JPH09330714A - Non-aqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery employing a low-cost coke as a negative electrode material and having a great charge and discharge capacity and a high actuation voltage. SOLUTION: Coke in which the content of carbon is 55wt.% or more according to element analysis specified by JIS M8813, ash component specified by JIS M8812 is 5wt.% or less, and the atomic ratio O/C of oxygen to carbon is 0.03 to 0.4, is heated at a temperature in the range of 800 to 1500 deg.C in inert atmosphere, and the obtained coke is employed as a negative electrode material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery. More specifically, the present invention relates to a non-aqueous secondary battery such as a lithium secondary battery, which is suitable as a power source for small and lightweight electric devices and electric vehicles.

[0002]

2. Description of the Related Art In recent years, cleaner non-aqueous batteries, especially lithium secondary batteries, which replace lead-acid batteries and NiCat batteries have been attracting attention from the standpoints of weight saving, power saving and environmental protection of electronic devices, and they are in the stage of practical application. Arrived However, when lithium metal is used for the negative electrode, there is a problem that the lithium metal grows in a dendrite shape during charging and causes an internal short circuit. As a countermeasure, carbon materials capable of absorbing and releasing lithium atoms are being actively developed, and among them, those using coke are considered promising in terms of low cost and high capacity. (Japanese Patent Publication No. 5-3110, Japanese Patent Publication No. 5110)
-17669, Japanese Patent Publication No. 5-44143, Japanese Patent Publication No. 5-50818, Japanese Patent Publication No. 5-78910, Japanese Patent Publication No. 5-80110, and Japanese Patent Publication No. 5-8011.
No. 1, JP-A-62-90863, JP-A-1-
221859 and JP-A-63-1212257).

[0003]

However, when a coke-based carbon material is used as, for example, a negative electrode material of a Li secondary battery, the average potential measured from the oxidation-reduction potential of Li during the discharging process is a graphite-based carbon material. However, there is a problem that the battery voltage becomes lower than that in the case of using. Further, due to the demand for higher capacity of batteries, further increase in capacity is required.

[0004]

Means for Solving the Problems The present inventors have conducted extensive studies to solve the above problems, and as a result, have found that the above problems can be solved by heat treating coal having a specific amount of oxygen. Arrived That is, the gist of the present invention is:
A non-aqueous secondary battery comprising a positive electrode, a negative electrode and an electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent, wherein a non-aqueous secondary battery comprising a positive electrode, a negative electrode and an electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent. In the secondary battery, the carbon content in the elemental analysis according to JIS M8813 is 55 wt% or more, the ash content according to JIS M8812 is 5 wt% or less, and the atomic ratio O / C of oxygen to carbon is 0.03 to.
Coal 0.4 to 800-150 in an inert atmosphere
A non-aqueous secondary battery is characterized in that coke obtained by heat treatment at a temperature of 0 ° C. is used as a negative electrode material.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The carbon content is the carbon content determined by the method specified in JIS M8813, and is a trace component of sulfur,
Phosphorus and carbonate do not have to be quantified, and may represent the content of carbon with respect to carbon, nitrogen, hydrogen and oxygen.
When coal having a low carbon content is used, a large number of fine pores remain in the coke obtained by heat treatment to increase the specific surface area thereof, and particularly in a non-aqueous lithium secondary battery having a high voltage between electrodes, electrolysis is performed. It is not preferable because the irreversible capacity increases due to decomposition of the liquid. The carbon content is 55 wt% or more, more preferably 60 wt% or more. What is ash?
It is determined by the method specified by M8812 and defines the amount of impurities. That is, when the ash content is high, the amount of impurities in the coke, which is heat-treated and used as a negative electrode material, is also increased, which leads to a reversible decrease in capacity. Ash in coal is 5
% Or less, preferably 3% or less.

The atomic ratio of oxygen to carbon, O / C, is obtained by calculating the contents of other elements from the contents of carbon, hydrogen and nitrogen obtained by the usual method, and then subtracting the above ash content. Coal having a low oxygen content is, for example, a method of oxidizing the coal in air at 200 to 400 ° C.,
It may be used by increasing the oxygen concentration. The oxidation treatment includes
Wet treatment using nitric acid, sulfuric acid or a mixed acid thereof can also be used. This patent is not particularly limited by the method of the oxidation treatment, and the main point of this patent is to use coal having an appropriate amount of oxygen or acid-added to an appropriate amount. The atomic ratio O / C of oxygen to carbon is preferably 0.03 or more and 0.4 or less, and more preferably 0.07 or more and 0.3 or less. When the oxygen content is low, the average electric potential becomes high and is the same as the existing coke-based carbon material. On the other hand, if the oxygen content is too high, the average potential again increases and the discharge capacity decreases, which is not preferable.

The heat treatment in an inert atmosphere is not particularly limited as long as it is a method generally used for heat treatment of coke and carbon materials. Examples of the inert gas include nitrogen, argon, helium, and a mixed gas thereof, but nitrogen is preferable for practical purposes. Further, a combustion gas such as natural gas containing carbon dioxide or carbon monoxide as a main component may be used. Further, heat treatment in vacuum can also be used. The heat treatment equipment may be a batch type or a continuous type, using a general electric furnace, a kiln, or the like.

If the temperature of the heat treatment is too low, organic compounds remain and the ratio of the initial discharge capacity to the initial charge capacity decreases,
In addition, the average potential becomes high, and there is no advantage over common coke-based carbon materials. Further, if the heat treatment temperature is too high, the average potential becomes high, and there is no advantage over common coke-based carbon materials. Therefore, the temperature of the heat treatment is 800
-1500 ° C is preferable, and 900-1300 ° C is more preferable. The holding time at the temperature is not particularly limited as long as it is about 10 minutes or more. If the holding time is extremely short, the carbonization reaction is not sufficiently carried out, and coke having an apparently low heat treatment temperature is not preferable. Also, 800 to 150
Within the range of 0 ° C., the holding time may be relatively short if the heating temperature is high, and conversely, if the heating temperature is low, the holding time may be lengthened. In the present invention, the particle size of the coal subjected to the heat treatment at 800 to 1500 ° C. is not particularly limited, but is usually selected from 1 mm or less.

In the present invention, the coating obtained as described above is used.
Cus is used as a negative electrode material for non-aqueous secondary batteries. Positive electrode
And an electrolyte solution prepared by dissolving an electrolyte in a non-aqueous solvent.
As long as it is the one used in the conventional non-aqueous secondary battery,
It is not particularly limited. Specifically, as the positive electrode,
LiCoO₂, MnO₂, TiS₂, FeS₂, Nb _Three
S_Four, Mo_ThreeS_Four, CoS₂, V₂O_Five, P₂O_Five, C
rO_Three, V_ThreeO_Three, TeO₂, GeO₂Etc. are used
You. Above all, LiCoO 2 from the viewpoint of capacity and battery voltage.₂
Is most preferred. As the electrolyte, propylene carbonate
Ite, ethylene carbonate, tetrahydrofuran,
1,2-dimethoxyethane, dimethyl sulfoxide, di
Oxolane, dimethylformamide, dimethylacetoa
Mido and mixed solvents of two or more of these are used
You. Among them, propylene carbonate and other
Most preferred is a mixture with a medium. As the electrolyte, LiC
10_Four, LiBF_Four, LiPE₆Can be used
You.

As the battery constitution, a spiral structure in which a strip-shaped positive electrode and a negative electrode are spirally formed with a separator interposed therebetween, or a method in which a pellet-shaped positive electrode and a disk-shaped negative electrode are inserted into a button-shaped case through a separator is adopted. To be done. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples without departing from the gist thereof.

[0011]

【Example】

[Example 1] Bituminous coal was pulverized to 45 µm or less and then heated at 310 ° C in the atmosphere for oxidation treatment. The elemental analysis and ash content of the obtained coal are measured by "CHN meter 240C" manufactured by Perkin Elma Co., and the carbon content is 71w.
t%, ash content was 2.0 wt%, and O / C was 0.25. Coke obtained by subjecting this to heat treatment at 1100 ° C. for 3 hours in a nitrogen stream was used as a negative electrode material. The X-ray diffraction pattern of this coke measured by the reflection method using CuKα rays is shown in FIG.

Approximately 10 parts as a binder were added to the obtained negative electrode material.
Add wt% PVDF (polyvinylidene fluoride),
After pressure bonding to the SUS316 mesh, heat vacuum dry and test.
It was used as a test electrode. The secondary battery performance is that the counter electrode is made of metallic Li.
Then, 1 mol / L of LiFP was added to the non-aqueous electrolyte solution.₆including
PC (polycarbonate) at room temperature in Ar atmosphere
I went there. In the process of doping the negative electrode material with Li from the counter electrode
For the first charge, first set the current density at the test electrode to 0.5 mA.
/ Cm²Where the inter-electrode potential is 0.01 V
The inter-electrode potential is maintained at 0.01 V and the flowing current is 0.
04mA / cm ²I waited until it decayed below. The first charge
In the first discharge following, the current density at the test electrode was 0.5 mA /
cm²Constant until the inter-electrode voltage reaches 1.5V.
Then, the initial discharge amount was obtained from the total capacity flowing between the electrodes.
The capacity per 1g of negative electrode material excluding binder is the initial discharge amount 3
It was 63 mAh / g. At this time, the voltage between the electrodes is 0 to 0.
The discharge capacity up to 4 V is 234 mAh / g,
Measured from the redox potential of Li with a voltage of 0 to 1.5V
The average discharge potential was 0.37V. Figure 3 shows the discharge curve
Shown in

Example 2 Bituminous coal was pulverized to a size of 45 μm or less, which was then heated at 380 ° C. in the atmosphere for oxidation treatment.
The carbon content measured by the same method as in Example 1 is 64 wt.
%, Ash content was 3.7 wt%, and O / C was 0.32. Coke obtained by subjecting this to heat treatment at 1100 ° C. for 3 hours in a nitrogen stream was used as a negative electrode material. The X-ray diffraction pattern measured by the reflection method using CuKα ray of the coke is shown in FIG.

The battery characteristics were measured by the same method as in Example 1. The capacity per 1 g of the negative electrode material excluding the binder was an initial discharge amount of 329 mAh / g. At this time, the voltage between electrodes is 0 to
The discharge capacity up to 0.4 V was 204 mAh / g, and the average discharge potential measured from the oxidation-reduction potential of Li at an interelectrode voltage of 0 to 1.5 V was 0.38 V.

[Example 3] Bituminous coal was pulverized to 45 µm or less and then heated in the atmosphere for oxidation treatment. The carbon content measured by the same method as in Example 1 was 82 wt% and the ash content was 1.2 wt%. , Coal having an O / C of 0.095 was obtained.
Coke obtained by subjecting this to heat treatment at 1100 ° C. for 3 hours in a nitrogen stream was used as a negative electrode material. The battery characteristics were measured by the same method as in Example 1. Anode material 1 excluding binder
The capacity per gram was 314 mAh / g of initial discharge.
At this time, the discharge capacity when the voltage between electrodes is 0 to 0.4 V is 18
It is 5 mAh / g, and the average discharge potential measured from the oxidation-reduction potential of Li at an interelectrode voltage of 0 to 1.5 V is 0.43.
It was V.

Example 4 A negative electrode material was obtained in the same manner as in Example 3 except that the heat treatment was performed at 900 ° C. for 3 hours. The battery characteristics were measured by the same method as in Example 1. The capacity per 1 g of the negative electrode material excluding the binder was an initial discharge amount of 397 mAh / g. At this time, the discharge capacity when the inter-electrode voltage is 0 to 0.4 V is 180 mAh / g, and the inter-electrode voltage is 0 to 1.5 V.
The average discharge potential measured from the redox potentials of Li was 0.57V.

Comparative Example 1 Coke obtained by preheating the pitch at about 500 ° C. and then heat-treating it at 1100 ° C. in a nitrogen stream was used as a negative electrode material. The battery characteristics were measured by the same method as in Example 1. The capacity per 1 g of the negative electrode material excluding the binder was an initial discharge amount of 265 mAh / g. At this time, the discharge capacity when the voltage between electrodes is 0 to 0.4 V is 137 mA.
It was h / g, and the average discharge potential measured from the oxidation-reduction potential of Li at an inter-electrode voltage of 0 to 1.5 V was 0.48 V. The discharge curve is shown in FIG. [Comparative Example 2] Comparative Example 1 except that the heating temperature was set to 900 ° C.
Same as. The battery characteristics were measured by the same method as in Example 1. The capacity per 1 g of negative electrode material excluding binder is 34
It was 4 mAh / g. At this time, the voltage between the electrodes is 0 to 0.4.
The discharge capacity up to V was 135 mAh / g, and the average discharge potential measured from the oxidation-reduction potential of Li at an interelectrode voltage of 0 to 1.5 V was 0.62 V.

[0018]

According to the present invention, it is possible to provide a non-aqueous secondary battery having a large charge / discharge capacity and a high operating voltage, using low cost coke as a negative electrode material.

[Brief description of drawings]

1 is an X-ray diffraction pattern for showing the structure of coke described in Example 1. FIG. It measured by the reflection method using CuKα ray. The circles are the diffraction lines from Si intentionally mixed to identify the peak position.

FIG. 2 is an X-ray diffraction pattern for showing the structure of coke described in Example 2. It measured by the reflection method using CuKα ray. The circles are the diffraction lines from Si intentionally mixed to identify the peak position.

FIG. 3 shows the relationship between the discharge capacity of the coke described in Example 1 and Comparative Example 1 and the negative electrode potential measured from the Li redox potential. The counter electrode was metallic Li, and the non-aqueous electrolyte solution was 1
PC (polycarbonate) containing mol / L of LiFP ₆ was used and it was performed at room temperature in Ar atmosphere. The current density was 0.5 mA / cm ² .

FIG. 4 is a cross-sectional explanatory diagram of a button type non-aqueous electrolyte secondary battery which is an example of the non-aqueous secondary battery of the present invention.

[Explanation of symbols]

 Reference Signs List 1 negative electrode 2 negative electrode current collector 3 negative electrode can 4 insulating packing 5 positive electrode can 6 positive electrode current collector 7 positive electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruko Machino Inventor Haruko Machino 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Yokohama Research Institute

Claims (1)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, wherein the carbon content is 55 wt% or more in elemental analysis according to JIS M8813. And JIS M881
Obtained by heat-treating coal having a 2N ash content of 5 wt% or less and an atomic ratio O / C of oxygen to carbon of 0.03 to 0.4 at a temperature of 800 to 1500 ° C in an inert atmosphere. A non-aqueous secondary battery, characterized in that the obtained coke is used as a negative electrode material.