JPH0143682B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing modified graphite fluoride. More specifically, the present invention provides a lubricant characterized in that graphite fluoride (hereinafter often referred to as "GF") is dispersed in an aqueous solution and irradiated with electromagnetic waves to partially decompose the graphite fluoride. This invention relates to a method for producing modified graphite fluoride (hereinafter often referred to as "modified GF") with improved properties and battery properties. GF is a solid powder with unique lubricity, water and oil repellency, and excellent chemical resistance.
It is used as a solid lubricant, wet-proofing agent, antifouling agent, water and oil repellent, etc. On the other hand, it is well known that it is also useful as a battery active material and provides a primary battery with high energy density and good storage stability. As described above, GF is highly evaluated industrially in a wide range of fields, and is a compound that can be expected to be applied and developed in many more fields in the future. One of the GFs is polymonocarbon monofluoride represented by (CF) _o , which is well known to be useful as a battery active material as mentioned above (Japanese Patent Publication No. 48-25565). (see book).
(CF) _o is produced by reacting an amorphous carbon material such as petroleum coke with fluorine at about 200°C to about 450°C, or reacting a crystalline carbon material such as natural or artificial graphite with fluorine. It is obtained by reacting at about 500°C to about 630°C. Yet another GF is polydicarbon monofluoride, represented by (C ₂ F) _o , discovered by Watanabe et al. (C ₂ F) _o can be obtained in relatively high yield and at low cost. _This (C ₂ F)
As detailed in Re30667, graphite material is heated to 300 mmHg under a fluorine pressure of 100 to 760 mmHg.
Obtained by heating at ~500°C.
The graphite material used in the production of (C ₂ F) _o is
Natural graphite, artificial graphite, hardwood graphite, pyrolytic graphite or mixtures thereof can be used. (C ₂ F) _o , which has a crystal structure, has a laminated structure in which layers forming a lattice structure are stacked with an interlayer distance of approximately 9.0 Å, and the crystal structure is approximately 6
It is different from the crystal structure of (CF) _o with an interlayer distance of Å. Also, while each carbon in each layer is bonded to one fluorine atom in the case of (CF) _o ,
In the case of (C ₂ F) _o , every other carbon in each layer is bonded to one fluorine. But (CF) _o and (C ₂ F) _o
Both of these compounds have CF ₂ and CF ₃ groups as peripheral groups at the ends of the carbon hexagonal network layer of the compound.
Therefore, if graphite is completely fluorinated, (CF) _o
The F/C ratio of (C ₂ F) _o is 0.5 or more and 1.0 or more, respectively. The amount of excess fluorine attributable to surrounding CF ₂ and CF ₃ groups increases as the size of the crystal in the a- and b-axis directions of the GF crystal becomes smaller [Journal of American Chemical Society,
Volume 101, page 3832 1979 {J.Amer.Chem.Soc., 101 ,
3832, (1979)}. As you can see from the above,
Depending on the reaction conditions and the crystallinity or type of carbon material, (CF) _o , (C ₂ F) _o or a mixture thereof can be obtained. or,
It is also possible to leave unreacted carbon material in these GFs. As is clear from the above, the composition of GF produced by fluorination of a carbon material depends on the reaction temperature and the type or crystallinity of the carbon material. (CF) _o is about amorphous carbon material such as petroleum coke and fluorine.
(CF) _o rich compositions obtained by reacting at 200°C to about 450°C and consisting of (CF) _o or (CF) _o and (C ₂ F) _o are crystalline carbons such as natural and artificial graphite. The material is approx.
It is obtained by reacting at 500°C to about 630°C. Performing the fluorination reaction at temperatures below 630°C prevents the decomposition of (CF) _o .
This is because corrosion is accelerated at temperatures exceeding 630°C, and there is no material for the reaction vessel that can withstand corrosion by fluorine even at such high temperatures.
(CF) _o Compounds can be obtained with various degrees of crystallinity, but those with high crystallinity are white solids. on the other hand,
( _C2F ) _o , or a ( _C2F ) _o rich mixture consisting of ( _C2F ) _o and (CF) _o , is a mixture of crystalline carbon materials such as natural and artificial graphite and fluorine at about 300℃. ~about 500℃
It can be obtained by reacting with The color of ( _C2F ) _o is black under its generated conditions, but up to 600℃
Through heat treatment, the color changes from black to gray to white, and the degree of crystallinity also increases. When natural graphite is used as a starting material, if the fluorination reaction is carried out at a temperature exceeding about 500°C, the produced GF will be (CF) _o rich;
When fluorination is carried out at temperatures up to about 500°C, the resulting GF is (C ₂ F) _o rich. That is, the higher the reaction temperature, the more the (CF) _o content of the product increases, and the lower the reaction temperature, the more the (C ₂ F) _o content of the product. The same can be said when artificial graphite is used as a starting material. However, when using artificial graphite (CF)
_o rich or (C ₂ F) _o The boundary temperature for becoming rich is approximately 500℃
It is about 470℃ instead. Reaction time is not critical. If the carbon material is to be completely fluorinated, the fluorination reaction may be continued until no increase in the weight of the produced GF is observed. As mentioned above, solid powder GF is known to be represented by (CF) _o or (C ₂ F) _o .
Some reports say (CF _x ) _o . Also
As mentioned above, GF is useful in a wide range of fields, but the low surface energy characteristic of GF may actually be a drawback in some fields, as its water and oil repellency is too strong. For example, when GF is used as a battery active material, it is generally necessary to add a binder or a conductive agent because GF itself does not have moldability or conductivity. Because it has poor solubility and GF itself is an insulator, a relatively large amount of binder and conductive agent must be added. The present inventors dispersed GF in a dispersion medium and irradiated it with electromagnetic waves in order to modify GF, reduce water and oil repellency, improve compatibility with resins, etc., and make it conductive. When we attempted to degrade a part of GF, such as the surface, we surprisingly found that, in addition to the expected effect of reducing water and oil repellency, GF treated in this way showed lower levels of GF compared to untreated GF. We found that the battery characteristics were significantly improved. As a result of further research, we discovered that the desired decomposition of GF can be achieved in a short time by using water or an alkaline aqueous solution as a dispersion medium, and that the initial discharge voltage drop, which is a drawback of GF batteries, can be significantly improved. The present invention has now been completed. Therefore, an object of the present invention is to provide a method for efficiently producing modified fluorinated graphite which has improved initial discharge voltage drop and excellent battery characteristics. The above and other purposes, features and benefits are:
It will become clearer from the following detailed description with reference to the accompanying drawings. According to the present invention, there is provided a method for producing modified graphite fluoride, which comprises dispersing graphite fluoride in water or an aqueous solution and irradiating it with electromagnetic waves to partially decompose the graphite fluoride. The modified graphite fluoride of the present invention is obtained by dispersing GF in water or an aqueous dispersion medium by means of stirring or the like, and irradiating this with electromagnetic waves to partially decompose the graphite fluoride. Graphite fluoride (GF) as used in the present invention applies to all the graphite fluorides that are generally called graphite fluoride, such as (CF _{) o} and (C ₂ F) _o mentioned above. ₂ F) _{o It} may be used alone or in a mixture thereof, or it may be one in which unreacted carbon material remains. There is no limit to the particle size of the GF used in the present invention, but 0.01μ to 100μ is generally used. The modified graphite fluoride of the present invention is preferably obtained by decomposing graphite fluoride by electromagnetic wave irradiation at a decomposition rate (described later) in the range of 0.01 to 50%. Decomposition rate is 0.01
If it is less than 50%, the effect of the present invention will be small, and if it exceeds 50%, it will take time to decompose the graphite fluoride, which is not efficient, and the battery characteristics will deteriorate, which is not preferable. A more preferable range of the decomposition rate of the modified fluorinated graphite of the present invention is 0.1 to 10%. The electromagnetic waves used in the present invention may be of any wavelength as long as they are in the wavelength range generally called electromagnetic waves (approximately 10 ^-17 to ^{10 5} m), but from the viewpoint of effectiveness in decomposing GF, wavelengths shorter than 10 ^-4 cm are preferred. It is preferable that
In addition, from the viewpoint of adverse effects on the human body, electromagnetic waves with wavelengths longer than 10 ^-7 cm are preferable. In other words, as an electromagnetic wave
Visible light, ultraviolet rays, X-rays, etc. within the range of 10 ^-4 to ^{10 -7} cm are preferably used. The intensity and irradiation time of the electromagnetic waves are not critical, and may be any intensity and irradiation time that can provide the above-mentioned decomposition rate. Generally, the stronger the intensity of electromagnetic waves, the shorter the irradiation time, so the intensity of the electromagnetic waves and the irradiation time can be changed as necessary. Examples of the dispersion medium for dispersing GF include organic solvents such as ethanol and acetone, and water to which a surfactant is added. but,
Compared to using an organic solvent as a dispersion medium, using water with a high dielectric constant has a higher decomposition rate, allows a modified GF with a predetermined decomposition rate to be obtained in a shorter time, and is easier to handle. Further, in order to accelerate the decomposition rate of GF, it is preferable to use an alkaline aqueous solution in which an alkali such as potassium hydroxide or sodium hydroxide is dissolved in water. Moreover, when an alkaline solution is used as a dispersion medium, the voltage drop at the beginning of discharge, which is a major problem when used as a battery active material, can be suppressed with a smaller decomposition rate than when an organic solvent is used. A small decomposition rate means that less fluorine is eliminated. In a battery using fluorinated graphite as a battery active material, the greater the amount of fluorine contained in the battery active material, the greater the discharge capacity; therefore, a small decomposition rate is preferable from the viewpoint of discharge capacity. The concentration of this alkaline aqueous solution is generally 0.1 wt% to 30 wt%. When GF is dispersed in a dispersion medium and irradiated with electromagnetic waves, decomposition occurs first at the surface of GF, but if irradiation continues, the decomposition progresses to the inside of GF,
It can be efficiently decomposed up to a decomposition rate of about 50%. When a battery active material made of modified fluorinated graphite obtained by the production method of the present invention is used in a battery, it can be used as a positive electrode. In that case, an alkali metal such as lithium, an alkaline earth metal such as magnesium or calcium, or aluminum can be used alone for the negative electrode, or an alloy containing these as main components can also be used. The electrolyte varies depending on the type of negative electrode used, but both non-aqueous and aqueous electrolytes can be used. Specifically, propylene carbonate, dimethyl sulfite,
Further, when zinc is used for the negative electrode, an alkaline aqueous solution such as a potassium hydroxide aqueous solution can be used as the electrolyte. A battery constructed using a battery active material made of modified graphite fluoride, which can be efficiently obtained by the production method of the present invention, as a positive electrode, and the negative electrode and electrolyte described above, has a discharge potential, a discharge capacity, and a GF concentration. The elemental utilization rate (described later) is also the rate before decomposition by irradiation with electromagnetic waves.
It is higher than GF, and the initial discharge voltage drop is also improved. Furthermore, the modified graphite fluoride of the present invention has a lower resistivity than GF before being decomposed by irradiation with electromagnetic waves, and its compatibility with resins is improved, so when used as a battery active material, it can be used as a conductive agent or adhesive. A very advantageous high energy density battery can be provided which has the advantage that less binder is required. As described above, the modified fluorinated graphite of the present invention exhibits better battery characteristics than the already known GF through simple treatment, and also enables the development of new applications, which has great industrial significance. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is not limited to the Examples. The fluorine content in the raw GF and modified GF in the examples was determined by the following method. 100 mg of GF was accurately weighed in a platinum crucible and mixed uniformly with a flux (2.5 g each of potassium carbonate and sodium carbonate). This homogeneous mixture of GF and flux is
After melting at °C, the resulting melt was dissolved in a predetermined amount of water to form an aqueous solution. A certain amount of this aqueous solution was taken, the pH was adjusted to 3.4, and the fluorine content was determined by titration with a standard thorium nitrate solution using Alizarin Red S as an indicator. At this time, an automatic photometric titration device was used for the titration. The decomposition rate of GF by electromagnetic wave irradiation was determined by the following formula, where x ₁ is the fluorine content of GF before electromagnetic wave irradiation, and x ₂ is the fluorine content of GF after electromagnetic wave irradiation. GF decomposition rate (%) = x ₁ − x ₂ / x ₁ × 100 Example 1 As an electromagnetic wave irradiation device, a 400W high-pressure mercury lamp (irradiation wavelength: 3126 to 3132 Å, 3650 to 3663 Å,
A UVL-400HA photochemical reaction device manufactured by Riko Kagaku Sangyo Co., Ltd. equipped with 4047-4058 Å, 5461 Å, and 5770-5791 Å) was used. 2wt% surfactant (trade name: ADEKA NOL, manufactured by Asahi Denka Co., Ltd.) was used as a dispersion medium in the above photochemical reaction device.
200c.c. of water added with (CF) as the _raw material (GF containing 62.69wt% fluorine content, F/C ratio
1.06, average particle size 14μ) was added, and the mixture was irradiated with light from the high-pressure mercury lamp for 30 minutes while stirring and cooling with water. After irradiation with light, GF was overseparated and dried to obtain modified GF. Table 1 shows the results of measuring the fluorine content of the modified GF and the decomposition rate F/C ratio. The discharge characteristics when the obtained modified GF was used in a battery were measured by the following method. 20 mg of the modified GF obtained above was mixed with 20 mg of expanded graphite manufactured by Toyo Tanso Co., Ltd. as a conductive agent and a binder.
The mixture was compressed for 1 minute at a pressure of about 8800 kg/cm ² and formed into a pellet with a diameter of 10 mm, which was used as a positive electrode. A 10 mm diameter pellet cut from a lithium block was used as the negative electrode. Lithium perchlorate (LiClO ₄ ) is used as an electrolyte.
A 1 mol/dissolved propylene carbonate solution was used. These battery components were placed in a Teflon container, and all experiments were conducted in a dry box at 30°C in an argon atmosphere. In addition, experiments were conducted with a distance between electrodes of 10 mm. The discharge characteristics of this battery (sample No. A) under a constant resistance load of 20 kΩ are shown in curve A in FIG. or,
Table 1 shows the measured discharge capacity (mA·hr) and the fluorine utilization rate (%) in GF when the electrode was discharged at an OCV potential and a final voltage of 2V. At this time, the fluorine utilization rate was determined according to the following formula. Fluorine utilization rate (%) in GF = measured discharge capacity (m
A・hr)/Theoretical discharge capacity (mA・hr)×100=yt/96500
×X/19×100 However, X is the amount of fluorine contained in the positive electrode (g), y is the current (milliampere) that flows when the electrode is discharged, and t is the discharge time (hours). Comparative Example 1 A battery (sample no.
B) Discharge characteristics and discharge capacity (m
A・hr) and fluorine utilization rate (%) were measured. The obtained discharge characteristics are shown in curve B of FIG. or,
OCV (open circuit voltage), discharge capacity (mA·hr), and fluorine utilization rate (%) are shown in Table 2. As is clear from Figure 1 and Table 2, when the modified GF obtained in Example 1 was used (Sample No.
A), OCV, discharge potential, and fluorine utilization rate were all improved compared to the GF before modification in Comparative Example 1 (Sample No. B). Furthermore, as is clear from Tables 1 and 2, the GF before modification of Comparative Example 1 (Sample No.
Compared to sample B), the modified GF obtained in Example 1 (sample No. A) showed a high discharge capacity despite the reduced fluorine content. Comparative Example 2 Modified GF was obtained in the same manner as in Example 1, except that ethanol was used as the dispersion medium and the irradiation time was 3 hours or 1/2 hour. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. Using the modified GF obtained above as a battery (sample No. C)
The discharge characteristics when used in Example 1 were measured in the same manner as in Example 1. The obtained discharge characteristics are shown in curve C in FIG. Further, Table 2 shows the measured discharge capacity (mA·hr) and fluorine utilization rate (%) when the electrode was discharged at an OCV potential and a final voltage of 2V. As is clear from Figure 1 and Table 2, when the modified GF obtained in Example 1 was used (Sample No.
A), OCV, discharge potential, and utilization rate are the same as the modified GF (sample No. C) in Comparative Example 2, but as is clear from Table 1, it takes a short time to decompose to the same degree All it takes is irradiation. Example 2 Modified GF was obtained in the same manner as in Example 1, except that an ethanol (40 vol%)-water (60 vol%) solution to which 1 wt% KOH was added was used as a dispersion medium. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. Using the modified GF obtained above as a battery (sample No. D)
The discharge characteristics when used in Example 1 were measured in the same manner as in Example 1. The obtained discharge characteristics are shown in curve D in FIG. Further, Table 2 shows the measured discharge capacity (mA·hr) and fluorine utilization rate (%) when the electrode was discharged at OCV and final voltage of 2V. As is clear from Figure 1 and Table 2, when the modified GF obtained in Example 2 was used (Sample No.
D) OCV, discharge potential, and fluorine utilization rate are similar to those of the modified GF in Example 1 and Comparative Example 2, but the voltage drop at the initial stage of discharge is improved. Also,
As is clear from Table 1, compared to Comparative Example 2, a shorter irradiation time is required to achieve the same degree of decomposition. Example 3 Modified GF was obtained in the same manner as in Example 1, except that an ethanol (40 vol%)-water (60 vol%) solution was used as the dispersion medium and the irradiation time was 3 hours. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. The decomposition rate is higher than that of Comparative Example 2. Comparative Example 3 Modified GF was obtained in the same manner as in Example 1 except that hexane was used as the dispersion medium and the irradiation time was 5 hours.
Fluorine content, decomposition rate, F/ of the obtained modified GF
The C ratio is shown in Table 1. Comparative Example 4 Modified GF was obtained in the same manner as in Example 1 except that toluene was used as the dispersion medium and the irradiation time was 5 hours.
Fluorine content, decomposition rate, F/ of the obtained modified GF
The C ratio is shown in Table 1. Example 4 Modified GF was obtained in the same manner as in Example 1, except that an ethanol (40 vol%)-water (60 vol%) solution to which 1 wt% LiOH was added was used as a dispersion medium. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. As is clear from Table 1, the decomposition rate is higher than that of Comparative Examples 1 to 4. Example 5 GF containing (C ₂ F) _as the main component (fluorine content 51.55 wt%, F/C ratio 0.67, average particle diameter
20μ) and the irradiation time was 1 hour.
Modified GF was obtained in the same manner as in Example 1. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. The discharge characteristics of this battery (sample No. I) under a constant resistance load of 20 kΩ are shown in curve I in FIG. or,
OCV, the measured discharge capacity (mA·hr) when the electrode was discharged at a final voltage of 2V, and the fluorine utilization rate (%) in GF are shown in Sample No. I in Table 1. Comparative Example 5 A battery (sample no.
Discharge characteristics and discharge capacity (m
A・hr) and fluorine utilization rate (%) were measured. The obtained discharge characteristics are shown in curve J in FIG. or,
OCV, discharge capacity (mA・hr), and fluorine utilization rate (%) are shown in Table 2. As is clear from Figure 2 and Table 2, when the modified GF obtained in Example 5 was used (Sample No.
I), OCV, discharge potential, and fluorine utilization rate were all improved compared to the GF before modification in Comparative Example 5 (Sample No. J). Furthermore, as is clear from Table 1,
Compared to the unmodified GF of Comparative Example 5 (sample No. J), the modified GF obtained in Example 5 (sample No. I) has a high fluorine content even though the fluorine content is reduced. It shows the discharge capacity. Comparative Example 6 Modified GF was obtained in the same manner as in Example 1 except that the GF used in Example 5 was used as a dispersion medium in ethanol and the irradiation time was 3 hours. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. Using the modified GF obtained above as a battery (sample No.K)
The discharge characteristics when used in Example 1 were measured in the same manner as in Example 1. The obtained discharge characteristics are shown in curve K in FIG. Further, Table 2 shows the measured discharge capacity (mA·hr) and fluorine utilization rate (%) when the electrode was discharged at OCV and final voltage of 2V. As is clear from Figure 2 and Table 2, when the modified GF obtained in Example 5 was used (Sample No.
I), OCV, discharge potential, and utilization rate are similar to the modified GF in Comparative Example 6 (sample No. K), but as is clear from Table 1, it takes a shorter time to decompose to the same extent. All you need is irradiation. Example 6 1wt% of GF used in Example 5 as a dispersion medium
Modified GF was obtained in the same manner as in Example 1, except that an ethanol (40 vol%)-water (60 vol%) solution containing KOH was used. Table 1 shows the fluorine content, decomposition rate, and F/C ratio of the obtained modified GF. Using the modified GF obtained above as a battery (sample No.L)
The discharge characteristics when used in Example 1 were measured in the same manner as in Example 1. The obtained discharge characteristics are shown at L in FIG. Further, Table 2 shows the measured discharge capacity (mA·hr) and fluorine utilization rate (%) when the electrode was discharged at OCV and final voltage of 2V. As is clear from FIG. 2 and Table 2, when the modified GF obtained in Example 6 (sample No. L) was used, OCV, discharge potential, and utilization rate were It has the same characteristics as quality GF, but
The voltage drop at the beginning of discharge is improved. Furthermore, as is clear from Table 1, compared to Comparative Example 6, a shorter irradiation time was required to achieve the same degree of decomposition. Experimental example 1 GF used in Example 1 was used as a dispersion medium at 1wt%
Modified GF was obtained in the same manner as in Example 1 using an ethanol (40 vol%)-water (60 vol%) solution to which KOH was added and at each irradiation time. The discharge characteristics when the modified GF obtained above was used in a battery were measured in the same manner as in Example 1.
To investigate the voltage drop at the beginning of discharge, we compared the voltage at 0.5 hours after the start of discharge (V _0.5 ), when the voltage drops the most, with the voltage at 10 hours after the start of discharge, when the voltage is highest and stable (V ₁₀ ). The relationship between the difference V _0.5 −V ₁₀ and the decomposition rate is shown in FIG. 3A. As is clear from FIG. 3, the voltage drop at the initial stage of discharge improves with the decomposition rate, and the voltage drop disappears when the decomposition rate is approximately 2.5%. Experimental Example 2 Modified GF was obtained in the same manner as in Example 1 using ethanol as a dispersion medium for the GF used in Example 1 and at each irradiation time. The discharge characteristics when the modified GF obtained above was used in a battery were measured in the same manner as in Example 1.
As in Experimental Example 1, the relationship between (V _0.5 −V ₁₀ ) and decomposition rate is shown in FIG. 3B. As is clear from FIG. 3, the voltage drop at the beginning of discharge becomes worse at a small decomposition rate, but improves thereafter as the decomposition rate increases. The voltage drop disappears at a decomposition rate of about 6.5%, which is 2% lower than in Experimental Example 1.
A decomposition rate that is more than double that is required.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 and FIG. 2 show the relationship between discharge potential and discharge time for a battery using modified graphite fluoride obtained by the production method of the present invention and a comparative battery using graphite fluoride. A...Example 1, B...Comparative example 1, C...Comparative example 2, D...Example 2, I...Example 5, J...
Comparative example 5, K... Comparative example 6, L... Example 6. Figure 3 shows the aqueous dispersion medium and non-aqueous dispersion medium.
The relationship between the decomposition rate of GF and the initial discharge voltage drop of a battery containing the GF is shown. A... Dispersion medium: water-ethanol-KOH (Experimental example 1), B... Dispersion medium: Ethanol (Experimental example 2).

Claims (1)

[Claims] 1. A method for producing modified graphite fluoride, which comprises dispersing graphite fluoride in water or an alkaline aqueous solution and irradiating it with electromagnetic waves to partially decompose the graphite fluoride.