JPH08250154A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery which has high capacity and long cycle life by using a specific compound as negative electrode material. CONSTITUTION: This lithium secondary battery comprises a negative electrode 6, a positive electrode 4 placed to sandwich a separator 5 between it and the negative electrode 6, and a nonaqueous electrolyte, all of which are enclosed in a container 1. At least one kind selected from a condensed aromatic compound, a petroleum type pitch containing the condensed aromatic compound, and a coal type pitch containing the compound is dehydrogenation condensed in the presence of a Lewis acid catalyst to form a precursor. The negative electrode contains a polymerized condensed aromatic compound which stores and releases lithium ions and which can be obtained when the precursor is heated at 400 to 800 deg.C in an inert gas atmosphere or a vacuum atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having an improved negative electrode structure.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries. Non-aqueous electrolyte primary batteries using manganese dioxide (MnO ₂ ), fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl ₂ ) etc. as positive electrode active materials have already been used as backups for calculators, clock power supplies and memories. It is often used as a battery.

Further, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, the demand for high energy density secondary batteries as their power source has increased, and lithium secondary batteries using lithium as a negative electrode active material. Batteries are being actively researched.

A lithium secondary battery is a negative electrode such as metallic lithium; propylene carbonate (PC), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-BL),
LiC in a non-aqueous solvent such as tetrahydrofuran (THF)
electrolytes such as non-aqueous electrolytes and lithium ion conductive solid electrolytes in which lithium salts such as 10 ₄ , LiBF ₄ and LiAsF ₆ are dissolved; and mainly TiS ₂ , MoS ₂ , V ₂ O
_The use of positive electrode active materials such as compounds that undergo a topochemical reaction with lithium such as ₅ , V ₆ O ₁₃ , and MnO ₂ has been studied.

However, the lithium secondary battery described above has not yet been put into practical use. The main reason for this is that the charging / discharging efficiency is low and the number of times charging / discharging is possible (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the metallic lithium of the negative electrode and the non-aqueous electrolyte. That is, the lithium dissolved in the non-aqueous electrolytic solution as lithium ions during discharging reacts with the solvent of the electrolytic solution when deposited on the surface of the lithium negative electrode during charging, and the negative electrode surface is partially inactivated. For this reason, when charge and discharge are repeated, lithium is deposited on the surface of the negative electrode in the form of dendrites (dendritic) or small spheres,
Furthermore, phenomena such as desorption of lithium from the current collector occur.

In view of the above, a lithium secondary battery provided with a negative electrode containing a carbonaceous substance that absorbs and releases lithium ions, such as coke, a resin fired body, carbon fiber, and pyrolysis vapor-phase carbon, has been proposed. ing. In such a secondary battery, since the negative electrode is configured to include a carbonaceous material, the surface of the negative electrode is suppressed by suppressing reaction with the solvent of the electrolytic solution when lithium ions are deposited on the negative electrode surface during charging. It is possible to prevent partial inactivation. As a result, the deterioration of the negative electrode characteristics due to the deposition of dendride can be improved. However, since the negative electrode containing the carbonaceous material has a small amount of insertion and extraction of lithium ions, it has a negative electrode specific capacity (unit: mA).
h / g or mAh / cm ³ ) becomes small. Moreover,
Increasing the storage capacity of lithium ions, that is, increasing the charging capacity, for example, deteriorates the structure of carbonaceous material,
The phenomenon that the solvent in the non-aqueous electrolyte is decomposed occurs. further,
When the charging current is increased, the storage amount of lithium ions decreases, and lithium metal is deposited on the surface of the negative electrode. Therefore, the cycle life of the lithium secondary battery incorporating the negative electrode is reduced.

On the other hand, in recent years, it has been attempted to use a fired body of a π-electron conjugated polymer such as polyacene as a negative electrode material of a lithium secondary battery. However, the lithium secondary battery in which the negative electrode including the fired body is incorporated has a low capacity, and there is a problem that the cycle life is shortened when the capacity is increased.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having a high capacity and a long cycle life.

[0009]

A lithium secondary battery according to the present invention comprises a fused aromatic ring compound, a petroleum-based pitch containing the fused aromatic ring compound or a coal-based pitch containing the same, which is housed in a container. A polymerized condensed aroma that absorbs and releases lithium ions obtained by dehydrogenative condensation in the presence of a Lewis acid catalyst to produce a precursor, which is heat-treated at 400 to 800 ° C. in an inert gas atmosphere. It is characterized in that it comprises a negative electrode containing a ring compound, a positive electrode housed in the container and arranged with the separator sandwiched in the negative electrode, and a non-aqueous electrolyte solution housed in the container. .

Another lithium secondary battery according to the present invention is
It is housed in a container and the carbon body (00
2) It has a peak corresponding to diffraction, the average interlayer distance d ₍₀₀₂₎ obtained from the diffraction is 0.39 nm or less, and has absorption due to aromatic ring skeleton vibration at around 1600 cm ^{-1 in} infrared spectroscopy, the absorption strength and the intensity of the absorption peak due to the aromatic ring surface outside deformation vibration respectively I _a, when the I _B, meets _{0 ≦ I B / I a ≦} 2 relationship is further true density 1.2 A negative electrode containing a polymerized condensed aromatic ring compound that absorbs and releases lithium ions of 2.0 g / cm ³ , a positive electrode that is housed in the container and is sandwiched between the negative electrode and a separator, and the inside of the container And a non-aqueous electrolytic solution housed in.

Hereinafter, a lithium secondary battery (eg, a cylindrical lithium secondary battery) according to the present invention will be described in detail with reference to FIG. The bottomed cylindrical container 1 has an insulator 2 at the bottom.
Is arranged. The electrode group 3 is housed in the container 1. The electrode group 3 has a structure in which a band-shaped material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound so that the negative electrode 6 is located outside.

An electrolytic solution is contained in the container 1. The insulating paper 7 having a central opening is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is
The sealing plate 8 is arranged in the upper opening of the container 1 and the vicinity of the upper opening is caulked inward.
Is liquid-tightly fixed to the container 1. The positive electrode terminal 9 is
It is fitted in the center of the insulating sealing plate 8. Positive electrode lead
One end of the battery 10 is connected to the positive electrode 4 and the other end is connected to the positive electrode terminal 9
Respectively connected to. The negative electrode 6 is connected to the container 1, which is a negative electrode terminal, via a negative electrode lead (not shown).

The container 1 is made of, for example, stainless steel. The positive electrode 4 is prepared by suspending a conductive agent and a binder in a positive electrode active material in an appropriate solvent, applying the suspension to a current collector, and drying the suspension to form a thin plate.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Examples thereof include lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium cobalt oxide (LiCoO
₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ , LiMnO ₂ )
Is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black and graphite. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
E), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and the like can be used.

Examples of the current collector include aluminum foil, stainless steel foil, nickel foil, expanded metal,
A metal net or the like can be used. The separator 5
For example, a synthetic resin non-woven fabric, a polyethylene porous film, a polypropylene porous film, or the like can be used.

The negative electrode 6 is a condensed polymer aromatic ring compound (1) which absorbs and releases lithium ions as described below,
Including (2). Polymer condensed aromatic ring compound (1) This polymer condensed aromatic ring compound is a fused aromatic ring compound, a petroleum-based pitch containing the condensed aromatic ring compound, and a coal-based pitch containing the same compound. It is obtained by dehydrogenative condensation in the presence of an acid catalyst to produce a precursor, which is heat-treated at 400 to 800 ° C. in an atmosphere of an inert gas such as Ar, He or N ₂ or a vacuum atmosphere.

As the condensed aromatic ring compound, for example, naphthalene, anthracene, phenanthrene, naphthalene, pyrene, perylene, ovalen, acenaphthylene and the like can be used. Such fused aromatic ring compounds, petroleum-based pitches containing the same compounds and coal-based pitches containing the same compounds (hereinafter referred to as raw materials) may be used alone or in 2
It is used in the form of a mixture of one or more kinds.

Examples of the Lewis acid catalyst include AlC
l ₃ , AlBr ₃ , GaBr ₃ , GaCl ₃ , FeCl
₃ , SbCl ₅ , SnCl ₄ , TiCl ₄ , ZnCl
₂ , MoCl ₅ , or HF, which is a protonic acid, H ₂ S
Examples thereof include O ₄ and H ₃ PO ₄ . These Lewis acid catalysts may be used alone or in the form of a mixture of two or more kinds. When using the Lewis acid catalyst, CuCl
It is permissible to use an oxidizing agent such as ₂ .

The dehydrogenative condensation is carried out by mixing the raw material with a Lewis acid catalyst or mixing the raw material with a Lewis acid catalyst in an organic solvent such as nitrobenzene, CS ₂ or benzene. It

The dehydrogenative condensation is performed at 20 ° C. or higher and 400 ° C.
Preference is given to carrying out at temperatures below. The reaction temperature is 20
When the temperature is lower than 0 ° C, the rate of dehydrogenative condensation reaction is low, the degree of condensation of the obtained polymerized condensed aromatic ring compound is low, and the capacity and cycle life of a battery including a negative electrode containing the compound may be reduced. is there. On the other hand, if the reaction temperature is 40
If the temperature is higher than 0 ° C, the Lewis acid catalyst may be decomposed and the dehydrogenative condensation reaction may not be sufficiently performed. The more preferable temperature during the dehydrogenative condensation is 80 to 200 ° C.

The product after the dehydrogenative condensation is preferably washed with water, an acid, an aqueous acid solution or an alkaline aqueous solution to remove the Lewis acid catalyst before being heated in an inert gas atmosphere or a vacuum atmosphere.

The heat treatment temperature of the product after the dehydrogenative condensation is specified for the following reason. When the heat treatment temperature is lower than 400 ° C., unreacted substances or impurities in the polymerized condensed aromatic ring compound remain. For this reason, the capacity and cycle life of the secondary battery provided with the negative electrode containing the polymerized condensed aromatic ring compound are reduced.
Further, the heat treatment is carried out in order to further promote the dehydrogenative condensation of the product, but when the temperature is lower than 400 ° C., the dehydrogenative condensation becomes difficult to occur. On the other hand, when the heat treatment temperature exceeds 800 ° C., carbonization is promoted and the aromatic ring characteristics of the polymerized condensed aromatic ring compound are lost. For this reason, the capacity and cycle life of the secondary battery provided with the negative electrode containing the polymerized condensed aromatic ring compound are reduced. A more preferable heat treatment temperature is 500 to 700 ° C.

Polymeric substance (2) This polymerized condensed aromatic ring compound has the following (a) to (a)
It has the properties and structure of (c).

(A) In the X-ray diffraction method, 2θ is 16 to 3
There is a peak corresponding to the (002) diffraction of the carbon body in the range of 0 °, and the average interlayer distance d ₍₀₀₂₎ obtained from the diffraction.
Is 0.39 nm or less.

(B) 1600 cm ^-1 in infrared spectroscopy
There is absorption due to the vibration of the aromatic ring skeleton in the vicinity, and the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively, where 0 ≦ I _B / I _A ≦ 2. Meet

(C) True density is 1.2 to 2.0 g / cm ^3.
Is. The property (a) is defined for the following reason. A substance having almost no three-dimensional orientation, such as graphite, does not have a clear (002) diffraction peak. Such a substance having an amorphous structure impedes the movement of lithium ions, so that the battery including the negative electrode containing the substance has a reduced cycle life and a reduced voltage. In addition, the average interlayer distance d obtained by the X-ray diffraction method
_{When (002)} exceeds 0.39 nm, the true density of the negative electrode containing the polymerized condensed aromatic ring compound decreases, and the capacity per volume decreases.

The property (b) is defined for the following reason. When absorption by the aromatic ring skeleton vibration is no longer observed in the vicinity of 1600 cm ^{−1 in the} polymerized condensed aromatic ring compound by infrared spectroscopy, the capacity of the battery including the negative electrode containing the polymerized condensed aromatic ring compound decreases. To do. This is because a graphite structure is generated by carbonization (graphitization) of the polymerized condensed aromatic ring compound. On the other hand, in the polymerized condensed aromatic ring compound, when the number of condensed aromatic rings is low, the conductivity is decreased and the storage capacity of lithium ions is also decreased. Therefore, a negative electrode including the polymerized condensed aromatic ring compound was provided. Batteries have reduced capacity and cycle life. In such a polymerized condensed aromatic ring compound, the amount of hydrogen bonded to the aromatic ring is large, so that the above I _B / I _A becomes large. _A battery provided with a negative electrode containing a polymerized condensed aromatic ring compound exhibiting an infrared absorption spectrum of I _B / I _A of 2 or less has excellent capacity and cycle life. More preferable I _B / I _A is 0 ≦ I _B / I _A ≦ 0.95.

The property (c) is defined for the following reason. When the true density of the polymerized condensed aromatic ring compound is less than 1.2 g / cm ³ , the packing density of the polymerized condensed aromatic ring compound in the negative electrode is reduced, and the capacity of the battery including the negative electrode is decreased. Can not be improved. On the other hand, when the true density of the polymerized condensed aromatic ring compound exceeds 2.0 g / cm ³ , diffusion of lithium ions in the negative electrode containing the polymerized condensed aromatic ring compound is hindered, and the battery provided with the negative electrode. It becomes impossible to improve the capacity and cycle life. A more preferable true density is
It is 1.4 to 1.8 g / cm ³ .

The polymerized condensed aromatic ring compound (1),
It is preferable that (2) has a specific surface area of 500 m ² / g or less measured by the BET method. Since the negative electrode containing the polymer substance having such a specific surface area has a reduced reactivity with the non-aqueous electrolyte, the secondary battery including the negative electrode is charged / discharged with high efficiency.
The capacity and cycle characteristics are improved. More preferable specific surface areas of the polymerized condensed aromatic ring compounds (1) and (2) are
It is 1 to ²⁰ m ² / g.

The polymerized condensed aromatic ring compound (1),
(2) is preferably contained in the negative electrode 6 in the form of particles or fibers. Such particles have an average particle size of 3
It is preferably ˜100 μm. The fibers preferably have an average diameter of 3 to 100 μm.

The negative electrode 6 is prepared by mixing the polymerized condensed aromatic ring compounds (1) and (2) with a binder and applying the mixture to a current collector. Examples of the binder include polytetrafluoroethylene (PTFE),
Polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (C
MC) or the like can be used.

As the current collector, for example, copper foil, stainless foil, nickel foil or the like can be used. The non-aqueous electrolytic solution contained in the container 1 is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane and diethyl ether. , Tetrahydrofuran, 2-
Methyl tetrahydrofuran etc. can be mentioned. The non-aqueous solvent may be used alone or in combination of two or more.

As the electrolyte contained in the non-aqueous electrolyte, for example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenide hexafluoride ( LiAsF
₆ ), lithium trifluorometasulfonate (LiCF
₃ SO ₃ ), lithium salt (electrolyte) such as bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ] and the like. Above all, LiPF ₆ , LiB
It is preferable to use F ₄ and LiN (CF ₃ SO ₂ ) ₂ . In particular, when LiN (CF ₃ SO ₂ ) ₂ is used, there is little reaction with the positive electrode active material at high temperature (for example, 60 ° C.), and excellent charge / discharge cycle characteristics can be obtained at high temperature. In addition, it has the advantage that it is stable with respect to the polymer substance and that the cycle life is improved. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / l.

[0036]

According to the present invention, at least one selected from a condensed aromatic ring compound, a petroleum pitch containing the condensed aromatic ring compound and a coal pitch containing the same is dehydrogenated in the presence of a Lewis acid catalyst. To produce a precursor, which is then treated with an inert gas atmosphere or a vacuum atmosphere, 400 to 800
A negative electrode containing a polymerized condensed aromatic ring compound that absorbs and releases lithium ions, which is obtained by heat treatment at ℃;
In the X-ray diffraction method, 2θ has a peak corresponding to (002) diffraction of the carbon body in the range of 16 to 30 °, the average interlayer distance d ₍₀₀₂₎ obtained from the diffraction is 0.39 nm or less, and the red In the external spectroscopy, it has an absorption due to the aromatic ring skeleton vibration near 1600 cm ^-1 , and the intensity of this absorption and the intensity of the absorption peak due to the aromatic ring out-of-plane bending vibration are respectively I _A ,
When the _{I B, 0 ≦ I B /} I A ≦ 2 of satisfying the relationship, further true density polymerized fused aromatic ring compound lithium ions absorbing and releasing a 1.2~2.0g / cm ³ It is possible to provide a lithium secondary battery having a high capacity and a long cycle life by including the negative electrode including the.

That is, a conventional carbonaceous material used in a lithium secondary battery has a graphite layered structure shown in the chemical formula 1 below, and lithium ions are inserted / released between the graphite layers. Therefore, the storage amount of lithium ions is stoichiometrically one lithium atom is bonded to six carbon atoms (LiC ₆ ) and no more is bonded. Therefore, when a carbonaceous material having a graphite layered structure is used as a negative electrode material of a lithium secondary battery, the capacity (mAh / g) of the negative electrode is the theoretical limit value of graphite (372 mAh / g).
g) cannot be exceeded.

[0038]

Embedded image

On the other hand, naphthalene (C ₁₀ H ₈ ) which is a condensed aromatic ring compound reacts with metal Li in an organic solvent to form a charge transfer complex with lithium ions. At this time, one molecule of naphthalene combines with two lithium ions to form C ₁₀ H ₈ ^2-
-Forms Li ₂ ²⁺ . This suggests that in a fused aromatic ring compound such as naphthalene, one lithium ion is bonded to each aromatic ring.

Naphthalene cannot be used as a negative electrode of a lithium secondary battery because it has no conductivity, but a polymerized condensed aromatic ring compound having a large number of two-dimensionally condensed aromatic rings is conductive or semiconductive. To show sex. Further, assuming that one lithium ion is bonded to one aromatic ring in the condensed aromatic ring compound, the theoretical limit is higher for a negative electrode containing a polymerized condensed aromatic ring compound having a larger number of condensed aromatic rings as shown in Chemical formula 2 below. Larger capacity. as a result,
The polymerized condensed aromatic ring compound, which is the negative electrode material used in the secondary battery of the present invention, can remarkably increase the storage amount of lithium ions as compared with the conventional carbonaceous material. Further, since the polymerized condensed aromatic ring compound is composed of an aromatic 6-membered ring, it is chemically stable.

[0041]

Embedded image

Furthermore, when the number of condensed aromatic rings in the polymerized condensed aromatic ring compound is small, not only the capacity of the negative electrode is decreased, but also the conductivity is decreased due to the small π-electron conjugated system. The voltage characteristics and the cycle life of the secondary battery including the negative electrode containing the condensed aromatic ring compound are reduced.
On the other hand, when the number of condensed aromatic rings in the polymerized condensed aromatic ring compound is too large, it has a two-dimensional spread like graphite. In such a polymerized condensed aromatic ring compound, repulsion between lithium ions is increased, so that one lithium cannot be bonded to the aromatic ring 1, and a negative electrode including the polymerized condensed aromatic ring compound is provided. The capacity of the secondary battery decreases. Further, the above-mentioned polymerized condensed aromatic ring compound has a large absorption of the visible light of the conjugated system and spreads to the infrared region, so that the absorption due to the vibration of the aromatic ring skeleton is not seen in the infrared spectroscopy.

Therefore, at least one selected from the condensed aromatic ring compound, the petroleum-based pitch containing the condensed aromatic ring compound and the coal-based pitch containing the same is subjected to dehydrogenative condensation in the presence of a Lewis acid catalyst to give a predetermined amount. The polymerized condensed aromatic ring compound (1) obtained by heating at a specific temperature in the atmosphere or the polymerized condensed aromatic ring compound (2) having the above-mentioned properties (a) to (c). ) Has a low degree of graphitization and has an appropriate number of condensed aromatic rings, so that the storage amount of lithium ions is significantly increased. As a result, the polymerized condensed aromatic ring compound (1),
The lithium secondary battery including the negative electrode including (2) has a high capacity and a long cycle life.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to FIG. Example 1 <Production of Positive Electrode> First, lithium cobalt oxide (Li _x
80% by weight of CoO ₂ (0.8 ≦ x ≦ 1) powder was mixed with 15% by weight of acetylene black and 5% by weight of polytetrafluoroethylene to form a sheet, which was then pressure-bonded to a collector made of expanded metal. A positive electrode was produced.

<Preparation of Negative Electrode> First, 500 g of anthracene (molecular weight 178) was mixed with 100 g of anhydrous aluminum chloride, and heated at 120 ° C. for 5 hours in a nitrogen atmosphere to obtain a black solid substance. Then, this solid is 20
After pulverizing to 0 μm or less, washing with water was repeated 5 to 6 times to obtain a brown powder. This brown powder in Ar stream, 5
By heating at 00 ° C. for 5 hours, 200 g of a black powder was obtained.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the spectrum diagram shown in FIG. 2 was obtained. From FIG. 2, the black powder is 160
There is absorption due to the aromatic ring skeleton vibration near 0 cm ⁻¹ , and when the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively, I _B / I _A is 1. 9
It was confirmed to be a high molecular weight condensed aromatic ring compound of 2. Further, the X-ray diffraction spectrum of the black powder was measured. As a result, the spectrum diagram shown in FIG. 3 was obtained.
From FIG. 3, the black powder had a peak corresponding to carbon (002) diffraction in the range of 2θ of 16 to 30 °, and had an average interlayer distance d ₍₀₀₂₎ of 0.369 nm. Furthermore, the black powder had specific surface areas and true densities of 3.5 m ^{2 /} g and 1.6 g / cm ³ as measured by the BET method. 98% by weight of particles having an average particle size of 10 μm obtained by crushing the black powder (polymerized condensed aromatic ring compound) having such characteristics
Was mixed with 2% by weight of ethylene propylene copolymer,
This was applied to stainless steel as a current collector and dried to prepare a negative electrode.

The positive electrode, the separator made of a polyethylene porous film, and the negative electrode were laminated in this order, and then spirally wound so that the negative electrode was located outside to prepare an electrode group.

Further, lithium hexafluorophosphate (LiP
F ₆ ) is a mixed solvent of propylene carbonate, ethylene carbonate and dimethoxyethane (mixing volume ratio 25:
25:50) and dissolved in 1.0 mol / 1 to prepare a non-aqueous electrolyte.

The electrode group and the electrolytic solution were respectively housed in a stainless steel cylindrical container having a bottom, and the cylindrical lithium secondary battery shown in FIG. 1 was assembled. (Example 2) First, anthracene (molecular weight 178) 50
100 g of anhydrous aluminum chloride and 50 g of anhydrous copper chloride (CuCl ₂ ) were mixed with 0 g, and the mixture was added to 200 g under a nitrogen atmosphere.
A black solid was obtained by heating at ℃ for 5 hours. Subsequently, this solid was ground in a boiling 30% hydrochloric acid aqueous solution and then washed four times in a 30% hydrochloric acid aqueous solution to obtain a black powder. This black powder is placed in an Ar stream at 600
By heating at 5 ° C. for 5 hours, 315 g of a black powder was obtained.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the spectrum diagram shown in FIG. 4 was obtained. From FIG. 4, the black powder is 160
There is absorption due to the aromatic ring skeleton vibration near 0 cm ⁻¹ , and when the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively, I _B / I _A is 1. 6
It was confirmed to be a high molecular weight condensed aromatic ring compound of 2. In addition, the X-ray diffraction spectrum of the black powder was measured, and as a result, 2θ was in the range of 16 to 30 °, the carbon (00
2) A peak corresponding to diffraction was recognized. From this peak, the average inter-layer distance d ₍₀₀₂₎ of the black powder was 0.372n.
m was confirmed. Further, the black powder is B
Specific surface area and true density by ET method are 2.2m each
It was ^{2 /} g and 1.7 g / cm ³ .

Example 1 was carried out by using the particles obtained by crushing the black powder (polymerized condensed aromatic ring compound) and having an average particle size of 8 μm.
A negative electrode was produced in the same manner as in. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Example 3 First, liquid petroleum pitch 1 having an infrared absorption spectrum shown in FIG. 5 in infrared spectroscopy
30 g of anhydrous aluminum chloride was mixed with 00 g, and heated at 150 ° C. for 5 hours in a nitrogen atmosphere to obtain a black rubber-like substance. Subsequently, 300 ml of concentrated sulfuric acid was added to this black rubber-like substance, the mixture was stirred at room temperature, and then 300 ml of water was added to precipitate a black powder. The black powder was separated by filtration, washed with water until the pH became 5 to 7, and then heated in an Ar stream at 600 ° C. for 5 hours to obtain a black powder.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the spectrum diagram shown in FIG. 6 was obtained. From FIG. 6, the black powder is 160
There is absorption due to the aromatic ring skeleton vibration near 0 cm ⁻¹ , and when the intensity of this absorption and the absorption peak intensity due to the aromatic ring out-of-plane bending vibration are I _A and I _B , respectively, I _B / I _A is 0. 8
It was confirmed that the polymerized polycyclic aromatic ring compound was No. 5. In addition, the X-ray diffraction spectrum of the black powder was measured, and as a result, 2θ was within the range of 20 to 30 °.
2) A peak corresponding to diffraction was observed, and the average interlayer distance d
₍₀₀₂₎ was 0.381 nm. Further, the black powder had specific surface areas and true densities of 3.5 m ^{2 /} g and 1.4 g / cm ³ according to the BET method.

A negative electrode was prepared in the same manner as in Example 1 by using the above-mentioned black powder (polymerized condensed aromatic ring compound) pulverized and using particles having an average particle diameter of 12 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Example 4 First, 100 g of liquid petroleum pitch similar to that of Example 3 was mixed with 30 g of anhydrous aluminum chloride and 15 g of anhydrous copper chloride (CuCl ₂ ) and heated in a nitrogen stream at 150 ° C. for 5 hours. A black solid was obtained at 350 ° C. for 5 hours. Subsequently, this solid substance was pulverized in a boiling 30% aqueous hydrochloric acid solution and then washed four times in a boiling 30% aqueous hydrochloric acid solution to obtain a black powder. This black powder was heated in an Ar stream at 700 ° C. for 5 hours to obtain a black powder.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the black powder has an absorption due to the aromatic ring skeleton vibration at around 1600 cm ⁻¹ , and the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively. _B / I _A
It was confirmed to be a polymerized condensed aromatic ring compound having a ratio of 0.71. Further, as a result of measuring the X-ray diffraction spectrum of the black powder, a peak corresponding to the (002) diffraction of carbon was observed, and the average interlayer distance d ₍₀₀₂₎ was 0.370 n.
It was m. Further, the black powder has a BET specific surface area and a true density of 2.7 m ^{2 /} g and 1.8, respectively.
It was g / cm ³ .

A negative electrode was produced in the same manner as in Example 1 by using the above-mentioned black powder (polymerized condensed aromatic ring compound) pulverized and using particles having an average particle diameter of 12 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Example 5 First, a specific gravity of 1.175 (20
/ 20 ° C.), a Mettler method softening point of 99.5 ° C., xylene-insoluble content of 0.8% by weight of solid petroleum pitch of 500 g, and 100 g of anhydrous iron chloride (FeCl ₃ ) are mixed, and the mixture is heated in a nitrogen stream at
A black solid was obtained by heating at 0 ° C. for 5 hours. Subsequently, this black solid was crushed in a boiling 30% aqueous hydrochloric acid solution and then washed four times in a boiling 30% aqueous hydrochloric acid solution to obtain a black powder. The black powder was obtained by heating the black powder in an Ar stream at 550 ° C. for 5 hours.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the black powder has an absorption due to the aromatic ring skeleton vibration at around 1600 cm ⁻¹ , and the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively. _B / I _A
Was 1.85, which was confirmed to be a polymerized condensed aromatic ring compound. Further, as a result of measuring the X-ray diffraction spectrum of the black powder, a peak corresponding to (002) diffraction of carbon was observed, and the average interlayer distance d ₍₀₀₂₎ was 0.382n.
It was m. Further, the black powder has a BET specific surface area and a true density of 5.8 m ^{2 /} g and 1.6, respectively.
It was g / cm ³ .

A negative electrode was produced in the same manner as in Example 1 by using the particles obtained by pulverizing the black powder (polymerized condensed aromatic ring compound) and having an average particle size of 20 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Example 6 First, a specific gravity of 1.098 (15
/ 4 ° C), viscosity 177cst (80 ° C), 714cst
50 g of anhydrous aluminum chloride and 50 g of anhydrous iron chloride (FeCl ₃ ) are mixed with 500 g of liquid tar (at 60 ° C.),
In a nitrogen stream, 100 ° C for 2 hours, 200 ° C for 4 hours, 3
A black solid was obtained by heating at 00 ° C. for 5 hours.
Subsequently, this black solid was crushed in a boiling 30% aqueous hydrochloric acid solution and then washed four times in a boiling 30% aqueous hydrochloric acid solution to obtain a black powder. This black powder is Ar
Black powder was obtained by heating at 600 ° C. for 5 hours in an air stream.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the black powder has an absorption due to the aromatic ring skeleton vibration at around 1600 cm ⁻¹ , and the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively. _B / I _A
Was confirmed to be a polymerized condensed aromatic ring compound having a value of 0.64. As a result of measuring the X-ray diffraction spectrum of the black powder, a peak corresponding to (002) diffraction of carbon was observed, and the average interlayer distance d ₍₀₀₂₎ was 0.375n.
It was m. Further, the black powder has a specific surface area by BET method and a true density of 1.3 m ^{2 /} g and 1.8, respectively.
It was g / cm ³ .

The black powder (polymerized condensed aromatic ring compound) was pulverized to obtain particles having an average particle size of 6 μm.
A negative electrode was produced in the same manner as in. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Comparative Example 1 First, 500 g of the same solid petroleum pitch as in Example 5 was heated in a nitrogen stream at 600 ° C. for 5 hours, and further heated in an Ar stream at 550 ° C. for 5 hours to give a black solid. Got Subsequently, this black solid substance was crushed to obtain a black powder.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the spectrum diagram shown in FIG. 7 was obtained. From FIG. 7, the black powder is 160
When there is absorption due to the aromatic ring skeleton vibration near 0 cm ^-1 , and the intensity of this absorption and the absorption peak intensity due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively, I _B / I _A is 2. 5
Was confirmed to be a polymerized condensed aromatic ring compound. In addition, as a result of measuring the X-ray diffraction spectrum of the black powder, it was found that when 2θ was in the range of 20 to 30 °, carbon (002)
A peak corresponding to diffraction was observed, and the average interlayer distance d
₍₀₀₂₎ was 0.375 nm. Further, the black powder had a specific surface area and a true density measured by the BET method of 6.8 m ^{2 /} g and 1.3 g / cm ³ , respectively.

A negative electrode was produced in the same manner as in Example 1 by using the particles obtained by crushing the black powder (polymerized condensed aromatic ring compound) and having an average particle diameter of 30 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

Comparative Example 2 First, 500 g of the same liquid tar as in Example 6 was mixed with 50 g of anhydrous aluminum chloride and 50 g of anhydrous iron chloride (FeCl ₃ ), and the mixture was placed in a nitrogen stream for 10 minutes.
A black solid was obtained by heating at 0 ° C. for 2 hours, 200 ° C. for 4 hours, and 300 ° C. for 5 hours. Then, after crushing this black solid in a boiling 30% hydrochloric acid aqueous solution,
A black powder was obtained by washing 4 times in a boiling 30% aqueous hydrochloric acid solution. This black powder was placed in an Ar stream for 350
A black powder was obtained by heating at ℃ for 5 hours.

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the black powder has an absorption due to the aromatic ring skeleton vibration at around 1600 cm ⁻¹ , and the intensity of this absorption and the intensity of the absorption peak due to the out-of-plane bending of the aromatic ring are I _A and I _B , respectively. _B / I _A
Was confirmed to be a polymerized condensed aromatic ring compound having a value of 5.32. Further, the X-ray diffraction spectrum of the black powder was measured. As a result, the spectrum diagram shown in FIG. 8 was obtained. From this FIG. 8, it was confirmed that the black powder does not have a clear peak corresponding to (002) diffraction of carbon in the range of 2θ of 16 to 30. Further, the black powder is BE
Specific surface area and true density by T method are 1.2 m ² each
/ G and 1.0 g / cm ³ .

A negative electrode was produced in the same manner as in Example 1 by using the particles obtained by crushing the black powder (polymerized condensed aromatic ring compound) and having an average particle size of 20 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

(Comparative Example 3) A black powder produced by the same method as in Comparative Example 2 was heated in an Ar stream at 350 ° C for 5 hours and further heated in an Ar stream at 1000 ° C for 5 hours to obtain a black powder. Got

The absorption spectrum of the obtained black powder was measured by infrared spectroscopy. As a result, the spectrum diagram shown in FIG. 9 was obtained. From this FIG. 9, it was confirmed that the black powder was a carbon body having no absorption due to aromatic ring skeleton vibration. Further, the X-ray diffraction spectrum of the black powder was measured. As a result, the spectrum diagram shown in FIG. 10 was obtained.
From this FIG. 10, it was confirmed that the black powder had an average interlayer distance d ₍₀₀₂₎ of 0.360 nm. Further, the black powder had a specific surface area by BET method and a true density of 1.5 m ^{2 /} g and 1.9 g / cm ³ , respectively.

A negative electrode was produced in the same manner as in Example 1 by using the particles obtained by crushing the black powder (carbon body) and having an average particle size of 20 μm. The cylindrical lithium secondary battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that such a negative electrode was used.

The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were charged up to 4.2 V with a charging current of 50 mA, and repeatedly charged and discharged to discharge up to 2.5 V at a current of 50 mA. 1st cycle of each battery and 30
The discharge capacity at the cycle was measured. The results are shown in Table 1 below.
Shown in

[0074]

[Table 1]

As is clear from Table 1, Examples 1 to 6
It can be seen that the above lithium secondary battery has an extremely high discharge capacity even after 30 cycles. In addition, the secondary batteries of Examples 3, 4, and 6 provided with the negative electrode including the polymerized condensed aromatic ring compound having the above-mentioned I _B / I _A value of less than 0.95 are the same as those of Examples 1, 2, and It can be seen that the capacities at the first cycle and the 30th cycle are higher than those of the secondary battery of No. 5.

[0076] On the other hand, comprising a negative electrode containing Example 5 and polymerized fused aromatic ring compound obtained by the process without using a Lewis acid catalyst using the same raw materials _{(I B / I A = 2.5} ) Since the secondary battery of Comparative Example 1 has an I _B / I _{A value} of more than 2, it can be seen that the intended capacity and cycle capacity are greatly reduced as compared with the secondary battery of Example 5.

The secondary batteries of Comparative Examples 2 and 3 are the same as those of Example 6.
Comparative Example 2 provided with a negative electrode containing a material synthesized from a raw material similar to the above, but provided with a negative electrode containing a polymerized condensed aromatic ring compound which is amorphous and has an I _B / I _{A of more} than 2, and a negative electrode containing a carbon body It can be seen that in Comparative Example 3 including the above, the capacity is significantly reduced as compared with the secondary battery of Example 6.

In addition, although the example applied to the cylindrical lithium secondary battery has been described in the above embodiment, the present invention can be applied to a prismatic lithium secondary battery in the same manner. Further, the electrode group housed in the battery container is not limited to the spiral shape, and may have a form in which a plurality of positive electrodes, separators and negative electrodes are laminated in this order.

[0079]

As described above, according to the present invention, a lithium secondary battery having a high capacity and a long cycle life can be provided.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical lithium secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing an infrared absorption spectrum of a polymerized condensed aromatic ring compound in Example 1 of the present invention.

FIG. 3 is a characteristic diagram showing X-ray diffraction of a polymerized condensed aromatic ring compound in Example 1 of the present invention.

FIG. 4 is a characteristic diagram showing an infrared absorption spectrum of a polymerized condensed aromatic ring compound in Example 2 of the present invention.

FIG. 5 is a characteristic diagram showing an infrared absorption spectrum of liquid petroleum pitch which is a raw material used in Example 3 of the present invention.

FIG. 6 is a characteristic diagram showing an infrared absorption spectrum of a polymerized condensed aromatic ring compound in Example 3 of the present invention.

7 is a characteristic diagram showing an infrared absorption spectrum of a polymerized condensed aromatic ring compound in Comparative Example 1. FIG.

8 is a characteristic diagram showing X-ray diffraction of a polymerized condensed aromatic ring compound in Comparative Example 2. FIG.

FIG. 9 is a characteristic diagram showing an infrared absorption spectrum of a carbon body in Comparative Example 3.

10 is a characteristic diagram showing X-ray diffraction of a carbon body in Comparative Example 3. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylindrical container with a bottom, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 8 ... Insulating sealing plate, 9 ... Positive electrode terminal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahisa Osaki 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (2)

[Claims] 1. A fused aromatic ring compound housed in a container,
At least one selected from a petroleum-based pitch containing a condensed aromatic ring compound and a coal-based pitch containing the same compound is dehydrogenatively condensed in the presence of a Lewis acid catalyst to produce a precursor, which is prepared under an inert gas atmosphere. Or vacuum atmosphere, 400
A negative electrode containing a polymerized condensed aromatic ring compound that absorbs and releases lithium ions, which is obtained by heat treatment at ˜800 ° C., and a positive electrode that is housed in the container and is disposed with the separator sandwiched between the negative electrodes. A lithium secondary battery, comprising: a non-aqueous electrolyte solution contained in the container. 2. An X-ray diffraction method has a peak corresponding to the (002) diffraction of a carbon body in an X-ray diffraction method in the range of 20 to 16 °, and the average interlayer distance d _{( 002)} is 0.39 nm or less and has absorption due to aromatic ring skeleton vibration at around 1600 cm ⁻¹ in infrared spectroscopy, and the intensity of this absorption and the intensity of absorption peak due to out-of-plane bending of aromatic ring are respectively I _A , I _B , 0 ≦
The relationship of I _B / I _A ≦ 2 is satisfied, and the true density is 1.2.
A negative electrode containing a polymerized condensed aromatic ring compound that absorbs and releases lithium ions of up to 2.0 g / cm ³ , a positive electrode that is housed in the container and that is disposed with a separator sandwiched between the negative electrode, and the container A lithium secondary battery, comprising: a non-aqueous electrolyte solution contained therein.