JPH09312160A - Manufacture of lithium secondary battery and carbonaceous negative electrode material to be used for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbonaceous negative electrode material having a large charging and discharging capacity and having a large number of time of charging and discharging by performing the infusible treatment to a carbon precursor in the oxidizing atmosphere, and thereafter, carbonizing it. SOLUTION: A pitch of the aromatic compound, which can react for electrophilic substitution, such as condensed heterocyclic compound, aromatic group oil, petroleum group and cokes group is made to react with bifunctional cross linking agent such as aromatic dimethylene halide, aromatic dimethanol, aromatic dicarbonyl halide and aromatic aldehyde in the existence of acid catalyst so as to obtain carbon precursor. At this stage, this precursor is crushed, and infusible treatment is performed in the oxidizing atmosphere. Thereafter, heating is performed in the non-oxidizing atmosphere for carbonizing so as to obtain the carbonaceous negative electrode material. At the time of infusible treatment, oxygen gas, ozone gas and NOx gas is used as the oxidizing gas, and a treatment is performed within a range at 50 deg.C/min. or less of temperature rising speed and within a range at 200-450 deg.C of heating temperature. Yield of fixed carbon at the time of carbonizing carbon precursor is thereby increased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery and a carbonaceous negative electrode material used therein.

[0002]

2. Description of the Related Art As electronic equipment is becoming smaller, thinner and lighter, it can be charged with high energy density and discharged with high efficiency as a battery for powering electronic equipment and as a backup power supply for electronic equipment. Lithium secondary batteries have been attracting attention as possible secondary batteries. In addition, since lithium has little impact on the environment and is highly safe, it is being developed as a power source for electric vehicles and as a distributed power source for power storage.

A typical lithium secondary battery of the prior art is
Metallic lithium is used as a foil for the negative electrode active material.
This foil-shaped metallic lithium has a problem that the number of charging / discharging is small because dendritic lithium is deposited on the foil surface during repeated charging / discharging and comes into contact with the anode to short-circuit both electrodes.

As a method for improving this, US Pat.
In No. 002492, a fusible alloy containing aluminum, lead, cadmium, and indium is used as a negative electrode active material, lithium metal is deposited as an alloy in these fusible alloys during charging, and lithium metal is dissolved from the alloy during discharging. The method of making it proposed is proposed. With this method, the deposition of dendritic lithium can be suppressed, but the fusible alloy is expensive, the workability is poor, and lead, cadmium, and the like have an adverse effect on the environment.

It is also conceivable that a carbon material is used as the negative electrode active material and lithium is carried in the carbon material in an ionic state, but it is difficult to increase the amount of lithium ions released into carbon. There is a problem that the charge / discharge capacity of the secondary battery cannot be increased. For example, when graphite is used as a carbonaceous material, lithium metal has a composition of C ₆ Li, and the theoretical charge / discharge capacity of this material is 372 Ah.
/ Kg. This is as low as 1/10 or less of the theoretical charge / discharge capacity of lithium metal of 3800 Ah / kg (lithium base).

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having a large charge / discharge capacity, a high initial charge / discharge efficiency, and a large number of charge / discharge cycles, and a method for producing a carbonaceous negative electrode material used therein. That is.

[0007]

The present invention comprises a first step of reacting an aromatic compound capable of an electrophilic substitution reaction with a bifunctional cross-linking agent in the presence of an acid catalyst to obtain a carbon precursor. It is characterized by including a second step of crushing the carbon precursor and infusibilizing it in an oxidizing atmosphere, and a third step of carbonizing the carbon precursor which has been infusibilized by heating it in a non-oxidizing atmosphere. The method for producing a carbonaceous negative electrode material used for a lithium secondary battery. In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and completed the present invention. According to the invention, by using the carbon precursor obtained in the first step and performing infusibilization (oxidation) treatment before carbonization treatment,
It was possible to obtain a carbon material from which lithium metal was easily released as ions. That is, the infusibilization treatment reduces the disappearance of crystal defects generated in the carbon structure by the cross-linking agent, and increases the proportion of effective amorphous parts involved in the absorption and desorption of lithium ions. The charge / discharge capacity of the negative electrode for the secondary battery can be improved. The aromatic compound capable of the electrophilic substitution reaction is not particularly limited, but includes naphthalene, azulene, indacene, fluorene, phenentrene, anthracene, triphenylene,
Two or more condensed polycyclic hydrocarbons such as pyrene, chrysene, naphthacene, picene, perylene, pentaphene, and pentacene; 3 such as indole, isoindole, quinoline, isoquinoline, quinoxane, phthalazine, carbazole, acridine, phenazine, phenanthrodine Fused heterocyclic compounds in which a heterocyclic group having at least a member ring is condensed with an aromatic hydrocarbon; anthracene oil, decrystallized anthracene oil, naphthalene oil, methylnaphthalene oil, tar, creosote oil, ethylene bottom oil, carbole oil, solvent Aromatic oils such as naphtha; petroleum-based or coal-based pitches are exemplified. These aromatic components may have a substituent that does not adversely affect the crosslinking reaction, such as an alkyl group, a hydroxyl group, an alkoxy group, a carboxyl group, or the like. These aromatic compounds may be used alone or in combination of two or more. Further, it can be used in combination with a ring assembly compound such as biphenyl or binaphthalene. Two
As the functional crosslinking agent, various bifunctional compounds capable of crosslinking a plurality of components of the aromatic compound capable of the electrophilic substitution reaction or a single component can be used. Specifically, aromatic dimethylene halide such as xylene dichloride;
Aromatic dimethanol such as xylene glycol; aromatic dicarbonyl halide such as terephthalic acid chloride, isophthalic acid chloride, phthalic acid chloride and 2,6-naphthalene dicarboxylic acid chloride; benzaldehyde, p-hydroxybenzaldehyde, p-methoxybenzaldehyde, 2 Aromatic aldehydes such as 5,5-dihydroxybenzaldehyde, benzaldehyde dimethyl acetal, terephthalaldehyde, isophthalaldehyde and salicylaldehyde are exemplified. These cross-linking agents may be used either individually or in combination of two or more. The amount of the cross-linking agent to be used can be selected within a wide range according to the characteristics of the aromatic compound capable of the electrophilic substitution reaction, and the amount of the cross-linking agent to be used per 1 mol of the condensed polycyclic hydrocarbon and / or the condensed heterocyclic compound is It is about 0.1 to 5 mol, preferably about 0.5 to 3 mol. For an aromatic compound mixture such as pitches, the amount is 0.01 to 5 mol, preferably 0.05 to 3 mol, based on the average molecular weight. The crosslinking reaction with the crosslinking agent is usually performed in the presence of an acid catalyst. As the acid catalyst, a commonly used acid such as Lewis acid or Bronsted acid can be used. Lewis acids include, for example, ZnCl ₂ ,
_{BF 3, AlCl 3, SnCl 4} , such TiCl ₄ is included, the Bronsted acids such as p- toluenesulfonic acid, trifluoromethanesulfonic acid, organic acids such as xylene sulphonic acid, hydrochloric acid, sulfuric acid, mineral such as nitric acid Includes acid. The acid catalyst is preferably Bronsted acid. The amount of the acid catalyst used can be selected according to the reaction conditions and the reactivity of the aromatic compound capable of the electrophilic substitution reaction, and is, for example, 0.01 to 10 molar equivalents, preferably 0 to the crosslinking agent. 0.5 to 3 molar equivalents. The cross-linking reaction can be carried out using a solvent, but it is preferably carried out in the absence of a solvent. The reaction is carried out, for example, at 80 to 250 ° C, preferably 100 to 200 ° C. The reaction is nitrogen, helium,
It is possible to use either an atmosphere of an inert gas such as argon or an oxidizing atmosphere such as air or oxygen, but an oxidizing atmosphere is preferable in order to shorten the infusibilizing treatment time.
The reaction is carried out with stirring, and the time point at which the stirring becomes impossible is the end point of the reaction. The reaction time is usually about 30 minutes to 24 hours. The obtained carbon precursor can be recovered as a solid resin when cooled to room temperature. The carbon precursor recovered as a solid resin, crushed by a general crusher such as a hammer mill, a ball mill, a jet mill,
By heating from room temperature in an oxidizing atmosphere, an insoluble and infusible cured resin can be obtained. This process is generally called infusibilizing process. By performing the infusibilization treatment, the yield (fixed carbon amount) when the carbon precursor is carbonized can be increased by 10% or more, and the shape is fixed due to the infusibilization, which is generated by the crosslinking agent. It is possible to carbonize the defective portion in the carbon structure without disappearing.
The carbon precursor subjected to the infusibilization treatment is carbonized by heat treatment in a non-oxidizing atmosphere to obtain a carbonaceous negative electrode material having an increased amorphous portion. The heat treatment is performed in an inert gas such as nitrogen, helium, argon or neon at 600 to 1800 ° C., preferably 700 to 1500.
This is done by firing the infusible carbon precursor at ℃.

Further, the present invention is characterized in that the infusibilizing treatment is carried out at a temperature rising rate of 0.1 to 50 ° C./min and a temperature of 200 to 450 ° C. According to the present invention, it is preferable that the infusibilizing treatment is carried out at a heating rate of 50 ° C./min or less and at a heat treatment temperature of 200 to 450 ° C. When the rate of temperature increase is higher than 50 ° C./min, the infusibilization reaction becomes difficult to occur uniformly and a phenomenon of partial melting occurs. The lower the heating rate is, the more infusible the reaction becomes, and the more stable the infusible reaction occurs.
It is preferably 0.1 ° C./min or more. On the other hand, when the heat treatment temperature is lower than 200 ° C., the infusible reaction is temperature-controlled, the reaction takes a long time, the reaction cannot proceed sufficiently, and the uniform reaction cannot be promoted. On the other hand, 450
The infusibilization treatment at a temperature higher than ° C increases the amount of carbon lost, resulting in a decrease in the infusibilization yield. The type and supply amount of the oxidizing gas at the time of infusibilization are not particularly limited. For oxidizing gas, general oxidizing gas,
For example, air, oxygen gas, ozone gas, NOx gas and the like can be used, but it is most preferable to use air from the viewpoints of influence on the environment, ease of handling, and cost. Gas supply is necessary for infusible reaction,
It is sufficient that a sufficient amount is present in the reaction system. For example, the amount of air supplied in the case of the multistage static system is 0.1 to 10 L /
It is preferably about min. When it exceeds 10 L / min, the amount of oxygen supplied becomes excessive and the economical efficiency decreases, and because the flow rate of the supplied gas is too high, the amount of the crushed carbon precursor scattered to the outside of the heat treatment environment increases, resulting in infusibilization. Treatment can cause a decrease in yield. Further, when the air supply amount is less than 0.1 L / min, the infusible reaction is rate-controlled for the oxygen amount, and the uniform reaction cannot be promoted. The amount of gas supplied when an oxidizing gas other than air is used may be an amount calculated by the partial pressure of oxygen contributing to the oxidation reaction.

Further, the present invention is a lithium secondary battery characterized by using a negative electrode active material obtained by impregnating a carbonaceous negative electrode material produced by the above method with lithium ions. According to the present invention, the carbonaceous negative electrode material produced above is used for a lithium secondary battery. Generally, carbon atoms have a structure in which secondary carbon network structures are three-dimensionally stacked. When a carbonaceous material is used as the negative electrode active material of a lithium secondary battery, lithium is occluded in the above-mentioned carbon structure in a certain ionic state during charging, and is discharged into the electrolytic solution through the reverse path during discharging. . Incorporation and release reactions of different elements between the carbon layers are generally called intercalation and deintercalation reactions. When a carbon material is used as a negative electrode active material in a lithium secondary battery, exactly this reaction is utilized.By incorporating lithium from the electrolytic solution into the carbon material, electrical energy is stored as a battery, and lithium is stored in the electrolytic solution. Electric energy is taken out of the system by releasing. However, the composition of the negative electrode of the lithium secondary battery using such a carbon crystal structure is C ₆ Li, and the capacity thereof is theoretically 372 Ah / kg, which is actually lower. On the other hand, the carbon material is considered to be a polycrystal having both a crystal part and an amorphous part at the same time, and the amount of lithium absorbed using the amorphous part in the carbon structure is not restricted by the composition of C ₆ Li. It is considered possible to occlude lithium more densely. In the carbonaceous material produced by the above method, the amorphous portion generated in the carbon precursor in the first step is stably present without being lost by the infusibilizing treatment in the second step. On the other hand, it is presumed that the amorphous portion disappears in the carbonaceous material that has been heat-treated without infusibilizing treatment. Therefore, the lithium secondary battery of the present invention can prevent the deposition of dendritic substances even when charging and discharging are repeated, and can increase the charging and discharging capacity.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically with reference to Examples.

FIG. 1 is a sectional view showing the structure of a lithium secondary battery 1 according to an embodiment of the present invention. The lithium secondary battery 1 has a positive electrode 2, a negative electrode 3, and a separator 4 interposed between these two electrodes. Then, these are housed in the case 5, and the opening of the case 5 is sealed by the opening plate 6 and the insulating packing 7.

The active material used for the positive electrode 2 is TiS.
₂ , metal chalcogenides having a layered structure such as ₂ , MoS ₂ , NbSe ₃ , FeS, VS ₂ , VSe _2, etc., CoO ₂ , Cr ₃
O ₅ , TiO ₂ , CuO, V ₃ O ₆ , Mo ₃ O, V ₂ O ₅ (・
Examples thereof include metal oxides such as P ₂ O ₅ ) and Mn ₂ O (.Li ₂ O), and conjugated polymer materials having conductivity such as polyacetylene, polyaniline, polyparaphenylene, polythiophene, and polypyrrole. Of these, V ₂ O ₅ , M
Metal oxides such as n ₂ O are preferred. Such a positive electrode material is used by being bound with a binding material such as polytetrafluoroethylene.

The active substance used for the negative electrode 3 is an electrolytic solution containing a carbonaceous material described later and containing lithium ions or alkali metal ions such as sodium and potassium mainly containing lithium ions, for example, LiClO having a concentration of 1 mol / L.
_It is immersed in ₄ , and a lithium metal simple substance is used for the anode, and a carbonaceous material is used as the cathode for electrolytic impregnation.

The separator 4 is made of a liquid-retaining material, for example, a porous polypropylene nonwoven fabric impregnated with a non-aqueous solvent electrolyte. As the non-aqueous solvent-based electrolytic solution, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, sulfolane, 1,2-dimethoxyethane,
Aprotic solvents such as dimethyl sulfoxide, acetonitrile, N, N-dimethylformamide, diethylene glycol and dimethyl ether, preferably ether solvents which are stable even in a strong reducing atmosphere such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane and 4-methyldioxolane. , Or a mixed solvent of two or more of the above-mentioned solvents, LiPF ₆ , LiClO ₄ , LiBF
₄ , LiAsF ₆ , LiSbF ₆ , LiAlO ₄ , LiAl
Illustrative examples include salts in which a salt that is difficult to solvate, such as Cl ₄ , LiCl, and LiI, to generate an anion is dissolved.

The secondary battery may have any shape such as a cylindrical shape, a square shape or a button shape.

[0016]

Example 1 [Preparation of carbon material] Pyrene and para-xylene glycol (2,3-dimethyl-1,4-dimethanol) were used as starting materials, and para-toluenesulfonic acid was used as an acid catalyst at a reaction temperature of 155 ° C. Carbon precursor (T in GPC
The number average molecular weight of the HF soluble component was 1640). Then, it is cooled to room temperature, the obtained solid carbon precursor is crushed by a ball mill, the temperature rising rate is 2 ° C / min, and the air supply rate is 2L.
/ Min, the temperature was raised to 300 ° C. to perform infusibilization treatment. Then, using a normal heat treatment furnace in a nitrogen stream, 110
A carbonaceous material was obtained by raising the temperature to 0 ° C. and holding it for 2 hours.

[Preparation of Negative Electrode Body] 99 parts by weight of the carbonaceous material after heat treatment and 1 part by weight of dispersion type PTFE (D-1 manufactured by Daikin Industries, Ltd.) were mixed and uniformly mixed in a liquid phase. After stirring, it was dried to give a paste. 30 mg of the negative electrode material thus obtained was pressed onto a nickel mesh to prepare a negative electrode body.

[Preparation of Battery] The negative electrode body obtained above,
LiCoO ₂ as a positive electrode body and 1 m as a separator
A polypropylene non-woven fabric was impregnated with propylene carbonate in which LiClO ₄ was dissolved at a concentration of ol / L to prepare a lithium secondary battery as shown in FIG.

[0019]

Example 2 In [Preparation of Carbon Material] of Example 1,
A lithium secondary battery was produced in the same manner as in Example 1 except that the infusibilizing temperature was 200 ° C.

[0020]

Example 3 In [Preparation of carbon material] of Example 1,
A lithium secondary battery was produced in the same manner as in Example 1 except that the temperature rising rate during the infusibilizing treatment was 10 ° C./min.

[0021]

Comparative Example 1 In [Preparation of Carbon Material] of Example 1,
A lithium secondary battery was produced in the same manner as in Example 1 except that the infusibilizing treatment was not performed.

[0022]

Comparative Example 2 In [Preparation of carbon material] of Example 2,
A lithium secondary battery was produced in the same manner as in Example 2 except that the infusibilizing treatment temperature was 150 ° C.

[0023]

Comparative Example 3 In [Preparation of Carbon Material] of Example 3,
A lithium secondary battery was produced in the same manner as in Example 3 except that the temperature rising rate during the infusibilizing treatment was 20 ° C./min.

The discharge characteristics of the lithium secondary batteries obtained in the above Examples and Comparative Examples were measured. The results are shown in Table 1.
Shown in

[0025]

[Table 1]

Note: doo ₂ indicates the plane spacing of the laminated carbon mesh planes. Lc is the thickness direction (c
(Axis) indicates the size of the crystallite size. La represents the crystallite size in the spreading direction (a-axis) of the plane parallel to the carbon net plane. The measurement was performed under a constant current charge / discharge of 0.1 mA / cm ² , and the discharge capacity was the capacity until the battery dropped to 2.0V.

From Table 1, Comparative Example 1 without infusibilizing treatment
It can be seen that Comparative Examples 2 and 3 which have extremely low discharge capacities and in which the infusibilizing treatment is not performed under the preferable conditions of the present invention have lower discharge capacities than the Examples.

[0028]

As described above, according to the present invention, it is possible to increase the proportion of the amorphous portion present in the carbonaceous negative electrode material,
Since this carbonaceous negative electrode material can contain many lithium ions, the lithium secondary battery using this material has a large discharge capacity per unit weight. In addition, the number of times of charge and discharge can be dramatically increased.

[Brief description of drawings]

FIG. 1 is a sectional view of a lithium secondary battery 1 according to an embodiment of the present invention.

[Explanation of symbols]

 1 Lithium secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 5 Case 6 Opening plate 7 Insulating packing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Fujimoto 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture Osaka Gas Co., Ltd. (72) Inventor Takanori Kazaka 4 Chome 1-2 Osaka Gas Co., Ltd.

Claims (3)

[Claims] 1. A first step of reacting an aromatic compound capable of electrophilic substitution reaction with a bifunctional cross-linking agent in the presence of an acid catalyst to obtain a carbon precursor, and crushing and oxidizing the carbon precursor. Second infusibilizing treatment in the atmosphere
A method for producing a carbonaceous negative electrode material used in a lithium secondary battery, comprising: a step; and a third step of carbonizing the carbon precursor which has been subjected to the infusibilizing treatment by heating in a non-oxidizing atmosphere. 2. The infusibilizing treatment has a temperature rising rate of 0.1 to 50.
The method for producing a carbonaceous negative electrode material used in a lithium secondary battery according to claim 1, wherein the method is performed at a temperature of 200 to 450 ° C./° C./min. 3. A lithium secondary battery comprising a negative electrode active material obtained by impregnating a carbonaceous negative electrode material produced by the method according to claim 1 with lithium ions.