JPH09330716A - Non-aqueous solvent secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous solvent secondary battery with its high capacity and superior cycle characteristics. SOLUTION: A non-aqueous solvent secondary battery having a positive 6, a negative electrode 4 composed of a carbonaceous material capable of storing and discharging lithium ions, and a lithium ion conductive electrolyte, wherein the non-aqueous solvent secondary battery is its main mixture of which the carbon material is 2 to 40μm in average fiber diameter, a graphitized mesophase pitch based carbon fiber is 10 to 100μmin average fiber length, and the coke-based carbon particles has 50 to 100μm average particle size. Here, it is preferable that the component ratio of graphitized mesophase pitch based carbon fiber in the carbonaceous material is 30 to 90wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous solvent secondary battery, and more particularly to a non-aqueous solvent secondary battery having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for development of a secondary battery that is small and lightweight, has a high energy density, and can be repeatedly charged and discharged.

In this type of secondary battery, lithium or a lithium alloy is used as the negative electrode active material, and oxides, sulfides or selenides of molybdenum, vanadium, titanium, niobium and the like are used as the positive electrode active material. Things are known. However, in a secondary battery system composed of lithium or a lithium alloy as the negative electrode active material,
When charge and discharge are repeated, dendrite of lithium is generated on the negative electrode surface, so that there is a problem that the charge and discharge cycle life is short.

With respect to the problem of dendrite generation, it has been proposed to form a negative electrode with lithium and a carbonaceous material as a carrier, and it is attempted to extend the life of the charge / discharge cycle. In addition, this type of non-aqueous solvent secondary battery has a high operating voltage, and has been attracting attention as a battery capable of significantly improving charge / discharge cycle life. However, when the graphitized mesophase pitch-based carbon fiber is used alone as the carbon material, the filling density of the negative electrode molded body (negative electrode) cannot be sufficiently obtained, and therefore the negative electrode deteriorates with repeated charging and discharging. This is apt to occur, and as a result, there is a problem that charge / discharge cycle characteristics are adversely affected.

[0005]

As a measure for improving the charge / discharge cycle characteristics of a non-aqueous solvent secondary battery using lithium or a lithium alloy as a negative electrode active material, it is necessary to select a carbonaceous material carrying lithium. Various attempts have been made. For example, (a) a non-graphite carbon material having an interplanar spacing d ₀₀₂ of (002) of 0.37 nm or more and a true density of less than 1.70 g / cm ^{3 of} (002) determined by X-ray diffraction and X-ray diffraction (002)
A mixed system of graphite carbon materials having a surface spacing d ₀₀₂ of less than 0.34 nm and a true density of 2.1 g / cm ³ or more, (b) mesophase pitch carbon fibers (fiber length 10 to 100 μm, fiber diameter 4 to 15 μm),
And the interplanar spacing d ₀₀₂ of (002) determined by X-ray diffraction
Mixing of carbonaceous material of less than 0.338 nm and carbonaceous material containing 70 Vom% or more of powder having a particle size of 15 μm or less and having an interplanar spacing d ₀₀₂ of (002) of 0.338 to 0.380 nm as determined by an X-ray diffraction method. It has been proposed to use a system, (c) a mixed system of carbon fibers having a unit area weight of 10 to 500 g / m ² and carbon powder having an average particle size of 30 μm or less as a lithium carrier (JP-A-7- 192724, JP-A-8-83608, JP-A-8-8
3609, JP-A-8-31405, etc.).

However, in the case of a non-aqueous solvent secondary battery in which the negative electrode having the above-mentioned structure is incorporated, further improvement and improvement are desired in terms of high capacity and the like. That is, in the case of a lithium-carbonaceous material-based negative electrode having a conventionally known configuration, the packing density of the negative electrode molded body is low, and as a result, the battery capacity is relatively small, so that its use as a power source is also restricted. There's a problem. Therefore, in order to fully utilize the features of the small power source, it is necessary to first increase the capacity of the non-aqueous solvent secondary battery.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a non-aqueous solvent secondary battery having a high capacity and excellent cycle characteristics.

[0008]

According to a first aspect of the present invention, there is provided a non-aqueous solvent secondary comprising a positive electrode, a negative electrode made of a carbonaceous material capable of absorbing and releasing lithium ions, and a lithium ion conductive electrolyte. A battery, wherein the carbonaceous material is a graphitized mesophase pitch carbon fiber having an average fiber diameter of 2 to 40 μm and an average fiber length of 10 to 100 μm, and an average particle size of 50 to 100.
It is a non-aqueous solvent secondary battery characterized in that it is mainly composed of a mixture of coke-based carbon particles of μm.

The invention of claim 2 is characterized in that, in the non-aqueous solvent secondary battery of claim 1, the mixture contains 30 to 90% by weight of graphitized mesophase pitch carbon fiber.

That is, as a negative electrode material having a function of storing and releasing lithium ions, graphite mesophase pitch carbon fibers having an average fiber diameter of 2 to 40 μm and an average fiber length of 10 to 100 μm, and coke-based carbon particles having an average particle size of 50 to 100 μm. The main idea is to use a mixture with.

In the present invention, the mixing ratio of the coke-based carbon particles is 10 to 70% by weight, more preferably 10 to 50% by weight. Here, the mixing ratio of the coke-based carbon particles is 10% by weight.
If it is less than the above range, the packing density of the negative electrode molded body is not so improved, and a sufficient effect cannot be obtained. Further, if it exceeds 70% by weight, there is no improvement in the packing density of the negative electrode molded body according to the increase in the amount,
It is desirable to select the amount within the range of 10 to 70% by weight, because the tendency due to the effect of the coke-based carbon particles causing the reduction of the capacity is warped.

In the present invention, the graphitized mesophase pitch carbon fiber is made of petroleum pitch, coal tar, heavy oil, organic resin, synthetic polymer material or the like as a raw material and fired in an inert gas stream or in the air. -It is a carbonaceous fiber obtained by carbonization. More specifically,
The carbon fiber used can be obtained as follows. That is, (1) petroleum pitch, coal tar, heavy oil, organic resin, synthetic polymer material, etc. are used as raw materials, and this is used in an inert gas such as nitrogen, argon, etc.
Obtained by carbonizing under conditions of temperature of 1000 ℃ and normal pressure or pressure, or (2) by graphitizing in inert gas at temperature of 1000 to 3200 ℃ and conditions of normal pressure or pressure. To be In particular, it can be produced by melting a mesophase pitch-based raw material, spinning the fiber to make it infusible, and then carbonizing or graphitizing it.

The carbonization temperature is 2000 ° C. or lower, preferably 600 to 1500 ° C., and the graphitization temperature is 1000 to 1000 ° C.
It is 3200 ° C, preferably 2500-3200 ° C.

The carbon fiber may have a so-called orientation, a random orientation, or a mixture of a portion having orientation and a portion having random orientation. Good. In addition, the orientation and the form of the carbon layer in the cross section of the carbon fiber include a radial structure,
Radial structure on the fiber surface side and random structure, strip structure, or lamella structure on the inside can be mentioned. And
Graphite structure of the carbon fibers is defined by obtained by X-ray diffraction (002) plane lattice spacing (d ₀₀₂₎ and the c-axis direction of the crystallite size of the (L _c), the surface spacing (d ₀₀₂₎
A graphite structure having an average value of 0336 to 0.380 nm and an average value of crystallite size (L _c ) of 1 to 70 nm is desirable. On the other hand, the interplanar spacing (d ₀₀₂ ) of the (002) plane obtained by X-ray diffraction of the coke-based carbon particles and the crystallite size (L
_c ) is preferably 0.340 to 0.370 nm and 0.5 to 10 nm, respectively.

That is, when the average value of the interplanar spacing (d ₀₀₂ ) and the average value of the crystallite size (L _c ) are out of the above ranges, the lithium ion storage / release amount at the negative electrode is reduced, and the graphite structure is reduced. Deterioration, gas generation due to reductive decomposition of the solvent in the non-aqueous electrolyte, and the like are caused, and a tendency such as reduction in capacity of the secondary battery is recognized.

Further, the coke-based carbon particles are 50-100
The diameter of the graphitized mesophase pitch carbon fiber is 1 to 100 μm, preferably 2 to 40 μm, and more preferably 4 to 20 μm. If the fiber diameter, fiber length, and particle size are less than 1 μm, it may easily pass through the holes of the separator that is interposed between the positive electrode and the positive electrode, and a short circuit may occur between the positive electrode and the specific surface area. Since it is large, side reactions with the electrolytic solution are likely to occur. On the other hand, if the fiber diameter and the fiber length exceed 100 μm, the specific surface area decreases, and the lithium ion storage / release amount decreases. Therefore, in forming the negative electrode, it is effective to adjust the average diameter, the particle diameter, and the like in advance within the above range by crushing carbon fibers and particles.

By mixing the graphitized mesophase pitch carbon fiber and the coke carbon particles, particles having different shapes are mixed. Then, by changing the compounding ratio, it is possible to control the porosity of the negative electrode molded body by the pressure press and improve the packing density of the negative electrode molded body.

In the present invention, as the positive electrode, a lithium manganese compound prepared from a lithium salt and manganese dioxide, an oxide or sulfide of molybdenum, vanadium, titanium, niobium or the like is used as an active material, and a conductive material and For example, a binder may be blended and molded into a pellet state.

Here, examples of the conductive material include carbon black such as acetylene black and nickel powder. Further, as the binder, polyfluoroethylene, polyethylene, polypropylene, poly (meth) acrylic acid, poly (meth) acrylic acid salt, poly (meth) acrylic acid ester and (meth) acrylic acid and / or (meth) Examples thereof include copolymers with acrylic acid esters and other copolymers.

In the present invention, as the lithium ion conductive electrolytic solution, a lithium salt (electrolytic solution) is added to a non-aqueous solvent.
Examples thereof include a non-aqueous electrolytic solution dissolved at a rate of about 0.5 to 1.5 mol / l and a lithium ion conductive solid electrolyte.

Here, as the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, 2- One or a mixture of two or more selected from methyltetrahydrofuran, dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate can be mentioned. On the other hand, as lithium salt (electrolyte), lithium perchlorate (LiClO ₄ ),
Examples include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and the like. Further, as the lithium ion conductive solid electrolyte, for example, a polymer solid electrolyte in which a lithium salt is compounded with a polymer compound can be mentioned.

In the present invention, the separator interposed between the positive and negative electrodes and having the function of carrying the lithium ion conductive electrolyte is, for example, a nonwoven fabric of polyolefin resin such as polyethylene or polypropylene, or a porous film of these. Is mentioned.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described below with reference to FIG.

Example 1 (1) Preparation of Positive Electrode Vanadium pentoxide was prepared as an active material, artificial graphite was prepared as a conductive material, and polytetrafluoroethylene was prepared as a binder. Next, the active material, the conductive material, and the binder are mixed and kneaded at a weight ratio of 90: 10: 5, and the mixture is pressure-molded by a pressure press machine into a pellet shape. Was produced.

(2) Preparation of Negative Electrode Pitch-based carbon fibers made from mesophase pitch were finely pulverized and fired at a temperature of 2800 ° C. to obtain carbon fibers having an average fiber diameter of 9 μm and an average fiber length of 40 μm. Using tar as a raw material, carbon particles having an average particle size of 75 μm obtained by subjecting to distillation and high temperature heat treatment were mixed at a weight ratio of 90:10 to prepare a carbonaceous material. Then, butadiene-styrene rubber was added as a binder at a ratio of 5 parts by weight to 95 parts by weight of this carbonaceous material, and mixed and kneaded.
This mixture was pressure-molded into a pellet shape with a pressure press to prepare a negative electrode. The packing density of this negative electrode molded article was 1.250 g / cm ³ .

(3) Assembly of Battery FIG. 1 is a cross-sectional view of a coin-shaped non-aqueous solvent secondary battery according to this example, which was assembled as follows.

First, a negative electrode current collector 2 made of nickel expanded metal having a diameter of 12 mm and a thickness of 0.05 mm is welded to the inner surface of the negative electrode container 1 made of stainless steel, and the negative electrode container 1 and the insulating gasket 3 are integrated. did. Next, a metal lithium plate having a thickness of 0.19 mm and a diameter of 15 mm was pressure-bonded onto the negative electrode current collector 2, and the negative electrode 4 was attached on the surface of the lithium plate. In addition,
The metallic lithium plate is inserted in the negative electrode 4 after the battery is assembled.

Then, a polypropylene non-woven separator 5 impregnated with an electrolytic solution was placed on the surface of the negative electrode 4. That is, a polypropylene non-woven fabric was impregnated with an electrolytic solution prepared by dissolving lithium borofluoride to a concentration of 1 mol / l in a non-aqueous solvent in which ethylene carbonate and γ-butyrolactone were mixed at a volume ratio of 2: 1. The separator 5 was placed on the surface of the negative electrode 4.

Next, a positive electrode (positive electrode molded body) 6 is placed on the surface of the separator 5, and then colloidal carbon (a positive electrode current collector) is formed on the inner surface of the opening of the negative electrode container 1 via an insulating gasket 3. ) 7 is applied and the positive electrode container 8 is fitted,
The opening of this positive electrode container 8 is caulked to form the negative electrode container 1.
In the positive electrode container 8, the negative electrode 4, the separator 5, and the positive electrode 6 are provided.
Then, a coin type non-aqueous solvent secondary battery with an outer diameter of 20.0 mm and a thickness of 2.5 mm was assembled.

(4) Battery Aging The assembled coin-shaped non-aqueous solvent secondary battery at room temperature
Aged for 14 days. The battery open circuit voltage of the coin type non-aqueous solvent secondary battery after this aging was 3.4V.

(5) Charge / Discharge Cycle Test Regarding the coin type non-aqueous solvent secondary battery, a charge / discharge cycle test of discharging to a battery voltage of 2.0 V at a constant current of 1.0 mA and then charging to 3.4 V was conducted at 20 ° C. After 50 cycles at temperature, the discharge capacity at the 50th cycle was measured. Table 1 shows the results of the ratio of the discharge capacity obtained under these conditions to the initial (first cycle) discharge capacity as the discharge capacity retention ratio at 50 cycles.

(6) High-temperature storage characteristic test A coin type non-aqueous solvent secondary battery aged in the same manner as above was prepared, stored at 60 ° C. for 20 days, and then subjected to constant resistance discharge of 15 kΩ to 2.0 V. The results of measuring the discharge capacity are shown in Table 1.

Example 2 Coin-type lithium was used under the same conditions as in Example 1 except that the compounding ratio of the graphitized mesophase pitch carbon fiber and the coke carbon particles was changed to 75:25 (wt%). After assembling the secondary battery and aging the battery, the results of the charge / discharge cycle test and the high temperature storage characteristic test are shown in Table 1 together with the packing density of the negative electrode molded body.

Example 3 Under the same conditions as in Example 1, except that the compounding ratio of the graphitized mesophase pitch carbon fiber and the coke carbon particles was changed to 30:70 (wt%), a coin-shaped After assembling the water solvent secondary battery and aging the battery,
The results of the charge / discharge cycle test and the high temperature storage characteristic test are shown in Table 1 together with the packing density of the negative electrode molded body.

Comparative Example 1 Same as Example 1 except that coke-based carbon particles having an average particle size of 200 μm were used and the blending ratio with the graphitized mesophase pitch-based carbon fiber was changed to 25:75 (wt%). Then, a coin type non-aqueous solvent secondary battery was produced, the battery was aged, and then the charge and discharge cycle test was performed. The results are shown in Table 1 together with the packing density of the negative electrode molded body.

Comparative Example 2 Same as Example 1 except that coke-based carbon particles having an average particle diameter of 30 μm were used and the blending ratio with the graphitized mesophase pitch-based carbon fiber was changed to 25:75 (wt%). Then, the coin-shaped non-aqueous solvent secondary battery was assembled, the battery was aged, and then the charge and discharge cycle test was performed. The results are shown in Table 1 together with the packing density of the negative electrode molded body.

Comparative Example 3 Average fiber length 200 μm The same as Example 1 except that graphitized mesophase pitch carbon fiber was used and the blending ratio with coke carbon particles was changed to 75:25 (wt%). A coin type non-aqueous solvent secondary battery was produced, the battery was aged, and the charge / discharge cycle test was performed. The results are shown in Table 1 together with the packing density of the negative electrode molded body.

Comparative Example 4 Same as Example 1 except that graphitized mesophase pitch carbon fiber having an average fiber length of 5 μm was used and the mixing ratio with coke carbon particles was changed to 75:25 (wt%). A coin type non-aqueous solvent secondary battery was produced, the battery was aged, and then the results of charge / discharge cycle test and high temperature storage characteristic test were shown in Table 1 together with the packing density of the negative electrode molded body.

[0039] As can be seen from Table 1 above, the negative electrode molded body mounted on the coin-type non-aqueous solvent secondary battery of the example has a relatively high packing density and exhibits not only good charge / discharge cycle characteristics but also battery capacity. It is also high and has excellent performance as a compact power supply.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. For example, even if the average fiber diameter, average fiber length, and average particle diameter of coke-based carbon particles of graphitized mesophase pitch-based fibers that form the main component of the negative electrode molded product are appropriately changed within the permissible range, the same operational effect is obtained. Is obtained. Further, the battery may have a cylindrical shape other than the coin shape.

[0041]

EFFECTS OF THE INVENTION According to the present invention, the packing density of the negative electrode compact is improved by using the negative electrode carbonaceous material as the mixed system of the graphite-based mesophase pitch carbon fiber having the predetermined properties and the coke-based carbon particles. As a result, a non-aqueous solvent secondary battery having high capacity and excellent cycle characteristics is provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a coin type non-aqueous solvent secondary battery of an example.

[Explanation of symbols]

 1 ………… Negative electrode container 2 ………… Negative electrode current collector 3 ………… Insulation gasket 4 ………… Negative electrode molded body 5 ………… Separator 6 ………… Positive electrode molded body 7 ………… Positive electrode current collector 8 …… … Positive electrode container

Claims (2)

[Claims] 1. A non-aqueous solvent secondary battery comprising a positive electrode, a negative electrode made of a carbonaceous material capable of inserting and extracting lithium ions, and a lithium ion conductive electrolyte, wherein the carbonaceous material is an average. Fiber diameter 2-40 μm, average fiber length 10
A non-aqueous solvent secondary battery, which is mainly composed of a mixture of graphitized mesophase pitch carbon fibers having a particle size of ˜100 μm and coke carbon particles having an average particle size of 50 μm to 100 μm. 2. The non-aqueous solvent secondary battery according to claim 1, wherein the mixture contains 30 to 90% by weight of graphitized mesophase pitch carbon fiber.