JPH10255791A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide negative electrode material which has a high discharge capacity and a low cost, by using coke containing Si which can be obtained by heating a mixture of polymer containing petroleum or coal pitch and Si in a specific temperature range under inert atmosphere. SOLUTION: Negative electrode material is made by coke containing Si which can be obtained by applying heat treatment to a mixture of polysilane shown in a formula at 800-1500 deg.C under inert atmosphere. For another method, the negative electrode material is made by inactive coke which can be obtained by applying heat treatment to pitch containing Si obtainable by removing organic solvent at 800-1500 deg.C under-inert atmosphere after mixing petroleum or coak pitch dissolved in advance in organic solvent and polymer in the formula containing Si dissolved in advance in organic solvent. In the equation, R, R' is substituent of alkyl group or aryl group; R, R' is methyl group or phenyl radical is preferable for R'.

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 particularly suitable for small and lightweight electronic devices.

[0002]

2. Description of the Related Art In recent years, from the standpoint of reducing the size and weight of electronic devices and the like, saving power and protecting the environment, clean non-aqueous batteries, especially lithium secondary batteries, replacing lead-acid batteries and nickel-cadmium batteries have attracted attention and have been put into practical use. Reached. 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, lithium metal atoms are absorbed and
Materials that can be released have been actively developed, and among them, those using coke have been regarded as promising in terms of low cost and high capacity (Japanese Patent Application Laid-Open Nos. 62-90863 and 1-221859). And JP-A-63-121257). On the other hand, carbon materials containing Si obtained by heat treatment of polysiloxane are also considered promising in that they have high charge / discharge capacities (JP-A-5-144474, E.
P06922833A1).

[0003]

However, coal-based or petroleum-based coke is inexpensive, but its discharge capacity is a value proposed as the theoretical capacity of carbon (372 mA).
h / g), which is about half of the above, and reforming to further increase in capacity is desired. On the other hand, S
Although the carbon material containing i has a high discharge capacity, there is a problem that the heating yield is low and the cost is high.

[0004]

Means for Solving the Problems The present invention has been studied variously in order to solve the above-mentioned problems, and has reached the present invention. That is, the gist of the present invention is to provide a non-aqueous secondary battery including a positive electrode, a negative electrode, and a solution in which an electrolyte is dissolved in a non-aqueous solvent, and a mixture of petroleum or coal pitch and a polymer containing Si. From 800 to 15 in an inert atmosphere
A nonaqueous secondary battery characterized in that Si-containing coke obtained by heat treatment at a temperature of 00 ° C. is used as a negative electrode material.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. In the present invention, a Si-containing coke obtained by heat-treating a mixture of a pitch and a Si-containing polymer is used as a negative electrode material. Raw materials for pitch include petroleum heavy oils such as FCC (fluid catalytic cracking) residual oil, EHE oil (by-product of ethylene production by naphtha cracking), atmospheric residual oil, and vacuum residual oil, and coal tar. Can be

The pitch can be prepared from the above-mentioned pitch raw material by any method conventionally used for producing pitch having desired properties, such as distillation, solvent extraction, and a combination of both. As the polymer containing Si, polysilane or the like is used. Preferably, (1)
The substituents R and R 'in the formula are an alkyl group having up to C1 to C4 (methyl group, ethyl group, etc.), or C6 to C1.
Polysilane having an average molecular weight of 500 to tens of thousands including an aryl group up to 4 (phenyl group, naphthyl group, etc.) is used. More preferably, a polysilane having an average molecular weight of 800 to 10,000 or less, including a structure in which the substituents R and R 'are a methyl group, or a structure in which the substituent R is a methyl group and R' is a phenyl group, is used.

[0007]

Embedded image

In the present invention, these pitches and a polymer material containing Si are mixed in a powder or liquid state to obtain a Si-containing pitch. Preferably, the pitch and the polymer containing Si are dissolved in an organic solvent in advance, then mixed, and then the organic solvent is removed to obtain a Si-containing pitch in which Si is uniformly dispersed. Here, the organic solvent is a solvent in which both the pitch and the polymer containing Si are dissolved, and THF, pyridine, aniline, quinoline, or the like is used. Preferably, THF is used as the organic solvent.

In the present invention, 5% by weight of Si is usually contained in a mixture of pitch and a polymer containing Si such as polysilane.
As described above, coke obtained by heat-treating the Si-containing pitch containing 30% by weight or less is used. Preferably, Si is 1
Coke obtained by heat-treating a Si-containing pitch containing 0% by weight or more and 20% by weight or less is used. If the Si content in the Si-containing pitch is less than 5% by weight, the rate of improvement in the discharge capacity is small, which is not preferable.

The production of coke by heat treatment of pitch is as follows.
Most simply, the pitch is 800-150 in an inert atmosphere.
It can be performed by heat treatment at 0 ° C. 80
If coke produced at a temperature lower than 0 ° C. is used as the negative electrode material, the ratio of the charge / discharge capacity after the second charge to the initial charge capacity becomes small. Conversely, if a material coked at a high temperature exceeding 1500 ° C. is used as the negative electrode material, the charge capacity decreases. A preferred heat treatment temperature is 1000 to 1400 ° C.

The time required for the heat treatment varies depending on the heat treatment temperature, but is usually 10 minutes or more, preferably 20 minutes to 10 hours after the pitch is coked. Generally, the higher the heat treatment temperature, the shorter the heat treatment time. As the inert gas forming the inert atmosphere, nitrogen, argon,
Helium or the like is used, but usually nitrogen is used.

The production of coke by heat treatment of pitch is as follows.
Pitch pitch below 650 ° C, usually 400-650 ° C
Pre-heat treatment to at least partially carbonize the pitch, then at 800-1500 ° C., preferably 1000-1000 ° C.
A method of performing heat treatment at 1400 ° C. can also be used. According to this method, since the pitch is solidified by the preliminary heat treatment, the subsequent heat treatment at a high temperature becomes easy. Also, since part of the pitch decomposition reaction has already progressed in the preliminary heat treatment,
The coke yield in the heat treatment at a high temperature is improved. Therefore, heat treatment equipment at a high temperature can be reduced. When carbonized by the preliminary heat treatment, it is preferable that the carbide is pulverized to a maximum particle size of 1 mm or less and then subjected to heat treatment at a high temperature. Generally, the performance of the negative electrode finally obtained is often improved by this pulverization. Preferably,
After pulverizing to a maximum particle size of 100 μm or less, particularly 50 μm or less, it is subjected to a heat treatment at a high temperature.

[0013] The Si-containing coke prepared in this manner uses a low-cost pitch as a raw material.
There is an advantage that the polymer containing Si can be manufactured at a lower cost than when heat-treated as it is. Further, this Si-containing coke is different from a simple mixture (1) in which coke obtained by heat-treating the pitch and carbon obtained by heat-treating the Si-containing polymer are mixed at an arbitrary ratio.
That is, in the X-ray diffraction pattern shown in FIG.
The d002 peak of carbon of i-containing coke is much broader than that of coke without Si, and is not a mere composite peak of the mixture (1). Therefore, it is presumed that mixing the Si-containing polymer before the pitch heat treatment not only adds Si to the coke, but also changes the carbon structure of the coke. On the other hand, Si in coke is not crystalline Si, SiC, or SiO _{2 as} can be seen from the X-ray diffraction pattern.

According to the present invention, 6
Coke that has been heat-treated at 50 to 1500 ° C. is used as a negative electrode material.
Except that the non-aqueous electrolyte secondary battery is
Can be manufactured. For example, as the positive electrode material, Li
CoO_Two, MnO_Two, TiS _Two, FeS_Two, Nb
_ThreeS_Four, Mo_ThreeS_Four, CoS_Two, V_TwoO_Five, P_TwoO_Five,
CrO_Three, V_ThreeO_Three, TeO_Two, GeO_TwoEtc. are used
It is. As the electrolyte, LiClO_Four, LiBF
_Four, LiPF₆And the like. these
Non-aqueous solvents that dissolve the electrolyte include propylene
Nate, tetrahydrofuran, 1,2-dimethoxyethane
Dimethylsulfoxide, dioxolane, dimethylphos
Lumamide, dimethylacetamide and their two
The above mixed solvents and the like are used. For example, according to the present invention,
The coke provided is used as a negative electrode material, and LiCoO_TwoTo
Propylene carbonate and 1,2-dimethyl
LiPF in mixed solvent with toxicethane₆What dissolved
Batteries with an electrolyte as one of the most preferred
You.

As a separator for separating the positive electrode and the negative electrode, a non-woven fabric made of polypropylene or the like or a porous body made of an organic solvent-resistant material such as a glass filter is used to reduce the internal resistance of the battery. The battery has a spiral structure in which a belt-shaped positive electrode and a negative electrode are spirally stacked with a separator interposed therebetween, or a button-shaped battery case, a pellet-shaped positive electrode and a disk-shaped negative electrode, and a separator. Any structure that is commonly used, such as a structure that is housed via a cable, can be used.

[0016]

【Example】

(1) Preparation of Si-Containing Coke Example 1 A coal tar pitch (A) having a Mettler softening point of 98 ° C., a toluene-insoluble content of 40%, and a quinoline-insoluble content of 0% was put in a flask and degassed at 110 ° C. under reduced pressure for 30 minutes. , THF after cooling
Was added and mixed to obtain a THF-dissolved pitch. Polymethylphenylsilane (B) having an average molecular weight of 3940 synthesized from methylphenyldichlorosilane was placed in a flask, and T
HF was added and mixed to obtain THF-dissolved polymethylphenylsilane. The weight ratio of (A) and (B) is 1.34 to 1 (S
i weight / (A + B) = 10 wt%), and the mixture was stirred for 2 hours.
A contained pitch was obtained. 1000 ° C in an argon stream
For 2 hours to obtain Si-containing coke. The yield before and after the heat treatment at this time was 56%.

Example 2 Instead of (B) in Example 1, polymethylphenylsilane (C) having an average molecular weight of 1300 was used, and (A) and (C) were used.
Is 2.68 to 1 (Si weight / (A + C) = 5w)
t%), except that the mixture was prepared in the same manner as in Example 1. The yield before and after the heat treatment at this time was 53%.

Example 3 Instead of (B) in Example 1, dimethylsilane (D) synthesized from dimethyldichlorosilane was used, and the weight ratio between (A) and (D) was 1.42 to 1 (Si weight / (A + D)
= 20 wt%), except that the mixture was prepared in the same manner as in Example 1. The yield before and after the heat treatment was 4
8%.

Example 4 A poly (dimethyl / methylphenyl [composition ratio: 12:88]) silane random copolymer (E) having an average molecular weight of 8,800 synthesized from dimethyldichlorosilane and methylphenyldichlorosilane was used, and (A) ) And (E) were prepared in the same manner as in Example 1 except that they were mixed so that the weight ratio was 1.64 to 1 (Si weight / (A + E) = 10 wt%). The yield before and after the heat treatment at this time was 56%.

Example 5 An Si-containing pitch prepared in the same manner as in Example 3 was heat-treated at 1200 ° C. for 2 hours in an argon stream to obtain a Si-containing coke. At this time, the yield before and after the heat treatment was 32%. Example 6 The Si-containing pitch prepared in the same manner as in Example 3 was heated at 1400 ° C. for 2 hours in an argon stream to obtain a Si-containing coke. At this time, the yield before and after the heat treatment was 36%.

Example 7 Using a polymethylphenylsilane (E) having an average molecular weight of 1430, a Si-containing pitch prepared in the same manner as in Example 1 was heated at 1400 ° C. for 2 hours in an argon stream to obtain a Si-containing pitch. Got coke. At this time, the yield before and after the heat treatment was 46%.

(1) Preparation of coke with no Si added Comparative Example 1 The same coal tar pitch (A) as in Example 1 was heat-treated at 1000 ° C. for 2 hours in an argon stream to obtain coke. Comparative Example 2 The same coal tar pitch (A) as in Example 1 was heated at 1200 ° C. for 2 hours in an argon stream to obtain coke. Comparative Example 3 The same coal tar pitch (A) as in Example 1 was heat-treated at 1400 ° C. for 2 hours in an argon stream to obtain coke.

(2) Battery Evaluation of Negative Electrode Material The Si-containing coke obtained in Examples 1 to 7 and the Si-free coke obtained in Comparative Examples 1 to 3 were each replaced by 45%.
Approximately 10 wt% as a binder after grinding to micron or less
Of PVDF (polyvinylidene fluoride)
After pressure-bonding to a 316 mesh, it was heated and dried under vacuum to form a test electrode. Secondary battery performance, the opposite electrode is metal Li,
PC containing 1 mol / L LiFP ₆ in non-aqueous electrolyte
This was performed at room temperature in an Ar atmosphere using (polycarbonate). In the initial charge, which is the process of doping Li into the negative electrode material from the counter electrode, first, the current density at the test electrode is set to 0.5 mA / c.
m ² , and when the potential between the electrodes becomes 0.01 V, the potential between the electrodes is maintained at 0.01 V.
It waited until it decreased to mA / cm ² or less. In the initial discharge following the initial charge, the current density at the test electrode is 0.5 mA / cm.
² and waited until the voltage between the electrodes reached 1.5 V, and the initial discharge amount was determined from the total capacity flowing between the electrodes. The results are shown in Table 1. The initial discharge capacity is a value per 1 g of coke.

(3) Analysis of negative electrode material The Si-containing coke obtained in Examples 1 and 3 and the Si-free coke obtained in Comparative Example 1 were subjected to CuKα radiation at 2θ = 3 ° to 90 °. X-ray diffraction measurement was performed on the range by a reflection method. The results are shown in FIG. In all samples, peaks of Si, SiC, and SiO ₂ were not observed in the X-ray diffraction patterns. At the same heat treatment temperature, the d002 peak of carbon of Examples 1 and 3 was broader than the peak of Comparative Example 1.

[0025]

[Table 1]

[0026]

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

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view of a button-type nonaqueous electrolyte secondary battery which is an example of the nonaqueous secondary battery of the present invention.

FIG. 2 shows the results of X-ray diffraction measurement of the Si-containing coke obtained in Examples 1 and 3 and the coke without Si added obtained in Comparative Example 1 by a reflection method using CuK lines.

[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

Claims (6)

[Claims] In a non-aqueous secondary battery comprising a positive electrode, a negative electrode and a solution in which an electrolyte is dissolved in a non-aqueous solvent, a mixture of petroleum-based or coal-based pitch and a polymer containing Si is used. 800 to 1500 in an active atmosphere
A non-aqueous secondary battery characterized by using, as a negative electrode material, Si-containing coke obtained by heat treatment at a temperature of ° C. 2. 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, comprising: a petroleum-based or coal-based pitch previously dissolved in an organic solvent; After mixing the polymer containing Si dissolved in water, the Si-containing pitch obtained by removing the organic solvent is mixed in an inert atmosphere at 800
A non-aqueous secondary battery using a Si-containing coke obtained by heat treatment at a temperature of about 1500 ° C. as a negative electrode material. 3. A polymer containing Si is represented by the following formula (1):
3. The non-aqueous secondary battery according to claim 1, wherein the non-aqueous secondary battery is a polysilane having the following structure. 4. Embedded image 4. A mixture of pitch and polysilane (Si-containing pitch) containing Si (Si weight / [pitch weight + polysilane weight] × 100) in an amount of 5% by weight or more and 30% by weight or less. The non-aqueous secondary battery according to claim 3. 5. The non-aqueous secondary battery according to claim 4, wherein the non-aqueous secondary battery is a polysilane having a structure in which the substituents R and R ′ in the formula (1) are methyl groups. 6. The non-aqueous secondary battery according to claim 4, wherein the polysilane is a polysilane having a structure in which the substituent R in the formula (1) is a methyl group and R ′ is a phenyl group.