JP3241839B2 - Electrode materials for secondary batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode material for a secondary battery.

[0002]

2. Description of the Related Art In recent years, downsizing of electronic equipment has been progressed, and accordingly, high energy density of batteries has been demanded, and various non-aqueous electrolyte batteries have been proposed. For example, conventionally, as a negative electrode for a non-aqueous electrolyte battery, lithium metal has been known mainly for a primary battery, and a lithium alloy represented by an aluminum / lithium alloy, a carbon negative electrode, and the like are also known.
However, when lithium metal is used as a negative electrode of a secondary battery, it is known that cycle stability is inferior due to generation of dendrites and the like. A lithium alloy negative electrode represented by an aluminum / lithium alloy also has improved cycle stability compared to metallic lithium, but is not sufficient to sufficiently bring out the performance of a lithium battery.

[0003] In order to solve such a problem, it has been proposed to use a carbon anode utilizing the fact that lithium intercalation compounds can be electrochemically easily formed. There are many kinds and various kinds of such carbon anodes. For example, a carbon material obtained by calcining crystalline cellulose at 1,800 ° C. under a nitrogen gas flow (Japanese Patent Application Laid-Open No. 3-1769693), coal pitch or Petroleum pitch which has been graphitized at 2,500 ° C. or higher in an inert atmosphere (Japanese Patent Laid-Open No. 2-8
No. 2466), and those having advanced graphitization treated at a high temperature exceeding 2,000 ° C. are used, and although the capacity is reduced as compared with lithium metal and lithium alloy, those having cycle stability are used. Have been obtained. However, even with such a negative electrode, sufficient cycle stability has not been obtained in charging and discharging at a high current density.

[0004]

As described above, when metal lithium is used as the negative electrode of a lithium battery, dendrite is generated during charging and discharging, which causes not only deterioration but also contact with moisture. This causes a problem of causing a violent reaction and increasing the possibility of deterioration. Also,
Lithium alloys, though more stable than metallic lithium, are not satisfactory.

On the other hand, the carbon anode has a sufficiently mild reaction with water even in a charged state, that is, in a state where lithium is intercalated in carbon, and has a dendrite accompanying charge / discharge as compared with lithium metal or a lithium alloy. The formation was excellent with almost no formation. However, depending on the type of carbon, there are many carbons that can hardly be charged and discharged, and those whose capacity is extremely low as compared with the theoretical capacity (assuming the state of LiC ₆ at the time of charging as the maximum capacity). In addition, even if the initial capacity is relatively large, it deteriorates due to repeated charging and discharging, and the capacity rapidly decreases. Conventional carbon anodes have not been able to provide satisfactory performance with conventional carbon anodes, such as being so violent that the performance as a secondary battery cannot be satisfied.

In order to solve these problems, polyparaphenylene is heat-treated in an inert atmosphere such as argon at a relatively low temperature, that is, at 500 ° C. to 1,500 ° C., thereby achieving high capacity and cycle stability. A negative electrode material which is excellent and can cope with high output (high current density) charge / discharge has been proposed (Japanese Patent Application No. 3-329676). However, even with this material, the charge / discharge capacity is not sufficient. The present invention has been made against the background of the conventional technical problems as described above, and has a high capacity and excellent cycle stability.
It is an object of the present invention to obtain a secondary battery electrode material that can handle high output (high current density) charge and discharge.

[0007]

SUMMARY OF THE INVENTION The present invention, in the repeating structural units, o- position bond, seen contains at least one structure selected from the group consisting of m- position coupling and branching structures, o- position forming
When the ratio of the m-position bond or the branched bond is 1 to
20 mol% of an aromatic polymer compound is heated at 500 ° C.
An object of the present invention is to provide a secondary battery electrode material obtained by heat treatment at 1,500 ° C. and pulverization to obtain an average particle size of 5 μm or less.

[0008] Carbon has different physical properties and crystal structures depending on its starting material and production method, and there is a large difference in performance when used as an electrode for a secondary battery. In the present invention, as a starting material, not a linear polymer,
An excellent electrode material can be obtained by using a polymer having an o-bond, an m-bond, or a branched structure and performing a heat treatment at a temperature of 500 ° C. to 1,500 ° C.

In the present invention, the aromatic polymer compound has at least one structure selected from the group consisting of an o-position bond, an m-position bond and a branched structure in its repeating structural unit. Such an aromatic polymer compound may contain, for example, o-dihalogenated benzene, m-dihalogenated benzene, or a mixture thereof in an amount of 1 to 20 mol% if it contains an o-position bond or an m-position bond. And 99-80 mol% of p-dihalogenated benzene and p-dihalogenated benzene as starting monomers, and polymerized using a Grignard reagent in the presence of a nickel (II) catalyst. If the compound has a branched structure, 1,2,4-trihalogenated benzene, 1,3,5-trihalogenated benzene, or a mixture thereof and p-dihalogenated benzene are prepared in the same manner as described above. It can be obtained by polymerization. Any method other than the above method (Yamamoto method) may be used as long as the binding position can be regulated. For example, dihalobenzene or trihalobenzene may be polymerized in the presence of a nickel (0) complex catalyst. By these methods, an aromatic polymer compound in which the repeating structural unit is a phenylene group can be obtained. In the aromatic polymer compound used in the present invention, o
- position coupling, m- position bond, or the proportion of branched bonds, 1 20 mol%, favorable Mashiku is 2-10 mol%, exhibit only polyparaphenylene characteristics equivalent is less than 1 mole%.

In the present invention, the heat treatment is performed at 500 to 1.5.
When the temperature is lower than 500 ° C., the carbonization does not proceed. On the other hand, when the temperature exceeds 1,500 ° C., the graphitization proceeds excessively, so that the capacity of the battery decreases. By subjecting the aromatic polymer compound to heat treatment at 500 to 1,500 ° C. (according to the X-ray diffraction pattern), a partially graphitized amorphous carbon can be obtained. , Except for carbon (generally, hydrogen), which is the most suitable as an electrode material for a lithium battery. Preferably, a heat treatment at around carbonization temperature of the aromatic polymer compound. The carbonization temperature is a temperature at which elimination of hydrogen or the like from an aromatic polymer compound as a starting material occurs,
It is measured by TG (thermogravimetry) and DTA (differential thermal analysis). The carbonization temperature varies depending on the starting materials and the optimum heat treatment temperature also varies.
The range of about 00 ° C. is preferable, and usually, 600 to 1,000.
It is about 0 ° C, more preferably 600 to 800 ° C.

The heating time is from 0 to 6 hours, preferably from 0 to 2 hours.
Time is appropriate. Here, the heating time is the set temperature,
That is, it is the time after the heat treatment temperature is reached, and this time is 0
However, there is no significant effect on the performance as an electrode. As a specific heat treatment method, the temperature may be raised from room temperature to the weight reduction start temperature at any rate, and the performance of carbon obtained as an electrode material is not affected.
It is preferable to carry out the heating at a constant heating rate from the temperature at which the weight starts to decrease to the heat treatment temperature.
Min. Is appropriate, preferably 0.5 ° C./min to 15 ° C./min.
Min, more preferably 1 ° C / min to 10 ° C / min.

Next, heating is preferably performed in a neutral atmosphere, a reducing atmosphere, or in the air until significant oxidation starts, and then in a reducing atmosphere, a neutral atmosphere, or an oxidizing gas. Examples of the neutral atmosphere include argon, helium, and nitrogen. Examples of the reducing atmosphere include a hydrogen atmosphere, an ammonia atmosphere, and an ammonia-hydrogen atmosphere. The reducing and active hydrogen reduces dangling bonds (unstable carbon bonds that are not bonded to other atoms). It is preferable because it can be performed. Further, heat treatment may be performed in the air until remarkable oxidation starts, as described above. The temperature at which significant oxidation starts depends on the starting material, but is usually 200 to 5
It is preferable that the heat treatment is performed in the air at a temperature of 00 ° C. to 200 to 400 ° C. In this case, after that, heat treatment must be performed in a reducing atmosphere, a neutral atmosphere, or an oxidizing gas atmosphere. As the oxidizing gas, NO / N ₂ O (volume ratio = 1/9)
9 to 99/1), H ₂ O / N ₂ O (volume ratio =
1/999 to 2/8) mixed gas. Such a treatment is preferable because it is considered that a low-molecular aromatic polymer compound is polymerized through a bond of oxygen and evaporation at a temperature lower than the carbonization start temperature can be reduced.

[0013] The heat treatment, except when performed in air,
The heating is performed in a predetermined gas, and the gas may be flowed at a flow rate that does not affect the control of the heating rate. Cooling may be returned to room temperature by natural cooling in a predetermined gas flow. Further, there is no need for post-treatment such as heat treatment and surface modification. As described above, an electrode material made of the carbon material of the present invention is obtained.
The electrode material thus obtained is usually a powder or a solid, which can be mechanically pulverized to obtain an excellent electrode material.

[0014] When producing an electrode using the electrode material, it is possible to make a high-performance electrode by flat Hitoshitsubu diameter of the electrode material is used as the 5μm or less. In the case of the present invention , an electrode can be prepared by adding a binder such as polyethylene powder to a powder having an average particle diameter of 5 μm or less , rolling the mixture with a roll, and the like. The compounding amount of the binder is 2 to 30 parts by weight, preferably 5 to 30 parts by weight based on 100 parts by weight of the electrode material.
20 parts by weight. Here, any of organic and inorganic binders can be used as the binder.
As the organic binder, in addition to the polyethylene,
Many binders can be used, such as fluororesins such as polytetrafluoroethylene, polyvinyl alcohol, polyvinyl chloride, and the like. In this case, except for polyethylene, heat treatment is required at around the carbonization temperature of the binder.

As the inorganic binder, a silicon-based binder such as silicon glass can be used. In this case, however, a heat treatment at a temperature exceeding the melting point is required in order to exhibit the performance as a binder. In this case, the electrode body can be directly obtained by mixing and molding the aromatic polymer compound as a starting material and these binders and performing the heat treatment as described above. In this case, it is necessary to pay attention to the shape change of the electrode body, but the performance as an electrode for a secondary battery is equivalent to that obtained by compacting the electrode material of the present invention and polyethylene. The electrode body thus obtained can be used as a lithium battery electrode by supporting lithium or an alkali metal mainly composed of lithium on the electrode body.

As a method of carrying the compound, any conventional method such as contacting and thermally diffusing a lithium foil, electrochemically doping lithium in a lithium salt solution, or immersing in molten lithium can be used. Method may be used. The electrode material of the present invention can be widely used as a negative electrode of a secondary battery, and is combined with various positive electrodes, for example, a positive electrode using an aromatic polymer such as manganese dioxide, an oxide such as vanadium pentoxide, or polypyrrole, and the like. Can be used. In addition, not only the negative electrode, but also various negative electrodes, for example, a lithium metal, a lithium alloy having a lower potential than the electrode material of the present invention, and an electrode material such as Li-GIC can be used as a positive electrode.

The non-aqueous electrolyte used in the battery using the electrode material of the present invention is chemically stable with respect to the positive electrode material and the negative electrode material, and lithium ions are chemically reacted with the positive electrode active material. Any non-aqueous substance can be used as long as it can move in order to perform the reaction. Particularly, it is a compound composed of a combination of a cation and an anion. Li ⁺ is used as the cation, and PF is used as the anion.
₆ ^-, AsF ₆ ^-, SbF ₆ ^- halide anion such Va group element as, ^I -, I ₃ ^-, Br ^-, Cl ^- halogen anion, ClO _4, such as ^- perchlorate anion such as, Compounds having anions such as HF ₂ ⁻ , CF ₃ SO ₃ ⁻ , and SCN ⁻ can be given, but are not necessarily limited to these anions. Such cation, specific examples of the electrolyte with _{anion, LiPF 6, LiAsF 6, LiSbF} 6, LiB
F ₄ , LiClO ₄ , LiI, LiBr, LiCl, L
iAlCl ₄ , LiHF ₂ , LiSCN, LiCF ₃ S
O _{3 and the} like. Among these, in particular, LiP
F ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , Li
ClO ₄ and LiCF ₃ SO ₃ are preferred.

The non-aqueous electrolyte is usually used in a state of being dissolved in a solvent. In this case, the solvent is not particularly limited, but a solvent having a relatively large polarity is preferably used. Specifically, propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, glymes such as diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphates such as triethyl phosphate, boric acid Borates such as triethyl, sulfolane, sulfur compounds such as dimethyl sulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane,
One or a mixture of two or more such as nitrobenzene and dichloroethane can be mentioned. Among these, propylene carbonate, ethylene carbonate, butylene carbonate, tetrahydrofuran, 2-
One or a mixture of two or more selected from methyltetrahydrofuran, dioxane, dimethoxyethane, dioxolane and γ-butyrolactone is preferred. Further, as the non-aqueous electrolyte, the above-mentioned non-aqueous electrolyte, for example, polyethylene oxide, polypropylene oxide, isocyanate cross-linked body of polyethylene oxide,
An organic solid electrolyte impregnated with a polymer such as a phosphazene polymer having an ethylene oxide oligomer in a side chain,
Inorganic ion derivatives such as Li ₃ N and LiBCl ₄ , Li
An inorganic solid electrolyte such as lithium glass such as ₄ SiO ₄ and Li ₃ BO ₃ can also be used.

A lithium secondary battery using the electrode material of the present invention as a negative electrode will be described in more detail with reference to the drawings. That is, in the lithium secondary battery using the electrode material of the present invention, as shown in FIG.
The inside of the button-shaped positive electrode case 10 sealed with 0 is partitioned by a separator 30 having fine holes, and the positive electrode 50 in which the positive electrode current collector 40 is arranged on the positive electrode case 10 side is accommodated in the partitioned positive electrode side space. On the other hand, the negative electrode current collector 60
Is disposed on the side of the negative electrode cover plate 20 and the negative electrode 70 is accommodated.

As the separator 30, a nonwoven fabric, a woven fabric, a knitted fabric, or the like made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, which is porous and through which an electrolyte can pass or is used, is used. can do. As the positive electrode material used for the positive electrode 50, fired particles such as lithium-containing vanadium pentoxide and lithium-containing manganese dioxide can be used. Reference numeral 80 denotes a polyethylene insulating packing which is provided around the inner peripheral surface of the positive electrode case 10 and insulates and supports the negative electrode cover plate 20.

[0021]

According to the present invention, the aromatic polymer compound is
By heat treatment at 00 ° C. to 1,500 ° C., this is carbonized to form carbon intermediate between graphite (crystalline) and amorphous, that is, having both graphite and amorphous characteristics. Furthermore, in the formed carbon, an organic component, that is, an element other than carbon (hydrogen in a normal case) contained in the starting material remains.
Normally, the higher the heat treatment at a higher temperature, the more the X-ray diffraction pattern
As a result, the degree of graphitization increases, and the carbon which has been graphitized more than a certain level causes a reduction in the capacity of the battery.

However, since the electrode material made of the carbon material of the present invention is processed at a relatively low temperature, it does not have a complete graphite structure, but has a one-dimensional graphite-like structure, so that lithium ions can diffuse smoothly. It is considered to show high capacity and high cycle stability.
Furthermore, in the present invention, since the molecular structure has an o-position, an m-position, or a branched structure in the molecular structure, the crystallinity of the polymer is reduced, and the crystallinity and interlayer distance of the electrode material obtained by the heat treatment are reduced. The range is suitable for increasing the capacity.

On the other hand, when the graphitization proceeds, lithium intercalation between the layers is performed, but the diffusion rate of lithium into the bulk is limited, and it becomes impossible to cope with high current density (high power) charge / discharge. it is conceivable that. However, in the electrode material of the present invention, since graphite is appropriately present in carbon, it is supposed that the electrode material has an effect of increasing conductivity and enhancing performance as an electrode.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The evaluation of the discharge capacity in the examples was measured as follows. That is,
Using the obtained negative electrode, Li was used as a counter electrode, and a solution obtained by dissolving LiClO ₄ at a concentration of 1 mol / L in a solvent of ethylene carbonate / dimethoxyethane (volume ratio = 1: 1) was used as an electrolytic solution to assemble a battery. And half-cell evaluation. Using Li as a reference electrode, charge / discharge current density 1.6 mA / c
The evaluation was performed under the conditions of m ² , end-of-charge potential +10 mV vs. Li / Li ⁺ , and end-of-discharge potential 3 V vs. Li / Li ⁺ .

EXAMPLE 1 10.6 g (45 mmol) of p-dibromobenzene and 0.787 g (2.5 mmol) of 1,3,5-tribromobenzene
mmol) in tetrahydrofuran.
By reacting with 22 g (50 mmol), a Grignard reagent was synthesized. To this, 65 mg of nickel chloride-2,2'-bipyridine complex was added and refluxed for 4 hours. The reaction mixture was poured into dilute hydrochloric acid, stirred, and then filtered. The filtered solid was washed with a solvent in the order of distilled water, ethanol, hot toluene, and ethanol, and then dried in vacuum at 80 ° C. As a result, polyphenylene containing 5.26 mol% of a benzene ring bonded at the 1, 3, and 5 positions was obtained.

The temperature of the branched polyphenylene is raised to 300 ° C. over 1 hour under a hydrogen stream,
The temperature was raised to 700 ° C. at a rate of 0 ° C./hour, and when the temperature reached 700 ° C., heating was stopped and the furnace was cooled. FIG. 2 shows an X-ray diffraction pattern of the electrode material made of the carbon material thus obtained. It is amorphous without showing a specific diffraction pattern. Polyethylene powder was mixed with the thus obtained electrode material so as to have a binder content of 20% by weight,
It was pressed at a pressure of 9.8 × 10 ⁸ P to form a negative electrode. Charge and discharge were repeated for the produced electrode. FIG. 3 shows the discharge capacity per weight.

Comparative Example 1 Polyphenylene was synthesized in the same manner as in Example 1 except that 11.8 g (50 mmol) of p-dibromobenzene was used without using 1,3,5-tribromobenzene. The polymer thus obtained was polyparaphenylene consisting entirely of the p-position bond. This polyparaphenylene was heat-treated in the same manner as in Example 1 to produce a negative electrode, which was evaluated for a half cell. The results are shown in FIG.

Example 2 The 1,3,5-tribromobenzene of Example 1 was replaced with 1,2,2
Synthesis and evaluation were performed in the same manner as in Example 1 except that 4-tribromobenzene was used. The results are shown in FIG.

Example 3 Synthesis and evaluation were carried out in the same manner as in Example 1 except that 1,3,5-tribromobenzene in Example 1 was replaced with 1.18 g (5 mmol) of o-dibromobenzene. The results are shown in FIG.

Example 4 Synthesis and evaluation were performed in the same manner as in Example 1, except that 1,3,5-tribromobenzene in Example 1 was replaced with 1.18 g (5 mmol) of m-dibromobenzene. The results are shown in FIG.

As apparent from FIG. 3, a branched structure was introduced into polyparaphenylene (Examples 1 and 2),
By introducing the-and m-position bonds (Examples 3 and 4), the discharge capacity as a negative electrode is increased as compared with the case of only the p-position bond (Comparative Example 1).

[0032]

By using the electrode material of the present invention,
An electrode for a secondary battery having excellent charge / discharge cycle stability, withstanding high current density charge / discharge, and improved charge / discharge capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view including a partial cross-sectional view of a lithium secondary battery using a secondary battery electrode material of the present invention.

FIG. 2 is an X-ray diffraction pattern of the electrode material obtained in Example 1.

FIG. 3 is a graph showing evaluation results of Examples 1 to 4 and Comparative Example 1.

[Explanation of symbols]

 30 Separator 50 Positive electrode 70 Negative electrode

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naohiko Oki 1-4-1 Chuo, Wako-shi, Saitama Pref. Inside of Honda R & D Co., Ltd. (72) Kazuhiro Araki 1-4-1 Chuo, Wako-shi, Saitama pref. (56) References JP-A-61-58810 (JP, A) JP-A-63-69155 (JP, A) JP-A-61-277164 (JP, A) JP-A-60-112264 ( JP, A) JP-A-60-264052 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/58-4/60 H01M 10 / 40

Claims (4)

(57) [Claims] 1. The repeating structural unit has an o-position bond, an m-
Position coupling and saw including at least one structure selected from the group of branched structure, o- position bond, m- position bond, or
After heat-treating an aromatic polymer compound having a branched bond ratio of 1 to 20 mol% at 500 ° C to 1,500 ° C,
An electrode material for a secondary battery obtained by pulverization to obtain an average particle size of 5 μm or less. 2. The electrode material for a secondary battery according to claim 1, wherein the repeating structural unit of the aromatic polymer compound is a phenylene group. 3. The aromatic polymer according to claim 1 or 2.
An electrode material for a secondary battery obtained by heat-treating a compound at 600 ° C. to 1,000 ° C. 4. A heat treatment for 0 to 6 hours after reaching the heat treatment temperature.
The product obtained by heating at a temperature.
Electrode material for secondary batteries.