JPH03134970A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To improve the high-voltage, high-capacity and high-rate charge/ discharge characteristics by forming a negative electrode with a carbonic material applied with expansion treatment. CONSTITUTION:A negative electrode is obtained by carbonizing or graphitizing an organism, numerous cracks are generated between layers, and an active material is stored in a carbonic material largely expanded in the C-axis direc tion. Coal pitch carbon fibers (spacing d<002>=3.37Angstrom ) are immersed in a complex solution mixed and stirred with naphthalene and metallic lithium at the 1:1 mol% in tetrahydrofuran, for example, they are reacted in the inert gas atmo sphere, then it is washed with tetrahydrofuran as a residual compound, and it is quickly heat-treated at a high temperature near 1,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a non-aqueous solvent secondary battery, and more particularly to a novel compact and lightweight secondary battery.

Conventional technology In recent years, consumer electronic devices have rapidly become portable and cordless, and there is an increasing demand for small, lightweight, and high-energy-density secondary batteries that serve as the power source for driving these devices. . From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, have great expectations as batteries with especially high voltage and high energy density, and their development is urgently needed.

Conventionally, manganese dioxide, vanadium pentoxide, titanium disulfide, etc. have been used as positive electrode active materials for lithium secondary batteries, and the battery is composed of this positive electrode, a lithium negative electrode, and an organic electrolyte, and is used for charging and discharging. It's repeating. However,
In general, secondary batteries that use lithium metal for the negative electrode have problems such as internal short circuits due to dendrite-like lithium generated during charging and side reactions between the active material and the electrolyte, which are major obstacles to the development of secondary batteries. Furthermore, no material has been found that satisfies high rate charge/discharge characteristics or overdischarge characteristics.

On the other hand, a new type of electrode active material that utilizes the intercalation reaction of layered compounds is attracting attention, and graphite intercalation compounds have been used as electrode materials for secondary batteries for a long time.

In particular, graphite intercalation compounds incorporating anit ions such as Cl0-PFBF- ions are used as positive electrodes, while graphite intercalation compounds incorporating cations such as Li SNa+ are considered as negative electrodes. However, graphite intercalation compounds that incorporate such cations are extremely unstable, and when a graphite material is used as a negative electrode, it lacks stability as a battery, has a low capacity, and is accompanied by decomposition of the electrolyte, making it difficult to use lithium. It could not be used as a substitute for the negative electrode.

Recently, n-doped pseudographite materials obtained by carbonizing various hydrocarbons or polymeric materials have been found to be effective as negative electrodes, have relatively high utilization rates, are excellent in battery stability, are compact, It has been discovered that a lightweight secondary battery can be provided, and research is being actively conducted.

Problems to be Solved by the Invention Generally, it is reported that the upper limit of the amount of lithium that can be intercalated between graphite layers is the first stage graphite intercalation compound C6L i in which one lithium atom is inserted for every six carbon atoms. In that case, the active material is 372mAh/
It has a capacity of g.

Using the aforementioned pseudographite material as an electrode material, the amount of lithium absorbed and released was determined to be 150 to 200 mAh/gca.
Since only a capacity of rbon can be obtained and the polarization of the carbon electrode is large during charging and discharging, it is difficult to obtain a satisfactory capacity and voltage when combined with a positive electrode such as LiCoO2.

The present invention solves the conventional problems as described above, and
The object of the present invention is to provide a non-aqueous solvent secondary battery that has a high capacity and also has excellent high rate charge/discharge characteristics.

Means for Solving the Problem In order to solve this problem, the present invention improves the utilization rate of the carbon electrode by using a carbonaceous material of the negative electrode subjected to an expansion treatment, preferably carbon fiber. It suppresses polarization.

As the carbonaceous material used as the working negative electrode material, a pseudographite material with a certain degree of turbostratic structure is preferred, but its utilization rate is low due to the effects of expansion and contraction between layers during charging and discharging, and polarization increases. High rate charge/discharge becomes difficult. However, the expandable carbon fiber according to the present invention has numerous cracks between the layers and expands in the C-axis direction, so the interlayer spacing is wide and lithium can be easily absorbed and released. As a result, the utilization rate is improved and the polarization is reduced, so it is possible to construct a secondary battery that has high voltage, high capacity, and can be charged and discharged at a high rate.

In general, expanded graphite is known to be obtained by rapidly heating a graphite-sulfuric acid intercalation compound or its residual compound using natural graphite powder as a raw material, and is used for gasket materials etc. by compression molding. It is being

However, when this expanded graphite is used as a negative electrode carbon material, the molded body swells during charging and discharging and cannot maintain its original shape, resulting in poor cycle characteristics. However, when carbon fibers are used, the shape of the fibers is maintained even after expansion, and good cycle characteristics can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. When naphthalene and metallic lithium are mixed in tetrahydrofuran (THF) at a molar ratio of 1:1 and stirred, a complex of lithium and naphthalene is formed in the solution.

Commercially available coal-pitch carbon fibers (planar spacing d002 = 3.37 A) were immersed in this complex solution and allowed to react for one day under an inert gas atmosphere. Then, naphthalene in the complex is replaced with carbon fiber, forming a ternary intercalation compound LiC2 that incorporates lithium and THF between the layers.
o(THE). was generated. The reaction product was washed with THF to form a residual compound, and then subjected to rapid heat treatment at a high temperature of nearly 1000°C.

As a result, the carbon fiber expands more than 10 times in the C-axis direction,
d002 was 3.50A. The obtained carbon fibers were crushed into powder. In this example, in order to examine the amount of lithium that can be occluded and released by the negative electrode carbonaceous material and the polarization characteristics of the carbon electrode, a coin-shaped battery was constructed and evaluated with the carbon electrode as the positive electrode and metallic lithium as the negative electrode. Ta. FIG. 1 shows a longitudinal cross-sectional view of the coin-shaped battery. In the figure, 1 is a battery case made of organic electrolyte-resistant stainless steel plate;
2 is a sealing plate made of the same material, and 3 is a positive electrode current collector made of stainless steel, which are spot welded to the inner surface of the case 1.

4 is a metallic lithium negative electrode which is pressed onto the sealing plate 2. 5
The positive electrode mixture was prepared by mixing 85 parts by weight of the carbon fiber powder described above with 15 parts by weight of a fluororesin binder, filling 0.05 g onto the current collector 3, and then molding the mixture. 6 is a microporous polypropylene separator, and 7 is a polypropylene insulating backing. The electrolyte contains propylene carbonate and 1
．． Lithium perchlorate was dissolved in an equal volume mixed solvent of 2-dimethoxyethane at a ratio of 1 mol/l.

In the evaluation test, a constant current charge/discharge test was performed under the conditions of a charge/discharge current density of 0.3 mA/ct, an end-of-charge voltage of 2, OV, and an end-of-discharge voltage of 0.05V.

The dimensions of this battery are 20mm in diameter and 1°6mm in total height.
It is.

FIG. 2 shows a comparison of charge-discharge curves at the 10th cycle of batteries using each carbon fiber. Battery 1 is a case in which conventional coal pitch-based carbon fibers are used untreated after being pulverized, and they similarly have pseudographitization properties and are made using different carbon precursors, such as petroleum pitch-based carbon fibers or polyacrylonitrile (PAN). system,
The variation when using vapor-grown carbon fiber is indicated by diagonal lines. Battery 2 uses expandable carbon. As is clear from the discharge curve, in the conventional example, the capacity, that is, the amount of lithium that can be occluded, was 140 to 160 mAh/g carb.
on, which is a low value, but this improved product has a low value of 350mAh/g.
It has a capacity more than twice that of conventional carbon, and has an upper limit of 372mAh/g carbon (C6L
It can be seen that it is very close to i). Furthermore, a comparison of the charging curves shows that the improved product has much smaller polarization than the conventional example. Therefore, it can be said that charging and discharging at a higher current density is possible.

Effects of the Invention As is clear from the above explanation, the nonaqueous solvent secondary battery according to the present invention using a negative electrode carbonaceous material in which an active material such as lithium is occluded in an expandable carbonaceous material such as an expandable carbon fiber has the following effects: , cation-doped layered compounds, e.g. LiCo
By combining it with a positive electrode such as O2, it is possible to obtain a secondary battery that has high voltage, high capacity, and can be charged and discharged at a high rate.

In the examples, expandable carbon fibers made from coal pitch-based carbon fibers were used; however, similar effects can be obtained even if petroleum pitch-based, PAN-based, or vapor-grown carbon fibers are used as the raw material carbon fibers. It worked.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a coin-shaped battery in an example of the present invention, and FIG. 2 is a diagram showing a comparison of charge-discharge curves at the 10th cycle. 1... Case, 2... Sealing plate, 3-... Positive electrode current collector, 4... Negative electrode, 5... Positive electrode, 6... Senokureta, 7... ...Insulating backing.

Claims (3)

[Claims] (1) In a non-aqueous solvent secondary battery comprising a rechargeable positive electrode, a non-aqueous electrolyte, and a rechargeable negative electrode; the negative electrode is obtained by carbonizing or graphitizing an organic substance. A non-aqueous solvent secondary battery is a non-aqueous solvent secondary battery in which an active material is occluded in a carbonaceous material which expands greatly in the C-axis direction by forming numerous cracks between the layers. (2) The non-aqueous solvent secondary battery according to claim 1, wherein the carbonaceous material is carbon fiber expanded by 10 times or more in the C-axis direction. (3) The above carbonaceous material is obtained by rapidly heating a ternary intercalation compound or its residual compound made of carbon fiber and incorporating an alkali metal such as lithium or sodium and a nonaqueous solvent between the layers at high temperature. 3. The non-aqueous solvent secondary battery according to claim 1 or 2, which is an expandable carbon fiber made of polyester.