JPS585966A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To obtain a graphite-fluoride light-metal system nonaqueous electrolyte battery having a large energy density and a stable discharge voltage by giving a conductivity to graphite fluoride by eliminating part of fluorine bound to the surface of molecules so as to form carbon layers over the surfaces of the molecules by irradiating gamma-rays on graphite fluoride. CONSTITUTION:Graphite fluoride obtained through gamma-ray irradiation treatment has an increased conductivity due to an increased amount of carbonaceous matter existing in its surface. Therefore, in preparing a positive mixture 5 by use of the above graphite fluodide, the amount of an added conductive agent can be greatly reduced, and the addition amount of a binding agent can be reduced. The F/C value of unirradiated graphite fluoride, which is 1.15-0.90, is preferred to be reduced by the irradiation by above 0.07 to above 0.75. As the result, the capacity and the discharge voltage characteristic of the battery can be improved effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte battery based on graphite hepta-light metal, which has a stable discharge voltage and a high capacity density.

Fluorinated graphite is an intercalation compound obtained by a direct reaction between carbon and fluorine, and two types are known: (CF)n and (02F)n. The present invention defines (CF)n as fluorinated graphite, and aims at improving a non-aqueous electrolyte battery using this as a positive electrode active material.

Fluorinated graphite has an extremely large theoretical capacity among solid active materials of 0.864Ah/y, but since it is non-conductive, it requires a relatively large amount of conductive agent to be used as a positive electrode, making it difficult to use in practical batteries. However, there was a problem in that the filling capacity had to be significantly sacrificed. Furthermore, in the early stages of the discharge characteristics, as shown in FIG. 1, there was a problem in that the discharge voltage slightly decreased at the portion A. Although the cause is not clear, it is presumed that the reaction resistance is large when the surface layer of fluorinated graphite reacts.
It is thought that the reaction of -+nC+nF"" occurs, and the conductivity is further improved by the production of carbon, resulting in flat voltage characteristics.

As a way to solve these problems, a method has been proposed that allows the battery to discharge slightly before using it, causing the battery to wear out.
However, the discharge capacity had to be sacrificed, and if the amount of conductive agent was reduced in order to increase the filling capacity of the heptanodinated graphite, there was a drawback that the voltage drop phenomenon at the beginning of discharge would occur significantly. .

The present invention solves the drawbacks of the conventional methods described above and provides a means for constructing a non-aqueous electrolyte battery based on hepta-nitrated graphite-light metal, such as lithium, which has a high energy density and a stable discharge voltage. be. Specifically, fluorinated graphite is irradiated with r-rays to remove some of the bound fluorine on the molecular surface, forming a carbon layer on the molecular surface, which gives the fluorinated graphite conductivity. It is used as a positive electrode active material. In this case, as will be described later, the amount of conductive agent added to obtain a certain level of conductivity is significantly smaller than when untreated fluorinated graphite is used. Since the effective amount of fluorine in graphite is also large, the volumetric density increases.

Furthermore, since the carbon layer is present in close contact with the surface of the fluorinated graphite from the early stage of discharge, the conductivity of the reaction particles is good from the early stage of discharge, and a stable voltage can be obtained.

At the end of each layer plane of (CF)n, which is an intercalation compound, >
If CF or 10F3 is present and F/C is 1 to 1.2, however, if the fluorination reaction is insufficient, unreacted carbon remains in the center and F/C is less than 1.0. However, since the surface is (CF)n, it has almost no conductivity. In the present invention, (CF)n containing such unreacted carbon is also defined as fluorinated graphite.

(CF)n is a chemically stable substance that can withstand high temperatures of 400'C or 600'C, depending on the raw material carbon, but when irradiated with r-rays, the aforementioned '-CF2 and -CF
It is said that decomposition takes priority from the end of the layer plane where 3 exists.

(By irradiation with CF radiation, gas is released, the color gradually changes from white to black, and the F/C decreases).

F/C here refers to the ratio of the number of atoms contained in fluorine and carbon.

For example, prepare fluorinated graphite (,) with F/C=1.15.

Add to this a co-60 source in the air at 1000 Mr per y.
When ad irradiated, as shown in Figure 2 (F/C = 1.08 (b
), in the case of 3000 Mrad, F/C-= 0, 9
5(c).

5oooMrad ty), then F/C=0.8(d)
, F/C-0, 7(e) in the case of 100 rad. In this case, CF4°F2 and the like are mainly emitted, and the surface becomes white, changes to gray, and approaches black. During this time, carbonaceous matter increases on the surface of fluorinated graphite, and some C--C bonds change to C--C bonds. In addition to the above-mentioned atmosphere during r-ray irradiation, the reaction rate is somewhat slow in vacuum, and the reaction rate is fast in oxygen.

Next, the conductivity of the fluorinated graphite obtained through the above irradiation treatment increases due to the increase in carbonaceous content on the surface, so when making a positive electrode mixture using this fluorinated graphite, the amount of the conductive agent added must be significantly reduced. Therefore, the amount of binder added can also be reduced.

First, Figure 2 shows the specific resistance of 7FL when the powders of the above (,) to (e) with different mixing ratios of acetylene black, which is a conductive agent, to fluorinated graphite are pressed at a pressure of 2 tons/d.
However, as the amount of r-ray irradiation increases and the F/C decreases, the specific resistance tends to decrease due to the addition of a small amount of acetylene black.

Acetylene black mixture with almost the lowest specific resistance (ratio is 17% for (,), 13% for (b), (C)
) is 8%, (d) is 6%, (e) is 3%,
For 100 parts by weight of a mixture with these mixing ratios, the binder of fluororesin (PTFE) that can sufficiently impart binding properties is 15 parts for (B), 10 parts for (B), 8 parts for (C), (
We experimentally determined what was required at a weight ratio of 5 parts for d) and 4 parts for (e), and a diameter of 1 part at a pressure of 2 tons/cd.
Figure 3 shows the amount of fluorine contained in the pellet and the theoretical capacitance at this time. From Figure 3, the effective amount of fluorine that can be filled into a certain volume is approximately 0 when R-ray irradiation is performed and F/C is approximately 0.
．． When it is 7 or more, it becomes larger than when it is not irradiated.

This is because the amount of the conductive agent and binder to be added can be reduced when F and /C are small.

Using each positive electrode pellet thus produced, the fourth
We prototyped a battery as shown in the figure and compared its discharge performance. In Fig. 4, 1 is a stainless steel sealing plate, 2
is welded to 1 with a nickel net negative electrode current collector.

3 is a lithium negative electrode pressed onto 2, 4 is a polypropylene nonwoven fabric separator, 5 is a fluorinated graphite positive electrode having each of the above-mentioned compositions, 6 is a stainless steel battery container, and 7 is a polypropylene gasket. Inside the battery, an electrolytic solution containing 1 mole of lithium borofluoride dissolved in a 1:1 mixture of glohylene carbonate and dimethoxyethane is sealed.

The shape of the battery is 201t11 in diameter and 2.5cm in height.
FIG. 5 shows the discharge curves of batteries prototyped using each of the positive electrodes at 20° C. and 15 Ω load. As seen in Figure 5, battery a using untreated fluorinated graphite has the most remarkable tendency to have a low initial discharge voltage, and the F/C decreases due to r-ray irradiation. I see, the initial voltage characteristics are good. On the other hand, 1 is the shortest discharge duration, followed by 1.

The length increases in the order of d and c, which is in the order of the filling theory in Figure 3. The above is an experimental result of fluorinated graphite with F/C = 1.1ei irradiated with r-rays. However, when fluorinated graphite with F/C = 0-90, in which some unreacted carbon is thought to remain in the center, is irradiated with r-rays, the radiation source produces approximately 8000 Mr a d of r-rays. F/C obtained by irradiation = 0.8
3 (7) Material f and F/C-0,75 material q obtained by irradiation with a dose of about 20,000 Mrad (7) were tested. The characteristics of the specific resistance of the mixture were f≠b and q≠C.

father, acetylene butinoc 13% by weight relative to f;
8% to q, and 1 part of binder (PTFE) to each mixture.

It was added at a weight ratio of 8 parts and the diameter was 16 mm at a pressure of 2 tons/d.
The theoretical electric capacity when molded into a pellet with a thickness of 1 chicken is approximately 110 mAh for f and approximately 105 mAh for g.
In each case, F/C without r-ray irradiation in Fig. 3 is 1.1.
When 5 was used, it was equivalent to or better than a. 4. Next, a battery with the configuration shown in Figure 4 using these positive electrodes was discharged at a temperature of 20''C with a Ω load of 5, and the results were as shown in Figure 5. , and a are shown in Figure 6. As seen in Figure 6, even when fluorinated graphite with F/C = 0.90 and unirradiated with r-rays is irradiated with r-rays, F/ In the range of C-〇-75 to 0.83, performance equivalent to or better than the case of using the untreated product d with F/C = 1.16 can be obtained for both initial characteristics and discharge '14M.From the above results, r By changing the irradiation conditions, fluorinated graphite with various values of F/C can be processed into fluorinated graphite with an appropriate F/C by radiation irradiation, and the characteristics corresponding to that can be obtained, so the initial characteristics.

The unirradiated material and irradiation conditions can be selected depending on which of the capacity is more important, but as far as a battery with excellent capacity and initial characteristics can be obtained, unirradiated fluorinated graphite F/C is recommended.
= 1.15 to 0.90, F/C value is 0.0 by irradiation
It is preferable to reduce the F/C value by 7 or more and keep the F/C value to 0.75 or more.

As described above, the present invention can effectively improve discharge voltage characteristics and capacity.

[Brief explanation of the drawing]

Figure 1 shows a typical example of the discharge characteristics of a conventional battery, and Figure 2 shows the specific resistance values when a conductive agent is added to fluorinated graphite obtained by r-ray irradiation and unirradiated fluorinated graphite. A diagram showing
Figure 3 is a diagram showing the relationship between the effective amount of fluorine in positive electrode pellets prepared under various conditions and the theoretical filling capacity, Figure 4 is a cross-sectional view of a 1° prototype battery used in the experiment, Figures 5 and 6 1 is a comparison diagram of discharge characteristics between an example battery of the present invention and a conventional battery. 3...Lithium negative electrode, 42. 6. Fluorinated graphite positive electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure Pi-? 1MiToiha (hnFigure 2a'tT'1m1l!+tfttJ-(z+Figure 3Figure 4

Claims (2)

[Claims] (1) A non-aqueous electrolyte battery characterized by using fluorinated graphite from which some fluorine has been removed by γ-ray irradiation as a positive electrode active material. (2) The ratio F/C of the number of atoms contained in fluorine and carbon is 1.16
A patent claim that uses a mixture of a positive electrode active material and a conductive agent whose F/C value is reduced by 0.07 or more by irradiating fluorinated graphite with a concentration of ~0.90 to 0.75 or more. The non-aqueous electrolyte battery according to item 1.