JPH0815071B2 - Secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an organic electrolyte secondary battery.

[Conventional technology]

Conventionally, as a secondary battery, there is a secondary battery in which a low density amorphous organic material fired body is brought into contact with lithium and which is used as a negative electrode material (JP-A-60-235372). [Problems to be Solved by the Invention] However, such a secondary battery has a problem that the charge / discharge cycle is short.

[Means for solving problems]

The inventors of the present invention have conducted intensive studies for the purpose of obtaining a secondary battery having an improved charge / discharge cycle, and have reached the present invention. That is, the present invention uses an organic solvent in which a lithium salt is dissolved as an electrolytic solution, a positive electrode material made of a chalcogen compound of a transition metal, and has a turbostratic structure and its density is 1.9 to 2.2 g /
The organic electrolyte secondary battery is characterized in that a negative electrode material is obtained by electrically contacting the calcined carbon of cm ³ and metallic lithium in the battery.

The fired carbon that constitutes the negative electrode material in the present invention has a turbostratic structure. This can be measured by the X-ray diffraction method. The turbostratic structure is described in "Carbon Black Handbook" (published by the book publisher, November 25, 1972), pages 159-165. Turbulent structure is excellent, and crystalline (graphite) and amorphous (amorphous) have poor charge / discharge efficiency.

Density greater than 1.8 1.0-2.2 g / cm ³ , preferably 2.0
Those exceeding the ~2.2g / cm ³ .1.9g / cm ³ and less than 2.2 g / cm ³ is charge-discharge efficiency is deteriorated. Density can be measured by the pycnometer method. Examples of fired carbon having a turbostratic structure include fired phenol resin and fired Pitch. Of these, the Pitch fired body is preferable. The fired Pitch and the fired phenol resin can be obtained by heating and firing Pitch (coal tar pitch, wood tar pitch, rosin pitch, etc.) and the phenol resin. As a method for producing a fired carbon having a turbostratic structure,
Usually, a method of heating and heat-treating a phenol resin or a pitch in a sealed atmosphere or in an atmosphere of an inert gas such as nitrogen gas can be mentioned. Heating temperature is usually 700 ℃ or more, preferably 1000-1
700 ℃, heating time is usually 1-50 hours, preferably 2-20
It's time. The heating is stepwise, for example, heating at 300-600 ° C. for 0.5 to 10 hours, heat treatment, and then heating at 600 to 1500 ° C. for 1 to 10 hours,
It can also be performed by heat treatment.

The negative electrode material has a turbostratic structure and its density is 1.9 to 2.2 g / cm.
The fired carbon of ³ and metallic lithium were electrically contacted in the battery. As a method of making this contact, there is a method of making direct contact by laminating metallic lithium on the surface of the fired carbon having a turbostratic structure. In the present invention, the transition metal in the chalcogen compound of the transition metal, which is the positive electrode material, includes metals of the IB to VIIB and VIII groups of the periodic table such as titanium, vanadium, chromium,
Manganese, cobalt, copper, iron, niobium, molybdenum and the like; chalcogen compounds include chalcogenides such as oxides, sulfides and selenides. Specific examples of transition metal chalcogen compounds include TiO ₂ ,
Cr ₃ O ₈ , V ₂ O ₅ , MnO ₂ , LiCoO ₂ , CuO, MoO ₃ and other oxides; Ti
Examples include sulfides such as S ₂ , VSe ₂ , Cr _0.5 V _0.5 S ₂ , CuCo ₂ S ₄ , FeS, and MoS ₃ ; selenides such as NbSe ₃ . Of these, preferred are MnO ₂ and V ₂ O ₅ . The positive electrode material is generally used as a molded body. As a method for obtaining a molded body, there is a method of pressurizing and molding a positive electrode material powder or a positive electrode material powder and a binder (powder such as Teflon, polyethylene, polystyrene) in a mold. In an organic solvent solution of a lithium salt used as an electrolytic solution, organic solvents include esters, ethers, 3
Substituted 2-oxazolidinones and mixed solvents of two or more of these may be mentioned. Examples of the esters include alkylene carbonate (ethylene carbonate, propylene carbonate, etc.) and lactone (r-butyrolactone, etc.), and preferably propylene carbonate. Examples of ethers include chain ethers (diethyl ether, 1.2-dimethoxyethane, tert-butyl methyl ether, tert-butyl ethyl ether, diethylene glycol dimethyl ether, etc.) and cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 2.5-dimethyltetrahydrofuran, 1.3 -Dioxolane, 1.4-dioxane, pyran, dihydropyran, tetrahydropyran, etc.), preferably tert-butyl methyl ether and 2.5-dimethyltetrahydrofuran.

Examples of 3-substituted-2-oxazolidinones include 3-alkyl-2-oxazolidinones (3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, etc.), 3
-Cycloalkyl-2-oxazolidinone (3-cyclohexyl-2-oxazolidinone, etc.), 3-aralkyl-2-oxazolidinone (3-benzyl-2-oxazolidinone, etc.), 3-aryl-2-oxazolidinone (3-phenyl-2- Oxazolidinone). It is preferably 3-alkyl-2-oxazolidinone, and particularly preferably 3-methyl-2-oxazolidinone. Among the organic solvents, preferred are propylene carbonate solvents and mixed solvents of propylene carbonate and ethers (volume ratio is usually 1: 9 to 9: 1, preferably 2: 8 to 8: 2)
Is. Lithium salts include lithium perchlorate, lithium borofluoride, lithium arsenide fluoride, lithium phosphorus fluoride,
Lithium chloride aluminate, lithium halide fluoride, lithium chloride, etc.) and lithium trifluoromethanesulfonate are preferred, and lithium chlorate is preferred. The concentration of the lithium salt in the composition is usually 0.1 to 5 mol / l, preferably 0.5 to 3 mol / l. The method for preparing the organic solvent solution of the lithium salt is not particularly limited as long as it is a method of dissolving the lithium salt in the organic solvent. Usually, a method of mixing the organic solvent and the lithium salt and stirring the mixture while heating the solution can be mentioned. Preferred organic solvent solutions of lithium salts are propylene carbonate solutions of lithium perchlorate and mixed solvent solutions of propylene carbonate and ethers of lithium perchlorate. In the battery of the present invention, the lithium metal is consumed by the self-discharge reaction by electrically contacting the calcined carbon having a turbostratic structure and the density of 1.9 to 2.2 g / cm ³ with metallic lithium in the battery. The fired carbon having a disordered layer structure contains lithium.

As an example, when a battery was manufactured using manganese dioxide as the positive electrode material, the battery immediately after manufacturing showed an open circuit voltage of about 3.3V, but when left in the dark for 1 week, metallic lithium disappeared completely, A reversible compound of fired carbon with a turbostratic structure containing is formed, and the open circuit voltage is about
It shows 3.0V. This self-discharge reaction can be expressed by the following equation. Calcined carbon with a turbostratic structure + Li → Calcined carbon with a turbostratic structure / Li Also, the electromotive reaction of the battery of the present invention can be expressed by the following formula. After the battery is manufactured, there is no problem if it is discharged between the positive electrode and the positive electrode without leaving it. In this case, the calcined carbon / Li having a turbostratic structure and a density of 1.9 to 2.2 g / cm ³ is not completely generated, and the negative electrode material has a turbostratic structure and its density is 1.9 to 2.2 g. / cm ³ of both fired carbon / Li and metallic lithium. In the battery of the present invention, the electric capacity of the negative electrode material is a reversible amount of lithium that has a turbostratic structure and has a density of 1.9 to 2.2 g / cm ³ that is contained in the fired carbon and can be put in and taken out electrochemically. Can be shown by. The electric capacity of the positive electrode material is usually 1 to 1.5 of the electric capacity of the negative electrode material.
Double, and preferably equal volume. The amount of metallic lithium is preferably about 1/2 of the total electric capacity of the positive electrode material and the negative electrode material. An example of the battery of the present invention will be described based on FIG. In the figure, (1) is a positive electrode can (positive electrode current collector), (2) is a metal net for current collection, (3) is a positive electrode material (positive electrode active material),
(4) is a separator containing an organic electrolyte, (5) is a gasket, and (6) has a disordered structure and its density is 1.
9 to 2.2 g / cm ³ of fired carbon, (7) metallic lithium,
(8) is a metal net for current collection, and (9) is a negative electrode can (negative electrode current collector). It has the turbostratic structure of (6) and its density is
1.9 to 2.2 g / cm ³ of fired carbon and metallic lithium of (7) are electrically connected in contact with each other. Next, the manufacturing method of the battery will be specifically described. Positive electrode can (1)
The metal net (2) for current collection is placed on the bottom surface of, and the positive electrode material (molded body) (3) is pressure-bonded onto it. Next, a separator (4) containing an organic electrolyte is placed on the positive electrode material (3), and then an L-shaped gasket (5) is inserted along the wall surface of the positive electrode can (1). Then, a calcined carbon (6) having a turbostratic structure and metal lithium (7) bonded to each other was adhered to a negative electrode can (9) with a metal net (8) for current collection interposed therebetween, and then a separator ( 4) Placed on the positive electrode can (1)
Bend the opening of inward and seal. FIG. 1 shows a state in which metallic lithium (7) is placed between the fired carbon (6) having a random layer structure and the separator (4) and electrically connected to the fired carbon having a random layer structure. However, the metallic lithium (7) may be placed at any position as long as it is in electrical contact with the fired carbon (6) having a turbostratic structure. For example, between the fired carbon (6) having a turbostratic structure and the metal net (8) for collecting current. [Examples] The present invention will be further described with reference to the following examples, but the present invention is not limited thereto. Example 1 40 g of coal tar pitch was placed in a quartz tube provided in an electric furnace, and nitrogen gas was passed through the quartz tube from room temperature to 70%.
The temperature was raised to 0 ° C. in 3 hours, and the temperature was left for 1 hour.
Next, the temperature was raised from 700 ° C to 1400 ° C in 3 hours, and firing was performed at that temperature for 1 hour. After that, cooling was performed while passing nitrogen gas to obtain 22.1 g of a black solid Pitch fired body. By X-ray diffraction, this fired body had a disordered layer structure with a crystallite size of 58.9Å and a density of 2.13 g / cm ³ . 2 g of this fired product and 0.2 g of polyethylene powder were mixed and kneaded well, then put into a mold to obtain a molded product with a thickness of 0.8 mm under a pressure of 400 kg / cm ³ G, and cut into a disc shape with a diameter of 16 mm. It was. The weight was 100 mg. A nickel net was placed on the bottom of a stainless steel positive can, and acetylene black and Teflon were added to manganese dioxide, and the kneaded and molded positive electrode material 130 mg was pressure bonded. Next, a separator made of a glass fiber mat containing an organic electrolytic solution which was a propylene carbonate solution in which lithium perchlorate was dissolved at a concentration of 1 mol / l was placed on the positive electrode material, and a gasket was inserted. Next, 8 mg of metallic lithium foil was bonded to 100 mg of the Pitch fired body prepared above, and the stainless steel negative electrode can was put in close contact with a nickel net and then placed on a separator, and the opening of the positive electrode can was placed inside. It was bent and sealed. The metallic lithium foil was placed between the fired body and the separator. Immediately after the battery was manufactured, the open circuit voltage was 3.3V, which was 1
The open circuit voltage after leaving for a week was 3.0V. When a charge / discharge cycle test was performed with a low current of 1 mA for 5 hours discharging and 5 hours charging, good reversible charging / discharging characteristics were obtained up to 300 cycles. Example 2 A battery produced in exactly the same manner as Example 1 immediately after production, 1 mA
Was discharged at a final voltage of 1.5 V with a constant current of. The obtained discharge capacity was 27 mAh. After that, charge with identification current for 5 hours, 5
After conducting a charge-discharge cycle test called time discharge,
Good reversibility was obtained up to 300 cycles. Cell of the invention [Effect of the Invention] The charging and discharging by using what has and density that a turbulent layer structure as the negative electrode material was electrically contact a sintered body of carbon and lithium metal 1.9~2.2g / cm ³ It has the features that it suppresses the deposition of dendrites of lithium on the negative electrode side due to the repetition of the above steps, has a high battery voltage, has a good voltage flatness during discharge, has a large battery capacity, and has a high energy density. Metal by the built-in self-discharge reaction in the battery in addition state battery of the present invention is negative electrode material has and its density turbostratic structure in which electrical contact causes the lithium metal to the sintered body of carbon atoms of 1.9~2.2g / cm ³ Lithium can be contained in the calcined body carbon having a turbostratic structure, and metallic lithium is contained in advance in the calcined carbon having the turbostratic structure, which is economically advantageous as compared with the method of assembling the battery thereafter. is there.

[Brief description of drawings]

 Figure 1 is a sectional view of the battery. (3) …… Cathode material, (4) …… Separator (6) …… Calculated carbon with random layer structure (7) …… Metallic lithium

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-90863 (JP, A) JP 60-235372 (JP, A)

Claims (2)

[Claims] 1. A calcined carbon having an organic solvent in which a lithium salt is dissolved as an electrolytic solution, a transition metal chalcogen compound as a positive electrode material, and having a turbostratic structure and a density of 1.9 to 2.2 g / cm ^3. An organic electrolyte secondary battery characterized in that a negative electrode material is obtained by electrically contacting lithium metal with metallic lithium in the battery. 2. The battery according to claim 1, wherein the calcined carbon is pitch calcined carbon.