A product formed into a sheet by mixing the E dispersion and compressing, extruding, or rolling the resulting viscous mixture, or a combination of these methods can be preferably used.

This sheet-like molded body can be further uniaxially or
Or biaxially stretched.

This stretching treatment is carried out at 20 to 380°C, preferably at 20 to 2
At 00 DEG C., the redundancy is preferably 1.1 to 5.0 times, particularly preferably 1.2 to 2.0 times, by a known method (for example, JP-A-59-166541). The stretched product thus obtained can be used as it is, but if necessary, it may be further rolled or compressed using a roll press or the like, and then fired or semi-baked before use.

The electrolyte used in the non-aqueous electrolyte energy storage device of the present invention is not particularly limited, and any electrolyte used in electrochemical devices using non-aqueous electrolytes such as lithium batteries and electric double layer capacitors may be used as appropriate. used. Examples of such a non-aqueous electrolyte include anions such as perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, bar-alkylsulfonic acid, or trifluoromethanesulfonic acid, and lithium ions, sodium ions, potassium ions, etc. The solute in combination with the alkali metal cation of propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1.2-
Examples include those dissolved in polar organic solvents such as dimethoxyethane, sulfolane, nitromethane, and tetrahydrofuran at a concentration of about 0.3 to 1.5 mol/β.

The non-woven fabric according to the present invention is manufactured by processing and molding the above-mentioned negative electrode and positive electrode according to the shape of the device, sandwiching a porous separator between the two electrodes, impregnating or filling the above-mentioned electrolytic solution, and sealing it in a case. A water electrolyte energy storage device is obtained. As the porous separator, for example, polypropylene fiber nonwoven fabric, glass fiber mixed paper nonwoven fabric, etc. are suitable. In addition, the thickness of the separator is 50 to 200μ
m is appropriate, and 100 to 150 μm is particularly preferable.

[Example] Hereinafter, an example of the present invention will be specifically described based on the drawings.

Example 1 Cresol resin powder produced from cresol and formaldehyde was thermally decomposed by heating to 700°C in a nitrogen atmosphere, and was further heat-treated to 3000°C to carbonize the cresol resin. The obtained carbon material was ground into fine powder to obtain a negative electrode material. The hydrogen/carbon atomic ratio of this material is 0
．． 03, the spacing between the (002) planes was 3.419. 90% by weight of this negative electrode carbon powder and 10% by weight of polyethylene powder were mixed in a ■-shaped blurredder. This mixture was press-molded into pellets with a thickness of 0.4 mm and a diameter of 15 mm. A 0.1 mm thick lithium foil was press-bonded to this molded product to form a negative electrode 2.

Petroleum coke was pulverized into 40 mesh, to which caustic potash was added about 3 times by weight, and in a nitrogen atmosphere, 38 mesh was crushed.
Calcination was performed at 5°C for 1 hour, and main firing was performed at 850°C for 2 hours. After cooling the obtained activated carbon powder, it is washed with water and dried.
Finally, the activated carbon for the positive electrode was obtained by vacuum drying at 110°C. This activated carbon had a specific surface area of 3000 m2/g.

A powder mixture of 70% by weight of this activated carbon, 20% by weight of carbon black, and 10% by weight of PTFE powder
20 lM of water was added to the slip part and mixed in a ■-type blender. The paste-like mixture obtained was rolled using a roll forming machine to form a sheet with a thickness of 1.4 mm. This sheet was preheated to 300°C and stretched in the uniaxial direction at a magnification of 1.1 to obtain a sheet-like molded body with a thickness of 0.9 mm.This sheet-like molded body was stretched with a diameter of 15 mm.
The positive electrode 1 was punched out into a disk shape.

A positive electrode 1 and a negative electrode 2 are housed in an outer container consisting of a cap 4 made of stainless steel and a case 5 made of stainless steel, with a separator 3 made of a nonwoven polypropylene fiber interposed therebetween. Next, 1 mol/I2 was added as an electrolyte in the unit cell.
After injecting a propylene carbonate solution containing lithium perchlorate to satisfactorily impregnate the positive electrode 1, negative electrode 2, and separator 3 with the electrolyte, the ends of the cap 4 and case 5 are inserted through the polypropylene backing 6. It was caulked and sealed. The electromotive force of the non-aqueous electrolyte energy storage device manufactured as described above was measured. Further, a charge/discharge cycle test was conducted using this device, and the end-of-charge voltage was set to 3.5 V, and the end-of-discharge voltage was set to 1.0 ■. Charge and discharge were repeated up to 50 cycles, and the discharge capacities at the 5th and 50th cycles were measured. The results are shown in Table 1.

Example 2 A battery was prepared in the same manner as in Example 1 except that the cresol resin of the negative electrode material in Example 1 was replaced with a phenol resin. The carbon material for negative electrode obtained by carbonizing the phenol resin had a hydrogen/carbon atomic ratio of 0.04 and a spacing between carbon (002) planes of 3.460. Table 1 shows the characteristics as a non-aqueous electrolyte energy storage device.

Example 3 A battery was prepared in the same manner as in Example 1 except that the cresol resin of the negative electrode material in Example 1 was replaced with pt-butylphenol resin. The hydrogen/carbon atomic ratio of the negative electrode carbon material obtained by carbonizing the pt-butylphenol resin was 0.03, and the interplanar spacing between the (002) planes of carbon was 3.430. Table 1 shows the characteristics of the non-aqueous electrolyte energy storage device.
It was shown to.

Example 4 Except that the carbonization temperature in Example 3 was changed to 2000°C,
It was created in the same manner as in Example 3. The hydrogen/carbon atomic ratio of the obtained negative electrode carbon material was 0.08, and the (002)
The distance between the faces was 3.547 people. Table 1 shows the characteristics as a non-aqueous electrolyte energy storage device.

Example 5 A sample was prepared in the same manner as in Example 3 except that the carbonization temperature in Example 3 was changed to 800°C. The hydrogen/carbon atomic ratio of the obtained negative electrode carbon material was 0.34, and the interplanar spacing between the carbon (002) planes was 3.805. Table 1 shows the characteristics as a non-aqueous electrolyte energy storage device.

Table 1

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing an embodiment of a non-aqueous electrolyte energy storage device according to the present invention. 1...Positive electrode 2...Negative electrode 3...Separator 4...Cap 5...Case 6...Backing

Claims (5)

[Claims] (1) The positive electrode is made of activated carbon powder or fiber molding,
A non-aqueous electrolytic energy storage device characterized in that a negative electrode is made of a carbonized aromatic condensation polymer compound and an alkali metal. (2) The carbonized product of the aromatic condensation polymer compound is hydrogen/
The non-aqueous electrolyte energy according to claim 1, wherein the atomic ratio of carbon is 0.35 or less, and the interplanar spacing of the carbon (002) plane determined by X-ray diffraction is 3.37 Å or more. Storage device. (3) The non-aqueous electrolyte energy storage device according to claim 1, wherein the aromatic condensation polymer compound is a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and formaldehyde. (4) The non-aqueous electrolyte energy storage device according to claim 1, wherein the negative electrode is a laminate of a molded product of a carbonized aromatic condensation polymer compound and a sheet-like alkali metal. (5) The nonaqueous electrolyte energy storage device according to claim 1, wherein the positive electrode is a sheet-like molded product of activated carbon with a specific surface area of 1500 to 3500 m^2/g.