JPH04115458A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain excellent battery properties of high voltage and high discharging capacity and improve the stability at the time of short circuit by using a carbonacesous material, which is a graphitized carbon consisting of mesophase small spherical bodies produced during carbonation of pitch and doped with lithium, as an anode active mass. CONSTITUTION:After heating pitch, mesophase small spherical bodies are separated by pyridine or quinoline. Then, firing at about 1500-3000 deg.C is carried out to graphitize the mesophase small spherical bodies. The graphitized carbon has high lithium-absorbing function and the voltage at the time of desorption of lithium and overvoltage at the time intercalation and desorption is low and high density is obtained as a combination agent. Then, the graphitized carbon is prepared into a negative electrode composing agent using a binder to prepare a negative electrode and doped with lithium.

Description

[Detailed Description of the Invention] The present invention provides high voltage,
The present invention relates to a non-aqueous electrolyte secondary battery that has excellent battery performance with a high discharge capacity and is also excellent in safety in the event of a short circuit.

In recent years, non-aqueous electrolyte batteries that use alkali metals such as lithium as negative electrode active materials have been used as memory pack amplifiers for personal computers, VTRs, etc. because they exhibit excellent self-discharge properties at high voltage and high energy density. It is attracting a lot of attention as a driving source for cameras and cameras.

However, in the case of secondary batteries that use lithium metal in the negative electrode to obtain high energy density, dendrite-like lithium may be formed as a result of repeated charging and discharging.
Another problem is that lithium tends to be electrochemically inactivated, resulting in a significant decrease in charge/discharge cycle durability.

In addition, lithium metal is highly active against moisture and has a low melting point, so it is easily ignited, and there are concerns that in the event of a sudden short circuit, heat will be generated due to high current, leading to an extremely dangerous situation.

Conventionally, one way to solve these problems is to use carbonaceous materials that can be doped with lithium between the eyebrows of crystals composed of carbon atoms, such as carbonaceous materials in which lithium is intercalated with graphite. It has been proposed to use this as a negative electrode (eg, US Pat. No. 4,423,125).

Here, the characteristics necessary for a carbonaceous material suitable for negative electrodes for high-energy batteries include not only a high ability to absorb lithium between layers of carbon atoms, but also a low voltage when desorbing lithium, It is desired that the overvoltage during insertion and deintercalation be low, and that the mixture prepared using carbon powder as a base exhibits high density.

From this point of view, the above-mentioned carbonaceous materials are still far from being sufficient. Furthermore, in the past, various optimal values have been proposed for the distance between the eyebrows of the (002) plane, the crystallite size, etc. of such carbonaceous materials; for example, 2000
It has been reported that graphitized materials subjected to high-temperature firing at temperatures above °C exhibit relatively good properties, but a carbonaceous material that satisfies the above requirements in a well-balanced manner has not been obtained. is the current situation.

The present invention was developed in view of the above circumstances, and has a large lithium storage capacity, low voltage during lithium desorption and low overvoltage during lithium insertion and desorption, and can provide a high density as a mixture. By developing a carbonaceous material and using it as a negative electrode active material, we provide a non-aqueous electrolyte secondary battery that has excellent battery characteristics such as high voltage and high discharge capacity, and also has excellent safety in the event of a short circuit. The purpose is to

In order to achieve the above objective, the present inventor has conducted intensive studies and found that a graphitized carbonaceous material consisting of mesophase small spheres produced in the pinch carbonization process is a lithium-ion carbonaceous material. It has a large storage capacity, low voltage during lithium desorption and low overvoltage during lithium insertion and desorption, and can obtain high density as a mixture, making it extremely suitable as a negative electrode material for non-aqueous electrolyte secondary batteries. It has been found that it has favorable properties.

In other words, mesophase carbon obtained from a pinch of oil or coal has a uniform spherical shape with an average particle size of 5-15 μm, and a mixture of this mesophase carbon with a binder has a shape similar to that of Therefore, they are packed with few gaps, making it easy to achieve close packing, and a very high density can be obtained as a mixture. Specifically, the highest level for conventional carbon materials was 1.5 g/cm2, but for this mesophase carbon, it was 1.8 g/cm2 for the above reasons.
A high density of 2 can be obtained. Furthermore, when this mesophase carbon is graphitized, the carbon atoms are arranged in layers in the latitudinal direction of the sphere, creating a structure in which the glabella is exposed over the entire surface of the sphere, allowing lithium to enter from all directions. For this reason, whereas in anisotropic materials such as coke, lithium can only enter from a certain direction, this graphitized mesophase carbon has a wide site area where lithium can be inserted and desorbed. Therefore, a high lithium storage capacity can be obtained, and at the same time, good high current discharge properties can also be achieved.

Furthermore, by firing carbonaceous materials at a high temperature of 1500°C or higher, it is possible to increase the ability to absorb lithium between layers and lower the lithium desorption potential, thereby increasing the battery voltage. However, mesophase spherules are much easier to graphitize than other carbonaceous materials, and graphitized mesophase materials have a
It achieves a lithium storage capacity of more than 1.5 g and a lithium desorption potential of 0.3 V or less relative to the oxidation-reduction potential of lithium, making it highly preferable as a negative electrode material for non-aqueous electrolyte secondary batteries.

Therefore, the present inventor constructed a negative electrode using the graphitized mesophase material as an active material, a positive electrode using a metal oxide, sulfide, or a conductive polymer as an active material, and a non-containing material containing lithium. It was discovered that a non-aqueous electrolyte secondary battery with excellent battery characteristics such as high voltage and high discharge capacity, as well as excellent safety in the event of a short circuit, can be obtained by combining it with an aqueous electrolyte. It is completed.

Therefore, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte containing lithium, in which pitch is carbonized as an active material of the negative electrode. Provided is a non-aqueous electrolyte secondary battery characterized by using a carbonaceous material in which graphitized carbon made of generated mesophase small spheres is doped with lithium.

The present invention will be explained in more detail below.

The negative electrode of the non-aqueous electrolyte secondary battery of the present invention uses, as an active material, a carbonaceous material in which mesophase small spheres are graphitized and doped with lithium, as described above.

Here, the mesophase spherules are obtained through a pinch carbonization process. Specifically, it is obtained by heat-treating a pinch obtained from petroleum, coal, etc. at a temperature of 400 to 450°C for 1 to 2 hours, and then separating it with pyridine or quinoline.

As a method for graphitizing these mesophase spherules, 1
A method of acidifying at a temperature of 500 to 3000°C, particularly 2000 to 2500°C for about 5 to 50 hours is preferably employed.

In this case, it is preferable to perform the firing in an inert gas atmosphere.

This graphitized carbon consisting of mesophase small spheres is made into a negative electrode mixture using a binder and constitutes a battery negative electrode. In this case, the graphitized carbon is doped with lithium. Methods for doping lithium include electrochemically doping lithium with a carbon material as a counter electrode in a non-aqueous electrolyte containing lithium ions, or forming this graphitized carbon into a plate shape using a binder. Then, this and lithium metal are pressure-welded,
A method of doping lithium within the battery after assembling the battery with the positive electrode and the non-aqueous electrolyte can be suitably employed. As the binder used for preparing the negative electrode mixture, any substance may be used as long as it has a binding effect and solvent resistance, but fluororesin is particularly preferable, and polytetrafluoroethylene powder is especially preferable. used.

The positive electrode of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited (the positive electrode materials used in ordinary non-aqueous electrolyte secondary batteries can be used; specifically, V2O5I V6O
13, LiCo0z, MnO2, MnO3, LiCo
Metal oxides such as 0z, Tl521 Mos! ! It is possible to use a positive electrode whose active material is a metal sulfide such as, a conductive polymer such as polyaniline, or the like.

Furthermore, the non-aqueous electrolyte used in the secondary battery of the present invention is one containing lithium, specifically lithium salt, especially LiClO4, LiB stain i P F b + L
One or more selected from r CF 3 S03 + and LiAsF are preferred. These electrolytes are
It is usually used in a dissolved state in a solvent, or in this case, the solvent includes, but is not limited to, propylene carbonate, tetrahydrofuran, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, dioxolane, butylene carbonate. and dimethylformamide, or a mixed solvent of two or more thereof is suitable.

The non-aqueous electrolyte secondary battery of the present invention is usually constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator may be interposed between the positive and negative electrodes to prevent current short-circuiting due to contact between the two electrodes. can. As a separator,
Materials that can reliably prevent contact between the electrodes and allow the electrolyte to pass through or contain them, such as nonwoven fabrics, porous woven fabrics, and nets made of synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, etc. However, a microporous film made of polypropylene or polyethylene having a thickness of about 20 to 50 μm is particularly preferably used.

In addition, as other constituent members of the non-aqueous electrolyte secondary battery of the present invention, those commonly used can be used without any problem. Further, the form of the battery is not particularly limited, and may be of various forms such as a coin type, button type, paper type, or spiral-structured cylindrical battery.

As explained above, the non-aqueous electrolyte secondary battery of the present invention is
Since graphitized mesophase small spherical carbon doped with lithium is used as the negative electrode active material, excellent battery performance such as high discharge capacity can be obtained, and it is also extremely safe.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples below.

Prior to the Examples, an example of manufacturing graphitized carbon made of mesophase small spheres constituting the negative electrode of the non-aqueous electrolyte secondary battery of the present invention will be described.

Production example: The quinoline-soluble content of a pinch of coal tar is heated to 430°C for 12
After heat treatment for 0 min, mesophase spherules were separated with pyridine.

This mesophase small sphere was placed in a nitrogen gas atmosphere for 2500 min.
The mixture was fired at ℃ for 24 hours to graphitize, thereby obtaining a carbonaceous material for a battery negative electrode.

For 100 parts (by weight, same hereinafter) of the above carbonaceous material, 10 parts of polytetrafluoroethylene powder was added as a binder.
After kneading with an organic solvent, a mixture sheet with a thickness of about 200 μm was prepared by roll rolling.

When the density of this mixture sheet was measured, it was found to be 1.75g/
cm3, and had high density.

On the other hand, pitch coke L PAN milled fiber,
10 parts of polytetrafluoroethylene powder was added to each 100 parts of acetylene black, and three types of mixture sheets each having a thickness of about 200 μm were prepared in the same manner as above.

When the density of these mixture sheets was measured, it was 1.42 g/cm3 for pitch coke and 1.42 g/cm3 for PAN milled fiber. , 48 g/cm'l', and 1.38 g/cm'' for acetylene black, both of which had a lower density than the mesophase carbon mixture sheet.

[Example, comparative example]

Each mixture sheet obtained in the above manufacturing example was punched out to a specified size,
A lithium foil with a thickness of 70 μm was bonded to the negative side of this, and a W4 foil with a thickness of 50 μm was further integrated as a current collector using a conductive adhesive, thereby producing four types of battery negative electrodes.

On the other hand, vanadium oxide represented by the chemical formula LiV, O, was used as an active material, 10 parts of acetylene black was added as a conductive agent, and 10 parts of fluororesin was added as a binder, and after thorough mixing, organic solvent The mixture was kneaded and rolled with a roll to a thickness of about 400 μm to obtain a mixture sheet. This sheet was punched out to a predetermined size in the same way as the negative electrode above, and was 50 μm thick.
A battery positive electrode was produced by integrating thick aluminum foil as a current collector using a conductive adhesive.

Using the above negative and positive electrodes, a 25 μm thick polypropylene microporous film was used as the separator, and the electrolyte was a mixed solvent of propylene carbonate and ethylene carbonate (volume ratio 1:1) with 1 mol/7 of LiPFb! The diameter is 20. Omr@ assembled four types of coin-shaped batteries with a thickness of 1.6 mm.

It should be noted that these batteries are expected to have a dischargeable capacity of about 28 mAH on the positive electrode, but the capacity on the negative electrode side is at most about 18 mAH, and it is clear that these batteries are regulated by the negative electrode capacity.

For the above four types of batteries, each charge/discharge current is 1 mA.
In, discharge end voltage 2.0■, charge end voltage 3.5
Charge and discharge were repeated under the condition of V, and cycle characteristics were measured up to 100 cycles. The results are shown in the drawing.

From the results shown in the drawings, it was found that a battery (Example 1) using a mixture of graphitized mesophase small spheres, which is a product of the present invention.
It was confirmed that the battery had the highest discharge capacity and the capacity deterioration due to charge/discharge cycles was very small.

In addition, in order to confirm the characteristics of a mixture sheet made of graphitized mesophase small spheres as a reference, four types of coin-type batteries were fabricated in the same manner as above except that the positive electrode was made of lithium metal, and each battery had a 1 mA current. The reaction proceeded in the direction of desorbing lithium ions from the negative electrode using an electric current, and the occlusion capacity up to +IV and the average voltage at the time of desorption with respect to the oxidation-reduction potential of lithium were determined. The results are shown in Table 1.

From the results shown in Table 1, it is confirmed that graphitized mesophase small spheres doped with lithium have a high lithium storage capacity and are capable of intercalating and deintercalating lithium at low potential. It was confirmed that this material is very suitable as a negative electrode material for electrolyte secondary batteries.

[Brief explanation of the drawing]

The drawing is a graph showing the discharge capacity and cycle characteristics of batteries of Examples and Comparative Examples of the present invention. Applicant Brideston Co., Ltd.

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode capable of intercalating and deintercalating lithium, and a non-aqueous electrolyte containing lithium, a small mesophase produced in the carbonization process of pitch is used as the active material of the negative electrode. A non-aqueous electrolyte secondary battery characterized by using a carbonaceous material in which graphitized carbon consisting of spheres is doped with lithium.